Cheryl Rofer worked on projects involving uranium chemistry, nuclear fuel cycle, and national security issues at the Los Alamos National Laboratory. She now writes at Nuclear Diner and on Twitter at @cherylrofer.
North Korea's nuclear test this week ratcheted up international tension. Six-party talks on the North Korean nuclear program ended in 2009, when North Korea walked out. North Korea has carried out four nuclear tests, in 2006, 2009, 2013, and this week.
The 5.1 earthquake magnitude associated with the test is too low to support North Korea's claim that the test was both successful and of a hydrogen bomb, at least by the standards of current nuclear arsenals. A rough calculation from that magnitude suggests that the yield was no more than 10 to 30 kilotons. That's still a lot of destructive power: 10,000 to 30,000 tons of TNT, enough to flatten a city.
Seismological stations around the world recorded the quake. Now they will pool and analyze their data to get a more precise estimate of the location and the test yield. The Organization for the Comprehensive Nuclear Test Ban Treaty operates a world-wide network (International Monitoring System) of seismological monitoring stations – and monitors radionuclides (radioactive isotopes), hydroacoustics, and infrasound as well. They are working overtime. Individual countries have additional monitoring capabilities.
The radionuclide results will be the most indicative of whether the test was of a fusion device. But North Korea has been adept at containing radionuclides from their tests. The radionuclides must be collected quickly; some have half-lives of hours to days and will disappear. Both airplanes and drones are being used to collect them.
Even under the best of circumstances, uncertainties will persist in interpreting what North Korea has done in this test. The geology of the test site, which affects calculations of the yield, is not well known in the West. Acquiring a full suite of radionuclides is unlikely. There is no reason to trust the official statement, although this and statements accompanying previous tests make clear that North Korea wants to develop a thermonuclear (hydrogen) warhead to fit on one of its missiles.
The relatively low yields of the four tests could suggest a number of things: 1) the tests are small-scale, to acquire data for modeling and technology development; 2) a focus on improving a particular nuclear weapon design; or 3) the tests are failed attempts at a final thermonuclear (hydrogen) design.
The North Koreans have a limited supply of fissile material, although that may be increasing with operation of their Yongbyon reactor and uranium enrichment facilities. They had to balance that against what they would gain from a test that would destroy some of that material. Whether the test was a success or failure, they learned something from it that will help them to improve their nuclear weapon design.
The test may be a celebration of Kim Jong-Un's birthday (Jan. 8). It may indicate a desire to wow the crowds at the Workers' Congress in May, the first such in 36 years. It may be a finger in the eye of the rest of the world. It may be a plea for more food and energy aid. It may be all of the above.
The sizes and progression of North Korea's four tests suggest that its purpose is to develop a thermonuclear weapon that can fit on one of their missiles. Until there is a much bigger test and their missiles improve considerably, there is no immediate danger to North America.
China and Russia have strongly condemned the test. They have no reason to want this neighbor to have a nuclear arsenal. They also are concerned about the stability of the Korean regime, which could result in a humanitarian disaster on their doorstep. Food supply in North Korea is fragile; war or regime collapse would make that worse. Refugees would stream out of North Korea into China. So China, which has more leverage over North Korea than other nations, will be careful in expressing its displeasure.
It will be necessary to resume talks with North Korea to stop its progress toward deliverable thermonuclear weapons. Their persistence in testing suggests that, just as it was impossible to persuade Iran to give up all its enrichment capacity, it may be impossible to persuade North Korea to give up all its bomb-making capacity. Hard choices lie ahead.