ML20011D607
| ML20011D607 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 12/18/1989 |
| From: | Manning F NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20011D520 | List: |
| References | |
| TASK-AE, TASK-T925 AEOD-T925, NUDOCS 8912280090 | |
| Download: ML20011D607 (6) | |
Text
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AEOD TECHNICAL REVIEW REPORT
' UNITS:
Zion Units 1 & 2 TR REPORT.NO.:
AEOD/T925 DOCKET NO: 5000295 & 304 DATE:
December 18, 1989 LICENSEE:
Commonwealth Edison Co.
EVALUATOR / CONTACT:
F. MANNING NSSS/AE:.
Westinghouse /Sargent and Lundy
SUBJECT:
EVALUATION OF SAFETY EQUIPMENT 00TAGES FOR SIGNIFICANCE AT ZION
SUMMARY
This report provides an-evaluation of four Zion event notifications (ens) reporting equipment outages on November 22-22,'1989.- An event noti fication is an immediate telephone notification to the NRC of significant nuclear plant operating events.
The event notification requirements are specified in 10CFR50.72, the code of federal regulations.
The four ens are-evaluated to estimate their combined effects on safety.
The problemn reported by these ens are related and this requires that they be evaluated together.
The ens involve
. outages or degradations of plant safety systems that are
.necessary to cope with a loss of offsite power (LOOP) event.-
1The ens are evaluated in the context of a postulated loss of offsite' power-(LOOP) during the period the equipment problems and outages could have coexisted.
If a LOOP had occurred ano emergency service water (ESW) heat removal had not been successfully provided for the operating diesel generators (DGs),
the DGs may have failed within about 5 minutes.
-Were that to occur,-and offsite power not be recovered within some critical time-period,. core damage could occur.
The critical time period depends on the likelihood of reactor coolant pun.p seal failure (s) gr station battery depletion in the' interval before recovery of offsite. power.
The occurrence of seal failure'(a small LOCA) would require AC power to provide makeup coolant injection to the reactor coolant ~ system, while the station battery depletion would cause loss of ability to control and monitor the auxiliary feedwater heat removal function.
Prevention of or mitigating the effects of either of these problems requires recovery of AC power.
The conditional core damage probability for the combined EN events is estimated to be about SE-5.
It is judged that these events are of moderate safety significance.
8912280090 892218 i
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y INTRODUCTION.
This report evaluates Zion ens 17174, 171*/5, 17183, and 17181.
The ens concern equipment failure or outages which could affect the plant response to a loss-of-offsite power event.
The plant information for this evaluation is taken mainly from the four ens.which provide basic information about the events.
Additional verbal information was obtained in a conference telephone call on November 28, 1989 with the Zion NRC resident inspector and senior resident inspector, and tae NRC project manager for Zion.
The ens variously refer to D/Gs (diesel generators) or EDGs (emergency. diesel generators).
This equipment will be referred to as diesel generators (DGs) in this report consistent with the Zion final safety evaluation report nomenclature.
DISCUSSION Event Descrintion.
The ens evaluated in this report are quoted
.below.
Only the first three events listed are felt to have a" measurable impact.
The ens are:
Event 17174, occurred 11/22/89 at 07:15 CST.
"The plant entered a LCO to be'in hot S/D within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> due to both service water pumps being declared inoperable.
This occurred during the performance of a safeguards test on unit 2 "O" D/G when it had a first out annunciator alarm showing bearing temperature high.
During this type of test the D/G does not get a trip signal ~, but it was secured and declared inoperable.
Since this.D/G is the emergency power supply for the "2A" emergency service water' pump, this pump was also declared inoperable. Also the "2B" Emorgency service water pump was out-for maintenance and it too was inoperable.
Therefore both ESW pumps were inoperable and the plant entered TS 3.8.7.C to be in hot S/D in 4 hrs.
They are investigating cause of the annunciator alarm.
The RI was informed."
Evant 17175, occurred 11/22/89=at 08:15 CST.
"The plant has started reducing power at the rate of 0.5%
/ Min 11n order to be in hot S/D in 4 hrs.
They are also working on the "2B" ESW pump to get it returned to service.
The RI was informed."
Uodate at 1227.
"The "2B" ESW pump was started at 1008 CST to begin a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> run prior to be declared operable.
The power decrease was terminated at 1035 CST per a discretionary enforcement agreement with Region 3.
The unit will continue to operate at its current power level, 23% until the test of the ESW pump is completed.
Licensee informed the RI."
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Undate at 1534.
"The Licensee terminated the s
. unusual event at 1430-CST after the "2B" ESW ptmp was declared operable.
The unit remains in 7 day technical-y specification action statement #3.15.2.C due to the "O"
diesel generator being inoperable.
Licensee informed the RI."
l Event 17183, occurred 11/23/89 at 11:20 CST.
"The l
common' swing EDG and #1 of 2 unit 2 EDGs inoperable while unit 2 at power.
With the_#0 swing EDG.
inoperable, plant operators were starting 1 of 2 unit _2 EDGs -- ( # 2 A) during'an operability test.
A local-operator noticed an exhaust gas test conr.ection on one of the cyljnder heads on #2A EDG vibrating open.
The local operator stopped the EDG and' turned DC control
~
power to the EDG off which rendered #2A EDG inoperable.
Licensee entered TS LCO A/S 3.0.3 which requires either
.1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or to be in at least hot S/D mode within the next 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. 'At'1200 (CST), Licensee completed repairs to #2A EDG, declared it operable, and exited TS LCO A/S 3.0.3. Licensee informed RI."
Event 17181, occurred 11/22/89 at 24:45 CST.
"The licensee discovered a service water ventilation fan aircraft crash damper in the open position with its associated fan off and fan breaker and solenoid valve energized..
In'this condition, the damper should have been closed.
The damper is designed to close in the L
event high temperatures, such as those caused by an aircraft crash, are sensed at the ventilation intake.
Thefproblem has been identified as the solenoid valve which was not allowing air through to close the damper.
L The licensee has initiated activities to replace the solenoid. valve.
Technical specifications require the y
damper to be closed-if the aircraft crash protection L
system is inoperable but the damper cannot be closed until the solenoid valve is replaced.
The damper fails in the open position to allow cooling of the service water pump motors during conditions other than those involving a fire outside the intake structure.
The licensee will inform the RI."
e PLANT AND EQUIPMENT STATUS
-Plant Status:
Unit 1 had finished refueling and was ready for startup except for DG maintenance and repair.
Unit 2 was operating at 99% power l-when potential DG and ESW problems were discovered.
Because of these problems, the plant could not comply with technical L
specification requirements regarding ability to respond to a LOOP 1
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.u and the plant entered a limiting condition for operation (LCO) requiring shutdown of the plant in 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
The status of the DGs and ESW were as follows:
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DG Status:
L Unit 1 DG 1A - In maintenance for rod bearing problems - not reccverable E
Unit 15DG 1B - In maintenance for testing & switchboard out -
possibly recoverable in about 30 minutes. (The DG is assumed failed in this analysis]
_ Unit 2 DG 2A'
'Had gas test connector leak found during performance test requiring 1/2 hour repair - The resident inspector (RI) thought the DG was stil'1 functionable if needed.
(The DG is assumed failed in this analysis]
Unit 2 DG 2B - Available Swing DG O - Indicated high bearing temperature during the performance of a surveillance test. [The DG is assumed failed in this analysis).
E8W Status The Zion station has a total of six ESW pumps.
All ESW pumps were operable except pump 2B.
ESW 2B was out of service for maintenance at the time of the 4
-hour S/D LCo.
The maintenance was halted and the pump restarted and was run-for a required' proving 4 hrs.
With ESW~2B proven-operable the LCO was exited about 7~ hours after entry (the plant was still in a 7 day LCO to restore 2nd DG & ESW train].
The ESW systems were cross connected at the time of the event with common parallel ESW feed to both units.
However, given a LOOP, unit 1 woul.I supply no ESW since both DGs were in maintenance.
Since only DG 2B was available, and since only one
'ESW pump can be powered from any 4160 volt emergency AC bus, only one ESW pump is assumed available during LOOP.
However, ESW 2B, which is powered by DG 2B during LOOP, was out of service for maintenance therefore effectively no ESW pumps may have been initially available.
Whether ESW pump 2B could be quickly put back in service is open to conjecture.
The Zion FSAR indicates one ESW pump per unit is required to achieve mitigation and shutdown given accident conditions.
(FSAR page 9.6-2, 2nd paragraph and page 9.6-3, 1st paragraph).
Event BionificaDee and Postulated Scenario:
The core damage scenario postulated herein-is for a randomly occurring LOOP to occur during the assumed seven day vulnerability period.
Diesel generator 2B would start but fail within a few minutes from lack of jacket cooling water.
The
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2other diesels are assumed not recoverable.
Therefore core damage.
would~ occur if offsite power for the station were not recovered
'before station battery depletion or reactor coolant pump seal g
LOCA occurs.
A LOOP occurrence frequency of 4E-2/RY is assumed.
A probability j
l-of failure to-recover offsite power within.1/2 hour after DDOP l
start of.39 is assumed.
A probability.of failure to recover i
offsite power before battery depletion or seal LOCA of.17 is
.i assumed.
These values are consistent with values from the i
I Accident Sequence Precursor program (Ref 1) and a study on
. station' blackout (Ref 2).
A fault duration estimate for DG 0 of seven days is assumed for this analysis.
For the 7 day exposure time to a~ LOOP, the conditional core damage probability (CDPr),
given the conditions and assumptions stated above is estimated to be:
CDPr =(exposure time fraction) (LOOP freq/yr) (fail. recover LOOP short term) (fail to recover LOOP long term or seal LOCA)
(7/364) (4E-2) (.39) (.17) = approximately SE-5 '
=
EN 17181 was also evaluated with the above three-ens. This event involved Unit 1.
The Unit 1 Service Water aircraft crash. damper failure (failed open) has no measurable effect on the abcve postulated scenario.
Even if it had failed closed (the opposite of what it did and is designed to do) it would have caused no problem by the NRC resident inspector's assessment because of the large area (room volume)'the ESW pumps operate in, the extensive amounts of concrete for heat absorption, and their relatively low ambient air temperatures due to physically being near Lake Michigan water.
CONCLUSIONS The four operating events reported for Zion on November 22-23,
.1989 were evaluated in the context of a postulated LOOP during the period the EN-described problems could have coexisted.
If a LOOP'had occurred and ESW heat removal had not been successfully provided for the operating DGs, the DGs may have failed'within about 5 minutes.
Were that to occur,-and offsite power not be recovered.before battery depletion, core damage could occur.
The core damage probability associated with these events is estimated to be about SE-5.
It is judged that these events are of moderate safety significance.
The corrective action taken by the licensee appears to~have been adequate.
Therefore, no further action by
)
AEOD other than monitoring this type of event is suggested.
References:
1.
NUREG/CR-4674, Volume 7. " Precursors to Potential Severe' Core r
Damage Accidents: 1987 A Status Report"
- 2. NUREG-1033, " Evaluation of Station Blackout Accidents at Nuclear Power Plants" 9
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