Part 21 Report - 1995-065
. REGION IV MORNING REPORT PAGE 2 MARCH 13, 1995 Licensee/Facility: Notification: Wolf Creek Nuclear Oper. Corp. MR Number: 4-95-0030 Wolf Creek 1 Date: 03/13/95 Burlington,Kansas RESIDENT INSPECTOR Dockets: 50-482 PWR/W-4-LP Subject: REACTOR TRIP RECOVERY AND ESTIMATED CRITICAL POSITION ANOMALY Reportable Event Number: 28504 Discussion: Following a reactor trip during the performance of reactor trip breaker testing on March 8, the licensee completed several corrective actions in preparation for reactor startup. The reactor trip was caused when a reactor trip breaker was being closed from the control room using the reactor trip switch. The switch failed to maintain circuit continuity and resulted in a reactor trip. Non-vital bus PA-01 failed to fast transfer and two reactor coolant trips were deenergized as a result. Corrective actions completed prior to restart included procedure changes to prohibit use of the reactor trip switch in the control room to close the reactor trip breakers if all rods were not fully inserted and preventive maintenance on the PA-01 breakers to improve breaker actuation time. During the reactor startup on March 12, the reactor was made critical at 10:36 a.m. (CST). Criticality was achieved at 56 steps on Control Bank C and the estimated critical position had predicted criticality at 72 steps on Bank D, a difference of approximately 1000 pcm. The licensee had been plotting a 1/m graph and observed that the reactor would achieve criticality earlier than predicted by the ECP. Following criticality and stabilization, the licensee decided to insert all control bank control rods while evaluation of the anomaly was in progress. Licensee procedures call for an evaluation if criticality is achieved more than 500 pcm different than the ECP. The licensee determined that the error was due to a reactivity bias in the Babcock and Wilcox software program that calculates ECPs and various other core performance related functions. Insertion of the same precritical data into a previously used program from a different vendor predicted criticality at a position that was only 21 pcm different from the actual critical position. Following the evaluation, and based on information from previous physics testing and core response, the licensee commenced a reactor startup utilizing the previously used ECP program, and was critical at 6:02 a.m. (CST) on March 13. Regional Action: The Resident Inspectors and Region IV personnel will be following the licensee's actions and will review the corrective actions during routine inspection followup activities. Contact: D. N. Graves (817)860-8141 J. Dixon-Herrity (316)364-8653
Page Last Reviewed/Updated Wednesday, March 24, 2021
Page Last Reviewed/Updated Wednesday, March 24, 2021