ML20213E322

Forwards Rev 3 to Auxiliary Sys Branch SER Input,Section 3.5.2, Structures,Sys & Components to Be Protected from Externally Generated Missiles. No Tornado Missile Protection for Diesel Exhausts Necessary

ML20213E322
Person / Time
Site:	Columbia
Issue date:	02/04/1983
From:	Rubenstein L Office of Nuclear Reactor Regulation
To:	Novak T Office of Nuclear Reactor Regulation
References
CON-WNP-0564, CON-WNP-564 NUDOCS 8302160310
Download: ML20213E322 (5)

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Distribution Docket File ASB Rdg. File ASB Members Docket No. 50-397 LRubenstein RB 4 1983 MEMORANDUM FOR: Thomas M. Novak, Assistant Director for Licensing, Division of Licensing, NRR FROM: L. S. Rubenstein, Assistant Director for Core and Plant Systems, Division of Systems Integration, NRR

SUBJECT:

REVISION N0. 3 TO SAFETY EVALUATION REPORT FOR WASHINGTON NUCLEAR PROJECT NO. 2, AUXILIARY SYSTEMS BRANCH Plant Name: Washington Nuclear Project No. 2 -

Docket Number: 50-397 Licensing Stage: OL Milestone Number: 24-02 Responsible Branch: Licensing Branch No. 2 Project Manager: R. Auluck ASB Reviewer: J. Ridgely Requested Completion Date: January 21, 1983 Review Status: Awaiting Information The Auxiliary Systems Branch Safety Evaluation Report (SER) input Revision 2 was forwarded to you on July 26, 1982. This SER input identified lack of tornado missile protection for the emergency diesel generator exhausts as an open item.

We have subsequently completed our review of the tornado nissile protection of the diesel generator exhausts and a probabilistic risk assessment submitted by the applicant in support of his position that missile protection is not required for the diesel generators' exhausts. Our evaluation of the applicant's submittal is provided in the Enclosure as a revision to Section 3.5.2, " Structures, Systems and Components to be Protected from Externally Generated Missiles." We conclude that the applicant need not provide tornado missile protection for the diesel exhausts nor administrative control over the surrounding terrain.

Please note that in the past year we have received several probabilistic based submittals from OL applicants, as well as operating reactors for relief from providing tornado missile protection for specific safety-related structures, l

systems or components. We are reviewing these in accordance with SRP Section 3.5.1.4, which provides guidance on estimating the probability per year of damage due to tornado missiles. We will be transmitting further SERs of this type to you in the near future. It is our expectation that our experience with this approach will shortly be sufficient enough to provide a basis for under-taking a revision to the SRP in this regard.

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V FEg 4 1983 l Thomas M. Novak By 'this revision, there are now four open items, namely, Internally Generated Missiles (Inside and Outside Containment), Overhead Heavy Load Handling Systems (NUREG-0612), and Functional Design of Reactivity Control System (NUREG-0803).

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'- U..~.'ar:g:_a L. S. Rubenstein, Assistant Director for Core and Plant Systems Division of Systems Integration e

Enclosure:

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R. Mattson D. Eisenhut .

O. Parr R. Auluck A. Schwencer R. Lobel J. Ridgely -

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. 9 SUPPLEMENTAL SAFETY EVALUATION REPORT No. 3 WASHINGTON NUCLEAR PROJECT NO. 2 AUXILIARY SYSTEMS BRANCH 3.5.2 Structures, Systems, and Components to be Protected

,from Externally Generated Missiles I In our SER we stated that except for the diesel generator exhausts, the safety-related structures, systems, and -

components were acceptably protected from tornado missiles. Regarding the diesel generator exhausts, we were concerned that the diesel exhaust openings of one of the two engineered safety features (ESF) diesels might be blocked by tornado borne missiles (e.g.,

utility pole). .Each ESF diesel has two exhaust openings.

The applicant stated that, with one diesel exhaust opening blocked, the corresponding diesel would not accept its required Load. Assuming a single failure i

in the redundant diesel (f ailure to' start) neither dieset would be available in the case of a loss of off-site power resulting from a tornado.

In evaluating the site for the source (s) of such missiles we utilized NUREG-0800 the Standard Revied Plan, Section 3.5.1.4, which states that a utility pole should be considered at eleva.tions up to 10 feet above aLL grade '

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1 Levels within 1/2 mile of the f acility structure. For l

this plant the exhaust openings are more than 30 feet l above grade; however, there is a bluff due south of the diesel generator building. We were concerned that this area might be used as a Lay down area-and that -

utility poles or other construction materials might be stored there.

We recommended that the appli cant provide administrative control over the bluff. In a submittat dated July 23, 1982, the applicant stated that it was extremely im-probable for a tornado to lift a, utility pole and trans-port it to the diesel. generator building. The applicant provided a probability risk assessment (PRA) to support this statement which indicates that the probability of -

a tornado generating a utility pole missile which would plug one of the ESF diesel generator exhausts while, at the same time, the redundant diesel deierator fails to start from an independent cause is on the order of 10" per year. ..

We have reviewed the applicant's PRA and conclude that the probability of the utility pole missile plugging one diesel generator exhaust while, at the same time,

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1 the second diesel generator fails to start, is very Low.

We also have examined the site terrain and conclude that ,

the possible sources of missiles is Limited. Further, l between the bluff and the diesel exhausts are six forced draft cooling towers and a pumphouse. A utility pole lifted from the bL6ff would have to traverse a very limited path between the intervening cooling towers to reach the diesel exhaust openings. We therefore conclude that there is reasonable assurance that missiles resulting from a tornado witL not prove to be a danger to the diesel generator exhausts.< We conclude that conformance to the requirements of General Design Criterion 4,

" Environmental and Missile Design Basis," has been demon-strated in that, through the use of probabilistic risk assessment, there is reasonable assurance that tornado missiles wilL not endanger the diesel generator exhausts.

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