A system has been developed to improve the efficiency of maintenance work while decreasing the radiation exposure of maintenance personnel in nuclear power plants. The input data for dose rate calculation are automatically generated by using computer-aided design data. Changes for the input data corresponding to the progress of maintenance work, such as installation of a radiation shield and removal of a component, are easily input interactively on a graphical user interface (GUI). A new method was proposed which searches the sets of source and detector points between which gamma-ray attenuation is changed by the component movement. The calculation is performed only for the changed sets, so that the change of the three-dimensional dose rate distribution is calculated rapidly according to the work progress. The dose rate distribution and the radiation exposure of maintenance personnel are displayed three-dimensionally in colour with plant components and pipes on the GUI.

In this study, we investigated the temperature dependence of magnetostriction in the twinned rhombohedral perovskite structure-based lanthanum cobaltite La0.8Sr0.2CoO3. The magnetostriction measured in a magnetic field applied along the pseudocubic [111]c axis showed large hysteresis and residual strains. The residual strains are caused by the twin deformation, which we observed using x-ray diffraction. We found that the critical magnetic field for the twin deformation of La0.8Sr0.2CoO3 increases with temperature. The twin deformation occurs in a sufficiently strong magnetic field (∼6 T), even in the paramagnetic region at room temperature. We also confirmed that the temperature dependence of the critical magnetic field for twin deformation is related to the temperature dependence of the magnetization.

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A plant operator performance evaluation system to analyze plant operation records during accident training and to identify and classify operator errors has been developed for the purpose of supporting realization of a training and education system for plant operators. A knowledge engineering technique was applied to evaluation of operator behavior by both event·based and symptom-based procedures, in various situations including event transition due to multiple failures or operational errors The system classifies the identified errors as to their single and double types based on Swain's error classification and the error levels reflecting Rasmussen's cognitive level, and it also evaluates the effect of errors on plant state and then classifies error influence, using "knowledge for phenomena and operations", as represented by frames. It has additional functions for analysis of error statistics and knowledge acquisition support of "knowledge for operations".The system was applied to a training analysis for a scram event in a BWR plant, and its error analysis function was confirmed to be effective by operational experts. KEYWORDS