ML20084R170

Comments on Status of Recommendations of GE Svc Info Ltr 402 Re Wetwell/Drywell Inerting.Evaluation of Nitrogen Inerting Sys Design Performed & Redundant Low Temp Shutoff Valve Added

ML20084R170
Person / Time
Site:	Hatch
Issue date:	04/05/1984
From:	Gucwa L GEORGIA POWER CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
NED-84-177, TAC-54150, NUDOCS 8405220204
Download: ML20084R170 (4)

Text

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Georgia Power Company 333 Piedmont Avenue Atlanta, Georgia 3&308 Tekmhone 404 526 6526 Matng Address.

i Post Ottice Box 4545 Atlanta, Gmrgia 30302 Georgia Power L Y. Gucwa tre sourtern ekxtoc system Manager Nuclear Engineenng and Ciref Nuclear Engineer NED-84-177 April 5, 1984 Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz, Chief ~

Operating Reactors Branch No. 4 Division of Licensing U. S. Nuclear Regulatory Cannission Washington, D. C.

20555 NRC DOCKETS 50-321, 50-3ti6 OPERATING LI NSES DPR-57, NPF-5 EDWIN I. HATCH NUCLEAR PIR7f UNITS 1, 2 STATUS OF SIL 402, "WETWELI/DRYWELL INERTING" Gentlemen:

The purpose of this letter is to report the status of Plant Hatch with respect to the recomiendations of Service Information Letter (SIL) 402, which was issued by General Electric in response to the vent header cracking discovery at Hatch Unit 2.

The specific recomendations of SIL 402, as well as the actions taken at Plant Hatch, are as follows:

Recomendation 1 - Evaluate Inerting System Design

" Evaluate the design of the nitrogen inerting systs.

Investigate the potential for introducing cold (less than 400) nitrogen and the orientation of the nitrogen port relative to the vent header, downcmers, or other equipnent in the wetwell and drywell which may be in the path of the injected nitrogen.

Assure that the temperature monitoring devices, the low temperature shutoff valve, and overall syste design are adquate to prevent the injection of cold nitrogen into the contalment."

Status An evaluation of the Plant Hatch nitrogen inerting system design has been performed.

In order to prevent the injection of cold nitrogen (less than 500) into the Unit 1 or Unit 2 contalment, a redundant temperature switch controlling the low temperature shutoff valve was added. The nitrogen ports in the Units 1 and 2 drywell and the Unit 1 l

wetwell (torus) are presently oriented such that no essential equipnent is in the path of injected nitrogen.

The nitrogen port in the Unit 2 torus is being relocated to a point where injected nitrogen will not impinge on essential quipnent.

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r GeorgiaPower A Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz, Chief Operating Reactors Branch No. 4 April 5, 1984 Page 'IWo l

'Ihis modification will be cmplete by the end of the current Unit 2 outage.

Recomendation 2 - Evaluate Inerting Syste Operation

" Review the operating experience of the inerting system to assure that the vaporizer, the low temperature shutoff valve and the temperature indicators heve functioned properly.

Evaluate the plant calibration, 4

maintenance and operating procedures for the inerting system.

Assure that cold nitrogen injection would be detected and prevented."

Status Operating experience and plant procedures related to use of the nitrogen inerting system have been reviewed. Operating experience indicates that malfunctions of the nitrogen inerting system have occurred.

The modifications being made will eliminate future malfunctions.

Plant procedures have been verified to contain adequate instructions for calibration, maintenance, and operation of the nitrogen inerting systs.

Cold nitrogen injection would be detected and prevented by the autmatic shutoff feature of the inerting syste.

Operators would be alerted to the low nitrogen temperature condition by an annunciator.

Plant personnel will monitor local nitrogen temperature indicators during future inerting operations to provide further assurance that a malfunction would be prmptly detected.

Recomendation 3 - Test for Drywell/Wetwell Bypass Leakage

" Perform a bypass leakage test as soon as convenient to confirm the integrity of the vent 'systm.

This test should be conducted during plant operation following nomal plant procedures.

If no procedures exist, the following is a general guide for preparing your procedure; pressurize the drywell to approximately 0.75 psi above the wetwell pressure, maintain this drywell pressure and measure the pressure buildup in the wetwell.

Any bypass leak area can then be calculated (and is limited by Technical Specifications on many plants) from the wetwell pressure and the drywell-wetwell pressure difference.

This will provide an indication that the vent system integrity is intact and that no gross failure exists."

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GeorgiaPower h Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz, 011ef Operating Reactors Branch No. 4 April 5, 1984 Page Three Status Imediately following discovery of the vent header cracking in Unit 2, a bypass leakege test was performed on Unit 1 in accordance with the existing plant procedure.

Leakage was found to be within the Technical Specification limit, indicating that no gross failure of the vent system existed. A similar test will be perf(srmed on Unit 2 at the end of the outage which is currently in progress in accordance with Unit 2 Technical Specifications.

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Recmmendation 4 - Inspect Nitrogen Injection Line

" Conduct an ultrasonic test (Ur) as soon as convenient of all accessible welds in the nitrogen injection line frm the last isolation valve to the wetwell and drywell penetrations.

Also UT the contaiment penetrations and the contaiment shell within 6 inches of the penetration.

UT is reemnended because cracks would be most likely to initiate on the inside of the pipe or on the side of the metal in contact with cold nitrogen."

Status visual inspection and limited magnetic particle testing have been performed on all accessible welds of the Units 1 and 2 nitrogen injection lines frm the contaiment penetrations to the inboard isolation valves.

No indication of cracking was found.

Ultrasonic j

t testing of these welds and the contaiment shell in the vicinity of the Penetration.were_ not _ performed _due_ to a 1pck of bas _ sideration.e line_ exmination l

data. Alternative inspect 10n~ techniques are und& con

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Recm nendation 5 - Inspect Containment "During the next planned outage, perform a visual inspection of the vent header, downcmers and other equipnent in the contaiment which might be expected to be affected by the injection of cold nitrogen.

The vent header should be inspected on the outside and the inside.

Also inspect the contaiment shell or steel liner for at least 6 inches around the nitrogen penetration."

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GeorgiaPower A Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz, Chief Operating Reactors Branch No. 4 April 5, 1984 Page Four Status Visual inspections of Hatch Units 1 and 2 have been performed.

All equipnent which could be affected by the injection of cold nitrogen, including the vent headers (inside and outside), downcmers, and the contalment shell in the vicinity of the nitrogen penetrations, was inspected.

No cracking was found other than that on the Unit 2 torus vent header. 'Ihe extent of the daage, as well as the plans for repair, have been comunicated to the NRC. The repairs will be cmplete by the end of the current outage.

Please contact this office if there are any questions.

Very truly yours,

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L. T. Gucwa JH/nb xc:

H. C. Nix, Jr.

J. P. O'Reilly (NRC-Region II)

Senior Resident Inspector i

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