ML20036A359
| ML20036A359 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 04/06/1993 |
| From: | Baxter T SACRAMENTO MUNICIPAL UTILITY DISTRICT, SHAW, PITTMAN, POTTS & TROWBRIDGE |
| To: | Chilk S NRC OFFICE OF THE SECRETARY (SECY) |
| References | |
| CON-#293-13857 DCOM, NUDOCS 9305110125 | |
| Download: ML20036A359 (2) | |
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recsuEe SHAW, PITTMAN, PoTTs & TROVEBhfDGE A PARTNE R5w.P shCL LDaNG PRO *'E S5 TONAL COAPO AATIONS
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April 6, 1993 Mr. Samuel J. Chilk Secretary U.S. Nuclear Regulatory Commission Washington, D.C.
20555 In the Matter of i
SACRAMENTO MUNICIPAL UTILITY DISTRICT (Rancho Seco Nuclear Generating Station)
Docket No. 50-312-DCOM
Dear Mr. Chilk:
Please refer to NRC Staff counsel Barth's letter to you of March 30, 1993, in which Mr. Barth reported that Licensee is reevaluating information it supplied the Staff and would report on the results of its reevaluation.
Please find enclosed a copy of District letter DAGM/NUC j
93-079, April 1, 1993, Clarification of the Permanently Defueled Technical Specification LOOP and SFP Decay Heat Analyses.
This is the revised information the District has filed with the Staff.
As stated in the District's letter, these analyses -- conducted for the Loss of Off-Site Power and Spent Fuel Pool decay heat analyses presented in the safety analysis for the Permanently Defueled Technical Specifications -- are based upon different assumptions than those used in the accident analysis for the Environmental Report supplement for the Decom-missioning Plan.
The ER analysis is more conservative and is unaffected by the enclosed revised information.
It is the ER analysis which is referred to in the "NRC Staff's Support of Lic-ensee's Motion for Reconsideration," March 26, 1993.
Respectfully submitted, k.
Thomas A. Baxter Counsel for Licensee cc:
(w/ encl):
Service List 3
9305110125 930406 J gD N
PDR ADOCK 05000312 g
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of
)
)
Docket No. 50-312-DCOM SACRAMENTO MUNICIPAL UTILITY
)
l DISTRICT
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(Decommissioning Plan)
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(Rancho Seco Nuclear Generating
)
ASLBP No. 92-663-02-DCOM Station)
)
r SERVICE LIST l
Administrative Judge office of the Secretary Charles Bechhoefer, Esq., Chairman Attn Docketing and Service Branch l
Atomic Safety and Licensing Board U.S. Nuclear Regulatory Commission U.S.
Nuclear Regulatory Commission Washington, D.C.
20555 Washington, D.C.
20555 Adjudicatory File Administrative Judge Atomic Safety and Licensing Board Dr. Richard F. Cole U.S.
Nuclear Regulatory Commission Atomic Safety and Licensing Board Washington, D.C.
20555 U.S. Nuclear Regulatory Commission l
Washington, D.C.
20555 office of Commission Appellate Adjudication Administrative Judge U.S. Nuclear Regulatory Commission Mr. Thomas D. Murphy Washington, D.C.
20555 Atomic Safety and Licensing Board U.S. Nuclear Regulatory Commission James P. McGranery, Jr., Esq.
Washington, D.C.
20555 1255 - 23rd Street, N.W.
Suite 750 Charles A. Barth, Esq.
Washington, D.C.
20037 office of the General Counsel U.S.
Nuclear Regulatory Commission l
Washington, D.C.
20555 l
Jan Schori, Esq.
General Counsel Sacramento Municipal Utility District P.o. Box 15830 Sacramento, CA 95813 0124/030 tab.93 I
O.uuo SACRAMENTO MUNICIPAL UTIUTY DISTRICT C P. O. Box 15830 Sacramento CA 95852 1830,(916) 452 3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA DAGM/NUC 93-079 April 1, 1993 U. S. Nuclear Regulatory Comnussion Attn: Document Control Desk Washington, D. C. 20555 i
Docket No. 50-312 Rancho Seco Nuclear Station License No. DPR-54 CLARIFICATION OF THE PERMANENTLY DEFUELED TECHNICAL SPECIFICATION LOOP AND SFP DECAY HEAT i
ANALYSES j
References:
1.
J. Shetler (SMUD) to S. Weiss (NRC) letter DAGM NUC 91-183, dated November 19,1991, Proposed Amendment No.182, Revision 3, the Permanently Defueled Technical Specifications 2.
D. Keuter (SMUD) to S. Weiss (NRC) letter AGM/NUC 91-081, dated May 20,1991, Proposed Decommissioning Plan 3.
J. Shetler (SMUD) to T. E. Murley (NRC) letter DAGM/NUC 91-136, dated October 21,1991, Supplement to Rancho Seco Environmental Report - Post Operating License Stage Attention: Seymour Weiss Based on our discussions with your staff regarding the Loss Of Off-site Power (LOOP) and Spent Fuel Pool (SFP) decay heat analyses presented in the safety analysis for the Permanently Defueled Technical Specifications (PDTS), we are providing the attached, modified LOOP and SFP Decay Heat Load safety analysis summaries. These summaries clarify the conclusions made in Reference 1. We are also providing additional supplemental information, based on our calculations and analyses performed for Reference 1.
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DISTRICT HEADQUARTERS O 6201 S Street, Sacramento CA 95817-1899
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- DAGM NUC 93-079 Seymour Weiss s
r Refer to the LOOP and SFP Decay Heat Load analyses that begin at the bottom i
of page 2 of 71 and the middle of page 3 of 71 of Attachment-II to Reference 1 i
respectively. Attached is the revised wording for these two analyses. The revised j
wording is shown in italics The PDTS safety analysis (Reference 1) provided information based on different assumptions and analyses than those used in the Rancho Seco Decommissioning i
Plan (DP) and Environmental Report Supplement (ERS) (Reference 2 and 3).
The DP and ERS assumptions and conclusions continue to be valid. We base our conclusions, as stated in the DP and ERS, on early, conservative District l
analyses. The PDTS analyses incorporate newer empirical SFP heat-up information that demonstrates the SFP can not reach boiling when assummg-i evaporative cooling.
Members of your staff requiring additional information or clarification may contact Jerry Delezenski at (916) 452-3211, extension 4914.
Sincerely, A
L 2
James R. Shetler Deputy Assistant General Manager Nuclear Attachment
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cc:
J. B. Martin, NRC, Walnut Creek S. Brown, NRC, Rockville i
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4 ATTACHMENT Revised LOOP and SFP Decay Heat Load Analyses (2 Pages) l l
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LOOP During normal power operations and post accident conditions, it is imperative that electrical power be available to support equipment needed to operate the 4
plant and mitigate the consequences of design basisaccidents associated with poneroperations. In the PDM, a LOOP would result in the loss of SFP cooling.
However, there is adequate time available feee+he 6FP i=y P.= lead-l wakedx SL; to take corrective action without a safety consequence, even in the event of an extended LOOP condition (i.e., a total LOOPfor a prolonged period oftime weHin excess ofxveralhours). As ofJune 7,1991, an extrapolation ofDistrict calculation Z-SFC-M2533 shons that for an initial SFP levelof23 feet 3 inches, it would take a minimum of15 days to boH down the SFP to the top ofthe spent fuel asamblics. This amount oftime does not i
consider the time to heat up the SFP waterfmm the maximum aDoned nonnal operating temperatum (140 'F) to the boding point (212'F).
Rancho Seco has six off-site power transnussion lines that are tied to the SMUD andPG&Eelectrica/ grids. SMUDhas the capability to mceive power dimetly.
from the District's hydroelectric or other electricalgenerating units in less than eight hours. A District evaluation of the off-site electrical grid for Rancho Seco, performed pursuant to 10 CFR 50.63, Station Blackout, verified the stability of the Western grid. The probability of a LOOP at Rancho Seco, as e'.aluated in accordance with the guidelines of Regulatory Guide 1.155, is less than once per 4
20 years. Therefore, the emergency diesel generators are not reqmred to ensure power availability to support SFP cooling equipment in the event of a LOOP.
i An alternate power supply can be made available well within the minimum time required to take corrective action to restore SFP cooling. A simple addition of water to the SFP, via the diesel driven limpump per theplant Loss ofSFP Cooling orLevelacoverypmcedum, wouldgnatly extend the time avaHable to recoverfrom a LOOP condition (see also SAR page 15 fora description ofthe a vailable SFP water makesup methods).
In addition, ifa LOOP event occurs at Rancho Seco, it is expected to be ofa short duration (on the order ofa fewhours). This conclusion is based on the o/T-site a/cpoweraliability analysis summarindin the abose paragraph. A short duration LOOP w21ha ve a neghgible impact on an analysis which looks at the Iong term e/Tects oflosing theprimaryspent fuelpoolcooling system. Fora 1
short duration LOOP condition coupled with an extendedloss oftheprimary SFPcooling system, District calculation Z-SFC-M2SS4 (summanad below in the SFP Decay Heat Load analysis) concludes that for any initial SFP level 223 feet 3 inches, it takes a minimum of 250 hours0.00289 days <br />0.0694 hours <br />4.133598e-4 weeks <br />9.5125e-5 months <br /> before the SFP bulk coolant temperature can reach a steady state value of approximately 185 *F, as of November 1,1991. Thus, based on this District calculation, SFP water will not boil following an extendedloss of the primarySFP cooling system that mayor may not include a short duration LOOP event.
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SFP Deeny Hen
- Load The controls required to protect the spent fuel in the PDM are predicated primarily on the level of decay heat in the SFP. The District calculated (SMUD Cakulation 2-SFC-M25S4) the decay heat load for the SFP in the defueled condition using the methodology described in ANSI /ANS 5.1-1979, Branch Technical Position (BTP) ASB 9-2, andempirics/SFPheat-up data. The decay heat load in the SFP, as a function of calendar date, is shown in Table 1 (see page 54 of this SAR). Also, this table provides the calculated SFP water heat-up i
rate following loss of the primarySFP cooling system with the fue/ storage building (FSB) ventilation system operating. The FSB sentilation system consists ofone oftno edundant Auxiliary Building exhaust fans and a FSB supplyfan. Specifically, Table I provides, r : f=& 9d:P i', the f
SFP decay heat load in BTU /hr, calculated using BTP ASB 9-2 andmodiSed using empidcalSFPhast-up data. Table 1 also presents the time (in hours) it takes following the loss of primarySFP cooling, as a function ofinitial SFP t
temperature, for the SFP temperature to reach 180*F and/or a steady state temperature, gisen initial SFP levels of 23 feet 3 inches and 37 feet. This District SFP heat-up rate evaluation concludes the SFP will not boil during the PDM if primarySFP cooling is lost at either of the two minimum allowed SFP levels with the FSB sentilation system operating. The maximum steady state SFP temperature that can be reached from them conditions is approximately 185*F.
During the defueled condition, the normal operating SFP temperature is maintained below 90*F. A SFP operating temperature near70*F is not 1
l uncommon. At an initial SFP temperature of 90*F and 140*F,if the primary SFP cooling system is lost, a minimum of 350 and 250 hours0.00289 days <br />0.0694 hours <br />4.133598e-4 weeks <br />9.5125e-5 months <br />, respectively, is available for operatom to take corrective action to restore theprimarySFP cooling system prior to exceeding 180*F when the initial SFP level is 223 feet 3 inches. Again, the maximum steady state SFP temperature that can be reached under them conditions is approximately 185*F.
No safety implications exist at a 23 feet 3 inch SFP level as long as personnel exposure is monitored and maintained as low as is reasonably achievable. The ruptured fuel assembly event does not require a specific minimum SFP water level to mitigate its consequences. Requiring a minimum water level of 23 feet 3 inches in the SFP provides adequate shielding above active fuel to protect individuals in the Fuel Storage Building when fuel handling operations are not in progress. Also, a minimum of 37 feet of water is maintained in the SFP during fuel handling operations for shielding and worker safety concerns only, not for accident mitigation concerns.
Based on this same District calculation summarimdabose for the SFPDray l
Heat Load severalhunded hours are available before significant evaporative l
losses of SFP water in ventory can occur due to a loss of primary SFP cooling.
Approximately I foot ofSFP water would evaporate every 70hoursifthe SFP water was at the steadystate temperatum ofapproximately 180*F A simple addition of water to the SFP would make up any evaporative water losses and extend the time to implement corrective actions to restore primarySFP cooling, if necessary. Specification D3/4.1 requires operators to take immediate actions to restore the SFP level if the level drops below the minimum allowed level. The evaluation on page 15 of this SAR lists several options available to operators for providing make-up water to the SFP.
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