ML20198D070

Proposed TS Change 166 to License DPR-36,revising Section 1.4 to Eliminate Ref to Containment Air Recirculation Sys from TS 1.4.D, Containment Purge Sys

ML20198D070
Person / Time
Site:	Maine Yankee
Issue date:	05/08/1992
From:	Frizzle C Maine Yankee
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20198D074	List: ML20198D070 ML20198D077
References
CDF-92-58, MN-92-48, NUDOCS 9205150211
Download: ML20198D070 (4)

Text

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MaineYankee m m e _ ,m, f f a tne 04336 W) 622 4868 May 8, 19!2 Mf4-92-48 CDF-92-58 UNITED STATES NUCLFAR REGULATORY COMMIS$10ft Attention: Document Control Desk Washington, DC 20555

References:

(a) License No. DPR-36 (Docket flo. 50-309)

(b) NUREG/CR-1575; " Hydrogen Mixing in a closed Containment Compartment - Based on a One-Dimensional Model with Convective Effects, September,1980 (c) EPRI NP-2669; Hydrogen Mixing and Distribution in Containment Atmospheres," March, 1983 (d) EPRI HP-3878; "Large Scale Hydrogen Combustion Experi m ts Volume 1" October, 1988

Subject:

Proposed lechnical Specification Change No. 166 - Administrative Change to Eliminate Reference to Containment Air Recirculation System Gentlemen:

Maine Yankee hereby submits, pursuant to 10 CFR 50.90, this application to amend section 1.4 of the Maine Yankee Technical Specifications. This proposed amendment would eliminate reference to the containment air recirculation system from Technical Specification 1.4.D, " Containment Purge System", as the recirculation system is no longer necessary for post-accident containment gas mixing, During a 1987 review, the recirculation system was determined not to be necessary for post-accident hydrogen mixing in lieu of the mixing provided by the containment spray system and natural convective circulation of the containment atmosphere. Reference to post-accident recirculation system mixing should have been removed from Technical Specifications at that time, but this reference appears to have been overlooked.

A proposed change to remove reference to the recirculation system and to otherwise update Specification.l.4.0 is provided as a revised Technical Specification page 1,4-2 in Attachment B.

Descriptions of the proposed change and a summary of the significant hazards evaluation are presented in Attachment A. As discussed in the attachment, this change is considered administrative in nature, and does not involve a significant L :\propchng\PC166 9205150211 920508 l PDR ADOCK 05000309 l I

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,_ [IldkDCI LGlTC UNITED STATES HUCLEAR REGULATORY COMMISSION MN-92-48 Attention: Document Control Page Two increase in the probability or consequences of an accident or malfunction of equipment important to safety previously analyzed. Nor does it create the possibility of a new or different kind of accident or malfunction important to safety. Lastly, it does not cause a significant reduction in the margin of

_ safety. -

This proposed change has been reviewed and approved by the Plant Operation Review Committee. The Nuclear Safety Audit and Review Committee has also reviewed this proposed change submittal. A representative of the State of Maine is being informed of this proposed change by copy of this letter.

. We request this proposed change be made effective within 30 days of approval by the NRC.

Very truly yours,

,/

/,h Charles D. Frizzle President CDF/sjj

-Attachment r c: Mr. Thomas T. Martin

.Mr.-E,.H. Trottier Mr. Charles S. Marschall Mr. Clough Toppan Mr. Patrick J. 00stie STATE'0F; MAINE Then personally appeared before me, Charles D. Frizzle, who being duly sworn dld state--that he is President of Maine Yankee-_ Atomic Power Company, that he is duly authorized to execute and file the foregoing request in the name and on behalf. of Maine Yankee Atomic Power Company, and that the statements'therein are >

true to the.best-of his knowledge and belief. ..

JELObtzruu 4lL/7L)

Notary Psblic /-

My commission expires 3-26-98.

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ATTACHMfRLA i

r Description of Proposed Chanat This proposed change is submitted to eliminate the ieference in Technical Specification 1.4.0 to the containment air recirculation system as providing post-accident containment atmosphere mixing.

During initial licensing of_ Maine Yankee in the early 1970's, the _ containment air recirculation system was credited for providing mixing of_the containment air volume, in response to questions related to hydrogen mixing raised during Atomic Energy Commission review of Maine Yankee's Preliminary Safety Analysis Report, the air recirculation system was credited for mixing the containment atmosphere following a design basis loss of coolant accident to prevent the localized accumulation of hydrogen gas.

, in 1987, Maine Yankee reviewed the containment atmosphere mixing requirements in view of then recent generic studies, References (b) and (c), and concluded that the Containment Spray-System and natural convective circulation provided adequate "

mixing of the containment volume. At that time, the safety analyses and environmental analyses were reviewed and found not to credit operation of the recirculation system and it was concluded that the recirculation system was not needed to serve a post-LOCA function. It appears that the reference to the recirculation system in Technical Specification 1.4.0 was overlooked, however, during that review.

Maine Yankee recently identified the oversight and reconfirmed the basis for not crediting recirculation system operation post-LOCA.

A ._ Containment Mixing:

Containment spray systems have been considered adequate to provide rapid mixing of the containment atmosphere by convective forces. This conclusion

! was confirmed in an experimental program conducted by the Electric Power Research Institute Reference (d). In these large_ scale experiments it was. -

concluded that " Spray-induced-turbulence produced uniform concentrations

= essentially immediately."

Adequate mixing.by containment spray systems was also recognized by the USNRC in the Standard Review Plan, which states:

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...a system should be provided to mix the combustible gasses...This system

- may consist of a fan, a fan cooler, or containment spray." (emphasis added) i_ Should a concentration gradient develop, the capability exists to determine this and a spray _ system qualified to operate in a post accident environment is available to restore the concentration homogeneity.

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B ,. Hydrogen Monitoring Maine Yankee is equipped with the capability to continuously monitor the hydrogen concentration in containment with two on-line hydiogen analyzers each with grab sample capability. (Maine Yankee FSAR, Section 9.5.7)

Hydrogen samples are taken from the dome area (Elevation (164' 11 1/2") and are capable of being realigned to take samples from the containment purge exhaust duct area (Elevation 23'6")]. Although stratification is not expected, the monitoring system is capable of detecting concentration gradients. Containment sprays can be reactivated should forced mixing be required.

C. Hydrogen Pocketing t

Containment walkdowns were performed to support Maine Yankee's Prcbabilistic Risk Assessment (PRA). One purpose was to determine if there was a potential for hydrogen pocketing post-LOCA. The walkdown found the Maine Yankee -

containment to be of a relatively open-design and not conducive tc pocketing.

That is, mostly open cubicles, common use of grating instead of steel plate, open tops on the Steam Generator cubicles and an annular opening several inches wide between most of each floor and the containment wall contribute to the avoidance of hydrogen pocketing post-t0CA.

D. Post-Accident Management Calculations-have shown that the hydrogen concentration in containment does not approach a flammable mixture (4M) until approximately 17 days after a design basis LOCA. Decisions related to managing hydrogen ,

buildup / stratification would then be the rasponsibility of the emergency l response staff. As the Plant is in long-term post accident recovery, with relatively quiescent conditions w"hin the containment, timely actions are measured-in hours. There is ample time for careful, measured response to the

- slow changes in plant status that would be occurring in this time-frame. The normal post-LOCA valve line up entails continued operation of the containment I spray system while at the same time injecting water to cool the core. This coolant path is designed and qualified to operate indefinitely. Were there to exist any uncertainty relative to the issue of hydrogen stratification after the sprays were secured (on RHR cooling), the sprays could be restarted at any point in time post-event.

E. PRA The Maine Yankee PRA does not credit the containment air recirculation fans.

Also, the recirculation system is not credited in either the Safety or LOCA .

analyses.

Based on this evaluation, Maine Yankee confirmed that the containment air L. recirculation system is not required for accident mitigation and/or following a loss-of-cool.ot accident. Reference to the recirculation system in i, Technical Specification 1.4.0, therefore, is unnecessary, and should be deleted. Other clarifying changes have been made previously to update this specification.

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Sionificani Hazards Evalualum The proposed change to lechnical Specification 1.4 to remove the containment recirculation system has been evaluated against the standards of 10 CfR 50.92 and has been determined to not involve a significant hazards consideration. This proposed change does not:

1. Involve a significant increase in the probability or consequence of an accident previously analyzed. The containment air recirculation system has not been credited in any of the FSAR Chapter 14 analyses and thus will not affect the current safety analyses. In addition, evaluations have shown that natural convective circulation mixing and/or containment-spray induced convection are adequate to provide a well mixed contain 9t atmosphere and, therefore, there will be no impact on accidenu previously analyzed. _

2. Create the possibility of a new or different kind of accident trom any previously evaluated. Us2 of the containment recirculation :,ystem and/or the containment spray system as indicated in this submittal does not create the possibility of a new or riif ferent kind of accident since the proposal involves aither a hardware modification nor the creation of a unique operating condition.

3. Involve a significant reduction in the margin to safety. Removing the contairunant air recirculation system f rom Technical Specifications does not change the results or conclusions of any of the FSAR Chapter 14 analyses. The containment spray system will provide containment mixing and its operation is already governed by Maine Yankee lechnical Specifications.

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