IA-98-345, Discusses Licensing Basis for Letdown Line Break Outside Containment for Plant,Unit 1

Discusses Licensing Basis for Letdown Line Break Outside Containment for Plant,Unit 1

ML20154B793
Person / Time
Site:	Three Mile Island
Issue date:	02/06/1998
From:	Marsh L NRC (Affiliation Not Assigned)
To:	Milano P NRC (Affiliation Not Assigned)
Shared Package
ML20154B776	List: IA-98-345, Discusses Licensing Basis for Letdown Line Break Outside Containment for Plant,Unit 1 ML20154B772 ML20154B780 ML20154B793
References
FOIA-98-345 TAC-M97748, NUDOCS 9810060014
Download: ML20154B793 (3)

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,,,,,# February 6,1997 MEMORANDUM TO: Patrick D. Milano, Acting Director Project Directorate 1-3 i Division of Reactor Projects - I/II FROM: Ledyard B. Marsh, Chief Plant Systems Branch -

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Division of Systems Safety and Analysis

SUBJECT:

THREE MILE ISLAND, UNIT 1 - LICENSING BASIS FOR LETDOWN LINE 4

PIPE BREAX OUTSIDE CONTAINMENT (TAC NO. M97748)

The Plant Systems Branch (SPLB) and the Mechanical Engineering Branch (EMEB) l have reviewed the subject issue described in a Special Inspection Branch l (PSIB) memorandum dated January 17, 1997. In that memorandum, the PSIB staff describes a licensing basis issue related to high energy line breaks (HELBs) in the auxiliary building at Three Mile Island, Unit 1 (TMI-1). These issues were identified during a NRR led design inspection performed in December 1996

- January 1997. The is!.ue relates to the licensee's definition of high energy lines and commitments made regarding the postulation of full diameter breaks in the normal letdown line from the reactor coolant system (RCS).

At YMI-1, high energy lines are defined as piping containing fluids that exceed both 200*F 3nj 275 pounds per square inch gauge (psig). The RCS letdown line in the auxiliary building normally operates below 200*F and, therefore, based on the existing licensing basis definition, full diameter breaks would not have to be postulated in this line even though the pressure i exceeds 275 psig. However, in Appendix 14A of the Final Safety Analysis 1 Report (FSAR) the licensee states that six full diameter breaks (six different locations) in the letdown line were postulated and the temperature, pressure, l and humidity environment in the vicinity of the breaks were determined and the resultant conditions analyzed. As a result of 9at analysis, the licensee determined (according to the FSAR) that, except for potential damage to cabling due to pipe whip, the valves and cabling in the areas of concern were environmentally qualified for post-accident containment service which is more severe than the six postulated full diameter breaks. However, during the recent inspection, the licensee could not retrieve formally documented analyses or reports that supported the licensee's statements in the FSAR that the valves and t.abling were qualified to conditions more severe than resulted from the six postulated breaks in the letdown line. Additionally, in Appendix 6A of the FSAR, the licensee further states that a loss of coolant accident (LOCA) pipe break is not postulated to occur outside the containment for environmental qualification (EQ) of components, and that HELBs outside containment can only produce a harsh environment in the intermediate building (not the auxiliary building where the letdown line is located). Therefore, Appendices 14A and 6B appear to be in conflict.

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• In response to the inspection team's questions on the apparent inconsistency between the statements in the FSAR and the lack of documentation to support the FSAR statements regarding the letdown line break evaluation, the licensee stated that the TMI-l licensing basis did not include consideration of a letdown line break outside containment. The licensee also responded that the statement regarding the letdown line evaluation (six full diameter break locations) was made in response to a staff 1973 request for additional information (RAI) and, therefore, should not be considered as a licensing basis for THI-1. To address this inspection issue, the licensee has apparently initiated a FSAR revision to Appendix 14A to add a statement that, as described in Appendix 68, letdown line breaks are not considered as HELBs.

The PSIB memorandum requested NRR assistance to clarify the extent to which ,

TMI-l is required to consider the environmental, pipe whip, and jet l impingement effects of a letdown line break outside containment.

It is our opinion that the licensing basis for TMI-l includes the licensee's response to the staff's RAI in which the licensee analyzes the environmental consequences of six individual pipe rupture locations (outside containment) in the letdown line upstream of the letdown orifice. These analyses were apparently performed to conservatively bound the posM ble environmental effects that could occur from a break or crack in t W letdown line which can cause a loss of effectiveness of the letdown cooler due to higher flow rates caused by postulated piping failures. The licensee's statement in Appendix 14A that resultant pipe whip from these six postulated ruptures may result in damage to cables, implies that the breaks were postulated only as bounding assumptions for environmental analysis (excluding radiation) of the auxiliary building areas. It appears that this bounding environmental analysis was performed to forego the necessity for performing more complicated analyses involving the effectiveness of the letdown coolers under unanalyzed flow conditions due to piping failures. Additionally, the use of such a bounding analysis does not necessarily conflict with Appendix 6B which states that LOCA pipe breaks are not postulated outside containment.

We concluded that the licensing basis for pipe breaks in the letdown line upstream of the letdown orifice includes the environmental consequences of the six postulated full breaks (single ended circumferential breaks) identified in FSAR Appendix 14A. Therefore, the valves and cabling of concern should already be identified in the licensee's EQ program as they have been identified by the licensee to be qualified for the environmental effects of the six full breaks based on their being qualified for post-accident containment service. We also agree with the licensee that the licensing basis definition of high energy lines would exclude all of the letdown line outside containment and, therefore, without the commitment of the bounding analysis, only pipe cracks would have to be postulated in this line. Assuming that the licensee will propose a change to the FSAR to eliminate the postulated six pipe break locations as indicated to the inspection team, we believe that an unreviewed safety question (USQ) will exist and require prior staff approval.

if on the other hand, the licensee decides to recreate the environmental analysis associated with the six postulated breaks, resolution of this issue could be accomplished under 10 CFR 50.59. Also, the equipment of concern would have to be maintained (or added) to the plant EQ list.

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l A number of plants (7 or 8) include the same definition for high energy lines (above 200*F nins above 275 psig) as THI-1. Most plants define high energy lines as those that contain fluids above 200*F p_t above 275 psig. At these plants the letdown line from the containment to the letdown orifice would be considered a high energy line (pressure above 275 psig) and HELBs would have to be postulated. We are not aware of any significant concerns at those plants where a HELB is assumed in this part of the letdown line. We, therefore, believe that safe plant operation will not be significantly affected until resolution of this issue.

If you have any questions regarding this memorandum, please contact Bill LeFave of my staff at 415-3285. John fair (415-2759) of the Mechanical Engineering Branch was also involved in this review.

Distribution: SPLB R/F Coretta Saadu Sam Malur Central File John Fair Docket File Bart Buckley Plant File Robert M. Gallo DOCUMENT NAME: G:\SECTIONA\LEFAVE\TM197748 To receive a copy of this docunent, indicate in the box C= Cope w/o attachment /enetosure E= Copy with attechment/ enclosure u = No copy 0FFICE SPLB:DSSA C. EMEB _ _ _ C SC:SPLB:DSSA & BC:SPLB:DSSA C-NAME WLefave8h RWess GHubbard N LBMarshNO[6 DATE / /j//97 2/ p/97 / /)//97 4L /c6 /97 / /97 OfflCIAL RECORD COPY 3

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