ML20210P243
| ML20210P243 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 02/03/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20210P217 | List: |
| References | |
| NUDOCS 8702130340 | |
| Download: ML20210P243 (4) | |
Text
I-UNITED STATES
[
p, NUCLEAR REGULATORY COMMISSION t
J WASHINGTON, D. C. 20665 "s.,*****/
, SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION i
SUPPORTING APENDMENT NO. 48 TO FACILITY OPERATING LICENSE NO. NPF-11 C0tNONWEALTH EDISON COMPANY LA SALLE COUNTY STATION, UNIT 1 DOCKET NO. 50-373
1.0 INTRODUCTION
By letter dated December 15, 1986, Connonwealth Edison Company (licensee) requested several La Salle Unit 1 Technical Specification (TS) changes, applicable for the remainder of Cycle 2 only and relating to one control rod,10-47, which has experienced a problem in operations. The chan TS 3.1.3.2, 3 and 4 allow the rod 10-47 full out position to be 46 (ges to rather than the usual 48). The change to TS 3.1.3.6 exempts 10-47 from coupling requirements provided certain conditions are met. The request was accompanied by an analysis of the problem and proposed solution, including a safety evaluation by General Electric (GE).
The operational problem precipitating the proposed change began when it was detennined (during weekly exercisel that rod 10-47 was uncoupled from its drive. The reactor was part way through Cycle 2 with about a year of oper-ation still planned for the cycle. This rod had given no previous indication of a problem. The uncoupling was detected by the standard method of noting that from rod position 48 the rod drive could be moved into the overtravel position.
Following normal procedure, the rod was inserted a short distance to attempt recoupling. The unusual feature of this event was that in attempting to withdraw back to rod position 48 to check the coupling, the rod would not go to position 48, stopping at about position 47.
It thus i
could not be checked for coupling by overtravel.
It was then declared l
inoperable and fully inserted as required by TS 3.1.3.6.
The three rods i
synnetric to 10-47 were also inserted to preserve operational symmetry.
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_ It is not known for certain if the rod and drive are coupled or what the cause of the problem is. However, GE has analyzed the problem and concluded that the cause is most likely an improperly instat11ed coupling rod which, on moving around, has caused the uncoupling (with the rod at position 48) and has also bent a coupling spud finger so that it is preventing complete withdrawal.
If this is the case, there is probably sufficient coupling integrity to sustain normal scram loads.
The proposed TS changes are intended to permit operation for the remainder of the cycle with these rods returned during high power operation to the fully withdrawn position which is their planned position for the cycle.
(The reactor is operated as a Control Cell Core; and these rods, not being
" Control Cell" rods, are intended to be fully withdrawn during power oper-l ation.1 This would prevent the power distribution distortions and cycle reduction which would be produced by operation with them inserted.
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The basis for this proposal is that procedures for withdrawal and insertion of rod 10-47 can be specifically tailored to provide safe operation. This would involve withdrawal only above 20 percent reactor power and detemin-ation of rod positions by neutron flux measurements.
2.0 EVALUATTON Because coupling of the control rod and drive can not be confirmed, it must be assumed that they are uncoupled. The primary concern with an uncoupled rod is the increased possibility of a Rod Drop Accident (RDA), for which uncoupling is the first in a series of events which must occur to produce an RDA of significance.
The licensee has proposed two procedural changes for the remainder of Cycle 2 for la Salle Unit I to assure that rod 10-47 will not be subject to a significant (i.e. the generation of sufficient eneroy in the fuel to be of concern) RDA if withdrawn from the fully inserted position. First the rod will be fully inserted whenever the reactor power is less than 20 per-cent; and second, the neutron flux instrumentation in the vicinity of the rod will be used to check power distributions to verify that the control blade follows the drive movement. The latter will assure that the blade is following and is not sticking and separating from the drive and is therefore not setting up the second requirement for an RDA, blade hangup near full insertion. The full insertion below 20 percent power assures that, even if an RDA occurred (upon withdrawal above 20 percent power), it would be of no significance. The RDA has little effect in this power rance because of the i
magnitude of the transient parameters involved, including a low reactivity worth of a dropped rod.
(It is for this reason that the rod pattern control systems, e.g., the Rod Worth Minimizer (RWM), are not in operation above 70 percent.) This can be enforced by appropriate programming of rod 10-47 in the RWM, thus not permitting withdrawal until the RWM is turned off at 20 percent.
The licensee, has thus proposed two procedures, either of which would be sufficient to provide assurance that no significant RDA would occur as a result of the assumed uncoupling of rod 10-47. These are straightfomard procedures, and our review concludes that they are reasonable and acceptable solutions to the problem of preventing a significant RDA if rod 10-47 is uncoupled.
A second possible problem, if the rod is uncoupled, is equipment damage from scram loads. These loads would result from rod and drive separation during scram drive deceleration which might allow the velocity limiter (on the bladel to impact the fuel support casting. The GE analysis indicates that this might possibly damage the velocity limiter or, on rebound, the coupling spud or lock plug;,but there is not sufficient energy to dislodge fuel or fuel support.
The possible damage would not further aggravate the potential for the RDA and would not be expected to affect other aspects of reactor operation.
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' GE has provided recomended operating strategies to minimize possible scram load problems. Operation of rod 10-47 will follow these reconsnendations, and scram of the rod will be kept to a minimum and not occur under cold conditions.
If a scram time test is required for the rod during the cycle, an appropriate time will be added to the measurement to account for starting at position 46 rather than 48. The weekly tests of rod movement required by the TS will continue, thus assuring rod movement capability. Rod 10-47 is near the core periphery and thus has a reactivity worth less than the limiting rod. Should the rod fail to scram it would not result in a signifi-cant reduction of the scram reactivity worth function; and, based on Cycle 2 startup test measurerents, as reported by letter dated December 2, 1986, the reactor would still meet shut down margin requirements with rod 10-47 out along with the highest worth remaining rod.
It is, therefore, reasonable to conclude that operation with rod 10-47 fully withdrawn will not lead to any condition adverse to reactor safety.
The TS chances accompanying this mode of operation for rod 10-47 consist of footnotes added to several specifications. These footnotes are applicable only for Cycle 2.
Specifications 3.1.3.2, 3.1.3.3 and 3.1.3.4, all of which deal with the subject of control rod scram insertion times, hav'e the same added footnote indicatine that for rod 10-47 position 46 may be used as the fully withdrawn position for Cycle 2.
Specification 3.1.3.6, " Control Rod Drive Coupling," has an added footnote indicating that rod 10-47 is exempt from the coupling requirement for Cycle ? if the rod is fully inserted at less than 20 percent power and neutron instrumentation is used to verify rod movement. These TS changes adequately implement the reouired changes in rod operation and are acceptable.
We have reviewed the report submitted by the licensee proposing Technical Specification changes in the operation of control rod 10-47 in Cycle 2 for La Salle Unit 1.
Based on this review we conclude that appropriate documen-tation was submitted and that the proposed changes satisfy staff positions and reouirements in these areas. Operation with control rod 10-47 withdrawn under the guidance of the proposed procedures and Technical Specifications is acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
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This amendment involves a change in the use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes in surveillance requirements. The staff has determined that this amendment involves no sigriificant 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 radia-tion exposure. The Comission has previously issued a proposed finding that this amendmert involves no significant hazards consideration and there has been no public coment on such finding. Accordingly, this amendment i
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meets the eligibility criteria for categorical exclusion set forth in 10 CFR51.22(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 this amendment.
4.0 CONCLUSION
The Commission made a proposed determination that the amendment involves no significant hazards consideration which was published in the FEDERAL pEGISTER (51 FR 47074) on December 30, 1986, and consulted with the state of Illinois. No public comments were received, and the state of Illinois did not have any comments.
The staff has concluded, based on the considerations discussed above, that:
(1) 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 he conducted in compliance with the Commission's regula-tions and the issuance of this emendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
H. Richings, NRR Dated:
February 3,1987 l
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AMENDMENT NO.48 TO FACILITY OPERATING LICENSE NO. NPF LA SALLE, UNIT 1 DISTRIBilTION:
. Docket No.;50-373' NRC POR Local PDR PRC System NSIC BWD-3 r/f ABournia (2)
EHylton EAdensam Attorney, OELD CMiles PDiggs JPartlow BGrimes EJordan LHarmon TBarnbart(k)
FEltawila Mary Johns, RIII EButcher l
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