ML17333A821

Safety Evaluation Supporting Amend 215 to License DPR-58

ML17333A821
Person / Time
Site:	Cook
Issue date:	03/13/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML17333A820	List: ML17333A819 ML17333A821
References
NUDOCS 9703240212
Download: ML17333A821 (16)

Text

~

> ~g8 RE0II

+4 Po 0O Vl

,0 e 0

Y~

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001

. SAF TY EVA UATION TH OFF CE OF UC AR R ACTOR EGULATION 0 AMENDMENT NO. 2" 5 0

F C

I OPERATING L CENSE NO.

DPR-58 N

ICHGNP OM NY ONALD C.

COO UCLE ANT UNIT NO.

1

~KTT

. 00-0 1.0

~INTRMUCTIO By letters dated June 19,

1996, September 19,

1996, and December 20,

1996, American Electric Power (the licensee) submitted a request to amend the Donald C.

Cook Nuclear Plant, Unit 1 (Cook-1) Technical Specifications (TS).

The proposed amendment allows the use of a 2.0 volt steam generator (SG) tube support plate (TSP) repair criteria.

The voltage-based SG tube repair criteria allow tubes with axially oriented outside diameter stress corrosion cracking (ODSCC) confined within the thickness of the TSPs to remain in service based. on the magnitude of the bobbin coil voltage response.

On August 3, 1995, the NRC issued Generic Letter (GL) 95-05, "Voltage-Based Repair Criteria for Mestinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," which outlined generic criteria for licensees considering implementation of alternate repair criteria.

The licensee's proposed amendment request follows the guidance provided in GL 95-05 as discussed below.

The September 19,

1996, and December 20,

1996, supplements provided additional information that did not change'he scope of the original application and did not change the staff's initial proposed no significant hazards consideration determination.

2.0 ACKGROUND SG tube flaw acceptance criteria (i.e., plugging limits) are specified in the plant TS-.

The traditional strategy for achieving adequate structural and leakage integrity of the tubes has been to establish a minimum wall thickness requirement in accordance with NRC Regulatory Guide (RG) 1.121, "Bases for Plugging Degraded PNR Steam Generator Tubes."

Development of minimum wall thickness requirements to satisfy RG 1.121 was governed by analyses assuming a

uniform thinning of the tube wall.

This assumed degradation mode is inherently conservative for most other forms of SG tube degradation.

Conservative repair limits may lead to plugging tubes with adequate structural and leakage integrity for further service.

PDR 002i2 9703i3 97O3Z ~<< OSOOO3iq POR

(,I

~

'1 4 P

I

> ~

~

j The staff developed generic criteria for voltage-based limits for ODSCC confined within the thickness of the TSPs.

The staff published several conclusions regarding voltage-based repair criteria in draft NUREG-1477, "Voltage-Based Interim Plugging Criteria for Steam Generator Tubes" and in a draft GL titled "Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes."

The latter document was publi.shed for public comment in the Federal Register on August 12, 1994 (59 FR 41520).

On August 3, 1995, the staff issued GL 95-05 that took into consideration public comments on the draft GL cited above, domestic operating experience under the voltage-based repair criteria, and additional data made available from European nuclear power plants.

The guidance of GL 95-05 does not set depth-based limits on predominantly axially oriented ODSCC at TSP locations; rather it relies on empirically derived correlations between a nondestructive inspection parameter, the bobbin coil voltage, and tube burst pressure and leak rate.

The staff recognizes that although the total tube integrity margins may be reduced fol.lowing application of voltage-based repair criteria, the guidance in GL 95-05 ensures structural and leakage integrity continue to be maintained at acceptable levels consistent with the requirements of 10 CFR Part 50 and the guideline values in 10 CFR Part 100.

Since the voltage-based repair criteria do not incorporate a minimum tube wall thickness requirement, there is the possibility for tubes with through-wall cracks to remain in service.

Because of the increased likelihood of such flaws, the staff included provisions for augmented SG tube inspections and more restrictive operational leakage limits.

The licensee used interim plugging criteria for the last three cycles, with each cycle's application reviewed and approved by the staff [References 1-3].

The licensee's proposed amendment requests a permanent change to the Cook-1 TS to incorporate voltage-based repair criteria per the guidance of GL 95-05.

The guidance specifies, in part that (1) the repair criteria are only applicable to predominantly axially oriented ODSCC located within the bounds of the TSPs; (2) licensees perform an evaluation to confirm the SG tubes will retain adequate structural and leakage integrity until the next scheduled inspection; (3) licensees adhere to specific inspection criteria to ensure consistency in methods between inspections; (4) tubes must be periodically removed from the SG to verify the morphology of the degradation and provide additional data for structural and leakage integrity evaluations; (5) the operational leakage limit be reduced; (6) licensees implement an operational leakage monitoring program; and (7) specific reporting requirements shall be incorporated into the plant TS.

3.0

~EVALUAT OM The licensee will follow the requested

.actions of GL 95-05 for implementing the proposed voltage-based plugging criteria.

As permitted by GL 95-05, the licensee proposes to (1) use an alternative method to Section 3.c.3 of Attachment 1 to GL 95-05 to address bobbin coil probe wear and (2) include a

provision to use alternative inspection techniques in proposed TS 4.4.5.4.10.c.

3.1 Tube Repair Limits The proposed voltage criteria pertain specifically to predominantly axially oriented ODSCC flaws, and the proposed criteria (1) permit indications confined to within the thickness of the TSPs with bobbin voltages less than or equal to 2.0 volts to remain in service; (2) permit indications confined to within the thickness of the TSPs with bobbin voltages greater than 2.0 volts but less than or equal to the upper voltage limit to remain in service if an RPC probe or acceptable alternative inspection does not detect degradation; and (3) require indications confined to within the thickness of the TSPs with bobbin voltages greater than the upper voltage limit be plugged or repaired.

The licensee's proposed repair limits are based on the use of a correlation between the burst pressure and the bobbin coil voltage of pulled tube and model boiler data.

The licensee will use the burst pressure versus bobbin voltage correlation containing all applicable data consistent with the guidance in GL 95-05.

The proposed lower voltage limit of 2.0 volts is consistent with the recommended value specified in GL 95-05 for 7/8 inch SG tubing.

The upper voltage limit is based on the lower 95 percent prediction interval of the burst pressure/bobbin voltage correlation, adjusted for lower bound material properties evaluated at the 95 percent confidence level.

This voltage is further reduced to account for uncertainty in the nondestructive examination (NDE) technique and flaw growth over the next operating cycle.

Because licensees periodically update the burst pressure/bobbin voltage database with pulled tube data, the upper voltage limit may vary as additional data are included in the correlation.

3.2 Inspection Issues In the September 19, 1996 submittal, the licensee proposed to use an alternative to the probe wear reinspection requirements of GL 95-05.

The industry approach, developed through the Nuclear Energy Institute (NEI), is such that if any of the probe wear standard signal amplitudes prior to probe replacement exceed the +/- 15 percent limit, all tubes having indications with voltage responses measured at 75 percent or greater of the lower repair limit must be reinspected with a bobbin probe satisfying the +/- 15 percent wear standard criterion.

The voltages from the reinspection should be used as the basis for tube repair.

The NRC staff completed a review of the proposed alternative method and concluded the approach is acceptable because it provides adequate flaw detection sensitivity.

[Reference 4].

Therefore, the licensee's proposal to follow the industry approach to address bobbin coil probe wear is acceptable.

In the laboratory and field studies supporting the alternative probe wear

'riteria, the correlation of worn probe voltages with new probe voltages shows that for all significant voltage levels, the worn probe voltages are never less than 25X of the new probe voltage [Reference 5].

However, in a recent licensee 90 Day Report submittal, a comparison made between the worn probe voltage and the new probe voltage resulted in two data points where the worn probe voltage was substantially less than 25X of the new probe voltage.

The

~ i

~

~ '

licensee'evaluated these indications and concluded the criteria to retest tubes with worn probe voltages above, 75X of the repair limit is adequate and generally conservative due to the average trend for worn probe volts to exceed new probe voltages.

Comparison of the actual and projected end-of-cycle voltages did not show anything unusual attributable to the alternate probe wear criteria.

The staff concludes the aforementioned probe wear results do not indicate an immediate need to modify the NEI alternative probe wear criteria.

However, the staff. will continue to monitor the 90 Day reports of licensees using this approach to probe wear.

The proposed amendment includes a modification to TS 4.4.5.4. 10.c.

The change allows indications of potential degradation with bobbin coil signal voltages between the lower and upper repair limit to remain in service if they are not confirmed by either an RPC probe or an acceptable alternative inspection technique.

The licensee stated in the September 19, 1996 letter that all acceptable alternative inspection techniques will be qualified using similar criter ia used for qualifying RPC probes.

The NRC staff encourages licensees to use the most sensitive inspection techniques available.

As such, the staff concludes the proposed modification of TS 4.4.5.4. 10.c to allow the use of alternative inspection techniques is acceptable.

3.3 Structural and Leakage Integrity Assessments The NRC staff guidance for implementation of voltage repair criteria ensures SG tubes will retain adequate structural integrity during the full range of normal, transi'ent and postulated accident conditions with adequate allowance for eddy current test uncertainty and flaw growth projected to occur during the next operating cycle.

Tube structural limits based on RG 1. 121 criteria require maintaining a margin of safety of 1.43 against tube failure under postulated accident conditions and maintaining a margin of safety of 3 against burst during normal operation.

Because the GL 95-05 criteria address tubes affected with ODSCC confined to within the thickness of the TSP during normal operation, the staff concluded the structural constraint provided by the TSP ensures all.tubes to which the voltage-based criteria apply will retain a

margin of 3 with respect to burst under normal operating conditions, consistent with the criteria of RG 1.121.

For a postulated main steam line break (HSLB) accident,

however, the TSP may displace axially during blowdown such that the ODSCC affected portion of the tubing may no longer be fully constrained by the TSP.

Accordingly, it is appropriate to consider the ODSCC affected regions of the tubes as free standing tubes for the purpose of assessing burst integrity under postulated HSLB conditions.

In order to confirm the SG tubes will retain adequate structural and leakage integrity until the next scheduled inspection, GL 95-05 describes the methodology to determine the conditional burst probability and the total primary-to-secondary leak rate from an affected SG during a postulated HSLB event.

To complete these assessments, the licensee proposes to follow the methodology 'described in WCAP-14277, Revision 1,

"SLB Leak Rate and Tube Burst Probability Analysis Hethods for ODSCC at TSP Intersections,"

dated December 1996.

The conditional burst probability and accident leak rate calculations should incorporate all available pulled tube data.

The licensee referenced the support databases approved by the staff in Reference 6.

The datasets

contain all applicable data supporting the empirical models for use of these voltage-based repair criteria.

3.3.1 Conditional Probability of Burst The licensee proposes to follow the methodology described in Revision 1 of WCAP-14277 for performing a probabilistic analysis to quantify the potential for SG tube ruptures given an HSLB event.

The results of the probabilistic analysis will be compared to a threshold value of 1x10 per cycle in accordance with GL '95-05.

This threshold value provides assurance that the probability of burst is acceptable considering the assumptions of the calculation and the results of the staff's generic risk assessment for SGs contained in NUREG-0844, "NRC Integrated Program for the Resolution of Unresolved Safety Issues A-3, A-4, and A-5 Regarding Steam Generator Tube Integrity."

Failure to meet the threshold value indicates ODSCC confined to within the thickness of the TSP could contribute a significant fraction to the overall conditional probability of tube rupture from all forms of degradation assumed and evaluated as acceptable in NUREG-0844.

The NRC staff concludes the licensee's proposed methodology for calculating the conditional burst probability is consistent with the guidance in GL 95-05 and is acceptable.

3.3.2 Accident Leakage The licensee proposes to follow the methodology described in Revision 1 of MCAP-14277 for calculating the SG tube leakage from the faulted SG during a

postulated HSLB event.

The model consists of two major components:

(1) a model predicting.the probability that a given indication will leak as a

function of voltage (i.e., the probability of leakage model);

and (2) a model predicting leak rate as a function of voltage, given that leakage occurs (i.e., the conditional leak rate model).

The NRC staff concludes the licensee's proposed methodology for calculating the tube leakage is consistent with the guidance in GL 95-05 and is acceptable.

3.3.3 Primary-to-Secondary Leakage During Normal Operation An important implication of using voltage-based SG tube repair criteria is tubes may have or may develop through-wall or near through-wall cracks during an operational cycle, thus creating the potential for primary-to-secondary leakage during normal operation, transients, or postulated accidents.

The staff concludes adequate leakage integrity during normal operation is reasonably assured by the TS limits on allowable primary-to-secondary leakage.

GL 95-05 specifies the operational leakage limits of the plant TSs should be reduced to 150 gallons per day (gpd).

Cook-1 TSs currently limit the primary-to-secondary leakage through one SG to 150 gpd.

This requirement is consistent with the guidance in GL 95-05 and is therefore acceptable.

3.4 Degradation Monitoring To confirm the nature of the degradation occurring at the TSP elevations, tubes. are periodically removed from the SGs for destructive analysis.

'Tube pulls can confirm that the nature of the degradation observed at these

n t

~

g

~

l h

locations is predominantly axially oriented ODSCC, provide data for assessing the reliability of the inspection methods, and supplement the existing databases (e.g., burst pressure, probability of leakage, and leak. rate).

GL 95-05 contains guidance stating licensees should remove at least two tube specimens with the objective of retrieving as many intersections as practical (minimum of four intersections) during the plant SG inspection outage preceding initial application of the voltage-based repair criteria.

On an ongoing basis, additional tube specimen removals (minimum of two intersections) should be obtained at the first refueling outage following 34 effective full power months of operation or at the maximum interval of three refueling outages after the previous tube pull.

Alternatively, the licensee may participate in an industry-sponsored tube pull program endorsed by the staff as described in GL 95-05.

Upon initial implementation of interim voltage-based alternate repair criteria in 1992 (EOC-12), the licensee removed 3 tubes for burst and leak rate testing and metallographic examination from the Cook-1 SGs.

The metallurgical examination confirmed the dominant degradation mechanism for the indications at the TSP elevations was axially oriented ODSCC.

The staff concludes the tubes removed from the Cook-1 SGs satisfy the initial tube pull criteria in'L 95-05.

The licensee plans to remove at least one tube in the 1997 outage (EOC-15),

and future tube pulls will be scheduled in accordance with GL 95-05.

3.5 Technical Specification Changes The licensee proposed modifications.to TS 4.4.5.2.e which remove the cycle 15 limitation on implementation of the steam generator tube/tube support plate plugging criteria and to TS 3.4.6.2.c.

which. remove the cycle 15 limitation on primary-to-secondary leakage limits through the steam generators.

These changes allow use of the 2.0 volt tube repair limits on a continuing basis, are consistent with the prior discussions and are therefore acceptable.

The licensee proposed modifications to TS 4.4.5.4.10.,

TS 4.4.5.4.10.a.

and TS 4.4.5.4. 10.b. which provide more specificity than the previous TS which were granted on a cycle-by-cycle basis.

The proposed TS are consistent with the proposed repair criteria discussed above and are therefore acceptable.

Proposed changes to TS 4.4.5.4.10.c.

were addressed in section 3.2 of this SE.

A new TS 4.4.5.4. 10.d.

was proposed which provides specific repair limits if an unscheduled mid-cycle inspection is performed.

The proposed limits are consistent with and based on GL 95-05 and are therefore acceptable.

Proposed modifications to 4.4.5.5.d.

provide for reporting requirements, including the reporting of an unacceptable calculated conditional burst probability, which are consistent with the previous changes and are therefore acceptable.

Bases changes providing supporting discussion for the associated TS changes were also proposed and are acceptable.

~

y f J

4.0 SUR~

The licensee submitted an application for a TS amendment to permit the use of voltage-based SG tube repair criteria at Cook-1.

The staff reviewed the proposed amendment and concluded the methods proposed by the licensee are consistent with the guidance in GL 95-05.

The staff concludes adequate structural and leakage integrity can be ensured, consistent with applicable regulatory requirements, for indications to which the voltage-based repair criteria will be applied.

The staff's approval of the'roposed voltage-based repair criteria is based in part on the licensee being able to successfully demonstrate after each inspection outage the conditional probability of burst and the primary-to-secondary leakage during a postulated NSLB will be acceptable per the guidance in GL 95-05.

S.D KSIEEC ULT Tl N

In accordance with the Commission's regulations, the Michigan State official was notified of the proposed issuance of the amendments.

The State official had no comments.

6.0 NVIRONHENTAL CONSIDERATION The amendments change requirements with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements.

The staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released

offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.

The Commission has previously issued a

proposed finding that the amendments involve no significant hazards consideration and there has been no public comment on such finding (61 FR 40022).

The amendments also change record-keeping or reporting requirements.

Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9) and (c)(10).

Pursuant to 10 CFR 51.22(b),

no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.

7. 0 CONCLUSION The staff has concluded, based on the considerations discussed above, that:

(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed

manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical.to the common defense and security or to the health and safety of the public.

References:

~

Safety Evaluation by the Office of Nuclear Reactor Regulation Related to License Amendment No.

166 to Facility Operating License DPR-58, Indiana Michigan Power Company, Donald C.

Cook Nuclear Plant, Unit No. 1, Docket No. 50-315, dated July 29, 1992.

~

)

g 0 l

h

/

2..

3.

Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Amendment No.

178 to Facility Oper ating License No. DPR-58, Indiana Hichigan Power

Company, Donald C.

Cook Nuclear Plant Unit 1, Docket No. 50-315, dated Harch 15, 1994.

Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Amendment No.

200 to Facility Operating License No. DPR-58, Indiana Hichigan Power Company, Donald C. Cook Nuclear Plant

-'nit No.

1, Docket No. 50-315, dated Septemb'er 13, 1995.

4.

Letter from B. Sheron (NRC) to A. Harion (NEI), dated Harch 18, 1996.

5.

Letter from A. Harion (NEI) to B. Sheron (NRC),

"Eddy Current Probe Replacement Criteria for Use in ODSCC Alternate Repair Criteria," dated January 23, 1996.

6.

Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Amendment No.

198 to Facility Operating License No. DPR-66, Duquesne Light Company, Ohio Edison

Company, Pennsylvania Power

Company, Beaver Valley Power Station, Unit No. 1, Docket No. 50-334, dated April 1, 1996.

Principal Contributor:

Stephanie H. Coffin, NRR/DE/EHCB Date:

Harch 13, f997

~ gO

.l

)4 I'I r

'0

~

p r

March 13, 1997 Mr. E.

E. Fitzpatrick, Vice President Indiana Michigan Power Nuclear Generation Group 500 Circle Drive

Buchanan, HI 49107

SUBJECT:

DONALD C.

COOK NUCLEAR PLANT, UNIT NO.

1 ISSUANCE OF AMENDMENTS RE:

ALTERNATE REPAIR CRITERIA FOR STEAM GENERATOR TUBING (TAC NO.

M95894)

Dear Mr. Fitzpatrick:

The Commission has issued the enclosed Amendment No.

215 to Facility Operating License No.

DPR-58 for the Donald C.

Cook Nuclear Plant, Unit No.

1.

The amendments consist of changes to the Technical Specifications (TS) in response to your application dated June 19,

1996, and supplemented September 19,

1996, and December 20, 1996.

The amendments revise the TS to allow a permanent extension of the interim steam generator tube voltage-based repair criteria for steam generator tubes used in Cycles 13, 14 and 15 at the Donald C.

Cook Nuclear Power Plant, Unit

=

1.

The inspection and analysis methodology of the voltage-based plugging criteria approved for Cycle 15 was modified to incorporate the staff recommendations stated in Gene'ric Letter 95-05, "Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," issued August 3, 1995.

A copy of our related Safety Evaluation is also enclosed.

Notice of Issuance will be included in the Commission's biweekly Federal

~Re ister notice.

Sincerely, Original signed by:

John B. Hickman, Project Manager Project Directorate III-3 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos.

50-315

Enclosures:

1.

Amendment No. 215 to DPR-58 2.

Safety Evaluation cc w/encl:

See next page DISTRIBUTION:

See attached list DOCUMENT NAME:

G:iDCCOOKII,C095894.AMD

• see previous concurrence To receive a copy of tMa decrement. Irwfcate In tha homt 'C' Copy without attachment/enclcetee Y ~ Copy with attachment/erwdcaure N

~ No copy NAME JHickman DATE D/ 9 /9 EBarnhill JStrosnider*

8/t> /97 1/29/97 OFFICIAL RECORD COPY OFFICE PH: PD33 E

LA:PD33 E

BC: EHCB OGC NLO w chan es HYoun *, STreb

• 3/5/97

<o 4

0 Qg e.Ql 4

~