"[Arms Control Today] has become indispensable! I think it is the combination of the critical period we are in and the quality of the product. I found myself reading the May issue from cover to cover."

– Frank von Hippel
Co-Director of Program on Science and Global Security, Princeton University
June 1, 2018
United States

U.S. Raises Treaty Compliance Concerns

October 2019
By Shannon Bugos

The United States has concerns about Russian and Chinese compliance with nuclear weapons-related treaties, according to a newly released State Department report. The annual compliance report provides additional background details on Russia’s alleged violation of the Intermediate-Range Nuclear Forces (INF) Treaty and repeats Trump administration concerns about possible nuclear testing by Russia and China.

The U.S. State Department's annual compliance report reiterated that Russia's 9M729 cruise missile violated the INF Treaty, leading to the U.S. withdrawal from the treaty. (Photo: Vasily Maximov/AFP/Getty Images)The report, made public on Aug. 22 and titled “Adherence to and Compliance with Arms Control, Nonproliferation, and Disarmament Agreements and Commitments,” primarily covers activities during 2018. The State Department released a shorter version of the report in April, which sparked controversy in Congress about the potential politicization of intelligence with regard to Iran, as well as other countries.

The full report said that Russia continued to violate the INF Treaty in 2018, a charge the Trump administration cited before formally withdrawing the United States from the treaty on Aug. 2. The 1987 pact banned the possession or testing of all nuclear and conventional, ground-launched ballistic and cruise missiles with ranges between 500 and 5,500 kilometers. Since 2014, the United States has accused Russia of violating the treaty by testing, possessing, and fielding an illegal ground-launched cruise missile known as the 9M729. The report asserts that Russia began development of the missile “probably by the mid-2000s” and concluded in 2015 a “comprehensive” flight-test program. By the end of 2018, Russia fielded multiple battalions of the 9M729, the report says.

“The history of Russia’s anti-INF [Treaty] overtures leading up to missile tests, its attempt to covertly exploit a treaty exception permitting ground-based flight tests of intermediate-range missiles not subject to the treaty, its lack of an explanation for these tests, and its overall secrecy” about the 9M729, the report declares, “provide important context for Russia’s violation.”

The compliance report also raises concerns about alleged Russian nuclear weapons testing and compliance with the 1974 Threshold Test Ban Treaty (TTBT), which prohibits nuclear tests with explosive yields exceeding 150 kilotons. The report states that “based on available information, Russian activities during the 1995–2018 timeframe raise questions about Russia’s compliance with its TTBT notification obligation.”

In addition, the report echoes remarks made earlier this year by the director of the U.S. Defense Intelligence Agency (DIA) regarding Russian nuclear testing. In May, DIA Director Lt. Gen. Robert Ashley said that “Russia probably is not adhering to its nuclear testing moratorium in a manner consistent with the ‘zero-yield’ standard outlined” in the 1996 Comprehensive Test Ban Treaty (CTBT). (See ACT, July/August 2019.) The CTBT, although not yet in force, goes a step farther than the TTBT by prohibiting nuclear tests, no matter what the yield.

The August report said, “The United States…has assessed that Russia has conducted nuclear weapons tests that have created nuclear yield.” In an apparent attempt to back up this statement, the report adds that, “[d]uring the 1995–2018 timeframe, Russia probably conducted nuclear weapons-related tests at the Novaya Zemlya Nuclear Test Site.”

The report also mentions Ashley’s remarks regarding China. In May the DIA director said that China may be preparing to operate its nuclear test site year-round and is continuing to use explosive containment chambers at that site. According to the compliance report, these activities, as well as a lack of transparency from China, “raise questions” about Beijing’s adherence to the zero-yield nuclear weapons testing moratorium.

On Iran, the compliance report states that “Iran is not currently undertaking the key nuclear weapons development activities judged necessary to produce a nuclear device” and that the United States will continue with its “maximum pressure campaign” on Tehran until Iran agrees to “a comprehensive deal that resolves all U.S. concerns.”

The report says that the information in the cache of documents seized by Israel on Iran’s past nuclear weapons-related activities, known as the nuclear archive, has not revealed evidence of any ongoing weapons work. The report argues, however, that Tehran retained those documents, which are still under review by the U.S. intelligence community, to potentially “aid in any future decision to pursue nuclear weapons” and may have “taken active measures to deliberately deceive” officials of the International Atomic Energy Agency.

As for North Korea, the compliance report states that the United States “believes there is a clear likelihood” of “unidentified nuclear facilities in North Korea” besides those at Yongbyon, the country’s nuclear center. The report does not provide additional information on those secret facilities.

In response to North Korean leader Kim Jong Un’s declaration in 2018 that Pyongyang would end all nuclear testing and demolish the P’unggye Nuclear Test Site, the report states that the results of the demolition at the test site in May 2018 “are almost certainly reversible.”

The compliance report emphasizes that the administration “remains committed to continued diplomatic negotiations with North Korea toward the goal of achieving the final, fully-verified denuclearization of North Korea.”


An annual State Department report reinforces Trump administration charges of arms control treaty violations. 

U.S. Intel Sheds Light on Russian Explosion

October 2019
By Shannon Bugos

U.S. intelligence analysts have bolstered earlier assessments that an Aug. 8 explosion near a Russian missile test site involved a nuclear-powered cruise missile undergoing development and testing. (See ACT, September 2019.)

The incident began with a blast at the Nenoksa Missile Test Site, on the coast of the White Sea. According to a statement from Russia’s State Atomic Energy Corporation (Rosatom) two days later, five employees died in the accident, which involved “isotopic sources of fuel on a liquid propulsion unit.” Two military personnel also reportedly died from the blast.

A subsequent U.S. intelligence assessment determined that the blast was caused by a recovery mission to salvage a nuclear-powered cruise missile from the ocean floor from a previous test, CNBC reported on Aug. 29.

“There was an explosion on one of the vessels involved in the recovery, and that caused a reaction in the missile’s nuclear core, which lead to the radiation leak,” a person with direct knowledge of the intelligence assessment told CNBC. A number of media outlets have reported releases of a variety of radioactive isotopes.

Meanwhile, researchers at the Norwegian Norsar Research Institute suggested that there may have been two explosions at the test site. Anne Lycke, the institute’s chief executive, said that seismographic readings suggested an explosion first on the ground or water, and then an infrasonic air-pressure sensor pointed to a second explosion two hours later, likely in the air. The second one “coincided in time with the reported increase in radiation,” she said. The governor of the region in which the blast took place denied the possibility of a second explosion.

Some U.S. nuclear experts and intelligence officials initially assessed that the accident likely involved a failed test of a nuclear-powered cruise missile known as the 9M730 Buresvestnik by Russia and the SSC-X-9 Skyfall by NATO. Kremlin spokesperson Dmitry Peskov appeared to confirm this assessment Aug. 21, stating that a “nuclear-propelled missile” was being tested at the time of the accident.

No official explanations have come from Russia. President Vladimir Putin said only that “this is work in the military field, work on promising weapons systems.”

CNBC released another report on Sept. 11 citing an intelligence finding that, despite numerous test failures, the 9M730 would be ready for deployment in 2025, about five years earlier than previously assessed.


A mysterious August explosion at a Russian missile test site likely involved a prototype nuclear-powered weapon. 

Pentagon Seeks New Missile Interceptor

October 2019
By Kingston Reif

The U.S. Defense Department has formally canceled its program to design an upgraded kill vehicle for the U.S. long-range missile defense system and will instead seek to build a new interceptor for the system.

A U.S. plan to replace the exoatmospheric kill vehicle, shown here as an artists' conception, were formally cancelled in August. (Image: Raytheon)An Aug. 21 Pentagon statement said that effective the next day, the Pentagon would terminate the Boeing Company’s contract to build the Redesigned Kill Vehicle (RKV) “due to technical design problems.”

The announcement followed the department’s decision in May to order Boeing, the lead contractor for the $67 billion Ground-Based Midcourse Defense (GMD) system, to stop all work on the new kill vehicle. (See ACT, July/August 2019.) The GMD system is designed to defend the United States against a limited, long-range ballistic missile attack from North Korea or Iran.

“Ending the program was the responsible thing to do,” Mike Griffin, undersecretary of defense for research and engineering, said in the statement. “Development programs sometimes encounter problems. After exercising due diligence, we decided the path we’re going down wouldn’t be fruitful, so we’re not going down that path anymore.”

Congress has appropriated more than $1 billion for the RKV program, from the program’s inception in fiscal year 2015 through fiscal year 2019.

The RKV was intended to be more reliable and cost effective than the current generation of GMD kill vehicles that have seen mixed test results and face an evolving threat, particularly from North Korea. The system has an intercept success rate of just more than 50 percent in controlled testing.

The Missile Defense Agency (MDA) planned to deploy the RKV beginning in 2021 atop 20 new interceptors in Alaska to augment the existing fleet of 44 interceptors there and in California. The RKV was also intended to replace the aging kill vehicles atop the current fleet.

The demise of the RKV could delay the fielding of the additional interceptors “to the 2030 timeframe at the earliest under the current acquisition requirements” to compete, test, and certify a new interceptor “in operational and realistic conditions,” the Missile Defense Advocacy Alliance said in an Aug. 21 alert.

The termination will likewise delay the modernization of the existing fleet of ground-based interceptors, the oldest of which were fielded between 2004 and 2007.

According to the Government Accountability Office, ground-based interceptors “only have an initial service life of 20 years and [the] MDA previously decided not to make any upgrades to the [original interceptor] because of initial plans to begin replacing them with RKVs in 2020.”

In the wake of the failure of the RKV program, the Defense Department plans to develop an entirely new long-range interceptor that will also include a new kill vehicle.

John Rood, undersecretary of defense for policy, said at a Sept. 17 event in Washington that the department plans to issue “what we will hope will be the final request for proposals” to industry for the new interceptor in October.

“We are positioned for near-term responses from industry, and the Missile Defense Agency advises me that they’re poised to try to rapidly move to award,” he added.

The Pentagon has released few details about the requirements for the new interceptor, the proposed timeline to develop and field it, or the estimated cost.

Rood said the MDA will continue existing plans to build 20 additional missile silos in Alaska “to be ready to house” the new interceptors.

The plan to develop the new interceptor is part of “a realignment of over $12 billion in current budget plans for development of a Next-Generation Interceptor” for the GMD system, according to the report accompanying the Senate Appropriations Committee version of the fiscal year 2020 defense appropriations bill.

In addition to the Next-Generation Interceptor, the $12 billion figure includes funding for research, development, test, and evaluation; procurement; and operations and maintenance for the entire GMD program from fiscal year 2020 to fiscal year 2030, a defense official told Inside Defense on Sept. 13.

Unlike the other involved Senate and House committees, the Senate Appropriations Committee published
its defense bill after the cancellation of the RKV.

The bill supported the MDA proposal to shift $728 billion in fiscal year 2019 and 2020 funding for the GMD system to support “a competitive acquisition” of the new interceptor “while addressing current GMD requirements.” The bill would provide $222 million specifically for the new interceptor.


The Defense Department has ended a program to design a new missile defense kill vehicle after the system failed to overcome technical hurdles. 

Members Briefing on the Future of New START



October 1, 2019
3:00pm Eastern U.S. time

The New START agreement between the United States and Russia—now the only agreement limiting the world’s two largest nuclear weapons arsenals following termination of the INF Treaty—is scheduled to expire in February 2021 unless Presidents Donald Trump and Vladimir Putin mutually agree to extend it by five years.

Former National Security Advisor John Bolton was a harsh critic of extending New START. What does Bolton's departure from the administration in September mean for the future of the treaty?

Kingston Reif, director for disarmament and threat reduction, and Thomas Countryman, board chair and former acting undersecretary of state for arms control, briefed members on what could be the most important national security decision in a generation.

These calls are open to members of the Arms Control Association. Audio recordings of the call may be made available for nonmembers at some point following the call. Join or renew your membership today to receive details on how to join us for our next members call and be part of the conversation. 

AUDIO RECORDING: The Future of New START, October 1 Members Call


Join Kingston Reif and Thomas Countryman for a members-only briefing on the future of the New START agreement between the United States and Russia.

Country Resources:

U.S.-Saudi Nuclear Cooperation Policy Still Far from Adequate (UPDATED)

UPDATE, Sept. 19 : A day after we published this post, Bloomberg revealed that Energy Secretary Rick Perry's letter to the Saudi's also stated that "The terms of the 123 Agreement [with Saudi Arabia] must also contain a commitment by the kingdom to forgo any enrichment and reprocessing for the term of the agreement." This is good news and the right policy, as we describe below. Such a commitment should have a long-term duration, be legally-binding, and apply to both U.S.-origin and non-U.S. origin fuel. Over the past two years, the Trump administration and Saudi Arabia have been engaged in...

U.S.-Russian Nuclear Arms Control Watch, Sept 13, 2019

U.S. Tests Ground-Launched Cruise Missile On Aug. 18, less than two weeks after the official collapse of the 1987 Intermediate-Range Nuclear Forces (INF) Treaty, the United States tested a ground-launched variant of the Tomahawk sea-launched cruise missile that would have been prohibited by the treaty. The test was a clear signal that the United States can and will pursue such systems in the absence of the INF Treaty. In a statement, the Defense Department said the “test missile exited its ground mobile launcher and accurately impacted its target after more than 500 kilometers of flight. Data...

If Trump Ends Another Nuclear Treaty, it Will Be the Height of Folly

During his first two and a half years in office, President Donald Trump and his administration have laid waste to numerous international agreements originally designed to strengthen US security, bolster US alliances, and constrain US adversaries. The toll has been particularly high with respect to deals concerning nuclear arms control and nonproliferation. Over the past 14 months, the administration has withdrawn from the 2015 Iran nuclear deal and abandoned the 1987 Intermediate Range Nuclear Forces (INF) Treaty . Both of these valuable agreements have been discarded without a viable plan to...

Close the Door on Nuclear Testing

September 2019
By Daryl G. Kimball, Executive Director

Everybody knows that nuclear weapons have been used twice in wartime and with terrible consequences. Often overlooked, however, is the large-scale, postwar use of nuclear weapons: At least eight countries have conducted 2,056 nuclear test explosions, most of which were far larger than the bombs that leveled Hiroshima and Nagasaki. The United States alone has detonated more than 1,030 nuclear explosions in the atmosphere, underwater, and underground.

Daryl Kimball, Executive Director of the Arms Control Association, outside the P-1 area at the Semipalatinsk Test Site in Eastern Kazakhstan, August 2018.Hundreds of thousands of people have died and millions more have suffered from radiation-related illnesses directly caused by the fallout from nuclear testing. The global scale of suffering took too long to come to light.

Secrecy ruled over safety from the start, such as 70 years ago, on Aug. 29, 1949, when the Soviet Union conducted its first nuclear test in eastern Kazakhstan near the secret town of Semipalatinsk-21. Authorities understood that the test would expose the local population to harmful radioactive fallout, but they pushed ahead in the name of national security, only acknowledging the damage after information leaks in the late-1980s revealed that far more people were exposed to radiation, with more harmful effects, than the Kremlin had previously admitted.

Today, the Kazakh government estimates that Soviet-era testing harmed about 1.5 million people in Kazakhstan alone. A 2008 study by Kazakh and Japanese doctors estimated that the population in areas adjacent to the Semipalatinsk Test Site received an effective dose of 2,000 millisieverts of radiation during the years of testing. In some hot spots, people were exposed to even higher levels. By comparison, the average American is exposed to about 3 millisieverts of radiation each year. The rate of cancer for people living in eastern Kazakhstan is 25 to 30 percent higher than elsewhere in the country.

By 1989, growing concerns about the health impacts of nuclear testing led ordinary Kazakh citizens to rise up and demand a test moratorium. They formed the Nevada-Semipalatinsk anti-nuclear organization. The grassroots movement grew, and popular pressure against testing surged, prompting the Kazakh political establishment, including then-president of Soviet Kazakhstan, Nursultan Nazarbayev, to finally shut down all nuclear testing at Semipalatinsk on Aug. 29, 1991.

On Oct. 5, 1991, Soviet President Mikhail Gorbachev announced a one-year nuclear test moratorium, which led a bipartisan U.S. congressional coalition to introduce legislation to match the Soviet test halt. In 1992 the bill became law over the protestations of President George H.W. Bush. The following year, under pressure from civil society leaders and Congress, President Bill Clinton decided to extend the moratorium and launch talks on the global, verifiable Comprehensive Test Ban Treaty (CTBT), which were concluded in 1996.

The CTBT has established a powerful taboo against nuclear testing. Global support for the treaty, which now has 184 state signatories, is strong, and the treaty’s International Monitoring System is fully operational and more capable than originally envisioned. Today, for the first time since 1945, no nuclear-armed state has an active nuclear testing program.

Yet, the door to further nuclear testing remains ajar. Although the treaty has been signed by 184 states, its entry into force is being held up by eight states, most notably the United States, China, and North Korea, which have refused to ratify the pact.

Making matters worse, the Trump administration has accused Russia of cheating on the CTBT without providing evidence, has falsely asserted there is a lack of clarity about what the CTBT prohibits, and has refused to express support for bringing the CTBT into force.

Given their existing nuclear test moratoria and signatures on the treaty, Washington and Beijing already bear most CTBT-related responsibilities. But their failure to ratify has denied them and others the full security benefits of the treaty, including short-notice, on-site inspections to better detect and deter clandestine nuclear testing.

The treaty’s entry into force also would prevent further health injury from nuclear testing and allow responsible states to better address the dangerous legacy of nuclear testing. In Kazakhstan, for example, access to the vast former test site remains restricted. Many areas will remain unusable until and unless the radioactive contamination can be remediated.

In the Marshall Islands, where the United States detonated massive aboveground nuclear tests in the 1940s and 1950s, several atolls are still heavily contaminated, indigenous populations have been displaced, and some buried radioactive waste could soon leak into the ocean. The U.S. Congress should act to include the downwinders affected by the first U.S. test in 1945 in the health monitoring program established through the Radiation Exposure Compensation Act of 1990.

For the safety and security of future generations and out of respect for the people harmed by nuclear testing, our generation must act. It is time to close and lock the door on nuclear testing by pushing the CTBT holdout states to ratify the treaty and address more comprehensively the devasting human and environmental damage of the nuclear weapons era.

Everybody knows that nuclear weapons have been used twice in wartime and with terrible consequences. Often overlooked, however, is the large-scale, postwar use of nuclear weapons: At least eight countries have conducted 2,056 nuclear test explosions, most of which were far larger than the bombs that leveled Hiroshima and Nagasaki.

Risky Business: Four Ways to Ease U.S.-Russian Nuclear Tension

September 2019
By Sarah Bidgood

The era of traditional U.S.-Russian arms control appears to be ending.1 The latest casualty of the crisis in relations between the two nuclear powers, the 1987 Intermediate-Range Nuclear Forces (INF) Treaty, was suspended in February when Washington declared it would withdraw from the pact because of alleged Russian noncompliance. Moscow made no great effort to resist U.S. intentions, and with surprisingly little fanfare, the treaty expired in early August.

From left to right, Andrea Thompson of the United States, Fu Cong of China, and Nicolas Roche of France attend a Jan. 31 panel discussion following a P5 nuclear powers meeting in Beijing. P5 representatives could not agree to reaffirm the Reagan-Gorbachev Cold War motto: “A nuclear war cannot be won and must never be fought.” (Photo: Thomas Peter/AFP/Getty Images)This leaves just one bilateral arms control agreement in place, the 2010 New Strategic Arms Reduction Treaty (New START), which is itself due to expire in 2021. The treaty could be easily extended for up to five years, thus ensuring a vital degree of transparency and stability in U.S.-Russian relations, but the Trump administration has shown little outward enthusiasm for this step. If the clock is allowed to run out on this crucial element of strategic stability, it will mark the first time that the United States and Russia have not had an arms control treaty in place or under negotiation in nearly five decades.

The potential lack of treaty constraints on nuclear arms increases the need for other tools to minimize misunderstandings, avoid accidents, and build confidence between the United States and Russia. Such risk reduction measures have contributed to maintaining stability in the past, and they are needed now more than ever as U.S.-Russian arms control falters.

Arms Control in Trouble

The depth of the demise was illustrated in January 2019 when the P5—the five nuclear powers recognized under the nuclear Nonproliferation Treaty (NPT)—convened in Beijing for the eighth meeting of the P5 process.2 China, France, Russia, the United Kingdom, and the United States identified three measures to strengthen their coordination and safeguard the NPT, but they could not agree to endorse the simple motto established in 1985 by U.S. President Ronald Reagan and Soviet leader Mikhail Gorbachev: “A nuclear war cannot be won and must never be fought.”3 What should have been a relatively easy lift, delivering a joint statement capturing this sentiment, was torpedoed when only China was prepared to endorse it. In a climate where agreeing to this most basic principle is no longer tenable, it is not surprising that more ambitious actions required to sustain bilateral arms control now appear to be out of reach.

These circumstances make a return to nuclear arms racing more likely not only by established nuclear powers, but also by nations that have forsworn such weapons. Although Moscow and Washington worked closely to prevent new parties from acquiring a nuclear capability during the darkest days of the Cold War, these joint efforts have all but halted.4 Their disengagement has contributed to the turmoil within the nonproliferation regime, where past commitments are left unfulfilled and the way forward is far from clear.5

U.S. President Barack Obama (left) and Russian President Dmitry Medvedev shake hands after signing the New Strategic Arms Reduction Treaty in Prague on April 8, 2010. If the treaty expires in 2021, there will be no negotiated limits on U.S. and Russian nuclear weapons. (Photo: Joe Klamar/AFP/Getty Images)The degree to which the United States and Russia are now at odds in this domain has been impossible to ignore during the run-up to next year’s NPT review conference. Russia has accused the United States of violating the NPT through its NATO nuclear-sharing arrangement, while the United States has lambasted Russia for undermining the norm against the non-use of weapons of mass destruction and allegedly violating the INF Treaty. The two sides certainly have not seen eye to eye on all nonproliferation issues in the past, but they placed such a premium on presenting a united front to the other NPT states that they were often accused of “superpower collusion.”6 Today, however, there seems to be little interest in maintaining even the pretense of alignment on key issues. This development is revealing of the state of the bilateral relationship today, and it does not portend well for global security.

A less visible consequence of the collapse of U.S.-Russian nuclear engagement is the precipitous decline in opportunities for routine interaction between diplomats and policymakers from the two countries. The result is an erosion of trust that could make accidents, miscommunications, or misinterpretations more likely to escalate into nuclear use because there is no assumption of benign intent on either side. This development is especially problematic when reviewing the litany of close nuclear calls in U.S. and Soviet/Russian history.

That these have not culminated in nuclear use in the past is, in many cases, thanks to human decision-makers who determined, for example, that automatic missile warning systems were giving false alerts. This past January marked 25 years since one such scenario, in which Russia’s early-warning system misidentified a research rocket launched off the coast of Norway as a U.S. Trident II submarine-launched ballistic missile. Russian nuclear attack response procedures were reportedly triggered, but Russian President Boris Yeltsin ruled out the likelihood of a surprise U.S. nuclear strike and decided not to retaliate.7 Were there to be a replay of this incident today, is it realistic to assume that decision-makers on either side would act in a similar fashion? It is only a matter of time before this hypothetical is put to the test.

In the absence of cooperation on arms control and nonproliferation and faced with urgent crises that require U.S.-Russian efforts, the challenge for the nuclear policymaking community today is twofold. It must find and support feasible opportunities for U.S.-Russian engagement on nuclear issues so that more ambitious efforts to shore up strategic stability and the nonproliferation regime are possible in the future. It must also actively pursue steps to prevent a nuclear catastrophe while the two sides get their relationship in this domain back on track. Fortunately, these two goals are mutually reinforcing and served by a renewed focus on nuclear risk reduction.

Practical Steps to Reduce Nuclear Risk

The United States and Russia could pursue at least four meaningful risk reduction measures that would contribute to these efforts. Even more significant steps than these are needed, but this menu comprises points of entry that may be feasible under the current circumstances.

A Parallel Risk Assessment
U.S. and Russian officials could engage in a parallel risk assessment, where both sides would identify independently the technologies, behaviors, and past and future scenarios they believe are most likely to lead to nuclear use and then compare their answers.8 This exercise would lay the groundwork for determining what types of risk reduction efforts are most needed. It could also serve as an opportunity to clear up misconceptions about the other’s capabilities or practices, including with respect to the alleged Russian policy of “escalate to deescalate.” The 2018 U.S. Nuclear Posture Review report states that Russia might conduct a limited nuclear first strike to end a conventional conflict on its terms, but this strategy is not described in any official Russian documents pertaining to its nuclear doctrine. Determining conclusively that this policy is not part of Russian strategy would free up both sides to focus on mitigating actual, rather than assumed, nuclear risks.

The P5 process presents a useful forum to operationalize this recommendation, at least initially. Not only is it already in place, but conducting a parallel risk assessment in this setting would contribute to the nuclear-weapon states’ attempts to better understand each other’s nuclear doctrines. The fact that all five delegations committed to making the “utmost efforts” to prevent nuclear risks at their 2019 Beijing meeting suggests that this recommendation might be welcomed as a concrete first step.9 Furthermore, this exercise could appeal to states with different perceptions of risk because its focus would be on identifying similarities and differences in their views, rather than on a preordained list of concerns with which all states might not agree.

Revive Consultations on Nuclear Risk Reduction
While many channels for U.S.-Russian nuclear engagement have now shut down, recent strategic security meetings held by Russian and U.S. officials raise the prospect of renewed high-level dialogue on arms control, nonproliferation, and related topics.10 Washington and Moscow should capitalize on this opening to initiate regular consultations on nuclear risk reduction. The United States and Russia are destined to cooperate on this issue by virtue of their vast nuclear arsenals. Their shared responsibilities are even greater under the present circumstances, in which mutual suspicion, acrimony, and instability in their bilateral relationship increase the likelihood of nuclear use, intentionally or by mistake.

Bilateral dialogue has always been recognized as a key component of risk reduction. It is mandated in the 1971 USSR-U.S. Agreements to Reduce Risk of Nuclear War, which obliges the two sides to “hold consultations, as mutually agreed, to consider questions relating to implementation of the provisions of this agreement, as well as to discuss possible amendments thereto aimed at further implementation of the purposes of this agreement.”11

Reviving these consultations would contribute to international security while paving the way for more routinized and wide-ranging dialogue in the future. Not only would they provide a forum for officials to interact, which could itself reduce the likelihood of nuclear use, but they would also facilitate discussions on risks associated with emerging technologies, which have significant implications for the future of strategic stability. Given this orientation, these consultations would benefit from the involvement of scientific and technical experts, as well as policymakers and government officials. Cooperation on technical issues can flourish even during difficult moments in the bilateral relationship. Emphasizing this dimension of these consultations could increase the likelihood that they would generate meaningful results.12

The initial agenda for these consultations could focus on reviewing Cold War-era nuclear risk reduction measures and identifying ways to update and multilateralize them. Aside from the 1971 USSR-U.S. Agreements to Reduce Risk of Nuclear War, other relevant agreements include the 1972 U.S.-USSR Agreement on the Prevention of Incidents on the High Seas,13 the 1973 U.S.-USSR Agreement on the Prevention of Nuclear War, and the 1987 Agreement Between the United States of America and the Union of Soviet Socialist Republics on the Establishment of Nuclear Risk Reduction Centers. They could also meaningfully include risk reduction measures that were considered in the past but never formalized or adopted, such as this recommendation itself, which was borrowed from a similar proposal put forward by the Soviet delegation to the UN General Assembly in October 1977.14

Updating and multilateralizing U.S.-Soviet risk reduction agreements could open the door to engaging other nuclear-armed states in these efforts, particularly China. Doing so could introduce greater stability and predictability into the trilateral relationship while reducing the likelihood that nuclear entanglement in the three countries will escalate into nuclear exchange.15 Although Beijing has established its own crisis hotlines with Moscow and Washington, a host of other risk reduction measures are part of past agreements and could be meaningfully implemented today.16 Exploring opportunities to do so would represent a more realistic way to deliver President Donald Trump’s desire to include Beijing in a future arms control agreement with Moscow, which is unlikely to come to fruition anytime soon.

Despite these advantages, revisiting U.S.-Soviet proposals carries risks of its own, which include the potential for past points of contention to resurface with detrimental outcomes. For example, Russia could reprise failed Soviet calls for the United States to remove forward-deployed nuclear weapons from Europe in the name of preventing their accidental or unauthorized use.17 Although U.S. experts have made similar proposals in recent years, Washington may suspect Moscow of using risk reduction to advance its national interests, which could cause talks to fail. Similarly, efforts to multilateralize past agreements could falter if Russia and China press for limits on U.S. ballistic missile defense as a step toward reducing the risk of nuclear use.18 Avoiding these pitfalls will require thoughtful compartmentalization, where participants find ways to work around larger strategic stability concerns without dismissing them as illegitimate in the process.

Ban on Cyberattacks on C3 Systems
The United States and Russia could conclude an agreement that cyberattacks on nuclear command, control, and communications (C3) systems are off-limits.19 Such an agreement would be consistent with recent Russian and U.S.-sponsored UN General Assembly resolutions that emphasize the need for rules to govern state behavior in cyberspace. Although Russia’s interference in the 2016 presidential elections has made cooperation in the cyber domain exceptionally difficult in recent years, the potential risks posed by the cyber vulnerabilities of nuclear systems are significant enough to warrant treatment in a separate category. An agreement not to exploit these vulnerabilities would contribute significantly to reducing nuclear risk while complementing ongoing efforts to articulate and codify cyber norms in other areas of international security.20

Concluding such an agreement could be complicated by the reliance of many C3 systems on at least some dual-use assets. Because early-warning satellites are used to detect nuclear and non-nuclear missile launches, for instance, a cyberattack intended to limit an adversary’s ability to defend against a conventional strike would also constitute an attack on its nuclear C3 system.21 The United States and Russia would need to determine how to disentangle these assets in a way that still addressed their potential to precipitate nuclear escalation. In this process, the two sides should consider how best to make use of the cyber hotline, which was installed in the U.S. and Russian Nuclear Risk Reduction Centers in 2013. The hotline was designed to allow both sides to “make inquiries about cybersecurity incidents of national concern.”22 It could provide invaluable crisis stability during a cyberattack without requiring significant changes to existing infrastructure.

Joint Statement at the 2020 NPT Review Conference on Risk Reduction
The United States, Russia, and potentially the other nuclear-weapon states should issue a joint statement at the 2020 NPT Review Conference reaffirming the importance of nuclear risk reduction and reporting on any concrete measures they have adopted during the review cycle. Considering that the five countries will likely have little progress to report on nuclear disarmament, doing so would demonstrate some progress toward fulfilling the commitments they made at the 2010 NPT Review Conference.

Secretary of State Hillary Clinton cuts the ceremonial ribbon at the opening of the updated U.S. Nuclear Risk Reduction Center at the State Department on Oct. 24, 2012. The center and its Russian counterpart are operational at all times and intended to reduce the risk of nuclear conflict. (Photo: State Department)A particular selling point of this recommendation is the importance of nuclear risk reduction in avoiding the catastrophic humanitarian consequences that would result from nuclear use. From this vantage, nuclear risk reduction may constitute one of only a small handful of issues on which nuclear-weapon states, proponents of the Treaty on the Prohibition of Nuclear Weapons, and supporters of the humanitarian initiative could agree. The nuclear-weapon states would need to be careful not to frame risk reduction as a substitute for nuclear disarmament in the NPT setting, but if they succeed, this issue could represent an opportunity to find common ground at a time when few others exist. A focus on risk reduction would also align with the NPT preambular language, which recognizes the “devastation that would be visited upon all mankind by a nuclear war and the consequent need to make every effort to avert the danger of such a war.” Reaffirming the shared assumptions that underpin the NPT would be appropriate at the 50th anniversary of its entry into force.

Little Risk in Risk Reduction

These recommendations represent four steps that the United States and Russia could take to reduce nuclear risks today. They appear to align with both countries’ national security interests, which should increase their appeal among policymakers and may make it possible to implement them in spite of the current crisis in relations. In Washington, at least, these proposals may benefit from the lack of constraints they would place on U.S. military flexibility. Their narrow scope could help them gain traction with the current U.S. administration when more far-reaching and effective measures such as the defunct INF Treaty, the Comprehensive Test Ban Treaty, and New START have not.

If these recommendations nevertheless prove too ambitious, the United States and Russia could take a host of other, more modest steps to reduce the risk of nuclear use. Indeed, because bilateral relations are in such a deep state of crisis, virtually any activity that fosters dialogue or lends predictability to the two countries’ interactions would likely hit this mark. Moreover, risk reduction, unlike arms control, can take many different forms, from treaties to confidence-building measures to the installation of dedicated crisis-management infrastructure.23 This flexibility provides scalable options that may appeal to decisionmakers in both Moscow and Washington.

The latitude afforded by nuclear risk reduction may help explain why some U.S.-Russian engagement in this domain continues, albeit on an insufficient scale. The National Risk Reduction Centers in Washington and Moscow still operate 24 hours a day, providing an uninterrupted channel for crisis communication as they have for the last three decades. Likewise, the United States and Russia continue to co-chair the Global Initiative to Combat Nuclear Terrorism, where they have overseen efforts to prevent unauthorized nuclear use for more than 15 years. These operational channels reinforce the notion that, if expanded, risk reduction measures could preserve what is left of the bilateral relationship while laying the groundwork for closer cooperation. In a quickly deteriorating environment with few other alternatives, this argument is as good as any for seeing where these efforts could lead.



1. See Steven Pifer, “Nuclear Security, Arms Control, and the U.S.-Russia Relationship,” American Ambassadors Review, Spring 2019, https://www.americanambassadorslive.org/post/nuclear-security-arms-control-and-the-u-s-russia-relationship.

2. The P5 process was established in 2009 with the goal of identifying transparency and confidence-building measures leading toward progress on nuclear disarmament. See Andrea Berger and Malcolm Chalmers, “The Art of the Possible: The Future of the P5 Process on Nuclear Weapons,” Arms Control Today, October 2014.

3. Li Song, “Briefing on P5 Beijing Conference,” February 5, 2019, https://www.unog.ch/80256EDD006B8954/(httpAssets)/2A29BA6AFFA30F6CC125839B0051305C/$file/China_for+website.pdf (presented to the Conference on Disarmament); Jerry Brown and William Potter, “Open Forum: Time for a reality check on nuclear diplomacy,” San Francisco Chronicle, April 24, 2019 <https://www.sfchronicle.com/opinion/openforum/article/Open-Forum-Time-for-a-reality-check-on-nuclear-13793344.php?psid=ftMG0>

4. For examples of cooperation, see William C. Potter and Sarah Bidgood, eds., Once and Future Partners: The United States, Russia, and Nuclear Non-Proliferation (London: International Institute for Strategic Studies [IISS], 2018).

5. Paul Meyer, “Creating an Environment for Nuclear Disarmament: Striding Forward or Stepping Back?” Arms Control Today, April 2019.

6. William Potter and Sarah Bidgood, “The Good Old Days of the Cold War: U.S.-Soviet Cooperation on Nonproliferation,” War on the Rocks, August 7, 2018, https://warontherocks.com/2018/08/the-good-old-days-of-the-cold-war-u-s-soviet-cooperation-on-nonproliferation/.

7. Patricia Lewis et al., “Too Close for Comfort: Cases of Near Nuclear Use and Options for Policy,” Chatham House Report, April 2014, p. 17, https://www.chathamhouse.org/sites/default/files/field/field_document/20140428TooCloseforComfortNuclearUseLewisWilliamsPelopidasAghlani.pdf.

8. For more, see William C. Potter and Sarah Bidgood, “Chapter 8: Lessons for the Future” in Once and Future Partners: The United States, Russia, and Nuclear Non-Proliferation, ed. William C. Potter and Sarah Bidgood (London: IISS, 2018).

9. Song, “Briefing on P5 Beijing Conference.”

10. “Deputy Secretary Sullivan’s Participation in Strategic Security Dialogue With Russian Deputy Foreign Minister Sergey Ryabkov,” U.S. Department of State, July 17, 2019 < https://www.state.gov/deputy-secretary-sullivans-participation-in-strategic-security-dialogue-with-russian-deputy-foreign-minister-sergey-ryabkov/>

11. “Agreement on Measures to Reduce the Outbreak of Nuclear War Between the United States and the Union of Soviet Socialist Republics,” September 30, 1971.

12. For examples, see Siegfried S. Hecker, ed., Doomed to Cooperate (Los Alamos, NM: Bathtub Row Press, 2016).

13. The continuing relevance of this agreement was underscored by the near collision of U.S. and Russian warships in the Pacific Ocean in June 2019. See “U.S. Navy: Russian Warship’s ‘Unsafe’ Move Nearly Caused Collision With Cruiser,” National Public Radio, June 7, 2019, https://www.npr.org/2019/06/07/730593184/u-s-navy-russian-warships-unsafe-move-nearly-caused-collision-with-cruiser.

14. “32 UNGA: New Soviet Initiative,” October 18, 1977, https://aad.archives.gov/aad/create
(cable from secretary of state to U.S. Mission to NATO).

15. For a definition of entanglement and an explanation of how it could precipitate nuclear use, see James Acton, Tong Zhao, and Li Bin, “Reducing the Risks of Nuclear Entanglement,” Carnegie Endowment for International Peace, September 12, 2018, https://carnegieendowment.org/2018/09/12/reducing-risks-of-nuclear-entanglement-pub-77236.

16. Avery Goldstein, “First Things First: The Pressing Danger of Crisis Instability in U.S.-China Relations,” International Security, Vol. 37, No. 4 (Spring 2013): 49–89.

17. Soviet Deputy Foreign Minister Vladimir Semenov issued this call in an October 1974 meeting on SALT II. “Deputy Minister Semenov’s Statement of October 4, 1974,” October 4, 1974, https://aad.archives.gov/aad/createpdf?rid=221079&dt=2474&dl=1345 (cable from U.S. delegation to SALT II to the secretary of state).

18. Laura Grego lays out arguments both countries could reasonably make. See Laura Grego, “The Faulty and Dangerous Logic of Missile Defense,” Scientific American, April 24, 2018, https://blogs.scientificamerican.com/observations/the-faulty-and-dangerous-logic-of-missile-defense/?redirect=1.

19. Wilfred Wan also makes this proposal in Nuclear Risk Reduction: A Framework for Analysis (Geneva, Switzerland: UNIDIR, 2019), p. 29, < http://unidir.org/files/publications/pdfs/nuclear-risk-reduction-a-framework-for-analysis-en-809.pdf>

20. See Global Commission on the Stability of Cyberspace, “Norm Package Singapore,” November 2018, https://cyberstability.org/wp-content/uploads/2018/11/GCSC-Singapore-Norm-Package-3MB.pdf.

21. For an overview of the challenges that dual-use command-and-control assets create for risk reduction, see James M. Acton, “Inadvertent Escalation and the Entanglement of Nuclear Command-and-Control Capabilities,” International Security Policy Brief, October 29, 2018, https://www.belfercenter.org/publication/inadvertent-escalation-and-entanglement-nuclear-command-and-control-capabilities.

22. The White House, “Fact Sheet: US-Russian Cooperation on Information and Communications Technology Security.” June 17, 2013 < https://obamawhitehouse.archives.gov/the-press-office/2013/06/17/fact-sheet-us-russian-cooperation-information-and-communications-technol>

23. Joseph Nye made a similar point in 1984. See Joseph S. Nye Jr., “U.S.-Soviet Relations and Nuclear-Risk Reduction,” Political Science Quarterly, Vol. 99, No. 3 (Autumn 1984), p. 404.

Sarah Bidgood is director of the Eurasia Nonproliferation Program at the James Martin Center for Nonproliferation Studies (CNS) in Monterey, California. She also leads the Young Women in Nonproliferation Initiative at CNS.

Risk reduction measures are needed more than ever as just one U.S.-Russian treaty limits the size of the two nations’ strategic nuclear arsenals.

Probabilistic Verification: A New Concept for Verifying the Denuclearization of North Korea

September 2019
By Mareena Robinson Snowden

Although U.S.-North Korean talks have stalled, North Korean leader Kim Jong Un has abided by an apparent moratorium on nuclear testing, keeping alive hopes that an agreement can be reached to denuclearize North Korea. Implementing such an agreement with North Korea, if one can be negotiated, would constitute an unprecedented challenge for the international community.

IAEA inspectors used seals such as these, among many other tools, when it was asked to verify the shutdown of North Korean nuclear activities in the past. The IAEA has maintained readiness to participate in a future verification regime if any nuclear agreement is concluded. (Photo: Dean Calma/IAEA)Verifying such an agreement would require building a monitoring regime that goes well beyond traditional international safeguards and bilateral arms control approaches while accommodating legitimate North Korean concerns over intrusiveness, which would practically preclude “anytime, anywhere” inspections. Creativity will be needed to design a verification scheme to which the United States and North Korea could agree and that could be implemented in affordable and practical ways and that politicians would deem credible.

Verification is the means by which parties to an agreement assure themselves that the agreement is being implemented faithfully. A central tension lies at the heart of verification: the need to balance confidence on one side with the sensitivities regarding intrusive monitoring on the other. In nuclear activities negotiations, verification traditionally has been accomplished through two means: international safeguards inspections on fissile material production and bilateral arms control monitoring of nuclear delivery vehicles, such as missiles and bombers. Both systems focused narrowly on just a few activities or items intrinsic to nuclear weapons and constructed monitoring approaches that would provide high confidence of detecting noncompliance.

Over time, the distinctions between these two types of verification regimes have blurred as some states pursued clandestine nuclear weapons programs. In South Africa in 1990, Iraq after 1992, and Libya in 2003, the International Atomic Energy Agency (IAEA) undertook activities that went beyond the narrow confines of fissile material accountancy to verify that all three states had ceased nuclear weapons-related activities. More recently, the IAEA investigated “possible military dimensions” of Iran’s nuclear activities, including experiments related to nuclear weapons design and testing.

The North Korean verification challenge is more substantial than these prior examples. Complete, irreversible denuclearization would require defining and implementing “disarmament” of a whole category of weapons and the pertinent infrastructure to develop, produce, and upgrade them—in real time. Still, as challenging as nuclear verification in North Korea may be, these historical approaches and ad hoc innovations offer lessons on how to design an approach that can work in North Korea. Experience from other verification regimes, such as the Chemical Weapons Convention, also can be helpful.

A Unique North Korean Verification Challenge

North Korea’s unique challenge demands innovation in the way verification is approached in practice and is conceived in theory. Since the inception of nuclear arms control and international safeguards, decision-makers, particularly in the United States, tended to frame international treaties and their associated verification regimes in binary terms akin to law enforcement: either actors are complying with the terms of the treaty or not. This legalistic view is reinforced by the belief that adherence to all parts of an agreement demonstrates the intent and trustworthiness of the participants. By extension, unwillingness to tolerate even low-level violations, regardless of military significance, signaled parties’ resolve to detect everything, hold each other accountable, and deter cheating.

This framing of verification narrows the scope of what an agreement can cover. To provide the desired near-certain confidence in monitoring compliance, the verification system must cover fewer activities in a more limited geographic area. This narrow scope served a related purpose in the case of U.S.-Soviet arms control, namely to limit reciprocal inspections and monitoring activity in order to protect national security information and mitigate other security concerns. The consistently narrow focus on missiles and their associated launchers in the last three U.S.-Soviet and U.S.-Russian nuclear arms control agreements—the Intermediate-Range Nuclear Forces (INF) Treaty of 1987, the Strategic Arms Reduction Treaty (START I) of 1991, and New START of 2010—reflects these considerations.

Achieving the complete denuclearization of North Korea, however, will require negotiators to take a broader view of proscribed activities and items. The tendency of negotiators to focus on easily verified items or activities will be too minimalistic. In addition to monitoring fissile material and nuclear missiles, as done under traditional approaches, a denuclearization regime will need to account for weapons research and development and military-related activities. Additionally, it will need to provide flexibility to resolve inevitable confusion around ambiguous behavior by North Korea.

Stephen Biegun, who leads the U.S. working delegation to negotiate a denuclearization agreement with North Korea, speaks with South Korea's special representative for Korean Peninsula Peace and Security Affairs Lee Do-hoon at the Foreign Ministry in Seoul  on June 28. (Photo: Jeon Heon-kyun/Getty Images)For these reasons, U.S. insistence on a traditional verification framework in negotiations with North Korea—implicit in the U.S. goal of final, fully verified denuclearization in North Korea—does not match the scope of the challenge, nor does it provide negotiators the flexibility needed to reach meaningful agreement. North Korea’s reported resistance to providing an up-front comprehensive declaration of its nuclear program for fear of creating a “target list” shows the need for a new approach.1 The picture is complicated further by the high probability that North Korea will insist on retaining at least some nuclear weapons until the very end of the denuclearization process, as well as missiles that can carry nuclear or conventional warheads. Moreover, given its penchant for secrecy and extreme concerns about regime stability, North Korea probably would not permit on-demand access to sensitive facilities, especially military bases. Beyond resistance by the regime, verifying denuclearization within North Korea also presents specific operational challenges that increase complexity: a poor infrastructure that constrains energy supply, inadequate roads and transportation, risks to the health and safety of inspectors, and topography and tunneling capability that is conducive to the concealment of major items.

All of this amounts to the need to adopt an approach to denuclearization and its verification that is appropriate to this unique combination of challenges and allows for the broad prioritization of key activities and items of military significance. Shifting from the traditional to a probabilistic approach to verification could help negotiators address these challenges and diminish the likelihood that verification becomes an insurmountable obstacle to an agreement.

A Probabilistic Approach to Verification

For a denuclearization agreement to be comprehensive, it would need to prohibit or restrict a broad array of activities and capabilities beyond fissile material production. An associated verification regime requires a high probability of detecting a violation of one or more proscribed activities in time to allow an international response before North Korea could gain a military advantage from the violation. Achieving this target would not require 100 percent confidence that compliance with each and every term of the agreement can be verified. Rather, 100 percent confidence is needed that violation of at least one significant term will be detected in time. This is a critical distinction: though different in its theoretical approach, probabilistic verification in practice can still yield the high confidence required by policymakers in compliance assessments.

Probabilistic verification meets international security needs in situations where perfect or near-perfect verification arrangements are not possible, either because they cannot be imposed on one or more of the parties or because physical or fiscal realities do not allow them. Whereas traditional nuclear verification has focused on one or two readily observable objects or behaviors, such as missile dismantlement efforts or the nonoperation of plutonium-production reactors, probabilistic verification would encompass the many more capabilities and activities that enable a country to build and deploy a nuclear arsenal. In addition to fissile material production, this would cover weapons research and development, delivery vehicle production and systems integration, and military induction of nuclear weapons. This approach draws on the Carnegie Endowment for International Peace’s Nuclear Firewall Project, which identifies key technical and contextual indicators across the range of activities required to develop a nuclear arsenal as a means of distinguishing weapons-related programs from peaceful ones, whether in the context of nonproliferation or nuclear rollback.

The benefit of probabilistic verification comes from an aggregation of detection probabilities that provides an overall monitoring confidence across the full range of activities required for nuclear weapons. Monitoring confidence is a judgment made by nuclear negotiators and the intelligence community about the ability of a monitoring technology to achieve its stated objective.2 For example, if a ban on static rocket motor testing was ever to be negotiated as part of a denuclearization deal between the United States and North Korea, infrared satellite imagery would likely be included as a monitoring technology. As part of this future deal, North Korea would agree not to interfere with remote information gathering by using shields and other masking approaches. The ability of the satellites to observe covert motor tests would be based on how well and how frequently the satellite system was able to observe key zones of interest.

Assessing confidence in monitoring capability can vary based on a number of factors. For example, how effectively an indicator of noncompliance can rise above the background noise of other information will affect confidence in that indicator. The maturity of a monitoring technology will influence its perceived reliability, while its incorporation in previous verification regimes will affect its perceived negotiability. The timeliness of the result will directly affect whether the inspecting state is able to respond to a potential violation before it approaches the threshold of military significance. In the case of satellite-based monitoring of static rocket motor testing, the confidence judgment would be high, based on overall advances in spatial, temporal, and spectral resolution of satellite technology, the increased timeliness of image delivery, and the familiarity with satellite use as a proven information-gathering technology in a military and verification context.

Probabilistic Verification in Practice

A future denuclearization deal would need to monitor a broad range of activity in a variety of technical and military domains simultaneously in order to provide the international community adequate assurance of an end to the North Korean nuclear threat. Some activities for which there are established verification procedures, for example, fissile material production activities traditionally inspected by the IAEA or the deployment of nuclear delivery vehicles under the New START verification protocol, would be relatively straightforward to monitor.

How should negotiators think about the monitoring of activities not historically covered under nuclear agreements, such as the decoupling of warheads from missiles or a ban on weaponization activities and production of large rocket engines? Verifying the absence of such activities would be crucial to ensuring progress toward denuclearization, yet would require a level of access and intrusiveness that has not been negotiated in any previous arms control or international safeguards agreement. A notable exception here pertains to weapons design and development activities proscribed under Section T of the Joint Comprehensive Plan of Action agreement with Iran, the implementation of which by the IAEA has proven complicated.3 Negotiators would seem to face a choice between omitting weapons-relevant activities because the probability of detecting noncompliance on each and every activity is low or proscribing these activities and accepting that cheating on some may not be detected. In reality, though, a probabilistic verification system makes the latter option clearly preferable and overall more valuable than the traditional approach.

Generically speaking, in traditional and probabilistic verification regimes, some activities are exceptionally important and must be verifiable with high confidence. Examples could include plutonium production, uranium enrichment, and nuclear explosive testing. Under a probabilistic system, these top-tier activities would be supplemented with the monitoring of a range of other activities or capabilities deemed militarily significant, such as hydrodynamic explosions or static rocket motor testing. Even if 100 percent confidence in verification of these activities is not possible, they still merit proscription.

The innovation here is in shifting the focus of nuclear negotiations to overall monitoring confidence: the ability to detect violation in at least one monitored activity rather than confidence in detecting cheating on every proscribed activity.4 With this flexibility, negotiators can find agreement on a collection of monitoring activities that meets the U.S. requirement for a high overall monitoring confidence while providing a broader range of verification options to offer should North Korea object to any single approach during negotiation. Further, inclusion of activities with medium or low monitoring confidence does not incentivize cheating. In fact, probabilistic verification introduces an additional benefit by expanding the North Korean perception of the risk of cheating to a much broader range of activities that would be critical for sustaining a parallel program or a reconstitution capability.

As shown in table 1, the aggregation effects in a monitoring regime mean that the probability of detecting violation in at least one activity (Pat least one) increases as the number of monitored activities (i) increases. So even in cases where the majority of monitored activities are judged to be of low confidence, for example, in an inspector’s ability to monitor weaponization activities, increasing the number of monitored activities drives up the overall likelihood of detecting violation in at least one. This approach assumes that the probability of detecting violation in any one given activity is independent from others in the collection of monitored activities and items.

Verification experts may debate what constitutes low-, medium-, or high-confidence levels, but the important shift introduced by a probabilistic view on verification is the prioritization of deterrence value alongside detection probability. The U.S. intelligence community treats monitoring technologies with no better than a 50 percent chance of detecting violation, or with 50 percent uncertainty in a measured quantity, as low confidence.5 Yet, this perspective ignores the deterrent value of wide-scale, multimethod monitoring. For state leaders debating whether to cheat on a nuclear deal, a 50 percent chance of being detected is likely perceived as quite high and would be an important consideration in decisions to cheat in a militarily significant way.

In practice, it would be the job of the negotiating delegations, through the use of expert input from the technical, intelligence, and policy communities, to prioritize the activities and items to be included in the monitoring portfolio and estimate the likelihood of detection for each approach. The figure below shows representative examples of portfolio configurations at either end of the confidence spectrum and illustrates that even when activities outside of traditional verification practice are included, high overall monitoring confidence can be achieved. This alternative perspective sees value in the inclusion of activities and technologies that would be disregarded under a traditional verification framework, understanding that deterrence value should be considered alongside the overall confidence of a monitoring technology.



The advanced state of the North Korean military nuclear program, coupled with the unique nature of U.S.-North Korean relations, makes the denuclearization verification challenge unlike anything the international community has faced. Traditional approaches alone, safeguards and arms control monitoring, will not provide the coverage needed to confidently assess the elimination of the North Korean nuclear threat, nor are they likely to prove negotiable with North Korea. Thus, the North Korean verification challenge requires innovative thinking and problem solving well beyond the bounds of traditional verification approaches.

Critically, verification must be negotiated hand-in-hand with proscriptions on activities. Verification considerations should guide the prioritization of activities to limit, but in a way that broadens the scope and creates flexibility for how such limitations might be verified over time. If Pyongyang accepts proscription of an activity or technology, it would be foolish not to proscribe it merely because North Korea objects to a particular verification approach. The history of breakdowns in the 1994 Agreed Framework with North Korea and the later six-party talks, largely over differences of view on verification, underscores the importance of synergy between limitations and monitoring approach. A more flexible approach to verification, one that preserves monitoring confidence, provides negotiators with more options, and more fully contains the qualitative and quantitative improvements to North Korea’s nuclear program, is the best chance to provide sufficient verification and, over time, help create conditions under which North Korea would fully disarm.



1. “Trump to Meet With Kim Jong-un, Despite North Korea’s Lapses, Bolton Says,” The New York Times, December 4, 2018.

2. Howard Stoertz Jr., “Monitoring a Nuclear Freeze,” International Security, Vol. 8, No. 4 (Spring 1984): 95.

3. See Jarrett Blanc, “There Is No Crisis in JCPOA Section T,” Carnegie Endowment for International Peace, October 17, 2017, https://carnegieendowment.org/2017/10/17/there-is-no-crisis-in-jcpoa-section-t-pub-73454.

4. The probability of detecting violation in at least one proscribed activity is 1-Pnone=1-∏i1-Pi, where Pi is the violation detection probability in activity/item i.

5. Stoertz, “Monitoring a Nuclear Freeze,” p. 95.


Mareena Robinson Snowden is a senior engineer at the Johns Hopkins University Applied Physics Laboratory. Prior to this, she served as a Stanton Nuclear Security Fellow at the Carnegie Endowment for International Peace, where her research focused on nuclear arms control verification, nonproliferation, and modernization.

An innovative verification approach could help build confidence that North Korea is complying with any denuclearization agreement in the future.


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