ML20028C835
| ML20028C835 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 01/06/1983 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| REF-SSINS-6820, REF-SSINS-SSINS-6 IEB-80-11, TAC-42918, NUDOCS 8301140197 | |
| Download: ML20028C835 (3) | |
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esuuo SACRAMENTO MUNICIPAL UTILITY DISTRICT O 6201 S street, Box 15830. sacramento, California 95013; (916) 452-3211 January 6,1983 DIRECTOR OF NUCLEAR REACTOR REGULATION ATTENTION JOHN F STOLZ CHIEF OPERATING REACTORS BRANCH #4 US NUCLEAR REGULATORY COMMISSION WASHINCTON DC 20555 DOCKET 50-312 RANCHO SEC0 NUCLEAR GENERATING STATION UNIT 1 MASONRY WALL DESIGN, IE BULLETIN 80-11 The Sacramento Municipal Utility District has received your letter of November 22, 1982, requesting additional information on masonry wall design at Rancho Seco Unit 1.
The response to your request is attached to this letter and should provide the information needed for your evaluation of our design, hI f)Lt7d +c_
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John J. Mattimoe General Manager Enclosure 8301140197 830106 PDR ADOCK 05000312 O
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Ah ELECTRIC SYSTEM SERVING MORf IHAN 600.000 IN THf HEART OF CAllf0RNiA
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14-L G ?,. 4 i RESPONSE TO REQUEST FOR-ADDITIONAL"INFORMATION DATED NOVEMBER? 22, 1982 Q:
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1.
Question:-
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Provide an evaluation of the-design adequacy of the masonry. walls to-postulated missile impact including your evaluation criteria..You should also address the effects of secondary raissiles, as applicable.
If thiL evaluation indicates the inadequacy of. these masonry walls 1to withstand missile impact, sthen please commit to. strengthen these.
walls to meet SEB criteria -(see enclosure).
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Response
The Rancho Seco Nuclear Generating Station design bases do 'not include.
tornado and tornado missiles. See response on question number 2.
2.
Question:
If you consider that' these walls are not safety-related with respect ltio the tornado event, then a logical explanation indicating why these walls.
are safety related with respect to seismic but not safety related with regard to tornado events should be provided for the staff's review.
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Response
Tornado and tornado missiles are not postulated as a design basis for Rancho Seco Unit 1 because these-events are incredible. The Rancho Seco Generating Station Updated Safety Analysis Report (USAR), chapter'5, paragraph 5.1.2.1.7 states, in part:
"The coincident' events of a tornado and a loss of coolant accident are of sufficiently low probability that tornado criteria need not be applied to safety related equipment."
Table 5.1-7, Hypothetical Wind Borne Missiles, is not a design basis but a part of the exercise performed under NRC's request (USAR, same paragraph).
In no instance have tornado and tornado missiles been explicitly or implicitly postulated as a design basis.
Second, none of the masonry walls being investigated are Category I walls.
l In reference (2), Appendix D, a detail description of safety related equipment, systems, or components which are either supported by the wall or located near the wall are provided for each wall. Since there is absolutely no safety related piping, conduit or instrument-lines supported by the walls (see reference 2, Appendix D), and except for these isolated conditions which are identified below, these masonry walls are located far enough fmm safety related equipment, that:any postulated failure of these walls will not cause damage to any safety =related equipment, regardless of tornado and missile criteria.
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' 2-The three-isolated conditions identified are:'
~ (1) : The nuclear service station transformer (App'endix D, sketch 528.4) is enclosed by 12-inch reinforced concrete block walls.- ' Although these block walls'are not intended as missile-barriers,. they will sustain the design. basis pressure from the 101 mph wind and the impact from missiles postulated in Table 5.1-7 for the 101~ mph wind
. velocity without gross failure.
(2)_ Wall' No.!181.1, which is adjacent to C0 storage' equipment No. V998 2
is also desigr.ed to withstand wall design basis criteria of the -
USAR.
Equipment No. V998,'moreover, is not in-a strict sense-Category I equipment. This wall is also adjacent.to.two 4"9 safety related conduits (Appendix D, sketch No.181.10). The distance between the nearest part of,these, conduits to the wall is 5'-5".
Since the wall is 8' jiigh,,any postulated missile must hit the wall precisely ~at the right location 'and;the wall must be assumed to completely collapse in order to damage'the" conduits. Since the conduits are also subject to the' postulated missile strike, the missile _ capability of thetwall, at;this location, becomes a mute.
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(3) WallNo.'181i5 Sis'ioc^afedfAear,t'he' Con' dens'ateStorageTa'nk-(T-358).
(Appendix D, sketch'No; 181;11) This ta.nk#is the source for emergency feedwater but otherwise does not-serve ~a safety related function -
during normal operation.. It is also' pointed out that the 12"0 pipe (line No. 35823) and'the'4"0-pipe (line No. 35821) are both nonsafety related. ~ They were shown as safety related on sketch No.181.11 in error.
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In. view of the insignificance df these isolated conditions, it is concluded through exhaustive study by the' District and its consulting architect engineer (.Bechtel Power Co.) that the masonry walls currently in-place at the Rancho Seco plant do not pose a safety; hazard with or without the application of any tornado and missile criteria, and are, therefore, adequate as designed and constructed.