ML20215J234

Forwards Description & Status of MSIV Leakage Reduction Program Mods.Program Plans Include Monitoring & Evaluating Valves Already Modified & Mod of Addl Valves Failing Local Leak Rate Test If Disassembly Required for Repair

ML20215J234
Person / Time
Site:	Browns Ferry
Issue date:	10/15/1986
From:	Gridley R TENNESSEE VALLEY AUTHORITY
To:	Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8610240359
Download: ML20215J234 (5)

Text

TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 374o1 SN 157B Lookout Place ,

g gg; qh DCT 15 sa6 U.S. Nuclear Regulatory Commission Region II

{ C2 ' C26o Attn: Dr. J. Nelson Grace, Regional Administrator 101 Marietta Street, NW, Suite 2900 1 Atlanta, Georgia 30323 /

Dear Dr. Grace:

BROWNS FERRY NUCLEAR PLANT (BFN) UNITS 1, 2, AND 3 - MAIN STEAM ISOLATION VALVE (MSIV) LEAKAGE In response to a verbal request from your staff, we are submitting a description and status of the MSIV Leakage Reduction Program Modifications for BFN.

If you have any questions, please get -in touch with M. J. May at (205) 729-3566.

To the best of my knowledge, I declare the statements contained herein are complete and true.

Very truly yours, TENNESSEE VALLEY AUTHORITY

/ */

R. ridley, Director Nuclear Saf ty and Licensing Enclosure cc (Enclosure):

Mr. J. Taylor, Director Mr. R. J. Clark Office of Inspection and Enforcement Browns Ferry Project Manager U.S. Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission Washington, D.C. 20555 7920 Norfolk Avenue Bethesda, Maryland 20814 Mr. F. Jape U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW Atlanta, Georgia 30323 8610240359$h hS9 PDR ADOCK PDR P nu q

• 0 eA me . v.GKW W An Equal Opportunity Employer OffI g Y  !

. . u 1

MAIN STEAM ISOLATION VALVE (MSIV) LEAKAGE HISTORY' l TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)

DOCKET NUMBERS 50-259, 50-260, and 50-296 i_

) As previously discussed Uith NRC, TVA has been implementing the MSIV leakage .

y reduction program at BFN since the unit 2, cycle 4, refueling outage began in July 1982. TVA participated in the Boiling Water Reactor Owners Group (BWROG)

- subcommittee concerning MSIV leakage. This began because, industry-wide, the MSIVs were repeatedly failing their "as-found" local" leak rate test'(LLRT),

j even though the valves were being refurbished each outage.

i I The results of this effort were the development of a series of recommendations that would reduce MSIV seat leakage. Because of the number of " gross" leakers

already identified by TVA, design changes were already in progress concurrently with the subcommittee meetings.

{

These modifications are continuing to be implemented on those valves which fail the "as found" LLRT acceptance criteria of 11.5 SCFH and are disassembled for i repairs. Valves passing the LLRT have been reviewed for special maintenance or j history that would indicate that we can expect relatively low leakage from these i valves in the near future.

The modifications that TVA determined to be applicable to BFN are part of the BWROG recommendations for " gross" leakers. We chose the " gross" lenkers approach because approximately 67 percent of our valvea^eyhibited leakage greater than 1000 standard cubic feet per hour (SCFH) at least once, and many i were repeat offenders or showed erratic behavior. The other approximate 33 j percent have not exceeded 85 SCFH since the unit 1, cycle 1, refueling outage.

l The modifications are divided into the following groups:

i

a. Weld buildup, machine, and verify clearances of the lower rib guides.

, clearances are verified by a poppet mockup manufactured to exact vendor -

I drawing specifications. Lapping of the valve body seat and honing of the

, upper bore are performed as required to ensure adequate clearances and to align the seat with the guides.

b. Weld stellite to lower guide ring on poppet, check and weld buildup, as l required, the upper guide rings, and machine poppet to ensure upper-to-lower i guide concentricity, as well as overall poppet dimensional consistency.

j c. Install two-inch diameter stems, rework corresponding bonnet backseating and i stuffing box parts, and install anti-rotational devices. The anti-rotation j assemblies are to prevent poppet rotation during operation and valve d

closure, and the two-inch stems are to accommodate future use of devices to i provide higher operator forces, if needed.

l l d. Use of forged steel poppet in place of existing cast steel ones. i 1

i i

.O e MSIV LEAKAGE HISTORY (continued)

The list below sununarizes the current status of the MSIVs:

UNIT 1 MODIFICATIONS LLRT RESULTS PREVIOUS (Note A) COMPLETED AFTER MODS (SCFH) STATUS A-inboard Parts a, b, and e A-line LLRT-combined 38.8 History of being a

" gross" leaker A-outboard a, b, and c ---------

" Gross" leaker B-inboard a, b, and e B-line combined 18.7 History of being a

" gross" leaker B-outboard ----

Low leaker C-inboard a, b, and c C-line combined 263 Erratic C-outboard a, b, c, and d -== ==

Erratic D-inboard n, b, and e D-line combined 50.1 " Gross" leaker D-outboard a, b, and c ---------

Erratic UNIT 2 MODIFICATIONS LLRT RESULTS PREVIOUS (Note B) COMPLETED AFTER MODS (SCFH) STATUS A-inboard a and b A-line passed 9.6 Erratic ,

A-outboard a and b -- --

" Gross" leaker B-inboard a, b, an'd c 1101.7 (Note D) " Gross" leaker B-outboard a and b 4 Low leaker C-inboard a, b, and c 2793 (Note D) Erratic

~

C-outooard a, b, and c 25 Low leaker D-inboard -----

D-line passed at 10.7 Low leaker D-outboard a and b =

" Gross" leaker 2

o .

MSIV LEAKAGE HISTORY (continued)

UNIT 3 MODIFICATIONS LLRT RESULTS PREVIOUS (Note C) COMPLETED AFTER MODS (SCFH) STATUS A-inboard a, b, and c A-line 19 " Gross" leaker A-outboard a, b, and e -

---

" Cross" leaker B-inboard ----- B-line passed 3.0 Erratic up through cycle 3, low leaker since then B-outboard - - = - Erratic through cycle 4 rib guide repair, a low leaker since then C-inboard -

C-line combined 14.18 Low leaker C-outboard a, b, and c ---- Low leaker D-inboard a, b, and c D-line passed 3.1 " Gross" leaker D-outboard ----- - -

Low leaker Note A: Unit 1 modifications were performed during cycle 5 refueling outage.

"As-found" LLRT is line leakage only because valves have not been disassembled to quantify individual leak rate values.

Note B: Unit 2 modifications a and b performed during cycle 4. "As-found" leakage is for cycle 5 refueling outage. Modification c being completed during current unit 2, cycle 5, outage.

Note C: Modifications performed during cycle 5 outage. "As found" LLRT is line leakage because valves have not been disassembled to quantify individual values. 3B outboard had rib guide welding maintenance performed during cycle 4 outage to return rib guide to original configuration because it was worn. B-line passed cycle 5 at 7.0 SCFH so outboard has not failed since modifications have been implemented.

3

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. i=

l Note D: 2B inboard and 2C inboard were among the first valves modified during cycle 4 and BFN personnel were on a learning curve. Since then, more stringent measuring techniques, better methods for body seat to poppet

. aligament, improved machine tooling design, and the anti-rotation assemblies have been incorporated in the MSIV leakage reduction program.

A long-term goal is to justify raising the MSIV leakage rate limits at BFN.

This will be done by performing either a generic or BFN plant specific numerical analysis for the calculation of post accident radiological dose as a function of MSIV leakage.

Currently, two improved dose assessment models have been developed to support the resolution of Generic Safety Issue C-8.* 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 CE 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 modifications have been performed on valves which fail the LLRT and require disassembly for repair. Seven of eight MSIVs en unit 1 have been completely modified with significant improvement in LLRT results, after one operating cycle. Three of eight are completely modified in unit 2 with seven of eight having the rib guide and poppet modifications. Even though BFN was on a learning curve at the time, LLRT results show improvements have been made.

Pour of eight have been completely modified for unit 3, and during four months of operation before shutdown no line leakage exceeded 20 SCFH.

The HSIV program plans are to continue to monitor and evaluate the MSIVs already modified, modify others as they fail the LLRT if disassembly is reqaired to repair, and pursue the feasibility of technical specification chenges to the LLRT values as a participant in the BWROG study on dose assessment.

TVA believes 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 needed to prove the success of the program.

• " Resolution of Generic Issue C-8, an Evaluation of Boiling Water Reactor Main Steam Isolation Valve Leakage and the Effectiveness of Leakage Treatment Methods" (letter to J. Fulton from J. Ridgely, January 28, 1986).

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