ML20212G496

SER Accepting Pressurized Thermal Shock Assessment for Beaver Valley Unit 2 Reactor Vessel

ML20212G496
Person / Time
Site:	Beaver Valley
Issue date:	10/28/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20212G484	List: ML20212G479 ML20212G496
References
NUDOCS 9711060202
Download: ML20212G496 (6)

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4 SAFETY EVALUATION BY THE OFFICE OF NUCI FAR REACTOR REGULATION PRESSURl7FD THERMAL SHOCK EVALUATION QUQUESNE LIGHT COMPAMY BEAVER VAL t FY UNIT 2 DOCKET NO. 50-412 1,0 INTRODUCTION By letter dated February 13,1997, the Duquesne Light Company submitted WCAP 14784, Revision 2, " Evaluation of Pressurized Thermal Shock for_ Beaver Valley Unit 2 " which provided the Beaver Valley Unit 2 (GV 2) 10 CFR 50.61 pressurized thermal shock (PTS) assessment regarding the reactor vesselintegrity,- This submittal was provided in response to item 3 of an NRC request for additional information issued October 18,1996, concerning WCAP-14484,

" Analysis of Capsule V from the Duquesne Light Company Beaver Valley Unit 2 Reactor Vessel Radiation Surveillance Program,"

The PTS rule adop*ed on July 23,1985 and revised on May 15,1991, and December 19,1995 established screening criteria that are a measure of a limiting level of reactor vessel material embrittlement beyond which operation cannot continue without further plant specific evaluation.

The' screening criteria are given in terms of reference temperature, RT,rs, The screening criteria are 270*F for plates and axial welds and 300*F for circumferential welds. The RT,1,is -

defined as:

RT,7s = RT,.ru + ART,13 + M where: (a) RT,erm la the initial reference temperature, (b) ART,7 is the mean value in the adjustment in reference temperature caused by irradiation, and (c) M is the margin to be added to cover uncertainties in the initial reference temperature, copper and nickel contents, fluence, and calculational procedures.

The initial reference temperature is the measured unirradiated value as defined in ASME Code, Paragraph NB-2331, if a measured value is unavailable for the heat of material of interest, a generic value may be used. Generic values are based on the data for materials of all heats that were made by the same vendor using similar processes, Generic values of initial reference temperature for welds are defined in the PTS rule.

The ART,rs depends upon the amount of neutron irradiation and the amounts of copper and nickel in the material and is calculated as the product of a fluence factor and 3 chemistry factor (CF). The fluence factor is calculated from the best estimate neutron fluence at the clad-weld-metal interface on the inside surface of the vessel at the location where tne material receives the highest fluence at the end of the period of evaluation. The CF may be determined using _

credible surveillance data or from the CF tables in the PTS rule. The CFs in the tables are

_. dependent upon the best-estimate values of the amount of copper and nickelin the material.

The term "best-estimate" is not well defined statistically, but has normally been interpreted as the mean of the measured values.

ATTACHMENT g%Y y2 P

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.4-2 The revised PTS rule cordains criteria for determining whether surveillance data is credible.

The rule also contains the procedure for calculating the vessel weld CF from the adjusted nr measured values of ARTns. Specifically, the rule states that if there is clear evidence that the copper and nickel content of the surveillance weld differs from that of the vessel weld, the measured values of ARTn, should be adjusted by multiplying them by the ratio of the CF of the vessel weld to that of the surveillance weld The CF is calculated by multiplyi_ng each adjusted or measured value of ARTns by its corresponding fluence factor, summing the products, and dividing by the sum of the squares of the fluence factors. The resulting CF will give the relationship of ARTn, to fluence that fits the plant surveillance data in such a way as to minimize the sum of the squares of the errors.

The margin term is intended to account for variability in initial reference temperature and the adjustment in reference temperature caused by irradiation. The value of the margin term is dependent upon whether the initial reference temperature wr.s a measured or generic value and whether the adjustment in reference temperature was determined from credible surveillance data or from the CF tables in the PTS rule.

2.0 DISCUSSION The BV 2 reactor vessel beltline includes the intermediate sheH plates B90041 and B9004 2 (heat identification numbers C05441 and C0544-2, respectively), the lower shell plates B9005-1 and B9005-2 (heat identification numbers C1408-2 and C1408-1, respectively), the intermediate and lower shell vertical seams, and the girth weld between the intermediate and lower shell plates (all welds were fabricated using weld wire heat identification number 83642).

The material with the greatest amount of embrittlement (limiting material) is plate B90041.- The limiting plate in the BV-2 reactor vessel beltline, B9004-1, has an initial reference temperature value of 60*F. The licensee's best estimate values of the amount of copper and nickelin the limiting plate for BV-2 are 0.07% and 0.55%, respectively. Linear interpolation of the CFs in -

Table 1 of the PTS rule indicates that the CF is 44 degrees F. The best estimate values of copper and nickel are mean values from the plate certification test and the Combustion Engineering analysis from a sample obtained at 1/4 thickness of the plate.

The licensee calculated the margin value for the limiting plate in accordance with the methodology in 10 CFR 50.61. The standard

.. deviation of the initial reference temperature (RTery) is zero since the RT.1% is a measured value. The standard deviation for the adjustment in the reference temperature for the plate is 17 degrees F. The licensee calculated a margin value of 34 degrees F. This value is -

acceptable since it was calculated in accordance with the methodology in 10 CFR 50.61.

The RTns value calculated by the licensee for the limiting plate at EOL is 149 degrees F. The RTns value calculated by the staff for BV-2 is 148.48 degrees F. The staff's value is calculated using (a) a measured value of the initial reference temperature, (b) best-estimate value of

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i l 3 copper and nickel for the vessel ste, (c) a CF determined from the CF table for plates in 10 i

CFR 50.61, (d) an EOL neutron fluence of 3.85E19n/cm', and (e) a margin value of 34 degrees ,

F, The slight difference between the staffs and the licensee's RTpt, values is due to round off -

error (149 degrees F calculated by the licensee and 148.48 degrees calculated by the staff).

, The intermediate shell plate, B9004 2, is the surveillance program base metal material for BV 2.

l- The chemistry data for B9004 2 was obtained from material test certifications from the original fabricatiori The staff independently verified that the surveillance data for this base metal was l

credible. This is explained in detail, below, in addition, the staff verified that the RTpre value for j the intermediate shell plate, B9004-2, is significantly lower than the RTer, value for the limiting L plate, i

Th9 chemistry data for the best-estimate chemistry for the beltline welds were obtained from i their surveillance welds, material test certifications from the original fabrication, as well as the two additional material chemistry tests performed for St. Lucie Unit 2 and Almaraz Unit 2. The BV 2 surveillance weld and the St. Lucie Unit 2 and Almaraz Unit 2 welds were made of the same weld wire heat identification number and flux type as the intermediate and lower shell vertical seams and the girth weld between the intermediate and lower shell plates for BV 2

(3/16 inch diameter weld wire type B-4, heat number 83642, Linde 0091 flux, lot number 3536),

i The licensee revised the best-estimate chemistry for the beltline welds in WCAP-14784, Revision 2. The licensee added two new data points of copper / nickel values for the weld metal i (0.04% Cu/0.06% Ni and 0.03% Cu/

l 0.06% Ni) sad removed the last data point of the weld metal copper / nickel values (0.04%

l Cul0.07% Ni) that had been previously reported. The revised values were indicated in i Attachment 2 of the Florida Power & Light Co. letter, JPN-PSL-SESP-93-47 Revision 0, ' Table i 1: St. Lucle Unit 2 Reactor Vessel Beltline Weld Material."

I As a result of the revised chemistry data, the licensee's best-estimate chemistry for the beltline

welds and surveillance welds are 0.05% Cu and O.07% Ni. According to Regulatory Guide (RG) 1.99, Revision 2, the chemistry factor for welds with this chemistry is 34.1 degroes F. The weld samples have low Cu and Ni values and the i RTpr values for the weld metal is significantly lower than the RTpts value for the limiting plate.

Therefore, the changes in the Cu and Ni values are not significant in '5is assessment, l The licensee found the base metal and weld surveillance data to be credible. However, the i method of determining credibility did not satisfy Regulatory Guide 1.99, Revision 2, because the

'1 east squares" method for curve fitting -

cf the best-fit line did not go through the origin for the BV-2 surveillance data. As a result, the staff independently performed the "least squares" method for curve fitting with the best fit line going through the origin.

. Credibility Criterion (C) in section (c)(2)(i) of 10 CFR 50.61 indicates that the scatter of the measured ARTpr3 values must be less than 17 degrees F for base metals and 28 degrees F for

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4 welds. Evaluation of this criterion was the basis for the licensee's dete mination that the BV-2 base metal and weld surveillance data met the credibility criteria in 10 CFR 50.61. As stated ,

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above, the staff independently evaluated the scatter of the measured ARTp13, and determined that the base metal and weld surveillance data satisfy Criterion (C) in section (c)(2)(i) of 10 CFR 50.61. In addition, the licensee's calculated CFs are in agreement to the staffs calculated CFs (approximately 35.3 degrees F for plates and 15 2 degrees F for welds). Hence, the surveillance data are credible and should be used to determine the CF for the base metal and vessel weld.

The licensee's chemistry values for the weld heat identification number 83642 are 0.05% Cu and 0.07% Ni. The chemistry values for this heat in the Combustion Engineering Owners Group Final Report, CE NPSD-1039, Revision 02, are 0.046% Cu and 0.086% Ni. Because the difference in the chemistry values is small, the change in the RTpy, value for the subject weld is not significant.

The staff verified that all of the beltline region materials in the BV 2 reactor vessel have EOL RTpys values well below 149 degrees F at EOL (32 EFPY).

3.0 CONCLUSION

The licensee and staff assessment indicate that the reactor pressure vessel would be below the PTS screening criteria at the expiration of its license.

6 References

1. Regulatory Guide 1.99, Radiation Embrittlement of Reactor Vessel Materials, Revision 2, May 1988.

2. NUREG-0800, Standard Review Plan, Section 5.3.2: Pres'. re-Temperature Limits.

3. Code of Federal Regulations, Title 10, Part 50, Appendix G, Fracture Toughness Requirements.

j 4. Generic Letter 88-11, NRC Position on Radiation Embrittlement of Reactor

Vessel Materials and its impact on Plant Operations, July 12,1988.

5. ASME Boiler and Pressure Vessel Code, Section Ill, Appendix G for Nuclear Power Plant Components, Division 1, " Protection Against Non-ductile Failure."

6. WCAP-9615 Revision 1, "Duquesne Light Company Beaver Va! ley Unit 2 Reactor Vessel Radiation Surveillance Program," S.E. Yanichko, et. al., September 1989.

7. WCAP-14484, "Anelysis of Capsule V from the Duquesne Light Company Beaver Valley Unit 2 Reactor Vessel Radiation Surveillance Program," P.A. Grendys, et al., February 1996.

8. Attachment 2 to JPN-PSL-SESP-93-47 Revisicn 0, " Table 1: St. Lucie Unit 2 Reactor Vessel Beltline Weld Material."

9. Letter Report MT/ SMART-210(88), " Response to U.S. Nuclear Regulatory Commission Generic Letter 88-11 for the Beaver Valley Unit 2 Reactor Vessel," N.K. Ray, et al.,

November 1988.

10. WCAP-9228," Central Nuclear de Almaraz, Almaraz Unit No. 2 Reactor Vessel Radiation Surveillance Program," P.J. Fields, et. al.,

December 1977.

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SALPINPUT FACILITY NAME Beaver Valley, Unit 2 3UMMARY OF REVIEW ACTIVITIES By letter dated February 13,1997, the Duquesne Light Company (the licensee) submitted WCAP 14784, Revision 2, " Evaluation of Pressurized Thermal Shock for Beaver Valley Unit 2,"

which provided the revised Beaver Valley Unit 210 CFR 50.61 pressurized thermal shock assessment regarding the reactor vesselintegrity. The cubmittal was provided in response to item 3 of the NRC request for additionalinformation issued October 18,1996, concerning WCAP-14484, " Analysis of Capsule V for the Duquesne Light Ccmpany Beaver Valley Unit 2 Reactor Vessel Radiation Surveillance Program."

The staff concluded that the Beaver Valley Unit 2 reactor vessel is projected to be below the PTS screening criteria at the expiration of its license.

NARRATIVE DISCUSSION OF LICENSEE PERFORMANCE FUNCTIONAL AREA Enaineerina/ Technical Supp. pit The licensee svas very responsive to the staffs requests for assistance and clarification on minor technicalissues. The staff noted that the licensee provided good supporting technical information in their submittal. In addition, sufficient data and information was provided by the licensee to conduct an independent review of the PTS assessment.

Principal Contributor: M. Khanna (301)415-2150 i

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