SciCombinator

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

Concept: Nuclear weapon

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

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

26

Estimation of time changes in radiocaesium in foodstuffs is key to predicting the long term impact of the Fukushima accident on the Japanese diet. We have modelled >4000 measurements, spanning 50 years, of (137)Cs in foodstuffs and whole diet in Japan after nuclear weapons testing (NWT) and the Chernobyl accident. Broadly consistent long term trends in (137)Cs activity concentrations are seen between different agricultural foodstuffs; whole diet follows this general trend with remarkably little variation between averages for different regions of Japan. Model blind tests against post-NWT data for the Fukushima Prefecture showed good predictions for radiocaesium in whole diet, spinach and Japanese radish (for which good long term test data were available). For the post-Fukushima period to 2015, radiocaesium in the average diet followed a declining time trend consistent with that seen after NWT and Chernobyl. Data for different regions post-Fukushima show a high degree of mixing of dietary foodstuffs between regions: significant over-estimates of average dietary (137)Cs were made when it was assumed that only regionally-produced food was consumed. Predictions of mean committed effective internal doses from dietary (137)Cs (2011 to 2061) in non-evacuated parts of the Fukushima Prefecture show that average internal dose is relatively low. This study focused on average regional ingestion dose rates and does not attempt to make site specific predictions. However, temporal trends identified could form a basis for site specific predictions of long term activity concentrations in agricultural products and diet both outside and (to assess potential re-use) inside currently evacuated areas.

Concepts: Time, Japan, Nuclear weapon, Radioactive contamination, Prefectures of Japan, Fukushima Prefecture, Tōhoku region, Honshū

26

The cross-sections of (nat)Yb (n,x)(172,173) Tm, (174)Yb(n,p) (174) Tm, (174)Yb (n,α) (171)Er, (176)Yb(n,p) (176) Tm, (176)Yb(n,α)(173) Er, and (176) Yb(n,n')(176m)Yb have been measured at 14.6±0.3MeV neutron energy, among them two cross-sections (nat)Yb (n,x)(172,173)Tm are reported for the first time. These experimental cross-sections are compared with experimental data found in the literature, with evaluated nuclear data in JENDL-4.0 and TENDL-2010 libraries and with theoretically calculated values based on nuclear reaction modular codes EMPIRE-3.0 and TALYS-1.2.

Concepts: Nuclear physics, Neutron, Nuclear fusion, Nuclear fission, Neutron radiation, Nuclear weapon, Neutron capture, Nuclear reaction

25

Radionuclide signals from underground nuclear explosions (UNEs) are strongly influenced by the surrounding hydrogeologic regime. One effect of containment is delay of detonation-produced radioxenon reaching the surface as well as lengthening of its period of detectability compared to uncontained explosions. Using a field-scale tracer experiment, we evaluate important transport properties of a former UNE site. We observe the character of signals at the surface due to the migration of gases from the post-detonation chimney under realistic transport conditions. Background radon signals are found to be highly responsive to cavity pressurization suggesting that large local radon anomalies may be an indicator of a clandestine UNE. Computer simulations, using transport properties obtained from the experiment, track radioxenon isotopes in the chimney and their migration to the surface. They show that the chimney surrounded by a fractured containment regime behaves as a leaky chemical reactor regarding its effect on isotopic evolution introducing a dependence on nuclear yield not previously considered. This evolutionary model for radioxenon isotopes is validated by atmospheric observations of radioxenon from a 2013 UNE in the Democratic People’s Republic of Korea (DPRK). Our model produces results similar to isotopic observations with nuclear yields being comparable to seismic estimates.

Concepts: Ionizing radiation, Hypothesis, Isotope, South Korea, Nuclear weapon, North Korea, Cold War, People's Republic

25

Our acceptance of exposure to radiation is somewhat schizophrenic. We accept that the use of high doses of radiation is still one of the most valuable weapons in our fight against cancer, and believe that bathing in radioactive spas is beneficial. On the other hand, as a species, we are fearful of exposure to man-made radiation as a result of accidents related to power generation, even though we understand that the doses are orders of magnitude lower than those we use everyday in medicine. The 70th anniversary of the detonation of the atomic bombs in Hiroshima and Nagasaki was marked in 2015. The 30th anniversary of the Chernobyl nuclear power plant accident will be marked in April 2016. March 2016 also sees the fifth anniversary of the accident at the Fukushima nuclear power plant. Perhaps now is an opportune time to assess whether we are right to be fearful of the effects of low doses of radiation, or whether actions taken because of our fear of radiation actually cause a greater detriment to health than the direct effect of radiation exposure.

Concepts: Chernobyl disaster, Uranium, Nuclear fission, Nuclear weapon, Nuclear power, Nuclear safety, Atomic bombings of Hiroshima and Nagasaki, 2016

25

A 6- to 7-MeV high-energy gamma-ray field, produced by the nuclear reaction of (19)F(p, αγ)(16)O, has been established at the Facility of Radiation Standards (FRS) in Japan Atomic Energy Agency for calibration purposes. Basic dosimetric quantities (i.e. averaged gamma-ray energy, air-kerma-to-dose equivalent conversion coefficients and air kerma rates at the point of test) have been precisely determined through a series of measurements using the NaI(Tl) spectrometer and an ionisation chamber coupled with an appropriate build-up material. The measurements obtained comply with values recommended by the International Organization for Standardization for an ‘R-F field’. The neutron contamination component for the field has also been measured by means of a conventional neutron dose equivalent meter (the so-called neutron rem-counter) and determined to be ∼0.5 % of the total dose equivalent.

Concepts: Ionizing radiation, Metrology, Nuclear fission, Test method, International Atomic Energy Agency, Nuclear weapon, Gamma ray, Van de Graaff generator

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

21

Seventy years ago, the medical profession alerted the world to the devastating effects of nuclear weapons. Just weeks after the bombing of Hiroshima, Dr. Marcel Junod, a representative of the International Committee of the Red Cross in Japan, visited the devastated city and sent back one of the first eyewitness reports to reach the outside world: “The center of the city was a sort of white patch, flattened and smooth like the palm of a hand. Nothing remained.” Ever since that time, members of the medical profession have played a key role in warning governments and the public about the . . .

Concepts: Uranium, Nuclear weapon, World War II, Atomic bombings of Hiroshima and Nagasaki, Nuclear warfare, Hiroshima, Plutonium, Little Boy

17

Underground nuclear weapon testing produces radionuclide gases which may seep to the surface. Barometric pumping of gas through explosion-fractured rock is investigated using a new sequentially-coupled hydrodynamic rock damage/gas transport model. Fracture networks are produced for two rock types (granite and tuff) and three depths of burial. The fracture networks are integrated into a flow and transport numerical model driven by surface pressure signals of differing amplitude and variability. There are major differences between predictions using a realistic fracture network and prior results that used a simplified geometry. Matrix porosity and maximum fracture aperture have the greatest impact on gas breakthrough time and window of opportunity for detection, with different effects between granite and tuff simulations highlighting the importance of accurately simulating the fracture network. In particular, maximum fracture aperture has an opposite effect on tuff and granite, due to different damage patterns and their effect on the barometric pumping process. From stochastic simulations using randomly generated hydrogeologic parameters, normalized detection curves are presented to show differences in optimal sampling time for granite and tuff simulations. Seasonal and location-based effects on breakthrough, which occur due to differences in barometric forcing, are stronger where the barometric signal is highly variable.

Concepts: Petroleum, Igneous rock, Operations research, Monte Carlo method, Pressure, Gas, Computer simulation, Nuclear weapon