B12610, Responds to Questions Posed During 870701 & 21 Telcon Re Fluence Calculations & Util Intentions Re Evaluation of PTS Upon Conversion from Stainless Steel to Zircaloy Clad Fuel. NRC Should Approve Rt PTS Evaluation Per 10CFR50.61

Responds to Questions Posed During 870701 & 21 Telcon Re Fluence Calculations & Util Intentions Re Evaluation of PTS Upon Conversion from Stainless Steel to Zircaloy Clad Fuel. NRC Should Approve Rt PTS Evaluation Per 10CFR50.61

ML20237L669
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	08/21/1987
From:	Mroczka E, Sears C CONNECTICUT YANKEE ATOMIC POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
B12610, NUDOCS 8708280203
Download: ML20237L669 (4)

Text

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CONNECTICUT YANKEE AT O MIC POWER COMPANY B E R L I N, CONNECTICUT P o box 270 e HARTFORD. CONNECTICUT 06141-0270 TELEPHONE b 8 203MS 6000

Docket No. 50413 r ^

B12610 l Re 10CFR50.61 U.S. Nuclear Regulatory Commission Attn: Docyment Control Desk Washington, D.C. 20555

References:

1. 3. F. Opeka letter to C. I. Grimes, "Haddam Neck Plant, Millstone Nuclear Power Station, Unit Nos. 2 and 3,10CFR50.61 Compliance," January 23,1986.

2. E. 3. Mroczka letter to U. S. Nuclear Regulatory Commission, "Haddam Neck Plant, Request for Additional Information, 10CFR50.61 Compliance," April 1,1987.

Gentlemen:

Haddam Neck Plant Additional Information Regarding Pressurized Thermal Shock  ;

) In accordance with 10CFR50.61, Connecticut Yankee Atomic Power Company (CYAPCO) provided information regarding Pressurized Thermal Shock (PTS) for the Haddam Neck Plant to the NRC by letter dated January 23, 1986 (Reference 1). In response to NRC Staff questions regarding calculations of fluence for the Haddam Neck Plant, CYAPCO provided additional information by letter dated April 1,1987 (Reference 2). l During telephone conferences with the Staff on July I and 21, 1987, the Staff posed additional questions to CYAPCO regarding fluence calculations. Also discussed at that time were CYAPCO's intentions regarding evaluation of PTS upon conversion from stainless steel to zircaloy clad fuel at Haddam Neck. The Staff indicated that the requested information would enable closure of the PTS issue for the Haddam Neck Plant.

Staff Questions in the aforementioned telephone conferences, the Staff requested that CYAPCO assess the impact of using a P3 angular distribution rather than a P1 distribution in its fluence prediction. The Staff requested that CYAPCO confirm that an adequate margin to the RTPTS screening criteria remains even if a different distribution is used.(l) 8708280203 870821 PDR ADOCK 05000213

- p PDR (1) The Staff also requested an assessment of the impact of using an Sg quadrature, rather than 56, in the fluence calculations. CYAPCO used an Sg quadrature in its fluence calculations. Thus, this assessment is o unnecessary. t ,O

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U.S. Nuclear Regulatory Commission B12610/Page 2 August 21, 1987 Response to Staff Questions i

CYAPCO and the Staff recognize that to provide a plant-specific analysis with different distributions would require a considerable undertaking. Consequently, in order to assess the potential impact of a change, CYAPCO and the NRC Staff agreed that applying a conservative uncertainty value to the fluence calculation already performed for Haddam Neck would be appropriate. This approach is reasonable because of the significant margin between the predicted Reference Temperatures ( PTS) and the screening criteria established by

.10CFR50.61(b)(2).

• The existing analyses of the Haddam Neck vessel rnakes use of a P1 cross section approximation and a 1.05 MeV threshold. Although an updated evaluation has not l been performed, estimates of the P3 versus P1 effect as well as the effect of the reduced threshold can be based on analyses of other Westinghouse plants. Based on these similar evaluations, the use of current neutron transport methodology 1

I increases the fast neutron fluence projection for the Haddam- Neck vessel by approximately 20% About 15% is due to the P3 versus Pt effect and accounts for l the fact that the P 3 is benchmarked to the PCA experiment and the P1 is not.

The remaining five percent is due to the decreased energy threshold.

In accordance with the above, CYAPCO provides the following information. The predicted cor, trolling RTPTS value is based on a conservative assumption of 20%

uncertainty in estimated fluence at 32 EFPY.

Haddam Neck Controlling Materials Predicted 32 EFPY RTp rs (10CFR50.61) l Fluence @ RTPTS @ 20% Adjustment 20% Adjustment RTPTS I 32 EFPY 32 EFPY Fluence @ RTPTS Screening 1

l Location (N/cm2) (oF) 32 EFPY 32 EFPY (@OF) Criteria Weld 6.26 x 1019 168.59 7.51 x 1019 177.3 270 (ARCOS B-5 Flux)

Thus, a margin of over 920F remains between the predicted RTPTS at 32 EFPY

! and the screening criteria even assuming a total uncertainty of 20E l

(2) To illustrate this margin, CYAPCO notes that a change in the estimated fluence results in a significantly smaller increase in the predicted RTpTc because of the exponential power applied to the fluence value in the equations used for this purpose in accordance with 10CFR50.61(b)(2).

Applying those equations, CYAPCO assessed the actual degree to which estimated fluence values would need to change before the controlling value of predicted RTPTS would exceed the screening criteria. CYAPCO determined that the estimated fluence at the end of a 40-year operating life (32 Effective Full Power Years (EFPY)) would need to increase 600% before the RTPTS would exceed the screening criteria.

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U.S. Nuclear Regulatory Commission B12610/Page 3 August 21,1987 CYAPCO submits that the significant margin between the predicted RTPTS for the Haddam Neck Plant and the screening criteria of 10CFR50.61(b)(2), even making the additional assumptions proposed by the Staff, makes further assessment unnecessary.

Zircaloy Conversion In addition to the above questions, the Staff requested that CYAPCO confirm its intent to conduct updated PTS analyses for the Haddam Neck Plant upon commencement of the planned conversion to zircaloy cladding. This conversion is scheduled to occur beginning with Cycle 17 operation, probably in 1990. CYAPCO intends to perform and submit an updated assessment of PTS for the Haddam Neck Plant to support that conversion. These analyses will provide further assurance that the Haddam Neck reactor vessel will continue to satisfy require-ments concerning PTS set forth in 10CFR50.61 after zircaloy conversion.

Cor clusion CYAPCO requests that the Staff approve the RTPTS evaluation performed pursuant to 10CFR50.61 and provide to CYAPCO written confirmation of this closure.

Very truly yours, I

I CONNECTICUT YANKEE ATOMIC POWER COMPANY  :

i t e E. 3. Mroczka I Senior Vice President By: C. F. Sears Vice President cc: W. T. Russell, Region 1 Administrator F. Akstulewicz, NRC Project Manager, Haddt.,a Neck Plant

3. T. Shediosky, Resident Inspector, Haddam Neck Plant l