Improved core physics test method at HZP

In case of 3 loop nuclear plants in Korea, the error of control rod worth measurement which is one item of core physics test at HZP is increased considerably compared with previous cycle data since loading of V5H. The cause of error increase of control rod worth and the reactivity effect according to flux and background level are analyzed. The root cause of error increment is that the flux level which is detected by excore detector is decreased by applying low-low leakage or ultra low leakage loading pattern and the background level is increased due to reduction of planned outage and longer fuel cycle length. In current test method, it is limited to decrease or eliminate the effect of background. This is confirmed based on the data of physics test for Ulchin 1 cycle 9. In order to perform credible core physics test at HZP at this circumstance, the elimination of such background effect is reviewed and setup by adjusting electrometer used in reactivity computer by compensating the amount of background level. Therefore the improved core physics test method to perform the credible test at HZP is setup by this study regardless of any kind of loading pattern and cycle scheme