ML20207L736

Safety Evaluation Supporting Amend 24 to License DPR-21

ML20207L736
Person / Time
Site:	Millstone
Issue date:	10/11/1988
From:	Office of Nuclear Reactor Regulation
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ML20207L663	List: ML20207L660 ML20207L699 ML20207L736
References
NUDOCS 8810170421
Download: ML20207L736 (4)

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 24 TO FACILITY OPERATING LICENSE N0. DPR-21 NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION, UNIT N0. 1 DOCKET N0. 50-245

1.0 INTRODUCTION

By letter dated June 3,1988, the Northeast Nuclear Energy Company (NNECO or licensee) submitted a request for changes to the Millstone Nuclear Power '

Station, Unit No. 1.

The amendment reduces the Maximum Average Planar Linear Heat Generation Rate (MAPLHGR) limit by 2 percent. This reduction is necessar potentially degraded Emergency Core Cooling System (ECCS)y flow duetotocompensate debris- for induced strainer plugging following a loss-of-coolant accident (LOCA). l In March of 1988, NNECO completed a study to evaluate the acceptability of fibrous insulation in Millstone Unit No. l's drywell with respect to degradation of long-term ECCS recirculation. The conclusions of the study indicated that ECCS pump net positive suction head (NPSH) margin and operability could potentially be compromised if fibrous insulation migrated to the torus and to the low-pressure coolant injection (LPCI)/ core spray (CS) suction screens in sufficient quantities. NNECO informed the Millstone Unit No. 1 NRC Resident Inspector of the results of this studv on March 18, 1988, and subsequ,ently reported the results under 10 CFR 50.72(b)(iii) and a licensee event report (LER 88-004) on April 12, 1988 as required by 10 CFR 50.73(a)(2)(vi). After further discussions concerning this issue were held l with the NRC staff and detailed design of the new torus strainers raised  !

additional concerns, NNECO submitted a supplement to LER 88-004 on May 27, l 1988, 1 Specifically, NNECO indicated that a postulated break in the recirculation system piping could result in migration of some fibers from the insulation on the recirculation system piping to the suppression pool. Some of these fibers could subsequently collect on the strainers to the hydraulic header supplying i water to the ECCS pump suction lines. If this were to occe , the results of l the study indicated that a reduction in rated flow capability of approximately l 70 gpm from each of the CS pumps and approximately 110 gpm from each of the LPCI pumps might tm possible. These flow reductions were calculated assuming that all six ECCS pumps (two CS 6nd four LPCI) were operating at runout condition, thus maximizing the flow reduction.

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l 2.0 EVALUATION The licensee stated in its June 3, 1988 submittal that the limiting LOCA scenario which establishes the MAPLHGR limits for operation of Millstone Unit No. 1 is the double-ended fracture of a recirculation suction line with a i failure of the LPCI injection valve. For this postulated scenario, the systems remaining injection system (operable FWCI), and theare the two pressurization automatic CS systems, tre feedwater system (ADS).coolant This limiting scenario is the most sensitive to a small change in the ECCS flow rate because the core heat-up rate is faster for large breaks than small brea ks. In this scenario, the flow reduction in the CS systems due to strainer plugging would be less than 70 gpm since the LPCI pumps would be '.

running at minir..um flow conditions with flow into the reactor vessel precluded. However, a sensitivity analysis was performed to determine the impact of an assumed conservative value of 100-gpm reduction in the rated flow of each of the two CS systems for the limiting LOCA scenario. The results of this anslysi: indicate that the core reflooding time would increase by less than 3 seconos.

It was determined by the licensee that the peak clad tamperature (PCT) following a large-break LOCA would increase by less than 20*F due to this problem. Since the MAPLHGR limit is based on reaching 2200*F PCT, a MAPLHGR limit decrease is necessary in order to compensate for potential strainer clogging. The basis of the MAPLHGR limit is to ensure that the plant operates in compliance with 10 CFR 50.46 and 10 CFR 50, Appendix K, under all conditions. Lowering the MAPLHGR limit to compensate for a potential slight degradation of ECCS flow oue to strainer plugging ensures thet compliance is maintained. This decrease was determined to be on the order of 1 percent.

However, in order to be conservative, a 2 percent decrease in MAPLPGR limit is being applied by the licensee. With the MAPLHGR limit decrease, the consequences of the large-break LOCA are not adversely impacted.

The licensee also stated that the design basis small-break LOCA would not be adversely impacted for the following reasons:

(a) A smaller break results in much less debris. Thus, pump flow degradation would.be much less.

(b) The PCT for the limiting small-break LOCA is 50*F less than for the large break. Even adding the full 20'F penalty from the large-break case results in PCTs that are bounded by the design basis large-break LOCA.

NNECO's immediate corrective actions concerning this issue, as surmarized in LER 88-004-01, are as follows:

(a) A project assigninent has been initiated to replace the ECCS suction strainers with larger area strainers sized to allow ECCS operability under maximum credible insulation debris loading. Implementation of the strainer replacerrent is currently scheduled to be completed by the end of the 1989 refueling outage.

(b) Emergency Operating Procedures (E09s) relating to ECCS operation have been revised to account for insulation debris fouling.

(c) The PAPLHGR thermal limit has been administratively reduced to account for potential ECCS pump flow degradation until this license amendment request is approved.

By a memorandum from J. P. Stetz, Millstone Unit No.1 Superintendent, to R.

J. Palmieri, Operations Supervisor, and R. W. Vogel, Engineering Supervisor, dated May 13, 1988, the licensee imposed an administrative requirement to reduce MAPLHGR by 2 percent. This administrative requirement was to be used until a Technical Specification change was approved. The resident inspector at Millstone Unit i verified that the administrative requirement was in place and reviewed the associated Emergency Operating Procedures (EOPs) for adequa cy. The resident inspector's results are contained in Inspection Report 50-245/88-07, dated July 1,1988. The revised E0Ps were verified and validated by licensed operators on the plant-specific simulator. Training on the revisions was provided through the operator requalification program. The resident inspector found the training to be adequate.

The proposed amendment to the Technical Specifications would revise Figures 3.11.1.a. "Maximum Average Planar Linear Heat Generation Rate (PAPLHCR) Versus Planar Average Exposure, Fuel Type BP80R8300," and 3.11.1.b, "Maximum As erage Planar Linear Heat Generation Rate (NAPLHGR) Versus Planar Average Exposure for Most Liniting Lattice Type, Fuel Type BD33A (GE-8 x 8EB)" to refleci, a 2 percent reduction in the MAPLHGR limit. This reduction in the MAPLHCR limit will only be required until the ECCS suction strainers are replaced with larger area strainers. The licensee intends to request a restoration of the  :

100 percent FAPLHGR limit to coincide with the installation of the new strainers ano the HAPLHGR limit will also reflect the fr9sh fuel to be put in place during the spring 1989 refueling.

The staff has reviewed the Justification for Continued Operation (JCO) dated March 1988 and the revised JC0 dated May 1988 (submitted by letter dated July 21, 1988) and found the assumptions to be conservative and the JCOs to be acceptable. The staff has also reviewed the LER and revised LER (88-004-01) and the June 3, 1988 license amendment request and found the actions taken by the licensee to be appropriate and the reduction in the PAPLHGR limit to be acceptable.

ENVIRONMENTAL CONSIDERATION This amendment changes a requirement with respect to the installation or l use of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the i 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 published a proposed finding that l

the amendment involves no significant hn ards consideration and there has been no public comment on such finding. Accordingly, the amendment meets the eligibilit criteria for categorical exclusion set forth in 10 CFR 651.22(y)(9).

c Pursuant to 10 CFR 951.22(b), no environmental impact statement or environwntal assessment need be prepared in connection with '

the issuance of the amendment.

CONCt.USION We have concluded, based on the considerations discussed above, that  !

(1) there is reasonable assurance that the health and safety of the l will not be endangered by operation in the proposed manner, and (2) public such  ;

activities will be conducted in compliance with the Commission's regulations, '

and the issuance of the amendment will not be inimical to the common 1 defense and security or to the health and safety of the public.

Dated: October 11, 1988 i Principal Contributors: l l G. Thomas and M. Boyle l

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