ML20209G288

Safety Evaluation Supporting Amend 125 to License NPF-42

ML20209G288
Person / Time
Site:	Wolf Creek
Issue date:	07/08/1999
From:	NRC (Affiliation Not Assigned)
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ML20209G281	List: ML20209G277 ML20209G288
References
NUDOCS 9907190115
Download: ML20209G288 (5)

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UNITED STATE 8

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WASHINGTON, D.C. enana annt SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REAOTOR REGULATION RELATED TO AMENDMENT NO.125 TO FACILITY OPERATING LICENSE NO. NPF-42 WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STATION DOCKET NO. 50-482 1.0 INTRODUCTlQN

_ By lettar dated January 12,1999, as supplemented by letters dated May 11 and June 30,1999,

. Wolf Creek Nuclear Operating Corporation (the licensee) requested changes to the Technical Specifications (TSs), Appendix A to Facility Operating License No. NPF-42, for the Wolf Creek i

Generating Station (WCGS). The proposed changes would revise TS 3/4.7.5, Ultimate Heat i

Sink, by adding a new action statement to be used in the event that plant inlet water

- temperature exceeds 90*F. Specifically, the new action statement would allow, until September 30,1999, continued operation of the plant with plant inlet water temperature between 90 and 94*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. The licensee will pursue a pcmanent change to the inlet water temperature limit through the Westinghouse Owners Group as a proposed change to the Standard Technical Specifications.

The licensee's proposed amendment is the same proposal that the licensee submitted on July 17,1998, and the staff approved in Amendment 118 that was issued on July 18,1998.

The amendment was issued under emergency conditions, in accordance with 10 CFR

' 50.91(a)(5), because the cooling lue for WCGS exceeded 89*F and it was projected that the

- water temperature would exceed the TS limit of 90*F and the plant would have to unnecessarily shut down because of the then harsh meteorological conditions.

palen&nent 118 was effective until September 30,1998. In the letter of January 12,1999, the licens, s proposed a permanent change to TS 3/4.7.5; however, the staff concluded that the proposed change was ger.oric in nature and requested that the licensee propose a limited

. duration amendment similar to that approved in Amendment 118. The licensee's modified proposals are in the letters of May 11 and June 30,1999, both of which are of limited duration l

and would be effective only until September 30,1999.

The May 11 and June 30,1999, supplemental letters provided additional clarifying information,

~ did not expand the scope of the application as originally noticed and did not change the staff's or!ginal proposed no significant hazards consideration determination published in the Federal i

RePter on February 24,1999 (64 FR 9203), except that in the June 30,1999, letter the licensee proposed a maximum plant inlet water temperature of 95*F where the letters of January 12 and May 11,1999, proposed only 94*F.

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& The licensee's proposal that the statt is considering at this time is the plant inlet temperature limit of 94 F from the letters dated January 12 and May 11,1999, and the action statements but not the temperature limit from the letter dated June 30,1999. Thus, as limited, the letter of June 30,1999, does not expand the scope of the application as originally noticed and does not change the staff's original proposed no significant hazards consideration determination published in the Federal Register on February 24,1999 (64 FR 9203).

The current temperature of the cooling lake for WCGS is 85 F and rising. It is possible that the water temperature may exceed the TS limit of 90 F during the summer.

2.0 LICENSEE'S PROPOSAL The proposed new action statement to TS 3/4.7.5 being considered by the staff is the following:

NOTE: Until September 30,1999, the following actions supersede the above action (of

)

TS 3/4.7.5):

a.

With the pant inlet water temperature >90 F but <94 F:

1. Within one hour verify two trains of residual heat removal, two trains of component cooling water, and two trains of essential service water are

operable,

2. Verify at least once per hour that the plant inlet temperature is <94 F, and

3. Within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> restore the plant inlet water temperature to 90'F or less.

4. With any of the above requirements not satisfied, be in at least hot standby

. within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />, i

b.

With the ultimate heat sink (UHS) inoperable for any reason other than the j

temperature, be in at least hot standby wi'hin the 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in cold shutdown i

within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

The new action statement only applies to the case of the plant inlet water temperature is above the TS limit of 90*F, requires more frequent checking of the temperature above 90 F and plant cooling systems, only allows operation above 90 F for the limited time period of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, and does not change the time period in the current action statement to shut down.

3.0 E. VALUATION The ultimate heat sink (UHS) for WCGS is the normally submerged Seismic Category I cooling pond. The UHS is formed by providing a volume of cooling water behind a Seismic Category I dam built in one finger of the WCGS cooling lake. The two principal functions of the UHS are the dissipation of residua: heat after reactor shutdown, and dissipation of residJa! heat after an accident. The basic performance requirements for the UHS are that a 30-day supply of water be available, and that the design-basis temperatures of safety-related equipment not be i

R s-exceeded. The UHS design assures that the design temperature of safety-related equipment is not exceeded. The design temperature of water supplied to the plant is 95'F.

The UHS is the sink for heat removed from the reactor core following all accidents and 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 cooling 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, for the analysis, it was assumed that all of the water i

in the UHS was at 90*F at the start of the event.

l The analysis predicted 95'F as the highest plant inlet water temperature occurring during the maximum temperature period following the loss of the main dam with the average water temperature generally being below 94'F.

The licensee evaluated the effect of the proposed change on normal plant operation and normal plant 6,hutdown with the main dam intact, and safe shutdown or post-accident operation without the main dam.

Normal Plant Operation with the Main Dam Intact: Short term operation with an inlet water temperature of up to 95'F is not expected to negatively affect plant operation, with the possible exception of turbine backpressure. A slight load reduction may be necessary to maintain acceptable turbine backpressure. Existing plant guidance will be employed if any unexpected transients are experienced.

Shutdown with the Main Dam Intact: Increasing the inlet water temperature from 90'F to 95'F may cause the calculated single train time required to cool the unit below 200*F to exceed the cooldown time needed to comply with some TS. To compensate for this concern, the requested action statement requires verification of operability of two RHR trains when the inlet water temperature is greater than 90*F. This will ensure the cooling capacity is available to meet the shutdown time requirements.

LOCA with the Main Dam ininst: The effect of full power plant operation on plant inlet water temperature during worst case predicted summer environmental conditions is approximately 0.5'F. The peak heat rejection rate by the plant post-LOOA would be approximately 5 percent of the continuous heat rejection rate of the plant during normal operation. Thereforecthe effect of post-LOCA heat loads on plant inlet water temperature would be less than 0.1 *F. The current UHS analysis assumes that there has been a main dam failure and uses worst case environmental conditions. The results indicate that with an initial UHS temperature of 90P, plant intake water temperature will not exceed 95*F. The UHS analysis results also indicate i

that the environmental conditions have a much greater effect on peak plant intake water temperature than does the heat rejected from the plant. The current UHS analysis is recognized as bounding 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

a i '

i i

percent. The probabilliy of environmental conditions significantly worse than those causing entry into the limiting condition for operation is low. The probability of these conditions occurring simultaneously with a LOCA is even lower.

Safe Shutdown or Post-Accident Operation without the Main Dam: The TS limit of 90*F is not

- being changed; however, the license amendment provides an allowance for operation above that limit for a 12-hour period. The Wolf Creek accident analyses assume a plant inlet water temperature of 95'F. 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*F through diurnal 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 l

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

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water temperature is above 90*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 that of a large break LOCA. It is also noted that WCGS has a dam monitoring program in place to ensure continued integrity of the main dam.

Therefore, it is concluded that this proposed change is of low risk significance.

Based on the above review and the license amendment No.118 dated July 18,1998, the staff concludes that with the dem 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'F. Further, the staff concludes that the probability of a LOCA concurrent with a dam fahure is very low and, therefore, acceptable.

Based on the above, the staff 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*F and remains less than 95'F acceptable. Therefore, limiting the plant inlet water temperature limit to 94'F is also acceptable. The licensee's proposal to raise the plant inlet water temperature at 95'F will be addressed in a later evaluation,

4.0 STATE CONSULTATION

in accordance with the Commission's regulations, the Kansas State official was notified of the proposed issuance of the amendment on July 8,1999. The State official had no objections to the amendment.

5.0 ENVIRONMENTAL OONSIDERATlQN 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. 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 4

Commission has previously issued proposed findings that the amendment involves no significant hazards consideration, and there base been no public comment on such findings (64 FR 920?). 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 i

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Irr)act statement or environmental assessment need be prepared in connection with the issuance of the amendment.

6.0 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 amondment will not be inimical to the common defense and security or to the health and safety of the public.

PrincipalContributor: K. Thomas Date:

July 8, 1999 l

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