because of neutron absorption in the nitrogen in the nitrate compound. When the uranium and
plutonium in the EBR-II and TRR rods are dissolved in nitric acid in the dissolver, they will be in
solution as UO2(NO3)2 and Pu(NO3)4 respectively. Since the equivalent U-235 enrichment of the
EBR-II bundle is 0.77 %, and the equivalent U-235 enrichment of the TRR rod with the highest
plutonium content (79 grams) is 1.01 °/e, fully dissolved uranium and plutonium from the EBR-II
and TRR rods can not go critical (0.77 % and 1.01 % are both less than 1.96 %) regardless of the
quantity that has been dissolved.
6.4 Conservative Assumptions
The above criticality safety analysis includes the following conservative assumptions:
1. Use of data from Ref. 6 and 7 effectively assumed a fuel rod lattice with optimum diameter
fuel rods, optimum fuel rod spacing, and optimum water moderation and reflection.
2. Use of data from Ref. 6 and 7 effectively ignored neutron leakage from the fueled ports in the
inner annulus of the dissolver. An infinite system is thus assumed.
3. The highest plutonium content (79 g) is assumed for many of the TRR rod configurations.
4. All plutonium is assumed to be Pu-239. This assumption ignores the absorption in Pu-240.
Historically, the nominal composition of plutonium in TRR blanket rods received at SRS has
been listed (Ref. 1) as 90.45 % Pu-239, 8.92 % Pu-240, and 0.64 % Pu-241, but the
plutonium composition can vary significantly depending on the location and duration of the
5. Except for the use of data from Ref. 1, neutron absorption is ignored in the stainless steel
used for the dissolver walls and inserts, and in concrete used in the dissolver and the floor.
6. Neutron absorption is ignored in the fission products, in aluminum components and aluminum
dissolved in solution, and in nitrogen in the nitric acid.
7. A conservative value of 2.0 was used for the Plutonium Equivalency Factor, to calculate the
effective U-235 enrichment.
The effect of these conservative assumptions should produce significantly greater criticality safety
margins than discussed above.
The TRR bundles will be shipped from RBOF to the F-canyon dissolver according to existing
administrative controls. These procedures (Ref. 16) allow the shipping cask to hold up to 42
TRR rods. Based on data in Table 1, an average TRR rod would contain approximately