ML20112D247
| ML20112D247 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 01/04/1985 |
| From: | Musolf D NORTHERN STATES POWER CO. |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| GL-83-28, NUDOCS 8501140149 | |
| Download: ML20112D247 (3) | |
Text
o Northem States Power Company 414 Nicollet Mall Minneapohs. Minnesota 55401 Tewptione (612) 330 5500 January 4, 1985 Director Office of Nuclear Reactor Regulation U S Nuclear Regulatory Commission Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Response to NRC Request for Additional Information on Generic Letter 83-28 Items 4.2.1 and 4.2.2 The attached information is provided in response to your December 4, 1984 letter which requested additional information on Items 4.2.1 and 4.2.2 of Generic Letter 83-28 (Generic Implications of Salem ATWS Events).
Please contact us if you have any questions related to the information we have provided.
OdDR.
David Musolf Manager-Nuclear Support services DMM/EFE/ dab c: Regional Administrator-III, NRC NRR Project Manager, NRC Resident Inspector, NRC G Charnoff Attachment r
8501140149 850104 DRADOCK05000g fD I
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PRAIRIE ISLAND NUCLEAR GENERATING PLANT 1.
Item 4.2.1 - Periodic Maintenance Program for Reactor Trip Breakers 1.2 Periodic Maintenance Items a.
Ite.as 2, 6, 9,10 and 11 are included in the existing Reactor Trip Breaker Maintenance Procedure.
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b.
Items 3, 4, 5, 7 and 8 have been addressed in the past by the general inspection of breaker condition included in the reactor trip breaker maintenance procedure. A revision to the maintenance procedure presently under preparation will provide for improved documentation of these items and will address them in accordance with the guidance provided in the Westinghouse Maintenance Program.
c.
Item 14, like the items discussed in b., has been addressed in the past by the general inspection of breaker condition.
However, the Westinghouse procedure for semi-annual inspection of the positioning lever condition will not be specifically addressed by the revised reactor trip breaker maintenance procedure. Rather the condition of the positiening lever will be assessed during the refueling interval general inspec-tion of breaker condition and during the performance of cell interlock testing where the positioning lever is tested. This assessment of positioning lever condition will meet the intent of the Westinghouse guidelines.
d.
Items 1 and 13 will be included in the revised reactor trip breaker maintenance procedure.
e.
Item 12, Shunt Trip Attachment operation verification, will be incorporated into the appropriate procedures following completion of the shunt trip modifications.
The Prairie Island reactor trip breaker maintenance program will continue to be performed on a refueling outage basis (annual cycles). While the Westinghouse Maintenance Program for DB-50 Switchgear recommends a semi-annual frequency for these 15 maintenance activities,Section I of that document also states that the semi-annual activities may be extended to an annual basis if experience shows an annual maintenance frequency to be suf ficient and as long as 200 breaker cycles are not exceeded during that interval.
Prairie Island operating experience, which presently includes 34 test trips per reactor year for the main breakers and an average 6.8 manual or automatic trips per reactor year, shows that no reactor trip breaker has failed to operate upon demand in ten years of plant operation. This performance has been achieved using a breaker maintenance program that provides for maintenance on a refueling outage basis.
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Based on the past performance of the reactor trip breakers at Prairie Island and the preliminary results of the Westinghouse Owners Group (WOG) breaker testing, which do not indicate a need to reduce the maintenance interval, we find no basis.for increasing the frequency of breaker maintenance. Breaker maintenance based on the Westinghouse guidelines, but performed on a refueling outage basis, will assure a highly reliable reactor trip system at Prairie Island without causing unnecessary wear of the equipment from excessive testing.
1.2 Refueling Interval Maintenance Items a.
Items 1 and 2 will be included in the revised reactor trip breaker maintenance procedure. Item 2 was performed on the breakers during their last maintenance cycle.
b.
Items 3 and 4 are presently performed during pre-startup surveillance testing.
2.
Item 4.2.2 - Trending of Reactor Trip Breaker Parameters to Forecast Degradation of Operability.
The final WOG breaker life cycle testing recommendations related to trending are not yet available. This WOG work is being supported by NSP and final test results and recommendations will be issued in early 1985 in the form of a Westinghouse Topical Report (WCAP). NSP will provide a list of parameters to be trended within 60 days following the receipt of the WOG recommendations. The organization which will perform the trend analysis, how of ten the analysis will be performed and how the information derived from the analysis will be used to affect periodic maintenance will be discussed at that time.
l Paragraph 2.2 of your request for additional information specified breaker insulation resistance as a parameter that must be trended.
Through review of the Westinghouse Maintenance program for DB-50 Switch-l gear and discussions with the NRC Staff we find measurement of that parameter was only specified by Westinghouse for the DS-416 reactor trip breakers not for the DB-50 breakers. Discussions with Westinghouse indicate that measurement of breaker' insulation resistance is not necessary to assure the reliability of the DB-50 breakers. Such measure-ments are recommended for the DS-416 switchgear because of characteristics unique to their design. Such measurements were not considered necessary i
for the DB-50 switchgear.
l The imposition of the breaker insulation resistance measurement on DB-50 switchgear appears to be inappropriate and should be reconsidered. We ask that the imposition of this requirement be coordinated with the WOG in the same manner as the previous reactor trip breaker maintenance recommendations since it appears to be a new requirement being applied generically to all plants utilizing DB-50 switchgear. A coordinated review through the WOG would provide assurance that the proposed breaker insulation resistance measurement would indeed enhance the DB-50 reactor trip breaker reliability. i L