ML20086R325
| ML20086R325 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 07/26/1995 |
| From: | Carns N WOLF CREEK NUCLEAR OPERATING CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20086R326 | List: |
| References | |
| WM-95-0118, WM-95-118, NUDOCS 9507310104 | |
| Download: ML20086R325 (4) | |
Text
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W$1LF CREEK NUCLEAR OPERATING CORPORATION Neil S. " Buzz" Carns Chairman. President and Chief ExecutweOfficer July 26, 1995 WM 95-0118 U.
S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-137 Washington D.
C.
20555
Reference:
NRC Letter dated June 20, 1995, from James C.
Subject:
Docket No. 50-482: Comments on the Preliminary Accident Sequence Precursor Analysis of the Drain'Down Event at-Wolf Creek Generating Station Gentlemen:
The attached comments are submitted by Wolf Creek Nuclear-Operating Corporation (WCNOC) in response to the Reference.
The Reference provided WCNOC with the opportunity to review a copy of the NRC's report, " Preliminary Accident Sequence Precursor Analysis of Drain Down Event At Wolf Creek," and to provide comments on the technical adequacy of the analysis.
The submittal of these comments after the date requested in the Reference was discussed with Mr. J. Stone, NRR Project Manager for Wolf Creek.
WCNOC appreciates the oppcrtunity to comment on this preliminary analysis.
If you have any questions concerning this information, please contact me at (316) 364-8831 extension 4100 or Mr. Richard D. Flannigan at extension 4500.
Very truly yours,
~
-w Neil S. Carns
)
NSC/jra Attachment Enclosure cc:
L.
J.
Callan (NRC), w/a, w/e j
D. F. Kirsch (NRC), w/a, w/e I
0g J. F. Ringwald (NRC), w/a, w/e J.
C. Stone (NRC), w/a, w/e g\\
l 9507310104 950726 PDR ADOCK 05000482
^
S PDR O 1 U V 4. U PO Box 411/ Burlington, KS 66839 / Phone (316) 364-8831 An Equal opportunity Employer M T/HC/ VET j
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Attcchment to WM 95-0118 Page 1 of 2 WCNOC COMMENTS ON THE NRC's PRELIMINARY ACCIDENT SEQ 7ENCE PRECURSOR ANALYSIS OF THE DRAIN DOWN EVENT AT WOLF CREEK GENERATING STATION Wolf Creek Nuclear Operating Corporation (WCNOC) has reviewed the copy of the Preliminary Accident Sequence Precursor Analysis of the September 17,
- 1994, Reactor Coolant System (RCS) Drain Down Event at Wolf Creek Generating Station, and offers the following comments concerning the technical adequacy of the preliminary analysis:
- 1. Both sections A.1.1 (second sentence) and A.1.2 (last sentence of third paragraph on page A.1-2) are worded such that it could be implied that the operators did not initiate action to close valve EJHV-8716A until 66 seconds into the event.
Interviews with plant operators on shift at the time of the event indicate that the problem was identified and the button to close EJHV-8716A was pushed less than 66 seconds after the initiation of the event.
The 66 seconds included the time for diagnosis of the event, operator action to close the valve, and time for the valve to cycle from full open to full closed.
2.
Section A.1.1, first sentence - the drain down event was initiated approximately 28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br /> following shutdown, instead of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
This is based on a review of the operating logs, which note that the draindown event was initiated at about 0400 on September 17, 1994, subsequent to the manual trip of the reactor occurring at about 0000 on September 16, 1994.
These times are listed in the Control Room Logs, which were provided to the AEOD team investigating the event.
- 3. Section A.1.1
- Westinghouse analysis, using actual event conditions, indicates that core uncovery could have occurred in approximately 30 minutes (not the 25 minutes discussed throughout the preliminary analysis),
assuming the RCS was vented to the Refueling Water Storage Tank (RWST) and there was no makeup available to the RCS.
The 25 minute time used throughout the preliminary analysis should be changed to 30 minutes.
Note that for the worst case conditions (at the earliest entry time for Mode 4),
the Westinghouse analysis indicates that core uncovery could occur within 24 minutes.
These results are documented in the Westinghouse analysis of the draindown event.
This analysis is summarized in a report entitled
" Wolf Creek RCS Drain Down Evaluation Summary Report," dated February 1995.
This summary report was provided to Mr.
J.
Stone, NRR Project Manager for Wolf Creek, in early March 1995, and was subsequently placed on the docket.
This summary report was also attached to the Incident Invcetigation Team (IIT) report for the draindown event (IIT Report 94-04, Revision 2,
- Transfer Of Water From The RCS To The RWST of September 17, 1994"), which was previously provided to the NRC.
- 4. Section A.1.1 and A.1. 4 (page A.1-4) both indicate that the conditional core damage probability (CCDP) for the event is 3.0E-03.
This CCDP is about an order of magnitude greater than the preliminary CCDP estimated by WCNOC in the IIT report for this event.
In consideration for the difference between the two CCDP values, and due to the concerns recently identified by the NRC with the human reliability analysis methodology utilized by WCNOC in performing the Individual Plant Examination, WCNOC requested NUS Corporation to perform an evaluation of the event using their human interactions analysis methodology.
NUS calculated the conditional
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Atttchment to WM 95-0118 Page 2 of 2 i
WCNOC COMMENTS ON THE NRC's PRELIMINARY ACCIDENT SEQUENCE PRECURSOR ANALYSIS OF THE DRAIN DOWN EVENT AT WOLF CREEK GENERATING STATION core damage probability to be 3.5E-04.
The assumptions and methodology used in the determination of the 3.5E-04 conditional core damage i
probability value are documented in the NUS report, " Human Interactions Evaluation," dated July, 1995, which is enclosed for your review.
j i
- 5. Section A.1. 4, paragraph 5 - The first sentence states that after the RCS loops void at 5 minutes, RCS pressure would rapidly drop.
However, the Westinghouse analysis of the draindown event (identified above) indicates j
that the RCS pressure would drop to saturation conditions within 30 to 60 l
seconds, after which the RCS pressure would slowly increase due to the absence of decay heat removal capability.
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1 Enclosure to WM 95-0118 1