This paper illustrates the applicability of exterior differential forms to reactor theory by using them to represent the time dependent diffusion equation suitable for neutronic calculations. This formalism allows one to express the equation straightforwardly and easily in any orthogonal coordinate system. Because of present interest in CTR designs an application is made to a toroidal geometry with a general elliptical cross section.

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This paper deals with local sodium boiling in the downstream of a six-subchannel blockage in an electrically heated LMFBR fuel subassembly mock-up.
The first series of experiments were conducted to measure temperature distributions in the downstream of the blockage under non-boiling conditions. The measured temper-ature rise due to the blockage agreed fairly well with the calculation by the LOCK code.
The second series of experiments were performed to investigate local boiling phe-nomena. In the local boiling region, no flow instability was observed since the sub-channels near the wrapper wall were still filled with subcooled liquid. In the nearly bulk boiling region, however, considerable upstream voiding occurred and then the inlet flow decreased, leading to final dryout.
The boiling caused a considerable increase in acoustic noise intensity. The root-mean-square (RMS) noise level of approximately 20 mbar obtained in the present local boiling experiments with sodium was much higher than that (approximately 0.5 mbar) in the ordinary nucleate boiling experiments with water. The peak observed in the hertz ranges was due to the repetition of bubble formation and collapse. In the kilohertz ranges, however, resonance peaks were superposed on a smooth curve with a broad peak at approximately 7 kHz.
The frequency (2.9 and 20.2 sec^-1) of bubble formation decreased with the increase of the bubble size at its point of maximum development. The product of the bubble frequency and the equivalent diameter was found to be constant.

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A new analytical method is presented for analyzing, in three dimensions, the mechan-ical response of fuel pins with wire spacers, to their thermal and neutronic environment in a fuel assembly of a LMFBR. It analyzes the mechanical interactions between fuel pins in the assembly in each of three directions, which form an angle of π/3 radians with one another, based on the mathematical relationship between the displacements at the contact points and the associated contact forces with respect to all fuel pins forming a line in one of the three directions.
Based on this method, a new computational code, the Subchannel Deformation Analysis Code for Wire-Wrap Assemblies (SHADOW) has been developed, and is applied to a fuel assembly of a prototype fast breeder reactor in order to analyze the deformation of 169 fuel pins due to thermal bowing.
Conclusions drawn from the study confirm that the SHADOW code can be an effec-tive tool for analyzing or evaluating thermal and structural designs of a LMFBR fuel assembly.

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An evaluation is made to estimate the transient xenon behavior in an MSBR for several representative patterns of operation. Such analysis is indispensable for detailed evaluation of reactivity balance under transient conditions. The results are compared with those of a typical PWR. The xenon behavior does not differ between the two types of reactor to the extent that might be expected from the fact that in the MSBR, xenon behavior is additionally conditioned by the processes of migration into the circulating bubbles and into the graphite, as well as by diffusion therein.
It is shown that the reactivity transients due to xenon buildup can be held within the range of counteraction by control rod movement for any normal change of reactor output, so long as the reactor is not shut down. After a shutdown, insertion of the control rods will not suffice to override the xenon buildup, but then the fuel processing system could be conveniently utilized to increase the quantity of ²³³U contained in the fuel and regain required reactivity of the core.

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The possibility was examined of extracting U(VI) from sea water by adsorption on gel particles containing various metal hydroxides, including Ti(OH)₄ and Zn(OH)₂, dis-persed in polyacrylamide gel particles. The hydroxide adsorbent thus prepared in gel form was packed in a column for processing the sea water (both sea water sampled from harbor and artificially prepared solution). The U(VI) collected in the column was eluted with 0.10 M Na₂CO₃ solution. Factors affecting the performance of the hydroxide adsorber were examined : The kind of metal hydroxide used, the degree of cross-linking of the polyacrylamide, the content of hydroxide in the gel and the concentration of U(VI) in the original sea water. Of the five kinds of metal hydroxides tried, only titanium hydroxide was found to function usefully as adsorbent for the U(VI). The degree of polyacrylamide crosslinking was found have no relation to adsorption performance, which, on the other hand, was significantly influenced by changes in titanium hydroxide in the gel : The amount of U(VI) adsorbed reached a maximum at 2 mg Ti/ml gel. Also, the adsorption improved consistently with decreasing concentration of U(VI) contained in the original sea water, down 10^-6 M.

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In a study aimed at the application of solid state track detectors to the quantitative analysis of boron, track detector plates of cellulose nitrate were set in polypropylene test tubes, filled with various concentrations of boron-agar solution, and irradiated with thermal neutrons. After irradiation, the cellulose track detectors were separated from the solution, and etched with suitable chemical reagents. The number of etch-pits observed on the plate surface was counted by means of an optical microscope. The experiments proved that the number of etch-pits per unit area P (cm^-2) is proportional to the product of the ¹⁰B-concentration τ (atom•cm^-3) and the thermal neutron fluence φ (cm^-2) : P=bτφ, where b is the ¹⁰B-detection efficiency. If ρ is the number of ¹⁰B(n, a)⁷Li reactions per cubic centimeter, P=pρ, where p is the etch-pit formation efficiency. The maximum values of b and p obtained in these experiments were 1.3 X 10^-24 cm³, and 3.3 X 10^-4 cm, respectively. The mean effective range of a and ⁷Li particles in the solution was found to equal 2p.

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Temperature dependences of infinite multiplication factor k_∞ and neutron leakage from the core must be examined for estimation of moderator temperature coefficient. Temper-ature dependence on k_∞ has been investigated by many researchers, however, the depend-ence on neutron leakage of a BWR with cruciformed control rods has hardly been done. Because there are difficulties and necessity on calculations of three space dimensional and multi-energy groups neutron distribution in a BWR core.
In this study, moderator temperature coefficients of JPDR-II (BWR) core were obtained by calculation with DIFFUSION-ACE, which is newly developed three-dimensional multi-group computer code. The results were compared with experimental data measured from 20 to 275°C of the moderator temperature and the good agreement was obtained between calculation and measurement.
In order to evaluate neutron leakage from the core, the other two calculations were carried out, adjusting criticality by uniform absorption rate and by material buckling. The former underestimated neutron leakage and the latter overestimated it. Discussion on the results shows that in order to estimate the temperature coefficient of BWR, neu-tron leakage must be evaluated precisely, therefore the calculation at actual pattern of control rods is necessary.

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