Design and Stress Analysis of Extraterrestrial ... - The Black Vault

the fuel element's core and the temperature gradient can be a function
of the radius r of a circular fuel element or the distance from the
axis of symmetry of a flat fuel element. In this case, in the first
evaluation of strength we disregard the effect of end sections of the
core on the intensity and we find the stresses in the fuel element
at any point removed from the ends. A more precise evaluation of
thermal stresses is obtained if we take into account the deformation
of the end sections.
As a result of the temperature gradient in the core, there are
radial, circular, and axial stresses corresponding to the thermal
deformations of the core, i.e., it is in a three-dimensional stressed
state which should be taken into account in stress analysis.
To decrease the thermal stresses, cores are frequently made in
the form of peilets of fissionable material placed in a cylindrical
shell. Cracking and crushing of pellets during operation is undesirable;
therefore, temperature stresses should be checked. If the
pellet is thin-walied, it will be in a two-dimensional stressed state
and will experience loading in circular and radial directions; stresses
in the direction of the fuel element's axis will be small and are
not taken into account.
The shell surrounding the pellets of the fuel elements will be
loaded by the pi'essure cf gases given off during uranium fission.
To check the strength of the shell involves a number of calculations
concerning the strength of the reactor unit.
Then in a number of minimum calculations for the reactor the
calculation of the reactor housing and the support plate is involved.
To determine thermal stresses we shall assume that the temperature
gradient along the element of the part is known and given. Also
known are the main characteristics of the reactor material (some of
them are presented at the end of the book).
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