The etching behavior of fission fragment tracks in synthetic quartz plates concerning to +x, y and z planes was studied using NaOH solution as an etchant. Systematic experiments gave an optimum etching condition of 65% NaOH at 150°C suitable for track detection. Under this etching condition, following several properties were studied ; the bulk etching rate, the etched track opening shape and its growth rate, the critical angle of track etching, and the irradiation effect of low LET radiation. All of three different cuts were demonstrated to be useful for plates as fission track detectors. An application to neutron detection was studied for the +x-plane of an x-cut plate. The detection sensitivity of the plane in close contact with a Th, tradiator was 2.7× 10^-6 tracks/fluence for 14 MeV neutrons.

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A sealing function is essential for transportation casks of radioactive materials in order to prevent radioactive materials from being released into the environment. In the safety analysis report, the release rate of radioactive materials into the environment is evaluated from leak path diameter and length obtained from gas leakage test. In this paper, experimental results of gas leakage rates from a very narrow orifice and a capillary tube simulating a leak path experimentally investigated using helium, argon, nitrogen and air as working fluids are presented in order to understand hydrodynamics of choked flow, non-choked free expansion flow and laminar flow in a very narrow leak path : (1) The contraction coefficient of choked flow from very narrow orifices are obtained, (2) an evaluation model of gas leakage rate from a capillary tubes is proposed, in which the acceleration loss in the entrance region, the friction loss in laminar flow with expansion effect and the exit loss for choked flow or non-choked free expansion flow are modeled, and (3) as for gas leakage rates of 10-4 to 10-2 cm3/s which are closely related to the sealing performance of transportation casks of radioactive materials, the proposed simplified evaluation method is verified for various gases.

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A series of constant load & temperature creep tests and constant temperature creep tests with short period excessive loadings was carried out on a nickel-base heat-resistant alloy Hastelloy XR, which was developed for applications in the High-Temperature Engineering Test Reactor (HTTR), at temperatures ranging from 900 to 1, 000°C. The excessive loading levels were set at the design stress intensity values Sm for Hastelloy XR indicated in the HTTR
high-temperature structural design code. Five to six time excessive loadings did not cause significant changes of the minimum creep rate or the time to onset of tertiary creep. Excessive loadings repeated around ten times did not cause significant changes of the time to rupture or the rupture elongation. The results suggest that the design stress intensity values Sm for Hastelloy XR have been determined reasonably.

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In order to develop reduced-activation ferritic/martensitic steels potentially suitable for fusion reactor applications, the effect of principal alloying elements Cr, W and V on the micro-structural evolution, toughness and high-temperature creep strength was systematically investigated for relatively simple Cr-W-V steels. Based on the results on the simple steels, two kinds of martensitic 9Cr steels with low and high levels of W were alloy-designed : 9Cr-1WVTa and 9Cr-3WVTa. They exhibited excellent toughness and high-temperature strength. Irradiation hardening was the smaller for the reduced-activation 9Cr-1WVTa and 9Cr-3WVTa steels than for the conventional 9Cr-1MoVNb and it was smaller for the low W steel than for the high W steel. It is concluded that from the aspect of toughness the 9Cr-1WVTa steel is the most promising alloy for the first wall and blanket structures which will be operated at low temperatures below 773 K (500°C). Another 9Cr-3WVTa steel is the most promising in terms of high-temperature creep strength for the future power reactor structures which will be operated at temperatures higher than 773 K.

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Theoretical investigation was made on the dynamics of initial excitation process in molecular laser isotope separation for uranium hexafluoride (UF₆) based on the generalized N-level density-matrix equation derived by Goodman et al. Branched vibrational model due to anharmonic-splitting components for the ν₃ mode of UF₆ molecule were formalized and phase interferences of density-matrix elements were considered to analyze the selective excitation. Because of a power-broadening effect, no more than 0.05 J/cm² fluence of a laser pulse completely masks high enrichment peaks in broadband (Δν=2 GHz) pumping case. Even when matching the laser frequency with ν₃ band (n=0→4) of ²³⁸UFG₆ the enrichment factor (α≡Rproduct/Rfeed, R≡[²³⁸UF₆]/ [²³⁸UF₆] ; R is the abundance ratio and [ ] means the mole fraction.) does not decrease. A narrow spectral linewidth (Δν=-400 MHz) is shown to be essential to achieve a high concentra-tion ratio in the system with a branched N-level ladder as expected from a general two-level system. The exciting frequency, which does not necessarily accord with the ν₃ band of ²³⁵UF₆, gives the maximum enrichment peak. Both the detuning of the optimum frequency and the sharp enrichment peak suggest a direct excitation due to multiphoton resonance. Spectral stability of the laser pulse is also required to excite only the desired isotope for the system with complicated anharmonic-splittings.

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The ion extraction characteristics were investigated when a barium plasma was suddenly produced between alternately biased parallel plate electrodes by simultaneously illuminating a tuned dye laser and an excimer laser light. Time evolution of the ion density profile measured by means of laser-induced fluorescence indicated that the ions in the plasma are alternately extracted to both sides following voltage switching, and then, the plasma diffusion has little effect on the density change. As a result, the ion extraction time, which was measured by ion current detection, is reduced by about 0.71 times that for parallel plate electrodes when a constant voltage was applied. This curtailment rate can be deduced by applying the scaling relation established for constantly biased parallel plate electrodes.

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In a natural aerated zone, infiltrated water flows discontinuously because of repeated cycles of rainfall and evaporation. In order to study migration behavior of radionuclides in the aerated zone, migration experiment of ⁶⁰Co was carried out by a column method, in which deionized water was fed intermittently into sandy soil layer contaminated with ⁶⁰Co.
The ⁶⁰Co concentration in the deeper soil layer increased when the times of flow interrup-tion increased. It is very likely that this was attributed to the increase of movable {⁶⁰Co(OH)₂}n which was formed by pH-rise in the interstitial water during the interrupted period due to buffer action of the soil. A filtration model was developed and was found to be adapted to the concentration distribution of {⁶⁰Co(OH)₂}n fraction ; the amount of {60Co(OH)2}, , was esti-mated. It was concluded that about 1% of sorbed cationic ⁶⁰Co was changed to {⁶⁰Co(OH)₂}n by one time of the interruption.

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By using the two-dimensional rigorous numerical solution of flow and convection-diffusion equations, the ³He-⁴He separative performances of 0.3 mmφ hot-wire thermal diffusion column with 1, 500 mm-height, 15 mm-radius cold-wall was analyzed with pressure P, cold wall tempera-ture T_c and feed rate F being parametrically changed, while the temperature difference between hot wire and cold wall being constant 1, 200 K. Separative analysis using the Dymond-Alder potential for the cryogenic-wall (less than 77.35 K) column has revealed in comparison with the ordinary 288 K cold-wall column with the same condition except T_c that : (i) The degree of separation is remarkably larger and the total separation factor αβ exceeds 10⁵ (at 0.020 MPa) when T_c=10 K, F=1 cm³ (converted at 288.15 K, 0.1 MPa)/min and θ=0.1, while αβ=13 (at 0.148 MPa) for T_c=288 K. (ii) Even for the higher feed rate F of 50 cm³/min, αβ remains 2.1 ×103 (at 0.024 MPa), while αβ=7 (at 0.170 MPa) for T_c-=288 K. In addition, (iii) Pressure dependence of the total separation factor given for the column with continuous feed and draw-offs were found to follow the similarity relation derived for the total reflux operation.

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Simulations were carried out for thermodynamic activities of water and nitric acid in simulated reprocessing solutions under a high level liquid waste (HLLW) evaporation condition.A prediction method based on a "Hydration Model" was developed to evaluate the activity coefficients of nitric acid and water in nitric acid solutions containing fission products. Suitability of the "Hydration Model" was confirmed ; the changes in activity coefficient were well explained. Models predictions agreed well with the reported experimental results for changes of nitric acid concentration in the HLLW solution during the evaporation concentration process.The calculated activities of water and nitric acid were constant during the concentration process, except for the initial transient stage. Therefore nitric acid concentration changes should not have significant effects on chemical reactions, such as precipitation or volatilization, in the solution during HLLW concentration.

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The kinetic study of the reduction of U(VI) at the titanium electrode in nitric acid and hydrazine media was carried out at 25 0.5°C. Uranium (VI) is reduced through a totally irreversible process and kinetic parameters are affected by both the concentration of nitric acid and the electrolytic potential. An empirical equation to express the rate of the reduction of U(VI) was proposed and was confirmed to be in fairly good agreement with the amount of U(IV) produced by the controlled-potential electrolysis. The optimal condition for the prepara-tion of U(IV) from U(VI) was found to be the electrolysis at -0.5V vs. Ag-AgCl/sat.KCI in 12 M HNO₃ and 0.10.2 M hydrazine.

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For the criticality safety designs of the storage pools which store large number of spent fuels, neutron poison materials are useful for increasing capacity of the storage pool by minimizing the spacing between the fuel assemblies. Since few experimental data exist for examining the validation of calculation methods which evaluate the nuclear criticality safety of fuel storage using the borated SUS (B-SUS) plates, critical experiments with B-SUS plates in the water region of single and coupled cores were performed at the Tank-type Critical Assembly (TCA). The systematic data on the reactivity effect of B-SUS plate as a function of the thickness, the boron content and the position of B-SUS plates in the water region were obtained using the critical water level method. The interacting effect between the two cores was also measured to clarify the nuclear characteristics of the coupled two core system which is the simplest system among multiple unit system. Criticality calculations with the combination of a Monte Carlo code, KENO-IV, and the MGCL-137 neutron cross section library in JACS were carried out, and these calculations reproduced the reactivity effect of B-SUS plate within ±0.6%ΔK/K.

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