ML19296F581
| ML19296F581 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 12/16/1977 |
| From: | Sherwood G GENERAL ELECTRIC CO. |
| To: | Case E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| Shared Package | |
| ML19296F582 | List: |
| References | |
| REF-PT21-77-007-005 MFN-482-77, NUDOCS 8010210841 | |
| Download: ML19296F581 (8) | |
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G E N E R'A L h) E L E CT R I C
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NUCLEAR ENERGY SYSTEMS DIVISION GENERAL ELECTRIC COMPANY,17s CURTNER AVE., SAN JOSE, CALIFORNIA 9s12s NUCLEAR ENERGY MC 682, (408) 925-5040 PROJECTS DIVISION MFN-482-77 December 16, 1977 Mr. Edson G.' Case, Acting Director 77' 07' 08 bO Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory. Commission Washington, D.C.
20555'
Dear M. Case:
SUBJECT:
SELECTION OF BWR/6 RELIEF VALVE CONTROL SYSTEM MODIFICATION On October 6, 1977, General Electric advised representatives of Inspection and Enforcement and Nuclear Reactor Regulation of a reportable condition under 10CFR21.
That condition was connected with the relief valve control ystem which, under certain transient isolation events, would allow more than one relief valve to reopen resulting in load combinations not currently specified in the licensing documentation.
On October 11, 1977 General Electric submitted a report which described the relief valve control system deficiency under 10CFR Part 21.
Since that tire, General Electric has met with members of the NRC staff on October 13, 1977 and November 11, 1977 to discuss this matter.
Although this letter identifies tne selection of a relief valve control system modification in the context of BWR/6 plants, the modification selected to remedy this condition can be applied generically for use on BWRs in Mark I and Mark II plants if required.
This modification to the relief valve control system is referred to the low-low set relief logic.
This letter provides a summary of the information presented to the NRC staff regarding low-low set relief logic addition to the relief valve control system.
The low-low set relief logic assure:, that the number of relief valves which could reopen following a reactor isloation event do not exceed those currently used as the licensing basis for design.
It is a further purpose of this letter to seek concurrence by the staff that the approach being taken by General Electric for resolution of this item is acceptable.
Discussion The low-low set relief system logic improvement has been selected to resolve the concern for multiple valve subsequent actuation on BWR/6 Mark III.
This selection was made on the basis that when compared to other alternatives, it best satisfies all design objectives and require-ments.
The design objectives and design requirements for the relief system logic are summarized on Page 1 of the attachment.
Page 2 of the 0010210 hf
GENERAL
.LECTRIC d
E. G. Case Page 2 attachment summarizes the setpoint arrangement for both the normal pressure relief setpoints and for the low-low set relief portion of the control system.
Note that the design is single-failure proof and further does not compromise margins for either overpressure protection or inad-vertent relief valve opening. The design is also testable during nomal operation.
The low-low set relief logic system adds circuitry which imposes pre-established lower opening and closing set points for selected valves which override the normal setpoints following the initial opening of these valves.
This logic is armed or activated by the existing pressure sensors of the second normal relief setpoint group.
Once the transient has ended, the low setpoints can be disengaged by manual reset.
A schematic logic diagram for the BWR/6 relief valve control system with the low-low set feature is attached.
See Pages 3 and 4 of the attachment to this letter.
The reactor performance during an isolation event with the low-low set relief system is summarized on Page 5 of the attachnent.
All valves would be expected to open on the first pressure rise after isolation when conservative design assumptions /models are employed.
Subsequent pressure peaks will result in no more than one relief valve experiencing subsequent actuations, with a margin of 4 0 psi existing between the lowest set valve and the next lowest set valve in the armed logic.
The low-low set relief system maintains the current design documented basis for containment and NSSS equipment evaluation methods and for overpressure transients.
Thus, no additional load cases for containment or NSSS equipment are required and the overpressure transients will not have to be redone.
In addition, introduction of this system will result in a significant reduction in containment fatigue duty cycles resulting from relief valve cycling during the decay heat dominant period late in an isolation transient.
This represents an increase in design margins in the fatigue area.
It will not be necessary to reevaluate any transient analyses presented in Chapter 15 of GESSAR because the current submittals will not be invalidated.
The purpose of the events presented in Chapter 15 is to demonstrate that established overpressure protection and fuel thermal limits criteria are met for the expected spectrum of abnormal transients.
This is accomplished by making conservative assumptions with regard to equipment performance and initial conditions.
For example, the upper range of the nominal opening relief valve setpoints are conservatively used. Any effect of low-low set relief on transient response occurs m-.
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E. G. Case Page 3 considerably later in the transient than the time of minimum margins, i.e., peak vessel pressures and minimum itCPRs for the limiting events occur on the initial pressure rise, wherets low-low set affects subse-quent pressure peaks.
Although the subsequent pressure signature after the initial peak may change due to low-low set, the established peak vessel pressures and minimum therr margins will not change from that currently presented in Chapter 15 of GESSAR.
Future Actions In accordance with discussions with members of the NRC Staff, General Electric has agreed to provide, in January 1978, additional information regarding the design and analyses of the low-low relief set alternative.
This information will be of the same level of detail as that contained in the 238 Nuclear Island GESSAR.
The following identifies the contents of the January 1978 submittal which will be transmitted by letter on the 238 Nuclear Island GESSAR, Docket STN 50-447:
o Replacement documentation for portions of the GESSAR affected by addition of the low-low relief set logic.
o System description, analyses, FCD's, P&ID's and elementary wiring diagrams as they pertain to low-low relief set logic.
.o Typical information as identified above for the ADS Inhibit feature
'should GE propose it as part of the standard design.
We request that the NRC staff concur that the addition of the low-low set relief logic to the BWR/6 relief valve control system, if designed in accordance with the criteria described herein, is acceptable as the remedy to the condition as reported in our letter of October 11, 1977.
Because of the critical schedules associated with this item, we would appreciate receiving your concurrence on this matter as early in Jan-uary 1978 as is feasible.
If you have any questions or comments regarding this matter, please contact Mr. J. F. Quirk of my staff.
Very truly yours, G. G. Sherwood, Manager Safety and Licensing BWR Projects Department Mail Code 676, Ext. 5040 GGS:sj/59-61 Attachment cc:
R. Boyd V. Stello, Jr.
R. J. Mattsen E. Volgenau L. S. Gi fford 3,y -
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MARK III BWR/6 SRV C0iiTROL SYSTEM EVALUATIONS FOR SUBSEQUE!!T ACIUATI0fl DESIGN OBJECTIVES 1.
OliE SRV SUBSEQUENT ACTUATION 2.
MAINTAlti CURREtlT DESIGN BASIS e
CONTAltmEtri LOADS e
OVERPRESSURE TRANSIENTS 3.
SIMPLICITYbFIMPLEMF!!TATI0tl 4.
GEllERIC APPLICATInti 5.
REDUCE LO!1G TERM SRV CYCLitlG
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DESIGN REQUIREMENTS 1.
RETAIN CURRE!1T LOAD ENVELOPE 3 SRV'S SUBSEntlEllT ACTUATION e
2.
ACCEPTABLE OVERPRESSURE PROTECTInN 3.
D0 fl0T OPEN S/R VALVES Ofl SPRIT!G (SAFETY)
SET POINT 4.
ACCEPTABLE MARGIf! AGAINST If!ADVER. TENT OPEtlING 5.
SINGLE FAILURE PROOF LOGIC 6/
TESTABLE DURII1G linPFAL OPERATION
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MARK III Bl.'R/6 SRV CONTROL SYSTEM EVALUATION LOW-LO',I SET RELIEF DESCRIPTION ADD INSTRUMENTS AND LOGIC WHICH W0ULD SET D0WN B0TH THE OPENINGS AND CL0 SING SET POINT 0F SOME VALVES F0LL0 WING THE INITIAL LIFT.
GROUPS EXISTING LOM-LOW SET NO. (ADS)
E NO.
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1 1103 1
10]O/880 B
9(4) 1113 1
1050/900 C
9(4) 1123 4
1090/940 SRV OPENING F0R ARMED FR0M N,0 R M A L RELIEF AND REACT 0R PRESS >
i NORMAL RELIEF 2
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ATTACHMENT e
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i MARK III B"R/6 SRV C0f! TROL SYSTEli EVALUATI0t!S LOW-LOW SET RELIEF PERFORi'At!CE o
ISOLATI0il EVENT PERFORtWlCE ALL VALVES 1ST ACTUATION 1 VALVE SUBSEQUENT ACTUATION SUBSEQUENT P AK PRESSURE MARGIN To MULTIPLE VALVE E
REOPENING ~40-50 PSI.
o NORMAL OPERATI0f! MAPGIll TO RELIEF SET POINT ~60 PSI MAltlTAINS CURREi!T MARGIt!
o SATISFIES ALL IDEllTIFIED DESIGil OBJECTIVES AND REQUIREMEl!TS
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