ML20209C621
Text
Nov 151983
- i DISTRIBUTION
Central Files H. Richings CPB r/f R. Mattson L. Rubenstein
!!E"CPAInU" F0r: !rarold 4. enton, nirector h(j Office of "uclear Reactor Dequlation C. Berlinger G. V.nighton T. Novak F9C*!:
por}cr J. P'.attson, Director D. Fieno b
Division of Svstens Integration B, Buckley SUP.1ECT:
r"ITICALITY STf.TUS AT DIADLO CA'lVD!: "IT!! COL'CWEEI*T CO'ISTWCTInt' Ann FUEL If1 THE CORE This nemnrandu" discusses the relationship at Diabl6 Canyon betwocq construction work concurre1t with fuel in the reactor core and any resulting effe::t on the nossibility of inadvertent criticality.
1.
Constructfon Activities (a)
Inside Containnent - No construction activities will be perfomed durino feel loading, vessel interns 1s insta17Ation and reactor vessel head installation.
Following vesfel iiead installation and during pre-critica.1 testinq only lient weiqht nodification cor.struction activities are reouired.
Peview and approval of work procedures of construction activities rust h obtained fror, Dacific ras A Electric (pG',E) and will be continuousiv sunervisM by MtE.
01scussiors with Pecion V indicate that onsite inspections, otservations and discussions concerninn nodifications inside containment after fuel load were the basis for Region V
,i Administrator J. D. "artin's position at the October 29, 1903 Cynission briefing that he could support Diabin Canyon fuel loading with the planned ninor nodiffections inside contain-nent.
(b) Outside Containnent - Construction activities outside contain-nent will be restricted to systens not needed to surror+. nodes 5 and 6 oreration. Ilork control procedures and review, aoproval and sunervision by PGAE will also be reouired for these cel-struction activities.
(c)
Deactor Coolant Systen - Reactor coolant systen currently contains 2000 ppm borated water which is required for node 6 (fuel loading).
The licensee plans to c.afntain boron concen-tration at 2000 ppn for node 5 (4200*F), which is nere con-servative than Technical Specifications requirenents, to further preclude inadvertent criticality.
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(T3M162N# PPD Contacts: 4 Dic51nos, DSI: CDP.
D. Pucklev, OL:LP03 t
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, - NOV 151983 Haruld R. DInton 2'-
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,3 (d) Staffino - In addition to PG8E personnel, PGAE has contracted ' ~
with Westinghouse Corporation (!!) to provide the following expertise for startup of the plant.
Fuel 1.oad Technical Advisor Core Load Instrunent Specialist Two Fuel Surveillance Engineers One Nuclear Steam Start-up Engineer per Shift Nuclear Testing Advisor Rod Control Systems Specialist 2.
Criticality Margins ir The reactor core will be maintained substantially suberitical. Only two areas are possibly relevant to an increased problem of reactor criticality with concurrent construction work. They would be associated with (1) falling loads compacting the core and (2) di-;
lution of the boron in the core moderator.
No work will be done which could lead to unusual falling objects.
when fuel is loaded in the core and the. core is uncovered (hea'd off).
In addition, compaction or distortion of the core in such a manner would not lead to significant reactivity increases sinc ~e the i
normal core geometry is very close to an optimum configuration of the fuel and noderator.
As indicated above there are no construction activities which should appreciably increase the likelihood of a significant boron dilution event. 1he nomal source range neutron flux instrumentation for detecting increases in reactivity when shutdown, including audible count rates, will be operating. The source range is continuously displayed and recorded in the control room. A high flux shutdown annunciator will alam if the count rate is equef to 5 times the shutdown count rate.
Following fuel loading an operator will log the source range count rate ead " sift. Boren concentrations will be chenically sampled duriq Asl loading every four hours and every day otherwise. The boror c cent )f the moderator will be maintained at greater than 2000 ppm, 6th uHng the loading (refueling) and cold shutdown modes (modes 6 and 5) during the construction phase. The maximum boren concentration for criticality, with all control rods out of the core will be about 1300 ppm. However, except for brief test oeriods, all of the control rods will be inserted, with a resulting critical concentration of about 700 ppm.
Control rod drive breaker will be racked open except during control rod drop testing. At most there will be one control rod bank cut for the tests, with a resulting critical concentration of about 900 ppm.
Thus with the critical concentration level less than 1000 ppn,
'"'"h.................d ilution ofcthe primary systeri Dy over a factor of two would De i
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NOV 151983
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Harold R. Denton y required for criticality. This is over a factor of two greater margin than is nomally considered available in Westinghouse reactor mode 6 boron dilution analyses (criticality assumed at 1500 ppm),
and is an even greater margin for mode 5 where the nomal dilution event analysis assumes the reactor to be initially only about 100 ppm above the critical concentration. Based on the conservative dilution assumptions nomally used by W, for a mode 5 or 6 event analysis, well over two hours of dilution (over a factor of two greater than usual) would be required to reach critical assuming the unlikely possibility that unborated water were available to provide the large dilution re-quired. There would be ample tine for warning from the monitoring system and for action to stop dilution.
The boron analysis which will be perfomed once every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following fuel load, the racking out of the control rod drive breakers, and the logging of the source range once per shift are note conservative than Technical Specifications requirements.
All these steps will help to assure no inadvertent criticality will occur during mode 6 and mode 5.
3.
Conclusion It can be concluded that there is no significantly increased likelihood of a reactor criticality event occurring as a result of the planned construction work concurrent with fuel in the reactor.
The construction activities should not increase the nomal proba-bility of a dilution event and the margins to criticality are greater by over a factor of two than nonna11y assumed in design basis accident analysis.
Original signed ty:
Roger J. Mattson, Director Division of Systems Integration N
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