ML20151G094

Safety Evaluation Supporting Amend 102 to License DPR-61

ML20151G094
Person / Time
Site:	Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date:	04/08/1988
From:	Office of Nuclear Reactor Regulation
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ML20151G070	List: ML20151G068 ML20151G087 ML20151G094
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NUDOCS 8804190220
Download: ML20151G094 (7)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REAC10R REGULATION RELATED TO AMENDMENT N0.

10 FACILITY OPERATING LICENSE NO. DPR-61 CONNECTICUT YANKEE ATOMIC POWER COMPANY HADDAM NECK PLANT DOCKET NO. 50-213 1.0 _ INTRODUCTION Pursuant to 10 CFR 50.90 and 50.91 Connecticut Yankee Atomic Power Company (CYAPCO) proposes to amend Facility Operating License No. CPR-61 for the Haddam Neck Plant. By letter dated April 5, 1988, CYAPC0 proposed to revise Technical Specification Figures 3.17-1A and 3.17-1B, "Axial Offset", and Section 3.17.2, "Linear Heat Generation Pate."

This Technical Specification change is required due to the discovery of an Errergency Core Cooling System (ECCS) flow calculational error used in the large break loss of coolant accident (LBLOCA) analysis. This change will ensure that the interim acceptance criteria (IAC) for peak clad tenperature (PCT) will not be exceeded.

2.0 DISCUSSION AND EVALUATION The Northeast Utilities Service Conpany (NUSCO) and CYAPC0 have been on an extensive upgrade prcgrarn of the Haddam Neck safety analysis. This is an effort to gain tetter understanding of the Haddam Neck Plant's response to transients, to aid in performing safety evaluations for plant changes, to respcnd to certain TMI action iten,s and SEP issues, and to facilitate Final Safety Analysis Report (FSAR) updates and En:ergency Operating Procedures (EOP) upgrades. As part of an extensive effort to upgrade the large break LOCA analysis for Haddam Neck, NUSCO performed in-house ECCS flow calculations to use as an input in the LBLOCA analysis.

The original ECCS perforniance analyses for Haddam Neck were docketed in 1971.

The Haddam Neck Plant ECCS perfourance is governed by the Interim Acceptance Criteria (IAC) because, with the exception of four zircaloy clad lead test assenblies, only stainless steel clad fuel is used at the facility. The IAC is in the FEDERAL REGISTER, Vol. 36, No. 125, dated June 29, 1971. The NRC approved the use of the zircaloy assen.blies in a letter from W. A. Paulson to W. G. Counsil, "Exerrption from 10 CFR 50.46 and Appendix M," dated October 2, 1984, ar,d a letter from W. A. Paulson to W. G. Counsil, "Zircenium Clad Ccronstration Assenblies," dated October 15, 1984 As an exemption frcm 10 CFR E0.46, the peak cladding ten.perature liniit is ?300" F rather than ??00* F.

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2 The results of the in-house ECCS flow calculations revealed that the limiting case single failure safety injection (SI) flow rate is approximately 1600 gpm less than the limiting case flow rate used in the original LBLOCA analysis. This is because the original analysis was based on the failure of an emergency diesel generator which deenergized a train of safety injection. The recent more liniting in-house analysis is based on the failure of a low Pressure Safety Injection (LPSI) valve. When the flow rate discrepancy was discovered, NUSCO initiated evaluations to verify the accuracy of its calculations and to determine the impact on the LBLOCA analysis.

A letter for justification for continued operation (JCO) was submitted (letter from E. J. Mroczka to NRC, dated March 25,1988), and the plant has operated -

at reduced power since then pending completion of a revised LBLOCA analysis. -

The Haddam Neck Plant is a four loop Westinghouse plant of an early design.

The original ECCS performance analyses were docketed in 1971 and were governed by the IAC as noted above. With the discovery of the calculational error, a reanalysis was made to account for the reduced SI flow rate.

The design basis accident affected by the change is the LBLOCA. A reduced ECCS flow rate increases the duration of the adiabatic fuel rod heat-up during the refill phase. (The blowdown phase of the LBLOCA is not affected since ECCS injection does not begin until after the blowdown phase. The reflood phase is only affected by the change in fuel temperature at the beginning of core recovery.) The fuel temperature, therefore, is higher at the beginning of the core recovery phase. The approved IAC SATAN and LOCTA codes were used in the reanalysis of the Haddam Neck large break LOCA to support a reduction in the SI flow from 7,740 gpm to 6,128 gpm. Only the input pertaining to this decrease in SI flow was changed, all other input is iden,ical to the previous analysis. Since SI flow does not come into play during tne blowdown phase of the transient, that portion of the analysis was not reanalyzed. It was also determined that due to the blowdown transients remaining the same, the limiting break size wculd not change. Therefore, rerunning the limiting break from the previous ar.alysis (DECLG, CC=1.C) was determined to be sufficient.

The largest impact on the results was the increase in the PCT adiabatic heat-up period between the end of blowdown and the bottom of core recovery (80CREC) tires. Decreasing the SI flow increases the time to fill the lower plenum, which determines the time of BOCREC. For four-loop operation, the 80CREC tire increased 13 seconds in the latest analysis, thus increasing the adiabatic heat-up period. The PCT in the reduced SI case occurred at C6.1 seconds into the transient, compared to the PCT tire of 81.1 seconds in the previous analysis.

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With the reduced ECCS flow rate, and without the preposed changes to the power distribution limits, a PCT of greater than the 2300' F IAC limit is predicted (approximately 2420'F). With the proposed changes to the Technical Specifi-cations, by reducing the peak linear heat generation rate (LHGR) to 13.3 kW/ft, the 230C' F limit is not exceeded (2296*F). Previcusly, the PCT was 2295'F.

Hence, the consequences of the accident are not significantly increased from those previously calculated.

The effect of the reduction in SI flow on the three-loop operation of Haddam Neck was also evaluated. Using the sensitivity deterrined by reanalyzing the fcur-loop operation on three-loop operation cases would be conservative due to the fact that the three-loop analysis was run at 68 percent power with a peak linear power of 12.0 kW/f t. The LHGR Technical Specification limits for three-loop operation are conservatively established at less than 10.1 kW/ft. '.

The SI flow rate reduction would cause the adiabatic heat-up rate to be less than the full-power case. Since the main effect on the three-loop case would also be the increased tire between end of blowdown and BOC time, and that increase would be the same 13 seconds as the four-loop, assuming the same PCT penalty as the four-loop case would be conservative. Therefore, for three-loop operation, compliance with the IAC can be maintained for a total SI flow of 6,128 gpm.

As a result of the above analysis, changes were proposed to the Technical Specifications that offset the LHGR and the axial offset limits for four-loop operation. (The current Technical Specification limit for LHGR for four-loop operation are 14.3 kW/ft for 0-125 EFPD, 14.5 kW/ft for 125-250 EFPD, and 15.5 kW/ft for 250 EFPD-EOL.) The proposed changes to the Technical Specifications limit the LHGR for four-loop operation to 13.3 kW/f t for 0-250 EFPD and 14.6 kW/ft for 250-EOL. The LHGR limit for three-loop operation remains unchanged.

These changes in LPGR limits necessitate a n.odification also of the axial offset limits in Figures 3.17-1A and 3.17-1B of the Haddam Neck Technical Specifications.

The licensee has used acceptable codes in the LBLOCA analysis and the analysis neets the following criteria of the IAC.

(1) The calculated peak fuel eierent clad temperature does not exceed 23CO' F.

(2) The amount of fuel element cladding that reacts chemically with water or steam does not exceed 1% of the total amount of zircaloy in the reactor.

(3) The clad temperature transient is terminated at a time when the core geometry is still amenable to cooling and before the cladding is so embrittled as to fail during or after quenching.

(4) The core temperature is reduced and decay beat is removed for an extended period of time, as required by the icng-lived radioactivity remaining in the core. I i

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The following Technical Specifications were required to be modified in order for the PCT to be in the acceptable range based on the new analysis.

1. 3.17.2.1, Linear Heat Generation Rate (LHGR) - Page 3-31a The LHGR was reduced by approximately 1 kW/ft to the values shown for the three categories of EFPD below:

a. Less than 125 EFPD 13.3 kW/ft

b. 125 to 250 EFPD 13.3 kW/ft

c. Greater than 250 EFPD -

but less than END-0F-CORE LIFE 14.6 kW/ft These changes are acceptable as discussed above.

2. Figure 3.17-1A, Power Level vs. Axial Offset Limits. 0-250 EFPD, Four loop Operation .

The axial offset band above 70% power was narrowed to achieve the reduction in LHGR and is acceptable as noted in above.

3. Figure 3.17-1B, Power Level vs. Axial Offset Limits, 250 EFPD-E0L, Four loop Operation The axial offset band above 70% power was narrowed to achieve the reduction in LHGR and is acceptable as noted above.

The propoeed Technical Specification change to reduce the LHGR and axial offset limits to compensate for the impact of the reduced limiting ECCS flow on the LBLOCA analysis for the Haddam Neck Plant has been evaluated by the staff and found to be acceptable as noted above. The LOCA analysis used acceptable codes and the IAC criteria were met. The Technical Specifications were modified in an acceptable manner in agreement with analyses.

3.0 EMERGENCY CIRCUMSTANCES In its April 5, 1988 letter, the licensee requested that this amendment be treated as an emergency because unless approved the plant would have to remain derated. As a result of a reanalysis of the large break LOCA for the Haddam Neck Plant, CYAPCO detertained that the ECCS flows were approximately 20 percent less than previously analyzed. To compensate for this loss in flow, it was determined that the LHGR needed to be reduced and the axial offset limit curve needed to be redefined. The NRC had limited power operation to 80 percent power until the licensee performed a reanalysis of the large break LOCA. The licensee performed this reanalysis and submitted a Technical Specification change to reflect this analysis. This Technical Specification change assures that ..ie IAC PCT limit is not exceeded and therefore 100 percent power operation would not be permitted unless the requested change is approved. Thus, unless this amendment is promptly authorized, resumption of power up to the licensed power level would be delcyed for a matter which does not affect plant safety.

4 t ,, o In accordance with 10CFR 50.91(a)(0 , the licensee has explained that it could not have avoided this emergency situation since the problem with the calculated reduced ECCS flow rates for large break LOCAs was only recently detemined. The reanalysis of the large break LOCAs is a licensee-initiated progran. in an effort to use up-to-date calculational methods and modeling techniques in the Haddam Neck Plant licensing basis safety analysis. There is no regulatory requiremer', for this analysis or was there any reason to suspect any error in the original licensing basis analysis. Thus, the NRC staff does not believe that the licensee has abused the energency provisions in this '

instance. Accordingly, the Comission has detemined that there are emergency circunstances warranting prompt approved by the Comission.

4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION

DETERMINATION The Commission's regulations in 10CFR 50.92 state that the Commission may make a final detemination that a license anendment involves no significant hazards considerations, if operation of the facility, in accordance with the amendment would not:

(1) Involve a significant increase in the probability or consequences of any accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin or safety.

This anandnent has been evaluated against the standards in 10CFR 50.9?. It dces not involve a significant hazards consideration because the changes would not:

1. Involve a significar,t increase in the probability or consequences of en accident previously evaluated. The design basis accident affected by the change is the LBLOCA. A reduced ECCS flow rate increases the duration of the adiabatic fuel rod heat-up during the refill phase.

(The blowdown phase of the LBLOCA is not affected since ECCS injection does not begin until after the blowdown phase. The reflood phase is onb affected by the change in fuel temperature at the beginning of core recovery.) The fuel temperature, therefore, is higher at the beginning of the core recovery phase. With the reduced ECCS flow rate, and without the proposed change to the power distribution limits, a PCT of greater than the 2300'F IAC limit is predicted (approximately 2420*F). With the proposed change to the Technical Specifications, the 2300*F limit is not exceeded (2296*F). Hence, the consequences of the accident are not significantly increased from those previously calculated.

s 6-There are no design basis accidents for which failure modes associated with the change can be an initiating event. Since the change is a reduction in the power distribution limits as the result of a calculational error found in the original analysis, and since there are no plant modifications associated with the proposed change, there is no increase in the probability of failure of the ECCS or any safety system.

The large break analyses performed in support of containment response evaluations are not affected since these models conservatively maximize ECCS flow in order to determine mass and energy releases to the containment. The large break analyses to support fuel mechanical design are not affected since mechanical loads are evaluated during the blowdown phase of the accident, prior to the

• delivery of ECCS flow.

Therefore, the proposed change does not involve an increase in the probability or consequences of an accident previously analyzed.

2. Create the possibility of a new or different kind of accident from any previously evaluated. There are no new failure modes associated with the proposed change as no design changes are being made to the plant. The reduced ECCS flow rate used as an input to the LBLOCA analysis results in reduced LHGR and axial offset limits, but the plant response and the trend observed in the plant response are as expected. Thus, no new or different kind of accident is created.

3. Involve a significant reduction in a margin of safety. Using the corrected ECCS flow rate as input into the LBLOCA analysis, without the proposed change to the power distribution limits, results in a calculated PCT in excess of the 2300'F IAC limit (approximately 2420'F).

With the proposed change, however, the LBLOCA analysis results in PCT less than 2300'F (2296*F). Clearly then the proposed change does

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not involve a significant reduction in this margin of safety--rather it restores the margin of safety previously assumed to exist. The reduction in the allowable LHGR assures that the safety limit (2420'F PCT) is not exceeded and the protective boundary (cladding) is not affected. There is no change in the basis of the Technical Specifi-tetions. Thus, no margin of safety is reduced.

Accordingly, the Comission has detennined that this amendment involves no significant hazards considerations.

5.0 STATE CONSULTATION

In accordance with the Commission's regulations, efforts were made to contact the Connecticut State representative. The state representative was contacted and had no coments.

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6.0 ENVIRONMENTAL CONSIDERATION

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. The staff has determined that the amendnent 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 individu?1 or cumulative occupational radiation exposure. The Comission has made a final no significant hazards consideration finding with respect to this amendroent. Accordingly, the amendrrent meets the eligibility criteria for categorical exclusion set forth in 10 CFR 951.22(c)(9).

Pursuant to 10 CFR QSI.22(b), no environmental impact statement or environ-mental assessment need be prepared in connection with the issuance of the amendment, ,

7.0 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 compliar.ce with the Commission's regulations, and the issuance of the ame9dnent will not be inimical to the common defense and security or to the health and safety of the public.

Dated: April 8, 1988 Principal Contributor: H. Balukjian

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