ML20236S215
| ML20236S215 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 07/18/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20236S208 | List: |
| References | |
| NUDOCS 9807240204 | |
| Download: ML20236S215 (5) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.118 TO FACILITY OPERATING LICENSE NO. NPF-42 l
i WOLF CREEK NUCLEAR OPERATING CORPORATION l
WOLF CREEK GENERATING STATION DOCKET NO. 50-482
1.0 INTRODUCTION
By letter dated July 17,1998, Wolf Creek Nuclear Operating Corporation (WCNOC, the
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licensee) requested changes to the Technical Specifications (TS) (Appendix A to Facility
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Operating License No. NPF-42) for the Wolf Creek Generating Station (WCGS). The proposed l
changes would revise TS 3/4.7.5, Ultimate Haat Sink, by adding a new Action Statement to be l
used in the event that plant inlet water temperature exceeds 90 degrees F. Specifically, the i
new action statement would allow, until September 30,1998, continued operation of the plant 1
with plant inlet water temperature between 90 and 95 degrees F for up to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> before requiring shutdown of the plant.
j 2.0 EVALUATION t
The ultimate heat sink (UHS)is the normally submerged Seismic Category I cooling pond. The UHS is formed by providing a volume of cooling water behind a Seismic Cetegory I dam built in one finger of the WCGS cooling lake. The two principal functions of the Uh3 are the l
dissipation of residual heat after reactor shutdown, and dissipation of residual heat after an
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accident. The basic performance requirements for the UHS are that a 30-day supply of water j
- be available, and that the design-basis temperatures of safety-related equipment not be j
exceeded. The UHS design assures that the design temperature of safety-related equipment
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are not exceeded. The design temperature of water supplied to the plant is 95 degrees F.
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l The UHS is the sink for heat removed from the reactor core following all accidents and l
anticipated operational occurrences in which the unit is cooled down and placed on residual heat removal (RHR) operation. Its maximum post-accident heat load occurs after a design basis loss-of-coolant-accident (LOCA) when the unit switches from injection to recirculation and the containment cogling system and RHR are required to remove the core decay heat. Section 9.2.5 of the Updated Safety Analysis Report (USAR) provides the details of the assumptions used in the heat transfer analysis for the worst-case LOCA, which include worst expected meteorological conditions, conservative uncertainties when calculating decay heat, and worst-case single failure, in addition, it was assumed that all of the water in the UHS was at 90 degrees F at the start of the analysis.
s The analysis shows that following the loss of the main dam, the highest plant inlet water temperature occurring during the maximum temperature period is predicted to be 95 degrees F.
The predicted plant inlet temperature was usually weil below 95 degrees F. Tne predicted plant i
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! 1 inlet average temperature over the entire period was slightly below 90 degrees F and,95 percent of the time, below 94 degrees F.
WCNOC evaluated the effect of the proposed change on normal plant operation and normal plant shutdown with tha main dam intact, and safe shutdown or post-accident operation without the main dam.
Normal Plant Ooeration with the Main Dam Intact: Short-term operation with an inlet water temperature of up to 95 degrees F is not expected to negatively affect plant operation, with the possible exception of turbine backpressure. A slight load reduction may be necessary to
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maintain acceptable turbine backpressure. Existing plant guidance will be employed if any unexpected transients arc experienced.
Shutdcovn with the Main Dam Intact: The effect of increasing the inlet water temperature from 90 degrees F to 95 degrees F causes the calculated single train time required to cool the unit below 200 degrees F to exceed the 36-hour TS limit. To compensate for this concem, the
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requested action statemer,t requires verification of operability of two RHR trains. This will i
ensure the cooling capacity is available to meet the shutdown time requirements.
LOCA with the Main Dam Intad: The effect of full power plant operation on plant inlet water temperature during worst case predicted summer environmental conditions is approximately 0.5 degrees F. The peak heat rejection rate by the plant post-LOCA would be approximately 5 j
percent of the continuous heat rejection rate of the plant during normal operation. Therefore, j
the effect of post-LOCA heat loads on plant inlet water temperature would be less than 0.1 1
degrees F. The current UHS analysis assumes that there has been a main dam failure and used synthetic worst case environmental conditions. The results indicate that with an initial UHS temperature of 90 degrees F, plant intake water temperature remains below 95 degrees F.
The UHS analysis results a!so indicate that the environmental conditions have a much greater effect on peak piant intake water temperature than does the heat rejected from the plant. The current UHS analysis is recognized as boundinC the LOCA condition without a main dam failure because the volume of the UHS is significantly smaller than the volume of the WCGS cooling lake, approximately 1 percent. The probability that environmental conditions significantly worse than those causing entry into the limiting condition for operation is low. The probability of these conditions occurring simultaneously Ph a LOCA is even lower.
Safe Shutdown or Post-Accident Ooeration without the Main Dam: The TS limit of 90 degrees F is not being changed; however, the license amendment provides an allowance for operation above that limit for a 12-hour period. Based on a review of recent WCGS cooling lake data,12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> may be necessary to restore the lake below 90 degrees F through diumal
' effects. Safe shutdown capability and post-accident operation without the main dam is ensured when the plant is operated within TS limits. The probability of main dam failure is low, comparable to the frequency of a large break LOCA initiating event. The probability of main dam failure during the 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> when the inlet water temperature is above 90 degrees F in conjunction with an accident is even lower. A seismic event is a possible initiating event for causing failure of the main dam. The frequency of the seismic initiator on an annual basis is nearly equal to a large break LOCA. It is also noted that WCGS has a dam monitoring program j
in place to ensure continued integrity of the main dam. Therefore, it is concluded that this proposed change is of low risk significance.
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,.. l Based on the above, the staff concludes that with the dam intact, adequate heat removal will be available during normal plant operation, shutdown, and LOCA conditions to maintain equipment temperatures at or below their maximum design temperature of 95 degrees F. ' Further, the staff concludes that the probability of a LOCA concurrent with a dam failure is very low, and therefore, acceptable.
Therefore, the etaff finds the proposed change to the WCGS TS to add a new Action Statement to support continued plant operation in the event that plant inlet water temperature exceeds 90 degrees F and remains less than 95 degrees F acceptable.
3.0 DESCRIPTION
OF EMERGENCY CIRCUMSTANCES The Commission's regulations in 10 CFR 50.91 contain provisions for issuance of an amendment where the Commission finds that emergency circumstances exist, in that failure to act in a timely way would result in derating or shutdown of a nuclear power plant. The emergency exists in this case in that the proposed amendment is needed to prevent shutdown of WCGS.
On July 14,1998, the WCGS cooling lake exceeded 89 degrees F, which is higher than previously experienced. The elevated lake temperature was due to recent harsh meteorological conditions (i.e., extremely high temperatures, high humidity and lack of wind). Due to predictions for continuing harsh meteorological conditions, the concern exists that the plant inlet water temperature may exceed 90 degrees F, forcing a unit shutdown in accordance with TS.
This unprecedented condition was not predictable. The licensee submitted the emergency TS amendment request when it determined that meteorological conditions were predicted to
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remain harsh over the next several weeks. The staff has determined that the licensee used its best efforts to make a timely application.
Accordingly, the Commission has determined that emergency circumstances exist pursuant to 10 CFR 50.91(a)(5) and could not have been avoided, that the submittal was timely, and that the licensee did not create the emergency condition.
4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The Commission't regulations in 10 CFR 50.92 state that the C:,mmission may make a final determination that a license amendment involves no significant hazards considerations il operation of the facility in accordance with the amendment would not:
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Inycive a significant increase in the probability or consequences of any accident previously evaluated; (2)
Create the possibility of a new or different kind of accident from any previously evaluated; or f
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Involve a significant reduction in a margin of safety.
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. This amendment has been evaluated against the standards in 10 CFR 50.92 and the staff's fir.al determination is presented below, it does not involve a significant hazards consideration because the change would not:
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Involve a significant increase in the probability or consequences of an accident previously evaluated.
The proposed change does not involve any physical alteration of plant systems, structures, or components. The proposed change provides an allowed time for the plant l
to continue operation with plant inlet water temperature in excess of the current TS limit of 90 degrees F for plant components. The plant inlet water temperature is not assumed to be an initiating condition of any accident analysis evaluated in the USAR. Therefore, j
the allowance of a limited time for the water temperett.e to be in excess of the current i
limit does not involve an increase in the probability of an accident previously evaluated in 1
the USAR. The UHS supports operability of safety-related systems used to mitigate the consequences of an accident. Plant operation for brief periods with plant inlet water i
temperature between 90 degrees F and 95 degrees F will not adversely affect the I
operability of these safety-related systems and will not adversely impact the ability of these systems to perform their safety-related functions. Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated in the USAR.
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Create the possibility of a new or different kind of accident from any previously evaluated.
The proposed change does not involve any physical alteration of plant systems, structures, or components. The temperature of the plant inlet water being between 90 and 95 degrees F for a short period does not introduce new failure mechanisms for systems, structures, or components not already considered in the USAR. Therefore, the possibility of a new or different kind of accident from any accident previously evaluated is not created.
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Involve a significant reduction in a margin of safety.
The proposed change will allow an increase in plant inlet water temperature above the current TS limit of 90 degrees F for the UHS, and delay the requirement to shut down the plant when the plant inlet water system temperature limit is exceeded by 12 tours. The proposed change does not alter any safety limits, limiting safety system settings, or limiting conditions for operation, and the proposed temperature increase will remain below the design limit cooling water input value for safety-related equipment. Thus, the proposed change does not involve a significant reduction in any margin of safety.
j Accordingly, the Commission has determined that the amendment involves no significant hazards consideration.
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5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the staff attempted to consult with Kansas State official for comment on the proposed issuance of the amendment. The State official could not be reached.
6.0 ENVIRONMENTAL CONSIDERATION
The amu.orisent 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. 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
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no significant increase in individual or cumulative occupational radiation exposure. The Con 4 mission has made a final finding that the amendment involves no s'anificant hazards consideration. Accordingly, the amendment meets the eligibility criteria for categorical l
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.
7.0 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 I
' cperation in the proposed manner, (2) such activities wil! 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 Contributors:
W. LeFave K. Thomas Date: July 18,1998 k
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