ML18005A995
| ML18005A995 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 06/20/1989 |
| From: | Manning F NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML18005A994 | List: |
| References | |
| AEOD-T911, NUDOCS 8907180278 | |
| Download: ML18005A995 (4) | |
Text
AEOD TECHNICAL REVIEW REPORT UNITS:
DOCKET NO.:
LICENSEE:
NSSS/AE:
Shearon Harris 50-400 Carolina Power 5 Light Co.
Westinghouse/Ebasco TR REPORT NO.:
AEOD/7911 DATE: 3une 20, 1989 EVALUATOR/CONTACT:
F.
M. Manning
SUBJECT:
EVALUATION OF INDIVIDUALLYREPORTED SAFETY SYSTEM LERs FOR THEIR COMBINED SIGNIFICANCE
SUMMARY
This report evaluates three licensee event reports (LERs) to assess their combined effects on safety.
The individual LERs concern failures or problems in the service water system, the emergency core cooling system, and the sodium hydroxide addition system.
The LERs indicate that these events could have simultaneously existed for various periods of time.
The co-existence of these events made the plant more vulnerable to accidents or initiating events that would have required these failed or degraded systems or functions.
The three LERs are evaluated in the context of a large LOCA randomly occurring during the time period these events co-existed.
If a large LOCA had occurred, the RHR system could be lost due to the co-existence of events I and 2, and the NAOH addition system would have been degraded (event 3).
Both the RHR system and the NAOH addition system are required to mitigate a
LOCA.
The combination of events referenced in this report are only moderately significant because of the relatively low occurrence likelihood of postulated scenarios impacted by these events.
The utility has taken steps to correct the problems noted herein and therefore we plan no further action on these events.
- However, we wi 11 continue to monitor Shearon Harris and other plants for those LER events which can be significant in combination.
INTRODUCTION This report provides an evaluation of three LERs reporting equipment or proce-dural failures at the Shearon Harris plant.
These failures or problems occurred or existed within an overlapping time-period.
The individual events are relatively innocuous in themselves, and they were individually evaluated to be of low
.significance.
- However, when these events are reviewed together, it becomes apparent that the combined effect of these individually occurring events could have been greater than their individual significance might indicate.
This report concerns the collective significance of these three events.
8907i80278 89'0620 PDR AGOCK 05000400 P
PDC DISCUSSION Event Descri tion Below are summary descriptions of the individual LER events evaluated in this report:
Event 1.
LER 400/88-008, event date 02-17-88.
During post mainte-
'"ddd "kk I'k d<<k, k
d" I'ervice water (ESW) pump "B" inadvertently started and then tripped on overcurrent.
The pump was declared inoperable.
The pump over-current relay was checked and recalibrated and the pump tested satisfactorily.
A review of plant records showed that ESW pump "B" experienced a similar overcurrent trip problem on January 2,
1988.
Because of these two recurring ESW pump trip problems, the overcurrent relay was replaced after the second failure.
Event 2.
LER 400/88-001-01, event date 01-15-88.
A deficiency existed in t e emergency operating procedure for switchover to recirculation after a loss of coolant accident.
This procedure deficiency existed for the period from December 1986 until the procedure was corrected on December 16, 1987.
This deficiency could have resulted in runout and overcurrent trip of a single operating residual heat removal (RHR) pump during the recircu-lation phase of a large LOCA.
The LER indicates that Shearon Harris Regulatory Compliance personnel determined this procedural deficiency to be a reportable occurrence on 01/15/88.
LER 400/88-001 was submitted (reported) on 02/15/88.
Event 3.
LER 400/88-004, event date 01-25-88.
After completing k
d~
P k
k p
ddk d
k level indicators, the resultant level indication revealed that the actual tank level was less-than that required by technical speci-fications.
The low level in the tank was due to incorrect level indication which was attributed to air in the sensing lines to the level transmitters.
The condition apparently existed since initial plant startup.
After discovery of this problem, the level transmitters were calibrated and the sensing lines properly vented.
Approximately 165 gallons of sodium hydroxide (NAOH) solution was pumped into the tank to restore the proper level, and the system was declared operable on January 26, 1988.
The purpose of the NAOH system is to.,inject into the containment spray given an
- accident, to enhance retention of iodine through chemical reac-tion.
The above events in combination could impact the plant response to a large loss of coolant accident.
A scenario that could have occurred and required the failed or degraded equipment follows:
Given the occurrence of a large LOCA, the emergency core cooling (ECCS) pumps and the emergency service water (ESW) pumps would start and initiate reactor core inventory makeup and heat removal.
(Refer to attached Figure 1 showing a sketch of plant systems affected by or affecting the
scenarios described).
If event number I -
ESW pump "B" failure occurred at startup, then this would result in the loss of RHR train "B" cooling.
For the injection phase of the
- LOCA, RHR cooling is not required, but cooling of heated sump water is required by the RHR Heat Exchangers during the recirculation phase of the LOCA. If RHR train B were turned off during the injection phase (due to train B
RHR heat exchanger loss of function),
then the remaining operating RHR pump could experience runout and failure per LER event 2 when the recirculation phase of LOCA mitigation were initiated.
This could result in the complete loss of the RHR system.
Finally, the NAOH system (event 3) which causes sodium hydroxide solution to be injected (by eduction) into the containment spray may have been only partially effective.
Therefore, another system required for mitigating the effects of the LOCA would also be compromised.
The ESW pump "B" first tripped on overcurrent (LER 88-008) on January 2,
1988.
The prior ESW pump "B" test was successfully performed on November 30, 1987.
The over current trip problem could have developed anytime between November 30, 1987 and January 2,
1988.
A best estimate is that it would have occurred half way through this 33 day interval or about mid December 1987.
If the problem causing overcurrent trip had occurred in mid December, then the coincidence of this and the emergency procedure runout problem (LER 88-001) would have been only a day or so.
However, the overcurrent trip problem could also have developed immediately after the November 30 successful test.
An upper bound estimate of coincidence of these LER described events would therefore be about one half month.
CONCLUSIONS The LER events evaluated herein are of themselves of relatively minor importance when considered individually.
However, these individual events, when considered and evaluated in combination could have a larger effect on safety than their individual importance might indicate.
If a large LOCA had occurred during the time period these events co-existed, the RHR system could be lost due to the co-existence of events 1 and 2, and the NAOH addition system would have been degraded (event 3).
Both the RHR system and the NAOH addition system are required to mitigate a
LOCA.
The concurrent failure of combinations of systems or functions can be important insofar as they collectively contribute to accident risks.
This is of particu-lar concern if the systems which have failed or become degraded are part of the ESF systems.
The LERs indicate that the events or conditions reported existed or could have simultaneously existed for various durations.
The existence of these events made the plant more vulnerable to accidents or initiating events that would have required these failed or degraded systems or functions.
We believe the combination of these events to be of moderate significance because of the low probability of a large break LOCA.
The actions taken by the Shearon Harris plant appear adequate to have resolved this potential
- problem, therefore we plan no further action on these particular events.
- However, we will continue to monitor Shearon Harris and other plants for these types of relatively minor individually reported events which can in sum be significant.
CCW-HE C
Surge
.Yang HPSI-Chg CVCS Normal Charging CL I
Ii9 Containment a4 ESW Pump 1A-SA CCW Pump VCT Xa HPSI-Chg Q
HL To CL I
I To HLI I
I 40 0a NAOH Tank A
~
ESW Pump p
To HL 1B-SB RHR Pump B ccw-m CCW PUNT RCP Seal Cooling BIT Tank g
To CL Sump m0 CP HPSI-Chg Figure 1 - Simplified sketch of Shearon Harris Safety Systems