ML20042B930

Draft Revised Tech Spec 5.2-1 Re Design of Reactor Core

ML20042B930
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	03/22/1982
From:	MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:
Shared Package
ML20042B929	List: ML20042B928 ML20042B930
References
NUDOCS 8203260300
Download: ML20042B930 (2)

Text

. . _ _ _ _

- g'4 . .

5.2 Reactor Core Applicability This specification applies to the design of the reactor core.

Obiective To assure compatibility of the reactor core with the present safety analysis.

Specifications -

1. The reactor core may consist of up to 27 fuel elements approxf.-

mately 2-3/8" on a' side. The fuel shall be plates of uranium in the form of UAl alloy or UA1 with a maximum of 50 w/o urani'um in the. fuel matrix clad by a layer of aluminum metal incorporating fins on the surface that enhance the heat transfer and having a nominal clad thickness of 0.015 inches at the base of the groove between the fins.

2. Design of in-core sample assemblies shall conform to the following criteria: .

a. they shall be positively secured in the core to prevent movement during reactor operation,

b. materials of construction shall be radiation resistant and co=patible with those used in the reactor core and primary

' coolant system,

c. sufficient cooling shall be provided to insure structural integrity of the asse=bly and to preclude any boiling of sthe primary coolant,

, d. the size of the irradiation thimble shall be less than 16 square inches in cross section.

Basis The thermal design analysis in the SAR and the power distributions on which the analysis was based assumed fuel elements of the type specified 8203260300 820322 PDR ADOCK 05000020 5-3 P PDR

+ .

in item 1. Any change in this design would requ. ire re-evaluation of the heat transfer and flow characteristics of the element.

The nominal clad thickness of 0.015" is based upon ctandard practice for MTR type elements with clad of similar thickness. Reference 5.2-1 states (p.148) that the release of radioactive fission ga's to the primary cooling water appears to be adequately prevented by cladding of uniform thickness (>0.2 mm, >0.008 in). This corresponds to the minimum nominal cladding permitted for ATR fuel, where the term " uniform" implies'a provision .

for minor manufacturing deviations (e.g. scratches, indentations, et,c.) from the uniform thickness. Ref. 5.2-2, (p. 672) shows that a thick clad increases the delay time for heat removal in event of' a fast transient. Therefore, the clad should be as thin as possible while still' re=aining compatible with fission product retention requirements.

In-core sample assemblies which satisfy Specification 2a cannot be credibly ejected during operation and are therefore considered part of the reactor structure.

Specification 2b and 2c insure the structural integrity of the assembly and prevent che=ical interactions with the core and primary coolant system.

Specification 2d limits the size of the irradiation area as required by 10 CFR 50.2(r).

References Ref. 5.2-1 Beeston, J.M., R.R. Hobbins, G.W. Gibson, and W.F. Francis,

" Development and Irradiation Performance of Uranium Aluminide Fuels in Test Reactors", Nuclear Technology, Vol. 49 p. 136-149 (June 1980).

Ref. 5.2-2 Thompson, T.J., and J.G. Beckerly (eds,), The Technology of Nuclear Reactor Safety,.Vol. I, the MIT Press, Camb. MA (1964).

5-4

__J