Qualification of a three-dimensional core dynamics analysis program coupled with a detailed mesh division for commercial boiling water reactors-I

In the stability, licensing analysis and evaluation of boiling water reacto rs (BWRs), frequency-domain stability analysis programs have been used in J apan. To back up the licensing analysis and evaluation, time-domain, multir egional analysis programs have been used because more detailed analytical r esults can be obtained by these programs with little more computer time tha n that used by the frequency-domain stability analysis programs. bl the bac kup calculation by time-domain, multiregional analysis programs, many trial -and-error experiments and much expertise on the reactor core radial region al division and on the initial disturbance input are necessary to analyze p roperly the stability of the BWR core, particularly its regional nuclear th ermal-hydraulic stability. A three-dimensional time-domain core dynamics analysis program called SUPER -STANDY,vas developed with a detailed mesh division that makes various tria l-and-error procedures and experience-based expertise unnecessary and that can tl-eat the stability peculiar to the BWR cole accurately. The program w as applied to a plant where regional instability was observed, and the resu lts were qualified. They showed that BWR stability can be analyzed using SU PER-STANDY by adding only the core uniform initial disturbance input withou t considering the reactor core radial regional division. It was determined that core regional mode instability can be properly analy zed by the multiregional analysis program (a) by dividing the core into six or more radial regions, (b) by specifying the hot fuel bundle as one regio n, and (c) by specifying the surrounding fuel bundles around the hot fuel b undle as one region. A visual display system was also developed for a huge number of stability d ata and core nuclear thermal-hydraulic characteristics, which are connected to each other in a complex way. These are obtained by the SUPER-STANDY pro gram.