ML20198S377

Safety Evaluation Supporting Amend 189 to License DPR-40

ML20198S377
Person / Time
Site:	Fort Calhoun
Issue date:	12/31/1998
From:	NRC (Affiliation Not Assigned)
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Shared Package
ML20198S366	List: ML20198S362 ML20198S373 ML20198S377
References
NUDOCS 9901110296
Download: ML20198S377 (4)

Text

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l urg c p k UNITED STATES s* j 2

NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30066-0001 i

SAFETY EVALUATION BY THE OFFICE OF NUCI FAR REACTOR REGULATION RELATED TO AMENDMENT NO.189 TO FACILITY OPERATING LICENSE NO. DPR-40 OMAHA PUBLIC POWER DISTRICT FORT CALHOUN STATION. UNIT NO.1

j. DOCKET NO. 50-285 l

1.0 INTRODUCTION

I By application dated March 26,1997, Omaha Public Power District (OPPD) requested changes to the Technical Specifications (Appendix A to Facility Operating License No. DPR40) for the Fort Calhoun Station, Unit No.1. The requested changes would amend the Fori Calhoun Station Technical Specifications (TS) to incorporate additional restrictions on the Operation of the main steam safety valves (MSSVs). On January 15,1997, the licensee determined that the piping pressure losses between the steam generator and MSSV inlets had not been fully l addressed in applicable safety analyses and MSSV setpoints. On January 17,1997, the i licensee received a 10 CFR Part 21 report from Asea Brown Boveri- Combustion Engineering i l' (ABB-CE) which identified the same issue, and recommended that licensees ensure that piping pressure losses were fully addressed in plant safety analyses and that licensees adjust MSSV L setpoints as necessary. On March 12,1997, the staff issued NRC Information Notice 97-09, L " Inadequate MSSV Setpoints and Performance issues Associated with Long MSSV Inlet  ;

Piping,"which also discussed this issue. To address this concem, the licensee performed an '

engineering analysis, and concluded that additional restrictions on the MSSVs were necessary.

. The licensee has requested that the Technical Specifications be changed to incorporate these additional MSSV restrictions.

The March 18,1998, and November 17,1998, supplemental letters provided additional

! clarifying information which did not change the staff's original no significant hazards consideration determination published in the Federal Register on July 16,1997 (62 FR 38137).

2.0 JISCUSSION Fort Calhoun has two steam generators (SGs). There are five MSSVs associated hith each SG, one 2 %-inch MSSV and four 6-inch MSSVs. The purpose of the MSSVs is to limit secondary pressure to less than or equal to 110% of the design pressure of 1000 psia when passing 100% of design steam flow. As discussed above, it was determined by the licensee ,

. that piping pressure losses between the SG and MSSV inlets were not fully addressed in the

plant safety analyses. The licensee has performed an analysis to address these piping losses using the CESEC-Ill transient analysis methodology and computer code which has been l

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previously approved by the NRC. The scope of the transient analysis was limited to eva!uating the pressure drops in the piping run for both the primary and MSSVs to determine the impact on peak primary and secondary system pressures, and to reflect recent changes including additional SG tube plugging (15.5 percent effective tube plugging) and the presence of the SG orifice plate.

The limiting transients are loss of load (LOL) and loss of feedwater (LOFW). Initial conditions and core physics parameters were conservatively selected to maximize the computed peak primary and secondary pressures. For the peak secondary pressure case for both the LOL and LOFW events, one MSSV was assumed to be inoperable per SG. The valves assumed inoperable in these cases were the 6-inch valves with the lowest set-pressure of 1000 psig. These valves were shown to be the most limiting valves to fail. For the LOFW peak primary system pressure case, all MSSVs were assumed to be operable. A sensitivity case was run to examine the effect of assuming one MSSV incperab'e per SG and it was concluded that the effect resulted in an increase of peak primary system pressure of 1 psia.

Since this case was not limiting, the impact of assuming all MSSVs operaole was not significant. For the LOL event, two cases were run to calculate peak primary system pressure, one with the TS allowable primary safety valve (PSV) drift of 1% and another case with assumed PSV drift of 6% (as discussed as a possibility in the bases for TS 2.1.6). The LOL case with 1% PSV drift which was used to update the USAR did not assume any MSSVs inoperable, however, the case with 6% PSV drift did assume one MSSV inoperable per SG, and this case generated the most limiting results.

For the LOL event, assuming +3% MSSV drift and +1% PSV drift as allowed by TS, a value of 2649 psia was obtained for worst case calculated peak primary pressure, and 1098 psia for worst case secondary system pressure. The LOL case with an assumed PSV drift of +6%

resulted in a calculated peak primary pressure of 2743 psia and a calculated peak secondary pressure of 1089 psia. For the LOFW event, assuming +3% MSSV drift, the worst case peak primary system pressure was calculated to be 2567 psia and the worst case secondary system pressure was calculated to be 1096 psia. These calculated peak pressures are below the design limits of 2750 psia and 1100 psia for the primary system and secondary system, respectively, and are therefore acceptable.

The results of the licensee's analyses demonstrate that the effective increase in MSSV setpoint due to piping pressure losses leading to the MSSVs is acceptable with the assumption that only one MSSV may be inoperable per SG. For the LOFW case (peak secondary pressure)it was necessary to credit the low SG level trip (LSGLT) in order to obtain acceptable results. The LSGLT was not credited in previous analyses of the LOFW transient, however, the trip is safety grade, and the staff considers crediting the LSGLT trip in this analysis to be acceptable.

3.0 EVALUATION The licensee's current TS 2.1.6, " Pressurizer and Mah Steam Safety Valves," requires that eight of the ten MSSVs be operable whenever the reactor is in power operation. The licensee performed an analysis, discussed above, to address piping losses and demonstrated that with one MSSV inoperable per SG, the design pressure is limited to below design limits. In order to

3-I conform to the results of this analysis, the licensee has proposed to change TS 2.1.6 to require that at least four of the five MSSVs associated with each steam generator be operable. The licensee has also proposed to change the MSSV TS applicability to include Mode 2 in addition to Mode 1, to ensure over pressure protection is provided whenever the reactor is critical.

These changes are more restrictive, provide greater assurance that applicable design limits will i be maintained, and are therefore acceptable.

In addition, the current TS does not contain any required actions if the limiting condition for operation (LCO) is not met, which would require entry into TS 2.0.1. The proposed TS includes i an action statement which states that with less than four of the five MSSVs associated with I each steam generator operable, be in at least hot standby within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and hot shutdown within an additional 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. This required action would place the plant in a condition where the MSSVs do not provide any safety related function, and the LCO is not applicable. The proposed action statement is consistent with the ABB-CE Improved standard TS, and is therefore acceptable. l l

The licensee has proposed that the TS 2.1.6 Basis be modified to state that the total relief capacity of the ten MSSVs is 6.606E6 lb/hr. This value is based on the rated nameplate capacity of the valves. The licensee stated that the basis for the current value of 6.54E6 lb/hr is not known, and that the higher value is more conservative for calculating pressure drops. The Bases have been modified accordingly.

The staff has reviewed the licensee's proposed TS changes to incorporate additional ,

restrictions on the operation of the MSSVs. Based on the review, the staff concludes that the l proposed TS changes are acceptable.

4.0 STATE CONSULTATION

in accordance with the Commission's regulations, the Nebraska State official was notified of the proposed issuance of the amendment. The State official had no comments.

5.0 ENVIRONMENTAL CONSIDERATION

The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has 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 the amendment involves no significant hazards consideration, and there has been no public comment on such finding (62 FR 38137). Accordingly, the 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 environmentalimpact statement or environmental assessment need be prepared in connection with the issuance of the amendment.

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6.0 CONCLUSION

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

PrincipalContributor: A. Cubbage Date: December 31, 1998 4