ML20138A964

Forwards Preliminary Safety Evaluation Proposed for Inclusion in Sser 3,to Support Util Conclusion That Single Recombiner Sufficient to Maintain post-accident Hydrogen Concentration Below 4% Vol

ML20138A964
Person / Time
Site:	Millstone
Issue date:	10/07/1985
From:	Youngblood B Office of Nuclear Reactor Regulation
To:	Opeka J NORTHEAST NUCLEAR ENERGY CO.
References
NUDOCS 8510110170
Download: ML20138A964 (8)

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l Docket No.: 50-423 007 0 7 1985 l

i Mr. John F. Opeka

Senior Vice President Northeast Nuclear Energy Company P. O. Box 270 Hartford, Connecticut 06141-0270

Subject:

Preliminary Safety Evaluation To Be Included in SER Supplement 3 for Millstone Nuclear Power Station, Unit 3 i

Enclosure 1 contains a safety evaluation which is proposed for inclusion in ,

SER Supplement No. 3 for Millstone 3. This evaluation is being transmitted 4

to you for your information.

i Sincerely, (0)

I B. J. Youngblood, Chief

, Licensing Branch No. I Division of Licensing

Enclosure:

As stated cc: See next page i

Distribution:-

.S-Docket J11em

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""NRC PDR Local PDR NSIC PRC System

• LB#1 R/F MRushbrook EDoolittle OELD ACRS(16)

JPartlow EJordan BGrimes LB 3 l Of1/DL i ED le/mac , JJYoungblood j (Q/]/85 to/ 7 /85 8510110170 85100743 DR ADOCK 0 y

Mr. J. F. Opeka Millstone Nuclear Power Station Northeast Nuclear Energy Company Unit No. 3 cc:

Gerald Garfield, Esq. Ms. Jane Spector Day, Berry & Howard Federal Energy Regulatory Commission City Place 825 N. Capitol Street, NE Hartford, Connecticut 06103-3499 Room 8608C Washington, D.C. 20426 Mr. Maurice R. Scully, Executive Director Connecticut Municipal Electric Energy Cooperative 268 Thomas Road Groton, Connecticut 06340 Robert W. Bishop, Esq.

Corporate Secretary ,

Northeast Utilities '

Post Office Box 270 Hartford, Connel ticut 06141 Mr. T. Rebelowski Senior Resident Inspector Office U. S. Nuclear Regulatory Commission i Millstone III  !

P. O. Box 615 Waterford, Connecticut 06385 ,

Mr. Michael L. Jones, Manager Project Management Department '

Massachusetts Municipal Wholesale -

Electric Company  !

, Post Office Box 426 +

Ludlow, Massachusetts 01056 l t

Regional Administrator U. S. NRC, Region I 631 Park Avenue -

King of Prussia, Pennsylvania 19406  !

i Mr. Karl Abraham Public Affairs Office, Region I  ;

U. S. Nuclear Regulatory Commission, i j King of Prussia, Pennsylvania 19406 r

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ENCLOSURE.1 6.2.1.1 Containment Structure The staff indicated in the SER that the applicant should provide a revised analysis of maximum external differential pressure since the original analysis was based on an assumed initial containment temperature representative of norral operation (100'F) rather than the limiting containment temperature permitted by Technical Specifications (120*F). This matter was classified as Confirmatory Item 23 pending receipt and review of the revised analysis.

In FSAR Amendment 14, the applicant provided information regarding a transient containment response analysis performed for Millstone, Unit 3, assuming inad-vertent actuation of one train of the containment quench spray system. This analysis was performed using the CONTEMPT-LT computer program, and resulted in a minimum containment internal pressure of 8.03 psia at the time the quench i

spray was assumed to be manually deactivated (10 minutes). The containment is designed for a minimum internal pressure of 8.0 psia. ,

The staff has reviewed the applicant's analysis and finds that the applicant's assumptions regarding initial containment conditions and quench spray system operation will tend to minimize the containment internal pressure. Further-more, the staff has performed a confirmatory analysis using the CONTEMPT-4 computer code, and assuming appropriate initial conditions, the actuation of both trains of the containment quench spray system, and no operator intervention.

The staff analysis produced a minimum containment internal pressure of 8.00 psia. On the basis of the two analyses, the staff concludes that the Millstone 3 containment can safely withstand the maximum external pressure resulting from an inadvertant spray actuation event.

t As part of the review of the maximum external differential pressure, the staff I has also considered the potential for excessive containment depressurization i

due to operation of the containment vacuum pump system or the steam-jet air ,

ejector system. The containment vacuum pump system is operated periodically during normal operation to maintain the containment at or below the maximum permissible pressure; the steam-jet air ejector is used to evacuate the cont 4'rment during startup operations. The applicant has indicated that both these systems are. manually operated and are capable of reducing the containment air pressure to below the 8.0 psia design value if they are permitted to operate uninterrupted for a sufficient period of time. However, continued operation of the systems after establishment of the desired containment pressure is not considered credible by the applicant on the basis that adequate control room indication and administrative controls are provided.

Based on a preliminary review of the instrumentation and control provisions to i preclude excessive containment depressurization, the staff has determined that there are no containment atmosphere low pressure alarms at Millstone, Unit 3.

(It should be noted that a statement in FSAR Section 9.5.10.3 incorrectly indicates that a low pressure alarm will annunciate in the main control room, i

notifying the operator that a low pressure condition exists; the applicant has indicated that the FSAR will be corrected by deleting the statement.) Hence, the control room operator would receive no direct indication if the containment pressure were reduced below the minimum permissible Technical Specification value (8.9 psia) or the design value (8.0 psia), other than through routine surveillance of the containment pressure at 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> intervals. Furthermore, the operator would not be aware of the operational status of the vacuum pump or air ejector systems except fo.r indicator lights on the main control board showing the position of the system isolation valves.

1 The staff will further evaluate the administrative controls regarding the use of the containment vacuum pump system and steam-jet air ejector system prior to concluding on the matter of maximum external differential pressure for Millstone, Unit 3. We will report the results of our review in a future supplement to the SER.

6.2.3 Secondary Containment functional Design I -

1 l In the SER, the staff indicated that the Supplementary Leak Collection and Release System (SLCRS) satisfies the requirements of GDC 16 provided that (1) all openings in the secondary containment are under administrative control and (2) door position indicators and alarm capability are provided in the main control room. This matter was classified as Confinnatory Item 26 pending verification by the applicant of compliance with the above stipulations.

In subsequent comunications with the staff, the' applicant stated that status indication and alarms for all doors within the SLCRS boundary at Millstone Unit 3 will be provided at the security alarm station rather than in the main control room, and that the responsibility for reporting door status would be delegated to the Security Department. As part of this arrangement, all doors within the SLCRS boundary will be designated as security doors, and will be locked and alarmed, and access-controlled in accordance with 10CFR73.55 (see station security plan). To confirm that the control room has been advised of SLCRS door status by the Security Department, the applicant has comitted to add a step to the appropriate plant operating procedure, and to require ap-proval from the operation shift supervisor prior to blocking open secondary f building doors for temporary routing of hoses, cables, etc.

The staff has reviewed the infonnation and comitments provided by the appli-cant regarding the secondary enclosure building. Based on our review, we con-clude that the applicants proposal to provide door position indicators and alarm capability in the security alarm station, and to delegate the responsi-bility for status reporting to the Security Department is acceptable provided -

that the applicant (1) identify the specific circumstances under which secondary building access doors will be pennitted to be maintained open during plant operation, and (2) incorporate in the technical specifications or ap-propriate plant procedures, additional controls to govern and limit the cum-ulative duration of such events. The basis for restricting the time that the access doors are open is twofold. Access to the enclosure building at Mill-stone Unit 3 is through single doors rather than dual doors in series, hence, I

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4 the SLCRS effectiveness is compromised during en'losurec building entry / exit, and whenever a door remains temporarily open for routing of hoses, c' ables, etc. Also, location of access door position indicators and alarms at the security alarm station rather than in the main control room, as recommended in SRP 6.2.3, would necessitate a communications link between control room oper-ators and security personnel in order to assess enclosure building door status, and could result in additional delays in taking appropriate action to close any doors that might be open.

Should the applicant be unable to demonstrate that the likelihood of having an open secondary building access door is sufficiently small, the staff will re-quire additional analyses of response times for assessing door status, and the effect of open doors on secondary building performance and offsite releases, prior to concluding on this matter. We will report the results of our further review in a future supplement to the SER.

6.2.5 Combustible Gas Control System i

4 The staff indicated in the SER that for initial containment atmosphere conditions which minimize the mass of air in the containment, the recombiners would need to be started earlier in the accident than assumed in the applicant's analyses, in order to maintain the containment hydrogen i

concentration below 4 volume percent. Accordingly, the matter of re-f combiner actuation criteria was classified as Confirmatory Item 25 pending i

receipt and review of the plant procedures for '-tuating the recombiners.

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By letter dated October 1, 1984, the applicant submitted the Emergency Operating Procedures Generation Package for Millstone, Unit 3. The Emergency Operating Procedures described therein call for recombiner actuation whenever the hydrogen concentration is greater than or equal to 0.5 volume percent.

The applicant, by letter dated September 24, 1985, affirmed that this criterion is invoked in all sections of the procedures which involve recombiner actuation. The staff has performed a combustible gas control analysis for

Millstone using the COGAP computer code, and assuming the appropriate limiting conditions for operation and the actuation of a single recombiner at 0.5 volume percent hydrogen. The staff's analysis supports the applicant's conclusion that a single recombiner is sufficient to maintain the post-accident hydrogen concentration below 4 volume percent. On this basis, the staff concludes that i

Confirmatory Item 25 has been satisfactorily resolved.

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