ML18283B101

Responds to 12/18/1974 Letter Concerning Potential Consequences of Failure of No Seismic Category I Equipment at Browns Ferry Nuclear Plant

ML18283B101
Person / Time
Site:	Browns Ferry
Issue date:	02/14/1975
From:	Gilleland J Tennessee Valley Authority
To:	Stolz J Office of Nuclear Reactor Regulation
References
Download: ML18283B101 (11)

Text

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CONTROL NO 1857 Fl LE N D FRO ~: Tenn. Valley Auth. DATE Or DOC D "TE REC'D LTR OTI-:ER Chattanooga, Tenn. 37401 14-7 2 TO: ORIG CC OTHER SENT AEC PDR SENT, LOCAL PDR XX Mr. John F. Stolz 3 signed 37 CLASS UN(C LA~S PROP'I N'cO 'NPUT NO CYS R "C' DOC i-

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DESCr(IPTIO I: X,tr re our 12 18 74 ENCLOSURES:

furnishing info re the potential consequences failure of nonseismic category I equipment at Browns: Ferxy Plant. 1-2-3....

PLANT NA~;IE: Browns Ferry Plant Units 1-2>>3 FOR ACTIQ.'~! I(".FO ~,".IATIO'i BUTLER (S) SCIIIKNCER (S) ZIEW,VZ (S) REGAN (E)

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Mr. John P. Stolz, Chief Light Water Reactors Prospect Branch 2-1 Office of Nuclear Reactor Regulation ~o U.S. Nuclear Regulatory Commission 0//g~ ~1

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Dear Mr. Stolz:

In the Matter of the ) Docket Nos. 5 Tennessee Valley Authority ) 0-260 5 96 This is in response to your letter dated December 18, 1974, con-cerning the potential consequences of failure of nonseismic Category I equipment at the Browns Perry Nuclear Plant. We believe the following summary of TVA's past actions in this matter will put our position into proper perspective.

The first AEC request for information on this problem was prompted by an expansion bellows failure in a circulating waterline at Quad Cities unit 1. As a consequence, the AEC requested by letter of August 11, 1972, that TVA evaluate Browns Ferry to determine the I

potential for damage to Category equipment due to flooding resulting from failure of non-Category I equipment. The TVA response to this question was submitted as Amendment 40 to the PSAR on August 22, 1972.

The response included consideration of flooding by failure on non-

,Category I equipment in the reactor, diesel-generator, turbine, service, radwaste and off-gas buildings, and the intake structure and stack. The evaluations presented in the amendment included considera-tion of personnel and equipment access doors, building and pipe pene-tration seals, drainage systems, sumps and sump pumps, flooding detection, and flow interrupt capabilities. The applicable design bases including protection against natural phenomena were di,scussed.

Apparently, interest in this problem continued to develop. In a letter to TVA on December 18, 1972, the AEC expressed concern about the conse-quences of postulated pipe failures outside of the primary containment structure including rupture of the main steam and feedwater lines.

This concern included dynamic effects of the failure such as missile generation, pipe whipping and get actions, rather-than )ust simple

, flooding.

An Equal Opportunity Employer lan i'

Nr. John F. Stolz, Chief February 14, 3.975 TVA responded to this concern in a letter to AEC on June 12, 1973, in which we shared our own concerns about the problem, including the flooding potential. In this letter, TVA reconfirmed that during the design 'of Browns Ferry we considered a credible spectrum of pipe" failures and their consequential effects. Nevertheless, we committed to extending" these investigations, as required, to additional postu-lated breaks and a greater spectrum of potential interaction effects.

A followup on this commitment was the submittal of Amendment 49 to the FSAR on April 2, 1973. This amendment covered additional postu-lated failures in the main steam and feedwater lines and gave detailed consideration to dynamic effects such as pipe whip and gets and to environmental effects such as flooding. We showed that safe shutdown could be assured. In addition, we met with representatives of the Regulatory Staff on May 3, 1973, to discuss this submittal as well as any additional analytical requirements. The understandings from this meeting were factored into subsequent TVA criteria development and evaluation efforts.

Enclosed with the TVA letter of June 12 was a copy of an ll-page criteria document developed by TVA for use in evaluating the effects of a pipe failure outside of primary containment. This document con-sidered both Category I and non-Category I pipe failures and included dynamic effects as well as environmental effects such as flooding.

It presented in considerable detail the criteria to be used and their bases for the more important considerations such as determination of credible pipe failures, determination of the zone of influence of the failure, and evaluation of pipe failure interactions.

The final outcome of the TVA investigation of postulated pipe failures outside of containment for unit 1 was prepared as a formal concluding report (DED-&i-PPI, 43 pp.) and sent to the AEC on November 2, 1973.

In addition, we met with representatives of the Regulatory Staff on Hay 24, 1974, to discuss this submittal and to exhibit samples of the significant amount of detailed documentation available to back up the report and verify its conservatism.

The TVA concluding report presented in considerable detail the results of an intensive investigation of the pipe failure problem by several TVA system and design engineers for nearly one year. This effort included comprehensive onsite examinations of the plant configuration to assure that all potential targets in the zone of influence of each

0 Mr. John P. Stolz, Chief February 14, lgf5 postulated break location were fully evaluated and that all points of vulnerability were adequately considered in the pipe break location selection. Appropriate attention was, given to the flooding challenge.

The TVA concluding report indicated that implementation of the guide-lines as set forth in the December 18, 1972, letter from AEC, and subsequently clarified by the TVA evaluation criteria document, did lead to a need for certain corrective actions which are being imple-mented by TVA. Upon completion of these actions, Browns Ferry unit 1 should comply with the intent of the December 18 letter including any effects of flooding.

Similar steps have been taken to complete the TVA investigation and correction of postulated pipe failure problems outside of containment for Browns Ferry units 2 and 3. A formal concluding report (DED-TH-PP2, 45 pp.) was sent to the AEC on March 29, 1974.

On February 25, 1974, TVA proposed a change to its flood'rotection program which would allow four flood protection doors between the tuxbine and reactor buildings and two doors between the radwaste building and the personnel corridor leading to the turbine building .

to remain open. We are still awaiting a x'esponse from the NRC on this proposed change.

With regard to special design features at Browns Perry which concern flooding, provision for control room annunciation of impending flooding.

in areas such as the reactor building was a recognized requirement and was described"in Amendment 40. Critical access doors such as those located between units below grade are secured. Pipe penetrations between units below. grade are sealed against water leakage. Numerous other provisions such as an extensive floor drain system leading to redundant sumps and pumps are included as additional protection against flooding.

TVA has recognized for some time that the failure of certain non-Category I nuclear plant features such as cooling tower basins, holdup ponds, large storage tanks, or pipes leading thereto, or uncontrollable continuation of pump operation undex certain circumstances wherein offsite powex may not be lost, represents a unique challenge to Category I

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Mr. John P. Stol@, Chief February 14, 1975 features. The potential for extensive flooding or thermal dilution of emergency cooling water by such occurrences is under continuing review by TVA., As a typical example, the results of such an examina-tion of the circulating water system can be found in section 11.6.4 of the FSAR as revised by Amendment 56. A number of Category I pro-tective features have been added to this system by TVA to assure that the postulated',siphon action or uncontrollable continuation of pump operation will not occur.

As an ultimate backup to these various evaluations and design provi-sions, TVA claims credit for the following unique provisions at the Browns Ferry Nuclear Plant in the unlikely event of extensive flooding:

1. Standby coolant supply connection to the RHRSW pumps.

2. RHR unit crossties.

3. Provisions for backfeeding emergency power to the main turbine condenser components.

The standby coolant supply connection and RHR crossties are described in subsection 4.8.6.4 of the FSAR. These provisions permit the main-tenance of long-term reactor core and primary containment cooling should the RHR system on a given unit be lost. The provisions for backfeeding are described in subsection 8.4.6 and elsewhere in the FSAR. This provision assures availability of the main turbine con-denser for reactor core cooling should offsite power be lost.

Based on our reevaluation of the information already supplied in this matter, it is our position that the design provisions included the intent of the guidelines supplied by your in the plant meet letter of December 18, 1974, and that no additional changes or temporary protective measures are required.

Very truly yours, J. E. Gilleland Assistant Manager of Power CC: See page 5.'

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C Mr. John F. Stolz, Chief CC: Mr. R. B. Beers, M/C 349

.General Electric Company Nuclear Energy Division 175 Curtner Avenue San Jose, California 95125 Mr. William E. Buist General Electric Company 832 Georgia Avenue Chattanooga, Tennessee 37402 Mr. K. L. Sessions General Electric Company 9040 Executive Park Drive Knoxville,. Tennessee 37919

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