ML19341A185
| ML19341A185 | |
| Person / Time | |
|---|---|
| Site: | Aerotest |
| Issue date: | 01/15/1981 |
| From: | Newacheck R AEROTEST OPERATIONS, INC. |
| To: | John Miller Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8101220323 | |
| Download: ML19341A185 (4) | |
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AEROTEST OPER ATIONS, INC.
41 3455 FOSTORIA WAY. SAN RAMON CALIFORNIA 94583.(415) 837-4248 sue 15 January 1981
'Jr. J. R. Miller Chief, Standardization and Special Projects Branch
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Division of Licensing Nuclear Regulatory Co= mission Washington, D.C.
20555
Reference:
License R-98, Docket 50-228 Centlemen:
Aerotest Operations, Inc. has been in telephone communication with the Commission relative to a fuel element that cannot be removed from the ARRR core lattice in the normal manner. The element is free to lift 19 inches, until the interface of the lower fuel and graphite reach the upper grid plate. An inspection of the fuel element shows no major swelling or damage of the fuel element cladding. However, there is a slightly enlarged section of cladding at the fuel graphite interface estimated to be 15 or 20 mils in radia1 expansion and about 1/8"
.'.n length, just enough to cause an interference with the upper grfd plate. Attempts to remove the ele =ent through the grid plate have simply resulted in a galling of the aluminum cladding.
We wish to remove the fuel element from the reactor core to prevent any further swelling and potentially a more serious problem. The Aerotest technical staff has concluded that the safest method of removal would be from the underside of the upper grid plate. The procedure is relatively simple and straightforward for our reactor since we have one side of the core completely accessible; i.e., we do not have the typical TRIGA lazy susan or closed shroud.
One item of concern relative to our Technical Specifications must be resolved before we can proceed with the fuel element removal.
Specif1-cally, the Technical Specifications describe only two types of s torage facilities; 6 dry pie 2 for storage of 19 elements each and an in-pool rack on the tank wall for 21 elements. Although the Technical Specifi-cations appear to have no wording that would preclude the use of additional storage racks in the reactor pool, one could arg.ue that this was the intent since additional storage facilities are not mentioned. Actually, when the Technical Specifications were written, the authors did not recognize the need for temporary storage of all the fuel elements within the reactor lkC) pool. We believe the Technical Specifications are intended to describe 3
permanent storage facilities and that temporary storage facilities can be used if they are shown to comply with the stated condition that "Keff shall / I L
P f 3 0 ? 9 ' 123l2:3 A SUBSIDI ARY OF
r License R-98, Docket 50-228 15 January 1981 not exceed a value of 0.8,"
(d:ction 11.0, Paragraph 2, " Fuel Storage and Transfer").
We feel it is essential that temporary fuel storage of all the fuel elements be within the reactor pool in the interest of safety. Use of the dry storage pits would greatly enhance the probability of an accident during the numerous moves through the building and would not be in keeping with ALARA.
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We are enclosing a copy of the memo to the R.S.C. which includes the safety analysis of the temporary storage racks and shows that the Keff will be well under 0.8.
The storage rack and all the procedures involving the operations necessary to remove the " defective" fuel element were fully evaluated by the R.S.C. on 13 January 1981. They concluded that no unresolved safety question exists for this operation. Any of this information can be provided for NRC review if required.
We plan to proceed with the in-pool temporary storage allowing complete defueling when the " defective" fuel element is removed. The operation is presently scheduled for the weekend of 31 January 1981. Please advise us as soon as possible if you do not agree with our interpretation of the Technical Specifications regarding temporary storage.
If we do not receive such notice, we will assume that you agree with us that there is no concern.
Recognizing the short interval remaining for avaluation and reply by mail, we will verify your confirmation by telephone prior to actual fuel transfer.
Your review and comments will be appreciated.
Very truly yours, AER0 TEST OPERATIONS, INC.
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., f hard L. Newacheck President RLN:be Encl:
Memo to RSC dtd.1/12/81 cc:
J.L. Crews, NRC, Walnut Creek, CA.
P M E M 0 R A N D U M:
12 January 1981 TO:
Reactor Safety Co==ittee 21,
FROM:
R. L. Newacheck
SUBJECT:
Safety Analysis of Fuel Storage Rack and Simplified Critical Assembly Procedure IV-G proposes to remove and replace the fuel elements to per=it safe removal of the stuck fuel element in position F-10.
The procedure
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permits removal and storage of all fuel elements within the reactor tank.
This method of storage may not be in strict compliance with the ARRR Technical Specifications, which imply that only the storage rack located on the tank wall, 21 positions, and the 6 dry pits,19 elements each, are to be used for fuel element sotrage. Having participated in the preparation of the Technical Specifications, I am qualified to state that this limitation resulted from our limited consideration that the in-pool storage would be used for initial reactor fueling, fuel transfer operations and storage of surplus fuel elements. The dry storage pits were considered necessary for storing defective fuel elements or interin storage of all the elements in the event the reactor was deco =missioned. We had not considered the case where all elements had to be removed and stored temporarily while the core structure was repaired or for safely're=oving a stuck cceponent.
It is obvious that removal and transfer of the fuel elements from the reactor, through the building and into the dry pits, is a highly undesirable method for temporary storage. The potential for an accident and possibility of fuel element damage is a real concern when ecmpared to the proposed alternative of using additional storage capability in the pool. Additionally, personnel errcoures would be appreciable.
A preferred plan for storage of the fuel elements is proposed in order to circumvent the undesirable use of the dry storage pits. This plan has been discussed by telephone with Jess Crews, NRC, in Walnut Creek and Robert Carter, our project manager at the NRC in Washington, D.C..
Mr. Carter has suggested that we proceed on this basis and advise the NRC in writing prior to proceding with the work. He does not feel that a Technical Specification amendment is necessary and would not be practical in view of the time schedule for removal of the stuck fuel element. His primary concern was that we show our in-pool storage rack (s) to be less than 0.8 K effective.
We believe the determination of the K eff in our storage rack can be made most accurately by using experimental references. The fcondation for our safety analysis is based on two references, 1.) experimental tests performed by General Atomics to evaluate the safety of shipping TRIGA fuel elements,
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g Safety Analysis of Fuel Storage Rack and Simplified Critical Assembly 12 January 1981 and 2.) the critical assembly data for the AGNIR (now ARRR), dated July 18, 1966. Reference 1 was an experiment conducted by General Atomics under AEC License SNM-69 and showed that the minimum critical l
mass of TRICA fuel elements (the design used in the ARRR) was 59 when in an optimum configuration in water and surrounded by 6" of lead and l
4" of paraffin. Reference 2, confirmed a critical mass near this amount i
in the water reflected compact configuration of the ARRR. The ARRR was critical with 2.265 Kg, contained in 62 fuel elements.
Further, the critical experiment showed the number of fuel elements for Keff = 0.8 to be 58 (based on the most conservative of 5 multiplication measurements).
Therefore, any water reflected storage array with less than 58 elements will provide a Keff of 0.8 or less. To be ultra conservative, the in-pool storage racks are designed with a lh" edge to edge spacing between elements.
Thus the Keff would be well under 0.8 for an array of 58 elements. Again, to be ultra ccuservative, each rack is designed to hold only 28 elements which would result in a Keff of less than 0.1 for an optimum water reflected configuration.
A second safety question might be raised as concerns the reloading of the core without performing a critical experiment complete with suberitical measure =ents.
For a modified configuration, one could certainly make a case that a complete critical assembly would be necessary. However, over the years, several partial defueling and refueling operations have been carried out for unchanged core configurations and the resulting excess reactivity changes were insignificant.
Indeed, each time the fuel has been inspected the equivalent to a total defueling and refueling was performed, one element at a time, and these operations also resulted in a
no significant excess reactivity change.
For this total defueling and refueling operation, where the core config-uration is unchanged, we plan to stop short of total refueling by 8 fuel elements. This will permit a Kef f greater than one and yet will allow a controlled final approach to full loading with excess reactivity deter-mined after each fuel addition so that the final excess reactivity can be predicted. In this manner we can guarantee that none of the Technical Specification limitations will be exceeded.,
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