ML20235V734

Safety Evaluation Accepting Util Revised Temp Profile,Per GE EAS-98-0887, Drywell Temp Analysis for Pilgrim Nuclear Power Station

ML20235V734
Person / Time
Site:	Pilgrim
Issue date:	03/03/1989
From:	NRC
To:
Shared Package
ML20235V732	List: ML20235V731 ML20235V734
References
NUDOCS 8903100314
Download: ML20235V734 (4)

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Enclosure SAFETY EVALUATION DRYWELL TEMPERATURE ANALYSIS PILGRIM NUCLEAR POWER STATION, UNIT 1 DOCKET NO. 50-?93

1.0 INTRODUCTION

By letter dated March 15, 1988, Boston Edison (the licensee) submitted a proposal to revise the drywell temperature profile used for equipment qualification purposes. Attached to their submittal was a General Electric (GE) report containing the supporting analytical justification for the temperature modification. The GE report consisted of an evaluation of a spectrum of postulated Main Steam Line Breaks (MSLB) within the drywell. The purpose of the evaluation was to develop a temperature profile which bounded the individual profiles of the series of breaks considered. The resulting composite profile, when used for equipment qualification purposes, could then be assured of.being conservative with respect to any given MSLB. The licensee provided additional information via a letter dated September 7, 1988.

A critical assumption used by the licensee in the development of the series of temperature profiles was the time when the drywell sprays would be initiated.

Based on the information available to the operators and the availability of the RHR spray pumps, the licensee concluded that 30 minutes into the event was a reasonably conservative value. As a result, all analyses assumed full sprays 30 minutes into the event.

2.0 EVALUATION

'he GE report contained a series of computer code analyses which were run to etermine the drywell airspace temperature profiles resulting from various size main steam line breaks. The resulting temperature profiles were overlayed one on top of the other and a composite profile was developed which enveloped the resulting curve. In other words, only those portions of the individual profiles were used that represented the maximum temperatures for that selected time zone.

The staff concurs with the licensee's approach used to develop the equipment qualification temperature profile. Use of the composite curves in the manner described, results in a bounding profile. In addition to the overall approach, the staff also reviewed the modeling assumptions used by GE to maximize the integrated steam release via the line break. The assumptions were found to be similar to analyses previously found to be conservative by the staff. Based on this similarity, the staff also finds the specific modeling assumptions used in the present analyses acceptable.

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T A key factor in determining the short-tenn portion of the drywell temperature profile is the time when the drywell sprays are assumed to be actuated. This assumption is particularly important, since the sprays almost immediately remove all the superheat from tha dryw11 eirsnaca. Initially, the review focused on the procedures that directs the operator to initiate sprays. The licensee indicated that the Pilgrim emergency operating procedures require the operator to manually initiate sprays when either of two conditions exists; the drywell temperature exceeds the design value of 281 F or the wetwell pressure exceeds 11 psig. Both of these parameters are monitored in the control roora.

Based on discussions with the licensee, the instrumentation for both temperature and pressure monitors are safety grade. In light of the importance of this instrumentation, we require that the safety grade design of both the pressure and temperature instrumentation, used to determine when the sprays will be actuated, be included in the next update of the Updated Final Safety Analysis Report (FSAR).

Another important consideration which has a significant impact on the temperature profile is the actuation time of the sprays. The licensee believes that 10 minutes for operator action is appropriate, but they provided i analyses for both 10 and 30 minute actuation times. The staff has evaluated l the merits of both times and concludes that 30 minutes should be used in the development of the temperature profiles.

l The 10 minute actuation time was found to be unacceptable. First of all, the flow from one RHR pump must be diverted from its primary ECC function to initiate spray flow. Ten minutes is the absolute minimum time allowed for such diversion. Additionally, the consequences of not performing the task at this minimum time were felt to be too significant for such a small operating window. Finally, the amount of time the operator would realistically devote to equipment qualification level concerns was felt to be minimal during the first 10 minutes of the event. Based on the above rationale, the staff concluded that a 10 minute actuation time was unacceptable.

The 30 minute time, however, allows the operator about 20 minutes to monitor the containment conditions before a decision must be made relative to spray actuation. The selection of the two values which will be used to actuate the sprays are also important. The drywell temperature represents saturated conditions at design pressure. Therefore, any size steam line rupture will achieve the necessary initiation temperature, while breaks in the recirculation piping will not. However, the pressure set point of the wetwell pressure will actuate the sprays for almost all breaks.

The selection of the pressure and temperature set points, in a sense yields redundant instrumentation. For virtually all drywell breaks, the wetwell pressure will indicate the need for the sprays when all the drywell air is carried over to the wetwell. The temperature sensor, however, will only require sprays if some amount of superheat is present in the drywell. Since sprays are only required when superheat is present, this arrangement amounts to both redundancy and diversity of signal.

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1 Finally, the staff reviewed the modeling assumptions relative to the guidance provided in NUREG-0588. This NUREG provides specific guidance regarding the treatment of heat transfer to the structural heat sinks following a MSLB or LOCA for *quipment qualification purposes. Our revice indicates that the licensee conforms with this guidance and is therefore acceptable.

3.0 CONCLUSION

Based on the above, the staff concludes that the analysis presented by the licensee in the submittals dated March 15, 1988 and September 7, 1988, provides a reasonable basis for determining the drywell airspace temperature profile used for equipment qualification. This acceptance is based on the assumption that manual spray initiation occurs 30 minutes into the event.

Principal Contributors: J. Kudrick A. Notafrancisco

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Enclosure 2 SPLB SALP INPUT Plant Name: Pilgrim Nuclear Power Station SER

Subject:

Revised Drywell Temperature Profile TAC No.: 67809 Summary of Review / Inspection Activities The review was to determine whether or not the provided.drywell airspace temperature profile was acceptable for equipment qualification purposes. A major factor in the evaluation was the qualities and type of control room instrumentation which must be safety grade. It was determined that temperature instrumentation is safety grade after a series of telecons. .

Safety grade of the instrumentation should be explicitly stated in the docket.

Narrative Discussion of Licensee Performance - Functional Area The licensee has generally demonstrated understanding of the issue and provided information to resolve it.

Author: J. Kudrick Date:

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