ML20246E132
| ML20246E132 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 07/03/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20246E127 | List: |
| References | |
| NUDOCS 8907120120 | |
| Download: ML20246E132 (5) | |
Text
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UNITED STATES
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j NUCLEAR REGULATORY COMMISSION j
j WASHINGTON, D. C. 20555 i
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 60 TO FACILITY OPERATING LICENSE N0. NPF-29 l
SYSTEM ENERGY RESOURCES, INC.
GRAND GULF NUCLEAR STATION, UNIT 1 DOCKET N0. 50-416
1.0 INTRODUCTION
By letter dated April 18, 1989, System Energy Resources, Inc. (the licensee),
requested an ainendment to facility Operating License No. NPF-29 for the Grand Gulf Nuclear Station, Unit 1.
The proposed amendment changes the Technical Specifications (TS) by increasing the suppression pool low water level trip setpoint and allowable value in TS Table 3.3.8-2, " Plant Systems Actuation Instrumentation Setpoints."
In addition, the description of the trip function and the suppression pool bottom reference elevation would be changed to reflect as-built plant conditions.
2.0 EVALUATION The suppression pool makeup (SPMU) system consists of two 100% subsystems, each capable of dumping the makeup water from the upper containment pool to the suppression pool by gravity flow. Each SPMU subsystem consists of one line w11ch penetrates the separator end of the upper containment pool through the side wall and then is routed down to the suppression pool.
Each SPMU line has two normally closed motor-operated butterfly valves in series. The valves in each line are powered by the same electrical division.
The upper pool makeup water is dumped by gravity flow after opening the two normally closed valves in series in each line. The valves in both lines receive divisionally separate signals to open. The SPMU system is automatically initiated 30 minutes after a LOCA is detected (high drywell pressure or low-low reactor water level) or on low-low suppression pool water level following a LOCA. It can also be manually initiated provided a LOCA signal is present.
The function of the SPMU system is to transfer makeup water from the upper containment pool to the suppression pool after a LOCA to assure that steam vented from the drywell will be condensed. For a LOCA in the drywell, with ECCS injection from the suppression pool, a large volume of water can be held up in the drywell behind the weir wall. This holdup can significantly lower suppression pool water level. The water transfer from the upper containment pool insures a post-LOCA drywell vent submergence at least 2 feet above the top row vents so that steam condensation is maintained until the drywell atmosphere is sufficiently cooled by ECCS flow out of the P
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. pipe break. The additional makeup water is used as part
. of the long term suppression pool heat sink. The delayed transfer of this water to the suppression pool provides an initially low vent submergence to minimize vent clearing loads and drywell pressurization.
l The suppression pool water level measurement is provided by four instrumen-E tation channels. There are four wide range suppression pool level sensors, and four wide range suppression pool ins :rumentation channels. The four wide range level channels are used to cf.ntinuously monitor suppression pool level. During plant operation, the suppression pool water level is maintained between.a high level of 18 feet 9 inches and a low level of 18 feet 5 1/2 inches. An alarm.is annunciated at the high water level and at the low water level. The SPMU system is actuated at the low low water level setpoint.
TS 3.3.8 gives the requirements for the SPMU system actuation instruments-tion. The proposed amendment would change Table 3.3.8-2, Item 3.e from the current suppression pool water level low-low trip setpoint and allowable value of 16 feet 4 inches and 15 feet 6.5 inches to 17 feet 5 inches and 17 feet 2 inches, respectively. The proposed values are more conservative than the current TS values since the SPMU system would actuate at a higher suppression pool water level than required by the current TS.
The revised setpoint is determined based on operating considera H ons and conservative analyses. The setting is low enough to prevent
- Mvertent initiation of the SPMU system, but high enough to assure significant margin is maintained between the' actual setpoint and the setpoint assumed in the-safety. analyses (analytical limit). The analytical limit for low-low suppression pool. water level is 16 feet 10 inches. The difference between the allowable value and the analytical limit is the margin established to account for instrument inaccuracies and calibration uncertainties. The trip setpoint has additional margin to account for setpoint drift during the calibration intervals.
Instrument setpoints are adjusted to be equal to their specified trip setpoints at each calibration.
If during calibra-tion, an instrument setpoint is found to have drifted from its trip setpoint in a nonconservative direction, but not beyond the allowable value, the channel is still within the requirements of the applicable safety analysis.
The NRC staff has reviewed the licensee's requested changes which are proposed to correct errors in the TS. The SPMU system actuation setpoint
.for suppression pool low low water level is presently incorrectly less than the analytical limit used in LOCA safety analyses. The change in setpoiht and allowable value would make the setpoint and allowable value greater than the analytical limit, with sufficient margin to account for instrument drift, instrument inaccuracies and calibration uncertainties. The revised setpoint would not be likely to cause inadvertent actuation of the SPMU O
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system because.there is adequate margin between the normal operating low L
. level (18 feet 51/2 inches) and the low-low level setpoint (17 feet 5 inches) to account for'instrunent drift and inaccuracies. Accordingly, the staff concludes that the proposed changes are acceptable.
The trip function description.in TS Tables 3.3.8-1, 3.3.8-2 and 4.3.8.1.-1 would be changed from " Suppression Pool Water Level-Low" to " Suppression Pool Water Level-Low Low" in order to distinguish this function from the low level alarm function at 18 feet 5 1/2 inches.
In the TS Bases Section 3/4 3.8, " Plant Systems Actuation Instrumentation," the elevation of the-suppression pool floor relative to mean sea level would be changed from 93 feet 6-inches to 93 feet 0 1/4 inches. The changes in trip function
' description and reference elevation of the pool floor are administrative changes to reflect the as-built plant conditions and, therefore, are acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
This amendment changes a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes to the surveillance requirements.- The 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'off site; and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commis-i sion has'previously issued a proposed finding that this amendment involves 1
'no significant hazards consideration and there has been no public comment on such finding. The licensee also provided a no significant hazards consideration analysis, in which the staff concurs.
It is as follows:
1.
No significant increase in the probability or consequences of an accident previously evaluated results from the change.
a.
The SPMU system is used to supply the suppression pool with additional water inventory post-LOCA to maintain adequate drywell vent enverage end sufficient long-term heat sink capacity. The accidents previously evaluated that are applicable to the proposed amendment are suppression pool drawdown events associated with LOCAs and inadvertent SPliu system actuations (inadvertent dumps),
b.
The probability of a suppression pool drawdown event is not affected by the revised SPMU system trip setpoint or allowable value since the SPMU system has an accident mitigative function and not a preventive role. The revised trip setpoint and allowable value do not affect the probability of inadvertent dumps because the values are less than the spectrum of suppression pool water levels assumed in the inadvertent dump analyses and also pernitted by TS in the applicable Operational Conditions.
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, f The consequences of a suppression pool drawdown event c.
are not increased by the revised trip setpoint and allowable value because the SPMU system will now actuate at a higher suppression pool water level L
providing more margin to reduce the likelihood of the drywell vents ~being uncovered and increasing the amount of water available as a heat sink. The consequences of an inadvertent dump are not increased because the initial suppression pool water levels assumed in the analyses for inadvertent dump events are greater than the revised trip setpoint and allowable value and the volume of water being dumped by the SPMU
. system remains unchanged.
d.
The change of the trip function description and the revised suppression pcol bottom elevation are being made to reflect the as-built plant and are administrative changes.
e.
Therefore, there is no increase in the probability or consequences of previously analyzed accidents due to the proposed change.
2.
This change would not create the possibility of a new or different kind of accident from any previously evaluated, a.
The SPMU system is used to add water inventory to the suppression pool following a LOCA.
LOCAs and other suppression drawdown.
events are already analyzed.
Inadvertent SPMU system actuations have also been previously analyzed.
b.
The proposed revision to the TS setpoint and allowable value are consistent with the assumption of _ the current accident analysis and are requested to correct nonconservative values currently described in the TS. Therefore, revising.the trip setpoint and allowable value do not create the possibility of a new or different kind of accident from any previously evaluatso, c.
The revised trip function description and suppression pool bottom elevation reference are being made to match the as-built piant and are administrative changes.
d.
Therefore, the possibility of a new or different kind of accident from any previously evaluated is not created.
3.
The change would not involve a significant reduction in the margin of
- safety, a
The SPMU system is used to mitigate the consequences of a LOCA event. The s spression pool low-low water level trip function is needed to iMuate the SPNV system following a large break LOCA to durrp a a1tional water into the suppression pool to
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.. maintain adequate drywell vent coverage. The proposed amendment increases the trip setpoint and allowable value for this trip function. The SPMU system will actuate at a higher suppression pool water level; thereby, ensuring _ adequate drywell vent coverage post-LOCA. With respect.to inadvertent dump events, there will be no effect on the margin of safety since the proposed amendment does not alter the suppression pool water levels assumed in those events or the volume of water added by the SPMU system.-
b.
.The revised trip function description and suppression pool bottom elevation reference are being made to match the as-built plant and are administrative changes.
c.
Therefore, this proposed change will not involve a reduction in the margin of safety.
This 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 neeo be prepared in connection with the issuance of this amendment.
4.0 CONCLUSION
The Commissicn made a proposed determination that this amenament involves no significant hazards consideration, which was published in the Federal Register (54 FR 23325) on May 31, 1989, and consulted with the State of Mississippi. No public comments or requests for hearing were received, and the State of Mississppi did not have any comments.
The staff.has concluded, based on the considerations discussed above, that:
(1) there _is reasonable assurance that the health and safety of the ublic will not be endangered by operation in the proposed manner, and p(2) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and the security, or to the health and safety of the public.
Principal Contributor: L. Kintner Dated:
July 3, 1939
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