ML20112H255
| ML20112H255 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 03/26/1985 |
| From: | Lundvall A BALTIMORE GAS & ELECTRIC CO. |
| To: | John Miller Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-CR-3511 NUDOCS 8504020190 | |
| Download: ML20112H255 (4) | |
Text
x-BALTIMORE GAS AND ELECTRIC CHARLES CENTER P. O. BOX 1475 BALTIMORE, MARYLAND 21203 MHun E. LUNDVALL, JR.
%Cg PRESIDENT SUPPLY Directoi of Nuclear Reactor Regulation Attention: Mr. 3. R. Miller, Chief Operating Reactors Branch #3 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Subject:
Calvert Cliffs Nuclear Power Plant Units Nos.1 & 2; Dockets Nos. 50-317 and 50-318 Interim Reliability Evaluation Program (IREP) Report, Analysis of Calvert Cliffs Nuclear Power Plant Unit 1 NUREG/CR-3511, dated August 1984
Reference:
Letter from Mr. 3. R. Miller to Mr. A. E. Lundvall, Jr.,
dated January 22,1985, same subject.
Gentlemen:
As rea':csted in the letter referenced above, the Baltimore Gas and Electric Company is plewA u provide additional comments on the Calvert Cliffs' IREP report.
This study was performed using methods which were appropriate to the purpose of the project and consistent with those used in the other IREP studies.
Recognizing the limitations of probabilistic risk assessment and the level of PRA technology at che time the work was performed, we agree with the insights and conclusions of the report. However, it should be noted that the conclusions of the report and the resilts should be interpreted and utilized only by those who have an understanding of PRA terminology, methodology, limitations,and applications.
Of course, we have used these insights to improve both the facility and the procedures by which it is operated. We recognize that IREP was intended as a study of the plant at a particular moment, and that changes to the report because of plant hardware and procedure modifications were never contemplated. We have provided a summary of changes which may algnificantly influence the probabilities calculated for the IREP report, and have identified the relevant paragraphs of the report (Attachment 1).
A few minor discrepancies were noted in the report and are also provided (Attachment 2).
8504020190 850326 PDR ADOCK 05000317 P
PDR g
r Mr. 3. R. Miller M rch 26,1985 L
We have not yet received the Appendices to the report, and therefore cannot comment on them.
Should you have any questions regarding these matters, please feel free to contact us.
Very truly you s, s'
t'
- 3.tts & nrib ~
AEL/SMM/vf J
Attachments cc: D. A. Brune, Esq.
G. F. Trowbridge, Esq.
Mr. D. H. Jaffe, NRC Mr. T. Foley, NRC l
i i
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s ATTACHMENTI
SUMMARY
OF CHANGES COMPLETED FOLLOWING NUREG/CR-3511 IREP STUDY Paragraph 6.3.4, Item (2)
A manual override of the Recirculation Actuation Signal (RAS) to the Low Pressure Safety Injection (LPSI) pumps has been installed. This key operated switch would permit overriding the RAS signal to the selected LPSI pump only.
This would permit the operator to start the LPSI pump even if RWT level had not been raised to reset the RAS signal.
Paragraph 6.9.4 Manual valve AFW-161 for both units has had its internal parts removed. This eliminates the potential failure mechanism discussed in this paragraph.
Paragraph 6.17.4, items (1) & (2)
Manual valves SWS 196 and SWS 197 for both units have had their internal parts removed. This eliminates the potential failure mechanism discussed in these paragraphs.
Paragraph 8.1.5.4 See paragraph 6.9.4 above regarding AFW-161.
Procedures have been developed for using the cross-connect valve, MOV-4550, between Unit I and 2 AFW motor driven trains.
These procedures are available in Abnormal Operating Procedure 3D,Section II.
Paragraph 8.1.9.4 See paragraph 6.9.4 above regarding AFW-161.
Paragraph 8.1.10.4 Procedures have been developed which provide step-by-step operations necessary to connect the SMECO 69 kV transformer to the 13 kV electrical system. These procedures are available in Operating Instruction 27E,Section IV.
C
O 9
ATTACHMENT 2 MINOR ERRORS IN NUREG/CR-3511, IREP STUDY Pagraph 8.1.2.4 Turbine Pump #3 is incorrect, should be Turbine Pump #12.
Paragraph 8.1.10.1 This sequence implies the Calvert Cliffs AFW Turbine Pumps have a dependency on DC power.
There is no such dependency since the turbine driven pump steam supply valves are air operated, fail open valves. The AFW system can still be used to feed steam generators with manual operation, even after the batteries deplete.
- Note, however, that the monitoring instrumentation will fall due to loss of power upon battery depletion.
Table 8.3 Sequence 2 Category Total Value should be 1.62 E-5, vice 2.0 E-5.
The T4(category transients consisted of a large number of events, including - Spurious Cause Unknown). Auto-Trip - No Transient Condition and Manual Trip - No Trips Transient Condition. These three events contributed 2.3 of its 6.8 occurrences per year, or roughly 34%
While these events obviously involve successful operation of the RPS, no effort was made to distinguish between them and the other T4 events when considering the additional failure to scram the plant. As was the case for loss of offsite power events, the only cause for an ATWS associated with these events is a mechanical common mode failure of all or most of the control rod driva mechanisms, an event with " negligible" probability.
If the ATWS contributions from these events were eliminated, the new ATWS core melt contributions would be as follows:
New Old 5
5 ATWS (PSF) 2.4 x 10j/yr.
2.8 x 10j/yr.
T KU 4.4 x 10 /yr.
6.7 x 10 /yr.
T KQ 2.8 x 10 /yr.
4.3 x 10 /yr.
and would reduce the total core melt probability from 1.3 x 10~4/yr. to 1.2 x 10-4/yr.
The total ATWS contribution is reduced from 33% to 26%
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