|Entered date||Event description|
|ENS 53388||7 May 2018 16:31:00||On May 7, 2018, during an engineering review of mission time requirements for Technical Specification related equipment, a deficiency was discovered regarding the Emergency Operating Procedure (EOP) guidance for natural circulation cooldown with a stagnant loop. This condition could be the result of a postulated Main Steam Line Break with a loss of offsite power. During a natural circulation cooldown with a faulted steam generator, flow in the stagnant reactor coolant system (RCS) loop associated with the isolated faulted steam generator (SG) could stagnate and result in elevated temperatures in that loop. This becomes an issue when RCS depressurization to residual heat removal system (RHR) entry conditions is attempted. The liquid in the stagnant loop will flash to steam and prevent RCS depressurization. In this condition, the time required to complete the cooldown would be sufficiently long that the nitrogen accumulators associated with Callaway's atmospheric steam dumps and turbine driven auxiliary feedwater pump flow control valves would be exhausted. The atmospheric steam dumps and turbine driven auxiliary feedwater pump would not be capable of performing their specified safety functions of cooling the plant to entry conditions for RHR operation. This issue has been analyzed by Westinghouse in WCAP-16632-P. This WCAP determined that to prevent loop stagnation, the RCS cooldown rate in these conditions should be limited to a rate dependent on the temperature differential present in the active loops. The WCAP analysis was used to support a revision to the generic Emergency Response Guideline (ERG) for ES-0.2 "Natural Circulation Cooldown." Figure 1 in ES-0.2 provides a curve of the maximum allowable cooldown rate as a function of active loop temperature differential which is directly proportional to the level of core decay heat. At the time of discovery of this condition, Callaway's EOP structure did not ensure that the ES-0.2 guidance would be implemented for a natural circulation cooldown with a stagnant loop. Callaway has issued interim guidance to the on-shift personnel regarding this concern and is in the process of revising the applicable EOPs. This condition is reportable per 10 CFR 50.72(b)(3)(v) for any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to (A) Shutdown the reactor and maintain it in a safe shutdown condition, (B) Remove residual heat, or (D) mitigate the consequences of an accident." The licensee notified the NRC Resident Inspector of this condition.|
|ENS 53203||12 February 2018 11:21:00|
On February 12, 2018, during performance of a TSC Diesel Generator Functional Test, the TSC Ventilation could not be placed in Filter Mode. Filter Mode operation is credited in the TSC habitability analysis of record. The TSC was declared non-functional due to the unavailability of the filtration system. The Emergency Operations Facility (EOF) is available for use as a backup TSC. Additionally, the TSC would be available for emergency response purposes for events that do not involve a release in progress. The NRC Resident Inspector has been notified.
At 1258 CST, TSC ventilation was declared operable. A start permissive lever was adjusted to remedy interference. The licensee notified the NRC Resident Inspector.
|ENS 46814||3 May 2011 17:55:00||The following is a non-emergency notification in accordance with 10CFR50.72(b)(2)(xi), Offsite Notification. At 1036, May 3, 2011, Callaway Plant notified the Missouri Department of Natural Resources (DNR) of an issue with the potable water supply system at the facility. This notification to the Missouri DNR was made in accordance with 10 CSR 60-4.055, 'Disinfection Requirements,' due to circumstances that adversely affect the quality of potable water. Specifically, loss of function of the potable water chlorine pumps resulted in residual chlorine in the potable water system falling below the levels specified by the regulation. DNR has not restricted drinking of Potable Water at Callaway Plant. Required compensatory actions have been initiated, including planned repairs of the potable water chlorination system. The NRC Resident Inspectors have been notified.|