ML20245A204

Responds to NRC Bulletin 89-001 Re Potential Degradation of Westinghouse-supplied Steam Generator Mechanical Plugs. Susceptible Mechanical Plugs Installed in Hot Leg of Steam Generator B Will Be Repaired During Apr 1990 Outage

ML20245A204
Person / Time
Site:	Point Beach
Issue date:	06/16/1989
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-89-075, CON-NRC-89-75 IEB-89-001, IEB-89-1, VPNPD-89-341, NUDOCS 8906210143
Download: ML20245A204 (11)

Text

qw Wisconsin Electnc POWER COMPANY 231 W Michgan. Ro. Box 2046. Milwaukee. WI 53201 (414)221-2345 VPNPD-89-341 NRC-89-075 June 16, 1989 U. S. NUCLEAR REGULATORY COMMISSION Document Control Desk Washington, D.C.

20555 Gentlemen:

DOCKETS 50-266 AND 50-301 NRC BULLETIN NO. 89-01, FAILURE OF WESTINGHOUSE STEAM GENERATOR MECHANICAL PLUGS POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 This is in-response to NRC Bulletin No. 89-01 regarding potential degradation of Westinghouse supplied steam generator mechanical plugs similar to the plug which resulted in the steam generator tube leak at North Anna 1 on February 25, 1989.

Wisconsin Electric (WE) has installed Westinghouse supplied

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mechanical plugs in the four steam generators at Point Beach Nuclear Plant (PBNP) since 1980.

The issue of potential degradation of these plugs has been under our review since

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October, 1988.

As noted in LER 88-003-00, dated November 17, 1988, a mechanical plug was removed from the PBNP Unit 2 B steam generator during the annual refueling outage.

Subsequent evaluation revealed axially oriented cracking above and below the internal expander.

The plug was identified.as being from heat NX-3513.

I With respect to the specific actions requested under Bulletin 89-01, our responses are provided below.

1.

Verification of Information Steam generator maintenance records have been reviewed for both units at PBNP to identify the installation date, channelhead, and heat number for all installed mechanical plugs.

A summary of currently installed mechanical plugs.

from heats NX-351'3, NX-3962 and NX-4523 is provided.in the 4

attached Tables 1 and 2.

No plugs are installed-from heat NX-3279.

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D6cument Control Desk June 16, 1989 Page 2 PBNP Unit I has no plugs from the heats identified in WCAP-12244 revision 1 and consequently, was not included in the information provided.

For PBNP Unit 2, the applicable information contained in the WCAP is consistent with our records.

Westinghouse letter NS-NRC-89-3432,- dated May 1, 1989, added information for heat NX-4523 and consequently included both PBNP Units.1 and 2.

The applicable information is consistent with our records except for'one correction, as noted in the attached Table 2.

2.a.

Estimated Plug Lifetime Using the methodology of WCAP-12244 Revision 1, and the benchmark degradation rate for Millstone 2, estimated plug lifetimes have been determined for all mechanical plugs from the subject heats.

For PBNP Unit 1 all installed mechanical plugs are of the 7/8 inch design.

For PBNP Unit 2 both the 7/8 inch mechanical plug and the sleeve mechanical plug (essentially a 3/4 inch plug) are installed.

Plug lifetime estimates are determined for each plug size as a function of the hot leg and cold leg operating temperatures.

In addition to the plug lifetime _ estimates, the operational i

effective full power days (EFFD), as of May 31, 1989 and the j

expected remaining EFPD have been provided as of the next l

scheduled refueling outage.

The latest information available is summarized in the attached Tables 3 and 4 for PBNP Units 1 and 2 respectively.

2.b.

Remedial Action Plan Based on the estimated plug lifetimes discussed in 2.a.

above, and the availability of required technology, we plan to repair all mechanical plugs from heats NX-3513, NX-3962, and NX-4523.

The schedule for such repairs is as follows:

A)

Unit 1:

Susceptible mechanical plugs installed in the het leg of stean generator B will be repaired at the next refueling outage' scheduled to commence in April 1990.

Susceptible mechanical plugs installed in the cold leg of steam generator B will be repaired during future outages before exceeding their estimated plug lifetime.

I Based on an average unit cycle length of 300 EFPD, the 1

estimated remaining plug lifetime for plugs installed in steam generator B cold leg would not be exceeded for

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r Document Control Desk' June 16, 1989 Page 3 L

approximately ten additional cycles.

, Consequently,-

repair of these' plugs can be deferred to an outage j

beyond 1990.- 'The repair; schedule-for these plugs will be based on an evaluation of schedules,. estimated 1

radiological exposure and costs in conjunction.with

.J anticipat'd steam generator maintenance activities.

e No mechanical plugs are: installed in steam generator A.

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B)

Unit 2:

' Susceptible mechanical. plugs' installed in the'

-hot legs of steam generators A and B will be:repairedL I

during the next refuelingEoutage scheduled to commence i

f in September 1989.

Following thesefactions, no mechanical plugs from the. susceptible. heats will remain.

unrepaired in the steam generator-hot legs.

Susceptible mechanical plugs installed in the cold legs of steam generators A and B will be. repaired during future outages before exceeding-their estimated plug lifetime.

Based on an average unit cycle. length of'300 EFPD, the estimated remaining plug lifetime would not be exceeded for appro.simately ten additional cycles.

i Consequently, repair.of these plugs can be deferred to an outage beyond 1989.

The repair schedule'for these plugs will be based on an evaluation of schedules, estimated radiological exposure and costs in conjunction with anticipated steam. generator maintenance activities, j

2.c.

ALARA Considerations i

The evaluation of alternatives for~the disposition of the 1l susceptible mechanical plugs _ included a study of the j

estimated' radiological ex~posures.- The two options considered were plug replacement and. plug repair, using the plug-in-a plug (PIP) technique.

Based on similar Work performed at Millstone 2, Farley 2, and North Anna 1,,

i radiological exposures were estimated for repair programs'at i

PBNP.

A summary of the. estimated exposures is. presented in the attached Tables 5 and 6Lfor' Units I and 2 respectively.

y Based on a. direct comparison of the estimated _ exposures, it is concluded that the PIP option represents the best radiological alternative.

For the PIP alternative, the'

. estimated total personnel exposures are 1.2 man-rem for Unit 1 (manual operation) and 12.3 man-rem for Unit 2 (remote operation).

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D6cument Control Desk June 16, 1989 Page 4 As part of the ALARA review, potential exposure reductions resulting from steam generator channelhead decontamination (decon) were evaluated.

Two methods of decon were considered.

A)

Mechanical:

Mechanical decon (i.e.,

grit blasting) was employed at PBNP Unit 2 as part of the mechanical sleeving program performed in 1983.

The channelhead radiation levels were reduced, with an average decon factor (DF) of 2.6-2.7.

However, the process resulted in a total personnel exposure of 34.61 man-rem.

From this experience and the estimated PIP exposure, a potential savings of approximately.7.7 man-rem is l

estimated for the Unit 2 plug repair program.

However, l

when the personnel exposure due to the decon process is considered, deconning does not represent a savings-in personnel exposure.

In order for deconning to be of radiological benefit, it would be necessary to reduce the decon related personnel exposure by almost 80% over the exposure incurred in 1983.

Based on no net savings in exposure and the considerable cost of the decon process, mechanical decon is not considered an acceptable alternative.

l B)

Chemical:

Chemical decon has been used on a limited basis at PBNP.

In 1988 chemical deconning was performed on the blowdown evaporator reboiler prior to replacement.

This decon resulted in a DF of approximately 2 and the generation of approximately 1200 cubic feet of radioactive waste.

The costs associated with disposal of the waste and the corresponding personnel exposure incurred during this operation lead to the conclusion that chemical decon of the steam generators would not be of overall benefit in reducing personnel exposure.

Consequently, chemical decon is not considered an acceptable alternative.

1 Since the repair scope for Unit 1 is small and operations are expected to be performed manually, no decontamination will be performed.

Due to the relatively small repair scope for Unit 1, the use of local shiciding inside the Unit 1 steam generators is not expected to result in savings in personnel exposure consistent with the ALARA concept.

Due to the relatively

I Dbcument Control Desk June 16, 1989 Page 5 large repair scope for Unit 2 and the resulting use of robotic equipment, local shielding inside the steam generators is considered-impracticable, and consequently, no savings in perconnel exposure are expected.

Therefore, local shielding inside the steam generators will not be used.

Local shielding outside the steam generators is used routinely in conjunction with other steam generator maintenance activitiet such as eddy current inspections and mechanical sleeving.

This practice will continue where consistent with the principles.of ALARA.

2.d.

Future Plug Installation WE does not maintain an inventory of mechanical plugs-at PBNP and will not install Westinghouse mechanical plugs from heats NX-3279, NX-3513, NX-3962, or NX-4523 during future outages.

2.e.

Future Removal and Evaluation of Mechanical Plugs Should removal of mechanical plugs be necessary in the future, appropriate records will be maintained and the results of any examinations performed will be provided'to Westinghouse.

3.

Deferment for Partially-Expanded Tubesheet Joints The steam generators at PBNP Unit 1 are Westinghouse model 44F with fully expanded tubesheet joints.

Consequently, the one time deferment is not applicable to Unit 1.

The steam generators at PBNP Unit 2 are Westinghouse model 44 with partially expanded tubesheet joints.

Since the next scheduled unit outage will not end before October 1, 1989 (estimated completion'date November.17, 1989), the one time deferment also does not apply to PBNP Unit 2.

4.

Sentinel Type Plugs No sentinel type plugs are installed in either unit at PBNP.

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Dbcument Control Desk l

June 16, 1989 I

Page 6 l

Please contact us if you have any questions regarding our response to this subject.

Very truly yours,

<, f (hO C. W. Fay Vice President Nuclear Power Attachments l

Copies to NRC Regional Administrator, Region III NRC Resident Inspector R.

S. Cullen, Public Service Commission of Wisconsin Subscrib,qd and sworn to before me this }bD day of June 1989.

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Aun Notary Public, State of Wisconsin My Commission expires 5-27-70 1

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TABLE 1 PBNP' UNIT 1 SUSCEPTIBLE MECHANCAL PLUG HISTORY Number of Plugs SG A SG B Outage & Year Heat Used HL CL HL-CL U1R15 - 1988 NX-4523 0

0.

2 2

TABLE 2 PBNP UNIT 2 SUSCEPTIBLE MECHANICAL PLUG HISTORY Number of Plugs SG A SG B Outage & Year Heat Used HL CL HL CL i

U2R11 - 1985 NX-3962 0

0 9

10 NX-3513 0

0 34 0

U2R12 - 1986 NX-3962 r14 14 4

58 NX-3513(I) 0-0' 54 0

i II)

U2R13 - 1987 NX-3513 1

0 3

2 NX-4523 30(2) 30 14 14 l

Total

' 45 44 118

.84 j

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1) Sleeve mechanics! plug (s).

Essentially 3/4 inch plug.

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2) Correction to Westinghouse letter NS-NRC-89-3432, dated May 1, 1989.

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TABLE 3 PBNP UNIT 1 ESTIMATED PLUG LIFETIMES' BASED ON MILLSTONE 2 GROWTH RATE (As of May 31, 1989)

Effective Full Power Days (EFPD)

1. f To To Remaining Remaining 4) 2)

3)

Heat Year SG Leg-Plugs Min. Wall Date Lifetime SU1R17.

NX-4523 1988 B-HL 2

631 324 307

-3 NX-4523 1988 B-CL 2

4150 324 3826 3516

1) Reported Millstone 2 rate is 0.073 mils /EFPD.

2) April - May of indicated, year.

3) Based on T

= 596.7 F and Teold = 541.7 F.

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4) Assumes 310 EFPD between May 31, 1989 and U1R17 outage expected to commence on April 6, 1990.

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TABLE 4

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PBNP UNIT 2 ESTIMATED PLUG LIFETIMES BASED ON MILLSTONE 2 GROWTH RATE (As of May 31, 1989) f Effective Full Power Days (EFPD)

1. f T

To Remaining Remaining 4) 2)

3)

Heat Year SC Leg Plugs Min. Wall Date Lifetime

@U2R15 NX-3513 1985 B-HL 34 556 1084

- 528

- 642 NX-3962 1985 B-HL 9

607 1084

- 477

- 591 NX-3513 1986 B-HL 54 556 793

- 237

- 351 NX-3962 1986 B-HL 4

607 793

- 186

- 300 NX-3962 1986 A-HL 14 607 793

- 186 300 NX-3513 1987 A-HL 1

556 498 58 56 NX-3513 1987 B-HL 3

556 498 58 56 NX-4523 1987 A-HL 30 607 498 109 5

NX-4523 1987 B-HL 14 607 498 109 5

NX-3962 1985 B-CL 10 4046 1084 2962 2848 NX-3513 1987 B-CL 2

3710 498 3212 3098 NX-3962 1986 A-CL 14 4046 793 3253 3139 l

NX-3962 1986 B-CL 58 4046 793 3253 3139 l

NX.4523 1987 A-CL 30 4046 498 3548 3434 NX-4523 1987 B-CL 14 4046 498 3548 3434

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1) Reported Millstone 2 rate is 0.073 mils /EFPD.

2) October - November of indicated year.

3) Based on T

= 597.9 F and T hot cold *

4) Assumes 114 EFPD between.May 31, 1989 and U2R15 expected to commence on September 22, 1989.

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l TABLE 5 i

ESTIMATED RADIOLOGICAL EXPOSURE FOR MECHANICAL PLUG OPTIONS PBNP UNIT 1 Option 1:. Replace Plugs Man-Rem Plug Removal 3.0 Plug Installation 0.3 Total 3.3 Option 2: Plug in a Plug (PIP)

Man-Rem PIP Installation 1.2

1) Assumes 2 mechanical plugs repaired and an average general channelhead radiation level of 18 rem /hr.

2) Remote operations are not considered here since the exposure and costs associated with equipment handling are expected to greatly exceed the manual operations.

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S TABLE 6 ESTIMATED RADIOLOGICAL EXPOSURE FOR MECHANICAL PLUG' OPTIONS PBNP IINIT 2 1

Option 1: Replace Plugd Man-Rem Manual Remote Plug Removal 249.6

'8.

Plug Installation 24.6

_6 Total-274.2 14 Option 2: Plug in a Plug (PIP)

Msn-Rem Manual Remote Plug Installation 109.0 12.3

1) Assumes 164 mechanical plugs repaired and an average general channelhead radiation level of 18 rem /hr.

2) This opcion is presented for comparison purposes only. The majority of mechanical plugs in the Unit 2 steam generators'have been installed in sleeved tubes. Processes for removing and replacing' mechanical plugs in sleeved tubes have not been qualified for model 44 steam generators and are not likely to be available for the upcoming Unit 2 outage.

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