ML18026B215
| ML18026B215 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/04/1984 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18026B214 | List: |
| References | |
| NUDOCS 8409170217 | |
| Download: ML18026B215 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.
111 TO FACILITY OPERATING LICENSE NO.
DPR-33 AMENDMENT NO.
105 TO FACILITY OPERATING LICENSE NO.
DPR-52 AMENDMENT NO.
79 TO FACILITY OPERATING LICENSE NO.
DPR-68 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT, UNITS 1, 2 AND 3 DOCKET NOS.
50-259, 50-260 AND 50-296 1.0 Introduction The licensee, Tennessee Valley Authority (TVA), in its submittal dated November 5, 1982 requested certain modifications to the Technical Specifications appended to Facility Operating License Nos.
DPR-33, DPR-52 and DPR-68 for the Browns Ferry Nuclear Plant; Units 1, 2 and 3.
These modifications resulted from a feasibility study that was recommended by NUREG-0737, "Clarification of TMI Action Plan Requirements,"
Item II.K.3. 16.
This item called for a comprehensive study to be performed to determine feasible means to reduce=challenges to relief valves.
The record of relief valve failures-to-close for all boiling water reactors (BWRs) in the past 3 years of plant operation is approximately 30 in 73 reactor years (0.41 failures per reactor year).
This has demonstrated that the failure of a relief valve to close would b'e the most likely cause of a small-break loss-of-coolant accident (LOCA).
The high failure rate is the result, of a high relief valve challenge rate and a relatively high failure rate per challenge (0.16 failures per challenge).
Typically, five valves are challenged for each event.
This results in an equivalent failure rate per challenge of 0.03.
The challenge and failure rates can be. reduced in several ways one of which is reducing the testing frequency of the main steam isolation valves (MSIVs).
Item II.K.3. 16 recommends that an investigation of the feasibility and contraindications of reducing challenges to the relief valves should be conducted.
Other methods should also be included in the study.
It further recommends that those changes which are shown to reduce relief valve challenges without compromising the performance of relief valves or other systems should be implemented.
2.0 Evaluation A study was performed by the licensee to determine the feasibility of reducing the testing frequency of the MSIVs and associated instrumentation to reduce the challenges to the relief*valves while still maintaining overall system reliability (no degradation of safety systems operational 8409l70217 840904 PDR ADOCK 05000259 P
capability).
Information that the licensee provided showed that during a
typical 12-month operating cycle on each unit at Browns Ferry, there are approximately 100 functional tests and 14 integrated calibrations performed on instrumentation associated with the main steam line isolation logic.
From the Browns Ferry Nuclear Plant Unit Scram List, there have been approximately 41 inadvertent scrams or isolations in the history of Browns Ferry associated with,the MSIVs and associated logic.
Of these 33 (80 percent) have occurred while performing a surveillance instruction SI).
Using conservative operating information it was shown that for Units 1, 2
and 3, there has been an average of 2.75 forced scrams/isolations each cycle as a result of a main steam line instrumentation SI.
Therefore, reducing the number of functional tests performed during a cycle by over two-thirds will cause a reduction in the number of unnecessary scrams to less than one scram each cycle.
As a result of this reduction, unnecessary challenges to relief valves and other safety systems will be proportionally reduced.
The licensee provided the following discussion to show that the reduced testing frequency would not impact system operability.
The Browns Ferry Licensee Event Report (LER) list for Units 1, 2 and 3 indicates there have been ten LERs on minor setpoint deviations and only two LERs of any significance discovered during scheduled SIs.
The two major LERs were results of failed sensors.
To determine a
new functional testing frequency using the Technical Specification 4.1, bases, the total number of operating hours and the total number of identical components were needed.
Table 1
contains the information on each surveillance instruction required, the M
value calculated (the factor M is the exposure hours and is equal to the number of sensors in a group times the elapsed time), and the recommended testing interval found from figure 4.1-1 of the Technical Specifications using the M value and the number of undetected failures.
Using this information, it is shown that a test interval of greater than six months could be justified.
However, the licensee proposed a required test frequency of once each three months to maintain conservatism.
- 3. 0
~Summa'tem II.K.3.16 of NUREG-0737 calls for a comprehensive study to determine feasible means to reduce the challenges to relief valves.
One suggestion stated in item II.K.3.16 was to reduce the testing frequency of the main steam isolation valves.
The staff has concluded that this will produce a marked decrease in inadvertent reactor isolation events and scrams associated with testing.
Besides reducing challenges to the relief valves by a significant and quantifiable factor, it follows that the general reduction in initiator events wil.l have commensurate benefit in reducing challenges to other reactor 'protection and safeguard features.
3-TABLF 1
I<
=
nT T
=
105120 hours Surveillance Instruction 4.1.A-1J 4.1. A-11 4.2.A-6 4.2.A-7 4 '.A-G llumoer of IdenticaL Components(n)*
12 24 12 4S i<umber of
~Fa i 1.2ox10 6
2.52-x10 1.26x10 6
5.05x10 5.05x10 6
Interva Lk*
6 iionths /0 (n
6 months JO
, 6 months /D 6 months /4' months l~
- Total number of conponents for aLL 3 units.
- Interva L fron finure 4.1-1 of Drowns Ferry induc Lear PLant technicaL specifications.-
~
g
1 g ~
By reducing the MSIV isolation testing frequency from once each month to once each 3 months for main steam line isolation valve closure, main steam line low pressure, main steam line high flow, and main steam line high temperature, and from once each week to once each 3 months for main steam line high radiation, it still remains under the recommended frequency of six months as stated earlier and thus remains conservative.
This indicates that testing frequency may be reduced without impacting overall system reliability.
Therefore, the staff has concluded that the reduction of testing frequency will not reduce the margin of safety in detecting failed equipment below the recommended limit but will increase the overall margin of safety by reducing the challenges to the relief valves and other systems.
Therefore, we have concluded that the proposed Technical Specification revisions satisfy the recommendations of NUREG-0737
( Item II.K.3.16),
permit the operation of the facility in a manner that is consistent with the licensing basis and accident analysis, and are, therefore, acceptable.
h 4.0 Environmental Considerations The amendments involve a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and a change in surveillance requirements.
The staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the 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 issued a proposed finding that the amendments involve no significant hazards consideration and there has been no public comment on such finding.
Accordingly, the amendments meet 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 amendments.
5.0 Conclusion We have concluded, based on the considerations discussed above, that (I) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed
- manner, and (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of these amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
J.
Mauck Dated:
September 4,
1984
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