ML20236R957
| ML20236R957 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 09/23/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20236R947 | List: |
| References | |
| NUDOCS 9807240048 | |
| Download: ML20236R957 (6) | |
Text
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS,180 AND 184TO FACILITY OPERATING LICENSE NOS. DPR-24 AND DPR-27 WISCONSIN ELECTRIC POWER COMPANY l
POINT BEACH NUCLEAR PLANT. UNIT NOS.1 AND 2 DOCKET NOS 50-266 AND 50-301
1.0 INTRODUCTION
By letter dated January 18,1997 (TSCft-191), as supplemented on April 17, August 7, and August 27,1997, the Wisconsin Electric Power Company (the licensee) requested amendments to the Technical Specifications (TS) appended to Facility Operating Licenses Nos. DPR-24 and DPR-27 for the Point Beach Nuclear Plant, Unit Nos.1 and 2. Specifically, the proposed changes would increase the minimum volume and boron concentration for the I
refueling water storage tanks (RWSTs) from 24,100 gallons at 2000 parts per million (ppm) to
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26,600 gallons at 2700 ppm. The minimum required boric acid storage tanks (BASTS)
L volume, which ranges from 6860 gallons for a minimum 3.0 weight percent solution to 1750 l
gallons for a miriimum 11.5 weight percent solution, would be increased to 7950 gallons and 2000 gallons, respectively.. The minimum boron concentration in the safety injection accumulators would be increased from 1800 ppm to 2100 ppm. The minimum boron l
concentration for the primary coolant system during refueling operations would be increased from 1800 ppm to 2100 ppm. The minimum boron concentration for the primary coolant i
system during positive reactivity changes, when the containment integrity is not intact, would be increased from 1800 ppm to 2100 ppm. These increases in boron concentration are necessary to accommodate shutdown margin and safety analysis requirements based on preliminary evaluation associated with an extension of the reload cycle from 12 months to 18 l
months for Unit 1 following refueling outage U1R25, and for Unit 2 following refueling outage U2R24.
The April 17, August 7, and August 27,1997, letters provided clarifying information within the scope of the original application and did not change the staffs initial proposed no significant hazards considerations determination.
2.0 EVALUATION The staff reviewed the proposed changes for their impact on accident analyses and on the effects on the increase in boron concentration for removal of iodine from the post-accident containment atmosphere, corrosion of compoaents exposed to boric acid solutions, 9907240048 970923 F
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precipitation of boric acid from the solutions exposed to low temperatures, and precipitation of boric acid in the core region during a post loss-of-coolant accident (LOCA) safety injection.
' The licensee proposes to modify the following TS to account for higher inventories of boron in the plant:
TS Table 15.3.2-1 and TS 15.3.2 Bases in the TS would be revised to increase the amount of boron stored in the BASTS, by raising the minimum volume of the solution in the tank from 6860 gallons to 7g50 gallons for boric acid concentrations of 3 to <3.5 weight percent (w/o), from 1750 gallons to 2000 gallons for boric acid concentrations of 11.5 to s;12.5 w/o, and proportionally for the intermediate concentrations.
TS 15.3.3.A.1.s and TS 15.3.2 Bases would be revised to raise the minimum boron concentration in the RWST from 2000 ppm to 2700 ppm. Also, the minimum volume of the solution required for maintaining proper reactivity margin would be increased from 24,100 gallons to 26,600 gallons.
TS 15.3.3.A.1.b would be revised to raise the minimum boron concentration in the Sl accumulators from 2000 ppm to 2600 ppm.
TS 15.3.6.D and TS 15.3.6 Bases would be revised to increase boron concentration in the primary coolant during positive reactivity changes, when containment integrity is not intact, from 1800 ppm to 2100 ppm.
TS 15.3.8 would be revised to increase boron concentration in the primary coolant during refueling operation from 1800 ppm boron to 2100 ppm boron.
2.1 Accident Analyses Preliminary evaluations associated with the cycle extension to 18 months performed by Westinghouse indicate that an increase in boron concentration is necessary to accommodate shutdown margin and safety analysis requirements associated with the cyc.e extension. The boration volume available through any flow path must be sufficient to prov'de the required shutdown margin at cold shutdown, xenon-free conditions from any expected operating condition. The volume requirement is associated with boration from just critical, hot zero power, peak xenon conditions with control rods at the insertion limit, to xenon-free, cold shutdown conditions with the highest worth control rod assembly fully withdrawn. The preliminary evaluations indicate that the revised parameters for the RWST (26,000 gallons of 2700 ppm borated water) or the revised parameters for borated water in the BASTS specified in TS Table 15.3.2-1 are sufficient to ensurw adequate shutdown margin.
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Westinghouse also performed preliminary evaluations for the licensee to determine the potential effects of the new core designs resulting from the increased energy requirements for implementing 18-month core operating cycles. These preliminary evaluations indicate that the LOCA and the boron dilution events are the only analyses that specifically requ're i
changes to boron concentration parameters. The evaluation did not address all th ffects of the anticipated core design. The increased reactor coolant system (RCS) boron wit. result in a mote positive (less negative) modarator temperature coefficient (MTC). Therefore, prior to i
operation with a revised core configuration, the licensee confirmed that all of the accident analyses will be evaluated for continued applicability as part of the reload safety evaluation process. The licensee confirmed that, if any boron concentration limits are found to be inadequate to demonstrate acceptable accident response, the TS will be changed at that time.
2.1.1 LOCA Analysis The LOCA was evaluated to determine the post-LOCA suberiticality limit with typical 18-month cycle core designs. The RWST and accumulator boron concentrations were varied to establish the minimum required boron concentrations to maintain at least 100 ppm of margin to the required post-LOCA suberiticality limit. However, one effect of boration during a LOCA is the progressive increase over time of the boron concentration in the core. This occurs because the water vaporizes out of the break and leaves behind the boron it originally contained. If the concentration exceeds a critical value, boric acid can crystallize in the core and precipitate out of solution. The concem is that the precipitation of boric acid crystals could block core cooling. The licensee has implemented emergency operating procedures to ensure simultaneous cold leg and reactor vesselinjection within 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> of a LOCA.
Westinghouse has determined that this amount of time assures boron solubility within the core. The licensee has confirmed that, if the core reload safety evaluation identifies a more limiting time requirement, the emergency operating procedures will be revised accordingly.
t 2.1.2 Boron Dilution Events The proposed TS change to the minimum boron concentration of the primary coolant system for refueling operations has been evaluated and found to preserve the 5% suberiticality.
margin and provide the necessary response time for postulated boron dilution events. The boron dilution event during refueling must allow at least a 30-minute operator response time from the recognition of an audible high count rate signal to isolate the dilution source. The l
proposed change in the refueling boron concentration from 1800 ppm to 2100 ppm will l
ensure that adequate operator response time remains available during this dilution event.
2.2 lodine Removal After an accident in which core damage occurs, radioactive iodine would be released from l
the damaged fuel. To prevent it from escaping to the outside, the radioactive iodine should be removed from the containment atmosphere and kept dissolved in the containment water.
This process is significantly enhanced by maintaining high pH. Therefore, any reduction of pH may have a negative efibet on the post-accident dose rates. The licensee analyzed the l
impact of pH reduction on several iodine removal and retention mechanisms.
l 2.2.1 Retention of lodine in the RCS During a Fuel Handling Accident increasing boric acid concentration in the primary coolant during refueling operations will result in a lower pH. This could have some effect on retention in the primary coolant of the l
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l 4-iodine released from damaged fuel rods during a fuel handling accident. However, the proposed increase of boron concentration in the primary coolant from 1800 to 2100 ppm will result in a very small pH drop which will cause only an insignificant change of the primary coolant's iodine retention capability. There is no concem, therefore, that any significant amount of radioactive iodine could be released into the environment.
2.2.2 Removal of lodine From the Containment Atmosphere By Sprays As a consequence of increasing boric acid concentration in the RWST, the containment spray solution during the injection phase will have a lower pH for the corresponding amount of sodium hydroxide added to it. Although the pH value will drop from its originally specified j
range of 9.0 to 10.0, the licensee has calculated that it still will remain above 8.5 which is j
adequate to ensure proper removal of iodine from the containment atmosphere.
2.2.3 Retention of lodine in the Containment Sump Water The pH of the containment sump water should be maintained at a sufficiently high value to retain all the iodine removed from the containment atmosphere by sprays. In the containment sump water the pH value is determined by the amount of boric acid transferred L
~ from the RWST, Si, and BAST tanks and the primary coolant system. After the proposed l
modification all these sources will have more boric acid and the resultant pH of the sump L
solution will decrease. However, the licensee has determined that the decrease will be l
relatively small and the minimum pH will remain at a value of about 7.5. According to i
Section 6.5.2 of the Standard Review Plan, when pH is maintained at a higher than 7 value, sump water has satisfactory iodine retention capability.
2.3 Effects on Materials Exoosed to Borsted Water At the current concentrations of boric acid, corrosion of the components exposed to boric l
acid solution is negligible. The proposed increata in boric acid concentration in the storage l
tanks will result in a minimal decrease in pH and it is not expected that this change will result in any significant increase in corrosion of sustenitic stainless steel or other corrosion-resistant materials. In the containment sump the components are exposed to boric acid solution l
whose pH is 7.5 or higher and at this value no corrosion of metallic surfaces will occur. Also, the equipment within the containment was qualified down to pH 7.5 and will not be affected by the increased concentration of boric acid.
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Solubility of boric acid in RWST and Si Tanks 1
-After the proposed increase in boron inventory, the highest concentration of boric acid in the storage tanks will be well below its solubility limits (2.48 w/o) at 32 'F which is a conservative estimate of the lowest temperature to which these tanks would ever be exposed. Therefore, there is no possibility for boric acid precipitation in these tanks or in the associated pipe lines.
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' 4 2.5 Boric Acid Precipitation in the Post-LOCA Core As a consequence of increasing boric acid concentration in the RWST and Si tanks that j.
provide the post-LOCA safety injection, the time when boric acid starts to precipitate in the l
core may be decreased. This will require a shorter switching time to simultaneous hot and cold leg injection. The presently calculated switching time is 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> and the licensee found l
that the change caused by increasing boric acid concentration is insignificant. However, as a safety precaution, the switching time should be verified for each new core reload.
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2.6 Summarv l
The stsW has reviewed the licensee's subrnittal on higher boric acid concentrations in the i
RWSTs, BASTS, Si accumulators, and in the primary coolant during refueling operation, and in the primary coolant when reactivity changes are made without establishing containment l
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integrity. The licensee proposes to introduce inese changes te offset higher reactivity fuel that it is planning to use in the future. In the submittal, the licensee has analyzed different plant operations that may be impacted by higher boron concentrations and found that none of them will cause reduction of the safety of the plant. The staff has evaluated the licensee's analyses and performed independent verifications. Based on this evaluation, the staff concludes that the increase in boric acid concentration proposed by the licensee will not degrade plant safety. The proposed increase in boron inventory is, therefore, acceptable.
The staffs evaluation has indicated that the licensee's analyses support PBNP's assertion that the proposed increase in boric acid concentration will not affect the performance of the plant and will not cause a decrease in the plant's safety functions.
3.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Wisconsin State official was notifed of the proposed issuance of the amendments. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
These amendments change 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. The staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluent that may be released offsite, and that there is no signi6 cant increase in individual or cumulative occupational radiation exposure. The Commission has previously published a proposed finding that these amendments involve no significant hazards consideration and there has been no public comment on such finding (62 FR 19836). Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(g). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the j
issuance of these amendments.
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5.0 CONCLUSION
f 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 Contributors: L.Kopp K. Parczewski Date: September 23, 1997 I
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