B15951, Provides Comments on Preliminary Accident Sequence Precursor (ASP) Program Analysis of Operational Events & Conditions Occurred at Plant.Calculation Encl
| ML20134E304 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 10/30/1996 |
| From: | Feigenbaum T CONNECTICUT YANKEE ATOMIC POWER CO., NORTHEAST UTILITIES SERVICE CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20134E307 | List: |
| References | |
| B15951, NUDOCS 9611010106 | |
| Download: ML20134E304 (3) | |
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l 1 7 seiden suut, ununa m,037 Northeast Utilities System Northeast Duities Service Company l P.O. Iku 270 l Ilartford, CT 06141 0270 l (860) 665-5323 l
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- l. Ted C. Feigenbaum Executive Vice President and Chief Nuclear Officer October 30,1996 Docket No. 50-213 B15951
! U.S. Nuclear Regulatory Commission l Attention: Document Control Desk I Washington, DC 20555 ;
iladdam Neck Plant Comments on Preliminary Accident l Seouence Precursor Analvsjs l The purpose of this letter is to provide Connecticut Yankee Atomic Power Company's (CYAPCO) commentf 4 on the preliminary Accident Sequence Precursor (ASP) Program analysis of operatiNal events and conditions
- which occurred at the Haddam Neck Plant (HNP).
CYAPCO has reviewed the preliminary ASP report and concurs that this event was a .
potentially c:gnificant accident sequence precursor although differing with some assumptions used in the ASP.' CYAPCO's specific comments are discussed below.
The preliminary ASP report calculated a conditional core damage probability increase of 2.4E-4 for pressure locking of the low-pressure safety injection valves at the Haddam Neck Plant. This is essentially the initiating event frequericy for a large-break LOCA assumed in the ASP program. No contribution from other valves (e.g., SI-MOV-861A through D) was estimated and any contribution from small or medium break LOCA was not considered.
On behalf of CYAFCO, Northeast Utilities Service Company's (NUSCO) PRA Section has performed a detailed analysis of the core damage frequency impact of the condition (see Attechrnent 1).
W S. Dembek letter to T. C. Feigenbaum, " Review of Preliminary Accident
( Sequence Precursor Analysis of Condition at Haddam Neck Plant," dated August 23,1996. ,
9611010106 961030 hd l l
, U.S. Nuclear Regulatory Commission
[ B15951\Page 2 of 2 The analysis took into account the following: i
- identification of valves potentially most affected
- identification of the initiators impacted, and :
- . - a best estimate assessment of the conditional probability of valve failure, by l adjusting the common mode failure probability of the valves. '
I The latter accounted for realistic thermal conditions, experience, as well as estimates
, of valve bonnet pressure and required opening forces. For example, the valves are cycled open and closed during plant heat-up to attempt to preclude the pressure- .
j locking condition. Moreover, a number of conservative design basis assumptions were made in the reportability decision, such as limiting undervoltage conditions, which j would not necessarily be present for most large break LOCA conditions. LER 50-l 213/95-010-01, states that when these conservative assumptions are removed, the low l pressure safety injection valves would have performed their function of opening with offsite power available.
l
! CYAPCO believes that the ASP report is too conservative in estimating the conditional ,
! core damage _ probability. The NUSCO quantification assumed a conditional probability {
i of valve failure other than 1.0. The basis for this assumption was provided in the LER i
as to why the valves would likely have functioned for a large break LOCA without Loss !
, of Offsite Power.
e in summary, CYAPCO concurs that this event was a potentially significant accident :
sequence precursor, although differing with some assumptions used in the ASP. *
, CYAPCO appreciates the opportunity to review this report and provide comments to the
- NRC Staff. Please contact Mr. G. P. van Noordennen at (860) 267-3938, if you should l have any comments or questions. i
! Very truly yours,
- CONNECTICUT YANKEE ATOMIC POWER COMPANY l M/ ~
j T. C. Feigenbaurf j Executive Vice President and ,
j Chief Nuclear Officer 1
i Attachment j cc: H. J. Miller , Region I Administrator :
1 S. Dembek, NRC Project Manager, Haddam Neck Plant
, W. J. Raymond, Senior Resident inspector, Haddam Neck Plant 1
J
Docket No. 50-213 B15951 Attachment 1 Haddam Neck Plant An Analysis of the Risk Impact Due to Pressure Locking and Thermal Bindina of CY ECCS MOVs October 1996