ML20078S875
| ML20078S875 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 02/16/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20078S873 | List: |
| References | |
| GL-91-08, GL-91-8, NUDOCS 9502270364 | |
| Download: ML20078S875 (4) | |
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UNITED STATES g
g NUCLEAR REGULATORY COMMISSION
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SAFETY EVALUATION BY THE OFI Ei' 0F NUCLEAR REACTOR REGULATION i
RELATED TO AMENDMENT N0.115 TO FACILITY OPERATING LICENSE NO. NPF-29 ENTERGY OPERATIONS. INC.. ET AL.
4 GRAND GULF NUCLEAR STATION. UNIT 1 DOCKET NO. 50-416
1.0 INTRODUCTION
By letter dated July 14, 1993, the licensee (Entergy Operations, Inc.),
submitted a request for changes to the Grand Gulf Nuclear Station, Unit 1 (GGNS) technical specifications (TSs). The amendment revises TS requirements for the hydrogen ignition system (HIS). These changes are consistent with i
generic TSs proposed by the Mark III Containment Hydrogen Control Owners Group (HC0G) as modified by the NRC staff's safety evaluation (SE) dated August 6, 1990 (available as NUREG-1417).
The amendment would also remove several tables related to the HIS in accordance with guidance contained in Generic Letter-(GL) 91-08, " Removal of Component Lists From Technical Specifications."
The proposed changes are consistent with guidance contained in NUREG-1434,
" Standard Technical Specifications - General Electric Plants, BWR/S."
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2.0 BACKGROUND
i The primary containment and drywell hydrogen igniters are a part of the ccmbustible gas control measures required by 10 CFR 50.44 and General Design Criterion (GDC) 41, " Containment Atmosphere Cleanup," to reduce the hydrogen concentration in the primary containment follcwing a degraded core accident.
The hydrogen igniters ensure the combustion of hydrogen in a manner such that containment overpressure failure is prevented as a result of a postulated degrade 0 core accident.
10 CFR 50.44 requires boiling water reactor units with Mark III containments to install suitable hydrogen control systems. The hydrogen igniters are j
installed to accommodate an amount of hydrogen equivalent to that generated i
from the reaction of 75% of the fuel cladding with water. This requirement was placed on reactor units with Mark III containments because they were not designed for inerting and because of their low design pressure.
Calculations indicate that if hydrogen equivalent to that generated from the reaction of 2
75% of the fuel cladding with water were to collect in primary containment, the resulting hydrogen concentration would be far above the lower flammability limit ruch that, without the hydrogen igniters, if the hydrogen were ignited j
from a random ignition source, the resulting hydrogen burn would seriously challenge the primary containment.
9502270364 950216 PDR ADOCK 05000416 P
. The hydrogen igniters are based on the concept of controlled ignition using thermal igniters designed to be capable of functioning in a post accident environment, seismically supported and capable of actuation from the control room.
Igniters are distributed throughout the drywell and primary containment.
The hydrogen igniters are arranged in two independent divisions such that each containment region has two igniters, one from each division, controlled and powered redundantly so that ignition would occur in each region even if one division failed to energize.
When the hydrogen igniters are energized they heat up to a surface temperature
- t 1700*F. At this temperature, they ignite the hydrogen gas that is present in the airspace in the vicinity of the igniter. The hydrogen igniters depend on the dispersed location of the igniters so that local pockets of hydrogen at increased concentrations would burn before reaching a hydrogea concentration significantly higher than the lower fismmability limit.
The hydrogen igniters cause hydrcgen in containment to burn in a controlled manner as it accumulates followir.g a degraded core accident.
Burning occurs at the lower flammability concentration, where the resulting temperatures and pressures are relatively benign. Without the system, hydrogen cauld build up to higher concentrations that could result in a violent reaction if ignited by a random ignition source after such a buildup.
The hydrogen igniters are not included for mitigation of a Design Basis Accident (DBA) because an amount of hydrogen equivalent to that generated from the reaction of 75% of the fuel cladding with water is far in excess of the hydrogen calculated for the limiting DBA loss-of-coolant accident (LOCA). The hydrogen concentration resulting from a DBA can be maintained less than the flammability limit using the hydrogen recombiners.
However, the hydrogen igniters have been shown by probabilistic risk analysis to be a significant contributor to limiting the severity of accident sequences that are commonly found to dominate risk for units with Mark III containment.
3.0 EVALUATION ReqJirements regarding operability of adjacent igniters and igniters in enclosed areas have been deleted. These provisions were originally included due to uncertainty regarding the mixing characteristics of hydrogen released to the containment atmosphere. The tests conducted by the HCOG indicated that hydrogen exhibits better mixing characteristics than originally assumed.
Based on these results, the HCOG concluded that these additional requirements, intended to preclude the formation of localized, high-concentration hydrogen pockets, were not warranted. Based on the information provided by the HC0G regarding hydrogen mixing, the staff concluded in the 1990 SE that there is reasonable assurance that deletion of these requirements would not have an adverse effect on the effectiveness of the HIS; therefore, deletion of these requirements is acceptable.
The specification has been revised to redefine the HIS as being operable based solely on subsystem status, in lieu of using circuit and subsystem criteria.
The licensee proposed to redefine an operable subsystem as consisting of "at
. least 90% of its igniter assemblies operable," in lieu of "two circuits...
with no more than two igniter assemblies inopert.ble per circuit," (i.e., no more than four inoperable igniters per subsystem). The staff considers this to be an acceptable administrative change, since the number of operable igniters required has not been changed (i.e., "at least 90% of a subsystem's igniter assemblies operable" is equivalent to "no more than four inoperable igniters per subsystem").
Table 4.6.7.2-1, " Number of Igniters by Circuit," has been deleted.
This table identifies the minimum number of igniters required to be operable per circuit.
Since operability of the igniter system will be based solely on subsystem status, as noted above, this table is no longer required.
This change is acceptable to the staff.
The required action for one inoperable subsystem has been revised by increasing the time allowed fcr restoration of an inoperable system to operable status from 7 days to 30 days.
The 30 day completion time is based on the low probability of occurrence of the degraded core accident for which the system is designed, the amount of time available following event i
initiation for operator action to prevent hydrogen accumulation, and the low probabilty of failuro of the operable igniter system.
The staff concluded in the 1990 SE that a 30 day restoration time for one inoperable subsystem is appropriate.
Table 3.6.7.2-1, " Hydrogen Igniter Circt.its," and Table 3.6.7.2-2, " Hydrogen Igniters and Locations," have been relocated to plant procedures in accordance with NRC GL 91-08, " Removal of Component Lists From Technical Specifications."
10 CFR 50.36 does not require these tables to be retained in the TSs.
Requirements related to the operability, applicability, and surveillance requirements, including performance of testing to ensure operability of the hydrogen igniters is retained in the TSs due to the hydrogen igniters' importar.ce in mitigating the consequences of an accident.
However, the staff determined that the inclusion of specific information regarding igniter circuits i N iocations is a design detail related to the licensee's safety analyses 2-is adequately controlled by the requirements of 10 CFR 50.59.
Therefore, tne continued processing of license amendments related to revisions of the affected tables where the revisions to those requirements do not involve an unreviewed safety question under 10 CFR 50.59, would afford no significant benefit with regard to protecting the public health and safety.
The staff has concluded, therefore, that relocation of these tables is acceptable because (1) their inclusion in TSs is not specifically required by 10 CFR 50.36 or other regulations, (2) the affected tables have been relocated to plant procedures which are adequately controlled by 10 CFR 50.59, and their inclusion in the TSs is not required to avert an immediate threat to the public health and safety, and (3) changes that are deemed to involve an unrrviewed safety question will require prior NRC approval in accordance with 10 CFR 50.59(c).
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l The changes contained in this amendment are consistent with the generic TSs approved by the staff in its SE dated August 6, 1990, and with guidance contained in NUREG-1434. As required by the 1990 SE, the licensee has confirmed that the assumptions used to develop the generic TSs are also valid 1
for the Grand Gulf Nuclear Station configuration.
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4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Mississippi State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATLON The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements.
The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant 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 (58 FR 46232). 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.
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6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assarance 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 amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
R. Schaaf Date: February 16, 1995