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

qv2'0, .35. - 09.2.3. 1 (,-f)/ 2
S i - 1.0-3 .10 daN/m 2 .
This example shows that significant thermal stresses arise with
comparatively small dimensions of the fuel element rod.
Naturally an increase in the dimensions of the fuel element
increases its thermal loading and can cause stresses which exceed
the yield point. In this case, calculations should be performed
with allowance for plastic flow.
The physical picture of the stressed state will be as follows.
Since the stresses exceed the yield point, plastic flow of the
metal will occur in the fuel element core, due to which plastic
deformations will appear and the excess thermal stresses will be
relaxed. When the heat-releasing element is cooled, there will
appear, in its core residual stresses of opposite sign which can also
be called metal flow if the yield point is exceeded. Since the
temperature field is axisymmetrical, the form of the fuel element
remains unchanged, but its rupture resistivity will be weakened due
to the cyl Lc nature of thelloading.
In each individual case the stress level is determined by the
degree of the fuel element's thermal intensity N Y. In low-power
unstressed ieactors N < 1 kW/kg. After finding
0
ar o0, c
", the
strength of the fuel element core should be evaluated from formula
(1.23)
where
0 Imat
oi=