ML20147H811
| ML20147H811 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 10/20/1978 |
| From: | Schroeder F Office of Nuclear Reactor Regulation |
| To: | Vassallo D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7810270120 | |
| Download: ML20147H811 (4) | |
Text
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A. Ignatonis Dockat No.'S0-346 MEMORANDUM FOR:
A 5. Yassallo, Assistant Director for LWRs, DPM FROM:
Frank'Schroeder, Acting Ass'istant Director for Reactor Safety DSS e
04YIS-BESSE UNIT NO.1 TECHNICAL. SPECIFICATION CHANGES.~
SUBJECT:
FOR DECAT HEAT. ISOLATION VALVES AND PRESSURIZER HEATER k
.f INTERLOCKS
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1 Letter from D. F. Russ to D. B.;Yassallo, Subject -
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7 A,, Davis-Besse Unit No.'1 Safety Evaluation of Pressurizer e
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Heater Interlocks and Power Removal to DHR Valves, dated
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9 On March 20, 1978, the Toledo Edisco Company submitted proposed Technical Specification changes of trip setpofats for the' pressurizer heater and the decay heat isolation valves DH-11 and CH-12. This Technical Speci '
fication change reflects the incorporation of the pressurizar heater interlock design change submitted inst year (April 7,1977)1etter).
This design change has previously been evaluated and approved (letter
. dated October 5,1977); however..the trip setpoint values for the decay
~ heat isolation valves and the pressurizer heaters have since been revised.
Our evaluation reflecting these proposed trip setpoint changes is enclosed.
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's J Frank Schroeder, Acting Assistant Director
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Enclosure:
Report Evaluation,,i.
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L. Engle G. Mazetis A. Ignatonis
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Algis Ignatonis, NRR 49-27341 i
See previous Correspondence j
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A. Ignatonis Ignatonis Chron NDUM FOR:
D. B. Vassallo. Assistant Director for LWRs, DPM FROM:
D. F..Ross, Jr.. Assistant Director for Reactor Safety, DSS
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SUBJECT:
DAVIS-BESSE UNIT NO.1 TECHNICAL SPECIFICATION CHANGES--
FOR DECAY HEAT ISOLATION VALVES AND PRESSURIZER HEATER INTERLOCNS Reference 1:~.
. Letter from D. F. Ross to D. 8. Vassallo, Subject -
Davis-Besse Unit No.1 Safety Evaluation of Pressurizer ter Interlocks and Power Removal to DHR Valves, dated tober. 5,1977. -
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On March 20. 1978, Toledo Edison Company submitted proposed Technical Specification f trip setpoints for the pressurizer heater and the decay heat isolati valves DH-ll and DH-12. This Technical Speci-fication change reflects. he incorporation'of the pressurizer heater interlock design change su itted last year (April 7,1977 letter).
This design change has previ sly been evaluated and approved (letter dated October 5, 1977); howeve the trip setpoint valves for the decay heat isolation valves and the p surizer heaters.have since been revised.
Our evaluation reflecting these p sed trip setpoint changes is enclosed.
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, D. F. Ro
, Jr. Assistant Director for Reac r Safety
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Division of stess Safety
Enclosure:
I-F Report Evaluation cc:
L. Engle G. Maretis A. Ignatonis
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Contact": Algis Ignatonis, NN 49-27341
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DAVIS-BESSE UNIT NO. 1 Safety Evaluation of Pressurizer Heater Interlock and Decay Heat Isolation Valve Trip Setpoints The licensee has submitted changes to the Technical Specifications reflecting the implementation of pressurizer heater interlocks in addition to the existing decay heat isolation valve interlocks. The pressurizer heaters and the decay heat isolation valves DH-11 and DH-12 are tripped when the reactor coolant system pressure exceeds the currently proposed setpoint of 438 psig. This value is a revision to our previously approved trip setpoint 'of 280 psig as described in the licensee's letter, dated April 7,1977.I The applicant's basis for the proposed change of the trip setpoint from 280 psig to 438 psig is his previous underestimate of the minimum net positive suction head (NPSH) requirement of the reactor coolant pumps.
The actual minimum NPSH is 70 psi greater than the design value; l
therefore, if the setpoint of 280 psig were to be maintained the pumps t
l may not reach the minimum NPSH requirement subsequent to the pres _s_urizer FeRer trip and isolatlon of the decay _ heat _ system. _J In establishing a new trip setpoint for automatic closure of the decay heat isolation valves, the licensee based the setpoint on the protection I
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l.etter from D. F. Ross to D. B. Vassallo, Subject - Davis-Besse Unit No. 1 Safety Evaluation of Pressurizer Heater Interlocks and Power Removal to DHR Valves, dated October 5,1977.
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-2 of the decay heat removal system design pressure to 450 psig. Taking into account pressure differences due to elevation correction and instrument string inaccuracy and drift, the technical specification trip setpoint was determined to be 438 psig. We have reviewed the method and values used in obtaining the new trip setpoint of 438 psig.
and find it acceptable.
This trip setpoint would ensure that the decay heat removal system relief valve (nominally set at 320 psig) will actuate prior to automatic closure of the isolation valves and will allow the relief valve to be available for mitigating the consequences of an overpressure event.
In addition to the Technical Specification setpoint of 438 psig for the decay heat isolation valves and the pressurizer heaters, the licensee indicated use of a field setpoint of 333+ 10 psig. The reason for this setpoint is to provide margin in protecting the decay heat removal system from overpressurization.
Since the field setpoint is considerably lower
-than the Technical Specification for a postulated overpressurization event, we were concerned with the possfEITitLof not having the reTief~ilalve Tift /
following automatic closure of the isolation valves resulting in a potential violation of the Appendix G limit. Protective measures to prevent such an occurrence will be available.
The licensee will provide an alarm to alert the operator when there is control power available to the motors of the decay heat isolation valves ar.d they are open. Also, the applicant has indicated that the controls and instrumentation associated with the alarm are safety-grade.
This is acceptable to the staff.
Secondly, operating procedures 2di?24 I
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require that the reactor coolant temperaturd be no less than 280 F prior to decay heat isolation valve operation.
Thus, even if the alarm was to be ignored by the operator, by complying with the operating procedures the Appendix G limit will not be exceeded following an overpressure event with the decay heat isolation valves in a closed position for reactor coolant temperatures greater than 280 F.
We find the above described protective measures to prevent premature isolation of the decay heat system relief valve to be acceptable.
The licensee has indicated that the change to a higher trip setpoint of 438 psig from the previously approved 280 psig will not change the results of the previously analyzed overpressure transients. We agree with the licensee and conclude that the decay heat removal system design integrity would be maintained and the Appendix G limits would not be exceeded following an overpressure transient.
In summary, the proposed Technical Specification changes of trip setpoints l
for the pressurizer heater and decay heat isolation valves are acceptable to the staff.
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