ML20246H046
| ML20246H046 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 04/28/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20246H044 | List: |
| References | |
| NUDOCS 8905150333 | |
| Download: ML20246H046 (5) | |
Text
_ _ _ _ _
UNITED STATES
. f.
~ g NUCLEAR REGULATORY COMMISSION j
WASHINGTON, D. C. 20555
%...../
~ SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 76 TO FACILITY OPERATING LICENSE NO. NPF-12 L
SOUTH CAROLINA ELECTRIC & GAS COMPANY SOUTH CAROLINA PUBLIC SERVICE AUTHORITY VIRGIL C. SUMMER NUCLEAR STATION. UNIT NO. 1 i
DOCKET NO. 50-395 1.
INTRODUCTION By letter dated September 16, 1986, South Carolina Electric & Gas Company (SCE&G or the licensee,) requested a change to Technical Specifications (TS) Section 3/4.6.1.6, " Containment Structural Integrity," of the Virgil C. Summer Nuclear Station, Unit No. 1.
The purpose of the proposed change was to modify the tendon testing program. Specifically, the licensee wished to delete tables 4.6-la, 4.6-Ib and 4.6-2 which list the tendons to be inspected. This action would also reduce the minimum required average tendon force for each tendon group and would modify the tendon force base values.
On August 18, 1987, the licensee provided additional information in response to a June 23, 1987 request by the NRC staff for additional information. Subsequently, following a May 24, 1988 meeting, the licensee consnitted in a July 22, 1988 letter to revise their Surveillance Procedure, STP-160.001, " Containment Tendon Test."
This revision would require that a report be submitted to the NRC within 90 days if trends in the average normalized tendon force versus time indicate that the average nonnalized prestress force for any group of tendons could fall below the minimum level required by TS prior to the next regularly scheduled surveillance.
Following a September 21, 1988 meeting, the licensee requested in a September 29. 1988 letter approval to revise the Bases to TS 3/4.6.1.6 to include the reference to Surveillance Test Procedure, STP-160.001, Attachment I, for the purpose of specifying the tendons to be inspected and establishing the base values and normalizing factor for those tendons.
~ 2.
EVALUATION We have reviewed the licensee's modified proposals. Associated with these proposals are the present TS which contain the following statement:
l If the inspections performed at 1, 3, and 5 years indicate no abnormal degradation of the tendon system, the number of sample tendons may be reduced to 3 dome, 3 vertical,.and 3 hoop for subsequent inspection. Upon
.8905150333 890428 PDR ADOCK 05000395
.P-PDC
s
. r the completion of the five year inspection, the results of the first three inspections shall be evaluated to determine if an abnormal condition is evident for the tendon system.
Based on the conclusions of this evaluation, the sample tendons with their Base Values and Norwelizing Factors will be specified for all subsequent inspection.
However, the licensee has completed the first five year inspection and has discovered tenden prestress losses larger than predicted. These losses can be interpreted as an indication of abnormal degradation. On the basis of the evaluation performed, the licensee has proposed changes to the TS as presented
- below, a)
Modification of The Tendon Testino Program The licensee has proposed in TS 4.6.1.6.1.a that, instead of 15 tendons monitored in the first three surveillance, as specified in the TS, 21 tendons (6 dome, 7 vertical and 8 hoop) will be selected for the 10th year surveillance and 9 tendons (3 dome, 3 vertical and 3 hoop), will be sampled for the subsequent five year interval surveillance, with one tendon from each group kept unchanged throughout the. surveillance.
After a carefbl examination of the current TS, we feel that the proposed change in the TS is unnecessary since the current TS require a minimum of 15 sample tendons for inspections after 1, 3 and 5 years if there is abnormal degradation. The selection of 21 sample tendons in the 10 year inspection is in conformance with the current TS. The staff believes that the proposed change to TS 4.6.1.6.1.a is unnecessary.
Therefore, the staff does not approve this proposed change.
b)
Elimination of Tables 4.6-la, 4.6-Ib and 4.6-2 The licensee has proposed the deletion of Tables 4.6-la, 4.6-1b and 4.6-2 since these tables were provided to cover tendons to be inspected for the first three surveillance. These surveillance have been completed.
For future surveillance, most of the sample tendons to be inspected will be selected randomly and the inclusion of these tables for designated sample tendons no longer serves any useful purpose. To supplement the deletion of the tables, the licensee has revised TS Bases 3/4.6.1.6 to include Station Su teillance Test Procedure STP - 160.001, " Containment Tendon Test," Attachment I, Revision 2.
This procedure includes the tendons to be sampled, the minimum required average tendon forces and the tendon base values for the tendons to be inspected. We agree with the reference in the TS Bases to the station surveillance test procedure since it fixes in time the tendons to be inspected, the minimum required average tendon forces and the tendon base values.
Therefore, the proposed change to the Bases 3/4.6.1.6 is approved.
=
3-i.
c)
Reduction of the Minimum Required Average Tendon Forces The licensee has' proposed reductions in the minimum required average tendon forces in TS 4.6.1.6.b from 1195. kips.to 1160 kips for vertical tendons, from 1115 kips to 1063 kips for dome tendons and from 1181 kips to.1000 kips for hoop tendons.
The reduction has been made-based on the observation that the tendon forces will increase as the tendons elongate when subjected to the postulated internal pressure of 1.5 times the design pressure for which the tendon forces are designed.
For the hoop tendons, additional reduction has been realized as a' result of more accurate analysis which eliminates some of the unrealistic conservatism in the original calculation procedure.
The staff has checked the detailed computation on the required tendon forces as provided by the licensee in support of.the reduction and found the reduction to be reasonable and, therefore, acceptable.
d)
Modification of the Tendon Force Base Values The tendon force in each tendon group must meet not only the minimum-required tendon force, but also the tendon force base value established for the group on the basis of the age of the containment, structure at the time of surveillance. The tendon force base value is affected by creep and shrinkage of concrete and relaxation of the tendon wire, and is, therefore, time dependent. According to the current TS, the tendon force.for each group must be equal to or greater than 95% of the base value established for the time when surveillance is performed. The results of the third tendon surveillance indicated that most of the sample tendons cannot meet the 95%-of-the-base-value criteria specified in current TS. An investigation was conducted by the licensee. They determined that the reduction in the tendon forces is mainly due to the actual tendon wire stress relaxation being larger than that originally used in the calculation of the base values. From the tests done at Lehigh University, the licensee determined that the prestress loss due to stress relaxation should be about 12.8% instead of 8.5%
originally used. We have reviewed the.information provided by the licensee for tendon wire stress relaxation. We agree that the use of 12.8% is reasonable. On that basis, the licensee proposed to revise the tendon force base values by using the 12.8% stress relaxation for computing prestress loss at 40 years and also the non-interaction method instead of the interaction method originally used to calculate the loss due to stress relaxation at the time of each surveillance.
j The difference between the interaction and non-interaction methods can be explained as follows:
(1) In the interaction method, the time-dependent concrete strains due to shrinkage and creep of the l'
concrete are used to interactively adjust the stress relaxation f
property curve of the tendon wire which is, by definition, based on l
g
l-
,.m
. r
- a. constant strain test.
(2) In the non-interaction methods, the individual losses due to concrete elastic shortening, shrinkage and creep, and steel relaxation'are combined without considering the l
interaction.between the concrete and prestressing steel. However, I
we consider that the interaction method gives more accurate results.
From the example of computation provided by the licensee, the maximum difference between the non-interaction' method and the interaction method in predicting tendon loss is about 5%, which is within the-5% to 10% range of acceptable variation of the tendon forces.
Further..the non-interaction method predicts greater losses than l-the interaction method which is judged to be conservative. Therefore, l
the use of the non-interaction method in calculating the loss of-prestress due to stress relaxation is justified. We concur with the change of method as revised.
e)
Consideration of Tendon Force Trend The results of a tendon surveillance may indicate that the average l
normalized tendon force for any group is projected to be below the minimum required average tendon force for that group before the next surveillance. We requested, and the licensee in their July 22, 1988-letter committed to, modification of STP 160.001 to requjre the filing of. a report for abnormal results to the NRC within 90 days after the completion of the tendon surveillance. Such a. report is needed only if the average nomalized tendon force for any group is projected to be below the minimum average tendon force prior to the l
next surveillance.
3.0 ENVIRONMENTAL CONSIDERATION
This amendment involves a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes to the surveillance requirements. The 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 off site, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Comission has previously
)
issued a proposed finding that this amendment involves no significant hazards consideration, and there has been no public comment on such finding. Accordingly, this amendment meets the eligibilit categorical exclusion set forth in 10 CFR Section 51.22(c)y criteria for (9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental i
assessment need be prepared in connection with the issuance of this amendment.
2 9
4.0 CONCLUSION
1 The Commission made a proposed determination that this amendment involves no significant hazards consideration, which was published in the Federal Register on November 5, 1986 (51 FR 40282) and consulted with the state of South Carolina. The additional information provided by the licensee in correspondence dated August 18, 1987 and July 22, and September 29, 1988 clarified certain matters in response to questions from the staff and contained an additional commitment for a report. This correspondence did not change substance of the amendment request.
No public comments were received, and the State of South Carolina did not have any comments.
We have 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 Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
- Principal Contributor
C. P. Tan Dated: April 28,1989 4
I l
l
. _ _ _ _ - _ _ _