Criticality safety assessment of tank 241-C-106 remediation Page: 69 of 83
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WHC-SD-W320-CSA-001 REV 0
Figure 5-4. Minimum Critical Areal Density.
N
d
O
.C
d
0
0
Q1000
900
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2000 10 20
R Pure Water30 40 50 60 70 80 90 100
Waste Solids (wt%)5.2.3 Neutron Absorbers
In the following discussion of the effects of neutron absorbers, two of
the most effective absorber materials (boron and cadmium) have been excluded.
Boron and cadmium are known to be present in Hanford waste tanks, sometimes in
substantial quantities in waste solids. Their absorption properties would
dominate the other absorbers such that they have been purposely excluded in
order to better defend the conservatism of the waste model. Their exclusion
adds considerable conservatism to the following discussion.
Neutron absorbers reduce the reactivity of any fissile assembly. There
is a unique minimum absorber to plutonium ratio (X/Pu) for all absorbers,
above which the system will remain subcritical, independent of any other
influences. This mass ratio is calculated for a homogenous mixture of
plutonium, absorber, and water and is applicable when the waste is
homogeneous. Since waste is sent to tank farms as a more or less homogenized
mixture, the absorber-to-plutonium ratio is a good indicator of
subcriticality. This minimum has been calculated for the various elements in
the sludge. The results are reported in Tables 5-1 and 5-2.- --- --- -- --- --- --- ---- - - --
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Waltar, A. E. Criticality safety assessment of tank 241-C-106 remediation, report, July 19, 1996; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc702698/m1/69/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.