ML20127E400
| ML20127E400 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 01/11/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20127E376 | List: |
| References | |
| NUDOCS 9301190284 | |
| Download: ML20127E400 (7) | |
Text
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'o UNITED STATES
!" n NUCLEAR REGULATORY COMMISSION
{ WASHINGTON, D. C. 20555
\....*/
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0. 60 TO FACILITY OPERATING LICENSE N0. DPR-21 NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT 1 DOCKET NO. 50-245
1.0 INTRODUCTION
By letters dated September 29, November 4, and November 6, 1992, the licensee requested a one-time exemption and Technical Specification change to provide relief from the accelerated Type A containment integrated leak rate test (CILRT) frequency required by Appendix J to 10 CFR Part 50 when two consecutive Type A tests have failed to meet their acceptance criteria.
Appendix J to 10 CFR Part 50, Paragraph III.A 6(b), requires, in part, that if two consecutive periodic Type A tests fail to meet the applicable acceptance criteria in III. A 5(b), a Type A test shall be performed at each plant-shutdown for refueling or approximately 18 months, whichever occurs first, until two consecutive Type A tests meet the acceptance criteria in III.A.5(b),
after which time the normal retest schedule specified in III.D (three tests in 10 years) may be resumed.
However, Information Notice (IN) No. 85-71, " Containment Integrated Leak Rate Tests," states that if Type B and C local leakage rates constitute an identified contributor to the failure of the "As-Found" Type A test, the licensee may submit a Corrective Action Plan (CAP) with an alternate leakage test program propose.1 as an exemption request. If the submittal is approved and an exemption granted, the licensee may implement the corrective action and alternate leakage rate test program in lieu of the required increase in Type A test frequency incurred after the failure of two successive Type A tests.
Millstone Unit 1 experienced failures of the "As-Found" Type A tests in 1987 and 1991. In both instances, Type C local leakage rates (of containment isolation valves) were the reason for the "As-Found" failures. Due to the l failure of two consecutive periodic Type A tests, Millstone Unit 1 is subject
! to the increased Type A test frequency requirements of both Appendix J and the l plant's Technical Specifications. These accelerated testing requirements I
require that Type A tests be performed at approximately 18-month intervals.
l The last failed Type A test was performed on June 27, 1991; therefore, a Type A test is currently required to be performed during the present operating cycle, in late December 1992 or January 1993. The plant has experienced I
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various forced outages which have considerably lengthened the present operating cycle, such that the next refueling outage is scheduled for February 1994. In order to perform thit required Type A test, Millstone Unit I would have to undergo a forced shutdown. Such a shutdown would result in an increase in occupational radiation exposure and would entail a significant expenditure of resources. Therefore, the subject exer.ption is being requested to gain relief from the accelerated testing requirements of Appendix J, Paragraph Ill.A.6(b), and return to the normal test schedule of three tests in 10 years. With the normal test schedule, Type A tests would be scheduled to be performed at the next two plant shutdowns for refueling (currently expected to be in 1994 and 1996).
The plant's Technical Specifications repeat the requirement of Appendix J, so the licensee has also proposed a change to the Technical Specifications in order to provide the same relief being requested in the exemption.
2.0 EVALVATION The licensee's justification for the proposed exemption is that the Type A tests failed in the "As-Found" condition in 1987 and 1991 because of a few specific penetrations which have (except for one) been demonstrably corrected; corrective action has been taken on the remaining penetration, but-the success of the corrective action has not yet been fully confirmed. For the one potentially questionable penetration, the licensee will per' form mid-cycle Type C testing. Further, additional corrective action will be taken at the next refueling outage. The following paragraphs provide details of the problems experienced and the corrective actions in-place and planned.
2.1 Analysis of 1987 and 1991 Tyne A Test Results The following table provides the "As-Lef t" leak rates for the 1987 and 1991 Type A tests, and also the "As-Found" leak rates that would have been present if the problem penetrations (valves IC-6 and IC-7 in 1987, and penetration X-25/202D [ valves AC-7 through AC-12] in 1991) had been excluded. This shows that the problem penetrations were the cause of the "As-Found" failures, because without them both the "As-Found" and "As-Left" leak rates would have been less than 0.9 wt.%/ day, which equals 0.75 La, the acceptance criterion provided by Appendix J (where La is the maximum allowable leakage rate at peak containment pressure during a design basis LOCA, the value of which is specified in the plant Technical Specifications and used in the plant accident analysis). Thus, the licensee's CAP has identified and addressed the problem penetrations.
"As-Left" "As-Found" Leak Rate Leak Rate minus problem penetrations 0.75 La (wt.%/ day) (wt.%/ day) (wt.%/ day) 1987 0.441 0.623 0.9 1991 0.4077 0.619 0.9 I
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I -3 2.2 Corrective Action Plan 2.2.1 Corrective Action Taken to Address 1987 "As-Found" Type A Test Failure The 1987 "As-Found" Type A test failed due to excessive leakage from valves IC-6 and IC-7 (Isolation Condenser System vent valves) during the performance of the Type A test. Prior to 1987, these valves were being maintained under the plant's preventive maintenance program. This preventive maintenance program entailed inspection and modification (if required) of the valves during each outage in which a Type A test was scheduled. Due to a personnel error in properly adjusting the valve during reassembly, the va?ves were not properly seated and did not perform the required isolation function during the Type A test. The valves were isolated and the test was successfully completed.
Valves IC-6 and IC-7 were subsequently properly set and their local leakage ,
was demonstrated to be acceptable prior to startup. In addition to properly adjusting these valves in 1987, the penetration was modified to allow it to be local leak rate tested (LLRT), or Type C tested. Due to the modifications it was possible for the first time to measure local leakage from the penetration.
Valves IC-6 and IC-7 are now included in Millstone Unit l's LLRT program. The modifications which allow these valves to be Type C tested in accordance with Appendix J have provided further assurance that the valves are properly
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adjusted. Any error in valve adjustment would be identified and corrected during the performance of the LLRT. The results of subsequent LLRTs for these valves indicate that the actions taken in 1987 were successful in addressing the leakage problem. No subsequent maintenance has been required to be performed for these valves, to maintain their leak tightness, since the 1987 adjustment. Results for these valves during the 1989 and 1991 LLRTs were 0.210 SCFH and 0.280 SCFH for the "As-Found" condition (0.0005 wt.%/ day and 0.0007 wt.%/ day, respectively). This shows that the acceptance criterion of 18.8 SCFG (0.045 wt.%/ day) was met with significant margin for these LLRTs (Millstone Unit 1 is unusual in that Technical Specifications provide an individual leak rate limit for each penetration). The corrective action taken for this cause for failure of the 1987 "As-Found" Type A test demonstrates the success of the corrective actions implemented for valves IC-6 and IC-7, 2.2.2 Corrective Actions Related to the 1991 "As-Found" Type A Test Failure The 1991 "As-Found" Type A test failure was caused by leakage through valves in the Atmospheric Control System. Corrective actions for these valves, which began in 1985, are described below.
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A. Atmospheric Control System Valves--1985 Corrective Actions 1 Penetration X-26/205 (Atmospheric Control System valves AC-4, AC-5, AC-6, AC-17) and X-25/2020 (Atmospheric Control System valves AC-7 through AC-12) failed their respective LLRTs during the 1985 refueling outage. As reported in Licensee Event Report 85-023-01, the excessive leakage for both penetrations X-25/202D and X-26/205 was attributed to worn seat rings for all valves. The poor performance of these penetrations was determined to be the result of an internal inventory control problem. It appeared that the seat rings for the Allis-Chalmers butterfly valves were all being stored in one area of the storeroom. These valve seats are supplied in both natural rubber and Nordel (DuPont trade name). The natural rubber is for use only in cooling water systems and is not suitable for the Atmospheric Control Systems valves.
All of the Allis-Chalmers butterfly valve seats in the Atmospheric Control System were replaced with Nordel seat rings during the 1985 outage.
Subsequently, under the preventive m:.intenance program, 50% of the seat rings are replaced each outage. Visual inspection of the seat rings has indicated no significant degradation or signs of wear. In order to avoid similar occurrences, quality assurance requirements for packaging, identification, and shelf life have been established as part of inventory control of Atmospheric Control System valve seat rings.
Although penetration X-25/2020 has failed since 1985 (see section B below),
penetration X-26/205 has passed all the "As-Found" LLRTs sfnce the problem with valve seats was identified and corrected.
B. Corrective Actions Taken to Address 1991 "As-Found" Type A Test Failure Penetration X-25/202D (Atmospheric Control System valves AC-7 through AC-12) has failed its LLRTs for the following years: 1982, 1985, 1987, 1989, and 1991. In addition, penetration X-26/205 (Atmospheric Control System valves AC-4, AC-5, AC-6, AC-17) failed the LLRT during' the 1985 refueling outage.
Penetrations X-25/2020 and X-26/205 are multi-valve penetrations. When an LLRT is performed on these penetrations, all of their associated valves are subjected to the test pressure. These multi-valve penetrations are treated-as a single penetration with an acceptance criteria of 18.8 SCFH (0.045 wt.%/da.y) per Technical Specifications.
The 1991 "As-Found" Test A test failed as a result of excessive Type C leakages experienced from penetration X-25/202D, Other penetrations did not meet the individual penetration LLRT leakage rate acceptance criterion in 1991; however, these other penetrations only slightly exceeded the LLRT acceptance criterion and their combined leakages were not the identified contributor to the 1991 "As-Found" Type A test failure.
Through extensive investigation and testing, two problems were identified as the probable cause of the continued poor performance of penetration X-25/202D.
This paragraph discusses the corrective actions taken to address the first problem and section C. (below) discusses the corrective actions taken to address the second problem. The first problem noted was that there was a slight shift in the actuator mounting bracket each time the valve was cycled.
This shif ting affected the repeatability of the valve closing position and as a result, consistent values fcr leakage rates could not be established. Since the actuator is fixed to the valve through a tube steel mounting bracket, and th9 bracket is attached to the valve using only two mounting bolts, the clearance in the bolt holes in the bracket allowed a slight shifting of the actuator relative to the valve. Two modifications were made to all mounting brackets for the Atmospherk Control System butterfly valves for penetration X-25/2020. The first modification was to pin the mounting bracket to the valve body using two 1/4" stainless steel dowel pins to prevent shifting of the bracket. The second modification was to add stiffeners to the tube steel bracket to preclude any possibility of buckling that could affect the valve closure position. Similar modifications are planned for the Atmospheric Control System valves on penetration X-26/205 (Valves AC-4. AC-5, AC-6, AC-17) and will be accomplished during the next refueling outage to further enhance its ability to meet LLRT acceptance criteria.
C. Atmospheric Control System Valves--Additional 1991 C,orrective Actions in addition, during the modification of valves AC-3A and AC-10, it was noted that the carbon steel vane of the valve had a " scale" buildup producing a rough surface. The design of these valves is such that the vane slides into the seat ring to effect the full closure position. The rough surface on the vane could act as an abrasive surface, and over r.everal cycles of operation would result in the deterioration of the Nordel seat ring. The carbon steel vanes for these two valves were replaced with stainitss steel vanes. During the next scheduled refueling outage, as part of the plan to improve the reliability of penetrations X-25/2020 and X-26/205, the carbon steel vanes in the remainder of the Atmospheric Control System valvus will be removed and replaced with stainless steel vancs.
Excessive maintenance problems had been experienced with valves AC-9 and AC-12 (2" Dezurik plug valves). Therefore, these plug valves were replaced during the 1991 refueling outage with new valves as part of the program for maintaining the integrity of this penetration.
The licensee believes that with the corrective action taken on penetration X-25/2020 along with the planned modifications to the remainder of its associated valves, this penetration will maintain its capability to perform its containment isolation function. As discussed above, the Atmospheric Control System valves associated with penetration X-26/205 will also have I
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their valve vanes replaced and will undergo mounting bracket modifications, thereby improving the reliability of the penetration. Further, the valves in penetration X-25/2020 will undergo mid-cycle LLRT, as discussed in section 2.2.3 below.
It was noted above that the vane of valve AC-3A was replaced in 1991. Valves AC-3A and AC-3B are associated with penetration X-205. However, this penetration did not contribute to the 1991 "As-Found" Type A test failure.
The vane of valve AC-30 will also be replaced during the next refueling outage. The vanes for these valves require replacement because the valves are prone to the same " scale" buildup problem experienced with the other Atmospheric Control System butterfly valves.
2.2.3 Alternate Leakage Test Program An alternate leakage test program is not proposed for Isolation Condenser System vent valves IC-6 and 10-7. These valves were properly adjusted in 1987 and no subsequent maintenance has been required to assure their leak tightness. In addition, modifications made in 1987 to allow Type C testing of these valves will assure that any future valve adjustment problem is identified. As noted above, the success of the previously implemented corrective actions for these valves has been demonstrated during the 1989 and 1991 LLRTs. Therefore, the licensee has determined that an alternate leakage test program is not necessary for these valves, and the staff concurs.
The licensee will perform LLRT testing of the Atmospheric Control system valves associated with penetration X-25/2020 midway through the present operating cycle (late April of 1993; the next refueling outage is scheduled for February 1994). This mid-cycle LLRT will provide further data which should indicate that the corrective actions taken to address this penetration have been effective. Further corrective actions will be taken if the test results do not provide reasonable assurance that Millstone Unit I can pass the 1994 "As-Found" Type A test.
Since penetration X-26/205 has passed the 1987, 1989, and 1991 LLRTs, an alternate leakage test program is not proposed for this penetration. Due to the corrective actions that have already been taken and the commitment to replace the remainder of the valve vanes during the next refueling outage, the licensee has a high degree of confidence in the containment isolation function of the valves associated with penetration X-26/205. The staff concurs.
2.3 Dyerall Based on the foregoing evaluation, the staff finds that the licensee has identified the problem penetrations that caused the Type A test failures in 1987 and 1991, and has instituted an effective CAP to address these problems.
There is reasonable assurance that the containment leakage-limiting function
will be maintained and the staff finds that a forced outage to perform a Type A test in December 1992 or January 1993 is not necessary. Also, the ,
normal Appendix J Type A test schedule (three tests in 10 years) will require Type A tests at the next two refueling outages. Therefore, the staff finds .
that the requested exemption and associated Technical Specification changes are acceptable and the plant may resume the normal Type A test schedule (three teste in 10 years) given in Section IU ., of Appendix J.
3.0 SJAJE CONSULTATION In accordance with the Commission's regulations, the Connecticut State . .
official was notified of the proposed issuance of the amendmont. The State official had no' comments.
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4.0 ENVIRONMENTAL C0t{S10 ERAT 10N The amendment 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 significant increase in Individual or cumulative occupational radiation exposure. 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 (57 FR 55009). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR Sl.22(c)(9). Pursuant to 10 CFR 51.22(b) na environmental impact statement or environmental assessment-need be prepared in connection with the issuance of the 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 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: James Pulsipher Date: January 11, 1993 I
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