IR 05000259/1987010
| ML20205N377 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/06/1987 |
| From: | Jape F, Schnebli G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML20205N364 | List: |
| References | |
| 50-259-87-10, 50-260-87-10, 50-296-87-10, IEB-85-002, IEB-85-003, IEB-85-2, IEB-85-3, NUDOCS 8704030013 | |
| Download: ML20205N377 (18) | |
Text
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101 MARIETTA STREET, N.W., SUITE 2000
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Report Nos.:
50-259/87-10, 50-260/87-10, and 50-296/87-10 Licensee: Tennessee Valley Authority 6N 38A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Docket Nos.:
50-259, 50-260 and 50-296 License Nos.:
DPR-33, DPR-52, and DPR-68 Facility Name: Browns Ferry 1, 2, and 3 Inspection Conducted:
February 17-20, 1987 Inspector-(f44 W
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Date Sign d Approved by:
//940 A
F. Jape,3ection Chief f/ f/
Date Signed Engineering Section Division of Reactor Safety SUMMARY Scope:
This routine, announced inspection was conducted in the areas of followup on licensee actions to reduce Main Steam Isolation Valve (MSIV) seat leakage and Safety Relief Valve (SRV) setpoint drift problems.
Results: No violations or deviations were identified.
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8704030013 870319 PDR ADOCK 0500
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REPORT DETAILS 1.
Persons Contacted Licensee Employees E. Balch, Information Systems Specialist
- T. Bechnell, Mechanical Maintenance Group Supervisor J. Bennett, Regulatory Licensing Engineer
- R. Lewis, Plant Manager
- M. May, Manager of Licensing
- C. McFall, Compliance Engineer
- B. Pratt, Mechanical Maintenance Engineer
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S. Rowe, Systems Engineer
- J. Savage, Compliance Engineer Other licensee employees contacted included engineers, technicians, mechanics, security force members, and office personnel.
NRC Resident Inspectors
- C. Brooks, Resident Inspector
- C. Patterson, Resident Inspector
- G. Paulk, Senior Resident Inspector
- Attended exit interview
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2.
Exit Interview
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The inspection scope and findings were summarized on February 20, 1987, with those persons indicated in ~ paragraph 1 above.
The inspector described the areas inspected and discussed in detail the inspection findings.
No dissenting comments were received from the licensee. - The licensee did not identify as proprietary any of the materials provided to or reviewed by the inspector during this inspection.
3.
Licensee Action on Previous Enforcement Matters This subject was not addressed in the inspection.
4.
Unresolved Items Unresolved items were not identified during the inspection.
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5.
Maintenance Surveillance (62701)
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The main purpose of' this inspection was to followup on the licensee program in their MSIV leakage reduction program.
This subject was previously discussed in Inspection Report Nos. 50-259/85-04,50-260/85-04, and 50-296/85-04.
In addition,- the inspector reviewed the status of the licensee's efforts to correct the SRV setpoint drift problem.
a.
MSIV Leakage Reduction Program This interim inspection was conducted to obtain the current status of the licensee's MSIV leakage' reduction program and assess the effects.
of the program to date. MSIV seat leakage in excess of the Technical Specifications (TS) limit (normally 11.5 SCFH) has been a recurring problem for many years with BWRs throughout the industry.
TVA has been an active member of the Boiling Water Reactor Owners Group (BWROG) MSIV Leakage Control Committee since its inception.
In addition, the licensee has been a major contributor to the BWROG in identifying the probable causes and corrective actions.
The BWROG determined that the most probable cause for the typical MSIV failure was produced from combinations of the primary contributors, which include improper maintenance, valve orientation, excessive clear-ances, seat-to-quide misalignment, lack of concentricity, incorrect seat contact, and excessive coefficient of friction / corrosion.
The BWROG recommendations as corrective -actions for the primary contributors were based on the more common valve failure modes that produced moderate to high leakage rates.
These corrective actions focus on maintaining or establishing adequate internal valve geometry to produce acceptable valve leak rates. The recommendations included the establishment of a program to examine the valve internals, maintenance equipment to establish adequate poppet-to-valve body seat alignment, and modifications to produce an alignment-that would minimize unfavorable conditions and allow proper seat contact.
To implement the recommendations of the committee TVA has initiated two Engineering Change Notices (ECN) P0613 and P0614.
ECN P0613 allows for the weld buildup and remachining the lower rib guides inside the valve body.to align the poppet with the valve seat.
It also allows for the welding 'of Stellite 21.to the lower guide ring on the poppet, and the use of the newiv-supplied alternate forged steel poppet in place of the originally supplied cast poppet.
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ECN P0614 allows for the installation of the heavier two-inch diameter valve stems and the corresponding rework of the bonnet and back seat area.
It also allows for the installation of anti-rotation assemblies to ' prevent poppet rotation during
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operation and closure.
In addition, it originally requested the installation of an air-to-air booster to increase valve operator output.
However, the installation of this booster has been
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determined not to be feasible.
In addition to the implementation of the modifications through the ECNs, TVA has improved on MSIV maintenance through more detailed work procedures, more stringent measuring techniques including the use of mock-ups, and licensee development of improved machine tool design to meet the exacting tolerances required.
These maintenance related modifications are being performed on a valve by valve basis as a particular valve fails its Local Leak Rate Test (LLRT) and requires disassembly for repair.
The current status for modifications completed to date are as follows:
(See Attachment I for detail of modifications completed)
bnit 1 - Seven of the eloht valves were modified during the cycle 5 outage (April 1983').
Unit 2 - Three of the eight valves were modified during the cycle 5 outage (September 1984).
Partial modifications were performed on seven of the eight valves during the cycle four outage (July 1982) but were not completed due to parts avail-ability, Unit 3 - Four of eight valves were modified during the cycle 5 outage (September 1982).
In general, the modifications have been performed on valves which failed their LLRT and required disassembly for repair.
A review of the leak rate data and history of modification completed to date, as shown in Attachment I, confirms that the licensee's program has resulted in a significant improvement in MSIV leak rates.
The licensee stated their current plans for the leakage reduction program are to continue to monitor and evaluate the MSIVs already modified.
Other valves will be modified as they fail their respective LLRT if disassembly is required for repair. The licensee stated that they will perform LLRT and stroke time testing on all associated MSIVs prior to restart of a particular unit. Testing will be accomplished about six to eight weeks prior to restart in order to allow time for repairs, if required.
TVA stated their long term goal is to justify raising the TS MSIV leakage rate limits at BFN.
This will be done by' performing a generic or BFN plant specific numerical analysis for the calculation of post accident radiological dose as a function of MSIV leakage.
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Currently, two improved dose assessment models have been developed to support the resolution of this issue. The first model, developed by Pacific Northwest Laboratory (PNL) for NRC, utilized an elaborate transport model combined with the CRAC2 computer code.
The second code was developed by General Electric (GE) for the BWROG.
The GE code incorporated a less complex transport model than the PNL method.
At NRC's request, PNL reviewed the GE analysis and comments can be found in the proposed NUREG-1169. NUREG-1169 concludes, based on NRC analyses of the PNL and GE codes, that conservative plant-specific analysis will demonstrate that MSIV' leakage rates of 300 SCFH or more per valve, will be acceptable.
In summary, the licensee considers the BFN MSIV leakage reduction program to be a dedicated effort that is making strides in the right direction, but that additional operating time will be required to evaluate the results of steps-taken to date and to prove the success of the program.
The inspector agrees with the licensees' assessment of the program.
b.
SRV Setpoint Drift Problem The inspector also held discussions with responsible licensee engineers to obtain a current status of their actions to correct the SRV setpoint drift problem.
As with the MSIVs, this particular problem is applicable to BWRs and has been a problem for many years (since at least 1982).
TVA is also a member of the BWROG committee tasked with resolving this issue.
The major concern in this issue is the upward setpoint drift experienced with some Target Rock two-stage safety relief valves.
The BWROG has determined the causes to be:
labyrinth seal induced friction due to less than minimum required clearance between the pilot rod outside diameter and the pilot liner (guide) inside diameter and corrosion induced bonding of the-pilot-disc to the pilot seat.
The recommended corrective actions identified by the BWROG to prevent recurrence are:
(1)
Ir.spect SRVs for proper clearances and refurbish each SRV which demonstrates labyrinth seal induced setpoint drift.
(2) Establishment of a program to recommend a material change in the SRV which will resolve the corrosion induced bonding at the pilot disc to pilot seat interface.
TVA has completed item (1) and continues to accomplish this in their normal SRV test and refurbish, if required, program.
For item (2)
the BWROG selected PH 13-8 Mo material for use as the pilot disc. At present, the new pilot discs are installed in a selected sample of SRVs throughout the industry (Brunswick and Hatch facilities in.
RegionII).
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TVA did not elect to install the new discs in the SRVs at BFN at this time due to the fact, when the new discs were available they had just completed testing, refurbishment, and reinstallation of their SRVs.
In lieu of installed testing, TVA contracted GE to perform accel-erated corrosion testing on the new disc in their laboratories. Just prior to this inspection TVA learned there were problems with the testing fixture and the results to date were inconclusive.
The problem appeared to be caused by the autoclave oven used for the accelerated corrosion test.
The autoclave in use was lined with stainless steel which the BWROG, GE, and TVA consider caused increased corrosion of the PH 13-8 Mo test disc material and no corrosion of the satellite test discs.
At present GE is in the process of obtaining a different autoclave or will reline the present autoclave to ensure the test results are not biased by the test fixture.
Present plans call for resuming the lab tests at GE in the near future and continuing the test until plant Hatch disassembles their SRVs containing the new pilot disc material. An evaluation of the GE lab results and Hatch results will determine the future use of the PH 13-8 Mo pilot discs at BFN.
The licensee stated the test results should be available by May 1987.
Within the areas inspected, no violations or deviations were identified.
6.
FollowapOnIEBulletins(92703)
a.
(0 pen) 259, 260, 296/85-80-03, " Motor Operated Valve Common Mode Failures During Plant Transients Due to Improper Switch Settings."
The inspector held discussions with responsible licensee engineers to determine the current status of this Bulletin.
At present the licensee has completed action items "a" and "b" of the Bulletin.
Item
"a" requires that the licensee review and document the design basis for the operation of each valve which should include the maximum d/p expected during valve operation for both normal and abnormal operating events. BFN used the BWROG response for this item which is currently under review by IE.
Item "b" requires that the correct switch settings be established using the results of item
"a".
The licensee has determined these values using input from the actuator vendor, the valve vendor, and their engineering group. The remaining
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items required by the Bulletin are yet to be accomplished and will be followed in future inspections.
b.
(0 pen) 259, 260, 296/86-BU-02, " Static 0-Ring Differential Pressure Swi tches. "
Although the licensee does not have to address the concerns raised in this Bulletin until July 1987 or prior to critical operation of the facility, the inspector obtained the current status on the issue. The
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licensee stated that these switches are used in the Residual Heat Removal (RHR) System. The function of the switches is to control the RHR minimum flow control valve logic.
They have doubled the value for the static shift that the vendor (SOR) specified to ensure proper switch operation.
They also stated that SOR is publishing a new calibration procedure that includes steps to eliminate the. static shift pressure effect.
BFN will incorporate this new vendor procedure into their instructions when the procedure becomes avail-able. This item will be followed in future inspections.
Within the areas inspected, no violations or deviations were identified.
ATTACHMENT:
Main Steam Isolation Valve Leakage History i
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MAIN STEAT1 ISOLATION UALUE CMSIU) LEAKAGE HISTORY The modifications are divided into the following groups:
a.
Weld buildup, machine, and verify clearances of the lower rib guides.
Clearances are verified by a poppet mock-up ennufactured to exact vendor drawing specifications.
Lapping of the_ valve body seat and honing of the upper bore are performed as required to ensure adequate h
clearances and to align the seat with the guides.
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'deld stellite to lower guide ring on poppet, check an'd weld Eiildup b
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D as required, the upper guide rings, and eachine poppet to ensure E
upper-to-lower guide concentricity as well as overall poppet h
dimensional consistency.
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Install 2-inch diameter stems, rework corresponding bonnet c.
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backseating and stuffing box parts, and install anti-rotational devices.
The anti-rotation assemblies are to prevent poppet rotation during cperation and valve closure and the 2-inch stems are to accommodate future use of devices to provide higher operator forces, if needed.
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d.
Use of forged steel poppet in place of existing cast steel ones.
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l r1SIU LEAKAGE HISTORY j
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Note A:
Unit 1 modifications were performed during cycle 5 refueling.
j outage.
"As found" LLRT is line leakage onig because velves have
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Unit 2 modifications a and b performed during cycle'$i.
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found" leakage is for cycle 5 refueling outage, f1odification c z
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Modifications performed during cycle _ 5 outage.
"As found" LLRT i
is line laakage because valves have not been' disassembled to N
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quantify individual values.
3B outboard had rib guide welding I
maintenance, performed during cycle 51 outage to return rib guide to original configuration because it uses worn.
B-line passed
cycle 5 at 7.0 SCFM so outboard has not failed since i
lo modificatione have been implemented.
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Note d:
28 inboard and EC inboerd were part of the first valves modified F1 fn j
d during cycle 't and BFN personnel usare on a learning curve.
Since i
then, more stringent osamuring techniques, better methode for
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body seat to poppet alignment, improved machine tooling design,
O and the anti-rotation assemblies have been incorporated in the i
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rtSIU LEAKAGE HISTORY UNIT 1 F10DIFICATIONS LLRT RESULTS PREUIOUd
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(Note A)
EcttPLETED AFTER r10DS IN SCFM STATUS
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A-inboard Parts a, b, and c A-line LLRT-combined 38.8 Mistory of being a
" gross" leaker A-outboard a, b, and c
" Gross" lenker
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8-inboard a, b, and c B-line combined 18.7 Mistory of being a R
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B-outboard Low lenker m
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C-inboard a, b, and c C-line combined 283 Erratic w
l C outboard a, b, c, and d Erratic
D-inboard a, b, and c D-line combined SO.1
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F1SIU LEAKAGE HISTORY
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LLRT RESULTS PREUIDUS
UNIT 2 r10DIFICATIONS
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(Nota B)
CDt1PLETED AFTER MODS IN SCFM STATIJE A-inboard a and b A-line passed 9.8 Erratic
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F1SIU LEAKAGE HISTORY UNIT 3 r10DIFICATIONS LLRT RESULTS PREUIOUS (Note C)
COMPLETED AFTER MODQ_IN SCFM STATUS A-inboard a, b, and c A-line 19
"Groes" 1makme Q-outboard a, b, and c
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B-inboard
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B-line passed 3.0 Erratic up thro @ Cycle 3, low lenker si,nos then
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C-inboard C-line combined 14.18 Low lenker,,'
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D-inboard a, b, and c D-line passed 3.1
"Broes" laakme D-outboard,
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AnACHMENT I
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UNIT ONE MSIV A VALVES LEAKAGE
- ECN P0613/814 performed pdor to Cy6
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UNIT ONE MSIV 8 VALVES LEAKAGE
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ATTACHMENT I
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UNIT ONE MSIV C VALVES LEAKAGE
- ECN P0613/814W prior to Cy 8
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UNIT TWO MSIV C VALVES LEAKAGE cm 3 a.t - i. e
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