SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Nuclear proliferation

278

The contamination of Japan after the Fukushima accident has been investigated mainly for volatile fission products, but only sparsely for actinides such as plutonium. Only small releases of actinides were estimated in Fukushima. Plutonium is still omnipresent in the environment from previous atmospheric nuclear weapons tests. We investigated soil and plants sampled at different hot spots in Japan, searching for reactor-borne plutonium using its isotopic ratio (240)Pu/(239)Pu. By using accelerator mass spectrometry, we clearly demonstrated the release of Pu from the Fukushima Daiichi power plant: While most samples contained only the radionuclide signature of fallout plutonium, there is at least one vegetation sample whose isotope ratio (0.381 ± 0.046) evidences that the Pu originates from a nuclear reactor ((239+240)Pu activity concentration 0.49 Bq/kg). Plutonium content and isotope ratios differ considerably even for very close sampling locations, e.g. the soil and the plants growing on it. This strong localization indicates a particulate Pu release, which is of high radiological risk if incorporated.

Concepts: Mass spectrometry, Nuclear fission, Isotope, Nuclear weapon, Nuclear power, Nuclear proliferation, Radioactive contamination, Isotope ratio mass spectrometry

30

Plutonium (Pu) and non-natural uranium (U) originating from the Fukushima Daiichi Nuclear Power Plant (FDNPP) were identified in the atmosphere at 120 km distance from the FDNPP analyzing the ratio of number of atoms, following written as n(isotope)/n(isotope), of Pu and U. The n((240)Pu)/n((239)Pu), n((241)Pu)/n((239)Pu), n((234)U)/n((238)U), n((235)U)/n((238)U) and n((236)U)/n((238)U) in aerosol samples collected before and after the FDNPP incident were analyzed by accelerator mass spectrometry (AMS) and inductively coupled plasma mass spectrometry (ICPMS). The activity concentrations of (137)Cs and (134)Cs in the same samples were also analyzed by gamma spectrometry before the destructive analysis. Comparing the time series of analytical data on Pu and U obtained in this study with previously reported data on Pu, U, and radioactive Cs, we concluded that Pu and non-natural U from the FDNPP were transported in the atmosphere directly over a 120 km distance by aerosol and wind within a few days after the reactor hydrogen explosions. Effective dose of Pu were calculated using the data of Pu: (130 ± 21) nBq/m(3), obtained in this study. We found that the airborne Pu contributes only negligibly to the total dose at the time of the incident. However the analytical results show that the amount of Pu and non-natural U certainly increased in the environment after the incident.

Concepts: Spectroscopy, Mass spectrometry, Nuclear physics, Chemical element, Nuclear fission, Nuclear power, Nuclear proliferation, Plutonium

29

The Fukushima Daiichi Nuclear Power Plant accident (FDNPP) has caused serious contamination in the environment. The release of Pu isotopes renewed considerable public concern because they present a large risk for internal radiation exposure. In this review, we summarize and analyze published studies related to the release of Pu from the FDNPP accident based on environmental sample analyses and the ORIGEN model simulations. Our analysis emphasizes the environmental distribution of released Pu isotopes, information on Pu isotopic composition for source identification of Pu releases in the FDNPP-damaged reactors or spent fuel pools, and estimation of the amounts of Pu isotopes released from the FDNPP accident. Our analysis indicates that a trace amount of Pu isotopes (ca. 2 ×10-5 % of core inventory) was released into the environment from the damaged reactors, but not from the spent fuel pools located in the reactor buildings. Regarding the possible Pu contamination in the marine environment, limited studies suggest that no extra Pu input from the FDNPP accident could be detected in the western North Pacific 30 km off the Fukushima coast. Finally, we identified knowledge gaps remained on the release of Pu into the environment and recommended issues for future studies.

Concepts: Nuclear physics, Nuclear fission, Isotope, Nuclear weapon, Nuclear power, Nuclear proliferation, Plutonium, Spent fuel pool

28

Krypton-85 is mainly produced in nuclear reactors by fission of uranium and plutonium and released during chopping and dissolution of spent fuel rods in nuclear reprocessing facilities. As noble gas it is suited as a passive tracer for evaluation of atmospheric transport models. Furthermore, research is ongoing to assess its quality as an indicator for clandestine reprocessing activities. This paper continues previous efforts to compile a comprehensive historic emission inventory for krypton-85. Reprocessing facilities are the by far largest emitters of krypton-85. Information on sources and calculations used to derive the annual krypton-85 emission is provided for all known reprocessing facilities in the world. In addition, the emission characteristics of two plants, Tokai (Japan) and La Hague (France), are analysed in detail using emission data with high temporal resolution. Other types of krypton-85 sources are power reactors, naval reactors and isotope production facilities. These sources contribute only little or negligible amounts of krypton-85 compared to the large reprocessing facilities. Taking the decay of krypton-85 into account, the global atmospheric inventory is estimated to about 5500 PBq at the end of 2009. The correctness if the inventory has been proven by meteorological simulations and its error is assumed to be in the range of a few percent.

Concepts: Nuclear fission, Nuclear power, Nuclear proliferation, Spent nuclear fuel, Nuclear reprocessing, Plutonium, Nuclear fuel, Nuclear fuel cycle

28

The availability of (99m)Tc for single-photon imaging in diagnostic nuclear medicine is crucial, and current availability is based on the (99)Mo/(99m)Tc generator fabricated from fission-based molybdenum (F (99)Mo) produced using high enriched uranium (HEU) targets. Because of risks related to nuclear material proliferation, the use of HEU targets is being phased out and alternative strategies for production of both (99)Mo and (99m)Tc are being evaluated intensely. There are evidently no plans for replacement of the limited number of reactors that have primarily provided most of the (99)Mo. The uninterrupted, dependable availability of (99m)Tc is a crucial issue. For these reasons, new options being pursued include both reactor- and accelerator-based strategies to sustain the continued availability of (99m)Tc without the use of HEU. In this paper, the scientific and economic issues for transitioning from HEU to non-HEU are also discussed. In addition, the comparative advantages, disadvantages, technical challenges, present status, future prospects, security concerns, economic viability, and regulatory obstacles are reviewed. The international actions in progress toward evolving possible alternative strategies to produce (99)Mo or (99m)Tc are analyzed as well. The breadth of technologies and new strategies under development to provide (99)Mo and (99m)Tc reflects both the broad interest in and the importance of the pivotal role of (99m)Tc in diagnostic nuclear medicine.

Concepts: Nuclear medicine, Uranium, Nuclear weapon, Nuclear power, Nuclear proliferation, Depleted uranium, Enriched uranium, Light water reactor

24

Nuclear disarmament treaties are not sufficient in and of themselves to neutralize the existential threat of the nuclear weapons. Technologies are necessary for verifying the authenticity of the nuclear warheads undergoing dismantlement before counting them toward a treaty partner’s obligation. Here we present a concept that leverages isotope-specific nuclear resonance phenomena to authenticate a warhead’s fissile components by comparing them to a previously authenticated template. All information is encrypted in the physical domain in a manner that amounts to a physical zero-knowledge proof system. Using Monte Carlo simulations, the system is shown to reveal no isotopic or geometric information about the weapon, while readily detecting hoaxing attempts. This nuclear technique can dramatically increase the reach and trustworthiness of future nuclear disarmament treaties.

Concepts: Nuclear fission, United Nations, Nuclear weapon, Nuclear proliferation, Nuclear warfare, Cryptography, Missile, Nuclear disarmament

20

The gradient of Decapentaplegic (Dpp) in the Drosophila wing has served as a paradigm to characterize the role of morphogens in regulating patterning. However, the role of this gradient in regulating tissue size is a topic of intense debate as proliferative growth is homogenous. Here we combined the Gal4/UAS system and a temperature-sensitive Gal80 molecule to induce RNAi-mediated depletion of dpp and characterise the spatial and temporal requirement of Dpp in promoting growth. We show that Dpp emanating from the AP compartment boundary is required throughout development to promote growth by regulating cell proliferation and tissue size. Dpp regulates growth and proliferation rates equally in central and lateral regions of the developing wing appendage and reduced levels of Dpp affects similarly the width and length of the resulting wing. We also present evidence supporting the proposal that graded activity of Dpp is not an absolute requirement for wing growth.

Concepts: Gradient, Proposal, Length, Nuclear proliferation, Requirement, Associated Press, Requirements analysis

12

The newt, a urodele amphibian, has an outstanding ability- even as an adult -to regenerate a functional retina through reprogramming and proliferation of the retinal pigment epithelium (RPE) cells, even though the neural retina is completely removed from the eye by surgery. It remains unknown how the newt invented such a superior mechanism. Here we show that disability of RPE cells to regenerate the retina brings about a symptom of proliferative vitreoretinopathy (PVR), even in the newt. When Pax6, a transcription factor that is re-expressed in reprogramming RPE cells, is knocked down in transgenic juvenile newts, these cells proliferate but eventually give rise to cell aggregates that uniformly express alpha smooth muscle actin, Vimentin and N-cadherin, the markers of myofibroblasts which are a major component of the sub-/epi-retinal membranes in PVR. Our current study demonstrates that Pax6 is an essential factor that directs the fate of reprogramming RPE cells toward the retinal regeneration. The newt may have evolved the ability of retinal regeneration by modifying a mechanism that underlies the RPE-mediated retinal disorders.

Concepts: DNA, Gene expression, Actin, Retina, Eye, Smooth muscle, Retinal pigment epithelium, Nuclear proliferation

10

The verification of nuclear warheads for arms control involves a paradox: international inspectors will have to gain high confidence in the authenticity of submitted items while learning nothing about them. Proposed inspection systems featuring ‘information barriers’, designed to hide measurements stored in electronic systems, are at risk of tampering and snooping. Here we show the viability of a fundamentally new approach to nuclear warhead verification that incorporates a zero-knowledge protocol, which is designed in such a way that sensitive information is never measured and so does not need to be hidden. We interrogate submitted items with energetic neutrons, making, in effect, differential measurements of both neutron transmission and emission. Calculations for scenarios in which material is diverted from a test object show that a high degree of discrimination can be achieved while revealing zero information. Our ideas for a physical zero-knowledge system could have applications beyond the context of nuclear disarmament. The proposed technique suggests a way to perform comparisons or computations on personal or confidential data without measuring the data in the first place.

Concepts: Neutron, Nuclear fusion, Nuclear fission, Neutron radiation, Test method, Nuclear weapon, Nuclear proliferation, Nuclear disarmament

8

Six years after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, data for (236)U and (236)U/(238)U have remained limited to a few heavily contaminated samples. In the present study, activities of (236)U, (239)Pu, and (240)Pu, along with other U isotopes in 46 soil samples both heavily and lightly contaminated by this accident were measured by inductively coupled plasma-mass spectrometry (ICP-MS) and triple-quadrupole ICP-MS. The (236)U activities and (236)U/(238)U atom ratios in these soil samples were in the range of (0.469-24.4) × 10(-5) Bq kg(-1) and ((0.099-1.35) × 10(-7)), respectively. Higher (240)Pu/(239)Pu atom ratios (0.245-0.312) and (238)Pu/(239+240)Pu activity ratios (0.859-1.62) indicated Pu contamination originated from this accident and global fallout in some samples. For those soil samples along with black substances collected along roads in Fukushima Prefecture, high linear correlations were presented between (236)U activities and (239+240)Pu activities (Pearson’s r = 0.755, p < 0.01), and between (236)U activities and (238)Pu activities (Pearson's r = 0.844, p < 0.01). The analysis of these soil samples confirmed the release of (236)U, although in trace amounts, during the FDNPP accident.

Concepts: Nuclear physics, Nuclear fission, Isotope, Nuclear power, Nuclear proliferation, Electricity generation, Plutonium, Atomic Age