This evaluation was completed according to procedure manual WSRC-SCD-3 "WSRC Criticality
Safety Manual" (Ref. 4). Inherent in the requirements of SCD-3 are applicable ANS standards
and DOE Order 5480.24 (Ref. 5).
Computer code calculations were not needed for this NCSE due to the low fissile enrichment of
the EBR-II and TRR fuel rods being dissolved. Since these rods contain both U-235 and
plutonium, an equivalent U-235 content and enrichment was calculated for various configurations
of these rods, which were then compared to "safe" subcritical limits (13.1 kg U-235 for < 1.0 %
enriched, and 10.0 kg for 1.01 % enriched) published in national standards and other published
criticality data. These limits of 13.1 and 10.0 kg U-235 were obtained from an optimally
moderated and reflected lattice in a spherical configurations. In general, a critically "safe"
configuration means that the calculated K = 0.95. However, for this NCSE, a critically "safe" K =
0.98 was accepted for data coming from Ref. 6 and 7 because of their wide acceptance and long
use as sources of valid nuclear criticality data. A critically safe limit of 19 MT of uranium was
also used based on KENO calculations (Ref. 1) for the actual annular dissolver geometry and
steel material in the dissolver walls.
Since the dissolution of the EBR-II bundle is the main difference from previous campaigns where
TRR rods have been dissolved, the previous double contingency analysis (DCA) for TRR rods
(Ref. 2) was used for initiating events that are common between this EBR/TRR dissolution and
previous TRR dissolution. Possible initiating events that were altered by the presence of the
EBR-II bundle in this EBR/TRR dissolution, compared to the previous TRR dissolution, include
the EBR-II bundle falling over in the dissolver, a missing insert, and double batching. The
criticality safety of these events was considered, and it was found that these events can not cause
a criticality. The only new initiating event that could be found that might cause a criticality was
starting the EBR/TRR dissolution with a significant amount of fissile material already in the
dissolver solution from the previous dissolver campaign. A criticality safety limit, and criticality
safety controls, were specified to preclude this initiating event from occurring.
Discussion of Contingencies
DOE Order 5480.24 Ref. 5) and WSRC Nuclear Criticality Safety Manual (Ref. 4) require
sufficient factors of safety so that at least two unlikely, independent, and concurrent changes in
process conditions shall occur before a criticality is possible. The protection factors shall provide
either two independent process parameter controls or multiple controls (defenses) of a single