ML20203N796

Safety Evaluation Supporting Amend 79 to License DPR-54

ML20203N796
Person / Time
Site:	Rancho Seco
Issue date:	04/08/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20203N776	List: ML20203N774 ML20203N782 ML20203N796
References
NUDOCS 8605060061
Download: ML20203N796 (4)

Text

/ 'o g UNITED STATES 8 o NUCLEAR REGULATORY COMMISSION h r f WASHINGTON, D. C. 20555

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMEN 0 MENT N0. 79 TO FACILITY OPERATING LICENSE N0. DPR-54 SACRAMENTO MUNICIPAL UTILITY DISTRICT RANCHO SEC0 NUCLEAR GENERATING STATION DOCKET N0. 50-312 .

I. INTRODUCTION A. DESCRIPTION OF PROPOSED ACTION The proposed action would amend Section 3.8.4 of Appendix A of the Technical Specifications for the Rancho Seco Nuclear Generating Station (the facility) and the associated Basis for this specification. Section 3.8.4 prescribes the minimum boron concentration to be maintained in the reactor coolant system and refueling canal during fuel loading and refueling operations.

B. BACKGROUND INFORMATION By letter dated March 18, 1985, Sacramento Municipal Utility District (the licensee) requested amendment of Section 3.8.4 of the facility Technical Specifications and the associated Basis section. The proposed change would increase the min' mum boron concentration during refueling from 1850 ppm to 1974 ppm. The licensee states that based on the fuel loading for Operating Cycle 7, this is the minimum concentration needed durirg refueling to maintain a Keff of 0.95 or less with all control rods withdrawn from the core. The requirement for this value of Keff is stated in the Basis for Specification 3.8.4 Although it is not directly pertinent to the question of the acceptability of the licensee's request, it should be noted as background, that the identification of the need for the change in boron concentration was at least partially due to the condition identified in Licensee Event Report 85-003 dated March 5,1985. In this report, the licensee stated the facility had been advised by the fuel supplier that the then existing value of minimum boron concentration was in error. The error was stated to have occurred because the fuel supplier erroneously used a superseded value of the refueling Keff (0.99) in calculating the minimum boron concentration during refueling for Operating Cycles 5 and 6, rather than the value of 0.95, as currently stated in the facility Technical Specifications. The net effect of the discovery of this error was to increase the Cycle 6 minimum boron concentration during refueling from 1850 ppm to 1936 ppm. The licensee's proposal for Cycle 7 would further increase the refueling baron concentratinn to 1974 ppm.

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II. EVALUATION The licensee's initial submittal did not present a technical basis for the acceptability of the proposed change. Instead, the licensee simply requested the refueling boron concentration be changed to the value calculated by the fuel vendor as required during Operating Cycle 7. The required boron concentration is that needed to maintain Keff equal to 0.95 or less with all control rods withdrawn from the core. In order to confirm this value of refueling boron concentration, we examined the Updated Final Safety Analysis Report (UFSAR) for the facility (which contained nuclear data for Cycle 6) and the Reload Report submitted by the licensee to support facility operation in Cycle 7 (Rancho Seco Unit 1 Reload Report, BAW-1850, transmitted by licensee letter of December 17,1984). This review, however, did not provide a technical basis for verifying the acceptability of the proposed boron concentration. The licensee was therefore requested to submit the technical basis. This was provided by the licensee's letter of August 2,1985.

We have reviewed the analysis provided by the licensee. The analysis consisted of an initial calculation of system reactivity with a boron concentration of 2000 ppm. This calculation utilized a 1-zone (coarse mesh) PDQ model. The boron concentration was then adjusted to account for the calculated reactivity and for reactivity differences observed between 1-zone PDQ cases and multi-dimensional N0ODLE Code analyses which included axial blanket modeling. The results were also adjusted to account for observed biases between PDQ calculations and critical experiment data, and to account for axial flux shifts, non-uniform axial burnup and for the reactivity effect of Zircaloy fuel assembly spacer grids present in the core versus Inconel grids assumed in the base calculation. The reactivity adjustments were made using a cold inverse boron worth calculated with a 1-zone PDQ model for a boron concentration typical of that used during refueling. The resulting boron concentration required for a Keff=0.95 with all control rods withdrawn was 1974 ppm, which is the valua requested by the licensee. Based on the NRC staff's previous acceptt.nce of the N0ODLE code, the normalization of the 1-zone PDQ results to N0ODLE results and the application of other appropriate corrections, we conclude an acceptable method has been used to calculate the refueling boron concentration to be required during Cycle 7, and that the value of 1974 ppm is acceptable.

We note the licensee has proposed to revise the Basis for Specification 3.8.4 to specify that the boron concentration of 1974 ppm satisfies the reactivity condition stated in the Basis that Keff be 0.95 or less with all control rods removed from the core. This is an. editorial change which we find acceptable. We also note the Basis for the specification includes a second reactivity condition, viz. a boron concentration equal to or greater than 1800 ppm (the licensee must meet the more restrictive condition). The licensee was asked why, in view of the 1974 ppm requirement, this reactivity condition was being retained in the Basis for the Technical Specification. A licensee representative responded that this was retained as a permanent " floor" on the refueling boron

concentration. That is, even if future fuel loadings would allow the "Keff = .95 or less" requirement to be met with less than 1800 ppm boron, the 1800 ppm requirement would be applied. We also note this form of the Basis has existed since issuance of Amendment 29 to the facility license by NRC letter dated March 31, 1980. Accordingly, we find retention of the 1800 ppm boron provision acceptable.

Regarding environmental effects, the proposed 6.7% increase in refueling baron concentration would have no significant effect on the total quantity of radionuclides produced as a result of plant operations, but would cause some increase in the quantities of liquid waste and spent resin produced as a result of the need for somewhat more frequent regeneration of the deborating demineralizers. The acceptability of the size of the increase, however, must be evaluated in the context of the total quantity of liquid waste and spent resin otherwise produced. As shown in Section 11.1.2 of the UFSAR for this facility, deboration of the reactor coolant from its maximum value (during refueling) to a low value at the end of the operating cycle, is a major source of reactor coolant system waste. Several other sources related to the reactor coolant system, however, also exist. These include: deboration following shutdown, deboration of thermal expansion letdown following startups, deboration as needed to follow xenon swings, and ion-exchange removal of fission and neutron-activation products from the reactor coolant. In addition, liquid waste and spent resins are also produced as a result of processing liquids originating from the plant secondary system and from miscellaneous plant sources such as steam generator drain liquids, condensate demineralizer regeneration liquids, decontamination station drains, chemical analysis drains, miscellaneous plant drains, etc. Based on the variety of these sources, we conclude the proposed 6.7% increase in refueling boron concentration will not have a significant effect on the overall total quantity of radioactive or non-radioactive waste generated. Accordingly, we find the environmental effect of the proposed change acceptable.

III. CONCLUSIONS ENVIRONMENTAL CONSIDERATION This amendment involves a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.

We have 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 Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding.

Accordingly, 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 need be prepared in connection with the issuance of this amendment.

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• 4 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 this amendment will not be inimical to the common defense and security or to the health and safety of the public.

Dated: April 8, 1986 Principal Contributor: G. Zwetzig

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