ML20080E537
| ML20080E537 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 09/01/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20080E532 | List: |
| References | |
| NUDOCS 8309130482 | |
| Download: ML20080E537 (6) | |
Text
.__ _______________
g-po, UNITED STATES
.y i i m ' i NUCLEAR REGULATORY COMMISSION g
y MASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NOS. 65 AND 59 TO FACILITY OPERATING LICENSE NOS. DPR-42 AND DPR-60 NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNIT NOS. 1 AND 2 DOCKET NOS. 50-282 AND 50-306 Introduction By letter dated June 10, 1983, Northern States Power Company (NSP) (the licensee) requested technical specification (TS) changes for Prairie Island Nuclear Generating Plant Unit Nos.1 and 2 concerned with the sodium hydrox-ide concentration of the containment spray system.
Specifically, the TS changes would pennit a change of the sodium hydroxide (Na0H) concentration in the spray additive tank of the containment spray system from the existing 30% by weight to a range of 9% to 11% by weight, inclusive.
In addition, the amendments would permit the concentration to be out of specification limits for a period not to exceed 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> at which time the licensee would have to initiate shutdown procedures.
The licensee's analysis shows that, under various accident scenarios, the electrical equipment inside containment could be subject to an environment having a pH of 13 during the injection phase under the existing TS requiring that (Na0H) concentrations in the containment spray additive tank be limited to 30% by weight.
This exceeds a pH of 10.5, the environmental pH limit to which the electrical equipment inside the containment is qualified.
Reducing the NaOH concentration assures that an acceptable environmental pH limit for the electrical equip-ment inside containment will not exceed a pH of 10.5 at any time.
Discussion and Evaluation By letter dated June 10, 1983, the licensee requested TS changes that are in conformance with IE Bulletin 79-OlB, requiring an evaluation of the qualification of safety related electrical equipment when exposed to various harsh environmental conditions. The licensee's evaluation indicated that some accident scenarios result in a containment spray pH of greater than 13 during the injection phase which exceeds the 10.5 environment pH limit for the electrical equipment inside containment.
l The licensee proposes to increase the volume and decrease the concentration of Na0H in the spray containment spray additive tank.
The containment spray additive tank volume would be increased from 2190 to 2590 gallons and the decrease in NaOH concentration is such that the ratio of boric acid to NaOH is maintained at a ratio where the pH will remain greater than 7 after thorough mixing of the containment spray solution and containment sump O N 282 P
PDR j
water in the event of a LOCA.
Maintaining the pH greater than 7 meets our Standard Review Plan 6.1.1 Branch Technical Position MTEB 6-1 which recom-mends a minimum pH of 7.0 to reduce the probability of stress corrosion cracking of austenitic stainless steel.
We evaluated the pH of the containment sump water following mixing in the containment sump with the educted sodium hydroxide. We verified by independent calculations that 2590 gallons of 9 to 11 weight percent Na0H when mixed with 333,000 gallons of boric acid at 2000 ppm will raise the containment sump water pH to greater than 7.
Our verification shows that, with normal tank levels and solution concentrations, the sump pH would be 8.4.
Under worst case conditions, the sump pH would be 8.2.
Therefore, the proposed TS change meets the acceptance criteria of Branch Technical Position MTEB 6.1 of SRP 6.1.1.
On this basis we find that, from a coolant chemistry standpoint, the proposed TS change request is acceptable.
Based on the staff review, the proposed change is consistent with the Prairie Island Final Safety Analysis Report and with our guidelines of the Standard Review Plan with the following exception.
The Standard Review Plan (SRP) (NUREG-0800), Section 6.5.2, " Containment Spray as a Fission Product Cleanup System," states that, "Long-term iodine re-tention with no significant re-evolution may be assumed only when the equilibrium sump pH, after mixing and dilution with the primary coolant and ECCS injection, is above 8.5."
As noted above, because the minimum sump pH under worst case conditions (e.g. 8.2) could be lower than 8.5, some iodine re-evolution should be assumed in a recalculation of LOCA doses.
To address this concern, the staff re-evaluated the LOCA doses that were presented in the Units 1 and 2 Safety Evaluation Report, assuming diminished long-term iodine retention effectiveness for the spray system.
The Prairie Island Nuclear Generating Plant Units Nos.1 and 2 are designed to use containment sprays with Na0H additive to remove airborne elemental iodine from the containment atmosphere and retain it in the sump and spray water in the event of a LOCA.
The staff, as per the guidance of SRP 6.5.2, assumes that the long-term iodine retention efficiency in the sump and spray water is a function of the pH of the post-LOCA sump solution. At a pH of 8.2, the maximum elemental iodine decontamination factor of 200 suggested in SRP 6.5.2, is not appropriate.
The LOCA dose was re-evaluated using an elemental iodine decontamina-tion factor of 88 as suggested by the method contained in SRP 6.5.2.
This lower decontamination factor did not have a large effect on the total calculated dose, and for the worst case LOCA scenarios, the iodine retention would be more effective than assumed in this evalua-tion.
The dose calculations were made in accordance with SRP 6.5.2 and 15.6.5, Appendix A, and used the current estimate of the atmospheric l
. dispersion characteristics of the Prairie Island site. Assumptions regarding containment leakage and the shield building filtration and recirculation system operation were consistent with the September 1972 Safety Evaluation Report (SER), Supplement 2 to the SER (April 1973),
and a safety evaluation regarding containment leakage transmitted in a letter from R. C. DeYoung to the Northern States Power Company, November 29, 1973.
The parameters and assumptions used in the dose calculation are listed in Table 1.
The results of the dose calculations shown in Table 2 indicate that the re-evolution of iodine due to the sump solution having a pH of 8.2 instead of 8.5 is not significant. This is shown by the values given in Table 2 for thyroid dose rems for the 0-2 hours, Exclusion Area Boundary (e.g. 97 vs 96) and for 0-30 days low population zone outer boundary (e.g. 34 vs 32).
The whole body dose was essentially unchanged for pH changes in sump solution from 8.5 to 8.2.
In addi-tion, all dose levels are substantially below the 10 CFR Part 100.11 guideline values of 300 rems to the thyroid and 25 rems whole body.
On this basis, we find that a sump solution having a pH of 8.2 for the worst case LOCA scenarios will not significantly reduce the existing margin of safety for offsite doses and these calculated doses are well within the guidelines of 10 CFR Part 100.11.
We, therefore, find the proposed change is acceptable from the standpoint of airborne elemental iodine removal from the containment atmosphere during potential accident conditions.
The licensee's proposed change was modified to include the surveillance requirements for the level instrument on the NaOH spray additive tank.
The surveillance requirements that are put in place for this level instrument are the same as those existing for the level instruments of the refueling water storage tank since these two components (i.e. NaOH spray additive tank and refueling storage tank) are used together during potential accident conditions.
In addition these surveillance requirements are compatible with those appearing in the standard techni-cal specifications. These modifications were discussed with and agreed to by the licensee.
The proposed amendment would also allow the licensee 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to correct the concentration when found outside the technical specification limits before requiring a plant shutdown.
Such an allowance is consistent with standard practice for such a technical specification limit in order to permit the licensee a reasonable time period to take the corrective actions necessary to achieve an acceptable concentration before requiring a plant shutdown.
In addition, the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> period is consistent with the similar requirement appearing in our standard technical specifications.
On this basis we find the licensee's pro-posed request of the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to allow for a potential concentration correction acceptable, i
In conclusion, based on the above considerations, we find the licensee's proposed TS change request acceptable.
t
Environmental Consideration We have determined that the amendments do not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendments involve an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 51.5(d)(4), that an environmental impact statement or negative declaration and environ-mental impact appraisal need not be prepared in connection with the issuance of the amendments.
Conclusion We have 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, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of these amendments will not be inimical
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to the common defense and security or to the health and safety of the public.
Date: September 1, 1983 Principal Contributors:
P. Easely F. Witt' D. C. DiIanni i
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Table 1 Assumptions Used in Calculation of Thyroid and Whole Body Doses for a Postulated Loss-of-Coolant Accident at Prairie Island I and 2 j
Spray Effectiveness for Iodine Reinoval Elemental
- 6. per hour Organic 0.
Particulate 0.45 per hour Final Elemental Iodine Decontamination Factor, Based on Minimum Sump pH=8.2 88.
Total Containment Leak Rate Directly to Environment 0.01% of containment volume per day Total Containment Leak Rate that is Treated by Auxiliary Building Special Ventilation Zone 0.1% per day Total Containment Leak Rate to Shield Building 0.14% per day 0-6 minutes:
This leakage bypasses shield building filters 6-7 minutes:
This leakage is filtered and released without mixing 7-24 minutes:
Half of this leakage is filtered and released without mixing, half mixes in shield building at 2800 cfm, recirculation of 2760 cfm.
after 24 minutes: 18% of this leakage is filtered and released, 82%
mixes in shield building volume, filtered release from shield building at 1000 cfm, recirculation of 4560 cfm.
Atmospheric Dispersion Coefficients 0-2 hours at Exclusion Area Boundary 4.7 x 10-4 sec/m 3
0-8 hours at Low Population Zone 3
Outer Boundary 7.0 x 10- sec/m 8-24 hours Outer Boundary 5.0 x 10- sec/m3 1-4 days Outer Boundary 2.5 x 10- sec/m3 4-30 days Outer Boundary 9.5 x 10- sec/m Iodine Filter Efficiencies Elemental Iodine 90%
Organic Iodine 70%
Particulate Iodine 99%
RHR leakage (assumed negligible contribution to dose)2 gal per hour i
Table 2 A.
Calculated Offsite Thyroid and Whole Body Doses for a Postulated Loss-of-Coolant Accident at Prairie Island 1 and 2 Based on a Sump Solution having a pH of 8.2 Thyroid Dose, Rems Whole Body Dose, Rems 0-2 hours, Exclusion Area Boundary 97 2.9 0-30 days, Low Population Zone Outer Boundary 34 1.4 B.
Calculated Offsite Thyroid and Whole Body Doses for a Postulated Loss-of-Coolant Accident at Prairie Island 1 and 2 Based on a Sump Solution having a pH of 8.5 Thyroid Dose, Rems Whole Body Dose, Rems 0-2 hours, Exclusion Area Boundary 96 2.9 0-30 days, Low Population Zone Outer Boundary 32 1.4 I
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