ML20066L401
| ML20066L401 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 01/31/1991 |
| From: | Wallace E TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RTR-REGGD-01.097, RTR-REGGD-1.097 NUDOCS 9102070029 | |
| Download: ML20066L401 (4) | |
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w TENNESSEE VALLEY AUTHORITY CH ATT ANOOG A, TENNrSSEE 374o1 5B Lookout Place JAN 311991 U.S. Nuclear Regulatory Commission
-ATTN: Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAll NUCLEAR PLANT (SQN) - PERMANENT DEVIATION FROM REGULATORY GUIDE (RG) 1.97 - SHIELD BUILDING (SB) STACK INSTRUMENTATION t-
References:
1.
TVA letter to-NRC dated December 10, 1990, " Request for an Extension to Temporary Deviations from Regulatory Guide (RG) 1.97 - Shield Building Stack Instrums tation" 2.
TVA letter to NRC dated November 11, 1990, " Temporary Deviation f rom Regulatory Guide (R.G.) 1.97 - Shield Building Stack Radiation Monitoring" 3.
TVA letter to NRC dated May 7, 1990, " Regulatory Guide (RC) 1.97 - Finalized Program" The purpose of this letter is to provide NRC with TVA's permanent deviation from the accuracy requirements of RG 1.97 for SQN's SB stack instrumentation.
TVA's RG_1.97 pro 6 tam for SQN (Reference 3) currently contains 28 proposed deviations that are undergoing NRC review. The enclosed deviation for SQN's SB stack instrumentation is Deviation 29 and should be-reviewed with the information contained in TVA's Reference 3 letter.
By Reference 2, TVA submitted two temporary deviations-from RG 1.97 that resulted from unexpected calibration and reliability problems that were experienced on SQN's newly installed SB stack radiation and flow monitoring instrumentation. An extension for these temporary deviations was subsequently requested (Reference 1) because of questions concerning system accuracy.
These deviations provided an acceptable alternative for SQN's postaccident monitoring capabilities ~for the interim period until it could_be determined if the existing system could fully comply with the RG 1.97 requirements or
-whether a permanent deviation was necessary. TVA has now completed its evaluation of.SQN's SB stack instrumentation and has determined that a permanent deviation from the accuracy requirements of RG 1.97 is appropriate.
The enclosure provides the details regarding ';QN's SB stuck instrumentation capabilities and the justification for the deviation.
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- JAN 311991 U.S. Nuclear Regulatory Comission Picase direct questions concerning this issue to D. V..Goodin at (615) 843-7734.
Very truly yours.
TENNESSEE VALLEY AUTHORITY W
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.Nuclea v icensing and Regulatory Af fairs Enclosure cc (Enclosure):
Ms. S. C. Black, Deputy Director Project Directorate 11-4 U.S. Nuclear Regulatory Comission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. J. N. Donohew Project Manager U.S. Nuclear Regulatory Comission One White Flint, North 11555 Rockville Pike r
Rockville, Maryland 20852 NRC Resident Inspector Sequoyah Nuclear Plant
'2600-Igou Ferry Road Soddy Daisy, Tennessee 37379
.Mr. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Comission Region II 101. Marietta Street, NW, Suite-2900 Atlanta-Georgia 30323 l
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JV ENCLOSURE DEVIATION 29 1
VARIABLES (105) and (271 Shield Building (SB) Exhaust Flow Rate and Noble Gas Radiation Levt1 Deviation f rom Regulatory Guide (RG) 1.97 Guidance Sequayah Nuclear Plant (SQN) maximun design accident flow through the SB exhaust is 18,700 cubic feet per minute (cfm), which includes an additional 10 percent flow from the combination of two emergency gas treatment system (ECTS) f ans (rated at 4,000 cfm each) and one auxiliary building gas treatment system (ABGIS) fan (rated at 9,000 cfm).
The range of indicated flow at SQN is 0-28,000 cfm whero 28,000 cfm is the maximum flow expected with two containment purge f ans exhausting during Mode 5 (cold shutdown) operation.
RG 1.97, Revision 2, recommends a range of 0 to 110 percent (design) flow with overall system accuracies within a "f actor of 2" over the full range of indicated flow. TVA recommends that the factor of 2 only be applied for flows between 500-28,000 cfm. The SB radiation monitoring instrumentation that has been insta!1ed at SQN will satisfy the RG 1.97 accuracy requirements (factor of 2) over the full range of indicated flow (0-28,000 cfm) with the exception of the low flow range. The inability to achieve the factor of 2 accuracy in this low flow range can be attributed to the inherent inaccuracy associated with measuring low velocities (i.e., approximately 0-200 f eet per minute) in conjunction with the inaccuracy associated with the radiation monitoring equipment.
Justification At SQN, the A-Train ABGTS is aligned to the Unit 1 SB stack while the B-Train is aligned to the Unit 2 SB stack. During accident conditions, both trains of EGTS and ABCTS will start.
Both trains of ECTS will automatically align to the accident unit's SB stack. Given a single failure of the ABGTS aligned to the accident unit's SB stack, the total flow f rnm the SB stack would then be the EGTS flow.
Under steady-state conditions, af ter the initial drawdown of the SB annulus, the flow rate from the EGTS exhaust will remain essentially equal to the volume of air inteakage into the SB annulus as the system maintains a constant negative pressure of 0.5 inch of water.
During surveillance testing of the EGTS, measured inleakage has been in the range between 200 and 300 cfm.
TVA accuracy calculations indicate that the RG 1.97 required factor of 2 accuracy will be main *.ained unless SB exhaust flow drops below 180 cfm.
To maint.'.n some margin to the currently calculated lower flow limit at which the RG 1.97 accuracy requirements are met, TVA reenmuends that the factor of 2 requ'. red accuracy be applied to a lower limit of 500 cfm.
Existing calculations have demonstrated that the 10 CFR 100 offsite dose limits are not exceeded based on the assumption of a aaximum of 500 cfm air inleakage into the SB (reiference updated Final Safety Analysis Report Ser. ions 15.5.3 and 6.2).
With an inleakage less than 500 cfm, the SB annulus remains negative throughout the transient, thus allowing only filtered flow to exit the
d annulus area via the SB exhaust. As previously indicated, under steady-state conditions, the rate of inleakage will be approximately equal to the exhaust flow rate.
Thus, a flow rate 01 less than or equal to 500 cfm n.ay be assumed to be bounded by-the 10 CFR 100 calculations.
In sunanary, even though the SB radiation monitoring equipment that has been installed at-SQN is expected to satisfy the RG 1.97 accuracy requirements for indicated flows less than 500 cfm, a value of 500 etm is considered to provide appropriate margin to the value currently calculated (180 cfm).
It should be further nated that flows in this lower range will alno produce lower doses.
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