ML19312D487

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Forwards Response to NRC 791217 Request for Addl Info Re Operation of Facility W/One Recirculation Loop.Response Comprised of General Background & Operating Experience Info, Operating Histograms & Responses to Specific Requests
ML19312D487
Person / Time
Site: Browns Ferry Tennessee Valley Authority icon.png
Issue date: 03/17/1980
From: Mills L
TENNESSEE VALLEY AUTHORITY
To: Ippolito T
Office of Nuclear Reactor Regulation
References
NUDOCS 8003240494
Download: ML19312D487 (7)
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Tu TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 37401 400 Chestnut Street Tower II March 17, 1980 Director of Nuclear Reactor Regulation Attention:

Mr. Thomas A. Ippolito, Chief Branch No. 3-Division of Operating Reactors U.S. Nuclear Pegulatory Commission Washington, r; 20555

Dear Mr. Ippolito:

In the Matter of the

)

Docket No. 50-259 Tennessee Valley Authority

)

Enclosed is our response to your letter to H. G. Parris dated December 17,

-1979, which requested additional information regarding operation of the Browns Ferry Nuclear Plant unit 1 with one recirculation loop. The enclosed response is comprised of general background and operating experience information, operating histograms, and responses to each of your specific requests.

We have not prepared a formal report concerning our experience.

General Electric Company (GE) sent field engineers to Browns Ferry during the period of operation with one recirculation loop to record plant variables and may have more detailed information or analyses.

TVA believes that operation in single loop is highly practical and we intend to request permanent approval of single loop operation in the near future. Please get in touch with us if we can be of any further assistance.

Very truly yours, TENNESSEE VALLEY AUTHORITY L. M. Mills,11anager Nuclear Regulation and Safety Enclosure Aool s

///

(

An Equal Opportunity Employer F 8003240 494

~

i ENCLOSURE OPERATION WITH ONE RECIRCULATION LOOP RESPONSL TO REQUEST FOR ADDITIONAL INFORMATION (LETTER FROM T.-A. IPPOLITO TO H. G. PARRIS DATED DECEMBER 17, 1979)

BROWNS FERRY NUCLEAR PLANT UNIT 1 (DOCKET NO. 50-259)

BACKGROUND In September 1978 Browns Ferry Nuclear Plant unit 1 suffered a failure of, recirculation loop-A discharge valve which caused the loop to be

- inoperable. The unit was shut down within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in accordance with technical specifications. At that time, unit I was short of its refueling outage window by about 1-1/2 months. Also, the high density fuel storage racks had not yet been installed and there was insufficient fuel storage space to unloadfthe_ entire core to effect repairs. Unit 3 was in an outage and outage manpower was already committed. Accordingly, there was considerable incentive in operating unir 1 in single loop operation (SLO) until unit 3 was back in service and the high density racks were -

installed.

TVA, by its letter dated September 15, 1978, requested temporary technical specification changes to allow unit 1 to operate in SLO until the next scheduled refueling outage. After several licensing interchanges among TVA, General Electric Company, and NRC, the amendment was granted.

EXPERIENCE Brown Ferry unit 1 restarted on September 20, 1978, and operated continuously until shutting down for refueling on November 27, 1978.

The operating histograms for this time period are provided as Figures 1, 2, and 3.

TVA conducted power ascension tests to characterize operation in single loop mode and also to determine a suitable power level at which to operate for an extended time. Based on past startup test experience, a maximum power level of about 75 percent rated was thought achievable. During the power ascension tests, variations in the active recirculation jet pump flows, neutron instrumentation, core delta-p, and related ' parameters greater than normally observed were noted by the increased bandwidth on the recording charts. The variations increased as core power was increased.

No unusual variations were noted in recirculation drive flow, vessel level, vessel pressure,~or feedwater flow. At'the request of TVA, GE engineers came to Browns Ferry to record and analyzu the plant response. GE subsequently recommended operational guidelines as follows:

1.

Neutron flux variations should be kept less than 10 percent peak-to-peak.

I2.

Core plate pressure drop should be kept less than 1 psi peak-to-peak.

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1NTA ' considered;it prudent"to follow the reconnendations and therefore-steady! state powerfoperation was~ limited to about 60 percent.of_ rated.

In NovemberL1978 the control rod pattern was adjusted into a. rotational

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. symmetric pattern'in order to. perform the TIP/ power symmetry test.

Analysis.

- of the data shows no power asymmetry.

CONCLUSIONS

'TVA believes that SLO is both, practical and feasible _ for extended periods of time'.

SLO will no doubt improve capacity factor and avoid some recirculation system forced outages, particularly for plants with motor-generator sets which' tend to have fairly high maintenance requirements.

Concerning the trip of both~ recirculation pumps on unit 1 on September 26, 1979, no analysis was performed of the event. We have operated in natural circulation for short periods multiple times as a result of inadvertent pump trips or during startup testing.

Natural circulation operation is not particuarly interesting from an operations point of view. The avail-able data shows no unusual behavior and the situation is very similar to operating the unit with minimun recirculation flow (28-percent pump speed).

We 'are willing to furnish available data on request, although we do not believe it will bc very_useful for your stated intentions.

Our present

. technical. specifications allow 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> in natural circulation, although our experience indicates that this mode could be maintained indefinitely without-any problems.

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. NRC Request: Were there any indications of or obs2rved problems with'

. single loop operation?

Response: Unexpected variation occured only in jet pump flow, neutron flux and related parameters. Subsequent data taking and evaluations established that observed neutron flux variations were consistent with observed variations in core flow and core plate pressure drop.

NRC Request: 'What power levels were you able to achieve?

Response: During steady state operation, power level was limited to 60 percent of rated as' discussed in the preceding text.

Power.was raised slightly higher during testing.

NRC Request: At the power level you were operating at with one loop, did you have the exact same power distribution, control rcd positions and Xenon oscillations that would be expected at the same power level with equivalent flow from two loops?

- Response: -Because of the technical specification changes concerning APRM flow bias rod block and scram set points, it was necessary to adjust control rod patterns.

(The unit was operated on a lower load line than would have been necessary with both recirculation loops in operation.) Therefore, direct comparisons of rod position and power shapes are not possible. Xenon oscillations were, as usual, not a problem.

NRC Request: Have you any suggestions for us or other BWR licensees with respect to operation with one loop isolated?

Response: Operation in single loop mode is rather straight-forward. Cal-culated core limits tend to be tight due to reduced MAPLHGR restraints in the revised technical specifications and the

-conservative core flow calculations. Also, the discharge or suction valve on the inoperable recirculation loop had to be kept closed 'to keep the available LPCI status the same.

We suggest that the 24-hour allowance in single loop mode be maintained with no required changes in the applicable technical specifications since changing the rod block and scram lines is somewhat. time consuming. Most recirculation loop maintenance which might have a loop out of service can usually be accomplished within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. If the loop cannot be returned to service in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the new APRM lines should be enforced.

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