ML17223B199
| ML17223B199 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 05/23/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17223B198 | List: |
| References | |
| NUDOCS 9106040128 | |
| Download: ML17223B199 (6) | |
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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON,Q. C. 20565 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 50 TO FACILITY OPERATING LICENSE NO.
NPF-16 FLORIDA POWER 8t LIGHT COMPANY ET AL.
ST.
LUCIE PLANT UNIT NO.
2 DOCKET NO. 50-389
- 1. 0 INTRODUCTION By letter dated October 24,
- 1988, as supplemented June 1, 1989, October 19,
- 1989, March 27,
- 1990, November 8, 1990 and modified December 18, 1990, Florida Power and Light Company (FPL, the licensee) proposed to amend Facility Operating License NPF-16 to relax the maximum primary loop resistance temperature detector (RTD) delay time from 8.0 seconds to 16.0 seconds as shown in Table 3.3-2 of the Technical Specifications.
This change would provide increased operational flexibility by decreasing problems encountered with replacement of the RTDs.
Also, the Technical Specifications (TS) require RTD response time tests to be conducted approximately every 18 months to check the RTDs used for reactor protective instrumentation.
The loop current step response (LCSR) time test method is currently used.
During the tests, the licensee has encountered difficulties with RTD installation and removal because of the physical location of the support structures which interfere with access to some RTDs.
Also, the close proximity of the RTD element to the thermowell increases the potential for galling, which has a negative effect on RTO response time capabilities.
Therefore, the licensee desires more flexibility by allowing an increase in allowable response time to decrease the necessity of having to replace the RTOs when they reach the 8.0 second response time limit.
2.0 EVALUATION As a result of staff's request for additional information, the licensee responded by letters dated June 1, 1989, October 19, 1989, March 2?,
1990 and November 8, 1990.
The licensee stated that the original accident analysis was based on a
total RTD response time of 8 seconds, but that the current accident analysis incorporates a total RTD response time of 16 seconds.
Information was presented on the past results of RTO response time tests at the St. Lucie Unit 2 plant in the June 1, 1989 letter.
The older RTDs were manufactured by Rouge and de Forest Company (RdF) for which the RTD response time averaged approximately 6.0 seconds (the overall spread was from 2.0 to 7.2 seconds).
The largest difference in repeatabi lity at a given location was 1.35 seconds for the RdF RTOs.
The new RTOs installed at St. Lucie Unit 2 are manufactured by the Weed
- Company, for which the RTO response time has averaged a value of 3.0 seconds (the ssosooosas 9io523 PDR ADDCK 05000389 P
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W overall spread was 2.0 to 5.0 seconds).
The largest difference in drift/
repeatability at a given location was shown to be 2.81 seconds for the Weed RTDs.
The licensee indicated that they do not have a further analysis or a breakdown of data that determines plant-specific electronic delay or lag time.
The value for the total response time needs to consider other phenomena in addition to the RTD sensor response time alone.
Specifically, it is common to experience, a 1.0 to 2.0 second delay in response time due to electronic delay.
According to NUREG-0809, "Review of Resistance Temperature Detector Time Response Characteristics,"
August 1981, the LCSR method for response time checking is for field use and is not as accurate as a laboratory test.
The LCSR method is accurate only to within 10%.
- Also, RTDs experience some drift in response time during the 18-month interval between tests.
There may also be the repeatabi lity differences mentioned above.
In sum, the electronic delay and other uncertainties, such as accuracy of the LCSR method and aging/drift/
repeatabi lity, have to be accounted for to obtain the total RTD response time.
The licensee's letter of November 8, 1990 indicated that a
new analysis was performed in October 1990 in which an RTD response time of 19.0 seconds was found to be acceptable.
The analysis included conservative values for initial core power, coolant inlet temperature, initial reactor coolant system (RCS)
During a telephone conference held on November 28, 1990, the licensee stated that the limiting accident for this analysis was the excess load event.
Although the licensee indicated that the margin is estimated to be 3.0 seconds, specific breakdowns of the margin elements were not given.
For the TS, the largest acceptable RTD sensor response time can be obtained by working backwards from the 19.0 second analysis value of RTD response time and subtracting time values for LCSR accuracy and aging/electronic drift/repeatabi lity.
Using conservative estimates, this amounts to 19.0 - (1.5 + 3.5)
= 14.0 seconds.
For St. Lucie Unit 2, the Weed RTD response time average is 3.0 seconds, as shown in the data provided by the licensee in the letter dated June I, 1989.
Therefore, the 14.0 second response time allows approximately 11.0 seconds (14.0 - 3.0 seconds) to be available for operational flexibility.
The associated Bases pages are also being revised to reflect the change.
In summary, the licensee's original request was for increasing the allowable RTD delay time from 8.0 seconds to 16.0 seconds.
Based on the above evaluation, the staff believes that 14.0 second delay time is more appropriate and acceptable.
By letter dated December 18, 1990, the licensee agreed with the staff and accordingly modified its request.
As a result of this modification of the
- request, the staff finds the proposed change acceptable.
3.0 STATE CONSULTATION
Based upon the written notice of the proposed amendment, the Florida State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.
The NRC staff has determined that the amendment involves no significant
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increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding (53 FR 46146 and 56 FR 6873).
Accordingly, this amendment meets 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 this amendment.
5.0 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 wi 11 be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment wi 11 not be inimical to the common defense and security or to the health and safety of the publ,ic.
Principal Contributor:
H. Balukjian Date:
flay 23, 1991
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