ML20035C912
| ML20035C912 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 04/01/1993 |
| From: | Shetler J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| DAGM-NUC-93-079, DAGM-NUC-93-79, NUDOCS 9304090227 | |
| Download: ML20035C912 (5) | |
Text
Asuun GACRAMENTO MUNICIPAL UTluTY DISTRICT C P. O. Box 15830, Sacramento CA 95852-183o,(916) 452-3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA DAGM/NUC 93-079 April 1, 1993 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Docket No. 50-312 Rancho Seco Nuclear Station License No. DPR-54 CLARIFICATION OF TIIE PERM ANENTLY DEFUELED TECilNICAL SPECIFICATION LOOP AND SFP DECAY IIEAT ANALYSES
References:
1.
J. Sheller (SM UD) 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 (SM UD) to S. Weiss (NRC) letter AGM/NUC 91-081, dated May 20,1991, Proposed Decommissioning Plan 3.
J. Sheller (SM UD) 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 stafT 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 lleat 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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PDR DISTRICT HEADQUARTERS O 6201 S Street, Sacramento CA 95817-1899 i
4 Seymour Weiss DAGM NUC 93-079 Refer to the LOOP and SFP Decay Heat Load analyses that begin at the bottom of page 2 of 71 and the middle of page 3 of 71 of Attachment II to Reference 1, respectively. Attached is the revised wording for these two analyses. The revised i
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 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 analyses. The PDTS analyses incorporate newer empirical SFP heat-up 1
information that demonstrates the SFP can not reach boiling when assuming 1
evaporative cooling.
I Members of your staff requiring additional information or clarification may contact Jerry Delezenski at (916) 452-3211, extension 4914.
Sincerely,
.. 4 /
/
James R. Shetler f
Deputy Assistant General Manager Nuclear Attachment i
t ec:
J. B. Martin, NRC, Walnut Creel-S. Brown, NRC, Rockville i
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5 ATTACIIMENT Revised LOOP and SFP Decay Heat Load Analyses (2 Pages) i
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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 plant and mitigate the consequences of design basisaccidents associated with poweroperations. In the PDM, a LOOP would result in the loss of SFP cooling.
However, there is adequate time available(+ee+he-SFP4ewy-heaHond-
+ valuation-belove) to take corrective action without a safety consequence, even in the event af an extended LOOP condition (i.e, a totalLOOPfora prolongai period oftime weHin excess ofseveralhours). As ofJune 7,1991, an extmpolation ofDistrict calculation Z-SFC-M2533 shons that foran initialSFP level of23 feet 3 inches, it uvuld take a minimum of15 days to boil doun the SFP to the top ofthe spent fuelassemblies. This amount of time does not consider the time to heat up the SFP waterfrom the maximum aHowed normal opemting temperature (140"F) to the boHingpoint (212 F).
Rancho Seco has six off-site power transmission lines that am tied to the SMUD and PG&Ee/ectricalgridS. SMUD has the capability to receive power directly 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 evaluated in accordance with the guidelines of Regulatory Guide 1.155, is less than once per 20 years. Therefore, the emergency diesel generators are not required to ensure power availability to support SFP cooling equipment in the event of a LOOP.
An alternate power supply can be made available well within the minimum time required to take corrective action to restore SFP cooling. A simpleaddition of water to the SFP, via the diesel driven Dw pump per the plant Loss ofSFP Cooling or Levelmcm eryprocedum, wouldgreatlyertend the time available to recoverfrom a LOOPcondition Vee also SAR page 15 fora description ofthe a vailable SFP water make-up methods).
In addition, ifa LOOP event occurs at Rancho Swo, it is expected to be ofa short duration (on the order ofa few hours). This conclusion is based on the o/T site a/cpowerreliability analysis summarizedin the aboveparagraph. A short duration LOOP nin have a nephgible impact on an analysis which looks at the long term effects oflosing theprimary spent fuelpoolcooling s) stem. Fora short dumtion LOOPcondition coupled uith an ettendedloss oftheprimary SFP cooling system, District calculation Z-SFC-M2554 (summarized below in the SFP Dway lleat 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 ettendedloss of the primary SFP cooling system that may or may not include a short dumtion L OOP event.
SFP Decay Heat 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 Olculation Z-SFC-M2554) 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, andempirica/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 rate following loss of the primarySFP cooling system nith the fuelstomBe building (FSB) rentilation system operating. The FSB ventilation system consists ofone oftno redundant Auxiliary Building exhaust fans anda FSB supplyfan. Specifically, Table 1 provides ase4uection-of-calendaralatw the c
SFP decay heat load in BTU /hr, calculated using BTP ASB 9-2 andmod/ Bed using empiricalSFPheat-up data. Table I also presents the time (in hours) it takes following the loss of primarySFP cooling, as a function ofinitial SFP temperature, for the SFP temperature to reach 180*F and/or a steady state temperature, given 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 primary SFP cooling is lost at either of the two minimum allowed SFP levels uith the FSB ventilation system operating. The maximum steady state SFP temperature that can be reached from these conditionsis 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 uncommon. At an initial SFP temperature of 90*F and 140*F,if the primary SFP cooling systemis 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 operators 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 these 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 i
fuel handling operations for shielding and worker safety concerns only, not for accident mitigation concerns.
Based on this same District calculation summarizedabore for the SFP Decay -
Heat Load, severalhunded hours are available before significant evapcrative losses of SFP water inventorycan occur due to a loss of primarySFP cooling.
Approximately 1 foot ofSFP unter uvuld evaponte every 70hoursif the SFP water uasat the steadystate tempentum ofapproximately JS0'F A simpie addition of water to the SFP would make up any evaporative water losses and extend the time to implem ;nt 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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