This paper reviews the technical issues underlying space-based boost-phase missile defense and examines the current technology available for space-based interceptors and the characteristics of the missiles such a system would face. It then analyzes a particular space-based missile defense system that has been proposed to intercept in boost, ascent, and midcourse phases to illustrate the details of such an analysis and the constraints imposed on such systems by the physics of operating in space.
This work considers the direct use of 60%-enriched uranium in pure fission nuclear weapons. From numerical simulations and simple analytics this work shows that substituting a weapons-grade core for a 60%-enriched core reduces the yield by a factor of 4 to 5 that is fairly insensitive to classified design details. A weapon designed to achieve a nominal 10 kt yield using weapons-grade uranium could therefore still produce a modest yield of 2-3 kt using a core of lower enrichment.
Since North Korea left the Treaty on the Nonproliferation of Nuclear Weapons in 2003, its nuclear fuel cycle has continued to operate and develop further, without transparency to international inspectors. A recent addition is the Experimental Light Water Reactor that started operation in October 2023. One concern is that this reactor may be used to produce plutonium for nuclear warheads, in addition to or instead of being used for electricity production. In this work, fissile material production in the new reactor is explored by modeling a possible core design and integrating information from available remote monitoring, such as satellite imagery of cooling water outlets from the facility. The results indicate that running the reactor with an initial enrichment of 1.75% or lower could potentially produce up to 20 kg of weapons-grade plutonium annually, substantially increasing North Korean plutonium production.
We present an imaging system that employs zero-knowledge protocols to protect sensitive geometrical information, along with procedures to increase confidence in the result. The goal of this work is to enable the inclusion of warhead confirmation measurements in future arms control treaties. We present a demonstration of both true positive and true negative measurements that validate models and establish authenticating procedures toward meeting acceptance requirements for use in nuclear facilities. We use a two-dimensional time-encoded fast neutron imaging system with an anti-symmetric mask pattern; the fast neutron count values exceeding minimum or maximum thresholds indicate that two measured items are not identical. Laboratory measurements over twenty trials show that alarm rates for negative confirmation measurements are within uncertainties of model predictions. Positive confirmation measurements indicate that alarm rates are large enough to encourage treaty compliance.
This paper explores the applications and limitations of purely inertial navigation systems, the use of global navigation satellite systems, and the integration of inertial navigation systems with global navigation satellite systems. A full trajectory simulation accounts for gravitational anomalies, atmospheric effects, and instrumentation errors with Monte Carlo sampling for uncertain parameters and complete error propagation. This simulation disambiguates the contributions of each source of uncertainty to the total error in the final impact point for a range of ballistic trajectories with and without maneuverable reentry vehicles and estimates the limitations to accuracy at intercontinental ranges. Based on these results, the paper discusses the potential for integration of inertial navigation systems with global navigation satellite systems to improve the accuracy of intercontinental ballistic missiles.
This study assesses the vulnerability of silo-based ICBMs to conventional prompt strike weapons. The study's focus is on hypersonic boost-glide weapons, but its results are applicable to other hypersonic vehicles such as ballistic missile reentry vehicles. It finds that, if US hypersonic weapons achieve accuracies consistent with stated design goals, they would be able to defeat silo-based ICBMs with comparable efficacy to nuclear-armed ballistic missiles. Because these weapons do not follow ballistic trajectories for most of flight, the United States has argued they are not subject to numerical limits under New START, a position it could maintain under future arms control agreements employing similar counting rules. Thus, US precision-guided, conventional hypersonic weapons programs offer the United States a plausible means of expanding its counterforce capabilities unencumbered by limits imposed under nuclear arms control treaties. These programs, if pursued without constraints, are therefore likely to undermine great power strategic stability.
In future nuclear arms control treaties, it will be necessary to authenticate the hardware and software components of verification measurement systems, i.e., to ensure these systems are functioning as intended and have not been tampered with by malicious actors. While methods such as source code hashing and static analysis can help verify the integrity of software components, they may not be capable of detecting tampering with environment variables, external libraries, or the firmware and hardware of radiation measurement systems. In this article, we introduce the concept of physical differential fuzz testing as a challenge-response-style tamper indicator that can holistically and simultaneously test all the above components in a cyber-physical system. In essence, we randomly sample (or "fuzz") the untampered system's parameter space, including both normal and off-normal parameter values, and consider the time series of outputs as the baseline signature of the system. Re-running the same input sequence on a untampered system will produce an output sequence consistent with this baseline, while running the same input sequence on a tampered system will produce a modified output sequence and raise an alarm. We then apply this concept to authenticating the radiation measurement equipment in nuclear weapon verification systems and conduct demonstration fuzz testing measurements with a sodium iodide (NaI) gamma ray spectrometer. Because there is Poisson noise in the measured output spectra, we also use a mechanism for comparing inherently noisy or stochastic fuzzing sequences. We show that physical differential fuzz testing can detect two types of tamper attempts, and conclude that it is a promising framework for authenticating future cyber-physical systems in nuclear arms control, safeguards, and beyond.
After the start of the Russian invasion of Ukraine in 2022, missile defense systems became more prominent and sought after on a global scale. In 2023, Germany decided to purchase the Israeli Arrow missile defense system. This article derives technical capabilities of the Arrow missile defense system from publicly available information, with a focus on the Arrow 3 interceptor. This information is the basis for an analysis of Arrow's utility to defend Germany within a larger European context against existing and potential future missile threats from Russia. The interceptor's capabilities are assessed using a newly developed missile defense footprint calculation and comparison program. The program calculates trajectories of missiles and interceptors, and sectoral footprints. The results suggest that Arrow 3 is theoretically capable of intercepting Russia's current long-range and potential future intermediate-range ballistic missiles. It will be of no use against existing Russian short-range ballistic missiles and of limited use against existing medium-range ballistic missiles.
This paper analyzes hypersonic cruise missiles (HCMs) powered by hydrocarbon-fueled scramjets and compares their capabilities to other systems that might perform the same missions, including hypersonic boost-glide vehicles (BGVs) and maneuverable reentry vehicles (MaRVs). Most analysis of hypersonic weapon capabilities has focused on BGVs, while HCMs are a distinct technology with distinct characteristics. We analytically model the X-51A HCM vehicle that the United States flight tested in 2010-13 and use that model as a basis for assessing the potential performance of near-term HCMs for military use. We find that these HCMs can have lower masses than BGVs of the same maximum range, but significantly higher masses than MaRVs of the same range. Because these HCMs use hydrocarbon fuels, they are limited to flying at low hypersonic speeds relative to BGVs and MaRVs, giving them longer flight times than those systems over the same range and making them vulnerable to interception by terminal missile defenses. We find that HCMs can be more maneuverable than BGVs during the atmospheric portion of their flight, though less maneuverable than supersonic cruise missiles.
This paper provides a framework for assessing the vulnerability of strategic missile silos in the United States, Russia, and China to conventional weapons with any accuracy or explosive yield. Comparisons between ground motions induced by nuclear surface bursts and earth-penetrating conventional explosions were made to calculate the maximum distance at which a silo-based missile would be vulnerable to a conventional detonation. Single-shot kill probabilities then confirmed that U.S. long-range air- and sea-based precision conventional cruise missiles possess lethalities against missile silos comparable to U.S. nuclear ballistic missiles: typically well above 90%. This result suggests that long-range conventional weapons may not only be substituted for the silo counterforce targeting roles of nuclear weapons, but may have broader strategic stability and defense implications due to the relative survivability of and reliance on specific nuclear forces among nuclear powers and regional defense dynamics driving the acquisition of similar weapons by more countries.
Our work explores North Korea's 100 MW-th Experimental Light Water Reactor (ELWR) and its potential contributions to the country's nuclear weapons program. Built at the Yongbyon Nuclear Research Center, the ELWR began operations in October 2023 and represents North Korea's first attempts at a light-water reactor using domestically-enriched, ceramic fuel. Our study examines possible configurations for energy, tritium, and tritium-plutonium co-production. Assuming a single-batch core, the ELWR can be used to annually produce 48-82 grams of tritium, which can supply 2-4 new boosted warheads each year, up to a maximum arsenal of 88-150 warheads total. Concurrent production of tritium and weapon-grade plutonium is also possible but requires reprocessing of spent ceramic fuel. These findings underscore how North Korea's nuclear capabilities may be advanced through the ELWR's dual-use potential.
The idea of using neutrino detectors to monitor nuclear reactors has been discussed for decades, but it is not always clear what reactor-to-detector distances and detector sizes would be involved. The purpose of this study is to offer some concrete, historically grounded data points: namely, estimates of standoff distances and detector sizes for 64 reactors involved in plutonium production for weapons programs. This data set spans nine countries and 70 years. For each reactor, we estimate the distance from the core to the facility boundary, one conceivable standoff for cooperative monitoring. We also find the distance from the reactor to the nearest international border, the shortest possible standoff for non-cooperative monitoring. We estimate the neutrino detector size required in both cases, considering inverse beta decay and electron scattering channels. Overall, the data set provides a realistic orientation to the distances and detector size scales involved in reactor neutrino monitoring.
Reports suggest that Pakistan's indigenous, military nuclear program faces a natural uranium shortage, limiting fissile material production. However, Pakistan has recently built three new plutonium-producing reactors and significantly expanded its reprocessing capabilities. The solution to this apparent contradiction could be an optimized fuel cycle, in which reprocessed uranium is reused to produce more fissile material from the same natural uranium stocks. To estimate Pakistan's highly enriched uranium (HEU) and plutonium production, this article combines a statistical framework with fuel cycle and reactor simulation codes. It explores different scenarios that Pakistan could use to efficiently allocate its limited uranium resources. The results indicate that Pakistan cannot support simultaneous HEU and plutonium production in a once-through fuel cycle, and that HEU production can only be sustained in alternative cycles. Calculations suggest plutonium stockpiles of 370 to 660 kg and, depending on the scenario, HEU stockpiles of 3,090 to 5,540 kg by the end of 2022.
Nuclear verification includes confirmation measures of nuclear weapons and fissile material, which often rely on the detection of radiation signatures. It is an open research question whether these signatures are unique. Or in reverse, could a malicious actor imitate these signatures and compromise verification of disarmament processes by using hoax objects instead of real warheads? This article presents several warhead emission models and a simulation framework to assess the uniqueness of their passive gamma radiation signatures. A red team approach includes detailed simulations of three proposed confirmation systems: The Information Barrier eXperimental, and the Information Barrier eXperimental II, both developed at Princeton University, and the Trusted Radiation Identification System, developed at the Sandia National Laboratories. For these simulations, various hoaxes are analyzed: warheads using reactor-grade plutonium instead of weapon-grade plutonium, combinations of different gamma emitting isotopes, and combinations of neutron sources with radioactive isotopes. Our findings reveal that numerous radioactive signatures are not unique and may be susceptible to imitation. Moreover, confirmation systems based on passive gamma radiation signatures using low bin numbers demonstrate a limited ability to accurately handle warheads of varying ages.
China is constructing three new nuclear ballistic missile silo fields near the cities of Yumen, Hami, and Ordos as part of a significant buildup of its nuclear weapon arsenal. Once operational, these missile silos will likely be included as targets in U.S. strategic counterforce war plans. Such plans call for using one or two nuclear warheads to strike each silo. Such attacks can generate large amounts of radioactive debris that are then transported by local winds and can deliver lethal doses of radiation to population hundreds of kilometers away. Here, we compute radioactive fallout from counterforce attacks on the three new alleged missile silo fields using the combination of a nuclear war simulator and modern atmospheric particle transport software and recent archived weather data. We find that the construction of these new silos will put tens of millions of Chinese civilians at risk of lethal fallout including in East China. In particular, the relatively short distance between the Ordos missile field and Beijing and the local winds patterns for the region, suggest that about half of the 21 million inhabitants of the Chinese capital could die following a counterforce strike, even if given advanced warning to shelter in place.
Digital twin technology can improve the effectiveness of international safeguards inspectors by providing a tool that can perform an accurate acquisition pathway analysis, identify pathway indicators, develop required sensors to detect indicators, and monitor facilities in real time using critical data streams that benefit from this safeguards-by-design approach. Safeguards inspectors are required to visit facilities and verify the nuclear material to ensure no diversion has taken place and to detect facility misuse; however, this analysis and verification effort is time consuming, and with limited funding, it is imperative that time spent at a nuclear facility is focused on key areas. We developed a virtual digital twin of two general sodium-cooled fast reactors and explored diversion and misuse scenarios to determine how a digital twin could provide inspectors with an understanding of how proliferation may occur and where the most likely areas for proliferation would be. For each of the three reactors, an optimization algorithm was able to find core designs that would be difficult to detect via sensors alone; however, a machine learning adapter provided by the digital twin was able to show general trends in where proliferation is likely to take place.
Production rates of fissile materials are often used to independently assess the number of nuclear warheads a state may possess. One key constraint of a plutonium-based nuclear weapons program is the availability of natural uranium, where a shortage of uranium will constrain plutonium production in the fuel cycle. Recycling of the reprocessed uranium can be used to mitigate such a shortage. Furthermore, since military reactors operate in short cycles to ensure that the plutonium is weapon-grade, it may be possible to operate them using slightly depleted uranium, provided that there are sufficient reactivity margins. Using slightly depleted or recycled uranium, the plutonium production can increase by a factor 2-5 as compared to a once-through scenario, for the same input of natural uranium. For future assessments of a state's plutonium production, a uranium constraint should only be considered if there is clear evidence that no nuclear fuel cycle involving uranium recycling is implemented, or if evidence exists that the recycling is insufficient to mitigate the constraint.
Assessing the utility of hypersonic boost glide vehicles (BGVs) requires comparing their capabilities to alternative systems that could carry out the same missions, particularly given the technical difficulties and additional costs of developing BGVs compared to more established technologies. This paper discusses the primary motivations given for BGVs—most notably countering missile defenses—and summarizes current hypersonic development programs. It finds that evading the most capable current endo-atmospheric defenses requires that BGVs maintain speeds significantly higher than Mach 5 throughout their glide phase, which has implications for their mass and range. The paper then compares BGVs to maneuverable reentry vehicles (MaRVs) carried on ballistic missiles flown on depressed trajectories and shows that MaRVs can offer significant advantages over BGVs in a wide range of cases. Finally, the paper shows that BGV maneuvering during its glide phase can result in substantial costs in range and glide speed.
In March 2023, the UN Institute for Disarmament Research held a verification experiment that included a mockup onsite inspection at a former military facility in the municipality of Menzingen, Switzerland. The experiment included a visit to the site by an inspection team, accompanied by the host team. Among other activities, radiation measurements were used to confirm the non-nuclear nature of selected items stored onsite. In this paper, we discuss the neutron and gamma measurement systems used during the experiment and the inspection protocols followed to confirm the absence of nuclear weapons. Results from the experiment and a laboratory reproduction are presented, before concluding with lessons learned for how absence-confirmation measurements can help support verification of future arms control agreements.
