Event Notification Report for April 01, 2002

NITROGEN BACKUP SYSTEM FOR CHARGING PUMP SPEED CONTROL FOUND NOT TO SATISFY APPENDIX R FIRE ASSUMPTION.

At 0917 CT on 04/01/02, it was determined that a condition identified on 03/28/02 potentially represents a significant degradation of plant safety during response to an Appendix R event. The Appendix R credited nitrogen backup system for charging pump speed control is unable to satisfy its design function of controlling Charging System flow to the Reactor Coolant System (RCS) for the time required to place the plant in Mode 5 (Cold Shutdown). During an Appendix R fire it is assumed that the normal motive force (instrument air) for charging control is unavailable and an installed backup is credited. This installed nitrogen system allows inventory control while in Mode 3 (Hot Standby) and is used to control RCS inventory and pressure while the RCS is cooled down and depressurized from Mode 3 (Hot Standby) to Mode 5 (Cold Shutdown). A nitrogen bottle 12-pack is calculated to last for approximately 8 hours. PBNP has 1 spare approved nitrogen pack on site - - it has been calculated that up to 15 spares would be required for 72 hours of charging pump operation. Mode 5 (Cold Shutdown) is expected to be reached in 30 hours but may be as long as 72 hours.

This issue places the plant in an unanalyzed condition that has the potential to significantly degrade plant safety (RCS Inventory Control) and thus is reportable.

The associated charging pumps have been declared out of service for Appendix R use and compensatory actions undertaken that establish appropriate fire rounds. Fire rounds will be continued until the condition is corrected or a suitable evaluation is completed.

The NRC Resident Inspector was notified of this event by the licensee.

****RETRACTION ON 5/17/02 AT 13:10 FROM R. Robbins to R. Laura****

"ENS Event Notification #38819 was reported at 1205 CST on April 1, 2002. This event was reported in accordance with 10 CFR 50.72(b)(3)(ii)(B) for identification of an unanalyzed condition that had the potential to significantly degrade plant safety. The condition involved postulated Appendix R fire scenarios for which the safe shutdown analyses assumes that the normal motive force for charging pump control (instrument air) is unavailable due to fire-induced damage. Certain Appendix R fire scenarios require the availability of a single charging pump, operable at greater than minimum pump capacity, in order to meet the Appendix R performance goal of maintaining adequate RCS inventory control without loss of pressurizer level. An installed back-up nitrogen supply is credited with maintaining the ability to control charging pump flow for the duration of the 72 hour Appendix R coping period. The unanalyzed condition identified in this notification was that the installed back-up nitrogen supply, based on a conservative calculation, would have adequate capacity to provide the motive force for the Single Charging pump control function for only 8 hours. After that time, the variable speed charging pump would run back to minimum speed, which equates to a pumping capacity of approximately 18 gpm.

"We have subsequently completed an engineering evaluation to estimate the transient behavior of the RCS in the event of these Appendix R fire scenarios assuming only 8 hours of Charging pump speed control is available. This evaluation was based on conservative assumptions regarding reactor coolant pump seal leakage and unavailability of normal cooling and safety systems. This evaluation provided estimates of key RCS transient parameters based on engineering analysis and predicts that upon reducing the available charging pump flow to the pump minimum, pressurizer pressure and level will no longer be maintained. Although RCS sub-cooling is lost and some voiding in the RCS occurs, the core remains covered during the entire 72 hour Appendix R coping period and core cooling is maintained throughout the transient.

"We have therefore concluded that this previously unanalyzed Appendix R scenario would not have resulted in a condition that would have significantly degraded plant safety. Therefore, this condition is not reportable under 10 CFR 50.72 and we are hereby retracting this event notification.

"Until corrective actions are completed to ensure that the Appendix R safe shutdown performance goal to maintain reactor coolant inventory control within the level indication in the pressurizer can be satisfied, appropriate fire rounds will continue."

The NRC Resident Inspector was notified.

Notified R3DO (R. Gardner)

DURING SURVEILLANCE TEST "A" DIVISION OF CONTROL ROOM VENTILATION SYSTEM FAILED TO AUTOSTART ON A LOW FLOW SIGNAL.


At 1436 CT on 04/01/02, during a low flow start surveillance test the "A" division of the Control Room Ventilation System failed to autostart. At the time, the "B" division was disabled in order to perform the test. Thus, the Control Room Ventilation System accident mitigation function was lost. Division "B" Control Room Ventilation was restored to operability at 1600 hours CT. The "A" division is operating with the control switch in the run mode. The cause of the failure to Autostart is under investigation.

The NRC Resident Inspection will be notified of this event by the licensee.

CONTROL ROD DRIVE MECHANISM NOZZLE NO. 7 PENETRATION FOUND TO HAVE A SMALL LEAK PATH.

Qualified visual inspection of the Unit 1 reactor vessel head Control Rod Drive Mechanism head penetrations found two penetrations with very slight boron accumulations. Ultrasonic testing of these penetrations has determined that one nozzle (No. 7, near the center of the reactor vessel head) has a potential reactor coolant system leak path. Any reactor coolant system leakage from penetration No. 7 would have been so small it would be below the threshold of measurability by the reactor coolant system leakage measurement processes. The leaking nozzle will be repaired prior to restart from the present refueling outage.

The NRC Resident Inspector will be notified by the licensee of this event.