Many void gaps originated from assembly/disassembly concept of reactor structures exist in a tokamak reactor. Radiation streaming through these gaps causes hot spots in terms of irradiation of in-vessel components and of biological dose rate in personnel access area. For two-dimensional analysis of streaming through such a narrow gap, the discrete ordinates (S_N) method suffers from ray effects. In this paper, therefore, necessary conditions for angular quadrature were first investigated by comparing the S_N results with the line-of-sight results and the Monte Carlo results. As a result, it was found that the biased 166 angular quadrature (131 forward angles) gave results with practically sufficient accuracy for shielding design with some correction for the ray-effect. Also, local peaking factors due to the gap streaming were obtained as a function of gap width and shield thickness, and they are useful for future shielding design. Based on these preliminary investigations, the design calculation for the FER shield configuration was performed. It was made clear that the design criteria for superconducting magnet were satisfied even if the gap streaming effect was taken into account. Further, some measures to reduce the local peaking of dose rate in the personnel access area were proposed.

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Analysis of the TMI-2 core damage behavior has been performed with the SEFDAN code. The scope of the analysis is by the time of restarting the reactor coolant pump RCP-2B at 2 h 54 min into the accident. The analysis indicates that fuel temperature would have reached the melting point of UO₂ in the upper-most part of the most central region in the core. In a large portion of the upper part of the core, fuel cladding temperature would have reached the melting point of ZrO₂ and/or highly oxidized. Therefore it is expected that large amount of fuel rod material would have melted and relocated, or embrittled and have been thermally or mechanically shocked by restarting RCP-2B, resulting in formation of large amount of debris. The calculated maximum temperature of fuel rods and expected extent of the core void are in good agreement with the results of core examinations. Total hydrogen generation, however, is calculated to be about 1/3 of that estimated from the accident record. The discrepancy is probably due to heat-up and melting of the collapsed core after restarting RCP-2B in which zirconium-water reaction should have proceeded.

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This paper describes the results of in-pile experiments and analyses to study the influence of waterlogged fuel rod rupture to the adjacent fuel rods and channel box under reactivity initiated accident (RIA) conditions. A single waterlogged fuel rod surrounded by intact fuel rods in a flow shroud was irradiated by a large neutron pulse in the Nuclear Safety Research Reactor (NSRR) to simulate a prompt power excursion of RIA's. It was found that the pressure pulse generated at the rupture of waterlogged fuel rod had little mechanical influence on the adjacent fuel rods, but caused the ballooning of the flow shroud which included a rupture rod. The exclusion of coolant due to evaporation near the rupture region degraded the cooling of adjacent fuel rods and reduced the failure threshold. A 2-D analysis by STEALTH-J code revealed that a channel box of a BWR might be deformed by the pressure pulse to occupy the control rod path when a waterlogged fuel rod contained in a channel box ruptured in an RIA.

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In order to improve the performance of the sodium vapor trap, the sodium trapping efficiency has been analyzed using a simplified model of the mesh-packed region, supplemented by considering the effect of mist formation in the trap. The results led to the following conclusions :
(1) When mist containing sodium vapor is supplied to the trap, the sodium trapping efficiency is greatly lowered because of condensation of vapor to mist.
(2) Even if the sodium vapor contains no mist initially, it forms when nuclei for condensation exist which are larger than a critical value. This mist formation causes a decreased sodium trapping efficiency.
(3) The sodium trapping efficiency can be maximized by decreasing the gas temperature along the mesh in a manner inversely proportional to the trap length.

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Hydrogen evolution from ⁶⁰Co γ- and ³Hβ-irradiated molecular sieve 5A adsorbing HTO was measured. The results showed an additional evolution of H₂(HT) gas due to energy transfer from molecular sieve to adsorbed water in both γ- and /β-irradiations, and the yield at a given irradiation dose was higher than that from radiolysis of liquid HTO but lower than that in the silica gel-HTO system. The additional yield was formulated as a function of the amount of adsorbed water and irradiation dose. However a large difference in hydrogen yields was observed between γ- and β-irradiations contrary to silica gel-HTO system. A possible reason is considered.

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New compounds of technetium acetylacetonates synthesized by nuclear recoil technique in our laboratory have been further studied to clarify their formation characteristics. Technetium atoms were implanted in various metal acetylacetonates using ¹⁰⁰Ru(γ, p)^99m Tc reaction and nuclear fission of ²³⁵U. The yield of Tc(acac)3 decreased with increase of the force constant of metal-oxygen bond of the catcher system M (III) (acac)₃. No such relationship could be observed for the yield of Tc (acac)₃ in the catcher system M (II) (acac)₃.
An oxygen effect was examined in fission recoil implantation in Cr (acac)₃ or Co (acac)₃. Formation of ^99mTcO₂(acac)₂ was observed by irradiation in air while it was not observed by irradiation in vacuo. These experimental results indicated the presence of its precursor ⁹⁹MoO₂(acac)₂ which was most probably formed by chemical reactions among Mo atom (excited by β-decay), acetylacetone ligands and oxygen. This example showed the applicability of the "daughter tracer technique" to the ⁹⁹Mo-^99m Tc system.

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In order to immobilize Cs into pollucite structure, hydrothermal reactions of Cs with amorphous aluminosilicate (siliceous sinter) and with mixtures of low-quartz (silicastone) and Al(OH)₃, were performed. In both cases, pollucite was formed in 5-N NaOH solution above 200°C for 10 min. Synthesized pollucite was solid solution between pollucite and analcite. Waste forms in which Cs was immobilized in pollucite structure were successfully produced by the hydrothermal hot-pressing method using the silica matrix (mixture of low-quartz and amorphous aluminosilicate) containing Al(OH)₃ and NaAlO₂. Effect of hot-pressing conditions on leachability of the waste forms was investigated. The waste form containing 10 ?? CsOH produced at 300°C and 49 MPa for 24 h, had Cs leach rate of 3.15 g/m²•d by Soxhlet leach tests for 7 d. The waste form was porous, but had high compressive strength and thermal stability.

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The rig of safety assessment (ROSA)-III facility is a volumetrically scaled (1/424) boiling water reactor (BWR/6) system with an electrically heated core designed for integral loss-of-coolant accident (LOCA) and emergency core cooling system (ECCS) tests. Two 200% and two 5% recirculation pump suction line break LOCA experiments with and without heat generation difference among the bundles were conducted in order to investigate interaction of thermal-hydraulic phenomena in a multi-bundle core.
The axial propagation of quenching tends to become more nonuniform in the same bundle as well as in the core in both large and small break experiments when the heat generation difference among the bundles exists. The small flow imbalance among the bundles which is caused by void fraction difference due to the heat generation difference among the bundles is estimated to make the flow condition nonuniform and more agitated and increase the radial scattering of the quenching propagation.

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Flow rate distribution and total pressure loss of a coolant flow through a control rod channel in the Very High Temperature Gas Cooled Reactor (VHTR) were analytically and experimentally examined. Helium gas of atmospheric temperature was used in the experiment; and the total mass flow rates ranged 0.0050.05 kg/s and the gas pressures ranged 0.140.42 MPa. Pressure losses and flow rates in the control rod channel were measured. An analysis was made by using a one-dimensional flow network model for the inner and outer channels and the gap. The analytical results agreed fairly well with the experimental results on the flow rate distribution and the total pressure loss in the control rod channel.

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Amino acid formation from HCN or CN^- was first reported by Oro & Kamat⁽¹⁾. After that, the problem has been watched in regard to the origin of life, while Ogura et al. and others reported the problem related to radiations⁽²⁾⁽⁹⁾. The radiations used by all these researchers were γ-rays emitted from ⁶⁰Co radiation source.
The author used ¹⁰B(n, α)⁷ Li reaction as an inner radiation source in order to apply a low thermal neutron radiation dose to radiation chemistry. On the application of the inner source to cyanide or thiocyanate solution, amino acid formation was confirmed^(10)(12).
This article is reporting on the application of this method to nitrile solution in order to see if any different reaction mechanisms occur and what sorts of amino acid are produced. Although some reports regarding nitrile irradiation were presented^(13)(17) and also recognized some amino acid formation, these researches were carried out using ⁶⁰Co γ-rays as a radiation source. Therefore, in the use of the particle rays, such as α-rays or ⁷Li recoil nuclei, different results are expected.
In the present investigation, unlike ⁶⁰Co γ-rays irradiation, CH₃-CN bond cleavage and glycine formation were not seen, while alanine formation was most remarkable.

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