ML20247E655

Safety Evaluation Supporting Amend 120 to License DPR-61

ML20247E655
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	07/20/1989
From:	Office of Nuclear Reactor Regulation
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ML20247E648	List: ML20247E645 ML20247E650 ML20247E655
References
NUDOCS 8907260252
Download: ML20247E655 (4)

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, S b . , , , . *#,8 EUCLOSURE 1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 120 TO FACILITY OPERATING LICENSE NO. DPR-61 CONNECTICUT YANKEE ATOMIC POWER COMPANY l

HADDAM NECK PLANT DOCKET NO. 50-213

1.0 INTRODUCTION

By its April 24, 1989 letter (Ref. 1), Connecticut Yankee Atomic Power Company (CYAPCO/ licensee) proposed Technical Specification (TS) changes to support coastdown operation of the Haddam Neck Plant at the end of the current fuel cycle, Cycle 15. On June 16, 1989, CYAPC0 provided supplemental information (Ref. 2) to support the changes. That submittal did not alter the action noticed in the Federal Register on May 31, 1989, or affect the staff'r initial no significant hazards determination.

Our evaluation of the proposed changes follows. l 2.0 EVALUATION l

1 Coastdown operation commences when the reactor is at full power, all control l rods are withdrawn, the primary system boron concentration is essentially zero  !

ppm, and normal operating temperature can no longer be traintained. Coastdown j operation increases the cycle burnup and decreases operating temperatures.  !

Reference 3 is an addendum to the Cycle 15 reload report (Ref. 4) and examines I these effects on the fuel taechanical design, nuclear design, thermal-hydraulic )

design, and e.ccident and transient analyses. l 2.1 Fuel Mechanical Design The licensee estimates that coastdown operation will increase the cycle burnup l from 12000 MWD /MTU to 13000 MWD /MTU. The licensee assessed the effect of the increased burnup on the mechanical evaluation of the stainless steel and Zircaloy clad fuel rods provided in Reference 4. The Cycle 15 analyses were I found to bound the effects of coastdown operation on cladding collapse, cladding stress, cladding strain, cladding fatigue, and maximum fuel rod i internal pressure, i Prior to Cycle 15 operation, the licensee found that the Zircaloy clad lead test assemblies had insufficient gap between the top of the fuel rods and the bottom of the top nozzle to accorraodate the Cycle 15 projected burnep. As a  ;

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result of this finding, the licensee installed modified upper nozzles to accommodate a cycle burnup greater than 13000 MWD /MTU. The licensee reevaluated the fuel rod growth to account for the additional burnup due to coastdown operation and found that the peak rod had a burnup margin of 4000 MWD /MTU.

Based upon the licensee's evaluations, we conclude that the fuel mechanical i design has sufficient margin to accommodate coastdown operation.

2.2 Nuclear Design The licensee evaluated the nuclear design parameters that are used in the plant accident and transient analyses. This evaluation was perfonned for coastdown ,

conditions at a burnup of 13000 MWD /MTU. With the exception of the maximum '

diffe ential rod worth at subcritical conditions, the licensee found that the '

Cycle 15 safety analyses values in Reference 4 bound coastdown operation.

As a result of the large break LOCA analyses discussed below, the limiting Linear Heat Generation Rate (LHGR) was decreased. The decrease in LHGR required incorporation of new axial offset operating limits into the TS. These i new axial offset limits were determined using the approved Westinghouse methodology.

Since approved Ibethods were used, we find the licensee's review of the nuclear design acceptable.

2.3 Thermal-Hydraulic Design Since the enthalpy rise hot channel factor is unchanged and the maximum LHGR decreases during coastdown operation, the licensee concluded that the minimum DNBR and maximum fuel temperature are bounded by the Cycle 15 analyses in Reference 4. We find the licensee's analyses acceptable.

2.4 Accident and Transient Analysis The licensee reviewed the impact of coastdown operation on the non-LOCA transient analyses provided in Reference 4. As noted in Section 2.2, the only nuclear design parameter used in the Cycle 15 non-LOCA analysis impacted by the proposed coastdown operation was the uncontrolled rod withdrawal from suberitical . A small difference in the differential rod worth from 135 pcm/ inch in the Cycle 15 analysis to 136 pcm/ inch for coastdown operation, was l' calculated. The licensee concluded this difference would have a negligible

) effect on the minimum DNBR due to the low peak heat flux (15 percent of full power) calculated for this event. We find this conclusion reasonable.

The licensee reanalyzed the RCCA ejection, steamline break, and large break LOCA accidents to account for the changes in operating conditions which will occur during coastdown operation. For the RCCA ejection, the licensee found

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. that the peak fuel rod enthalpy, hot spot average cladding temperature, and radiological consequences were bounded by the Reference 4 analysis. The peak ,

RCS pressure was significantly higher than the Reference 4 analysis. However,  !

the pressure as still less than the faulted stress limit.

The consequences for the steamline break accident was found to be bounded by that in Reference 4, primarily due to the lower power peaking factors which are obtained during coastdown operation.

The licensee reanalyzed the design basis large break LOCA to account for the effect of reduced RCS temperatures. The reanalysis used bounding conditions for the coastdown and a reduced LHGR of 13.5 kw/ft. The peak clad temperature was 2269'F, thus satisfying the Interim Acceptance Criteria Limit (36 FR 12247) of 2300*F which is applicable to those plants that do not use zircaloy clad fuel.

Since the revised analyses meet the applicable licensing criteria, the staff l finds the safety analyses acceptable for the coastdown operation.

3.0 TECHNICAL SPECIFICATION CHANGES Technical Specification changes proposed for coastdown operation of the Haddam Neck Plant are:

1. Definition for END-OF-CORE-LIFE (1.40)

2. New axial offset limtts for coastdown operation (TS 3.17.1 and Figure 3.17-Ic)

3. R(vised LHGR for coastdown operation (TS 3.17.2).  !

The staff has reviewed these changes and find they are consistent with the safety analyses performed to support the coastdown operation. Therefore, we find the proposed TS changes acceptable.

4.0 ENVIRONMENTAL CONSIDERATE0 _0N This amendment changes 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. We have determined that the amendment involves no significant increase in the amounts, and no significant change in the types., of any efflu-ents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The staff has pre-viously published a proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding.

Accordingly, the amendment meets the eligibility criteria for categorical uclusion set forth in 10 CFR 651.22(c)(9). Pursuant to 10 CFR 651.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

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5.0 CONCLUSION

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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 (3) the issuance )

of the amendment will not be inimical to the common defense and security or to l the health and safety of the public. I l

6.0 REFERENCES

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1. Letter E. J. Mroczka (CYAPC0) to USNRC, "Haddam Neck Plant, Cycle 15 I Coastdown, Proposed Changes to Technical Specifications," April 14, 1989.

2. Letter, E. J. Mroczka (CYAPCO) to USNRC, "Haddam Neck Plant, Cycle 15 Coastdown, Asymmetric LOCA Loads on Reactor Vessel Internals " June 16, 1989.

3. NUSCO-155, Addend W , " Technical Report Supporting Cycle 15 Operation, Coastdown Addendum,'" April 1989. (Enclosed to Reference 1.)

4 Letter, E. J. Mroczka (CYAPC0) to USNRC, " Cycle 15 Reload, Technical Specification. Change Requests and Reload Report," June 1, 1987.

Dated: July 20,1989 Principal . Contributor: R. Jones i

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