The authors investigate the influence of the attenuation of magnetic induction on the current distribution etc. in the end regions of the diagonal type nonequilibrium plasma MHD generator by a two-dimensional analysis. The numerical calculations are made for an example of the cesium-seeded helium. As a result, a suitable attenuation of the magnetic induction can make the current distribution very uniform near the end region of generator duct and has little influence on the current distribution in the central part of generator, and the output electrodes can be used without large ballast resistors. Also the internal resistance of the end region and the current concentration at the output electrode edges decrease with the attenuation of magnetic flux density. By the author's investigation, it is made clear that the output electrodes of the diagonal type nonequilibrium plasma MHD generator should be arranged in the attenuation region of the magnetic induction, since arranging them in the attenuation region of magnetic flux density can become useful for the improvement of the electrical characteristics of generator.

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A series of critical experiments using mixed-oxide (PuO₂-UO₂) plutonium fuels was carried out at the Tank type Critical Assembly (TCA) in the Japan Atomic Energy Research Institute in cooperation with the Power Reactor and Nuclear Fuel Development Corporation. Isotopic compositions of the Pu were 68, 22, 7 and 2w/0 for ²³⁹Pu, ²⁴⁰pu, ²⁴¹Pu and ²⁴²Pu, respectively, and the U was natural uranium.
Critical mass, power distribution and neutron activation distribution of Au wire were measured for five kinds of lattices in which the ratios of atomic density of H to Pu were 295, 402, 494, 701 and 922, respectively. The codes LASER, UGMG42-THERMOS and GTB-2 were used for obtaining three neutron group constants and the PDQ-5 code was used in two-dimensional diffusion calculations for the lattices.
The maximum differences of the calculated multiplication factors from the measured values distributed from -1.32 to 1.72%Δk/k. Calculated thermal neutron density, epithermal neutron flux and Power distributions showed good agreement with measured data.

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In order to save the quantity of sample material, a possibility to assess group constants of a reactor material through measurement and analysis of neutron spectrum in a small sample pile surrounded by a reflector of heavy moderator, was investigated. As the sample and the reflector, we chose iron and lead, respectively. Although the time dispersion in moderation of neutrons was considerably prolonged by the lead reflector, this hardly interferes with the assessment of group constants. Theoretical calculation revealed that both the neutron flux spectrum and the sensitivity coefficient of group constants in an iron sphere, 35cm in diameter surrounded by the lead reflector, 25cm thick, were close to those of the bare iron sphere, 108cm in diameter.
The neutron spectra in a small iron pile surrounded by a lead reflector were experimentally obtained by the time-of-flight method with an electron linear accelerator and the result was compared with the predicted values.
It could be confirmed that a small sample pile surrounded by a reflector, such as lead, was as useful as a much larger bulk pile for the assessment of group constants of a reactor material.

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An evaluation was made of heat transfer tube failure propagation due to sodium-water reaction wastage in a sodium heated steam generator, by comparing an empirically derived wastage equation with leak detector responses.
The experimental data agreed well with the wastage equation even for different values of distance-to-nozzle diameter ratio, though the formula had been based on wastage data obtained for only one given distance. The time taken for failure propagation was estimated for a prototype steam generator, and compared with the responses characteristics of acoustic detectors and level gages. It was found that there exists a range of leak rate between 0.5 and 100g/sec, where the level gage can play a useful role in leak detection. The acoustic detector can be expected to respond more rapidly than the cover gas pressure gage, if noise is kept below ten times the value observed in an experimental facility, SWAT-2.

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Fe-N alloys containing 150 ppm N were neutron irradiated in the JMTR to 5.5×10¹⁹ n/cm², then deformed in tension at temperatures ranging from that of liquid nitrogen to 250°C. Irradiation was found to increase markedly the yield, tensile and fracture stresses, and to decrease the elongation. Irradiation further had the effect of shifting upward the range of testing temperature in which serrations appeared in the stress-strain diagram, and to lower the work hardening coefficient. The alloys were examined by transmission electron micrography both as irradiated and after being deformed to observe the changes in internal structure. Irradiation was found not to induce deffects in the iron matrix ; the precipitates, on the other hand, revealed in some parts the presence of radiation defect clusters.
Heat treatment at 300°C for 100 hr removed the precipitates in the irradiated specimens, leaving many dislocation loops in the matrix. These dislocation loops were of the vacancy type with Burgers vectors corresponding to a/2 <111>, and lay on the {111} plane. Radiation anneal hardening was observed in the irradiated specimens in the occurred range of heat treatment temperature between 100 and 600°C. It would appear that the stable phase Fe₄N and the remaining entangled dislocations tend to enhance the hardening due to the post-irradiation annealing, with an effect similar to that produced by nitrogen. vacancy complexes, interstitial cluster, metastable precipitates and dislocation loops.

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Environmental contamination with long-lived radiocesium (¹³⁷Cs) should cause difficulties in proceeding with deep sea disposal of radioactive waste solidified in cement. The problem would be solved, if ¹³⁷Cs could be isolated from the radioactive waste for separate disposal. For this purpose, a preliminary study was carried out on the isolation and removal of ¹³⁷Cs with zeolite, an inorganic exchanger.
Zeolites from Futatsui in Akita Prefecture and from Itaya in Yamagata Prefecture showed a strong selective affinity for Cs in preference to various other co-present ions. The best performance in practical isolation and removal was obtained with the zeolite (clinoptilolite) from Itaya sized to 40100 mesh, and with the liquid passed at a specific space velocity of 25.
In practical application, a selective zeolite column could be installed upstream of the conventional demineralizer equipping the liquid waste treatment system of nuclear power stations, in order to adsorb and eliminate 137Cs and prevent its reaching the conventional demineralizer. This should solve one of problems encountered in deep sea disposal of radioactive waste.

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An experimental study has been performed on neutron penetration in a two-dimensional heterogeneous structure consisting of graphite and aluminum. The results provide a basis for verification of the accuracy of two-dimensional shielding calculation codes. The experiments were performed at JRR-4 of JAERI and included measurements of the thermal neutron flux for five different arrangements of graphite and aluminum. Calculations were performed with a conventional procedure using the two-dimensional removal diffusion code, TRD-1. The calculated thermal neutron flux of TRD-1 agrees with the measured value within about 25%.

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