ML20002B096
| ML20002B096 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 11/24/1980 |
| From: | Novak T Office of Nuclear Reactor Regulation |
| To: | Jordan E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| NUDOCS 8012090430 | |
| Download: ML20002B096 (6) | |
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NUCLEAR REGULATORY COMMISSION E
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MEMORANDUM FOR: Edward L. Jordan, Assistant Director
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%g3 Division of Reactor Operations Inspection T' 2
Office of Inspection and Enforcement g
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s FROM:
Thomas M. Novak, Assistant Director 3
for Operating Reactors Division of Licensing
SUBJECT:
IE DRAFT CIRCULAR - COMMON CAUSE FAILURE OF SERVICE WATER SYSTEMS The review of the subject bulletin by NRR results in the following coments.
1.
After the first sentence, it should be explained that the Service Water (SRW) system at Calvert Cliffs is a dual loop recirculating coolant system providing r,oclant requirements for both safety related and non-safety related components.
2.
It would be helpful if a simplified sketch of the Calvert Cliffs design was included.
3.
It shcald be noted that for Calvert Cliffs a design change request has been implemented to remove air compressor cooling from the SWS
(
Reference:
Follow-up report for LER 80-27/1T by Baltimore Gas &
Electric Co., June 3, 1980).
4 In reference to Recomendation 1, use of check valves alone will not protect safety related portions of cooling systems from failure of non-safety related portions. Automatic, seismic Category I valves should be utilized to separate non-essential portions from essential portions of the system (
Reference:
SRP 9.2.1).
In addition to the above coments, it seemed, that the first page of the circular is confusing. Enclosed is a modified replacement page. Other miscellaneous changes marked in the enclosed pages,'were suggested to E. B. Blackwood by E. C. Conner.
&h Thomas M. Novak, Assistant Director for Operating Reactcrs Division of Licensing cc:
E. B. Blackwood
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SS2NS No: 6830 Accession No.:
UNITED STATES IEC 80-NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 November 12, 1980 IE Circular No. 80-
- COMMON CAUSE FAILURE OF SERVICE WATER SYSTEMS Descriotion of Circumstances:
On May 20, 1980 Calvert Cliffs Unit No. I experiences a total loss of service water (SRW) system flow due to a single failure. The SRW system for each Calvert Cliffs unit is a dual loop recirculating coolant system providing coolant requirements for both safety related and non-safety related components. Service Water Loop 12 had been securee, by shutting the associated SW heat exchanger outlet valve, for routine cleaning of the tubes on the salt water side of the heat exchanger. A leak in Instrument Air Compressor 11 after-cooler caused air to collect in No.12 SRW heat exchanger and in the dead leg from the heat exchanger back to the idle pump.
As the No.12 heat exchanger was returned to service, the air bubble acved througn the system causing low pressure in both loops as the operating SRW pumps became air bound. This occurred since both No. 11 and No. 12 SRW subsystems supply service water to the common loop turbine area SRW system with a common returns to both suction headers for all three SRW pumps. The result was a total loss of SRW flow. The reactor was manually tripped from 100% power upon receipt of high temperature alarms on steam generator feed pump bearings and increasing temperatures on main turbine bearings.
IEC 80-November 12, 1980 Page 2 of 5 je d ra ~ M Y **'O f l* i gad Unit 1 air compressors tripped after losing service water.
Unit 2 air ccm-7'fe 9
g d - s i.s n e d.
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pressort'autcmatically began supplying Unit 1 instrument air.*weng 2 ^::_;;',
2.-.
r.:-n Concerned with the possibility of losing instrument air, an attempt was made to supply Unit 1 compressors with Unit 2 service water via a temporary line installed during construction.
Low service JRW water header pressure alarms were received on both Unit 2 subsystems.
The j
cross connect was shut and Unit 2 service water pressure increased to normal.
Although constant vents are installed in the service water system, the volume of air that had leaked into the system exceeded constant vent capacity.
The system sas vented manually and the air leak was located and isolated.
Service water flow was restored approximately four hours after the system
. had become airbound.
Tne service water system provides cooling to safety related components including containment cooling units, spent fuel pool heat exchangers and emergency diesel generator heat exchangers.
The turbine area portion of the service water system cools main turbine, condenser and generator auxiliaries, condensate and feedwater pumps, instrument and plant air compressors and a nitrogen compressor.
Thiseventissignificantbecauseasf%g,iefail'reofnon-safetyrelatedequip-u ment in the turbine building disabled both Unit 1 service water subsystems for several hours.
The event demonstrated that utilization of check valves in safety system common suction piping to satisy single failure criterla does
IEC 80-November 12, 1980 Page 3 of 5 not p. event inoperability of multiple pumps caused by vapor binding in the even:. of vapor (compressed gases or steam) intrusion.
The Service Water Systec at Calvert Cliffs was designed to single failure criteria.
Non essential CI ufee-elit a fly services such as Turbine Building cooling are isolated with w operatec bloc k safety injerHm sel* %
j valves in the event of ang '3 fYIfC, signal.fGiE!!D cr t t ; - : xp p'.
- 'ic.
Suction sides of the subsystems utilize check valves to prevent backflow in the event of a line break.
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A similar event occurred at Calvert C.f"; 9ah 1 or. August 12, 1980. While
-cperating at 100% power, indicateo le vel in both #11 and #12 Service Water (SRW) head tanks went frgm normal opers.;ir.s 'evel to ful' About five (5) minutes later :
iscphase bus duct cooling iow flow alarm
- as received.
he Shift Supervisor immediately suspected '. hat air was being introduced into the system.
A subsequent investigation revealed that #11 Instrument Air Compressor after-agosh cooler had failed causing air ingress to both service water subsystems.
With j
both subsystems in operation the automatic vents provided adequate air removal capability to insure system operability.
System pressure did not drcp below the normal operating band in either subsystem during the event.
After C 1
.[nstrument[ir empressor aircooler was isolated, the service water system was restored to normal operation.
IEC 80-November 12, 1980 Page 4 of 5 Recommended Ac..on__for Power Reactor Licensee Consideration:
- lrculdig fyre p
.sys&- s t e
Reviewjcoolingwatersystems,suchasservicewaterjjCalvertCliffs, 1.
3 j
which provide cooling to safety related components to determine the following:
YeduS Susceptability to loss o{gcacting capatility to safety related compor.ents cue to intrusion of gasses (air, nitrogen, hydrogen, steam)
In case of hydrogen inleakage, the explosion potential in areas proximate to syctem constant vents Impact of nonsafety related subsystem or component failures that could be reflected to safety systems art use<l $9f is tl* fish Whether check valves er++l.;f at the interface between safety related cylitC A l and nonsafety portions of systems 4
Whether the common cause failure described in this circular could i
occur at your facilities.
2.
In instances where gas intrusion, air binding, explosion or other common cause failure is possible, consider methods such as design changes, c
y
,----s.
IEC 80-Novemb:r 12, 1980 Page 5 of 5 l
periodic maintenance and surveillance, procedure revisions and acminis-trative controls that will reduce the probability of occurrence of common cause failures to a level that is low enough so as not to impact on safety system unavai'.a.bility.
If you have questions regarding this matter, please contact the Director of the appropriate NRC Regional Office.
I No written response to thisg[ircular is required.
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