dissolution, the rinse solution must be sampled to assure that it contains < 0.1 grams fissile
(U-235 + Pu) per liter. When the pump removes the rinse from the dissolver, it will leave
approximately 100 liters of the solution, called the jet heel, in the bottom of the dissolver
tank. So if the fissile concentration is measured to be < 0.1 g/liter, then < 10 grams of
fissile material (0.1 g/liter x 100 liters) will be present in the dissolver just before the
EBR/TRR material is loaded for the first batch. This value of < 0.1 gram fissile/liter is the
criticality safety limit (CSL) for IE #3 to assure criticality safety.
If the fissile material in the previous dissolution campaign has an enrichment > 0.9635 %,
then the process operator must have dual independent sampling and chemical analysis
(blue label) to determine the fissile concentration of the last rinse prior to the EBR/TRR
material loading. The process operator must be assured that both values of the chemical
analysis of the fissile concentration are < 0.1 grams per liter in the last rinse of the
previous dissolution solution, and that this last rinse is transferred out of the dissolver (this
would leave a jet heel of approximately 100 liters) before the new liquids for the
EBR/TRR dissolution are brought into the dissolver.
Second Defense: The second sampling and analysis acts as a defense against the first
sampling and analysis producing a wrong value for the fissile concentration in the solution.
As a defense against operator error, a second individual such as a supervisor must
independently verify whether dual independent sampling and analysis was needed or not
(based on the enrichment of the material in the previous dissolution), and if it was needed,
whether dual independent sampling was done during the last rinse of the previous
dissolution campaign, whether the dual independent analysis values were both < 0.1 grams
fissile per liter, and whether the last rinse was transferred out of the dissolver. Only after
the completion of these items (as needed) shall loading of the EBR/TRR material be
Common Mode Failure (CMF) Potential: For both individuals to independently be
mistaken about the need for dual independent sampling and analysis is very unlikely, since
they would both know, or have access to information regarding the material that was
dissolved in the previous campaign. There are no other obvious CMF paths.
Evaluation and Results
Plutonium Equivalency Factor
Since the TRR and EBR-II fuel being dissolved contain both U-235 and plutonium, and Pu-239 is
more reactive than U-235, the determination of the nuclear criticality safety of the materials was
based on consideration of the equivalent U-235 enrichment This is defined as (U-235 + F x Pu ) /
(U + Pu ) wt. ≅ % U-235 + F x wt. % Pu-239, where F = Plutonium Equivalency Factor is the
effectiveness of an atom of Pu-239 in increasing the system K-eff compared to the effectiveness of
an atom of U-235.