To Catch a Proliferator: The Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization’s Verification Regime

Author: Drew Masada

One of the underlying assumptions of any robust nuclear arms control regime is the need to halt attempts at nuclear proliferation. Regimes develop and refine their nuclear programs through testing their weapons. Unlike chemical and biological weapons programs that are mobile, easily concealed, and not easily traced - due to the size of the laboratory, ready availability of base materials and ease of replication - nuclear facilities are large and nuclear tests emit energy that can be traced through air, land, and sea. Some nations have the independent capacity for monitoring, but the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO) is the only international organization that monitors for these tests. The CTBTO, whose mission is to prevent the testing of nuclear weapons everywhere on earth, has developed a verification regime consisting of 337 monitoring stations positioned worldwide. The system uses four different types of technologies: seismic, hydroaccoustic, infrasound and radionuclide. Data gathered at these stations is sent to the Information Monitoring System (IMS) center at the CTBTO headquarters in Vienna, where it is analyzed and disseminated. Putting aside for a moment the political aspects of how the verification system might work, understanding more about the technical aspects of the system can help the reader to make a more informed judgment as to the utility of a non-proliferation regime. When operating as intended, the system alerts the CTBTO to the possibility that a nuclear test has occurred.

Nuclear tests emit waves of energy that can be picked up by seismometers as they pass through the earth’s surface. Seismic waves can be caused by any number of events, such as plate shifts, mine explosions, and nuclear explosions. The CTBTO has fifty primary and 120 auxiliary seismic monitoring stations in seventy-six countries, placed in array formations that help eliminate background noise. In seconds to minutes after a nuclear event, seismic monitoring stations can pick up the waves, allowing analysts to determine the approximate location and strength of the event.

Hydroaccoustic stations, like the name suggests, use microphones to monitor sound waves that cause changes in water pressure. These changes in pressure can be caused by a number of events, such as underwater earthquakes, volcanic eruptions, military exercises, and nuclear tests. The CTBTO have eleven hydroaccoustic stations, six in the water and five near shores, covering the Atlantic, Pacific, and Indian Oceans.

Infrasound technology can also help pinpoint the location of the event. Designed to detect atmospheric nuclear explosions, sixty stations in thirty-five countries detect changes in atmospheric pressure caused by storms, meteors, rocket launches, earthquakes, volcanoes, and nuclear tests.

Radionuclide monitoring is the fourth and final technology used to detect nuclear tests. A radionuclide is an “isotope with an unstable nucleus that releases its excess energy in the form of radiation, or radioactive decay.” While other methods are able to locate and approximate the size of the event, only the presence of radionuclides can serve as a confirmation that the event was nuclear in nature. If the test occurs in a shallow underground area, underwater, or in the atmosphere, radioactive fallout from the explosion binds to particles in the air. Depending on weather patterns, these radioisotopes are picked up by monitoring stations days to weeks later. If tests are conducted in facilities deep underground or in natural structures that may contain such blasts, such as salt caves, radionuclides will not make it up to the atmosphere. However, noble gases have a higher chance of escaping into the atmosphere where they are picked up by noble gas monitoring systems.

The CTBTO has eighty stations in twenty-seven countries, forty of which are outfitted with a noble gas detector. These instruments take periodic samples of the atmosphere that pass through the station. Unfortunately there are times during which even the noble gases are not detected. While the CTBTO was able to quickly pinpoint the location and size of the 2009 nuclear test by the Democratic People’s Republic of Korea (DPRK), after three weeks, they could not detect any radionuclide emissions. Some believe that the deep underground explosion collapsed the rock, around the event, effectively containing any radionuclide/noble gas emissions. Others postulate that the nuclear weapon tested was of insufficient size to be detectable by the network. Finally, it is possible that it was not a nuclear weapons test at all, but merely a carefully designed explosion, intended to mimic the effects of nuclear weapon for the purpose of convincing international audiences of the DPRK’s progress towards a more advanced weapon.

And as with the other methods of detection, one must learn to filter out the background noises. Radioactive isotopes can come from a variety of sources, such as civilian nuclear generators, cyclotrons, and large radionuclide production facilities like Chalk River in Canada. Fortunately, an effort is underway to pinpoint and catalogue the locations and emissions of the facilities to better establish a normal “background level” of radioisotopes.

The work of the CTBTO verification regime has created a multinational institutionalized center for collection and dissemination of information with growing levels of coverage and experience in detection. Hopefully, this buildup of capacity can foster faith in the process so that it can be relied and called upon to detect and verify the efforts of would-be proliferators and deter attempts at defection from the regime. For the future, there is still much progress that must be made on the technical, as well as the political, side before the CTBTO verification regime becomes a reliable tool of the non-proliferation regime.