ML022190268

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Attachment: Dominions Additional Information on Reactor Vessel Neutron EMBRITTLEMENT-SURRY
ML022190268
Person / Time
Site: Surry  Dominion icon.png
Issue date: 08/05/2002
From:
NRC/NRR/DRIP/RLEP
To:
Virginia Electric & Power Co (VEPCO)
Tabatabai O, NRR/DRIP/RLEP, 415-3738
References
Download: ML022190268 (10)
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Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 1 OF 10 The following information concerning Reactor Vessel Beltline Neutron Fluence, Pressurized Thermal Shock, Charpy Upper Shelf Energy, and Limits for Heatup and Cooldown was prepared in support of Surry license renewal application. This information demonstrates an ability to comply with applicable regulations governing reactor vessel integrity including 10 CFR 50 Appendix G, 10 CFR 50 Appendix H, and 10 CFR 50.61 during a postulated 20-year license renewal period.

1. Calculated Beltline Fluence The reactor vessel beltline neutron fluence values applicable to a postulated 20 year license renewal period were calculated using the Virginia Power Reactor Vessel Fluence Methodology Topical Report [Ref. 1]. The methodology described in that report was developed in accordance with Draft Regulatory Guide DG 1053 [Ref. 2]. The reactor vessel fluence calculational methodology was benchmarked using a combination of Virginia Power surveillance capsules, pressure vessel simulator measurements, and Surry Unit 1 ex-vessel cavity dosimetry measurements.

The underlying requirement of DG-1053 is that the fluence determination should be made on a plant-specific, best-estimate basis rather than on a generic conservative basis. The methodology used to determine the best-estimate fluence must be demonstrated to have an associated uncertainty of +/-20 percent at the 1-sigma level. This level of uncertainty is consistent with the assumptions made in the development of the Pressurized Thermal Shock (PTS) screening criteria for vessel welds and plates.

The following fluence results were calculated for the Surry Unit 1 and Unit 2 reactor pressure vessels at the beginning and end of the license renewal period (BOLRP and EOLRP).

Table 1 Calculated Peak Fluence Values Surry Unit Number 1

2 EFPY at BOLRP 29.6 30.1 EFPY at EOLRP 47.6 48.1 Fluence* at Clad/Base Metal Interface BOLRP 3.530 3.520 EOLRP 5.400 5.340 Fluence* at 1/4 of wall thickness BOLRP 2.154 2.147 EOLRP 3.294 3.258 Fluence* at 3/4 of wall thickness BOLRP 0.802 0.799 EOLRP 1.226 1.213

  • Note: All fluence values are in units of 1019n/cm2 (E > 1.0 Mev)

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 2 OF 10

2. Pressurized Thermal Shock The following values were calculated in accordance with 10 CFR 50.61.

Table 2 Surry Unit 1 Values of RTPTS at 47.6 EFPY Lower Circ.

Long.

Limiting Materials Shell Weld Weld 4415-1 72445 299L44 Initial Ref. NDT Temp. (ºF) 20

- 5

- 7 Copper Content (%)

0.11 0.22 0.34 Nickel Content (%)

0.50 0.54 0.68 Surface Fluence (1019n/cm2) 5.40 4.70 0.79 Table* Chemistry Factor (ºF) 220.6 Table* Margin (ºF) 69.5 Table* Ref. PTS Temp. (ºF) 268.5 S/C** Chemistry Factor (ºF) 85.0 138.0 S/C** Margin (ºF) 17.0 48.3 S/C** Ref. PTS Temp. (ºF) 157.4 235.2 Table 3 Surry Unit 2 Values of RTPTS at 48.1 EFPY Lower Circ.

Long.

Limiting Materials Shell Weld Weld C4208-2 0227 8T1762 Initial Ref. NDT Temp. (ºF)

-30 0

- 5 Copper Content (%)

0.15 0.19 0.19 Nickel Content (%)

0.55 0.55 0.57 Surface Fluence (1019n/cm2) 5.34 5.34 1.08 Table* Chemistry Factor (ºF) 107.3 152.4 Table* Margin (ºF) 34.0 68.5 Table* Ref. PTS Temp. (ºF) 155.8 219.1 S/C** Chemistry Factor (ºF) 128.0 S/C** Margin (ºF) 48.8 S/C** Ref. PTS Temp. (ºF) 230.0

    • Note: Chemistry factor determined using credible surveillance capsule (S/C) data [Ref. 4].
3. Upper Shelf Energy The requirements on upper shelf energy are included in 10 CFR 50, Appendix G. 10 CFR 50, Appendix G requires utilities to submit an analysis at least 3 years prior to the time that the upper shelf energy of any of the reactor pressure vessel (RPV) material is predicted to drop below 50 ft-lb, as measured by Charpy V-notch specimen testing.

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 3 OF 10 There are two methods that can be used to estimate the change in upper shelf energy (USE) with irradiation, depending on the availability of credible surveillance capsule data as defined in Revision 2 of Regulatory Guide 1.99. For vessel beltline materials that are not in the surveillance program or not credible, the Charpy upper shelf energy is assumed to decrease as a function of fluence and copper content, as indicated in Regulatory Guide 1.99, Revision 2.

When two or more credible surveillance data sets become available from the reactor, they may be used to determine the Charpy USE of the surveillance material. The surveillance data are then used in conjunction with the Regulatory Guide data to predict the change in USE of the RPV due to irradiation.

Using the 1/4 thickness (1/4 T) fluence values per Section 1, the values of upper shelf energy (USE) in Tables 4 and 5 were calculated for the Surry Unit 1 and Unit 2 reactor pressure vessels at the end of the license renewal period being evaluated.

Table 4 Surry Unit 1 USE Values at 47.6 EFPY Lower Circ.

Long.

Limiting Materials Shell Weld Weld 4415-2 72445 299L44 Initial USE Value (ft-lbs)*

83 77 70 1/4 T Fluence (1019n/cm2) 3.29 2.87 0.482 Decrease (%)

26 45 38 USE Value (ft-lbs) 61.6 42.1 43.6 Table 5 Surry Unit 2 USE Values at 48.1 EFPY Intermed.

Circ.

Long.

Limiting Materials Shell Weld Weld C4331-2 0227 8T1762 Initial USE Value (ft-lbs)*

84 90 70 1/4 T Fluence (1019n/cm2) 3.26 3.26 0.659 Decrease (%)

27 43 30 USE Value (ft-lbs) 60.9 51.2 49.2

  • Note: Initial values are measured.

As shown by these results, the upper shelf energy (USE) values at the end of the license renewal period are greater than the NRC (10CFR50) Appendix G requirement of 50 foot-pounds for some of the limiting materials. For the other limiting materials (welds), an equivalent margins analysis was used to justify the acceptability of values below the 50 foot-pound requirement. Four service levels - A, B, C and D - are evaluated for an equivalent margins analysis. There are two conditions for each loading case to be met. They are:

1. The applied J-integral shall be less than J-integral of the material at a ductile flaw extension of 0.10 inches.
2. Flow extensions shall be ductile and stable.

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 4 OF 10 In addition to these two conditions, one more requirement has to be met for service level D, which is as follows:

3.

The extent of stable flaw extension shall be less than or equal to 75% of the vessel wall thickness, and the remaining ligament shall not be subject to tensile instability.

4. Limits for Heatup and Cooldown Figure 1 presents the heatup curves, without margin for instrumentation errors, for a maximum rate of 60ºF/hour for the limiting material in the Surry Units 1 and 2 reactor pressure vessel beltline. Note on these curves, that moderator temperature is Reactor Coolant system water temperature. Likewise, Figure 2 presents the cooldown curves, without margin for instrumentation errors, for a maximum rate of 100ºF/hour for the limiting material in the Surry Units 1 and 2 reactor pressure vessel beltline. The heatup curves of Figure 1 and the cooldown curves of Figure - 2 are based upon the limiting adjusted reference temperature (ART) values from Tables 6 and 7, and are valid for up to 47.6 EFPY in Unit 1 and for up to 48.1 EFPY in Unit
2. Since these curves provide sufficient margin on the operating window relative to the pump seal requirements, no additional actions are required for the license renewal periods of Surry Unit 1 and Unit 2.

Maximum allowable low temperature over-pressure protection system (LTOPS) power operated relief valve (PORV) setpoints have been developed which bound both Surry Units 1 and 2. They were developed based on end of license renewal heatup and cooldown curves using the current Westinghouse methodology (Ref. 5). The setpoints conservatively account for instrument uncertainties and the pressure difference between the wide range pressure transmitter and the reactor vessel limiting beltline region.

The following PORV setpoints will provide adequate margin to the Surry Units 1 and 2 Appendix G limits throughout a 20 year license renewal period with no restrictions on the number of RCPs running:

RCS Temperature PORV Setpoint TRCS< 325°F 399 psig Table 6 Surry Unit 1 ART Values at 47.6 EFPY Beltline Materials ART at 1/4 T ART at 3/4 T Lower Shell 4415-1 S/C** Chemistry Factor 148.6 ºF 126.8 ºF Circumferential Weld 72445 S/C** Chemistry Factor 220.0 ºF 183.9 ºF Longitudinal Weld 299L44 Table* Chemistry Factor 238.2 ºF 182.5 ºF

    • Note: Chemistry factor determined using credible surveillance capsule (S/C) data [Ref. 4].

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 5 OF 10 Table 7 Surry Unit 2 ART Values at 48.1 EFPY Beltline Materials ART at 1/4 T ART at 3/4 T Lower Shell C4208-2 Table* Chemistry Factor 144.5 ºF 117.0 ºF Circumferential Weld 0227 S/C** Chemistry Factor 216.5 ºF 183.7 ºF Longitudinal Weld 8T1762 Table* Chemistry Factor 198.0 ºF 157.8 ºF

    • Note: Chemistry factor determined using credible surveillance capsule (S/C) data [Ref. 4].
5. Reactor Vessel Surveillance Program The Surry Unit 1 and 2 surveillance capsule withdrawal schedules [Ref. 6], which include provisions for license renewal are provided in Tables 8 and 9, respectively. Specifically, Virginia Power has already acquired surveillance capsule data for Surry Units 1 and 2 that bounds, in terms of accumulated fluence, the predicted end-of-license-renewal inner surface fluence at the limiting beltline weld material (i.e. 0.79x1019 n/cm2 for the Surry Unit 1 lower shell longitudinal weld, SA-1526); surveillance data from the Surry Unit 1 surveillance program has been collected at fluences as high as 1.94 x1019 n/cm2. Additional Surry Units 1 and 2 standby surveillance capsules are available to provide additional material properties data and fluence monitoring during the license renewal period. Dominion anticipates implementation of the recommendation of GALL report for the withdrawal of the final plant-specific surveillance capsules.

==

Conclusion:==

The aforementioned information demonstrates an ability to comply with applicable regulations during a postulated 20-year license renewal period. Required analysis will be performed and implemented in accordance with the requirements of the applicable regulations, and in anticipation of the expiration of affected plant Technical Specifications.

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 6 OF 10 Table 8 SURVEILLANCE CAPSULE WITHDRAWAL SCHEDULE SURRY UNIT 1

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 7 OF 10 Table 9 SURVEILLANCE CAPSULE WITHDRAWAL SCHEDULE SURRY UNIT 2

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 8 OF 10 Figure - 1 Surry Units 1 and 2 Reactor Coolant System Heatup Limitations (Heatup Rates up to 60ºF/hr) Applicable to End of License Renewal (With Margins of 0ºF and 0 psi for Instrumentation Errors)

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 9 OF 10 Figure - 2 Surry Units 1 and 2 Reactor Coolant System Cooldown Limitations (Cooldown Rates of 0,20,40, 60 and 100ºF/hr) Applicable to End of License Renewal (With Margins of 0ºF and 0 psi for Instrumentation Errors)

Reactor Vessel Neutron Embrittlement - Surry 08/01/02 PAGE 10 OF 10

1.

Virginia Power Topical Report VEP-NAF-3A, "Reactor Vessel Fluence Analysis Methodology," dated November, 1997.

2.

Draft Regulatory Guide DG-1053, "Calculational and Dosimetry Methods for Determining Pressure Vessel Neutron Fluence," June 1996 previous draft was DG-1025, September 1993.

3.

NRC Reg. Guide 1.99 Revision 2, Radiation Embrittlement of Reactor Vessel Materials, May, 1988 4.

Letter from J. P. OHanlon to USNRC, Virginia Electric and Power Company, Surry and North Anna Power Stations Units 1 and 2, Surry 1 Reactor Vessel Surveillance Capsule X Analysis Report, GL 92-01, Revision 1, Supplement 1, Response to Request for Additional Information and Topical Report on Reactor Vessel Fluence Analysis Methodology, Serial No.98-252, dated June 18, 1998.

5.

WCAP-14040-NP-A, Rev. 2, Methodology Used to Develop Cold Overpressure Mitigating System Setpoints and RCS Heatup and Cooldown Limit Curves, January 1996.

6.

Tables 4.1-12 and 4.1-13, Surry Units 1 and 2 UFSAR

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