CTBT Monitors Assist in Fukushima Aftermath

Robert Golan-Vilella

The monitoring system associated with the Comprehensive Test Ban Treaty has tracked the spread of radioactive particles from Japan’s damaged Fukushima Daiichi nuclear power plant and used models to predict their future paths, the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) said in a recent series of statements.

The system’s seismic and hydroacoustic components also helped provide emergency warnings in the minutes immediately after an earthquake occurred off the coast of Japan March 11, the CTBTO said. The earthquake caused a tsunami that devastated the Fukushima reactor complex and the surrounding area.

Radioactive particles released from the damaged reactors and spent fuel storage pools have scattered across the world. The materials were detected the next day at the Takasaki radionuclide monitoring station in Japan, 250 kilometers from the plant, according to an April 13 statement by the CTBTO. The particles spread throughout the Northern Hemisphere over the next 15 days, and on April 13, they were detected in the Southern Hemisphere, the CTBTO reported.

The radionuclide monitoring stations that detected the Fukushima fallout are part of the International Monitoring System, a global network of facilities that, when completed, will consist of 337 stations designed to help detect nuclear weapons test explosions. There are four types of monitoring stations: radionuclide stations, which detect radioactive particles emitted from nuclear reactions into the atmosphere; seismic stations, which can detect tremors produced by explosions underground; infrasound stations, which monitor low-frequency atmospheric waves that are produced by nuclear test blasts; and hydroacoustic stations, which measure sound waves in the oceans.

According to the CTBTO, the levels of ionizing radioactivity detected outside Japan are “far below levels that could cause harm to humans and the environment” and are comparable to natural background radiation.

The CTBTO’s monitoring system and International Data Center in Vienna also have been used to forecast the spread of the radioactivity from the Fukushima reactors. The CTBTO’s atmospheric transport modeling tool uses meteorological data to calculate the travel path of a given radionuclide. In the case of a suspected nuclear explosion, the agency would use “back tracking” modeling to try to determine where the material originated. Following the Fukushima disaster, it used “forward” modeling to predict where the radioactive particles would go. The CTBTO’s statement said that its models were “95% correct as the radionuclides reached the stations mostly within hours of the time predicted.”

The CTBTO operates the global monitoring system in preparation for the test ban treaty’s entry into force. Nearly 80 percent of the system’s planned monitoring facilities are currently operational; another 13 percent are either being tested or under construction.

Two of the system’s other elements—the seismic and hydroacoustic stations—also played a role in the initial moments after the earthquake. According to a March 11 CTBTO press release, more than 20 seismic and hydroacoustic stations sent data in real time to tsunami warning centers in the region. The press release said that this information contributed to the warning centers’ ability to issue rapid alerts, as the CTBTO’s monitoring data arrives as much as three minutes faster than data from other sources.

CTBTO member states first decided to allow data from the monitoring system to be used for “disaster mitigation purposes” following the deadly Indian Ocean tsunami of 2004. In August 2008, the CTBTO and Japan signed a bilateral agreement that officially authorized Japan to use CTBTO data to issue warnings in the event of a tsunami, as it did after the March 11 earthquake.