ML19345A371
| ML19345A371 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 08/26/1976 |
| From: | Johnson W YANKEE ATOMIC ELECTRIC CO. |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| WYR-76-86, NUDOCS 8011210151 | |
| Download: ML19345A371 (3) | |
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YANKEE ATOMIC ELECTRIC COMPANY hL 20 Turnpike Road Westbcrough, Massachusetts 01581 u
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Attention: Office of Nuclear Reactor Regulation ~
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Subject:
Upper Hemispherical Head Temperatt. e
Reference:
(1)
License No. DPR-3 (Docket No. 50 29)
(2) Letter from W. P. Johnson to USNRC, WYR 76-84 (August 23, 1976).
(3)
Technical Specification, " Yankee Nuclear Power Station Core XII Performance Analysis", Appendix B, Additional LOCA Analysis, (February 20, 1976).
Dear Sir:
Concern over the effect of main coolant temperature in the upper hemispherical head of reactor vessels on the Loss-Of-Coolant-Accident (LOCA) analysis has come to our attention.
Yankee Atomic has promptly, initiated an evaluation of this effect (Reference 2) on the most recent IDCA analysis for Yankee Rowe (Reference 3).
This letter summarizes:
(1) interim results of the evaluation, and; (2) discussions between Yankee Atomic and the USNRC.
The design of the Yankee Rowe reactor vessel is such that it of the total main coolant flow at the inlet nozzles is directed to the upper head region to provide cooling, on that basis the Reference 3 analysis was performed using T ec an empera e n s
eold region.
In the absence of temperature measurements in this region to va.idate the assumption, Yankee is re-analyzing the most limiting LOCA Freak size identified in the Reference 3 analysis assuming T (560 F) for the coolant tempera me in the upper head. CurrentresuNsindicate that the peak LHOR must be reduced from 10.50 (current limir. imposed by Figure 8-1 of the Technical Specifications) to 10.15 kw/ft for the Exxon Fuel at the current burnup in the cycle life in order to keep clad temperature at ECBY equal to the value in the Reference 3 analysis (within 5 F).
This, in turn, will prevent the peak clad temperature (PCT) from being above the Reference 3 value. The re-analysis must be completed in order to determine the actual value of the revised PCT.
Yankee agrees with the NRC staff that a.35 kw/ft reduction in the peak LHGR for both Gulf and Exxon fuel, as shown in Figure 8-1, would be a conservative penalty to apply for the re.ainder of Core XII.
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L United States Nuclear Regulatory Commission August 26, 1976 Attn Office of Nuclear Reactor Regulation Page Two Yankee Atomic also agrees that an additional. 50 kw/ft would be a conservative penalty to account for the possibility of a shift in the most limiting break size.
In summary, based on interim evaluation results and discussions with the NRC, Yankee concludes that a 0.85 kw/ft reduction in,the limiting LHGR for both Exxon and Gulf fuel would be a conservative penalty to apply until a complete evaluation is available.
Very truly yours, YANKEE A'IOMIC ELECTRIC COMPANY
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