ML17331A773
| ML17331A773 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 07/29/1981 |
| From: | Hunter R INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| AEP:NRC:0570, AEP:NRC:570, NUDOCS 8108040257 | |
| Download: ML17331A773 (5) | |
Text
REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIOS)
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NO DOCKET' FACIL>>:50 315 Donald C;
Cook. Nuclear power Pl anti Unit 1< Indiana 8
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Cook Nuclear Power Pl antF Unit 2E Indiana 8 (05000316~
AUTH',NAHK AUTHOR>> AFFILIATION HUNTKRER'OS'ndi anal 8
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RECIPR VAMEi RECIPIENT AFFILIATION OENTONgH ~ RE Office of Nuclear'eactor Regulationr Director-SUBJECTS. Forwards comments in response to SA Varga 810506 ltr re reactor safety study methodology applications program evaluation of Sequoyah 1 'ased on plant design similar'itiesr results applicaole to Cook Units 1
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INDIANA IIt MICHIGAN ELECTRIC COMPANY P. O.
BOX 18 BOWLING GREEN STATION NEW YORK, N. Y. 10004 July 29, 1981 AEP:NRC:0570 Donald C. Cook Nuclear Plant Unit Nos.
1 and 2
Docket Nos.
50-315 and 50-316 License Nos.
OPR-58 and OPR-74 RSSMAP Analysis of Sequoyah Unit No.
1 as it Applies to the Donald C.
Cook Nuclear Plant Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Oenton:
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This letter and its attachment respond to Mr. S. A. Varga's letter of May 6, 1981 concerning the Reactor Safety Study Methodology Applicat-ions Program (RSSMAP) evaluation of Sequoyah Unit No.
1.
Based on Plant design similarities we believe that the results of the RSSMAP analysis are generally applicable to the Cook Plant.
We have reviewed the con-clusions of the Sequoyah RSSMAP with respect to their applicability to the Cook Plant and our comments are provided in the attachment to this letter.
Very g
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S.
Vice truly yours, Hunter President cc:
John E. Dolan - Columbus R.
WE Jurgensen G. Charnoff R. C. Callen D. V. Shaller - Bridgman Joe Williams, Jr.
Region III Resident Inspector at Cook Plant 8108040257 810729 PDR
- DOCK 05000315 P
PDR 0y(
ATTACHMENT TO AEP'NRC:0570 1.
RSSMAP CONCLUSION An important accident sequence occurring for the Sequoyah Plant results from the potential for blockage or closure of the drains" between the upper and lower compartments.
This causes a common-mode failure of the ECRS and CSRS when the sump runs dry (sequences S HF and S HF).
The probability of these sequences could be re-duced by ikproved checking procedures and improved fault detection capabilities.
COMMENTS The Cook Plant design includes three drains from the refueling cavity to the lower compartments (Sequoyah is reported in the RSSMAP to have two).
The drain lines at Cook are blanked-off (not valved closed) during refueling operations and verified to be open and free of debris prior to criticality and during periodic contain-ment inspections.
The presence of lower volume containment sprays at the Cook Plant would also effectively increase the time to sump "dry-out" in the unlikely event that the drains were to become blocked following a LOCA.
2.
RSSMAP CONCLUSION Failure of the ECRS alone caused by component failures other than the drains also results in some important accident sequences.
COMMENTS The ECRS is an important function not only for the Cook Plant but for most plants and the conclusion of the RSSMAP study logically reflects this fact.
The relative importance of ECRS as a dominant accident sequence and the quantification of the ECRS failure pr ob-ability may be somewhat different depending on individual plant designs.
3.
RSSMAP CONCLUSION Sequence V, in which check valve failures cause the high-pressure primary coolant to fail the low-pressure piping outside containment, remains an important sequence for Sequoyah.
This sequence could be improved by a more strategic testing procedure of the check valves over the limited testing capability which now exists.
COMMENTS The significant event "V" configuration in the Cook Plant is in the normal Residual Heat Removal (RHR) return line to the reactor cool-ant system.
Both the inboard and outboard check valves are leak rate tested in accordance with plant technical specifications after each refueling outage, whenever the plant has been in COLD Shutdown
-2>>
for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or more and if leakage testing has not performed in the previous nine months, and prior to returning valve to service following maintenance or replacement work on valve.
The maximum allowable leakage from any of these check is one gpm.
This testing effectively reduces the probability event "V" sequence at the Cook Plant.
been the the valves of an 4.
RSSMAP CONCLUSION 1
Unlike larger containments, core melting caused by failure of ECIS or ECRS fail the lower pressure, smaller ice condenser containment by over-pressure even though the containment cooling system continues to operate properly.
The analysis of accident processes by Battelle Columbus Laboratories revealed that the smaller containment pressure and volume design would not withstand the pressure exerted by the noncondensible gases generated in the core meltdown accidents.
(This result was similar to the RSS findings for the RSS BMR design).
COMMENTS The design pressure of the Cook Plant containment is 12.0 psig.
As reported in Attachment No.
3 to our AEP:NRC:00500E submittal dated July 2, 1981, the median limiting pr essure capacity of the Cook Plant containment (based on actual material properties) is estimated to be 57.8 psig.
5.
RSSMAP CONCLUSION Sequence TMLB'-S, which was important for the Surry Plant as analyzed in the RSS, does not appear to be as significant to risk for Sequoyah due to lower unavailability of on-site ac power.
COMMENTS The RSSMAP states that the load sequencing feature at Sequoyah was estimated to result in a decrease of at least one order of magnitude in the failure probability of the diesel generators (OGs),
when compared to Surry.
The Cook OGs also utilize a load sequencing feature and a similar reduction in failure probability should apply to the Cook Plant as well.
6.
RSSMAP CONCLUSION Failure of the containment cooling system causing core meltdown following a small LOCA (the S
C sequence in the RSS) does not appear to lead to core meltdown at Slquoyah due to the difference in sump water temperature at the time of containment failure.
COMMENTS The reduced sump water temperature noted for Sequoyah should also apply to the Cook Plant.
The heat capacity of the ice condenser itself should significantly reduce the likelihood of a sequence in-volving the "C" events.
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