ML20084P597

Forwards Final Design Criteria for Resolution of NUREG-0737, Item II.E.4.2(7), Purge & Vent Valve Isolation, Requiring Automatic Isolation of Containment Purge & Vent Valves on High Containment Radiation

ML20084P597
Person / Time
Site:	Hatch
Issue date:	04/10/1984
From:	Gucwa L GEORGIA POWER CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.E.4.2, TASK-TM NED-84-072, NED-84-72, TAC-56049, TAC-59542, NUDOCS 8405180276
Download: ML20084P597 (6)

Text

r' x Georgia Power Compaq 333 Predrnort Avenue

• Atlanta, Georgia 30308 '

Telephone 404 5264526 Maang Address:

At Post Off:ce Box 4545 Atlanta. Georgia 30302

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- U Georgia Power L T. Gucwa tre scornem elecinc !ystem Manager Nuclear Engineering .

a'd Chief Nuclear Eng:neer NED-84-072 April 10, 1984 Director of Nuclear Reactor Regulation  :

-Attention: Mr. John F. Stolz, Chief  ;

Operating Reactors Branch No. 4 Division of Licensing U. S. Nuclear Regulatory Ccenission Washington, D. C. 20555 NRC DOCKETS 50-321, 50-366 OPERATING LICENSES DPR-57, NPF-5 EDWIN I. HA'ICH NUCLEAR PIANP UNITS 1, 2 NURm-0737 ITEM II.E.4.2(7) PURGE AND VENP VALVE ISOIATION Gentlenen:

%e subject NUREG-0737 iten requires autanatic isolation of contaiment purge and vet valves on high contaiment radiation. In an August 31, 1983 letter, Georgia Power Canpany (GPC) subnitted a proposed plan for resolution  ;

of this iten. n e plan involved subnittal of a description of the intended -

modification and implenentation during the scheduled 1985 refueling ,

outages. In accordance with the former comitment, GPC subnits Enclosure 1, Systen Description, Contaiment Purge and Vent Valve High Radiation Isolation.

Please contact this office if th&e are any questions.

Very truly yours,  !

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/% L"'t - 4 L. T. Gucwa l JH/nw t

Enclosure l

xc (w/ encl): J. T. Beckham, Jr.

l H. C. Nix, Jr.

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

Senior Resident Inspector L

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ENCIOSURE 1 EDWIN I. HA'IGI NUCLEAR PIRff UNITS 1 AND 2 SYSTEM DESCRIPTION 00tffAIINENT PURGE AIO VElff VALVE HIGH RADIATION ISOIATION

y I. INm000CTION .

NUREG-0737 _Its II.E.4.2(7) requires that contaiment purge and vent valves close autmatically on a tiigh contalment radiation signal. %is ratuirment has been the subject of considerable debate between the BWR

-Owners _ Group- and the NRC. %e following backgound information stmnarizes this discussion _ and describes the final design criteria which were agreed upon by the Owners Group and the NRC.

A. INITIAL OWNERS GROUP SUIMITTAL A generic evaluation of this its was transitted by T. J. Dente's letter of June 29, 1981. We Owners Group position, which was endorsed by GPC, was that autmatic isolation of contaiment purge and vent valves on a high radiation signal was not necessary. %e bases for this conclusion were that: (1) the purge and vent

-valves are normally closed, (2) there are existing redundant and diverse signals for autmatic closure of these valves, (3) various signals -would alert operators to manually - close the valves, and (4) . the radiological consequences of a break which would not autmatically isolate these valves are acceptably low.

B. INITIAL NRC SAFETY EVALUATION

%e October 14, 1981 NRC letter.to T. J. Dente transitted a Safety Evaluation in which the Owners Group position was rejected. We Owners Group met with the NRC on November 19, 1981 to obtain clarification of the NRC position. %e bases for the NRC position, as expressed at the meeting,' were that: (1) the radiation signal would provide additional safety margin, (2) additional redundancy-would be provided if one of the existing signals should fail, and (3) there would be . additional protection against ' low rates of -

reactor coolant leakage which would not result in autmatic isolation with the current design. In response to the first two concerns, the Owners Group- presented data deonstrating the high

reliability of the signals which isolate the purge and vent valves. %e third concern was addressed in an additional Owners Group subnittal.

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• o C. ADDITIONAL OWNERS GROUP SUINITIAL T. J. Dente's letter of June 14, 1982 tranmitted an evaluation for a typical plant of the radiological consequences of the limiting ,

reactor coolant system break which would not result in purge and '

vent valve isolation frm existing signals. We result was an off-site thyroid dose of approximately 0.01 Rs. This dose is well below the EPA Protective Action Guide (PAG) limit, which was recomended by the NRC in the Novmber 19, 1981 meeting as the acceptance criterion for this event. It was proposed that plants which may not meet the PAG criterion in this scenerio be allowed to adopt a more restrictive Technical Specification limit for primary ,

coolant . iodine concentration during purging and venting so that the  ;

acceptance criterion could be satisfied. The Ownerr, Group conclusion was that calculation of the off-site dose and revision of Technical Specifications as necessary to meet the PAG criterion was an acceptable alternative to high radiation isolation of the purge and vent valves.

D. FINAL NRC SAFEIY EVAIDATION

%e final Owners Group position was not accepted by the NRC. The NRC decision was appealed by the Owners Group in an April 18, 1983 telephone call to R. Mattson. Mr. Mattson agreed to a cmprmise position which would require isolation of purge and vent valves on high radiation but not necessarily frm safety grade instrumentation. %e Safety Evaluation transmitted by the NRC letter of May 31, 1983 reflected this emprmise and re-affirmed all other aspects of the October 14, 1981 Safety Evaluation.

II. MODIFICATION DESCRIPTION A. CONTADMENT PURGE AND INERTING SYSTEM Figures 1 and 2 provide simplified diagras of the Primary Contaiment Purge and Inerting Systems for Hatch Units 1 and 2, respectively. The current Primary Contaiment Isolation Systs (PCIS) autmatically closes the isolation valves in the presence of a low reactor water level, high drywell pressure, high reactor building radiation, or high refueling floor radiaton signal. %e "A" isolation signal serves the inboard valves while the "B" isolation signal serves the outboard valves. .

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B. HIGH RADIATION ISOIATION OF PURGE AND VENP VALVES

%e 18 inch contaiment purge and vent valves will be included in a new isolation group. %is group of valves will close autmatically on low . reactor water level, high drywell pressure high reactor building: radiation, high refueling floor radiation, or high contaiment radiation. %e 2 inch purge and vent valves will not isolate on high contaiment radiation because: (1) the off-site >

dose resulting fra an accident which would not autmatically l isolate these valves would be insignificant, and (2) the NRC Safety [

Evaluation of 5/31/83 does not require _i. solation of lines smaller j

C. HIGH RADIATION ISOIATION SIGNAL s

%is signal will originate fra the high-range contaiment ,

radiation monitors which were installed in response to NUREG-0737  ;

Its II.F.1.3. Each of the Hatch units was provided with redundant  !

monitors having ranges of 1 to 107 R/hr gama radiation. Each  !

channel consists of_ a detector located inside the primary

contaiment, a readout module with adjustable high radiation alarm in the Main Control Rom, and a recorder in the Main Control Rom.  ;

%e high radiation alarm contacts of channel "A" will be added to the control logic for the inboard 18 inch purge and vent valves and the channel "B" alarm contacts will be added to the control logic for the outboard 18 inch purge and vent valves.

D. HIGH RADIATION ISOIATION SETPOINT

%e setpoint for the isolation signal will be 100R/hr. This setpoint was calculated such that no accident would produce i~ radiation doses at the site boundary exceeding the PAG limits of 1 Re whole body and 5 Rm thyroid.

4 E. ISOIATION IOGIC Presence of low reactor water level, high drywell pressure, high reactor building radiation, high refueling floor radiation, or high contalment radiation signals will result in autmatic closure of the 18 inch purge and vent valves. Amber indicating lights for each of the 18 inch purge and vent valves will be provided on the Main Control Rom panel and will illuminate upon a high contaiment radiation isolation. %e valves will reain closed until: (1) the contaiment radiation level drops below the setpoint, (2) the high contaiment radiation alarm is reset at the readout module, and (3) the isolation logic is - reset manually by means of a control switch located on the Main Control Rom panel.

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r-F. 'IECHNICAL SPECIFICATIONS Technical Specifications will be revised to re:[uire that at least one radiation monitor which initiates high radiation isolation be operable at 'all times except cold shutdowns and refueling outages.

If this operability requirement is not met, the plant will be required within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to either close the purge and vent valves or begin proceeding to cold shutdown.

III. CONCLUDING SIIHARY

'Ihe proposed modifications are considered by Georgia Power Cmpany to fulfill the requirements of Iten II.E.4.2(7) as clarified by the Owners Group /NRC discussions. %e NRC concerns are satisfied as sumarized -

below:

A.- ADDITIONAL SAFE 1Y MARGIN

- Although the existing containment isolation design ensures off-site

- doses less than 10 CER 100 limits, the high contalment radiation isolation of purge and vent valves will further limit the consequences of a release through these valves.

B. ADDITIONAL REDUNDANCY Although existing purge and vent valve isolation signals have been demonstrated to be highly reliable, the contaiment radiation signal will ensure isolation capability should one of the existing signals fail.

C. PROFIECTION FOR SMALL BREAKS

%e contalment radiation signal will ensure timely closure of the purge and vent valves for low rates of reactor coolant leakage which would not result in isolation fran existing signals.

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