ML20195B559
| ML20195B559 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 06/03/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20195B539 | List: |
| References | |
| NUDOCS 8806210452 | |
| Download: ML20195B559 (4) | |
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o UNITED STATES g
E NUCLEAR REGULATORY COMMISSION o
p WASHING TON, D. C. 20655
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 24 TO FACILITY OPERATING LICENSE N0. NPF-47 GULF STATES UTILITIES COMPANY RIVER BEND STATION, UNIT 1 DOCKET NO. 50-458
1.0 BACKGROUND
By letter dated June 5, 1987 as modified May 13, 1988, Gulf States Utilities Company (GSU) (the licensee) requested an amendment to Facility Operating License No. NPF-47 for the River Bend Station, Unit 1.
The proposed amendment, as modified, would (1) raise the drywell average air temperature from 14C"F to 145*F; (2) raise the allowable tem north from 122 F to 135'F; and (3)perature for the main steam line (MSL) tunnel increase the main steam line tunnel north instrur'entation setpoints and allowable temperature values for (a) MSL isolation, reactor core isolaticn cooling (RCIC) system isolation, and reactor water cleanup (RWCU) system isolation; and (b) MSL tunnel (cooler) high temperature differential temperatures for MSL isolation, and RCIC and RWCU isolation.
The licensee's May 13, 1988 submittal withdrew that portion of the TS change request relating to items 2.h.1 and 2.h.2 of Table 3.3.2-2 in Attachment 3 of the June 5,1987 application. This evaluation addresses the proposed changes to the TS as specified in Attachment 3 of the application (item (3), abcVe).
The staff's evaluation of Attachments 1 and 2 will be the subject of separate correspondence.
2.0 INTRODUCTION
MAIN STEAM LINE TUNNEL NORTH (MSLTN)
DESCRIPTION OF MSLTH: MSLTN has a velure of 26,775 cu.ft. and is cooled by a heat exchanger type cooler, UC-8(-R) mounted outside the MSLTN in the Auxiliary Building drawing and returning air to the tunnel at 18,000 cfm.
For a heat sink, the cooler is supplied with a fixed amount [116 gpm] of service water (SW).
The SW is supplied by SW pumps drawing directly from the basin of the plant cooling tower and is therefore subject to variation with seasonal ambient conditions. The Technical Specifications include a maximum SW temperature of 95'F.
Any moisture separation in the cooler resultin in the MSLTN, is drained to an individual open sump (g from steam / water vapor then drained to an Auxiliary Building Floor Drain Sump (DFR-TKSA))which collects DFR-DNH 2120 which is from many sources.
Three principal high energy piping systems connected to the Reactor Coolant System (RCS) and through Reactor Coolant Pressure Boundary (RCPB)/ Containment isolation valves, are routed through this tunnel section:
the Main Steam Line System (MSLS), the steam supply for the Reactor Core Isolation Cooling System PumpTurbineDrive(RCIS),andtheReactorWaterCleanUpSystem(RWCU).
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. The initial design basis for this MSLTN with a SW temperature and flow of 95'F and 63 gpc respectively, and a dry tunnel heat load of approx. G.340 MBtu/h.
resulted in an ambient temperature in the tunnel of 122 F with a delta T across the UC-8(-R) heat exchanger of 19.3*F.
Since comencement of operations at the facility, evidence has shown larger dry heat loads than design.
Further, recent experience shows that this load is approximately 0.64 MBtu/h.
Consequently, service water flow to the cooler has been increased to 116 gpm, which with a SW temperature of 95'F will result in a maximum MSLTN operating temp of 137'F at zero steam leakage conditions.
During plant operation, the licensee has noted that during the winter months, MSLTN temperatures rarely were less than 105*F.
3.0 EVALUATION 3.1 Leak Detection To identify potential cracks in those RCS interconnected piping systems inside MSLTN, a leak detection system as an early warning for effective procedural and protective action, is provided as indicated in the FSAP. The leak detection systen as installed consists of an ambient temperature (T) measurement and a delta T measurement across the UC-8(-R) cooler.
3.2 Flevated MSLTN temperatures as a setpoint for a 5 gpm Leakage Alarm l
This temperature set point was determined based upon the expected ambient temperature in the tunnel and for the temperature increase expected from a 5 gpm of steam leakage.
It currently activates an audible and visual alam.
The value for the setpoint was conservatively calculated by the licensee on the basis of an expected nomal tunnel temperature of 105*F. However, as service water ter.perature increased with the warmer months of the year so did the observed tunnel temperature so that the alam setpoint could be reached without any evidence of steam leakage. After visually checking for steam leakage inside MSLTN, the licensee cancelled the audible alam and proceeded with power cperations. When the next temperature increase was reached, the licensee again inspected and in this manner operating alarm temperatures have been increased up to approximately 131*F.
At this time, the licensee plans to remove the 5 gpm leakage alarm point and use the same channels to alarm a) the maximum temperature on the tunnel for which the equipment is environmentally qualified during nomal operation, and b) as on early warning of the approach to the proposed Isolation setpoint of 141*F.
NRC audit calculations for a 5 gpm steam leak into the tunnel (from 137'F MSLT temperature) show a range of maximum tunnel temperatures from 154*F tc 180*F. The results show the temperatures proposed by the licensee for a 25 gpm stean leakage rate will in fact detect a 5 gpm steam leak and that the proposed value of 141*F (setpoint) is acceptable for this purpose, for a range of starting tunnel temperatures from 105*F to 137'F.
. Therefore, 5 gpn steam leak into MSLTN can be detected in an acceptable manner by the setroint values being proposed for isolation purposes. Also the proposed precursor alann of 135'F is an acceptable early alarm for reviewing the need for precautionary and/or protective action.
3.3 25 gpm Leakage / Isolation Setpoint The purpose of this alann setpoint is to identify a relatively large crack which is a potential precursor of a major pipe rupture.
Its function is anticipatory protective action for the major rupture.
1 3.3.1 Main Steam Line Tunnel (MSLT) Ambient Temperature High Using an initial MSLTN temperature of 105'F, for a 25 gpm leakage, the licensee proposed an expected increase in tunnel temperature to be greater than 142.5 F over a one hour period. The licensee proposed an allowable value of 142.5'F and a corresponding isolaticn setpoint value of 135*F.
However, because of increases in tunnel temperatures without any steam leakage, it has beccme necessary to take action to prevent an unnecessary (inadvertent) cctuatier cf the related protective logic with potentially severe, but "accept-able" circunstances. The licensee proposes to increase the allowable value tc 148.5'F with an increase in the related isolation setpoint value to 141.0*F.
The ERC review shev:s that the proposed increase in setpoint and allowable values fer FSLT ambient temperature high remains conservative with respect to a 25 gpm leakage rate. We, therefore, find the proposed change acceptable.
3.3.2 Main Steam Line Tunnel Cooler Temperature Differentia'.
As a result of the increasing ambient tunnel temperatures the licensee also proposed to increase the MSLT differential temperature alarm setpoint from 51*F to 57cF and corresponding allowable temperatures from 55 F to 61'F.
By increasing the allowable and setpoint ambient temperature values the licensee acknowledged that when operating at reduced ambient tunnel temperatures of 105'F, isolation would occur at a leakage of 32 gpm which was beyond the licensee's 25 gpm design criteria. Additionally, as ambient temperatures increase, isolation will be initiated by lower leak rates.
The NRC finds that the proposed increase in the setpoint to 57'F and the allowable value to 61'F, are nominal changes which do not significantly alter the threshold at which a leak will be detected and automatic isolation will occur. Based on this, we accept the change.
As discussed above, the staff finds the proposed changes to MSLTN allowable and isolation setpoints to be conservative with respect to leak detection and therefore, acceptable.
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4.0 ENVIRONMENTAL CONSIDERATION
The amendment involves a change in the installation or use of a facility conponent 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 types, of any effluents that may be released cffsite, and that there is no significant increase in individual or cumulative occupational radiation exposures. The Commission has previously issued a proposed finding that the amendment involves no significant hazards censideration and there has been no public comment en such finding. Accordingly, the amendment nects the eliaibility criteria for categorical exclusion set forth in 10 CFP Section 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statenent or environtental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSI0f!
The staff has concluded, based on the considerations discussed above, that:
(1) there is reascrable assurance that the health and safety of the public will not be endangered by cperation ir. the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of the arendn.ent will not be inimical to the common defense and security or to the health and safety of the public.
Date: June 3, 1988 Principal Contributor:
J. Vudrick
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Gulf States Utilities 2-June 3, 1988 purposes. The staff plans to further evaluate these concerns as a general issue.
If after further evaluation these concerns prove valid, they will bu resolved on a generic basis.
Sincerely, Original signed by Walter A. Paulson, Project Manager Project Directorate - IV Division of Reactor Projects - III, IV, V and Special Projects Office of Nuclear Reactor Regulation Ecclosures:
1.
Amendn:ent No. 24 to License No. NPF-47 2.
Safety Evaluation cc w/ enclosures:
See next page DISTRIBUTION:
Docket File JPartlow NRC PDR TBarnhart(4) local F'R Wanda Jones PDA Peading EButcher PNoonan (3)
ACRS (10)
WPaulson GPA/PA JCalvo ARM /LFMB CGC-Rockville DHagan EJordan Plant File C0CUMENT N/EE: RB AMENCFENT PD4/L PD OGCy' '.;;e PD4/D /
PNoon WPaulfon:kb 6 6[/o/k JCalve 06@ /
06/V/88 06/J/88 06/ 3 /88 1
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