Silencing the Bomb Read online

  MONITORING NUCLEAR TESTING BY NORTH KOREA

  North Korea is one of the few countries that have not signed the Comprehensive Nuclear Test Ban Treaty (CTBT). It withdrew from the Nonproliferation Treaty in 2003. In 2005 North Korea declared that it possessed nuclear weapons, testing underground in 2006, 2009, 2013, and 2016 at Punggye-ri, a remote site in the northeastern part of the country. Five North Korean tests were well recorded and occurred very close to one another.

  Although isolated, North Korea is a relatively small country and can be monitored readily by stations in South Korea, China, eastern Russia, Mongolia, and Japan. It consists largely of old rocks through which seismic waves are transmitted easily. Figure 14.2 shows the large numbers of stations of the International Monitoring Service that detected the North Korean nuclear explosion of 2013 with a yield of about 10 kilotons.

  FIGURE 14.2

  Seismic and infrasound stations of the International Monitoring System that detected the North Korean nuclear explosion of 2013.

  Source: Comprehensive Test Ban Treaty Organization, 2013.

  Kim and Richards calculated ratios of high-frequency seismic waves for events in North Korea, which are very similar to those shown for China in figure 14.1. Though not shown here, those ratios readily identify the five North Korean nuclear tests from 2006 to 2016 and a few rare, small earthquakes and chemical explosions. Seismograms of the North Korean tests are characterized by large P and a small Lg waves. Seismograms of small earthquakes exhibit the reverse: large Lg waves and relatively small P waves.

  Well-coupled nuclear explosions in North Korea, like these five, can be detected and identified down to a few tens of tons—a small fraction of a kiloton. Stations in South Korea detected infrasound signals—low-frequency sound waves in the atmosphere—for the 2009 explosion. They also were detected in Japan and eastern Russia and South Korea in 2013. Bomb-produced noble gases were identified for the 2006 and 2013 explosions.

  Monitoring a large underground explosion called the “chemical kiloton” at the Nevada Test Site in 1993 showed that two nonradioactive gases included in the explosive charge—sulfur hexafluoride and helium 3—could be detected in minute amounts along cracks and joints at the surface in the general vicinity of the shot point. Typically, they were detected at times of low atmospheric pressure and not at times of high pressure. Bomb-produced noble gases from an underground test are expected to behave similarly. Xenon isotopes were detected relatively late for the North Korean explosion of 2013, perhaps because leakage occurred many days later.

  Some scientists have questioned whether the 2009 test by North Korea was, in fact, a large chemical explosion because radioactive gases were not detected in surrounding countries but were observed for the even smaller explosion of 2006. Huge chemical explosions detonated suddenly and of similar yield (several kilotons) and seismic magnitude to that of the 2009 test are exceedingly rare. Most are detonated sequentially over times as long as a second to break rock effectively and to reduce damage to nearby structures. In addition, transporting that much chemical explosives to the North Korean test site would have required huge numbers of trucks or train cars, which presumably would have been detected by satellite imagery. I doubt the 2009 test was anything other than a nuclear explosion.

  North Korea announced all five tests ahead of time as nuclear and made no attempt to hide that fact, except possibly by detonating them at deeper than normal containment depths. They wanted other countries, particularly the United States, to know that they had nuclear devices. The main danger of North Korea’s possessing nuclear weapons is not that they might be used to attack the United States or its allies, because the United States undoubtedly would counter that massively. Instead, the real danger is that materials, plans for weapons, or nuclear weapons themselves could be sold or transferred either to other countries or to terrorists. Countering those threats deserves higher priorities.

  INDIA’S NUCLEAR TESTS

  The main reason India conducted a nuclear explosion first in 1974 and again in 1998 was fear not of Pakistan, but mainly of China, which captured territory from India during the Himalayan war of October 1962. China tested its first nuclear device in 1964 and its first multimegaton thermonuclear device in 1967.

  The modern Pakistani station at Nilore provided near real time seismic data for the nearby Indian nuclear tests of May 11, 1998, to the IRIS seismological data center in the United States. The test site at Pokhran is located in northwestern India near the Pakistani border.

  India and Pakistan, which have signed neither the CTBT nor the Noproliferation Treaty, do not send data to the International Monitoring Center. For India this likely stems from its not obtaining the language it wanted in the treaty in 1996, coupled with its unstated desire to test more sophisticated nuclear devices than the one it first detonated in 1974. The nationalist BJP party authorized the 1998 Indian tests when it came to power. Indian scientists later published high-quality seismograms for the Indian tests of May 11 and the Pakistani tests of 1998. Published reports indicate that the United States was caught off guard by the first Indian tests in 1998.

  Routine transmission of data from seismograph stations in India would be very helpful in monitoring Pakistan, China, Iran, and other parts of southern Asia. Near real time transmission of data would have aided assessment of the very damaging giant earthquake and tsunami off Sumatra and the Andaman Islands in December 2004. The seismic array in Niger in central Africa is one of the best monitoring stations for explosions and earthquakes in southern Asia, including India and Pakistan.

  The Indian prime minister said on May 11, 1998, that the yields of its tests earlier that day were as expected and that they consisted of fission, low-yield, and thermonuclear devices. He said they were contained and that no radioactivity was released into the atmosphere. This was followed six days later by a statement from Indian scientists that “there was no harmful radioactivity [my italics] from the contained nuclear tests.”

  The three nearly simultaneous nuclear explosions by India on May 11, 1998, produced craters and damage that can be seen on unclassified satellite images as well as in photographs released by India. It is hard to believe that radioactive materials, especially noble gases, were not vented, because explosions shallow enough to produce craters often leak radioactive gases. India’s explosions at Pokhran in 1998 were within 2 miles (3 km) of the crater produced by its first nuclear test in 1974.

  The magnitude of 5.3 determined from global data for the three simultaneous explosions on May 11, 1998, indicates a total yield of about 14 to 20 kilotons. The combined yield for the three tests as announced by the India’s Bhabha Atomic Research Centre, however, was considerably higher, 58 kilotons. It is hard to comprehend that the yield based on global data could have been underestimated by a factor of three to four. India’s official yield for the 1974 test, called the Smiling Buddha, was 20 kilotons, also higher than estimates made by other countries.

  India obtained the plutonium for its 1974 explosion from a non-safeguarded reactor that followed a Canadian design. The United States provided the heavy water moderator for the reactor. India claimed the 1974 test was a peaceful nuclear explosion and that it did not violate the Limited Test Ban Treaty, which it had signed. Still at issue is whether India violated its peaceful use agreements with Canada and the United States.

  Debate has raged in the media among Indian nuclear scientists about whether their country obtained a dependable thermonuclear (hydrogen) device through its tests in 1998. Its relatively small seismic magnitude indicates it may have failed to produce its full yield. Thermonuclear devices typically are triggered by fission explosions with yields of about 10 to 20 kilotons. Some Indian nuclear scientists, in fact, claim India needs to test a larger thermonuclear device to make sure they have an H-bomb capability. Others in India say they do not need such a test. India, which has not tested a nuclear weapon since 1998, might well have tested a boosted fission weapon at that time.

  Indi
a and Pakistan each have aircraft that can carry nuclear weapons to the other. India has tested ballistic missiles that can reach China and, of course, Pakistan. Future nuclear explosions by either India or Pakistan could lead the other to test. China then might test as well.

  The use of nuclear weapons by India, China, or Pakistan against one another represents a great nuclear threat today. Huge populations are at risk. Each continues to pursue more advanced delivery systems. Pakistan’s nuclear arsenal continues to grow. Of particular concern is that neither India nor Pakistan may have mechanisms on their nuclear weapons to insure against unauthorized use or unplanned nuclear detonation during an accident or fire.

  India also claimed soon afterward that it tested two small experimental nuclear devices with yields of 0.2 and 0.6 kilotons nearly simultaneously two days later, on May 13, 1998, at 06 hour 51 minutes. I know of no seismic stations that recorded those claimed very small explosions. The Nilore Pakistani station had a signal-to-noise ratio of about 1000 for the combined explosions two days earlier on May 11. My colleague Paul Richards found that Nilore had the capability to detect a combined yield on May 13 of about 0.025 kilotons (25 tons). Those estimates of yield assume they were conducted in the same rock type as those on May 11. This is much smaller than the announced Indian combined yield of 800 tons. India described one of the tests on May 13 as having been detonated in a sand dune, a poor coupling material. If so, the combined yield could have been one to a few hundred tons, still smaller than the combined announced yields.

  Possible explanations of these inconsistencies are: (1) the two events detonated but were much smaller than one to a few hundred tons; (2) either they both failed to detonate or only the one of 200 tons did; (3) the yields were poorly calibrated by India, as they were for the explosions of May 11; or (4) the yields were exaggerated.

  The implications for monitoring are that if craters were formed today as claimed by India for the two very small explosions on May 13, 1998, they would be detectable by satellite imagery and synthetic aperture radar (INSAR). If radioactivity was released, such an event set off today should be detectable. In any case, if one or both of those explosions on May 13 occurred in a sand dune, as claimed by India, it would be difficult to hide because dry sand is not a good medium for hiding a sub-kiloton clandestine nuclear explosion at shallow depth.

  PAKISTAN’S NUCLEAR PROGRAM AND TESTS

  The loss of East Pakistan (now Bangladesh) in a civil war may have triggered a 1972 political decision in Pakistan to begin a secret nuclear weapons program. India’s 1974 nuclear explosion likely gave additional urgency to the program. Pakistan and India clashed several times after the partitioning of the two countries in 1947 when each gained independence from Britain. The two countries have fought over territory in Kashmir many times. Pakistan’s conventional forces being inferior to those of India, whose population is considerably greater than Pakistan’s, likely contributed as well to its quest for nuclear weapons.

  Pakistan announced it conducted two series of nuclear explosions in late May 1998, soon after India tested on May 11. It said that the first set consisted of five explosions, which were detonated nearly simultaneously. Many people have speculated that Pakistan wanted to “up India’s claim” of five tests earlier in May. Pakistan’s two sets of explosions were well recorded internationally. The combined yield of the first set was about 10 kilotons, the second about 5 kilotons.

  Pakistan gained uranium enrichment technology from many sources. It also obtained knowledge about nuclear weapons and missile technology from China. A. Q. Khan, widely regarded as the father of Pakistan’s nuclear program, learned about centrifuge enrichment when he worked at the Uranium Enrichment Corporation, URENCO, in the Netherlands. URENCO provides enriched uranium for many European nuclear power plants. Khan stated that Pakistan began uranium enrichment in 1978 and produced highly enriched uranium by 1983. He reportedly stated in an interview in a speech in January 2010 that Pakistan “had become a nuclear power” in 1984 or 1985.

  In 1990 President George H. W. Bush failed to certify that Pakistan did not possess a nuclear explosive device. The United States hesitated on several occasions to declare that Pakistan had a nuclear weapons program because of its desire to obtain Pakistani help in combating the Russian invasion of Afghanistan and in pursuing a war against the Taliban and Al Qaeda.

  Khan’s nuclear assistance extended to several countries was likely the most dangerous act of proliferation thus far during the nuclear age. The U.S. Congressional Research Service reported in May 2012 that Khan and his network had sold centrifuge technology for uranium enrichment to Libya in 1984. Libya revealed and gave up its nuclear facilities in December 2003. It then signed the CTBT and the Nonproliferation Treaty. One reason Libya did so was fear that the United States, Britain, and other countries would invade it. Materials that had clearly originated from Khan’s group in Pakistan were found in documents that Libya surrendered. Khan announced in 2005 that he and his associates had sold centrifuge technology to North Korea. They may have offered similar assistance to Iran, Egypt, and perhaps Syria and Saudi Arabia.

  In their 2009 book The Nuclear Express, Thomas Reed and Danny Stillman say they believe Pakistan tested its first nuclear bomb in 1990 at China’s Lop Nor site. China considered Pakistan to be a regional ally. Others have expressed more uncertainty about the amount of Chinese nuclear assistance.

  Reed was a former nuclear weapons designer at Livermore, secretary of the Air Force, and a special assistant to President Reagan for national security policy. Stillman worked at Los Alamos for decades in nuclear design, diagnostics, and testing. He directed the Los Alamos Technical Intelligence Division for thirteen years. They were experts on Soviet and Chinese nuclear weapons. Reed and Stillman also describe how various countries acquired nuclear expertise from others who already possessed nuclear weapons.

  In an interview in U.S. News and World Report, Reed said, “There are numerous reasons why we believe this to be true, including the design of the weapon and information gathered from discussions with Chinese nuclear experts.” Reed claims that the Pakistanis were so quick to respond to the Indian nuclear tests in May 1998 because the Chinese had already helped them prepare for a test to be conducted within Pakistan. Reed also noted, “It only took them two weeks and three days [to respond and test].” Reed and Stillman claim the Pakistani test on May 28, 1998, likely was a single explosion, not five. It was of an advanced HEU (highly enriched uranium) design. It is clear from seismic data that Pakistan conducted tests at two separate sites in May 1998.

  The United States was concerned several times about Pakistan’s ongoing production of nuclear weapons and its political instability that could lead to weapons’ falling into the hands of insurgents and perhaps terrorists. Pakistani officials and high military officers have stated many times, however, that their nuclear weapons are secure.

  Nettles and I worked on the identification of seismic events located in the vicinity of the two Pakistani nuclear tests. Pakistan is second only to Lop Nor in the number of earthquakes per year within 62 miles (100 km) of their test sites. We obtained focal mechanism solutions of the very long period type for ten moderate-size seismic events from 1980 to 2008, which indicated that they were earthquakes, not explosions. We found that all but one of the Pakistani earthquakes occurred at depths of 12 to 44 miles (18 to 61 km), indicating that they must have been earthquakes. Several other seismic events in Pakistan were identified as earthquakes using the Ms-mb technique.

  Identification of small earthquakes in Pakistan could be much improved by analyzing high-frequency seismic waves, which the Lamont group has not done. Seismic data from nearby stations in Afghanistan, Oman, and the United Arab Emirates have become available recently. Data from Indian and Iranian stations would be valuable as well to better monitor Pakistan. It is understandable that Pakistan did not make seismic data available for its tests later in May 1998. Monitoring, of course, needs to assume that a country testing a n
uclear device will not provide seismic data from its own stations, at least not immediately.

  ISRAEL’S NUCLEAR PROGRAM

  Although none of the countries in the Middle East has declared that it possesses nuclear weapons, Israel maintains a policy of nuclear ambiguity. In the arms control community, it is very widely thought that Israel started to acquire nuclear weapons in the 1960s and now possesses about eighty. Its Dimona reactor, constructed with French help, went critical in December 1963, according to Reed and Stillman.

  Israel, France, and Britain went to war with Egypt in October 1956 to reopen the Suez Canal, which had been seized by President Gamal Abdel Nasser. President Eisenhower publicly opposed the operation, and the Soviet Union issued an ultimatum to Britain, France, and Israel to desist, threatening actions that would menace the existence of Israel. Humiliated by the two superpowers, the three countries believed they could no longer count on American support.

  Reed and Stillman say, “It is quite clear that France and Israel undertook a joint nuclear weapons program in the aftermath of Suez. That relationship, on a commercial basis, continued for decades.” The Dimona reactor in Israel, which produced plutonium, was very similar to the reactor at Marcoule, France. Reed and Stillman state, “Some wags have noted that on February 13, 1960, the two nations went nuclear with one test [in Algeria].” If true, this would explain why Israel has a modern nuclear arsenal without having tested by itself in the 1960s. Israel, a small country, does not have a test site of its own and is easily monitored from surrounding countries.