Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966. Page: 16 of 47
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temperatures have given rise to internal tearing which has produced a gross
over-all enlargement of the fuel core diameter but has not created the longi-
tudinal type of split which was observed in the early fifties.
The impact of these reactor problems upon the fuel preparation sites was the
establishment of the following goals as the targets considered essential for
satisfactory uranium metal fuel performance:
1. The uranium structure should be as nearly random in crystal
orientation as possible.
2. The grain size resulting from heat treatment in the beta phase
should be as small as possible.
3. The uranium metal should be chemically as pure as possible and
should have a minimum quantity of nonmetallic compounds such as
oxides, nitrides, and hydrides.
4. Carbon introduced in the uranium ingot during the remelt of
derby and recycled scrap and existing almost entirely as
particles of UC was considered quite necessary (in the minds of
some) for achievement of fine grain size (but without effect
on this property in the views of others).
5. The hydrogen content of the uranium cores after beta heat
treatment should be less than 2 ppm to avoid generation of any
porosity in the aluminum-silicon braze layer between the
uranium and the aluminum cladding.
EARLY DEVELOPMENT EFFORTS AT MCW
The activities at the Uranium Division of MCW in the early fifties were directed
toward means of achieving improved purity of uranium metal and innovations in
heat treatment procedures which might be effective in attaining finer grain size.
The production of cast uranium ingot at the Destrehan Street Plant in St. Louis
was essentially on a virgin heat basis, the only recycle scrap being portions
of ingots rejected for surface imperfections. The cleanliness of these ingots
was therefore directly related to the condition of the derbies which made up
the charge. Experiments with various methods of cleaning the derby surfaces
such as pickling in nitric acid and sand- or shot-blasting gave evidence that
the quantity of stringers and striations of inclusions to be found in the final
core blanks could .be greatly reduced by such practices. This effect was due to
elimination of the appreciable amount of oxide and magnesium fluoride slag
which normally adhered to the derby. surface. Such improvements in metal
cleanliness gave improved yields in final inspection of the finished cores but
could never be positively identified as a source of specific improvement in
behavior under irradiation.
A study during this period of the chemical compositional gradients existing
within the derbies showed that beneath the external skin -the derby metal was of
extremely high purity and that if the outer surface layers amounting to perhaps
1/4 inch in depth should be removed by machining, a source of high purity metal
.v. FI L
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Fellows, J. A. Seven Years of Uranium Alloy Development at Weldon Spring, 1959/1966., report, January 1, 1966; Weldon Spring, Missouri. (https://digital.library.unt.edu/ark:/67531/metadc1033773/m1/16/: accessed March 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.