Energy-angle double-differential neutron emission cross sections of lithium isotopes were measured at incident neutron energies of 4.2, 5.4 and 14.2 MeV for ⁶Li and of 5.4, 6.0 and 14.2 MeV for ⁷Li using a time-of-flight spectrometer. Care was taken in background subtraction and in data correction for sample-size effects. Detailed comparison of the present results was made with the evaluated data in JENDL-3PR1. A spectrum fitting method was used to extract the ^{6, 7}Li(n, n'x)α and (n, 2n) reaction cross sections. Neutrons emitted from the (n, 2n) reactions were well described by the conventional evaporation model. A simple calculation with a final-state Coulomb interaction was effectively applied for the ^{6, 7}Li(n, n'x)α reactions. Angle-integrated cross sections of the ⁷Li (n, n't) α reaction were in good agreement with the JENDL-3PR1 data except the data measured at 6.0 MeV. The angular distributions of elastically and inelastically scattered neutrons were successfully analyzed with the coupled-channel method at the incident neutron energy of 14.2 MeV.

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A three-dimensional nuclear and thermo-hydrodynamic kinetics calculation code IBIS has been developed, envisaging the treatment of asymmetrical reactivity changes in a large fast breeder reactor. An example of calculation with this code is described, which reveals a difference of void propagation behavior, following a local disturbance, between homogeneous and heterogeneous cores, ascribable to the presence, in the latter case, of inner blanket layers, which act as barrier against void propagation. Of the two parameters of power-to-flow ratio and space-time variation in thermal power, the latter is the more influential on void propagation, and this makes it essential to perform three-dimensional space-dependent kinetic analysis for adequately simulating local perturbations in a heterogeneous core.

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A computer-based operator instruction system (COINS) for diagnosing fission product (FP) transport and release in nuclear power plants (NPPs) is applied to plant diagnosis in combination with the computational code "SACHET", which evaluates the dynamic FP inventories in the multiple compartment system of pressurized water reactor (PWR) plants.
The COINS can be described in the most general way as a computer-based information processing system which takes in plant data, processes it, and displays the results to the NPP's operating crew. Our major concern for the COINS is, however, not to evaluate general plant dynamics, but to monitor the distribution of the whole radioactive materials such as FP, and to diagnose the plant state in the view of FP transport during the NPP's lifetime.
An algorithm of the stochastic approximation for the adaptive pattern classification of the dynamic distributed parameter system is introduced in the COINS software, where a nonlinear functional of the set of monitored data and the system parameters is used.
By the use of the COINS, it becomes possible to understand PWR plant states precisely in the view of FP transport and release during normal operation, to identify the occurrenses of the unusual events clearly, and to forecast the potential hazards reasonably.

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The isotopic reduced partition function ratios (RPFR), (s/s')f, for the ³⁴S/³²S isotopic pair were calculated for 24 sulfur compounds between 10 and 2, 000 K. Their magnitudes were in the following sequences; at low enough temperatures at which ln(s/s')f depends only on the isotopic difference in frequency-sum, SF₆>SO₂F₂>SF₅Cl>SF₅Br>SO^2-₄>SO₂Cl₂>SO₃>NSF₃>SF₄>SOF₂>SOCl₂>Me₂SO>SOBr₂>SO₂>SPBr₃>SCBr₂>Me₂S>SPCl₃>SCCl₂>SCF₂>SPF₃>CS₂>OCS>H₂S, and at high enough temperatures at which ln(s/s')f is proportional to the isotopic difference in the sum of frequencies squared, SO₂F₂>SO^2-₄>SO₃>SF₆>SO₂Cl₂>SF₅Cl>NSF₃>SF₅Br>SOF₂>SO₂>SF₄>Me₂SO>SCCl₂>SOBr₂>H₂S>Me₂S>CS₂>SCF₂>OCS<SCCl₂>SCBr₂>SPF₃>SPCl₃>SPBr₃ where Me=CH_s. Correlation of the RPFR with molecular structure and molecular forces was discussed.
The equilibrium constants K for the 34S/32S isotope exchange reactions of all the possible pairs of 19 sulfur compounds selected out of the above 24 were calculated and their temperature dependences were investigated. Two types of temperature dependences were observed; one being smooth monotonic and the other having single cross-over with no preinflection.

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The diffusion of Cs, Sr, Am and Np into granite tablets has been examined. Sorption of these nuclides on the five kinds of rock : granite, granodiorite, basalt, andesite and rhyolite was measured and expressed as a function of interstitial water of the rock. The interstitial water was measured by weighing the penetrated water and also by counting the penetrated 99mTc. Technetium counting represents that the sorption is affected by the rocks and does not correspond linearly to the interstitial water content.
The ratio IC, amount of sorbed nuclide per unit of interstitial water divided by amount of nuclide per unit of solution, is introduced to make clear the relationship between nuclide sorption and interstitial water. Results indicate that there is a correlation between the sorption of nuclides and the amount of interstitial water. However, mechanisms that retard the movement of the nuclide are different from each other. Americium shows nearly equal If, values with different rocks. In contrast, Np varies greatly.

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A three-dimensional transport code "TRITAC" for solving eigenvalue problems in reactor cores has been developed on the basis of discrete ordinates method with the diffusion synthetic acceleration technique. The Larsen procedure for the diffusion synthetic acceleration method has been extended to three-dimensional geometry. With the procedure a spatially differenced diffusion synthetic equation has been derived and implemented in the TRITAC code. In the X-Y geometry the code yielded the same results as the TWOTRAN- II code. Three-dimensional eigenvalue problems for thermal and fast reactors have been solved and the computational time has been compared with that required for the three-dimensional dis-crete ordinates calculation with the rebalance acceleration technique.

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