ML20203H011
| ML20203H011 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 04/23/1986 |
| From: | Charemagne Grimes Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20203G979 | List: |
| References | |
| NUDOCS 8604290405 | |
| Download: ML20203H011 (4) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION CONNECTICUT YANKEE ATOMIC POWER COMPANY DOCKET N0. 50-213 ENVIRONMENTAL ASSESSMENT AND FINDING 0F N0 SIGNIFICANT IMPACT The U.S. Nuclear Regulatory Commission (the Commission) is considering issuance of a temporary exemption from the regulatory requirements of General Design Criterion No. 35 (GDC 35) of 10 CFR 50, Appendix A, and the Interim Acceptance Criteria for Emergency Core Cooling Systems for Light Water Reactors 10 CFR, Appendix A, Part 3 (36 FR 12249), concerning the consideration of single failures in emergency core cooling system evaluations' to the Connecticut Yankee Atomic Power Company (CYAPC0 or the licensee) for the Haddam Neck Plant, located at the licensee's site in Middlesex County, Connecticut.
ENVIRONMENTAL ASSESSMENT Identification of Proposed Action:
The proposed action would grant a temporary exemption from the regulatory requirements of GDC 35 and the Interim Acceptance Criteria (IAC) concerning the consideration of single failures in emergency core cooling systems (ECCS) evaluations for the period of one operating cycle.
On March 25,1986, CYAPC0 reported the identification of a small range of break sizes in one loop of the reactor coolant system (RCS) for which safety injection flow, during only the high pressure recirculation mode may be insufficient to provide adequate core cooling. By letter dated April 10, 1986, CYAPC0 identified measures to provide adequate core cooling in the event of a small-break loss-of-coolant accident (LOCA). CYAPCO's proposed interim measures included the use of the high pressure safety injection (HPSI) system, the residual heat removal (RHR) system and certain operator actions. However, CYAPC0 noted that two valves, which are used during the HPSI recirculation mode, 8604290405 860423 PDR ADOCK 05000213 P
did not meet the prescribed single failure requirements of GDC 35. CYApC0 connitted to impose monthly surveillance and cycling requirements for these valves to provide added assurance of valve operability.
By letter dated April 22,1986, CYAPC0 requested a temporary exemption from the regulatory requirements of GDC 35 and the IAC concerning the consideration of single failures in ECCS evaluations. The granting of the exemption from single failure considerations for the two valves outside containment is the proposed action being considered by the staff.
The Need for the Proposed Action:
Provisions requiring consideration of single failure in this context are set forth both in GDC 35 and the Interim Acceptance Criteria. GDC 35 provides in applicable part as follows:
"A system to provide abundant emergency core cooling shall be provided...
suitable redundancy in components and features... shall be provided-to assure that for onsite electric power system operation (assuming offsite power is not available) and for offsite electric power system operation (assuming onsite power is not available) the system safety function can be accomplished, assuming a single failure."
Further, the Interim Acceptance Criteria (IAC), to which Haddam Neck was originally evaluated, provide as follows:
The combination of systems used for analyses should be derived from a failure mode and effects analyses, using the single failure criterion.
Thus, for either GDC 35 or the IAC, a single failure requirement is imposed on ECCS evaluations of light water power reactors, including the Haddam Neck Plant.
The exemption is requested specifically with respect to two valves, both outside containment, which would be used under procedurally defined conditions to respond to a small break LOCA. CYAPC0 has implemented measures to assure valve operability of these valves, and' by procedure has established another alternative flow path in the event those valves are inoperable despite best efforts to assure operability. _
Environmental Impacts of the Proposed Action:
The proposed exemption affects the consideration of single failures for two valves which are used in the HPSI recirculation mode. One measure of environmental impact is whether the proposed exemption results in an overall reduction in the probability of adverse consequences from reactor operation that could affect the public health and safety.
In this instance, the original nigh pressure recirculation mode using the charging pumps has been found to be deficient for a narrow spectrum of breaks, whereas the safety benefits derived from using the HPSI pumps represent a credit for a much broader range of postulated breaks, CYAPC0 has estimated that the implementation of the proposed interim response measure (use of HPSI pumps during recirculation) decreases the overall core melt frequency associated with small and medium break LOCA's at Haddam Neck by a minimum of 27 percent over the original design.
CYAPC0 has stated that the HPSI recirculation option involves the recirculation of primary fluids outside containment in systems not previously analyzed for those conditions.
If gross fuel failure were assumed, there would be a potential for offsite radiological consequences in excess of the guideline values of 10 CFR Part 100. As a result, leakage tests were performed I
on the HPSI recirculation system pumps and valve and no leakage was apparent.
CYAPC0 concludes that operation of the recirculation mode will preclude gross fuel failures following the small break LOCA. Even if fuel failures were assumed, it is very unlikely that core damage would be so substantial as to cause offsite releases to approach those assessed in hypothetical accidents calculations carried out for Part 100 purposes.
Further, given the very low probability of any such release, the effect on overall plant risk would not be significant. The proposed exemption does not otherwise affect facility radiological impacts, does not affect plant non-radiological effluents and has no other environmental impact.
Therefore, the Commission concludes there are no measurable radiological or nonradiological environmental impacts associated with the proposed exemption.
Alternatives to the Proposed Action:
Since the Commission has concluded there is no measurable environmental impact associated with the proposed exemption, any alternatives with equal or greater environmental impacts need not be evaluated. One alternative to the exemption would be to require repairs be made to the subject ECCS to satisfy the prescribed regulatory requirements. -Such an action would not
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significantly enhance the protection of the environment, may not be the best long-term solution and would result in a diversion of utility engineering resources from determining a safe and reliable long-term solution.
Alternative Use of Resources:
This action does not involve the use of resources not considered previously in the Final Environmental Statement for the Haddam Neck Plant.
Agencies and Persons Consulted:
The NRC staff reviewed the licensee's request and did not consult other agencies or persons.
FINDING OF NO SIGNIFICANT IMPACT The Comission has determined not to prepare an environmental impact statement for the proposed exemption.
Based upon the environmental assessment, the NRC staff concludes that the proposed action will not have a significant effect on the quality of the human environment.
For further details with respect to this proposed action, see the
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licensee's letters dated April 1, April 10 and April 22, 1986. These letters are available for public inspection at the Comission's Public Document Room, 1717 H Street, N.W., Washington, D.C., and at the Russell Library,123 Broad Street, Middletown, Connecticut 06547.
Dated at Bethesda, Maryland, this 23rd day of. April 1986.
FOR THE NUCLEAR REGULATORY COMMISSION M1, wA Christopher I. Grimes, Director Integrated Safety Assessment Project Directorate Division of PWR Licensing - B
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