The double-differential cross sections (DDX) of α-particle emission from the reaction of 14.6 MeV neutrons with elemental nickel have been measured using a multitelescope system. The cross sections at sixteen reaction angles from 25° to 164.5° have been obtained. The angle-integrated spectrum and the angular distribution of α-particle emission have been deduced from the DDX. The total α-particle emission cross section was 102±8mb. The present result was compared with the evaluation of ENDF/B-VI and other measurements.

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Critical experiments in the FCA and ZPPR-9 assemblies were re-analyzed systematically by using a continuous-energy Monte Carlo code MVP with the JENDL-3.2 library. The experimental geometries were simulated almost as built and the neutronic parameters were calculated with the physics model where all neutron reactions given in the evaluated nuclear data library were treated explicitly. As a result, the calculated k_eff values underestimated the experimental ones by 0.5-0.8%Δk/k except for FCA X-2. The calculated results for most reaction rate distributions and central reaction rate ratios agree well with the measured ones within the uncertainties.
Furthermore, in order to investigate the cause of the underestimation of the k_eff values, re-calculations were performed using the modified JENDL-3.2 library where the inelastic scattering cross sections and the energy-angular distributions for ²³⁸U were replaced by those of the ENDF/B-VI library. The k_eff values increased by 0.4-0.5%Δk/k for the FCA assemblies, by-0.8%Δk/k for ZPPR-9, and the C/E values were improved. It is found that the cause of the increase in the k_eff values is attributed to the energy distribution for secondary neutrons scattered inelastically by ²³⁸U.

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In order to take into account the heterogeneity of the fuel assemblies of light water reactors by the nodal diffusion method, a method is used where the discontinuity boundary condition is applied for fluxes at the node or assembly interfaces, although the currents are continuous. Then a problem arises what kind of boundary condition should be used for the adjoint flux in solving the adjoint equation to perform subsequent perturbation calculations. As an appropriate boundary condition, it is shown mathematically, that the current of the adjoint flux must be discontinuous, although the adjoint flux itself must be continuous.

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This paper demonstrates that it is well possible to determine the kinetic parameter β_eff/Λ in a neutronically very slow system by means of noise measurements in the critical state. The advantages of this technique are that it can be conducted in a critical reactor directly, and that no special measurement equipment is needed. The comparison to calculated values for four configurations, which differ in the amount of moderation in the core region, shows a satisfactory agreement.

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Measurement technique of isotopic ratio of boron by laser-induced breakdown spectroscopy has been investigated. By irradiating a Q-switched Nd:YAG laser onto the boron disk sample in a low pressure of ambient air the emission spectra of BO molecule were observed in the wavelength region from 330nm to 560nm. Twelve bands of the ²Π-²∑ transition were identified by their spectral positions and by the aid of the computer calculation code developed in this study. Each band spectrum observed in the experiment was well reproduced by this calculation code. It was found that each band spectrum consists of three wide peaks and from their relative peak heights the isotopic ratios of boron can be evaluated. From the analysis of the (0-2) band spectrum it was found that the change of the relative peak heights could be detectable using this experimental arrangement if the concentration of ¹⁰B decreased by 5% from its natural abundance. Measurement precision can be improved by using a detection system with a spatial resolution and this technique is expected to be a simple method of measuring the boron isotopic ratio.

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In earlier work, we showed that within nonhomogeneous sorbing media the desorption process becomes fractal-like. In migration of radionuclides in geologic media, the adsorption is an essential factor retardating the migration. Moreover, geologic media is inherently nonhomogeneous. It is therefore probable that the migration is significantly influenced by the fractal-like feature. Based on this idea, we have analyzed migration behaviours by employing a new model and compared the results with those obtained using conventional models. The nuclides migrate in the media with the flow of ground water being continually trapped on adsorption sites and released (desorbed) to the flow. The concept of the overall residence-time distribution function for nuclides on the adsorption sites is introduced in the new model. This function obeys the power form, t^-1-α (α>0), for sufficiently large t (t denotes time). The migration behaviours predicted by our theory are qualitatively different from those by conventional theories, and the details of the differences are greatly dependent on the exponent a. In particular, the migration behaviour in cases of 0<α<1 is characterized by far larger retardation effects.

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A pyrometallurgical partitioning technology to recover actinides from high level radioactive wastes is being developed. In the process, actinides are separated from fission products by electrorefining in molten chloride systems. It is expected that REs (rare earth elements), main components of fission products are hardly separated from actinides. In order to estimate separation factors, electrorefining experiments to recover actinides from LiCl-KCl eutectic salt containing actinide (U, Np, Pu and Am) and RE (Y, La, Ce, Nd and Gd) chlorides were carried out at 450°C. Actinides were removed from a liquid cadmium anode and recovered as metal on a solid cathode. Typical cathode deposits were rough in appearance and contained 70-90wt% adhering salt. The current efficiency was low because some of the deposit occasionally fell from the cathode. It is shown that uranium, neptunium and plutonium are relatively easily separated from REs and that americium is accompanied by some of REs.

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A simulation model was proposed for prediction of H₂O-HTO separative performances of water distillation by a wetted-wall column. A wetted-wall column was assumed to be a circular tube, and mole-fraction profiles in the tube were obtained by coupling the equations which describe diffusion processes of both vapor and liquid phases and by solving the equations simultaneously. It was found that the calculations for constant mole-fraction boundary with high mass-transfer rate resulted in overestimations of degree of separation. The relative difference of the HETP value for constant mole-fraction boundary from that for the present model was -19% when P=101.3kPa, T=373K, R=0.8cm, H=100cm, k_{v, A}=1.0×10⁴cm/s and Re_v=660.

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An evaluation has been made for the covariances of neutron cross sections of ⁵²Cr, ⁵⁶Fe, ⁵⁸Ni and ⁶⁰Ni contained in JENDL-3.2. Reactions considered were the threshold reactions such as (n, 2n), (n, nα), (n, np), (n, p), (n, d), (n, t) and (n, α), the radiative capture reaction above the resonance region, and the inelastic scattering to discrete and continuum levels. Evaluation guidelines and procedures were established during the work.
A generalized least-squares fitting code GMA was used in estimating covariances for reactions of which JENDL-3.2 cross sections had been evaluated by taking account of many measured data. For cross sections that had been evaluated by nuclear reaction model calculations, the KALMAN code, which yields covariances of cross sections and of associated model parameters on the basis of the Bayesian statistics, was used in conjunction with reaction model codes EGNASH and CASTHY.
The evaluated uncertainties of a few percent to 30% in the cross sections look reasonable, and the correlation matrices show understandable trends. Even though there is no strict way to confirm the validity of the evaluated covariances, tools and procedures adopted in the present work are appropriate for producing covariance files based on JENDL-3.2. The covariances obtained will be compiled into JENDL in the near future. Meanwhile, new sets of optical model and level density parameters were proposed as one of byproducts obtained from the KALMAN calculations.

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To consecutively decompose ¹⁴CO₂ into carbon (¹⁴C) through its reaction with H₂, an apparatus using microwave discharge and its conditioning were investigated. The reaction produces CO as an intermediate, and proceeds in the two steps of (1) "CO₂+H₂→CO+H₂O" and (2) "CO+H₂+C_n→C_n+1+H₂O", where Cn denotes the carbon already deposited on the wall of the discharge tube. Preliminary dispersion of carbon to the wall of the discharge tube by sputtering of a graphite particle was effective to promote the reaction. Two silica discharge tubes (6mm O.D., 4mm I.D., and 150mm length each) were connected in series to proceed the former reaction in the first discharge tube and the latter one in the second one. When a 1:3 mixture of CO₂ and H₂ (total pressure 0.67kPa) was passed through the discharge tubes at a linear gas velocity of approximately 30mm/s and discharged for 60h under microwave of 30-40W supplied from two 2, 450 MHz power generators (200W each), more than 90% of CO₂ was converted into CO in the 1st tube and about 23% of the CO was then decomposed into carbon in the 2nd tube. However, about 50% of the CO escaped from the tube without being decomposed, and about 0.5% and 1% of the carbon fed were hydrogenated into CH₄ and C₂H₂, respectively. The rest about 25% which was not confirmed was probably evacuated from the 2nd tube as microparticles of carbon. To completely decompose CO₂ into carbon, additional discharge tubes are necessary downstream of the 2nd tube.

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