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The United States Transuranium and Uranium Registries (USTUR) is a unique resource of data and materials for studying biokinetics of uranium in the human body. In this study, bioassay data and post-mortem organ activities from a female whole-body USTUR donor who was exposed to highly enriched uranium were analyzed using the IMBA Professional Plus® software to derive the best estimate of the total intake. The resulting radiation doses delivered to this individual's whole body and major target organs were calculated from estimated intake based on case-specific dose coefficients derived using the AIDE® software. Both intake and dose calculations were carried out using the biokinetic and dosimetric models recommended by the International Commission on Radiological Protection (ICRP) in its Occupational Intakes of Radionuclides publication series. Different exposure scenarios including chronic and acute inhalation intakes were tested. A combination of a chronic inhalation intake and two acute inhalation intakes appears to best describe the bioassay data. To fit this female individual's autopsy data, the transfer rate from the liver to the blood was increased by a factor of 8 and the transfer rate from the kidneys to the blood was decreased by a factor of 2.2. This resulted in the best fit to all data (p = 0.519). The total intake was estimated to be 44.1 kBq, and the committed effective dose was 211 mSv with 96.8% contributed by 234U. 96.6% of the committed effective dose was contributed by the lungs. The remaining 3.4% of the committed effective dose was contributed by all systemic tissues and organs with the highest contribution (0.40%) from the red bone marrow. It is concluded that the current ICRP models, with the adjustment for smoking status, adequately describe uranium biokinetics for this individual except retention in the liver and kidneys. However, this study was based on a single case and may not be sufficient to identify any apparent sex-specific differences in uranium biokinetics. [ABSTRACT FROM AUTHOR]

Technitium-99m (99mTc), a widely used radioisotope, is used in tens of millions of medical diagnostic procedures annually. However, it is hard to store and must be immediately used upon production due to its short half-life (i.e., 6 h); thus, it is currently produced from 99Mo, which itself is a result of 235U fission. The majority of 99Mo supplies to U.S. patients are currently provided by foreign producers and produced using highly enriched uranium (HEU). In order to minimize the proliferation risks of HEU-based medical isotope production, the U.S. Department of Energy's National Nuclear Security Administration has funded a program to accelerate the development of technologies to produce 99Mo without the use of HEU. Today, the global supply of 99Mo depends on a limited number of nuclear reactors, and production has been interrupted unexpectedly since 2009 due to the fleet's advanced age. Alternative options for 99Mo production are discussed in this paper, and one potential option is to obtain 99mTc from molten salt reactors (MSRs). A MSR is a nuclear fission reactor that can operate at or close to atmospheric pressure with liquid fuel, which allows for producing isotopes in a timely manner. In this paper, the past and current production of 99Mo via nuclear reactors is described, and the future of 99Mo production by MSRs is discussed. The behavior and chemical properties of molybdenum in fluoride salts in MSRs and the possible extraction methods are also examined in addition to the limitation of current studies. [ABSTRACT FROM AUTHOR]

The Hypatia measurement campaign with YHx moderators and highly enriched uranium (HEU) was completed in January 2021 at the U.S. Department of Energy's National Criticality Experiments Research Center at the Nevada National Security Site. This measurement campaign provided unique integral measurements based on two experimental configurations and investigated the temperature effects of yttrium hydride (YHX = 1.8 and 1.9) in a critical reactor system, which is of potential interest for microreactor designs. The Hypatia experiment consisted of a fuel column composed of HEU, 93 wt% 235U discs, encapsulated YHX, aluminum oxide heater plates, and other moderator and reflector materials (beryllium, depleted uranium, and graphite) inserted into a thick beryllium reflector. During the Hypatia experiment, baseline measurements were taken at room temperature. The aluminum oxide heater plates were specially designed and used for this project to increase the central core temperature to a range of temperatures, after which additional reactivity measurements were taken. Thermal and neutronic calculations predicted that YHX is a unique material that can exhibit a positive temperature coefficient of reactivity (i.e., reactivity can increase as the temperature in the YHX increases). Reactors using YHX should account for this unique feature during design, and the results of the Hypatia experiment significantly aid that process. For configuration 1, six different temperature reactivity measurements were taken with four YHX cans in the fuel column. For configuration 2, six different temperature reactivity measurements were taken with two YHX cans in the fuel column. The use of these two configurations provide a comparison of neutronic effects from the YHX cans versus other components. Preliminary conclusions show the positive temperature coefficient is similar but slightly less than predicted by simulations. These two sets of data will be used to separate the reactivity coefficients of the fuel and other materials in the fuel column. [ABSTRACT FROM AUTHOR]

This study explores the feasibility of applying radiation tags as a Chain of Custody tool to confirm the dismantlement of individual warheads by investigating time dependent emissions from special nuclear material. Precedents of photon and neutron sources that have been used to irradiate warhead components are presented. Measurements of irradiated Highly Enriched Uranium (HEU) are used to benchmark simulations with the CINDER90 depletion code module within MCNP. Delayed gamma emissions are simulated as a function of time since irradiation of moderated HEU and Weapons Grade Plutonium with photon and neutron sources. Models of commercial 9 MV and 15 MV linacs were found to induce ∼ 10 9 f i s s i o n s / g and ∼ 10 11 f i s s i o n s / g , respectively, creating 3 to 4 orders of magnitude more delayed gammas than neutron sources, modeled at 10 10 n / s. However, a DT neutron source was found to induce sufficient fissions, ∼ 10 7 f i s s i o n s / g , to create quantifiable signatures relative to intrinsic emissions. Applied radiation tagging is determined to be technically feasible, but its operational context and practical implementation requires significant development. [ABSTRACT FROM AUTHOR]

If we had the technology to detect nuclear materials remotely it could help deter smuggling and make it easier to monitor international nuclear agreements. Several recent breakthroughs, if followed up with continued research and funding, could deliver on this promise. They include technological advances in x-ray and neutron radiography; a method that measures how plasma breaks down when exposed to a radioactive source; and developments in antineutrino detection. While all require more development and testing, they are important steps as the global need for ways to detect nuclear materials grows. [ABSTRACT FROM PUBLISHER]

The tripartite technology information agreement between Australia, the United Kingdom and the United States of America (AUKUS) was announced on 15 September 2021 and was discussed in an earlier article1. This article provides an update and interim progress commentary on AUKUS and the technology aspects mentioned in the announcement and in the more recent progress report, the further implications of the use of highly enriched Uranium (HEU) as submarine nuclear reactor fuel, and the broader geopolitical implications of AUKUS as it relates to the Nuclear Non Proliferation Treaty. [ABSTRACT FROM AUTHOR]

In this part, von Hippel discusses how his focus shifted in the first decade of the 21st century to a set of new concerns evoked by the terrorist attacks of 11 September 2001 and the G.W. Bush administration’s retrograde policies with regard to nuclear arms control and nonproliferation. During this period, he co-founded the International Panel on Fissile Materials so that policy activists working in opposition to nuclear arms races and fissile material production in different countries could work together. He also focused on fostering another generation of activist scientists engaged with the nuclear arms control and nonproliferation agenda.

Naval propulsion reactors account for the largest non-weapons use of highly enriched uranium (HEU) in the world. The largest stores of naval propulsion fuel are in the United States, the Russian Federation, and the United Kingdom. Using low-enriched uranium (LEU) for naval propulsion reactors would allow a significant reduction in non-weapons stocks of HEU and would have significant positive impacts on global nonproliferation and counterterrorism efforts. The US Navy holds the largest declared stock of HEU for propulsion purposes, and HEU-fueled reactors power all US submarines and aircraft carriers. In 1995 and again in 2014, the Navy reported to Congress on the potential for using reactors fueled with LEU instead of HEU. The Navy’s reports to Congress in both years are lacking in substantive analysis and transparency and arguably do not provide the straightforward assessment that Congress requested. The 1995 report provided Congress with a very negative assessment of the use of LEU and offered little hope that the Navy would consider LEU-fueled reactors. In 2013, Congress asked the Navy to provide an update to its 1995 report; in response, the Navy produced only a very brief analysis in 2014. Because the congressional mandate was for an update of the 1995 report, both reports need to be examined to determine the Navy’s current position on LEU use. Sadly, that position appears to have changed little over almost 20 years, despite advances in LEU use by other navies. However, the 2014 report does indicate that the Navy might be willing to support further studies of LEU use. While an optimist might see that as a change to the Navy’s adamant desire to continue to use HEU in naval reactors, a pessimist would view the Navy’s statements as a reflection of the desire to disingenuously use LEU studies to maintain the health of the service’s research and development programs. Congress should commission qualified experts to conduct an impartial review, at classified and unclassified levels, of naval LEU use. [ABSTRACT FROM PUBLISHER]

China will triple the number of nuclear power plants it has in operation by 2020 according to official plans, and the country’s nuclear fleet will increase 20-fold by 2050 under some not-yet-approved proposals. But how and where will China get the uranium to fuel them all? Will China need to resort to breeder reactors and reprocessing, with all the proliferation problems they incur? Or is there another way? The author suggests that between China’s domestic uranium mining, uranium purchased on the international market, and uranium mined by Chinese-owned companies overseas, China could meet even the most ambitious target, thus avoiding the troublesome and dangerous path of reprocessing. [ABSTRACT FROM PUBLISHER]

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