ML20053F041
| ML20053F041 | |
| Person / Time | |
|---|---|
| Site: | MIT Nuclear Research Reactor |
| Issue date: | 05/28/1982 |
| From: | Bernard H Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20053F036 | List: |
| References | |
| R-037-A-021, R-37-A-21, NUDOCS 8206100337 | |
| Download: ML20053F041 (2) | |
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o UNITED STATES g
NUCLEAR REGULATORY COMMISSION g
WASMNGTON, D. C. 20555 MASSACHUSETTS INSTITUTE OF TECHNOLOGY 3
DOCKET NO. 50-20 5
I AMENDMENT TO FACILITY OPERATING LICENSE Amendment No. 21 License No. R 37 1.
The Nuclear Regulatory Commission (the Commission) has found that:
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The application for amendment by Massachusetts Institute of Technology (the licensee) dated May 14, 1981, complies with the standards and requirements of the Atomic Energy Act of 1954, as amended, (the Act) and the Commission's rules and regulations set forth in 10 CFR Chapter I; B.
The facility will operate in conformity with the provisions of the Atomic Energy Act of 1954, as amended, and the rules and regulations of the Commission; C.
There is reasonable assurance (i) that the activities authorized by this amendment can be conducted without endangering the health and safety of the public, and (ii) that such activities will be conducted in compliance with the Commission's regulations; D.
The issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public; i
E.
The issuance of this amendment is in accordance with 10 CFR 50 of the Commission's regulation and all applicable requirements f
have been satisfied; and 1
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Publication of notice of this amendment is not required since it does not involve a significant hazards consideration i
nor amendment of a license of the type described in 10 CFR y
Section 2.106(a)(2).
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Accordingly, Facility Operating License No. R-37, Section 3.10 (f..g(,.y is amended by changes to the Technical Specifications as indicated 77 in the Attachment to this license amendment.
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The itcense amendment is effective 90 days from the date of its Mlf 1 E6:dy,;
issuance.
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2 r.,p im[s a 1d Bernard, Acting Branch Chief 19 ^
Standardization & Special (M
Projects Branch Division of Licensing O'd J MAY 2 81982
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Date of Issuance:
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SAFETY EVALUATION REPORT FOR MASSACHUSETTS INSTITUTE OF TECHNOLOGY AMENDMENT TO TECHNICAL SPECIFICATIONS
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TO CHANGE FUEL STORAGE AND HANDLING OPERATIONS 7
INTRODUCTION By letter dated May 14, 1981, MIT proposed changes to fuel storage and reallocation of unirradiated fuel storage from a vault in MIT Building NW12 (adjacent to the containment building) to a safe within the containment building. The MIT SAR discusses the proposed storage in the safe from the viewpoint of safety and criticality prevention.
The SAR also de' scribes other use and storage locations for irradiated and unirradiated fuels, and criticality prevention analyses. To implement the proposed changes, MIT proposed changes to the Technical Specifications and a period of 90 days following issuance of the amendment by NRC to pemit the requisite modifications to the storage facilities. A revised Physical Security Plan that includes the proposed changes has already been approved, and will become effective 90 days
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following issuance of this amendment.
FUEL STORAGE AREAS Fuel Storage Ring Fuel storage is provided in the storage rack located just above the core in the core tank. There are 29 vertical cells arranged in a single row annulus to provide criticality-safe storage of an entire core or of partially spent fuel awaiting recycling into the core. The individual fuel storage cells are rhombic sections about 1/4" larger than the fuel element and with a depth equal to the length of the fuel element. The cells have.020" of cadmium on all four sides.
f Dry Storage Holes on Reactor Top The reactor biological shield contains 22 holes for the storage of particily l
used fuel elements and other radioactive materials. These are located in the high density concrete shielding just outside the themal shield. They are lined with steel pipes having an inside diameter of about 5 in. Except for one single hole, the holes are grouped into clusters of three. Each of the three holes is located at the corner of an equilateral triangle having l
a side 8 in. long (center-to-center distance).
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. Fresh Fuel Storage Safe Unirradiated or very slightly irradiated fuel elements, fuel plates, and i
miscellaneous small items containing special nuclear material (such as fission counters) are stored in a steel safe in the containment building.
The interior dimensions of the safe are 20" wide x 20" deep x 48" high, f
and is equipped with an aluminum rack providing 20 vertical storage 7
positions, each one is approximately 4" x 4 3/4". The five rows of four positions each are separated by 0.020 inch thick sheets of cadmium sand-wiched into the aluminum partitions. The back and two sides of the rack contain similar cadmium sheets.
The vault is monitored by an alarm in accordance with 10 CFR 70.24. The monitor is equipped with a low level alarm as instrument failure protection.
It will be tested at hast once each year.
1 Spent Fuel Storage Tank s
A concrete tank 8 ft. in diameter and 20 ft. deep penetrates the floor of the reactor building basement (Fig. 3.2.3.3).
The tank wall is 6" thick with 3/4" steel lining on the inside. The tank is filled with demineralized
.q water.
Its top is located in a separate locked room.
Spent fuel elements are stored in cadmium-lined racks which rest on the bottom of the storage tank. These racks are 5 x 5 square arrays with 4 3/4" x
spacing, center-to-center. At present, there are three such racks in the f
tank. There is room for one more such rack on the floor of the spent fuel
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storage tank.
I CRITICAL.ITY CONSIDERATIONS The cadmium containing storage ring in the shroud tank is neutronically isolated from the reactor core by the cadmium of each individual box and by the six control blades surrounding the: reactor core (five blades, if one is removed for maintenance or replacement). The dry storage holes in the reactor top are separate pipes poured in the concrete of the reactor shielding. The pipe sizes and spacing are arranged in such a manner such as to be safe from criticality when fully loaded with fuel. The fresh fuel storage safe and the spent fuel storage pool both have carefully designed geometric arrays to assure that criticality will not occur.
Calculations indicate that at least 81/3 MITR-II fuel elements (510 grams of U-035 per element) with optimum spacing and total H 0 reflection are j
required for criticality. To provide for additional criticality control in the reactor, no more than one fuel element will be moved inside the reactor core tank at a time. To guard against any possibility of inadvertent criticality in the temporary fuel elements, including non-assembled plates, (maximum of 15 non-assembled fuel plates) storage will be in the areas l
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5, described above, except during the processes of receiving fuel at the site or shipping fuel from the site in approved containers.
The handling and storage procedures described in this section for MITR-II fuel are conservative for MITR-II fuel and will be used for any remaining MITR-II elements and plates.
1 As stated above, unirradiated fuel plates and fuel elements are noma 11y stored in the storage safe in the Reactor Containment Building monitored by an alarm in accordance with 10 CFR 70, Paragraph 70.24. This monitor is equipped with a low level alarm as instrument failure protection.
The staff agrees with the MIT fuel storage design for criticality prevention.
All criticality fuel storage locations have been arranged and/or fitted with
.s cadmium sheeting to preclude criticality when fully loaded with fuel. Changes to the Technical Specifications (T.S.) take into consideration the abcle mentioned facility and operation modifications. They delineate the various i
fuel handling, transfer and storage operations, and safety interlocks that protect against potential incidents. In addition, the T.S. stipulates that whenever fuel is removed from the core tank it must have decayed for at least four days. This requirement prevents melting of the fuel plates during transfer when the elements are cooled by natural convection.
CONCLUSION The modifications to the storage facilities and to the Technical Specificatter*
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prepared by MIT increase the criticality safety and the physical security of the fuel storage, handling and transfer operations in the MITR.
Accordingly, it is concluded that no significant hazards can accrue from the proposed facility modifications and amendments to the Technical Specifications.
1 There is also reasonable assurance (a) that the activity authorized can be conducted without endangering the health and safety of the public and (b) that such activities will be conducted in compliance with the regulations of the Commission set forth in 10 CFR Chapter 1.
Dated: May 28,1982 l
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ATTACHMENT TO LICENSE AENDMENT NO. 21
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- t FACILITY OPERATING LICENSE NO. R-37 g
y[p Dccket No. 50-20 j"4 Replace the following pages of Appendix "A" Technical Specifications with the enclosed pages. The revised pages are identified by Amendment Number and contain vertical lines indicating the area of change.
Remove Insert Pages 3-36 Pages 3-36 1
3-37 3-37 3-38 3-38 3-39 3-39 o
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3.10 Fuel Element and Core Component Handling and Storage
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Applicability i
This specification applies to the operations of storing and handling t
fuel elements and core components.
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To assure that fuel elements and core components will be handled at all times in a manner to protect the health. and safety of reactor personnel and 4
the public.
Specification t
1.
Fuel elements shall be stored in accordance with the requirements 3
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of the MITR Security Plan.
2:
2.
Unirradiated fuel elements may be stored at any of the following 4.
locations, subject to the MITR Security Plan and to Specification 4 below:
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- a. In-the reactor core provided the retetivity is below the shutdotm g
g margin given by specifica' tion 3.9-1, y
- b. In the cadmiu:n-lined fuel storage ring attached to the flow shroud,
- c. In the dry storage holes on the reactor top (one element / hole),
.d. In the storage safe in the Reactor Containment Building (Fuel plates d
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3.
Irradiated fuel elements can be stored in any of the folic, wing i
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lj locations:
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Amendment 21 y
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in.the reactor core provided the reactivity is below the j'
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JI shutdown margin given by Specification 3.9-1, N
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in the cadnium-lined fuel storage ring attached to the 1
flow shroud, f
4 in the dry storage holes on the reactor top,
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in the spent' fuel storage tank in the, basement of the y
I reactor building, A
in the fuel element transfer flask or other proper shie?,d e.
within the contrn11ed area.
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Handling of fuel elements: Only one fuel element at a time shall Not more than four'of the MITR fuel be moved in or out of the reactor core.
elements or the equivalent o,f two fuel elements including loose plates (maximum of 15 loose fuel pistes) shall be outside of the storage areas as
-l designated in items 2 and 3a, b, c, d except during the processes In all of receiving or shipping fuel from the site in approved containers.
cases of fuel element storage outside of the reactor core, the value of k,gg must be kept loss than 0.90.
Records of fuel element transfers shall be maintained. Prior to transferring an irradiated element from the reactor vessel to the transfer flask, the element shall not have been operated in s
the core at a power level above 100 kW for at least four days.-
h 5.
Removal of control blades: A control blade may be removed from f
the core only if the minimum shutdown margin relative to the cold, Xe-free
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i critical condition with the most reactive operable blade and the regulating f
f' rod fully withdrawn is 1% Ak/k af ter the control blade has been removed.
3-37 i
Amendment 21 J
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Basis _
6l The principal problem in regard to fresh fuel elements is that of lI The locstions specified in 2 and 3a, b, c, d provide accidental criticality.
t for complete criticality control. The reactor itself is, of course, shielded The
'l and appropriate written procedures assure that it is loaded properly.
lj fuel e2.ements in the cadmium containing storage ring in the shroud tank are neutronically isolated from the reactor core by the cadmium of each individual The dry box and by the six control blades surrounding the reactor core.
storage holes in the reactor top are separate pipes poured in the concrete of -
the reactor shielding. The pipe sizes and spacings are auch as' to be safe from criticality when fully loaded with fuel. The fresh fuel storage safe and the spent fuel storage pool both have carefully designed geometric arrays to assure e
The rows of storage positions in the safe are that criticality will not occur.
separated by cadmium, and each fuel element box in the pool is lined with The specification of no more than four elements outside of 1.he desig--
nated storage areas of 2 and 3a, b, c, d thus assures that no criticality will Calculations have been made, by using the methods described occur elsewhere.
in Section 3 of the SAR, which indicate that at least 81/3 MITR fuel elements with optimum spacing and total reflection are required for criticality.
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.Similar calculations show that 72 fuel plates with 27 grams U-235.are required I
for criticality, giving a safe handling limit of about' 30. No calculations i
have been done for 34 gram plates, and so a conservative limit of 15 un-
~ I assembled plates is established.
3-38 Anendment 21.
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J It has been calculated that fuel elements when stored in the locations Q
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specified in 2b, 2c, 2d, 3b, 3c, and 3d will have a calculated effective y l(
.I multiplication (k,ff) factor of less than 0.9 under optimum conditions of water moderation.
These specifications are also conservative for criticality safe handling of MITR-I fuel alone or in combination with MITR-II fuel.
The chief additional problems with ' spent fuel are those of shielding personnel froci the emitted fission product gamma rays and preventing melting from afterheat. The shielding requirement is met by utilizing a shielded transfer flask for movements and temporary storage and more permanent shield-s ing as indicated in 3a, b, c, and d.
The requirement to prevent melting is met by specifying that four days elapse between use of the fuel element in a o
core operating above 100 KW and removal of the element from the reactor pool.
9' This decay time was determined from experience with the MITR-I combined with
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l a conservative assumption of doubling the power density for the MITR-II.
b The specification on removal of control element provides that the stuck rod criteria will always be met, even when one blade is removed for repair.
f Thus, the reactor still would not go critical on the removal of a.second con-C3
.m trol element.
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Amendment 21
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