ML20204H665
| ML20204H665 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/14/1988 |
| From: | NRC OFFICE OF SPECIAL PROJECTS |
| To: | |
| Shared Package | |
| ML20204H651 | List: |
| References | |
| NUDOCS 8810240452 | |
| Download: ML20204H665 (5) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION n
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W4SHINGTON, D. C. 20046 s*..../
, ENCLOSURE SAFETY EVALUATION RY THE OFFICE OF SPECIAL PDOJECTS SUPPORTING AMENDNENT NO. 86 TO FACILITY OPERATING LICENSE NO. OPR-77 TENNESSEE VALLEY AUTHORITY SE0VOYAH NHCLEAR PLANT, UNIT 1 DOCKET NO. 50-377
1.0 INTRODUCTION
The Tennessee Valley Authority (TVA), by submittal dated August 15, 1988, proposes to rodify)the Sequoyah Nuclear Plant (SQN) Unit 1 Technicalto revise the Specifications (TS switch setpoint and tolerance band of Surveillance Requirement (SR) 4.5.1.2.c.1.
TVA provided supplemental information in its le$ter dated September 21, 1988.
The TVA submittal dated August 17, 1986 is a duplicate of the application dated August 15, 1988.
The proposed changes are being requested to implement corrective actions documented in a TVA Condition Adverse to Ouality Report (CAQR).
The CAQR identifies that the current level switches used in the UHI potentially tray allowmorewatertobein.iecteddurirgapgstulatedaccidentthanthe C
analytical limit of 1.130.5 cubic feet (ft ).
The over injection of water can result in the.ccidental injection of nitrogen into the reactor coolant system.
i Nitrogen in tL reactor coolant could result in the restriction of heat removal i
from the fuel cladding.
The UHI system is described in the Sequoyah Final Safety Analysis Report (FSAR) Section 6.3.2 and its functional analvtical perfc mance in response to various accident analyses is described in FSAR Section 15.4.1.1.4.
Section 50.46Ia)(1) of 10 CFR Part 50 recuir9s an acceptable analysis calculating the peak cladding temperature based on plant operating conditions prior to restarting the Sequoyah,linit 1.
Changing the amount of water injected from the UHI tank impacts the Appendix K Peak Cladding Temperature i
Analysis; therefore, a re-analysis of the peak cladding temperature is required I
prior to restart of Unit 1.
Also, corrections to the UHI calculation model are needed.
Since Westinghouse, the reactor supplier, is presently modifying the reactor code used to perfarn the Appendix K analysis, the revised Appendix K analysis will not be develooed before Unit 1 plans to restart from the current outace.
Because of this delay TVA has requested a temporary exemption to i
10 CFR 50.46fa)(1), in its letter dated September 19, 1988, in order to perform and submit to NRC the revised Apcendix X analysis after restart of l' nit 1.
The supplemental information in TVA's 'etter dated September 21, 1988 clarified information provided in TVA's spolirc.cion for this proposed amendment.
It did not chany the substance of the prnicsed action in the Federal Deqister Notice for the proposed atendment or affect the staff's initial determination.
G810240452 081014 DR ADOCK 0500 7
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2.0 EVALUATION TVA implemented two corrective actions to resolve the above mentioned CAOR.
Specifically, the first change is a proposed actual reduction in the total amount cf water iniegted by the UHI system from the current requirement 3 to 850 ft ; thereby, decreasing the probability of over injecting of 900 ft water from the UH! tank.
Supporting Westingheuse Electric Corporation (WEC) evaluations were provided by TVA in Attachment 1 of the August 15, 1988 su%ittal. TVA has also provided additional clarifying information by the su,mittal dated September 21, 1988. The second CAOR corrective action is the replacement of the level switches with a new model.
The new level switches are different only in the span of response.
The switch accuracy calculations, therefore, are different.
TVA has provided new calculations supporting the proposed 75 setpoint and setpoint tolerances.
2.1 UHI Iniected Water Volume As documented in FSAR Section 6.3.2, the DH! System is designed to p3551vely provide additional water inventory to the reactor core during the blowdown phase of a postulated Loss of Coolant Accident (LOCA).
The limiting case break, as documanted in Emergency Core Cooling System (ECCS) Analysis, (FSAR, Section 15.4.1.1.4), is the double-ended, cold-leg guillotine (DECLG) break 0.6 with the imperfect mixing of VHI water using a discharge coefficient, C 9=Thisgnalysisestablishedthelowerbound assumed in the vessel upper head.
value gf injected water volume at 900 ft. TVA proposed to lower this value to 850 ft and has provided a WEC analysis to support the conclusion that the i
increase in calculated fuel peak clad temperature (PCT) remains below the 10 CFR 50.46 regulatory rrluirement of 2200'F.
The reduction in the UHI water volume increased the PCT by 53'F and when PCT penalties for potential guide tube flexure failure and instrument guide tube filling during reflood are added, the limiting PCT reached 2198'F.
This is less than the maximum acceptance criterion (2200'F) in 10 CFR 50.46.
2.2 Level Switch Setpoint Calculation,
i level switches are used to automatically isolate the UHI System accumulators from the reactor coolant system (RCS) af ter the UHI System has in.iected the borated water.
Thi level switch setpoints are selected to enstre that the quantity of VH1 water delivered is within the linits calculated for the large break LOCA analysis.
TVA has performed an accuracy calculation (1-LS-87-21) to demonstrate that level switch setpoint and tolerances will be within the bounds of accident analysis.
The TVA calculation is based on Static-0-Ring test report. 8601-042, usinq the sum of the souares method for all independent "ariables that affect accuracy.
The bi-directional and uni-directional errors are combined in such a manner that the nenative uni-directional error is acted to the nenative portion of the bi directional error end tha nositive uni-directinnal error is added to the positive portion of the bi.directinntl error.
The result is a corrective rumber for the instrument accuracy.
The staff has reviewed tha sub.iect calculation ard finds that the accuracy calculation has bein conducted in a
. nanner which predicts the worse-case accuracy. TVA has established the level switch set point based on this calculation.
However, the caiculation is based on the assunption that the UHI system accumulator room tem;erature will be between 70 and 85* F.
UHI room temperature is monitored via SI606 which requires that UHf room temperature be maintained between 75 an 85'F.
Since the margin between the safety) limit and the instrument operating band is very sma
(.01" of water colume (WC ), the staff concludes that, anytime the temperature of the UH' room is not between 70 and 85*F, the level switches should be declared inoperable. TVA committed in its letter dated September 21, 1988 to revise the balence-of-plant temperature monitoring procedure to indicate that the UHI level switches are inoperable if the. ambient temperature in the area of the switches exceeds the values used in Demonstrated Accuracy Calculation 1-LS-87-21 to determine temoerature-induced reference water-leg er,ror.
These values are the temperature values discussed above. TVA stated that this procedure revision will be completed befor; Unit 1 entry into mode ?.
This should be included in the next scheduled update of the FSAR.
2.3 10 CFR Part 50.46 Appendix X Calculatinns To provide additional assurance that the PCT is below the 2700'F acceptance criterion, the following operational restrictions are imposed by TVA on Sequoyah, Unit 1:
- 1) The steam generator tube plugging limit wil' be administratively lowered from 10 percent to 5 percent. Westinghouse has performed an analysis which demonstrates that this restriction reduces the calculated PCT by 22*F.
- 2) The bes' flux hot channel factor (F (2)) linit will be lowered n
from 2. 37 to 2.15 by rem rancing tne control rod positions during power operation.
This reduces the calculated PCT an additional 87'F for the limiting imperfect mixino case.
These two procedural changes reduce the calculated PCT from 2196'F to 2089'F for the postulated DECLG break with a discharge coefficient (Co) of 0.6 and imperfect nixing. These procedural changes provide over 100*F of margin between the calculated PCT and the acceptance criterion in 10 CFR 50.46.
This margin is sufficient to offset any uncertainties in the ECCS cooling performance calculations for Unit 1 and sufficient for the staff to conclude that the PCT are less then the acceptance criterion (2200'F) in 10 CFR 50.46.
Section 50.46(a)(1) of to CFR Part 50 requires that the ECCS coolir,q performance be calculated on a plant specific basis using an approved ECCS calculatinn model.
The corrent approved calculated ECCS cooling performance, including the approved UHI calculation model, as referenced in Section 15.4 of the FSAR, is not based on the plant operating conditions for Unit 1 for the upconing Cycle 4 operation and there are corrections neered to the UHI calculation model.
TVA has nada ar evaluation based on ser.sitivity studies and the current aonrnved ECCS ccoling cerfer-anta in the FSAR to demonstrate that the calculated eCTs remain belew *ke acceptance seiterien in 10 CFR $0.46.
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4 These include the operational res*rictions discussed above.
TVA has requested a temporary exemption from 10 CFR 50.46(a)(1) in its letter dated September 19, 1988. This relief is until a revised calculated ECCS cooling performance has been completed using an approved ECCS model and Unit 1 operating cenditions and is submitted to NRC, but not later than May 31, 1989. This requested exemption is being evaluated by the staff anc will be the subject of a separate letter.
It is a separate issue from the proposed chcnges to the Unit 1 TS. Approval of the proposed amendment is necessary for Unit 1 to enter Mode 3 with the reactor coolant system pressure greater than 1900 psi.
Approval of the exemption is needed for Unit 1 to enter Mode 2 and restart from the current outage.
2.4 Staff Conclusions Based on the above, the staff concludes that the proposed changes to the Unit 1 TS in TVA's application dated August 15, 1988 are acceptable.
The staff also concludes that the Static-0-Ring level switches for the UHI System are inoperable if the room temperature is not between 70 and 85'F.
The requested temporary exemption to 10 CFR 50.46(a)(1) is a separate issue to TVA's application dated August 15, 1988 and will be addressed separately,.
3.0 ENVIRONMENTAL CONSIDERATION
This amendment involves a change to a requirement with respect to the installation or use of a facility component located within the restricted area as. fined in 10 CFR Part 20 and changes to the surveillance requirements.
The staff has determined that the amendment involves no tignificant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no sionificant increase in indiviotal or cumulative occupational radiation exposure.
The Commission has previously issued a prnposed finding that this amendmsnt involves no significant hazards consideration and there has been no rublic comment on such finding.
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.?2(c)(9).
Pursuant to 10 CFR 51.2?fb), no environmental impact statement nor environmental assessment need be prepared in connection with the issuance of the amendment.
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4.0 CONCLUSION
The Commission made a proposed determination that the amendment involves no sionificant hazards consideration which was published in the Federal Aeoister (53 FR 32960) on August 29, 1983 (nd consulted with the State of Tennessee on October 12, 1988.
No public comments were received and the State of Tennessee did not have any commants, i
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a The staff has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations, j
and the issuance rf the amendments will not be inimical to the comon defense and security nor to the health and safety of the public, a
Principal Contrioutors:
H. Garg, P. Hearn and T. Rotella Dated: Octot er 14, 1988 1
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