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Tensile and Charpy specimens of 9Cr–1MoVNb (modified 9Cr–1Mo) and 12Cr–1MoVW (Sandvik HT9) steels and these steels doped with 2% Ni were irradiated at 300 and 400 °C in the High Flux Isotope Reactor (HFIR) up to ≈12 dpa and at 393 °C in the Fast Flux Test Facility (FFTF) to ≈15 dpa. In HFIR, a mixed-spectrum reactor, ( n , α ) reactions of thermal neutrons with 58 Ni produce helium in the steels. Little helium is produced during irradiation in FFTF. After HFIR irradiation, the yield stress of all steels increased, with the largest increases occurring for nickel-doped steels. The ductile–brittle transition temperature (DBTT) increased up to two times and 1.7 times more in steels with 2% Ni than in those without the nickel addition after HFIR irradiation at 300 and 400 °C, respectively. Much smaller differences occurred between these steels after irradiation in FFTF. The DBTT increases for steels with 2% Ni after HFIR irradiation were 2–4 times greater than after FFTF irradiation. Results indicated there was hardening due to helium in addition to hardening by displacement damage and irradiation-induced precipitation.

Reduced-activation ferritic/martensitic steel, F82H (8Cr–2W–0.2V–0.04Ta–0.1C), and variants doped with isotopically tailored boron were irradiated at 673 K up to 51 dpa in the high flux isotope reactor (HFIR). The concentrations of 10B in these alloys were 4, 62, and 325 appm during HFIR irradiation which resulted in the production of 4, 62 and 325 appm He, respectively. After irradiation, transmission electron microscopy (TEM) was carried out. The number density of cavities increased and the average diameter of cavities decreased with increasing amounts of 10B. The number density decreased and the average diameter increased with increasing displacement damage. Swelling increased as a function of displacement damage and He concentration.

F-82H alloys isotopically enriched in 54 Fe up to 86% were irradiated in the high flux isotope reactor (HFIR) to determine the accelerated production of helium and hydrogen due to isotopic effects. Results are compared to calculations using isotopic helium production cross-sections from ENDF/B-VI or GNASH and measured neutron spectra. Helium measurements demonstrated an accelerated helium (appm)/dpa ratio of 2.3 after a 1.25-year irradiation, an increase of a factor of 4.3 over natural iron. The accelerated helium production is due to higher helium production cross-sections for 54 Fe and 55 Fe. Alloys doped with 55 Fe could achieve helium/dpa ratios up to about 20, well above the fusion reactor ratio of 10. Hydrogen measurements were performed using a newly developed quadrupole mass spectrometer system at PNNL. Calculations predict that hydrogen production will be accelerated by about a factor of 13 over natural iron. However, measurements show that most of this hydrogen is not retained in the samples.

The releases of xenon from three (Th, U)O2 specimens with different U contents were measured over a wide range of fission dose from 2.9 × 1019 to 2.2 × 1022 fissions m−3 by using a post-irradiation technique. The releases were found to decrease with dose and to level off at higher doses. Measurements of the changes in lattice parameter and specific surface area of the same specimens enabled one to conclude that the decrease in release originates in the trapping of xenon by the vacancies and vacancy clusters induced by fission fragments. And the release mechanisms of fission gas were proposed based on the proper evaluation of the observation on radiation damage and recovery in oxide fuel.

The release of 133Xe from (Th,U)O2 was studied at a low fission density by using a post-irradiation technique. The uranium concentrations of the specimens ranged from 0.15 to 20 mol% U02. Heating curves of the release gave almost the same pattern in shape, while the total release, which was the combination of an in-pile release and a post-irradiation release up to 1000°C, increased with uranium concentration except for the nominally pure ThO2. Effects of preparation conditions of specimens such as atmosphere, temperature and stoichiometry were also studied and found to be minor. Possible release mechanisms were discussed.

The polished hemispheres of ThO2 kernels were irradiated by fission fragments, which recoiled from the covered Al-U alloy foils. After irradiation, the lattice parameters of the kernels were measured by microbeam X-ray diffractometer. It was found that the lattice parameter increased initially in a linear relationship with increasing fission fragment dose and reached a saturation value at doses higher than about 1×1016 fission fragments⋅cm-3. The saturation value was smaller for the fine-grained specimen than for the coarsegrained. The recovery began at about 400°C for both the specimens and lasted to higher temperature for the coarse-grained.

In-pile release of fission gas from sintered UC pellets in the presence of 8–230 ppm of water vapor in the He sweep gas was measured over the temperature range of 160°–1,000°C. A very complex release behavior was observed and the mechanisms of release were deduced from the manner in which the release depended on the decay constant. It was established that the release of short-lived fission gases during irradiation was controlled mainly by pseudo-recoil, while chemical reaction between UC and water vapor, as well as knock-out, appeared to contribute much more significantly in the case of the longer-lived fission gases. The release of fission gas after reactor shutdown was shown to be governed by the UC-H2O reaction. The ratio of the release due to this reaction in reference to the total release was found to be dependent not only on the concentration of the water vapor but also on the amount present of the accumulated reaction products. Also, a discussion is given on the inordinately high release of 135mXe ...

レーザー法によるU濃縮には原子法と分子法とがあり,その将来性に関心が集まっている。そこで,レーザー法の原理,開発すべき装置の要件と課題,我が国における技術開発の現状と介後の計画,海外における開発状況などについて,より開発の進んでいる原子法を中心に紹介する。

The polished hemispheres of ThO2 kernels were irradiated by fission fragments, which recoiled from the covered Al-U alloy foils. After irradiation, the lattice parameters of the kernels were measured by micro-beam X-ray diffractometer. It was found that the lattice parameter increased with increasing fission fragment dose and reached a saturation value at doses higher than about 5×1016 fission fragments-cm-3. With increasing grain sizes from 4.0 to 19.3 μm, the saturation values of lattice parameter changes increased from approximately 0.07 to 0.18%. The recovery began at about 400°C in all specimens and the temperature of the complete recovery had a tendency to become higher with increasing grain size. These results lead to a conclusion that the grain boundaries act as a sink of the defects created by fission fragments.

An investigation was undertaken to determine the activation energy of iodine diffusion in graphite and the mechanism of diffusion and formation of the iodide. The heating curve of deposited iodide was found to have a peak at 530 deg C, while a diffusion peak occurred at 750 deg C, with an activation energy of 47 kcal/mole. The results are compared with diffusion of xenon and annealing of graphite irradiated with fast neutrons. (D.L.C.)

The high-temperature x-ray diffraction method was used to confirm the correlation between fission gas release from hematite and the crystal structure change. The release of absorbed recoil Kr and Xe and continuous x-ray diffraction lines are shown as functions of temperature. The usefulness of the method in studies of physical chemistry is discussed. (N.W.R.)

In-pile release of fission krypton, xenon and iodine from graphite was measured and the release mechanism is discussed in detail compared with the data of post-irradiation experiments. No temperature-independent release of fission gases and iodine was observed in the temperature range from 100 to 640 °C. After reactor shutdown with the specimen temperature constant, only xenon was released from the specimen and not krypton and iodine. To explain this phenomenon, a hypothesis is proposed that fission gas releases are induced by β-decay of precursor halogens trapped in defects in the specimen. By the hypothesis, the release behavior of fission gases and iodine can be explained satisfactorily.

白金,ロジウム,パラジウム,金などの貴金属中に含まれるイリジウムを非破壊的に定量する放射化分析法を検討した。これらの試料を2時間程度照射すると比較的短い半減期をもつ放射性核種のみを生じ,イリジウムのみは長寿命の半減期(74.4d)をもつ192Irを生ずる。適当な冷却期間をおいて短寿命の放射能の消滅をまって,γ線スペクトロメトリーを適用して192Irの各光電ピークを比較標準と比較して定量した。この方法は結果を得るまでに長時間を要する欠点はあるが,非破壊的に行なえる特徴をもっている。