ML17325B015

Provides Info Re Degradation of A-193 Grade B6 Type 410 Stainless Steel Retaining Block Studs in Darling Valve & Mfg Co Clear Waterway Check Valves Installed at Plant

ML17325B015
Person / Time
Site:	Cook
Issue date:	10/28/1988
From:	Alexich M INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
AEP:NRC:1054, NUDOCS 8811080073
Download: ML17325B015 (16)

Text

ACCEISRATED DISTRIBUTION DEMONSTRATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:8811080073 DOC.DATE: 88/10/28 NOTARIZED: NO DOCKET FACIL:50-315 Donald C.

Cook Nuclear Power Plant, Unit 1, Indiana 6

05000315 50-316 Donald C.

Cook Nuclear Power Plant, Unit 2, Indiana 05000316

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AUTH.NAME AUTHOR AFFILIATION ALEXXCH,M.P.

Indiana Michigan Power Co.

(formerly Indiana

& Michigan Elef(

RECIP. NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Provides info re degradation of A-193 Grade B6 Type 410 stainless steel retaining block studs in check valves.

DISTRIBUTION CODE:

A001D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: OR Submittal:

General Distribution NOTES R

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Indiana Michigan Power Company

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P.O. Box 16631 Columbus, OH 43216 AEP:NRC:1054 Donald C.

Cook Nuclear Plant Unit Nos.

1 and 2

Docket Nos.

50-315 and 50-316 License Nos.

DPR-58 and DPR-74 VOLUNTARY REPORT:

DEGRADATION OF RETAINING BLOCK STUDS IN DARLING VALVE AND MANUFACTURING COMPANY CLEAR WATERWAY CHECK VALVES U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C'.

20555 Attn: A. B. Davis October 28, 1988

Dear Mr. Davis:

The purpose of this letter is to provide you with information concerning recently observed degradation of A-193 Grade B6 Type 410 stainless, steel retaining block,.studs in Darling Valve and Manufacturing Company Clear Waterway check valves, installed at the Cook Nuclear Plant.

The'bserved condition did,not. result in 'any check valve failures,,'and we have determined. that, the condition"was not reportable under Title'0 CFR or our technical specifications (T/Ss).

However, because degradation of the type observed at the Cook Nuclear Plant has been of general industry interest in the past (e.g.,

INPO Significant Operating Experience Report

[SOER] 86-03),

we have elected to submit this voluntary report.

A summary of the observed condition and actions we have taken is provided below.

In conjunction with the performance of other maintenance on 8" Darling Clear Waterway swing check valve (2-SI-151W) installed in the low pressure emergency core cooling syst: em (ECCS),

an inspection of the valve internals was performed in accordance with the maintenance program that we established in response to INPO SOER 86-03.

During this inspection, one of the two retaining block studs was,found broken and the other cracked.

A diagram of the valve type in question is provided in Figure 1.

The"retaining block studs (Part No. 11542-61-5) retain the blocks (Part Nos. 1'1542-60/60-1),that hold the valve disc assembly in place.

As a result of this finding, the" corresponding check valve (2-SI-151E) in the redundant low pressure-ECCS train was

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Mr. A. B. Davis AEP:NRC:1054 inspected.

Again, one of the two retaining block studs was found broken and the other cracked.

Discovery of this second instance prompted the expansion of the inspection to all Unit 2 Darling check valves of the same design as those in which the degraded studs were found.

There are 12 valves of this design installed in the ECCS and RHR systems in each unit at Cook Nuclear Plant.

All of these valves are classified as pressure isolation valves'PIVs) and leak tested in accordance with our IST valve program.

They are:

o (4) 10" check valves at the accumulator outlet (SI-166L1, L2, L3, L4) o (4) 10" check valves ECCS injection to cold legs (SI-170L1, L2, L3, L4) o (2) 8" check valves low pressure ECCS (SI-151E

& W) o (2) 8" check valves normal RHR (RH-133,

-134)

Figure 2 provides a simplified flow diagram which identifies the locations of these check valves in either unit at Cook Nuclear Plant.

Soon after the decision was made to initiate the inspection of Unit 2 check valves however, Unit 1 went from power operation to hot shutdown (Mode 4) due to an unrelated event.

As a result, a

decision was made to immediately inspect all Unit 1 check valves of this design accessible in Mode 4.

In Unit 1, the only check valves accessible for inspection during the Mode 4 forced outage were 1-SI-151E, 1-SI-151W, 1-SI-166L1, and 1-SI-166L4.

The Unit 1 inspections found one broken stud in each of the check valves installed in the low pressure ECCS (1-SI-151E

& W) and stud material with an appearance not typical of Type 410 stainless steel in each of the two accessible accumulator outlet valves (1-SI-166L1,

& L4).

The continuing Unit 2 inspections identified one additional check valve with one cracked stud (2-SI-166L4),

and one valve (2-SI-166 Ll) in which, although the studs were intact, the stud material did not have the appearance typical of Type 410 stainless

steel, the material specified on the valve drawing for the retaining block studs.

Both valves are located on the accumulator outlet.

A summary of inspection results for the valves inspected in both Unit 1 and Unit 2 is provided in Table l.

Actions Resultin from Check Valve Ins ections In each of the cases discussed

above, the cracked or broken

studs, or studs of a material having an appearance not typical of

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Mr. A. B. Davis AEP:NRC:1054 Type 410 stainless steel were replaced with A-193 Grade B8 stud material.

This new stud material is recommended by the valve manufacturer for this application.

In addition, maintenance job orders were initiated to replace all A-193 Grade B6 Type 410 stainless steel studs with the new A-193 Grade B8 material regardless of whether any degradation is currently evident.

This action is also in accoidance with the valve manufacturer's recommendation.

To date, retaining block studs in 10 of the 12 Unit 2 check valves and 4 of the 12 Unit 1 check valves have been replaced with the new A-193 Grade B8 stud material.

The studs in the remaining Unit 2 check valves will be replaced during the current steam generator repair project outage.

The studs in the remaining Unit 1 check valves are to be replaced during the next scheduled outage, with the possible exception of those installed in the low pressure injection lines to the cold legs (1-SI-170Ll, L2, L3 and L4).

Service conditions for these valves may not be conducive to the type of stud degradation observed in the other systems inspected.

Westinghouse, who supplied the check valves under the original NSSS contract, and Darling, the valve manufacturer, were advised of the inspection findings discussed above.

Westinghouse is conducting metallurgical evaluations to determine the root cause of the stud degradation.

Evaluation of Safet Si nificance With regard to the evaluation of the safety significance of our valve inspection findings, the following key factors were considered:

1)

The check valves in their as-found condition had not failed, nor was valve operability impaired.

2)

Inadvertent pressurization of a low pressure ECCS system is precluded since in each case where a check valve with potentially degraded studs was found, at.

least two valves were available to prevent back leakage from the reactor coolant syst: em.

3)

'The check valves would have performed their intended function (i.e.,

opened) in the event of a LOCA regardless of whether the retaining block studs had completely failed.

4)

Of the 10 valves inspected on Unit 2, three showed degradation of the retaining block studs and one was found to have questionable stud material.

The corresponding Unit 1 valves which see the same service conditions as Unit 2 were inspected and studs replaced with the new stud material.

No anomalies were observed in the remaining Unit 2 check valves inspected.

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Mr; A. B. Davis AEP:NRC:1054 5)

The Unit 2 valves in the degraded condition had functioned successfully in passing the required flow during Mode 5 or 6 operation at the beginning of the steam generator repair outage.

Successful operation of these valves during this evolution is equivalent to passing the full flow test normally performed to confirm valve operability.

Unit 1 was returned to service on September 15,

1988, and the actions discussed above to replace retaining block studs on both units have commenced.

This document has been prepared following Corporate procedures which incorporate a reasonable set of controls to ensure its accuracy and completeness prior to signature by the undersigned.

Sincerely, M. P. Al xich Vice President ldp cc:

D. H. Williams, Jr.

W.

G. Smith, Jr.

- Bridgman R.

C. Callen G. Charnoff A. B. Davis NRC Resident Inspector

- Bridgman G. Bruchmann

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TABLE 1

SUMMARY

OF ANCHOR/DARLING CHECK VALVE INSPECTIONS Valve Size Service Location Retaining Block Stud Condition Unit 1 1-SI-151E 8 II Safety Injection (SI)

To Hot Legs One Broken S tud 1 1-SI-151W 81I 1-SI-166L1 10" SI To Hot Legs Accumulator Outlet One Broken Stud Questionyble Stud Material Unit 2 1-SI-166L4 10" Accumulator Outlet Questionable Stud Material 2-RH-133 2-RH-134 2-SI-151E 8 II 8 II 8 II Residual Heat Removal (RHR) To Cold Leg RHR To Cold Leg SI To Hot Legs OK OK One Broken Stud 3

One Cracked Stud 2-SI-151W 8 II SI To Hot Legs One Broken Stud One Cracked Stud 2-SI-166L1 10" 2-SI-166L2 10" 2-SI-166L3 10" 2-SI-166L4 10" 2-SI-170L1 10" 2-SI-170L4 10" Accumulator Outlet Accumulator Outlet Accumulator Outlet Accumulator Outlet Low Pressure Injection To Cold Leg Low Pressure Injection To Cold Leg Questionable Stud Material OK OK One Cracked Stud OK OK

Table 1 Notes:

1)

A broken stud is a stud that has completely sheared into two parts.

In each case where a broken stud is

reported, the break occurred at or near the plane of the interface between the valve body and the retaining block.

2)

Questionable stud material refers to studs that looked shiny instead of having the black appearance typical of Type 410 stainless

steel, the material listed on the valve drawings for the retaining block studs.

It appears that the "as-found" material is either Type 304 or 316 stainless steel.

3)

A cracked stud is a stud that has partially sheared but has not parted into two pieces.

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