ML20112E462
| ML20112E462 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 06/03/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20112E461 | List: |
| References | |
| NUDOCS 9606060097 | |
| Download: ML20112E462 (3) | |
Text
un n r.cg k
UNITED STATES NUCLEAR REGULATORY COMMISSION f
WASHINGTON, D.C. 20666-0001
'+,.....,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.147 TO FACILITY OPERATING LICENSE NPF-35 j
AND AMENDMENT NO. 141 TO FACILITY OPERATING LICENSE NPF-52 DUKE POWER COMPANY. ET AL.
CATAWBA NUCLEAR STATION. UNITS 1 AND 2 DOCKET NOS. 50-413 AND 50-414
1.0 INTRODUCTION
By letter dated April 3,1996, Duke Power Company, et al. (the licensee),
submitted a request for changes to the Catawba Nuclear Station, Units 1 and 2, Technical Specifications- (TS). The requested changes would adopt a specification in the Improved Technical Specifications for the hydrogen ignition System, as delineated in NUREG-1431, Revision 1, " Standard Technical Specifications, Westinghouse Plants", April 1995.
The proposed specification provides that if neither the Train A or Train B igniter is operable in any one containment region, then there is an allowance of 7 days to restore one J
hydrogen igniter to operable status, or be in hot shutdown within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. The licensee also proposed to revise the associated Bases.
4
2.0 BACKGROUND
Combustible gases can form in a containment under post-accident conditions due to fuel cladding reaction (with steam or water), corrosion (particularly of zinc-based paint and cable insulation), and radiolysis of water. Containment pressure vessels and equipment in the containment are not designed to withstand the additional loads that would result from large-scale combustion of hydrogen. Therefore, combustible gas control systems are provided to prevent the occurrence of a potentially damaging hydrogen combustion event.
The combustible gas control systems and equipment provided at Catawba include recombiners, vent / purge systems, containment atmosphere mixing and monitoring systems, and distributed ignition (hydrogen igniter) systems. The recombiners serve as the primary means of combustible gas control for design-basis accidents which involve quantities of hydrogen associated with approximately 5% fuel clad metal-water reaction. The vent / purge systems provide a backup hydrogen control capability for design-basis accidents. The distributed ignition (igniter) system (also known as hydrogen ignition system, HIS) is provided for mitigation of degraded core events (Three Mile Island-type events which are "beyond design-basis") involving up to 75% metal-water reaction.
9606060097 960603 PDR ADOCK 05000413 P
%g i
a.
i.
The design of those combustible gas control systems provided for the purpose of mitigating design-basis accidents is based on Regulatory Guide 1.7.
The L
design of HISS is based on the requirements of 10 CFR 50.44 (the " Hydrogen Rul e"). The protection provided by igniters is based on the knowledge that immediate local burning of lean mixtures of combustible gas will prevent the subsequent formation of a larger, richer combustible mixture capable of supporting a major deflagration or detonation.
4 j
The igniter system at Catawba consists of 70 glow plug igniters distributed equally to two trains.
Each protected area is served by two independently i
j, powered igniters. The most recent revision to Section 4.6.4.3 was by Amendment No. 136 (for Unit 1) and 130 (for Unit 2).
Requirements related to j
the HIS are contained in NUREG-1431, " Improved Standard Technical Specifications, Westinghouse Plants," Revision 1, April 1995.
)
I
\\
i 3.0 DISCUSSION AND EVALUATION 1
In its April 3, 1996, letter Duke Power Company requested amendments to the 1
i Catawba Units 1 and 2 Technical Specifications. The proposed changes would
)
adopt the Improved Technical Specifications requirements for the hydrogen l
' ignition system as delineated in NUREG-1431, Revision 1.
The major change pertains to the event of inoperable hydrogen ignitors. With 1
one HIS train inoperable, the inoperable train must be restored to operable status within 7 days or the operable train must be verified operable by energizing the supply breakers and verifying that at least 34 of 35 igniters are energized once per 7 days until the inoperable train is restored to operable status. The 7-day completion time is based on the low probability of occurrence of a degraded core event that would generate hydrogen in amounts equivalent to a metal-water reaction of 75% of the core cladding, the length of time after the event that operator action would be required to prevent hydrogen accumulation from exceeding this limit, and the low probability of failure of the operable HIS train. Alternative Required Action 4.6.4.3a performed once per 7 days, provides assurance that the operable train continues to be operable.
For the case of no operable ignitors in the same containment region, the proposed action requirement is to restore one hydrogen ignitor in the affected containment region to operable status within 7 days. When this condition exists, there would always be ignition capability in the adjacent containment regions that would provide redundant capability by flame propagation to the region with no operable ignitors. The 7-day completion time is based on the same reasons given in the preceding paragraph.
An additional action requirement is being added to address actions to take if the HIS subsystem cannot be restored to operable status within the associated action time. The unit must be placed in a mode in which the limiting condition of operation (LCO) does not apply. This is done by placing the unit
'in'at least Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. The allowed completion time of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is reasonable, based on operating experience, to reach Mode 3 from full-power conditions in an orderly manner and without challenging plant systems.
. An additional surveillance requirement (SR) (4.6.4.3b) is being added to verify at least one hydrogen ignitor is operable in each containment region.
This surveillance is to be performed on a 92-day frequency. This SR confirms that the two inoperable hydrogen ignitors allowed by SR 4.6.4.3a (i.e., one in each train) are not in the same containment region. The frequency of 92 days is acceptable based on the frequency of SR 4.6.4.3a, which provides the information for performing this SR.
The proposed changes to Section 3.6.4.3 and 4.6.4.3 provide assurance that hydrogen ignition capability is sufficient to prevent excess hydrogen accumulation in the event of a degraded core event and are therefore acceptable.
The proposed changes to the associated Bases Section B 3/4.6.4.3 are also acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the South Carolina State official was notified of the proposed issuance of the amendments. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (61 FR 16649 dated April 16,1996). Accordingly, the amendments meet 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 environnental assessment need be prepared in connection with the issuance of tie amendments.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will 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 amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
Michael R. Snodderly Date:
June 3, 1996 i
1
n
... -,