A survey is given of some of the parameters affecting radionuclide partitioning behavior described in terms of distribution coefficients (K_d values) in tbe solid-liquid system. Attention is focused on factors of physical, chemical and biological processes such as solid; liquid ratio, pH-Eh, oxides, reversibility, liquid phase composition, aging effect, organic substances, complexation and so on. The simplistic use in migration models of such coefficients measured in laboratory by batch tests is discussed and criticized. It is suggested that, in order to produce applicable K_d, effort should be focused on the measurements under conditions similar to the in situ situation.

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When components of a power plant, such as pumps or valves, are checked or repaired, those components should be isolated. This isolation follows the isolation list which describes the title of the work, the period of the work and the components to be operated. Although the isolation list is prepared by technical experts considering many diagrams about the plant and the plant status, making an isolation list is a rather time consuming and complicated task. A knowledge-based system called Isolation Support System has been developed to support an engineer while preparing an isolation list.
This system takes the components to be repaired or checked as a user's input. The framebased representation of the components is used to determine isolation boundary considering drainage of the specified components. The production rules for the isolation procedures are processed to determine the isolation operations. The switching interlocks are specified by simulating the plant response to the isolation operation. Technical experts tested Isolation Support System using reactor water cleanup system model, and the validity of isolation lists prepared by this system was confirmed.

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Neutronic behaviors, such as distributions of neutron flux, adjoint neutron flux in macroscopic aspects, and neutron spectra, adjoint neutron spectra, spacial distributions of fissile nuclei fission fraction and their burnup variations in microscopic aspects, and effects of ²³⁸U fission with high energy neutrons are compared and analysed for three type cores in 1, 000MWe class FBR plants, that is, homogeneous two region oxide and metal cores, and an axially heterogeneous oxide core, and then the following features are brought out.
(1) For neutron spectra in large volume cores, influences of Pu enrichment difference in core regions are fairly moderated by neutron migration and ²³⁸U fission, and variations due to burnup effects are also reduced by ²³⁸U fission and its high conversion to ²³⁹Pu.
(2) Adjoint neutron spectra have flattened distributions in common with three type cores and these are resulted in favorite effects on the stable behaviors of neutrons.
Based on these microscopic neutron behaviors with small spacial and cycle variations in these cores, some considerations to future prospects of FBR core design are discussed.

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Implicit difference schemes have been regarded as unconditionally stable methods. Iterative methods are however usually adopted to solve simultaneous equations resulting from the implicit schemes. If the iteration fails to converge, the unconditional stability cannot be obtained in practice. In the present study, convergency of the iterative methods for the implicit schemes with space-centered differencing was examined.
First, the convergency of linear iterative methods for the linear transport equation was analyzed with the spectral radius of the iteration matrix. This showed that the iteration diverges unless the Courant number less than about unity.
Next, numerical experiments were conducted to check the convergency of four iterative methods for the solution of the nonlinear simultaneous equation derived from Burgers' equation. It was confirmed that the iterative methods break the unconditional stability of the implicit scheme, except for the case that the direct methods are applied to solve the linearized equation obtained by the Newton method.
Lastly, the shock tube problem was solved using the four iterative methods. As a result, the unconditional stabitity could not be obtained. This experiment confirmed that the convergency is subject to the Courant condition, the Courant-Friedricks-Levy condition or the degree of discontinuity in state variables.

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