IR 05000423/1986029
| ML20215E032 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 09/16/1986 |
| From: | Gregg H, Wiggins J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20215E029 | List: |
| References | |
| 50-423-86-29, NUDOCS 8610140405 | |
| Download: ML20215E032 (7) | |
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U.S. NUCLEAR REGULATORY COMMISSION
REGION I
Report No.
50-423/86-29 Docket No.
50-423 License No.
NPF-49 Licensee: Northeast Nuclear Energy Company P. O. Box 270 Hartford, Connecticut 06141-0270 Facility Name: Millstone Nuclear Power Station, Unit 3 Inspection At: Waterford, Connecticut Inspection Conducted: August 18-22, 1986 Inspector:
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u 9 ~ldM Har d'I.GregggadReac r Engineer date Approved by:
C<f% e 4/ -/d O J. T/./Wiggins, phi
, Materials and date Pc6 cesses Sect'io, Engineering Branch, DRS Inspection Summary:
Inspection on August 18-22, 1986 (Inspection Report Number 50-423/86-29 Areas Inspected:
Routine unannounced inspection to review problem areas associated with Snubbers, Power Operated Relief Valves (PORVs), and Main Steam Safety Valves (MSSVs); review licensee's activities regarding these problem areas; review equipment and make independent observations and determinations of the problems; and to assess effectiveness of the licensee's actions.
Results: No violations were identified.
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DETAILS 1.0 Persons Contacted 1.1 Northeast Nuclear Energy Company (NNECO)
- K. Burton, MP3 Operations Supervisor
- G. Closius, QA/QC Supervisor S. Dessert, Maintc7ance Mechanic
- J. Harris, Engineering Department Head M. Hess, Assistant Engineering Supervisor S. Jonasch, Maintenance Engineer L. Loomis, ISI Coordinating Engineer
- W. Romberg, Station Superintendent
- R. Rothgeb, Acting Maintenance Manager J. Short, Maintenance Foreman 1.2 Northeast Utilities Service Company (NUSCO)
P. Quinlin, Piping System Engineer B. Roy, Piping System Engineer
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1.3 Westinghouse Nuclear Technical Service Division J. Moore, Site Operations Consultant 1.4 Westinghouse Site Engineering Team E. Covin, Mechanical Engineer 1.5 Paul-Monroe Incorporated T. Beddingfield, Field Service Representative 1.6 U.S. Nuclear Regulatory Commission
- E. Conner, Acting Resident Inspector
- Denotes those present at exit meeting.
2.0 Snubbers - First Visual Inspection The inspector reviewed the results of the first visual inspection of snubbers after commencing Power Operation, conducted by the licensee as required by Technical Specifications (TS).
I Prior discussion of this topic was made in paragraph 3.11 of IR 50-423/86-21 which described the occurrence of snubbers failing visual acceptance criteria due to boron build-up from leaking valves subsequent functional testing and preliminary evaluations. The background information as
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excerpted from the licensee's status report of August 8,1986 showed that, out of the 1138 Pacific Scientific (PSA) mechanical snubbers visually inspected, 262 didn't meet the acceptance criteria.
Initial evaluations of the 262 determined that all but 45 were acceptable.
For these remain-ing 45, functional testing and additional evaluation were deemed necessary.
The licensee replaced all 45 snubbers with spares that were tested and found to be in as received condition prior to installation.
The inspector reviewed the visual inspection data listing of the 45 removed PSA mechanical snubbers that were functionally tested to verify function-ability and enable a final determination of operability.
The data identi-fied each of the 45 snubbers by serial #, mark # and size and also included details of failure mode, NCR's, and stroking information. The listing showed that piping system operability at each snubber attachment was deter-mined satisfactory. The one snubber (3RCS-1-PSSP-468) that was found to be locked up was determined inoperable and final determination of snubber operability for the 15 snubbers which had drag forces in excess of 5% has not as yet been evaluated.
The inspector discussed the snubber inspection details and the methodology used in making the determination of system operability with NNECO and NUSCO engineering personnel. Additionally, calculation 79-23-747-GP applicable to snubbers 913, 914, and 110, and calculation 79-236-748-GP applicable to snubbers 468 and 442 were reviewed.
In the first calcula-tion, the effects of increased drag were shown to be not significant (i.e.
the code allowable stresses were not exceeded and the usage factor change was within 1%).
In the second calculation which was in process at the time of the inspection and which included the locked-up snubber, the stresses were shown to be within the code allowables, however, the usage factor, increased 8%. The base calculation 12179-NP(8)-X10800 has to be modified to reflect this increased usage condition.
The inspector also noted that the 3" x 3" x 2" tee at PT 120 on ISO 108A was the point of highest stress.
The licensee had contracted with Paul-Monroe Incorporated to disassemble the high drag snubbers and to make determinations of the cause of problems.
This work is to be performed with NNECO maintenance and NUSCO engineering overview.
The Paul-Monroe representative was on site and the work was ready to commence. The findings will be utilized in the determination of snubber operability which in turn affects the TS visual inspection period frequenc.
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This item remains unresolved pending the licensee's disassembly and deter-mination of cause of problem and disposition of snubber operability as required by TS; and NRC review of the finalized licensee's activities regarding this issue (50-423/86-29-01).
3.0 Power Operated Relief Valves (PORVs)
Millstone 3 has (2) 3 x 6 flanged solenoid operated PORVs. These valves were manufactured by Garrett Corporation (a manufacturer of aircraft equipment) and utilized by Westinghouse in the most recent PWR plants.
The Garrett PORV product line has since been purchased by Crosby Valve Company.
The inspector determined that Millstone Nuclear Power Station 3 performed major design rework of the PORVs prior to initial start-up (end of 1985 and early 1986) that was initiated by a Westinghouse FCN and c'one per Crosby procedure. The work included remachining of the bonnet, external porting of the solenoid piping, remachining of the body-bonnet gasket surface, remachining of the solenoid gasket surfaces, remachining of the cage ID and land, remachining of the plug OD, installation of a centering ring for the bonnet gasket, and changing of the gasket design from the thin grafoil rings to a flexitallic type at the body / bonnet and the sole-noid/ body joints. The inspector also determined that some internal sole-noid work was also done by Crosby at that time.
Significant leakage problems were evident through both valves from the time of start-up testing (plant went commercial 5/1/86). Due to the high leak rate, PORV 456 was isolated on 4/15/86 and PORV 455A was isolated on June 6, 1986; testing on 6/6/86 showed 1.1-1.2 gpm leakage thru 455A and 456 wasn't tested. At this time there was some thought that slight leak-ing of pressurizer safety valves may be contributing to the leakage attri-buted to the PORVs. Another problem, that of slow closing time, was also noted during surveillance testing of the PORVs.
After the July 24, 1986 shutdown, both PORVs were removed and were opened, inspected, and some repairs were made. At this time all the pressurizer safety valves were also changed out. The inspection of PORV 456 deter-mined that there was substantial steam erosion on one section of the plug and on the seat (the plug was worse). The socket head cap screws that hold the seat in place were loose (these screws also apply load to the underseat gasket). Valve 455A was taken apart next and plug and seat erosion was evident but to a lesser degree and on this valve the seat screws were tighter.
The licensee remachined the plugs and seats and spare underseat gaskets were installed upon reassembly. A Crosby representative was on site for this work. The inspector noted that plug and seat were lapped to each other and blue checked but this is done outside of the valve per the vendor's procedure. However, when these parts are reinstalled in the
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valve there is no check of any alignment or seating compatibility. The inspector observed one of the used underseat gasket and noted there was evidence of leakage across both top and bottom faces of this gasket, and also that the grafoil rings were not there. The restricting orifice outlet in the solenoid discharge porting to the main valve outlet was also removed during this repair effort in order to shorten the valve stroke time.
The inspector observed a new underseat gasket and noted that it was sprung in many locations (wasn't flat), the thin 1/8" wide bands of grafoil (2 on one side, one on the other side) overlapped at 2 joint locations and the gasket surface was raised in these areas.
Based on observations of
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both an old and a new gasket and the joint design, the inspector's deter-mination was that this gasket design appeared inadequate and will be a leak path. Other leak paths could occur in the seat or underseat arrange-ment in the solenoid. The solenoid was not disassembled due to unavail-ability of a spare.
Testing to find any of the possible leak paths through the main valve or the solenoid valve wasn't performed.
After restart of the plant on 8/17/86, measurements and calculations determined leakage through PORV 456 to be 0.86 gpm and through 455A to be 0.25 gpm. At the time of the inspection exit, the plant was being ope-rated with PORV 455A isolated (the highest leaker) and 456 unisolated.
The inspector verified that the leak rate purchase specification was 9cc/
hr. for these valves and this is thousands of times less than the actual leakage. The inspector concluded that a properly designed and repaired PORV should not leak at these observed rates, therefore, the design is suspect.
One positive feature observed by the inspector is that these PORVs are flanged (the only flanged PORVs to the inspector's knowledge at any U.S.
plant). Being a flanged valve enabled rapid removal and could also enable bench testing to verify leak paths.
The inspector also, determined that 10 additional RTDs were installed in the safety and relief valve piping.
They were installed close to the valve outlets (one on bottom and one on top of the pipe) in an attempt to determine leakage location.
The inspector expressed concerns about reporting requirements relating to the Crosby / Garrett PORV design and leakage problems.
In discussions with plant personnel, their position was that operation with leaking PORVs was within the TS requirements and reporting wasn't required. The inspector
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was concerned that other new plants with these same valves should be aware of the problem areas, design deficiencies, and design changes.
This becomes even more important if a different NSSS vendor has used this same type of valve. The inspector indicated that reporting per Part 21 should be evaluated.
The PORV final fix hasn't been completed (from information obtained during the inspection, the vendor had not developed corrective action for problems with the underseat gasket; leak paths through main valve and solenoid were not determined; new solenoids on order haven't been received; etc.) and more PORV work is scheduled for the February 1987 outage.
This item remains unresolved pending the licensee's successful completion of the PORV repairs, acceptable resolution of the reporting issue, and NRC review.
(50-423/86-29-02).
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4.0 Main Steam Safety Valves (MSSVs)
The inspector reviewed the licensee's effort relating to improper ring settings of the Dresser model 3707 RAX-RT25-XTF1 MSSVs.
Improper MSSV ring setting was the subject of IE Notice 86-05 and there was also discus-sion of this matter in paragraph 3.9 of IR 50-423/86-21.
Out of 25 MaaVs inspected by the licensee (5 spares and 20 installed), no two ring settings were alike. The lower ring setting varied from -5 to-46 notches while the upper ring setting varied from +45 to -178 notches.
Furthermore, on four valves the upper ring pin was too short and the ring was not locked in place.
The ring positions are important and directly affect valve performance.
Generally, the lower ring is adjusted to give good popping characteristics (too low increases simmer and too high affects good reclosure); the upper
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ring is adjusted to provide the proper blowdown and also affects valve lift which in turn affects capacity, (too low increases blowdown and lift, and too high shortens blowdown and can reduce lift).
The inspector determined the following reasons for the improper ring sett-ings of valves as shipped from the vendor. Most vendors did not (and presently do not) have the capability to full flow test large size safety valves.
(At present, there are several facilities that can test these MSSVs.) The vendors ring settings for large valves were extrapolated from small valve testing and results have been erratic.
Large valves in some instances were set at a nominal setting by the vendor in expectation of a final setting to be made during operation, however, operational setting of the rings isn't performed.
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The inspector reviewed the Plant Incident Report initiated by the licen-see, internal correspondence, Network information concerning Dresser valves from Davis Besse Station that were tested at Wyle Laboratories, and NNEC0 records of telecon with Dresser. Based on this best available in-formation, the licensee reset all twenty five MSSVs at -8 notches on the lower ring and +160 notches on the upper ring.
At the time of this inspection, the Plant Incident Report and the reportability reviews were not yet completed. These would be finalized at an upcoming PORC meeting.
The inspector discussed his concern that the-8, +160 ring settings may not be correct because Millstone 3 has the only MSSVs (the inspector is aware of) with double outlets (opposing outlets), and also there was no formal correspondence from the vendor that -8, +160 ring settings are what should be used.
This item remains unresolved pending the licensee's completion of the Plant Incident report and the reportability aspects, formal verification that the MSSV ring settings are correct and the NRC review of these items (50-423/86-29-03).
5.0 Un esolved Items Unresolved items are matters about which more information is required in order to ascertain whether they are acceptable items, violations or deviations. An unresolved item is discussed in paragraphs 2.0, 3.0, and 4.0 of this report.
6.0 Exit Meeting The inspector met with the licensee's representative (identified in paragraph 1.0) at the conclusion of the inspection on August 22, 1986, to summarize the findings of this inspection.
During this inspection, the inspector did not provide any written materfal to the licensee.