ML20215N663
| ML20215N663 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 10/28/1986 |
| From: | Papanic G YANKEE ATOMIC ELECTRIC CO. |
| To: | Mckenna E Office of Nuclear Reactor Regulation |
| References | |
| DCC-86-164, FYR-86-103, NUDOCS 8611070137 | |
| Download: ML20215N663 (3) | |
Text
-Y NKEE ATOMIC ELECTRIC COMPANY Tc':pho"' (6 ") ' - 'oo
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v, T ju 1671 Worcester Roatt Framingham, Massachusetts 01701DCC 86-164
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October 28, 1986 FYR 86-103 U. S. HUCLEAR REGULATORY COMMISSION Washington, D. C. 20555 Attention:
Eileen M. McKenna, Project Manager Project Directorate #1 Division of PWR Licensing - A
References:
(a) License No. DPR-3 (Docket No. 50-29)
(b) YAEC Letter to USNRC, Dated January 22, 1986 (c) USNRC Letter to YAEC, Dated August 26, 1986
Subject:
Fast Neutron Fluence for the Reactor Vessel - 10 CFR 50.61
Dear Ms. McKenna,
In Reference (b), you requested additional information to support Yankee's 10 CFR 50.61 assessment [Ryference (b)]. Attached is Yankee's response to the four questions.
We trust that you will find this information satisfactory, however, if you require additional information please contact us.
Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY a
George Papanic Jr.
Senior Project Engineer - Licensing f
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o 8611070137 861028 PDR ADOCK 05000029 p
u Attachment
).
2 Reply to Questions 1, 2 and 4
-The fluence methodology described in the subject report is characteristic of the standard Westinghouse design practice in place in the 1976 - 1983 time period. Key features of the analysis-approach involved the-use of aP expansion of scattering cross-sections and ENDF-II based cross-section g
library.
The overall analytical approach including the use of ENDF-II data files was benchmarked by comparison with power reactor surveillance dosimetry data as well as by comparison with the NRC sponsored PCA benchmark experimental results. Portions of the power reactor comparisons were provided as a part
'of the subject report.
Results of the PCA comparisons were documented in Sections 6.3 and 7 1 of-NUREG/CR-186, " LWR Pressure Vessel Surveillance Dosimetry Improvement Program:
PCA Experiments and Blind Te'st", July 1981. Pertinent data from that document are. summarized as follows for the 12/13 PCA configuration.
Flux (E > 1.0 MeV)
Location Measured West.
A Z
154X10[6 1.68X10[6 1.66 X 10 A0.
-6 A1 3 71 X 10 3.68 X 10 3.39 X 10 3 55 x 10
-7
-7 A2 3 88 X 10 3 89 X 10
-7
-7
-7 A3 1 33 X 10-3 94 X 10_8 3 96 X 10 3 99 X 10_8 4.30 X 10_8 1.21 X 10 1.21 X 10-1.29 X 10
-8 A4 8
8 A5 2.07 x 10 1.89 X 10 1.84 X 10 1.82 X 10
-9
-9
-9
-9 A6 9.11 X 10 8.33 X 10 7 88 X 10 7 87 X 10 In addition to the Westinghouse results, data is also provided for participants A and Z, both of whom employed a P scattering approximation and ENDF-IV 3
based cross-section libraries.
In the above Table, points A4, A5 and A6 lie within the pressure simulator.
~
'At those locations, all of the calculations are biased low from 9 - 14%,
with all of the Westinghouse calculations agreeing within 9% of the benchmark measurements. Furthermore, the analytical comparisons demonstrate that for the PCA benchmark configuration using P approximations and ENDF-II 3
cross-sections employed by Westinghouse is fully equivalent to-using P 3 approximations and ENDF-IV cross-sections used by participants A and Z.
Subsequent to 1983 the Westinghouse neutron exposure methodology was upgraded in several areas including input cross-sections and the approach to handling plant and fuel cycle specific neutron source strengths in the reactor core..
These upgrades were discussed with Yankee Atomic personnel at the time of submittal of PTS evaluations. Using the new methodology, PCA calculations are in essential agreement with measurements and, if this approach were used to re-evaluate the Yankee vessel fluence, exposure estimates would be expected to increase on the order of 10%. The 10% increase in the exposure estimate would slightly raise the calculated maximum RT in the limiting plate 4 F'at the end-of-plant-license. Thus,thecalculbdmaximumRT PTS s
-w.-
,,.y.-
r
- - ~ -.
,.---.---------gn---
,,e,
a would be 243 F at the end-of glant-license which is still well below the PTS screening criteria of 270 F for plate material.
Reply to Question 3 The power distributions used in the analysis were a linear average representing Cycles 12 through 15 Based on the information.available cycles prior to Cycle 12 were lower in power on the periphery by 2 to 8%. Cycles subsequent to Cycle 15 are higher on the periphery by 3 to 5%. Future fuel management will continue to keep the peripheral power approximately the same. Therefore, with early cycles being lower in peripheral power and future cycles being slightly higher in peripheral power, the power distribution used in the analysis is a representative average power to the end-of-plant-license (Approximately Cycle 24).