ML19290D047
| ML19290D047 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 10/16/1976 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML19290C953 | List: |
| References | |
| ACRS-R-0725A, ACRS-R-725A, NUDOCS 8002150549 | |
| Download: ML19290D047 (2) | |
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y,1 Lf 2 g}() 2 p2 d //f s Minutes of 198th ACRS Meeting Meeting Dates: October 14-16,51976 B. Millstone Point, Unit 2: Inocerability of Safety-Related Ecuillnent followin_g,Ioad Shcdding G. D. McDcnald, Jr., discussed the inoperability of certain safety-related equip ent following load shedding in the Connecticut pwer grid (see Appendix XXVIII).
He completed the report on this matter which he began at the 197th Meeting, discussing the circditry of the Millstone 345 kv switchyard, a su:r.arj of the July 5 events resulting in low grid voltage and blown control circuit fuses, a suruary of the July 21 events resulting in the failure of diesel generator load sequencing, the corrective actions and changes proposed by the operator, the generic considerations and NRC Staff actions, the equipaent pro-tective trips that cc.s result in inoperable diesel generators, s
' 10/20/69 ll4th ACRS Meeting
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1.
General Desien Criteria -- Criterion 17 (nDC-17) - Mr. Case presented the majority and minority S taf f positions on the CDC-17 statement regarding off-site power requirements, ".
preferably by two physically independent transmission lines." DRS has determined that most power statiens have two transmission lines, but it was not clear whether these were i= porting or j
exporting power. An examination of the reliability gained by having two j
versus one off-site transmission line results in a reliability improvement facjor of two.
However, the unreliability of the off-site eower evid is 10" / time the unreliability or the incomine power lines is 10-b/timet the re fo re, the majority of the Staff believes that one off-site transmissf os line is sufficient.
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Mr. Levine, speaking as the minority, stated that he believes the loss of all i
ac power for several hours can result in worse core melting than could occur Irom a DBA. He questions the on-site ac power capability. His survey reveals l
that 907. of the 51 nuclear power plants have mere than two of f-site power I
lines, and 70*. have more than two rights-o f-way.
He mentioned, as examples, that Commonwealth Edison and Philadelphia Electric believe that there should be two transmission lines, two rights-of-way, and two start-up trans formers.
i He believes that, if the off-site power reliabiltr.y of 10-4 obtained by the I
Staff is valid, this is unacceptable to the utilities.
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Mr. Case noted that a change in Criterion 17 is planned to require at 1 cast one, sepa rate incomine power line at each facility in addition to the line that is exporting power.
The Committee decided to refer the GDC-17 question regarding off-site emergency power supply requirements back to the Reactor Design and Operating Subcommittee for further review.
(A Subcommittee meeting has been tentatively set for November 5,1969, in Washington, D. C.)
EXCERPTS FROM ACRS LETTERS WHICH REIATE TO CRITERION NO.17 1.
Report on Maine Yankee Atomic Power Station - July 19, 1968.
"The Committee believes that the system for supplying off-site electrical power to the engineered safeguards equipment should be modified so that no single failure will prevent power from being available from this source."
2.
Report on Crystal River Unit 3 Nuclear Generating Plant - May 15, 1968.
"The Committee believes that the proposed off-site power system should be modified to fulfill criterion 39 so that no single failure will prevent the operation of mini =um electrically-powered safety features necessary to protect the core."
3.
Report on Oconee Nuclear Station, Units 1, 2 and 3 - July 11,1967.
" Emergency power sources for the ECCS and other safeguards are:. (a) the other Oconee units (each unit can withstand and will be tested to withstand instantaneous loss of load without a reactor trip or a. turbine trip); (b) two hydro-
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electric units at Keovee Station less than one mile away, with independent overhead and underground transmission lines; and (c) a gas-turbine unit thirty miles away with independent transmission line, trans former, and switchyard -- all in addi-tion to the usual multiple ties to the power transmission grid.
The applicant stated that switching and sequencing of sources, i
buses, 2-d loads would be such that no single failure would impair system availability."
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