ML20079B152
| ML20079B152 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/11/1991 |
| From: | Wallace E TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RTR-REGGD-01.097, RTR-REGGD-1.097 NUDOCS 9106140021 | |
| Download: ML20079B152 (4) | |
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U.S. Nuclear Regulatory Commission ATTN Document Control Desk Washington, D.C.
20555 Centlemen:
In the Matter of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAH NUCLEAR PLANT (SQN) - REGULATORY CUIDE (RC) 1.9 7 - DEVI ATION 29 -
MINIMUM FLOW FOR SQN'S SHIELD BUILDING (SB) STACK INSTRUMENTATION
Reference:
TVA letter to NRC dated January 31, 1991, "Sequoyah Nuclear plant (SQN) - Permanent Deviation From Regulatory Guide (RG) 1.97 - Shield Building (SB) Stack Instrumentation" This letter providos NRC with a revision to SQN's RC 1.97 program. This revision is associated with a deviat.Lon (i.e., Deviation 29) that was previously submitted by the referenced letter.
During an April 12, 1991, telecon between NRC project Management and SQN's Site Licenuing and Nuclear Engineering staffs, NRC requestod that Deviation 29 be revised to
'.ower the minimum SB stock flow for which RG 1.97 accuracy requirements would be satisflo1 to a flowrate that would be expected postaccident.
TVA previously utilized a flowrato of 500 cubic feet. por minuto (cfm), which provided a margin above the expected postaccident flowrato (i.e.,
200-300 cim).
It was also noted that actual values below 500 cfm would be conservativo relative to offsite dose assumptions and/or calculations.
In response to NRC's request, TVA revised Deviation 29 to establish 200 cfm as the minimum flowrato, which satisfies RG 1.97 accuracy requirements.
Enclosed is TVA's revised Deviation 29 that supersedes Deviation 29 previously provided in the roforenco letter. The revised deviation completos the information requestod by NRC for review of SQN's RG 1.97 program.
O 9,106140021 nom m'10/311,.o*w PDR F.
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U.S. Nuc1 car Regulatory Commission Please direct questions concerning this issuo to D. V. Goodin at (615) 843-7134.
Very truly yours.
TENNESSEE VALLEY AUTHORITY 7)'.id 'An<sE' E C ac, Manager NuclearLicensingap Regulatory Affairs Enclosure cc (Enclosuro):
Ms. S. C. Black, Deputy Director Project Directorato 11-4 U.S. Nucleur Regulatory Commission Ono Whito Flint, North 11555 Rockville Pike Rockv8110, Maryland 20852 Mr. D. E. LaBargo, Project Manager U.S. Nuclear Regulatory Commission One Wh8te Flint, North 11555 Rockville Piko Rockville, Maryland 20852 NRC Resident inspector Sequoyah Nuclear Plant 2600 Igou Ferr)~ Road Soddy Daisy, Tennensco 37379 Mr. B. A. Wilson, Project Chief U.S. Nuc1 car Regulatory Commission Region II 101 Harietta Stroot. NW, Suite 2900 Atlanta, Coorgia 30323 l
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6 ENCLOSURE i
EliYlAILONJ,9, YM1&EELO.91) and_LU1 shield Building (SB) Exhaust Flow Rato and Noblo Gas iladiation Level Drylauon f tm_liputtatery cuide180) L 97 Guidante sequoyah Nuclear plant's (SQN) maxinum design accident flow throust the SB exhaust in 18.100 cubic feet per minuto (cfm), which includes an additional 10 percent flow from the combination of two emergency gas treatment system (EGTS) fans (rated at 4,000 cfm each) and ono auxiliary building gas treatment system (ABGTS) fan (rated at 9,000 cfm).
The range of indicated flow at SQN is 0-28,000 cfm whero 28,000 cfm is the nmximum flow expected with two containment purgo fans exhausting during Mode 5 (cold shutdown) operations.
RG 1.97, Revision 2 recommends a rango of 0 to 110 percent (design) flow with overall system accuracies within a " factor of 2" over the full range of indicated flow. Yva recommends that the factor of 2 only be applied for flows betwoon 200-28,000 cfm. The SU. radiation monitoring instrumentation that has been installed at SQN will satisfy the RG 1.97 accuracy rcquirements (factor of 2) over the full range of indicated flow (0-28,000 cfm) with the exception or the low flow range. The inability to achlove the factor of 2 accuracy in this low flow range con be attributed to the inhoront inaccuracy associated with measuring lo" velocities (i.e., approximately 0-200 foot por minute) in conjunction with the inaccuracy associated with the radiation monitoring equipment.
Justifica(ipn At SQN, the A-Train ABGTS is aligned to the Unit 1 SD stack whilo the B-Train is aligned to the Unit 2 SH stack.
During accident conditions, both trains of ECTS and ABGTS will start.
Both trains of ECTS will automatically align to the accident unit's SB stack. Given a single failuro of the ABGTS aligned to the accident unit's SB stack, the total flow from the SB stack would then be l
the EGTS flow. Under steady-stato conditions, after the initial drawdown of the SB annulus, the flow rate from the ECTS exhaust will remain essentially equal to the volumo of air inleakage into the SB annulus as the system maintains a constant negative pressure of 0.5 inch of water.
During surveillance testing of the ECTS, measured inleakago must be maintained below 500 cfm. TVA accuracy calculations indicate that the RG 1.97 required factor of 2 accuracy will be maintained on the positive or nonconservativo side (indicated doso less than actual released doso). However, the instrumentation does not meet the RG 1.97 factor of 2 accuracy requirement on the negative or conservative side (indicated doso greator than actual roloaoed doso) below 180 cim. However, for this inaccuracy, dose estimates would always bo in the conservativo direct 8 an and would be bounded in all cason.
6 To maintain como margin to the currently calculated lower flow limit at which the HG 1.91 accuracy requiremento are mot, TVA recommends that the factor of 2 required accuracy be applied to a lower limit of 200 cim.
Extating calculations have demonstrated that the 10 Cl<R 100 offolto doon limits are not exceeded bored on the accumption of a maximum of 500 cfm air leakago into the CD (reference updated Final Safoi,y Analynio Report Sections 15.5.3 and 6.2).
With an intenkato less than 500 cfm. the SD annulus remains negative throughout the tranutent, thuo allowing only filtered flow to exit the annulus area via the SB exhaust.
As previously indicated, under ateady-atate conditions, the rate of inleakage will be approximately equal to the exhaupt flow rate.
Thus, a flow rate of less than or equal to 200 cfm may be accumed to bv bounded by the 10 CFH 100 calculations.
j In summary, even though the SB radiation monitoring equipment that has been installed at SQN is expected to satisfy the HG 1.91 accuracy requiremento for indicated flowo leco than 200 cfm a value of 200 cfm is considered to provide appropriate margin to the value currently calculated (180 cfm).
It should be further noted that flows in thio lower range also meet the f actor of 2 accuracy requirement except in the concorvative direction.
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