ML20036A614
| ML20036A614 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/05/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20036A612 | List: |
| References | |
| NUDOCS 9305120258 | |
| Download: ML20036A614 (3) | |
Text
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ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO 213 TO FACILITY OPERATING LICENSE NO. OPR-52 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT. UNIT 2 DOCKET NO. 50-260
1.0 INTRODUCTION
By letter dated December 23, 1992, the Tennessee Valley Authority (the licensee) proposed changes to the technical specifications for the Browns Ferry Nuclear Plant (BFN), Unit 2.
The proposed changes add requirements for new temperature switches to be installed in the Reactor Water Cleanup (RWCU)
System heat exchanger room. The switches are intended to detect a postulated RWCU pipe break, and provide a signal to isolate that system to prevent excessive discharge of high energy fluid from the reactor coolant system and ensure that vital plant equipment does not experience an environment which could compromise its function.
2.0 EVALUATION The NRC staff reviewed two aspects of the proposed change.
First, the staff considered the adequacy of the instrumentation design to fulfill its design function. The staff also evaluated the high energy line break (HELB) analysis results to ensure that an appropriate instrument setpoint was proposed. The two evaluations are presented below.
2.1 Adequacy of Instrumentation Design The safety function of the RWCU heat exchanger room temperature switches is to automatically isolate the system from the reactor coolant pressure boundary following detection of high temerature in the areas surrounding the RWCU system piping and components. This isolation prevents excessive discharge of high energy fluid which could create a severe operating environment for safety equipment. The reliability of this instrumentation is assured by providing i
sufficient redundancy and independence such that no single failure results in the loss of its protective function. The instrumentation is designed to permit periodic testing when the reactor is in operation. The licensee indicates that these new temperature detection loops consist of environmentally qualified resistance temperature detectors (RTDs) and Class IE qualified analog trip units (ATUs). This instrumentation will perform the same function as the existing temperature switches around the other areas of RWCU piping and will be included in the Technical Specifications. The four switches will be configured similarly to the presently installed switches in the RWCU leak '.tetection system instrumentation. Two instruments are assigned to both Divisi.!n I and Division II to ensure physical and electrical i
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- independence, and are arranged in a one-out-of-two taken twice logic. This arrangement will ensure the safety function of the RWCU system temperature l
instrumentation in case of a single failure of an RTD, an ATU, or the power supply, and will minimize spurious isolation.
The instrume t trip level setting is based upon the licensee's HELB analysis discussed below. This.setpoint is selected high enough to prevent spurious trips, and includes provision for instrument drift and other inaccuracies.
The applicable technical specification required Limiting Condition for l
Operation and Surveillance Requirements are exactly the same as-those for the existing temperature instrumentation in the RWCU leak detection system.
The i
staff finds that the proposed instrumentation meets applicable design l
requirements, and that the proposed technical specifications provide appropriate testing and operational limits.
l 2.2 Adequacy of Instrumentation Setpoint
.I In its HELB analysis, the licensee postulated a double-ended RWCU system line l
break at the exit of containment isolation valve (FCV-69-2) in the heat exchanger room.
Fluid mass and energy discharged from the broken piping was calculated by the staff-approved RELAP5 computer code. The MONSTER computer-code, developed by the licensee and based on the staff-approved CONTEMPT 4 and l
COMPARE computer codes, used the mass and energy calculated by RELAP5 to predict the temperature response in the RWCU heat exchanger room and other related compartments. The licensee uses the calculated temperatures as part of the required performance envelope for environmental qualification of safety equipment.
The licensee calculated a peak temperature (214*F) in the RWCU heat exchanger room four seconds vollowing the initiation of the RWCU pipe break.
The 3
licensee selected 170.0*F as the setpoint for the new temperature detection loops.
The licensee indicated that this setpoint ($; 170*F)'is high enough to ensure that spurious trips would be prevented during normal operation, and low
'I enough.to provide timely detection of the break and isolation of the RWCU system lines to and from the reactor.
Thus, excessive loss of reactor coolant resulting from a RWCU system line break in the reactor building will be.
l prevented.
i The staff has not approved or accepted the MONSTER computer code as a tool for i
compartment pressure / temperature response analysis.
Rather than reviewing and-
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approving the MONSTER computer code for the purpose of accepting the proposed i
technical specification change, the staff performed an independent calculation to verify the compartment temperature responses predicted by the licensee for a postulated HELB in the RWCU heat exchanger room. The staff did not perform an independent calculation of the mass and energy release, and did not review-details of the RELAP5 model used in the licensee's analysis.
Data required for the staff's calculation was provided at a meeting on i
April 1, 1993. At this meeting, the licensee also provided bounding temperature profiles used for equipment qualification. The staff's calculated compartment temperatures are comparable to those calculated by' the licensee.
Predicted temperatures are within the qualification envelopes provided by the l
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\\ o licensee. Therefore, the proposed temperature swit h setpoint of 170*F
.provides timely isolation of a postulated RWCU pipe break.
The staff accepts the proposed setpoint.
3.0
SUMMARY
The staff has found that the proposed instrument design meets appropriate requirements, and that the proposed technical specifications, including the temperature switch setpoint, provide adequate assurance that safety equipment will not be exposed to an excessively severe environment in the event of a RWCU pipe break. Therefore, the proposed changes are acceptable.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Alabama State official was notified of the proposed issuance of the amendment.
The State official i
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, and changes Surveillance Requirements and Bases.
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 i
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 (58 FR 16232).. 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 environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 CCNCLUSION f
I The Commission has concluded, based on the considerations' discussed above, that:
(1) there is reasonable assurance that the health and safety.of the l
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 i
defense and security or to the health and safety of the public.
Principal Contributors:
D. Shum and I. Ahmed Date: May 5, 1993 i
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