ML19281A274
| ML19281A274 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/01/1979 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | Ippolito T Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7903090270 | |
| Download: ML19281A274 (3) | |
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500C Chestnut Street Tower II March 1, 1979 Director of Nuclear Reactor Regulation Attention:
Mr. Thomas A.
Ippolito, Chief Branch No. 3 Division of Operating Reactors U.S. Nuclear Regulatory Cotsission Washington, DC 20555
Dear Mr. Ippolito:
In the Matter of the
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Docket Nos. 50-259 Tennessee Valley Authority
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50-260 50-296 Your letter to N. B. Hughes dated November 29, 1978, outlined several concerns regarding the design of safety actuation signal circuits and operations of the primary containment purge system and requested that TVA address these concerns with respect to the Browns Ferry Nuclear Plant. Enclosed is our response to each of your concerns as outlined in your November 29, 1978, letter.
TVA presently conducts a program of limited and intermittent purge and inerting at Browns Ferry. The approved technical specifications for each unit allow use of the primary containment purge systems 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> before unit shutdown and during the 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following unit startup.
In general, only approximately one-half of the allotted time is actually used. Additionally, purging is performed only when a primary containment entry is necessary. These tech-nical specifications provide necessary operating flexibility by allowing the time spent purging to be removed from critical path during outages in which the drywell or torus was entered.
Requiring purge operation in cold shutdown mode only would impose a significant economic penalty because of the additional time that would be adced to each outage requiring containment entry. Considering the limited time tnat purge systems are actually in service and pending definite identification of an actual safety problem, TVA intends to continue limited purging at Browns Ferry in compliance with our present operating license.
We trust that our responses as provided in the enclosure will resolve your concerns.
Very truly yours, J. E. Gilleland Assistant Manager of Power
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. d' Enclosure
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E:: CLOSURE RESPOSSE TO SRC CD::CERNS REGARDING COSTAIDEST PCRGING -
BRCil':S FERRY ::UCLEAR PLAST (EEFERESCE; LETTER FROM TiiOMAS A.
IPPOLITO TO '..
a.
!!CCHES DATED NOVEMBER 29, 1978) 1.
JUSTIFICATION FOR USLI:!ITED PURGING a.
Analysis of Valve Operability The valves and lines used for the purging and inerting operations at Browns Ferry Suclear Plant are considerably smaller than those for which SRC has stated a concern, the maximum line size being a single 20-inch inlet supply line.
All primary suppis and exhaust lines are, as usual, doubly isolated, i.e.,
two valves are in series, either of which can isolate the line.
These valves were manufactured to design specifications which qualify the valves to withstand the temperature and pressure resulting f rom a design basis loss-of-coolant accident (LOCA).
We have no reason to suspect that these valves will fail to close against the dynamic forces resulting from a LOCA.
Nevertheless, in order to fully acdress your concerns we are planning to conduct an analysis of the valves' ability to close against the pressures and flow rates experienced during a LOCA.
We have been in touch with the valve manufacturer and requested that he assess the feasibility of performing the analysis. TVA was in fo rmed that the manufacturer does not have the capability to per form the analysis inhouse, therefore, TVA is assessing the reasibility of performing the analysis internally We regret that
.e are unable to inforn you at this time of when the analysis results will be available.
?cu will be informed of the expected ccmpletion date as soon as a schecule is formulated.
b.
Imoact of Puraing During Goeration on ECCS Performanca We believe that operation of the emergency ccre cooling system at 3rowns Ferry will not be significantly impaired should a LOCA eccur durina purge operations.
This is based on the fact thct ECCS performance in 3WR's is relatively insensitive to containment pressure.
Ne, therefore, plan to conduc t no analysis ef f ort in this area.
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Radiolacical Concequentes of Desian F>a s i s LCCA Occurrine Durinc Purne Onerations The necessary input data to evaluate the radiological consequences of this event must be developed from the results of the purge valve operability analysis. Consequently this evaluation cannot be performed at this time.
2.
REVIE'.? OF SAFETY ACTUATION SIGNAL CIRCUITRY DESIC?.
TVA has reviewed the containment isolation valve control circuitry at Browns Ferry with regard to safety ac tuation signals, bypass configurations and annunciations, and manual override logic and has concluded that no problems of the type outlined in the November 29, 1978, letter are evident.
Except for the one particular case explained below, in every case the Primary Containment Isolation System (PCIS) trip signal will override both the normal controls and any bypasses in service, thus ensuring an automatic closure signal to the purge valves. All operating bypasses are properly annunciated. The Containment Atmosphere Dilution (CAD) system does have bypass controls that can align the exhaust side purge valves to provide a two-inch vent path f rom the torus or drywell to standby gas treatment.
This system configuration is designed to provide long-te rm post-LOCA venting of the primary centainment.
Therefore, it is necessary that these controls be operable even in the presence of the PCIS trip.
These bypass switches, operated only briefly durine a monthly CAD surveillance test, are keylock type and are administra tive1,. restricted. Therefort we believe that no further administrative controls are necessars