The Technological Assessment of the Fourth North Korean Nuclear Test and the Prospect of Future Tests

Publisher Han, Hong Jeon Editor-in-Chief KIM KWANGSIK www.kida.re.kr

ISSUE 17 MARCH 6, 2017

Sangmin Lee (Center for Security and Strategy, KIDA)

In order to prove that Pyongyang’s fourth nuclear test provides a significant contribution to the North Korea’s nuclear capability and that the test takes a role as a crucial watershed for future nuclear tests, this paper assesses the test with a viewpoint largely different from the previous assessments in technological terms. Furthermore, China’s careless judgment that the test was not worrisome seems to have led to strategies and policies towards North Korea supporting to maintain the status quo rather than to promote North Korea to change. Hoping China to acknowledge – although a bit late - that such judgments were misguided, this paper expects local and foreign North Korea experts to reassess the implication of the test.

he response of international society to the that of P5 nations, states known or believed to pos- Tfourth North Korean nuclear test has gone sess nuclear weapons, may have belittled the test awry from the beginning. The claimed power of the results; some pundits are now suggesting the test hydrogen bomb used for the test was far lower than was intended to experiment a boosted fission that of an average hydrogen bomb and rather weapon.2 However, the basis of overall responsive dwarfed the test which is widely deemed a failure.1 actions by the international society is highly influ- Comparing the recently tested hydrogen bomb with enced by the first assessment.3 Experts generally

assess that North Korea has not acquired the boost- Despite the use of a fusion reaction, the increase in ing technology, even from the viewpoint that the the generated energy is somewhat low - about 1%; as test was held to experiment a boosted fission the main purpose of fusion reaction is to increase the weapon.4, 5 fission reactions, it is distinguished from nuclear fusion weapons such as hydrogen bombs. The boosting technology was developed by major nuclear superpowers in early nuclear development stages as a measure to increase the yield while main- A successful test for boosted fission weapon taining the size and weight of a nuclear warhead. The use of fusionable materials is inevitable: nuclear It is highly likely that Pyongyang intended an fusion using deuterium and tritium is common. experiment on a boosted fission weapon.6 Tests on Creating a nuclear fusion under a condition of high the Megaton-level hydrogen bombs developed by temperature and pressure – generated in an early P5 nations cannot be conducted at the Punggye-ri stage of nuclear fusion by injecting a mixture of deu- underground nuclear test site. However, nuclear terium and tritium into a fissionable material called tests for hydrogen bombs requires boosted fission pit – results in multiple neutrons catalyzing nuclear weapons technology, and boosted fission weapons fission of the fissionable material that has not fis- sioned and therefore boosting the efficiency of over- with yields of tens of kilotons can be tested under- all nuclear explosion.”9 ground.7 Considering that the boosted fission weapon is used in a hydrogen bomb as its part, it is Prior to further discussions, the possibility that highly probable that North Korea has propagated North Korea intentionally set up a low yield for the the experiment on boosted fission weapons as a test of boosted weapon should be noted. Since hydrogen bomb test. This paper assumes that the boosting technology usually amplifies the yield of a “test” as in North Korea’s “test H-bomb” refers to a nuclear fission bomb by two to five times, the yield nuclear test on boosting technology – a prerequisite of the recently tested bomb can be anywhere for developing a hydrogen bomb.8 between 16 and 40kt10 if North Korea uses the tech- Prior to any further discussion, a basic under- nology acquired from the third nuclear test (i.e. standing for boosted fission weapons is necessary. approximately 8kt).11 However, the boosting tech- The following literature is cited for a reference to nology that can potentially multiply the yield ten- elucidate the principles in regards to the boosted fold may even cause other tunnels in the test site to fission weapon technology and its difference from collapse if the bomb’s yield reaches up to a nuclear fusion of hydrogen bombs. 80kt(8kt×10). To site an example, the tunnel entrance to Punggye-ri Site collapsed after North “The boosted fission bomb typically boosts the yield of Korea’s third nuclear test.12 It is assessed that nuclear explosions by utilizing only a small amount Pyongyang’s nuclear developers were concerned of fusionable material and thereby generating surplus that testing nuclear bombs with higher yield than of neutrons and increasing the frequency of nuclear those used for the third nuclear test may destroy the fission. Such an effect helps overcome the fizzle “branch tunnels” built to support additional nuclear effect caused by spontaneous fission occurring in tests. Although the boost ratio is not high, it is high- Plutonium bombs with less pure nuclear materials.

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ly probable that North Korea set up a lower yield tested an 8kt-bomb, testing a nuclear bomb with the for the nuclear test, bearing the risk of a tunnel col- yield of 4kt should pose no technological difficul- lapse. The nuclear researchers may have feared that ties. It is reasonable to assume that North Korea a failed nuclear test or a tunnel collapse may be can control the nuclear fission efficiency to test a held against them as responsible for the failure or 4kt-bomb, as Pyongyang’s second nuclear test delay in the nuclear program. demonstrated a yield of approximately 4kt. In addition, it is presumed that the researchers Those who understand the principles of nuclear refrained from conducting a nuclear test with a fission may point out that degrading the yield from yield higher than 20kt, with an apprehension of the 8 to 4kt may require more sophisticated technolo- nuclear waste leakage. Fully aware of China’s gies, as the latter uses a smaller amount of nuclear claims against the nuclear waste leakage ever since material. However, such a scenario only applies to its first nuclear test, North Korea has been shield- the case of developing a 4kt nuclear weapon; yield- ing its facilities with multiple layers of defilade in ing 4kt through a nuclear device in a test is a com- order to maintain ambiguity through suspending pletely different task. For states that already any exposure of its nuclear technologies. This is acquired the nuclear fission technology up to 8kt, substantiated by Pyongyang’s statements therefore, processing nuclear fission with a lower announced two hours after the test emphasizing yield would not be extraordinarily difficult. that the nuclear test was safely conducted with min- To sum up, North Korea is estimated to have imal impact to the environment. Although the max- intended a low yield that the fission would not imum yield of a nuclear test whose waste can be exceed 20kt, and its boosting technology is expect- effectively shielded in a horizontal underground ed to double the yield. If North Korea managed to tunnel may vary subject to geological features, boost the yield fivefold, intentionally or coincident- North Korea’s granite bedrock is generally expect- ly, the test would have demonstrated a yield of ed to defilade up to 20kt.13 20kt. If Pyongyang’s intent were to test nuclear capability under 20 kt, its boosting experiment could be evaluated as a success. In order to contain the yield below 20kt concerning the boosting ratio (i.e. two Pyongyang’s fourth nuclear test: techno- to five times), the optimal yield of the initial fission logical implications before the boosting should be around 4 kt. In other words, it is estimated that North Korea had pre- 1. North Korea is assessed to have acquired the pared the test with a minimum yield of 8kt (4kt × boosting technology required to miniaturize a 2) and a maximum of 20kt (4kt × 5), grafting the nuclear weapon. boosting technology (two- to fivefold) onto the 4kt- The capability to increase the efficiency of a fission. nuclear fission enables the boosting technology to From this, the next question may be on whether multiply the yield of a nuclear explosion while North Korea has the capability to produce 4kt-yield maintaining the existing design of nuclear fission equipment. As North Korea had already weapons. Even if North Korea did not achieve its

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targeted yield (e.g. 20kt) during the third nuclear the critical mass is used to miniaturize the weapon. test conducted in 2013 (8kt), achieving the target Such energy should form a high-temperature, high- yield may now have become possible through the pressure state, enabling the injected mixture of boosting ratio that can more than double the effi- small quantities of deuterium and tritium to fulfill ciency by injecting a few grams of mixture gas the conditions required for nuclear fusion reactions. composed of deuterium (D) and tritium (T). The misunderstanding originates from a lack of On the other hand, if North Korea acquired the understanding about nuclear fission. Such reason- boosting technology to amplify the fission efficien- ing overlooks the constraint that every fissionable cy fivefold, North Korea can reduce the amount of material cannot be chain-reacted, however success- required fissionable material compared to that used ful the chain reaction may be. The essence of in the third nuclear test and therefore support the boosting technology lies here: the purpose of the miniaturization of nuclear fission weapon nonethe- deuterium and tritium mixture is to help the less. Those who understand the concept of critical remaining fissionable material take part in the fis- mass, which refers to the minimum amount of fission reaction. This explanation may help under- sionable material required for nuclear fission, may stand the reason that the fissions can be boosted point out that there is a fallacy in the aforemen- two to five times, sometimes even tenfold. tioned logic. While the nuclear explosion requires Although the fission efficiency is overly low, the instant nuclear fissions triggered by a chain reac- yield generated from the fission can exceed the tion, the chain reaction would be ceased if the fis- expected level, given that a sufficient amount of sionable material is blown due to explosion before fusionable material is used. the material has enough chain reactions, which This is why the boosting multiplier alone does not would lead to an insufficient nuclear fission. suffice in assessing the overall maturity of nuclear Therefore, reducing the quantity of fissionable technologies. The boosting efficiency can be high material to a level lower than the critical mass for even with low nuclear fission prowess. The boost- chain reaction would discourage the nuclear fis- ing effect can be magnified due to a comparatively sion. As a result, the high-temperature, high-pres- abundant amount of fissionable material that has sure state that can trigger nuclear fusion reaction not been subject to fission. An advanced fission using deuterium and tritium cannot be achieved, technology, in contrary, may limit the boosting despite attempts to inject a mixture of deuterium multiplier: the amount of remaining fissionable and tritium to boost the fission. One therefore may material from the first fission is relatively low and misguidedly conclude that miniaturizing the may not be sufficient to trigger the second fission nuclear weapon by reducing the amount of fission- reactions with boosting technology. It therefore able material contradicts the application of boosting would be rash to assess that North Korea’s fission technology. Such misunderstanding, however, leads and boosting technologies are not advanced simply to one fundamental question of which occurs first: because the yield was boosted twofold during the fission or fusion – the fission does. Therefore, a recent nuclear test. certain level of fission reaction must occur, even when an amount of fissionable material less than

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2. Pyongyang’s future nuclear tests may involve through actual nuclear tests, the efforts must restart highly enriched Uranium (HEU). from the boosted nuclear test phase due to difficul- While it is highly probable that North Korea uti- ties in attributing the failure to a specific phase. lized Plutonium (Pu) as the fissionable material for Under a fear of harsh penalty for failure and high its first (2006) and the second (2009) nuclear tests, expectations from Kim Jong-un, the North Korean the material used for the third test is currently researchers may have preferred relatively safe paths unclear. Practically, however, it is highly likely that that yield a high rate of success to pushing an HEU has been used since the third test. Developing unfeasible plan that omits certain stages of devel- both types of nuclear technologies for Plutonium opment. It is therefore safe to assume that the North and HEU fission is unnecessary, provided that an Korean researchers continue to conduct nuclear abundant amount of HEU can be secured. From the tests based on HEU with boosting technology nuclear researchers’ point of view, quickly shifting applied. to the HEU-type technology would be a favorable If Pyongyang’s future nuclear programs do not option, especially considering the courses to take require additional supply of Plutonium, the deci- after the fourth test, such as a boosted nuclear test. sion to reactivate the 5MWe graphite moderated Relative convenience in acquisition makes HEU reactor (GMR) in August 2013 that had been obso- an attractive option for future nuclear weapons as lete since 2008 leaves room for a question. Since a opposed to Plutonium, acquisition of which will be small amount of Plutonium is needed during the rather limited. Whereas North Korea had been able nuclear fission phase for a hydrogen bomb, the to acquire 40 to 50kg of Plutonium for the past 30 remaining Plutonium is expected to be used for years, 20 to 30kg of HEU can be acquired within a nuclear tests and for the development of hydrogen year. bombs; the additionally produced Plutonium may Some experts assume that every nuclear test North be used for such purposes or smuggled abroad. The Korea has conducted used Plutonium, with a per- 5MWe GMR is a core facility necessary for a pro- ception that HEU does not require nuclear tests. duction of not only Plutonium but also tritium. The Application of the boosting technologies, however, nuclear materials produced in the reactor are neces- requires at least one nuclear test. sary for both fission and fusion. North Korea is not In order to develop a hydrogen bomb, as claimed likely to produce the materials depending on mea- by North Korea, boosting technology can only be surements of the exact amount of materials confirmed through nuclear tests. Even under gener- required for its nuclear program, but is instead ous conditions where every theory is revealed and a expected to sell the materials overseas in order to supercomputer enables a delicate modeling and replenish the fund for nuclear development when- simulation, developing a hydrogen bomb with a ever necessary. complex structure requires a boosting technology; theories and simulations alone cannot replace tech- 3. North Korea infers that the acquisition of a nological advance through actual nuclear tests. hydrogen bomb will be possible in the near If a hydrogen bomb test is recklessly pushed and future. fails without acquiring boosting technology As the boosting technology is critical for a hydro-

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gen bomb, securing critical fusionable materials nuclear weapon can be theoretically correct but such as Lithium-6 and overcoming additional may be proved unfeasible in reality. Use of Li-6 as nuclear tests may enable North Korea to pursue the fusionable material in large quantities to boost hydrogen bomb programs. Li-6 compounds that are the yield of hydrogen bomb to a Mt-level, however, more stable and have longer half-life than tritium suits both theory and the reality.16 Li-6 can theoreti- are more suitable as the fusionable material for a cally replace tritium and is more easily operable hydrogen bomb.14 However, tritium has a clear than tritium. advantage regarding the application of boosting Unfortunately, North Korea is expected to be technologies. Tritium, as gas or liquid,15 can be capable of acquiring Li-6, and thus it can be injected immediately prior to the use and can usual- inferred that North Korea is preparing for an addi- ly be stored separately, thereby enhancing safety of tional nuclear tests using the material. The follow- nuclear weapons; its yield can be adjusted depending article explains in detail the possibility of ing on the amount of injected mixture gas or liq- Pyongyang’s ability to acquire lithium and the fun- uids. In addition, the mixture of deuterium and tri- damental principle used to produce tritium with the tium has a simpler fusion process than that of a Li- lithium. 6 compound and can increase the amount of nuclear fission by producing comparatively more “According to NK Tech (www.nktech.net), North neutrons. Korean has large reserves of not only gold and tung- Every state possessing hydrogen bombs faces a sten but also minor minerals such as lithium and tan- dilemma: to store an absolute weapon that can talum, as the geographical structure of the nation is destroy one’s own soil. Therefore, a nuclear mainly composed of granite and granite gneiss. In weapon must be secluded by multiple layers of fact, North Korea chose 5MWe GMR because an safety measures to prevent an explosion by acci- abundant amount of natural Uranium and fine graphite is produced in North Korea, also known to dent or mistake, yet a swift launch has to be guar- be capable of producing lithium. Production of tri- anteed at the same time to optimize the weapon’s tium, which is required to produce a hydrogen bomb, effectiveness as a nuclear deterrence. The most may be a feasible option. In its natural state, most assured safety measure for a nuclear weapon is to lithium atoms exist as Li-6 (7.5%) or Li-7 (92.5%). separate the detonator. Although the fusionable Lithium commonly available in lithium ion batteries materials are isolated to prevent formation of consists mainly of Li-7, because Li-6 is separated fusionable material exceeding a critical mass level, from the extraction phase and is used for nuclear additional safety measures are required. Separating fusion. Projecting neutrons to the extracted Li-6 pro- the mixture of deuterium and tritium would be the duces tritium and helium. The technology used to most certain measure to prevent the fusion effect, separate Li-6 is already commercialized and can be which can develop a condition for a hydrogen easily obtained. Anyone who has a lab that can han- bomb’s fusion reaction, even in the event of an dle mercury can easily extract the material. Hoping accidental primary fission. North Korea does not possess a large quantity of Li-6 Therefore, the argument by some scholars that it is – a base material for production of tritium – would be feasible to use Li-6 rather than tritium for a boosted a complete naivety.”17

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Globally, only few states are known to produce and the test intentionally demonstrated a subdued lithium: Bolivia, the country famous for its salt yield to keep other branch tunnels safe and avail- lake, is one.18 Peculiarly, North Korea reserves an able for future nuclear tests. Provided that the abundant amount of minor minerals rarely found recent nuclear test yielded roughly 8kt, Pyongyang elsewhere. Technological advances that enable may need the next nuclear test to increase the boost lithium to be extracted from seawater were made ratio to the maximum – fivefold. only recently, implying that if North Korea had From the fifth nuclear test, North Korea is expect- secured lithium, it would most likely have been ed to include a full scale, not run-up, test for a extracted from mining, not from seawater. hydrogen bomb.19 Given that a “run-up” refers to Although the Korean Peninsula is small enough to the boosted nuclear test, it is reasonable to expect a safely assume uniform geological characteristics, full-fledged H-bomb test to follow. The purpose of North Korea reserves numerous mineral resources the South tunnel (#3) of the existing facility and the not available in the Republic of Korea. Although no new tunnel currently under construction (#4) is sufficient research has been conducted to explain highly likely to be full-scale tests of a hydrogen the peculiarity in the distribution of natural bomb. In reality, conducting a normal full-scale test resources, eruptions of Mt. Baekdu can be suspect- in North Korea would nearly be absurd, and North ed to have played a role. The existence of Cheonji, Korea is likely to be preparing a “new type” of the large volcanic lake located at the summit of the nuclear test of its own. mountain, presents evidence that an enormous vol- The readiness of the Punggye-ri site suggests that canic eruption occurred millions of years ago. It is it will be able to accommodate at least three more estimated that various types of minerals reserved nuclear tests. The estimation is evidenced by at underground were spewed as parts of volcanic ash. least one branch tunnel estimated to be inside the Ironically, Mt. Baekdu formulated a favorable envi- West tunnel (#2) and tunnels #3 and #4. ronment for North Korea to produce a hydrogen Considering feasibility, two tests for boosted bomb by providing Uranium, graphite, and even nuclear and one H-bomb test are probable. The lithium; and in return, North Korea’s nuclear tests yield demonstrated during the fourth test alone are creating chances for the mountain to erupt does not suffice in concluding that North Korea has again. perfected its boosting technology. Since the underground tunnels can withstand up to an yield of 20kt, the remaining durability of the tunnels imply that North Korea may expect to benefit from Outlook: Pyongyang's fifth nuclear test improved boosting technology and advancing its and onward nuclear capability through additional boosted tests. If a certain activity is observed inside the West tun- It is clear that North Korea will continue to con- nel (#2) in the foreseeable future, it will be highly duct nuclear tests. The fourth nuclear test was con- probable that Pyongyang's intention is to conduct ducted in a branched tunnel of the West tunnel (i.e. the fifth test in the branch tunnel. #2, where the three recent tests were conducted), In addition, a failed nuclear test or test launch of a

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ballistic missile is likely the worst possibility for for the recent nuclear test. Unlike the expectation the nuclear developers in a communist regime. of experts on North Korea and the hint by North Under an assumption that tunnel #3 is utilized for Korea, the three-month delay of carrying out the an H-bomb test, the tunnel #4, construction of test from September 10th, 2015, the anniversary of which was recently observed in 2015, can be a the Workers’ Party, can be due to delayed acquire- reserve tunnel available for such test. Tunnels #3 ment of fresh tritium. and #4 thus may be single tunnels without addition- The 5MWe GMR is expected to be continuously al branches prepared for a nuclear test with high active in order to conduct nuclear tests and produce yield. In order to prevent leakage of radioactive nuclear weapons. Consistence between Pyongyang’s materials due to the high yield, North Korea may future nuclear tests cycle (three years) and the oper- want to design a descending or a vertical tunnel ational cycle of the 5MWe reactor (also three years) with a horizontal entrance. Since the hill under may suggest a possible connection between these which tunnels #3 and #4 are located is lower than two elements. Tritium is an essential element of the adjacent hill where tunnel #2 is located, the idea boosted nuclear weapons, and its short half-life of excavating a tunnel with a descending slope in requiring regular replacements creates a continuous order to match the depth is somewhat likely. demand. Because the 5MWe GMR is such critical and useful a facility that it cannot be played down as a mere negotiation leverage, an extraordinary measure is called for.21 The 5MWe GMR is still a core facility for North Korea's nuclear program

The 5MWe GMR is an essential means in acquir- “Pressure and dialogue": strategy to ing tritium and Plutonium. Tritium's comparatively eliminate 5MWe GMR short half-life (i.e. 12 years) requires a stable supply. Since the amount of tritium halves every 12 Diplomatic efforts of neighboring states must aim years, it cannot be stored indefinitely once it is to blockade Pyongyang and eliminate the GMR. No acquired and must be regularly replaced. The heavy drastic changes are expected for China’s policy export restrictions imposed on tritium somewhat toward North Korea – to manage the business as limits smuggling, and its high costs may encourage usual – especially as it displayed a minor shift fol- North Korea to organically produce tritium instead lowing Pyongyang's third nuclear test. The fourth of relying on procuring from overseas. nuclear test did not bring about a significant change The only facilities in North Korea capable of pro- to Pyongyang’s nuclear capability, and China may ducing tritium are the reactor IRT-2000 for research have estimated that the US and the Western world purposes and the 5MWe GMR20 that resumed its would not change their stance toward North Korea. operation on Aug 28, 2013 and may have even US President Barack Obama intentionally omitted completed withdrawing a fuel rod. In such case, tri- comments on the fourth nuclear test in his annual tium produced from the GMR may have been used State of Union address.22 Considering the hawkish

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opinions prevailing in America and its government, North Korea nuclear development and will contin- the implied message may be that Pyongyang’s ue to take a key role of delaying the nuclear devel- fourth nuclear test does not even deserve a men- opment and denuclearization of Pyongyang. Had it tion. not been for the talks, North Korean would already US and China’s policies exerting pressure on have accomplished capabilities to test boosted North Korea will definitely favor Seoul, who nuclear test during its second nuclear test in 2009 should engage in a negotiation aiming for “block- and would have stepped up as a de facto nuclear ade” of North Korea instead of slightly intensifying power by now. It is therefore necessary to encour- the pressure. The key to a blockade lies in China age the neighboring nations to participate in the and Russia which border North Korea and thereby sanction with the mutual goal of blockading North take the nuclear proliferation seriously. North Korea and thereby exerting pressure on North Korea may have intentionally included the phrase Korea, urging Pyongyang to return to the six-party “related measures and technology will not be trans- talks. Because further delays in the deterrence of ferred,” to its statement after the fourth nuclear test nuclear program will only weaken Seoul's negotia- to dispel China’s and Russia’s concerns over tion leverage, North Korea should be brought back nuclear proliferation. to the dialogue. It is encouraging that the public opinion is form- ing in the Republic of Korea against recent arms trafficking by ISIS and North Korea.23 As the North Korean government nearly succeeded in developing a miniaturized nuclear weapon and is equipped with multiple delivery measures by developing SLBM and advanced submarines, a success in packaging a nuclear warhead with delivery means will drastically increase the probability of nuclear proliferation. The greatest victims of the proliferation would be the P5 nations that already possess nuclear weapons.24 Therefore, through sanctions and negotiations after the recent nuclear test, the minimum require- ment is that the 5MWe GMR must be eliminated. A complete elimination should be targeted, as freezing or deactivating the facility will only leave Pyongyang with leeway. Denuclearization of North Korea, a primary goal of the six-party talks, can only begin with Pyongyang returning to the dialogue. The six-party talks have demonstrated effectiveness in delaying

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9 Sang-min Lee. (Aug 14, 2014). “Study on the Possibility of 1 Joongang-ilbo (Jan 13, 2016) assessed the fourth nuclear test North Korea’s Development of Boosted Nuclear Weapons.” as failed, quoting a Republic of Korea government official Northeast Asia Strategic Analysis (NASA). Korea Institute for who commented “collected data shows that the nuclear test Defense Analyses (KIDA). only yielded 80% of what was yielded during the previous 10 The boosted yield is expected to be between 16kt (8kt x 2) nuclear test and testifies to a failed H-bomb test,” and citing and 40kt (8kt x 5). “Analysis on Unusual Signals (earthquakes and air sound 11 Though debatable in some aspects, it is safe to assume waves) in North Korea” published by Korea Institute of that the yields during the four nuclear tests were 1kt, 4kt, Geoscience and Mineral Resources (KIGAM). 8kt, 8kt, respectively. Minor discrepancies are possible but 2 Chosun-ilbo (Jan 21, 2016) underscored the possibility of a will not have significant changes on arguments made in nuclear test with the purpose of boosted fission weapon, this article. introducing US Congressional Research Service officer Mary 12 Although the collapses did not immediately follow the Beth D. Nikitin’s assessments on the fourth nuclear test nuclear test, the cracks generated during the test eventual- under article “ Pyongyang tested a boosted fission weapon, ly led to collapse of a large portion of the entrance during not an H-bomb.” Munhwa-ilbo (Jan 20, 2016), via the article precipitation. 38 North, a US-Korea Institute at Paul H. “North Korea to aim for a superlight nuclear warhead” Nitze School of Advanced International Studies (SAIS), pointed that Pyongyang’s fourth nuclear test is at least con- Johns Hopkins University website studying North Korea, tributing to miniaturization of North Korean nuclear provided a comparative analysis of images of Punggye-ri weapons, if not H-bomb per se, citing a Wall Street Journal test site taken on Apr 21 and June 1, 2013 respectively. commentary (Jan 19, 2016) jointly written by Victor Gilinsky 13 Lack of data on nuclear tests conducted in horizontal tun- and Henry Sokolski. nels under granite bedrock limits understanding about the 3 Despite hard-line policies of the Republic of Korea, US, and required capability and depth to contain radioactive mate- Japan, China has been rather tepid about sanctions against rials that need to be based solely on references made in US North Korea. See following article: Kookbang-ilbo (Jan 14, and China; experts at IAEA estimate the ceiling to be 2016) assessed China’s policy toward Pyongyang following around 20kt. the fourth nuclear test under the article “ China’s Stance Over 14 Li-6 is a stable isotope that is not subject to radioactive Pyongyang’s Recent Nuclear Test.” Dr. Young-hak Lee at decay. KIDA estimated that Beijing’s policy will display no drastic 15 Gas is normally converted to liquid through cooling and can shifts after the nuclear test, describing China’s policy as a be stored in the forms of liquid oxygen (-183℃), liquid dilemma between the need for the “ strategic asset” through hydrogen (-252.7℃), liquid helium (-268℃), or liquid a stabilized regime in North Korea and existence of the nitrogen (-196℃). “strategic burden” triggered by the North Korean nuclear 16 Fusionable materials for boosting purpose and nuclear test. fusion reaction purpose completely differ in terms of pur- 4 The boosted nuclear weapon is also referred to as boosted pose and effects. Whereas fusionable materials for boost- nuclear fission weapon or boosted fission weapon. ing purpose are used to generate additional neutrons and 5 The Korea Economic Daily (Jan 15, 2016), under the article improve fission efficiency, materials for fusion reaction “Pyongyang Has Secured Technologies for H-bomb purposes used in hydrogen bombs aims to use nuclear Program” estimated that North Korea failed in nuclear fusion fusion energy generated therein. attempts based on the reported yield of the tested bomb, 17 Sang-min Lee (Aug 14, 2014), op cit. although it juxtaposed an expert opinion that North Korea 18 0.006 percent of Earth’s crust contains Lithium stored as a has secured a large portion of technologies required to highly reactive compound. Saline lakes contain up to 1% of develop H-bombs. Lithium Chloride, suggesting a relatively high quantity of 6 The fourth nuclear test had long been predicted, and North Lithium compared to other minerals. Lithium is thus mainly Korea itself also suggested additional tests are possible, produced in Salar de Uyuni, Bolivia, Salar de Atacama, firstly using an expression “ a new type of nuclear test” on Chile, Argentina, USA, Canada, Australia, Zimbabwe, Tibet, 3/30/2014. Seven possible types of nuclear tests and priori- and Chaka Salt Lake, China. (Wikipedia) ties, necessities and possibilities, and limitations are listed 19 Nuclear fusion tests are normally referred to as hydrogen in June 2014 issue of Monthly North Korea. Sang-min Lee. bomb nuclear tests, and North Korea may have emphasized (June 2014). “ The New Type of Nuclear Test as Claimed by the term “ hydrogen bomb” to highlight the presence of the North Korea.” Monthly North Korea, Issue 510. p. 63. Seoul: warhead, as opposed to a bomb that is dropped from an Institute of North Korea Studies. airborne platform. 7 Choon-geun Lee. (2007). Scientific, Technological Understanding 20 The IRT-2000 reactor, although operational, is too obsolete About Underground Nuclear Tests(pp.13-46). Science and to continuously supply tritium in sufficient quantity that can Technology Policy Institute (STEPI). be used to manufacture nuclear weapons. 8 Korea Central TV.(Jan 6, 2016). “DPRK Regime Statement.” 21 It is important to note that although multiple options are

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available, including suspension of the reactor through talks, freezing, deactivation, kinetic strikes, and cyber attacks, stalling will only benefit North Korea. 22 State of Union address 2016, US White House. “ President Obama delivered his final State of the Union address on January on January 12th, 2016.” http:/whitehouse.gov/sotu. 23 Weekly Donga. (Jan 6 to 12, 2016). “ How North Korean AKs Ended Up in the Hands of ISIS’ Teenage Troops.” No. 1020. 24 Young-tae Jeong et al. (2015). North Korea’s Nuclear Strategy and South Korea’s Response. Korea Institute for National Unification (KINU).

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Sangmin Lee is an Active-duty Researcher at the Korea Institute for Defense Analyses. He joined KIDA in 2014 and his major research area includes NK’s WMD. [email protected]

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