Event Notification Report for April 28, 2000

ISOLATION OF THE CONTROL BUILDING VENTILATION SYSTEM TO THE RECIRCULATION MODE (CHLORINE MODE)

The following text is a portion of a facsimile received from the licensee:

"EVENT: On 04/28/00 at 1630, the control building ventilation system isolated to the recirculation mode (chlorine mode). Maintenance [personnel] had completed pressure testing the repairs that had been completed on the number 3 chlorinator with nitrogen and were venting the chlorinator. Residual chlorine with the nitrogen that was vented from the chlorinator caused the isolation. The chlorination system was isolated and under clearance in support of the scheduled maintenance activities during the event."

"INITIAL SAFETY SIGNIFICANCE EVALUATION: Minimal - The control building ventilation system responded per design."

"CORRECTIVE ACTION(S): The control room operators verified [that] all automatic actions occurred. Local chlorine levels were verified to be less than minimum detectable using portable chlorine monitors. Maintenance completed venting the number 3 chlorinator with no subsequent detection of chlorine. Control room ventilation was restored to the normal alignment."

The licensee stated that this issue placed both units in a 12-hour to Hot Shutdown limiting condition for operation (LCO) because the control room emergency ventilation (CREV) system emergency ventilation fans are inoperable (will not operate) during the chlorine mode. The LCO has since been exited, and there was no reduction in power for either unit.

The licensee notified the NRC resident inspector.

PLANT HAD A REACTOR TRIP FROM 21.6% POWER DURING SHUTDOWN FOLLOWING A TURBINE TRIP


THE UNIT 2 REACTOR TRIPPED DURING A POWER DECREASE FOR A REFUELING OUTAGE. THE SUSPECTED CAUSE IS A SPIKE ON THE 23B FEEDWATER HEATER INSTRUMENTATION GIVING A HI-HI LEVEL SIGNAL WHICH RESULTED IN A TURBINE TRIP/REACTOR TRIP. PLANT HAD LETDOWN ISOLATION, BUT THE AUX. FEEDWATER PUMPS DID NOT AUTOSTART AND WERE NOT REQUIRED TO START BASED ON THE STEAM GENERATOR LEVELS. ALL CONTROL RODS FULLY INSERTED, NO ECCS ACTUATED AND NO SAFETY RELIEF VALVES LIFTED. THEY ARE CONTINUING THE INVESTIGATION.

THE NRC RESIDENT INSPECTOR WAS NOTIFIED.

24 HOUR 91-01 BULLETIN - LOSS OF ONE CONTINGENCY

On 4/28/00 at 0951 hours, X-705 Chemical Operation personnel discovered an NCSA-705_076.A00 noncompliance when a 55-gallon burnable waste drum was left unattended in the X-705 high-bay with it's lid ajar. This could have resulted in the potential accumulation of an unsafe volume of solution in the drum had a leak developed in the overhead storage system which contains uranium-bearing solution. This was a loss of one control(volume) in the double contingency control matrix for the aforementioned NCSA. The second control (physical integrity of the storage system) was maintained throughout this event.

SAFETY SIGNIFICANCE OF EVENTS:

The safety significance or this event is low because the only credible nearby source of uranium-bearing solution is that contained in the overhead storage, which is inspected on a monthly basis for evidence of leaks. Also, the solution contained in the overhead storage is typically low in uranium concentration.

POTENTIAL CRITICALITY PATHWAYS INVOLVED (BRIEF SCENARIO(S) OF HOW CRITICALITY COULD OCCUR):

If a leak had developed in the overhead storage system such that the solution could have accumulated in the uncovered drum, an unsafe volume or solution could have accumulated, if the leaking solution had contained a sufficient amount of uranium, the resulting configuration could have been sufficient for a criticality to occur. It should be noted that the allowed safe geometry and volume limits established in NCSA-705_076 are based on optimally moderated, UO2F2, and water solution which contains uranium enriched to 100 wt%

CONTROLLED PARAMETERS (MASS, MODERATION. GEOMETRY, CONCENTRATION, ETC.):

The parameter which was violated during this upset was the volume of potential accumulation present in the uncovered 55-gallon drum (i.e.. the volume in which uranium-bearing solution could have accumulated in the event of a leak). The physical integrity of the system containing the uranium-bearing material was maintained.

ESTIMATED AMOUNT, ENRICHMENT. FORM OF LICENSED MATERIAL (INCLUDE PROCESS LIMIT AND % WORST CASE OF CRITICAL MASS):

No uranium-bearing material was actually introduced into the uncovered drum. However, the overhead storage system does routinely contain uranium-bearing solutions of various enrichment and concentration (typically less than 500 ppm uranium concentration and less than 10 wt% enrichment, although these parameters are not controlled as NCS requirements). Data from the latest sampling of solution at first stage microfiltration (which originates from the overhead storage) indicates a maximum of 80 ppm uranium, although it should be noted that this may not be indicative of the solution concentration currently contained in the overhead storage.

NUCLEAR CRITICALITY SAFETY CONTROL(S) OR CONTROL SYSTEM(S) AND DESCRIPTION OF THE FAILURES OR DEFICIENCIES:

NCSA-0705_076.A00 takes credit for the physical integrity of systems which contain uranium-bearing material and that unsafe volume/geometry containers are either modified, covered, or oriented to prevent an unsafe configuration from resulting in the event of a leak. The 55-gallon drum observed in the X-705 high-bay was not protected from a potential accumulation since the cover had been dislodged and left unattended.

CORRECTIVE ACTIONS TO RESTORE SAFETY SYSTEM AND WHEN EACH WAS IMPLEMENTED:

At 0951 hours, a NCS anomalous condition was initiated.

At 1029 hours compliance was re-established.

The NRC Resident Inspector and the DOE Representative were notified.

DISCOVERY THAT A SHUTDOWN COOLING (SDC) ISOLATION VALVE WAS NOT DISABLED AS REQUIRED BY APPENDIX R FOR MODES 1, 2, AND 3

The following text is a portion of a facsimile received from the licensee:

"On [04/22/00], while shutting down in Mode 3 for a planned refueling outage, it was discovered that a SDC isolation valve, 2-SI-651, was not disabled as required by the facility [Appendix] R compliance report for Modes 1, 2, and 3. Upon review and investigation of this deficiency, it was determined on April 28, 2000, that this condition could have resulted in an inability to achieve and maintain safe shutdown if a design basis fire-induced hot short of this valve had occurred."

"The [Appendix] R report credits disabling this valve to ensure that a fire-induced hot short would not result in the valve damaging itself such that it could not be opened, as needed to initiate shutdown cooling. Additionally, there have been no Appendix R events during this timeframe."

"A design modification was made in early 1999 (during the MP2 recovery outage) which changed the location of the coils which are removed in Modes 1, 2, and 3 to ensure the valve is disabled. When the modification was implemented, adequate guidance was not given in applicable facility procedures to ensure that the correct coils would be removed. This resulted in the valve not being disabled during the previous operating cycle."

The licensee notified the NRC resident inspector as well as applicable state and local agencies.