ML20205N360
| ML20205N360 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/12/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20205N358 | List: |
| References | |
| NUDOCS 9904160255 | |
| Download: ML20205N360 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 233 TO FACILITY OPERATING LICENSE NO. DPR-65 NORTHEAST NUCLEAR ENERGY COMPANY THE CONNECTICUT LIGHT AND POWER COMPANY THE WESTERN MASSACHUSETTS ELECTRIC COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT NO. 2 DOCKET NO. 50-336
1.0 INTRODUCTION
By letter dated January 18,1999, as supplemented by letters dated February 3 and March 17, 1999, the Northeast Nuclear Energy Company, et al. (NNECO, or the licensee), submitted a request for changes to the Millstone Nuclear Power Station, Unit 2, (Millstone Unit 2) Technical Specification (TS) regarding the hydrogen purge system. Specifically, TS 3/4.6.4.3,
" Containment Systems, Hydrogen Purge System,"would be deleted from the TS. The supplementalletters provided additional information that was within the scope of the original application and did not change the staff's proposed no significant hazards consideration determination.
2.0 BACKGROUND
The licensee's request includes the removal of information from the TS. Section 182a of the Atomic Energy Act (the "Act") requires applicants for nuclear power plant operating licenses to state TS to be included as part of the license. The Commission's regulatory requirements related to the content of the TS are set forth in 10 CFR 50.36. That regulation requires that the TS include items in five specific categories, including:
(1) safety limits, limiting safety system settings and limiting control settings; (2) limiting conditions for operation; (3) surveillance requirements; (4) design features; and (5) administrative controls.
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. On July 19,1995, the Commission published revisions to 10 CFR 50.36 specifying what nust be included in limiting conditions for operation (LCOs) in the TS (60 FR 36953). The four criteria added to 10 CFR 50.36 for determining whether a particular matter is required to be included in the TS, are as follows:
(1) Installed instrumentation that is used to detect, and indicate in the control room, a significant abnormal degradation of the reactor coolant pressure boundary; (2) a process variable, design feature, or operating restriction that is an initial condition of a design-basis accident or transient analysis that either assumes the failure of, or presents a challenge to, the integrity of a fission product barrier; (3) a structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design-basis accident or transient that either assumes the failure of, or presents a challenge to, the integrity of a fission product barrier; and (4) a structure, system, or component which operating experience or probabilistic safety assessment has shown to be significant to public health and safety.
As a result, existing TS LCOs which fall within or satisfy any of the criteria in 10 CFR 50.36 must be retained in the TS, while those TS requirements that do not fall within or satisfy these criteria may be relocated to other, licensee-controlled documents.
The licensee is proposing to remove the hydrogen purge system from the TS requirements,
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and is proposing to incorporate this system into the maintenance rule risk-significant system program (although the hydrogen purge system will be downgraded to a non-safety-related system).
3.0 EVALUATION The design and licensing bases for the hydrogen control system are contained in the Millstone Unit 2, Final Safety Analysis Report (FSAR) Sections 1.2.7, " Summary Description, Engineered Safety Features System," 1.8.2.2, " Hydrogen Control," 6.6, " Containment Post-Accident Hydrogen Control System," 6.7.3.1, " Enclosure Building Filtration System, Emergency Conditions," and 14.8.3,
- Hydrogen Accumulation in Containment," and in TS section 3/4.6.4.3,
" Containment Systems, Hydrogen Purge System."
The post-accident hydrogen control system includes independent and fully redundant subsystems to (a) measure the hydrogen concentration in the containment, (b) mix the atmosphere in the containment, and (c) control combustible gas concentrations without relying j
on purging of the containment atmosphere following a loss-of-coolant accident. These subsystems function to maintain the concentration of locally accumulated hydrogen below four volume percent. The post-accident hydrogen control system meets the recommendations of Safety Guide 7. Combustible gas controlis achieved using two full capacity electric recombiners which meet the recommendations of Safety Guide 7. A controlled containment hydrogen purge system is also provided, as a backup to the recombiner system, in accordance w,th the recommendations of Safety Guide 7.
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. In the January 18,1999, letter, the licensee proposes to downgrade the Hydrogen Purge System to non-safety-related. The licensee states that the Hydrogen Purge System is credited in the event that both safety-related hydrogen recombiners fail or in severe accident management scenarios. These scenarios are beyond the design basis. The staff agrees that numerous risk studies, such as NUREG-1150 and NUREG/CR-5662, have shown that the risk associated with hydrogen combustion is due to beyond-design-basis scenarios that lead to containment failure, not design-basis scenarios. In a February 3,1999, supplemental letter, the licensee states that the purge system, if it remains available post-accident, may be used as necessary during an event which is outside the existing licensing basis.
In further support of downgrading the purge system to non-safety-related status the licensee referenced Regulatory Guide 1.7, Rev. 2, Section (C), item (4), which states:
"All water-cooled power reactors should also have the installed capability for a controlled purge of the containment atmosphere to aid in cleanup. The purge or ventilation system may be a separate system or part of an existing system. It j
need not be redundant or be designated Seismic Category I (see Regulatory Guide 1.29), except insofar as portions of the system constitute part of the primary containment boundary or containment filters."
Rased on the above, the staff supports the licensee's contention that the Hydrogen Purge System can be downgraded to a non safety-related system except portions of the system
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which constitute part of the primary containment boundary. The non-safety-related parts of the i
Hydrogen Purge System are the parts located in the enclosure building down stream from the second containment isolation valves 2-EB-92 and 2-EB-99. As a result of this downgrade the staff agrees that the Hydrogen Purge System no longer meets the criteria of 10 CFR 50.36,
" Technical Specifications," Section c(2)(ii). Therefore, the staff finds the proposed changes to delete the TS related to the Hydrogen Purge system from the Millstone Unit 2 TSs to be acceptable. The proposed changes affect TS 3/4.6.4.3, " Containment Systems, Hydrogen Purge System," Index Page Vil, and the associated Bases.
The Hydrogen Purge System is still needed to support the plant's severe accident management guidelines. Because the system will no longer be supported by TSs, the staff believes that an appropriate availability and reliability controlis needed, in a letter dated March 17,1999, the licensee responded to the staff's concern. The licensee stated that, since 4
the Hydrogen Purge System is still an integral part of the Emergency Operating Procedures, NNECO will continue to maintain the system as a maintenance rule risk-significant system as before. The staff finds this commitment to continue f o maintain the Hydrogen Purge System as a maintenance rule risk-significant system to be acceptable, thereby providing an appropriate availability and reliability control.
The staff has reviewed the licensee's TSs amendment request and finds it to be acceptable.
The staff concludes that the Hydrogen Purge System is needed in the event that both safety-related hydrogen recombiners were to fail or in support of severe accident management.
Since these scenarios are beyond tne design basis of the plant, the Hydrogen Purge System m be downgraded to non-safety-related and its associated TS can be deleted. However, the dyJrogen Purge System is still needed to support the plant's severe accident management guidelines. The staff finds the licensee's commitment to continue to maintain the Hydrogen
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. Purge System as a maintenance rule risk-significant system more appropriate and to be an acceptable attemative to including the operability and surveillance requirements for the Hydrogen Purge System within the TSs.
4.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Connecticut State official was notified of the proposed issuance of the amendment. The State official had no comments.
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5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes requirements with respect to installation or we of a facilit/
component located within the restricted area, as defined in 10 CFR Part 20 and changes surveillance requirements. The NRC staff has determined that toe amendment involves no significant increase in the amounts, and no s;gnificant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (64 FR 6704, February 10,1999). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 CONCLUSION
The Commission has concluded, bar ' on the considerations discussed above, that: (1) there is reasonable assurance that the ha " mi safety of the public wi!! not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: M. Snodderly Date: April 12, 1999 J