Zone response analysis before and after refueling in Wolsong No. 2

The main interest in PHWR, which has daily refueling, is to prevent reactor trip during refueling by maximizing operation margin of Regional Overpower Protection(ROP) detector. And the observance of operation limits on channel and bundle powers, the flattening of flux shape, the suppression of fuel defects, and economical efficiency are also important. The power related parameters are being optimized with the tools of RFSP's Pre-Simulation, which has a great accuracy enough to give us a satisfaction. But, with reared to the ability of individual zone level prediction, it has been assessed not to have such a precise accuracy as we want. So, for the first time in Korea, we have grasped the individual liquid zone controller's characteristics unique to Wolsong unit No. 2 by collecting before and after refueling data. The upper zone's sudden drain events and cycling were investigated. It was reconfirmed that the variations of upper zones are bigger than those of others, as is known. But the fact that the actual boundary of each region affected by refueling is not same as that of design region, is also identified