ML20149G769

Responds to Requesting That NRC Respond to Concerns Expressed by Constituents Re Reactor Core Shroud Cracking at Plant & Forwards NRC Response to Constituent Concerns

ML20149G769
Person / Time
Site:	Pilgrim
Issue date:	10/31/1994
From:	Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
To:	Kerry J SENATE
Shared Package
ML19352E492	List: ML20149G769 ML20149G772
References
CCS, NUDOCS 9411040300
Download: ML20149G769 (1)

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• • • • • October 31, 1994  ;

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The Honorable John F. Kerry United States Senator One Bowdoin Square Tenth Floor Boston, MA 02114

Dear Senator Kerry:

l l I am responding to your letter of October 3, 1994, in which you asked the U.S.

Nuclear Regulatory Commission to respond to concerns raised by Ms. Ott and Dr. l Muirhead regarding the reactor core shroud at Pilgrim Nuclear Power Station.

i I am enclosing a copy of our response to Ms. Ott and Dr. Muirhead. This reply  !

I to you and the reply to Ms. Ott and Dr. Muirhead will not be publicly distributed, because we are treating the information supplied by Ms. Ott and .

Dr. Muirhead concerning two sources knowing of cracks in the Pilgrim core ,

shroud as an allegation. Our process purposefully limits distribution of related correspondence to reduce the possi'oility of revealing the identity of individuals bringing allegations to our attention.

I hope this is responsive to your concerns.

Sincerely, I

es M. ylor xecutive Director for Operations ,

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Enclosure:

Letter to Ms. Ott and Dr. Muirhead j I

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[ ,4 UNITED STATES 3

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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 4001

% **.<< October 26, 1994 Dr. Donald M. Muirhead, Jr.

Ms. Mary C. Ott Citizens Urging Responsible Energy Post Office Box 2621 Duxbury, MA 02331

Dear Dr. Muirhead and Ms. Ott:

I am responding to your September 16, 1994, letter regarding core shroud cracking at the Pilgrim Nuclear Power Station (PNPS). As you stated, the U.S.

Nuclear Regulatory Commission (NRC) is concerned about core shroud cracking and is acting to ensure safe operation of the affected plants.

On October 4, 1994, the Boston Edison Company (BEco) management made a presentation to NRC management and staff in a public meeting in Rockville, Maryland. During the meeting BECo presented information to support its belief that the condition of Pilgrim's shroud is acceptable. BEco also provided evidence to support its contention that the risk associated with allowing PNPS to operate until the scheduled refueling outage in April 1995, without performing a core shroud inspection or repair, is acceptable. During that refueling outage, BEco has committed to install a General Electric designed modification which will replace the structural integrity currently provided by the core shroud welds. I am enclosing (Enclosure 1) a copy of the slide presentation from the October 4,1994, public meeting. The NRC staff asked BEco to submit a sensitivity analysis that would provide the margin to unacceptable performance of the core shroud during a postulated large break loss-of-coolant accident. BECo submitted the analysis on October 13, 1994, and the staff is currently reviewing it. A decision on whether it is acceptable to wait until the April 1995 outage to perform repairs to the core shroud will be made after that review. We will inform you of our decision.

On September 27, 1994, the NRC staff informed you in a telephone conversation that we are also concerned about the information supplied to you by anonymous sources regarding the core shroud at PNPS. As the staff told you, BEco informed us that the core shroud has not been inspected in a manner that would allow BEco to determine if the shroud is cracked. Without additional information, NRC has no basis on which to substantiate the statements of the anonymous sources. As the staff requested, if you are contacted again, please l ask the sources to contact us directly. If they are reticent to do so, but i could supply additional information to substantiate their assertions, we will revisit the issue.

As requested, I am also enclosing (Enclosure 2) a copy of the slide presentation from the August 4, 1994, public meeting with BEco to discuss the reactor vessel inspection and a proposed intergranular stress-corrosion cracking (IGSCC) inspection relief request. The slide presentation was included in the meeting summary of August 9, 1994, during which time BEco proposed changing the frequency of inspection of 11 category D recirculation 1

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Donald M. Muirhead and Mary C. Ott j safe-end welds. This proposal is highlighted on the fourth slide of the l presentation. NRC informed BEco that relief is not required if they implement hydrogen water chemistry asstated in Generic Letter 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping." They do, however, need to submit a written description of their program for evaluation and approval by the NRC staff.

I hope this reply addresses your concerns, and I will await .iny additional information you may be able to supply regarding the PNPS core shroud.

Sincerely,

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a.e's M. T lor' ecutive irector for Operations

Enclosures:

1. Core Shroud Presentation (October 4, 1994)

2. Proposed IGSCC Inspection Relief Request (August 4, 1994)

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Pilgrim Nuclear Power Station Commitment to Safety f) Boston Edison ,

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Core Shroud Presentation

- E.T. Boulette - Senior Vice President Nuclear

- H.V. Oheim - Nuclear Engineering Services -

Department Manager

- R.V. Fairbank - Regulatory Affairs and Emergency Preparedness:

l Department Manager

- J. P. Gerety - Fluid Systems and

! Mechanical Components l

Division Manager

1. c; Boston Edison 2

Meeting Objectives .

Assure the NRC Staff that Pilgrim places safety as the foremost consideration in resolving the core shroud cracking issue Update the NRC Staff on status of Pilgrim's efforts to resolve this issue l

l Apprise the staff of the dynamic and complex nature of this issue Obtain feedback from the NRC Staff regarding Pilgrim's response to the Generic Letter Maintain open communications allowing for frequent status reports from Pilgrim and feedback from NRC Staff c; Boston Edison 3

6 f-Safety is Pilgrim's foremost consideration in responding to shroud -

cracking issue Our early recognition of significance and applicability dictated our sense of urgency Pilgrim plant-specific safety assessment provides interim safety assurance Industry experience continuously factored into planning Pilgrim is committed to permanent resolution as soon as practicable Pilgrim will provide frequent progress reports to the NRC Staff as our efforts continue

• c; Boston Edison a

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[ Our early recognition of significance and applicability dictated our sense of urgency l Pilgrim took a leadership role in industry k TOSponSe Preemptive repair eliminates risk Optimum repair completion is RFO #10 l

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& Boston Edison ,

4 Pilgrim took a leadership role in ,

industry's response to shroud cracking BWRVIP Executive Oversight Committee Member Assessment Subcommittee Representative

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Inspection Subcommittee Representative Mitigation Subcommittee Chairman Mitigation Subcommittee Representative Repair Subcommittee Representative Repair design and hardware fabrication are in progress to support RFO #10 g

() Boston Edison

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Preemptive repair eliminates '

risk l

- Inspection uncertainties continue

- Repair restores structural margin l

- Pilgrim likely to need eventual repair

- Do it right the first time -

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(; Boston Edison 7

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l Optimum repair completion is RFO #10 1

l - Safest implementation during planned RFO

- High Confidence in Interim Safety l - Provides necessary design and hardware lead times l

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- Pilgrim is presently in an outage -

- Implementation during current outage scope is

! uncertain and adds unnecessary risk 1

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l Safest implementation during planned RFO Vessel open for refueling Fuel movement planned Operators trained and prepared Equipment tested and prepared .

& Boston Edison

s Pilgrim is presently in an outage

- Plant trip 8/29/94 due to generator failure

- MCO commenced 26 days early 9/4/94

- MCO to complete 10/7/94

- Generator repair dictates restart  ;

- Restart target early December

- No plan to open vessel l

- Generator repair progress l

- 'B' Battery Cell replacement g  !

i; Boston Edison go

Implementation during current outage is uncertain and adds unnecessary risk

- Repair design uncertainties

- Inspection plan uncertainties

- Battery cell replacement

- Refuel floor and operator readiness  :

- Open the vessel

- Move fuel

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- RFO planning impacted

- Repair impacts vessel inspection

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Core Shroud repair design uncerteinties must be resolved prior to

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implementation Lead plant success

• Seismic loads

- PNPS loads > lead plant loads

- lead plant design may not be adequate for PNPS Pre-installation inspection uncertainties

- Gussetwelds .

- Vertical welds

- Ring Segment

- Others As-built configuration uncertainty

. Core support plate wedges LOCA Loads - RLB Code Classification

& Boston Edison n

w.c w Core shroud repair implementation concerns must be resolved

- Availability of hardware and people

- Refuel floor readiness

- Operator readiness

- 125 vdc Battery cell replacement -

- Potential regulatory support

- 125 vdc battery crosstie tech spec waiver

- approval of SGTSICRHEAF tech spec submittal

- agreement outage does not meet tech spec definition of l " Refueling Outage" l

l Boston Edison 43

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Pilgrim's plant specific safety .

assessment provides interim safety l

assurance

= Structural margin exists assuming conservative crack size estimates

= Plant safety functions assured assuming hypothetical complete shroud failure ~

- Normal Operation

- Anticipated Operational Events

- Design Basis Acccident ,

a Probabilistic risk assessment confirms acceptability of operation ds; Boston Edison 14

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Structural margin exists assuming ~

conservative crack size estimates t GE PLEDGE model based on conservative assumptions

- highest fleet conductivity i

- initial flaw size and shroud material condition

- potential IASCC contribution included

- typical residual stress considered Analysis indicates high flaw tolerance . .

- 64% of shroud circumference l - 95% through wall Crack growth rate slowed

- low conductivity

- hydrogen water chemistry

- crack growth to RFO #10 < 1%

Estimated crack size is acceptable

& Boston Edison ,g

Plant safety functions assured assuming hypothetical complete shroud failure -

Normal Operation

- detectable

- proper core geometry maintained Anticipated Operational Events

- assume preexisting undetected 360* through wall crack

- proper core geometry maintained

- no additional reactor components affected Design Basis Accident

- MSLB and RLB

- Shroud lift less than top guide depth

- Ability to SCRAM maintained

, Confirms Safe Operation l #;

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Probabilistic risk assessment confirms acceptability of operation Probability of undetected 360 through-wall crack Probability of MSLB or RLB

= Probability of shroud failure causing loss of mitigating systems and recovery actions: ,.

- Control Rods

- SBLC

- Core Spray Change in CDF < 10%

& Boston Edison 47

e Industry experience is continuously ,

factored into shroud project planning

- Inspection.results enveloped by predictive model

- Inspection difficulties

- Repair difficulties

- Public interest s .

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& Boston Edison J,g

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Safety is Pilgrim's foremost consideration in responding to shroud cracking issue

- Our early recognition of significance and applicability dictated our sense of urgency

- Pilgrim plant-specific safety assessment provides interim safety assurance

- Industry experience continuously factored into planning

- Pilgrim is committed to permanent resolution as soon as practicable

- Pilgrim will provide frequent progress reports to the NRC Staff as our efforts continue

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$ Boston Edison 49

PROPOSED IGSCC INSPECTION RELIEF REOUEST

1. BECO Response To NRC GL 88-01

2. IGSCC Inspection Program Scope

3. IGSCC Inspection Results .

4. IGSCC Relief Request Scope

5. Conclusion

BECO RESPONSE TO NRC GL 88-01

. GL Identified 13 NRC Positions for Conformance

. BECO Responded to the NRC GL by Aug. 4,1988 letter

- Provided Response to the Staff Positions.

Provided a List ofIGSCC Welds.

I. RFO # 6 (12/83-12/84) Pipe Replacemeni Project:

Entire Recirc. System Piping Replaced with 316NG Material Portions of RIIR, CS and RWCU Piping Replaced No unrepaired Cracked Welds remained in service at PNPS

2. IGSCC Mitigation Effort:

Ilydrogen Water Chemistry e

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8 TABt.E 1: IGSCC Related Wolds IGSCC Description Number of Safety Number of Number of Category , R M S W ohls Safety Related Non-Safety Excluding RWCU RWCU Related Welds (RWCU)

A Resistant 121 43 19 Matemil B Norwesestant 0 0 0 material, SI within 2 years of operaten C Norwesestant 0 2 1 metrial, SI ener 2 years of operaten D Norwesistant 35 12 3 matenais, no St E Cracked, 1 0 0 .

. reinforced by weld overlay or nutigated by St F Cracked, 0 0 0 inadequate orno repair G Norwesistant 4 4 45 matenals not inspected TOTALS 161 61 68

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Total IGSCC P_@ 5 . ,, ? ^ : 1 welds: 222 ,

Total IGSCC susceptible non-safety related welds: 68 TotailGSCC susceptible welds are: 290 '

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TABLE 2. PROPOSED GL 88-01 SCHEDULE FOR RECIRCULATION WELDS MatenalsfMitigation IGSCC  ! Inspection Extent & Number of Proposed Process C - i .. x1 PW Schedule Welds Changes Resistant matonal A 25% overy 10 years (at 61 N/C least 12% in 6 pars)

Non-resistant metanais B 25% overy 10 years (at 0 N/C (stress impnwoment[Sl] least 12% in 6 years) vnthm 2 years of operation)

Non-romstant metonals St C 50% overy 10 years (at 0 N/C after2 years of operation least 25% in 6 years) th - ' ' -f 1;g: *

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IMM) ._ y - mm  ? @? M kigi p p$iEIAGydgj M , fen d ' change by l?Mi ^ 96 y94 Ik' factororti Cracked romforced by E ' All every 4 Refueling 0 N/C weld overtay or metinated cycles SI Cracked irsG&psate or no F All eveiy refusing 0 N/C repair outage Non-resistant not G All next refuelmg outage O N/C inspected 2R-N2A-1 2R-N2F-1 2R-N18-1 2R-N28-1 2R-N2G-1 2R-N2C-1 2R-N2H-1 2R-N2D-1 2R-N2J-1 2R-N2E-1 -

2R-N2K-1

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IGSCC INSPECTION PROGRAM RESULTS L

. Inspection Program Conformed to:

i NRC GL 84-11 Upgraded to conform to GL 88-01

. 88 IGSCC Weld Examinations since GL 88-01 were performed

. 24 Examinations since IIWC Injection were performed

. One S-R and 3 N S-R Cracks Discovered in RWCU piping prior to continuous II J

Injection in Sept. 91; piping replaced during RFO # 9

- .,o Cracks after continuous llydrogen Injection

. Safety-Related Portion of RWCU piping undergoing Replacement during RFO # 10

. Non-Safety Re!ated RWCU Piping Fall under the Scope of NRC GL 88-01 Suppl. #1

. NO CRACKS IN ANY PIPING SINCE CONTINUOUS USE OF IIWC

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CONCLUSION

. Relief Request Based on NRC Approval of Generic BWROG Topical Report

. Proposed Inspection Frequency Change by a Factor of 2 to Category D Recire. Safe-End welds

. Proposed Relief Request to be Implemented Beginit:g RFO # 10 (4/1995) or 11

. Impicmentation of Relief Saves per Refueling Outage:

~ 3.66 man-rem Exposure and

~ $300K Expenditures

. Relief Request to be Submitted after NRC approval of BWROG Report.

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