Ultrasonic flaw detection data susceptible to influence of inspection factors disperse largely. To see the extent and cause, standard deviation has been analyzed in a number of papers on the factors of team, detector etc. This analysis does not lead to general conclusion, and where factors compound each other, the application is limited. This report is an explanation how variance analysis method is applied to solve the problem.

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A power change maneuvering method for BWR has been proposed to generate an optimal power control maneuver, which realizes the power change operation closest to a power change demand pattern under operating constraints. The method searches for the maneuver as an optimization problem, where the variables are thermal power levels sampled from the demand pattern, the performance index is defined to express the power mismatch between demand and feasible patterns, and the constraints are limit lines on the thermal power-core flow rate map and limits on keeping fuel integrity. The usable feasible direction method is utilized as the optimization algorithm, with newly developed techniques for initial value generation and step length determination, which apply one-dimensional search and inverse-interpolation methods, respectively, to realize the effective search of the optimal solution. Simulation results show that a typical computing time is about 5min by a general purpose computer and the method has been verified to be practical even for on-line use.

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The high temperature steam (500°C, 10.3MPa) test and observation of microstructure were conducted in order to investigate the effect of the solid solutional alloying elements on the nodular corrosion resistance of Zircaloy-4.
Needle-like structure, which resulted from rapid cooling from β- and α+β-temperature range, contained martensite produced by diffusionless transformation. The content of solid solutional Fe and Cr in the matrix increases with the increasing of quenching temperature and cooling rate. A good correlation between the weight gain after the steam test and the volume fraction of precipitates (fvol) was obtained. Nodular corrosion did not occur on the heat-treated specimens, in which fvol was less than 3×10^-5.
In the β-furnace cooled specimen, nodular oxides were observed in the α-grain near the grain boundary, where the precipitation of intermetallic compound Zr(Cr, Fe)₂ was remarkable.
From these results, it is considered that nodular corrosion initiates at the solid solutional Fe and Cr depleted zone.

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