ML20140F031
| ML20140F031 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/10/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20140F002 | List: |
| References | |
| NUDOCS 9706120285 | |
| Download: ML20140F031 (4) | |
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cu%k UNITED STATES g-S NUCLEAR REGULATORY COMMISSION U
WASHINGTON, D.C. 20665-0001 o
1.0 INTRODUCTION
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In a submittal dated August 22, 1996, and supplemented on March 28, 1997, the Tennessee Valley Authority (TVA), the licensee for Sequoyah Nuclear Plant (SQN), Units 1 and 2, proposed to change Section 3.6.5 of the SQN Technical Specifications (TS) to lower the minimum required weight of ice in each containment ice basket from 1,155 pounds to 1,071 pounds, thus reducing the overall ice condenser ice weight from 2,245,320 pounds to 2,082,024 pounds.
The licensee also proposed to extend the chemical analysis surveillance interval for the ice bed from 12 months to 18 months, based on guidance provided in Generic Letter (GL) 93-05. Also, the TS "20*C" test requirement at which the pH of the ice is determined is being deleted in favor of current testing criteria recommended by the appropriate code.
I 2.0 EVALUATION The operability of the ice beds in the ice condenser requires that the ice inventory be distributed evenly throughout the ice condenser bays in contain-ment and contain sufficient heat removal capability to condense the reactor coolant system volume released during a loss-of-coolant accident (LOCA).
Sufficient pressure suppression capability from the ice in the ice condenser is necessary to limit the containment peak pressure transient during a LOCA.
The ice inventory is contained in 1,944 ice baskets throughout the ice condenser.
TS Surveillance Requirement (SR) 4.6.5.1.d currently requires sampling every l
18 months to ensure that each basket contains at least 1,155 pounds of ice and that the average ice weight for each bay and each group-row combination not be less than 1,155 pounds per basket at a 95 percent level of confidence at the start of the surveillance interval.
Sequoyah's current 1,155 pounds TS limit is based on a containment analysis that assumes an even distribution of 993 pounds per basket throughout the ice condenser at the time of LOCA.
The 1,155 pounds per basket TS limit contains a conservative allowance for ice loss through sublimation during the surveillance interval and a conservative allowance for ice-weighing instrument error.
These values are currently 15 percent and 1 percent, respectively.
The above limits ensure, at a 95 percent level of confidence, a minimum total ice weight of 2,245,320 pounds is present in the ice condenser at the start of surveillance interval which is i
9706120285 970610 DR ADOCK 0500 7
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2 required by the Limiting Condition for Operation (LCO) 3.6.5.1.
The current containment analysis using the 993 pounds ice weight per basket yields a peak containment pressure of 10.9 psi following a design basis LOCA.
The licensee indicated that the revised containment analysis, utilizing the revised mass and energy model and an ice weight of 922 pounds per basket, calculated a peak design basis LOCA containment pressure of 11.45 psi which remains below the containment design pressure of 12.0 psi. Allowing a 15 percent margin to bound expected sublimation over one cycle with an additional 1 percent margin to account for instrument error, the minimum basket weight at the time of weight measurement will be 1,071 pounds.
This value translates into a total ice weight of 2,082,024 pounds at the current value of 95 percent level of confidence.
Both the current and the new 1996 analyses utilized " Westinghouse LOCA Mass and Energy Release Model for Containment Design - March 1979 Version,"
WCAP-10325-P-A, May 1983, for mass and energy releases and "Long Term Condenser Containment Code - LOTIC Code," WCAP-8354-P-A, April 1976, for calculation of the containment response to the mass and energy release.
The licensee indicated that the new analysis utilized revised input assumptions using current Sequoyah specific information and more realistic models to support ice weight reduction.
The_new analysis considered (1) assumed core stored energy, (2) decay heat release, (3) steam flow to turbine, (4) steam generator metal heat, and (5) steam generator depressurization and equilibrium.
The licensee stated that the current analysis used a core stored energy based on full core (193 fresh fuel assemblies) of fresh fuel.
The revised analysis used a core stored energy based on full core with 88 fresh fuel assemblies.
The 88 fresh feel assemblies is a conservative maximum core design limit.
The fuel cycle management at Sequoyah requires only approximately one-third (64) fuel assemblies of each core reload.
Both the current analysis and the revised analysis used the ANSI /ANS-5.1 1979 Decay Heat Standard (including the two sigma uncertainty).
The revised analysis used more realistic fuel modeling.
In the present analysis no credit for removal of steam from the steam generators at the start of the accident was taken.
In the revised analysis, a steam generator isolation time of 1.19 seconds (which represents a conservatively calculated minimum time for main steam turbine stop valve closure) was used. The current analysis considers all steam generator metal energy to be available for transfer to the primary loop.
Metal heat from those portions of the steam generator that have no potential for heat transfer to the reactor coolant system'during the effective time period (i.e, elliptical head, upper shell and miscellaneous internals) was not included in the revised analysis. The current analysis assumed a bounding condition for steam generator equilibrium and depressurization based upon assumed containment pressures that were lower than the final containment response. The revised analysis iterated on the depressurization and equilibrium to ensure that the pressure was close to, but not less than, the final containment response. The staff finds the revised assumptions as discussed above acceptable.
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The analysis was completed to provide the analytical basis for a reduction in the present SQN design basis ice mass of 993 pounds per basket but retain the current time interval (approximately 156 seconds) relationship between ice bed meltout time and containment spray switchover time and provide for peak pressure margin to design pressure.
The results of the analysis support the design basis ice mass of 922 pounds per basket, a calculated containment peak pressure of 11.45 psig, and containment spray switchover icemelt relationship of 149 seconds. Although the current margin between the design operating pressure and the peak LOCA pressure will be slightly reduced, the margin of safety provided by the containment design is not reduced. The margin of I
l safety is stated to be the structural (or ultimate) design pressure (16 psig) less the design operating pressure (12 psig). Both the current and the new analyses were performed by the Westinghouse Electric Coporation.
The new containment integrity analysis is presented in WCAP-12455, Rev. 1.
Based on the above review, the staff finds the proposed reduction in the ice l
weight reduction acceptable as the new analyses performed are consistent with current licensed methodology and the calculated containment peak pressure of l
11.45 psig remains below the containment design pressure of 12.0 psig.
With regard to the request to change the interval for SR 4.6.5.1.b (chemical analyses) from 12 months to 18 months, the licensee stated that past chemical
. analyses at 12-month intervals have not indicated problems meeting the boron l
concentration or pH requirements at SQN.
Because the current SR interval is every 12 months, it will not always coincide with a refueling outage since SQN l
operates on an 18-month cycle. Therefore, the present requirement requires a person to enter containment during power operation to perform this testing and l
receive a significantly higher radiation dose than if performed with the reactor shut down. This change in SR interval is recommended by GL 93-05 and is consistent'with NUREG-1431, Revision 1, " Standard Technical Specifications, Westinghouse Plants." Based on SQN's ice condenser operating experience, reduced radiation dose, and outside industry experience as indicated in NUREG-1366, TVA is justified in extending the surveillance interval to 18 months as it applies to ice bed chemical analysis requirements. The staff agrees with the licensee and finds the proposed change in SR interval for chemical analysis to 18 months acceptable.
The licensee stated that the normal recommended temperature to test liquids established in the Annual Book of American Society for Testing and Materials j
Standard is 25*C.
Eliminating the temperature at which the pH is determined j
from the TS allows testing to be performed at the current recommended testing i
criteria.
The elimination of this excessive criteria also provides consistency with NUREG-1431, Revision 1.
Based on above, NRC the staff finds the deletion of the "20*C" testing requirement in the present SR acceptable to allow testing in accordance with the recommended testing criteria.
3.0 CONCLUSION
i Based on the above evaluation, the NRC staff finds the licensee's three propo' sed changes (i.e., lowering the minimum TS ice weight of each ice basket from 1,155 pounds to 1,071 pounds, changing the SR interval for chemical analysis from 12 months to 18 months, and deletion of "at 20*C" from the testing requirements) to be acceptable.
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4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Tennessee State official was notified of the proposed issuance of the amendments.
The State official had no comments.
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5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a i
facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements.
The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no.ti occupational radiation exposure.gnificant increase in individual or cumulative The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (62 FR 19835 dated April 23,1997). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 CONCLUSION
The Commission 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, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Raj'Goel j
Dated:
June 10, 1997 l
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