Dissolution Process

DOE-STD-3007-93

2.4

Dissolution Process

In the first batch, the aluminum bundle and cladding will be dissolved using 50% sodium

hydroxide (NaOH), and the aluminum waste products will be transferred to waste. The U-Pu

metal will then be dissolved with nitric acid (HNO3), according to the following chemical

reactions:

U + 4(HNO3) ? UO2(NO3)2 + 2(NO) + 2(H2O)

U + 8(HNO3) ? UO2(NO3)2 + 6(NO2) + 4(H2O)

Pu + 4(HNO3) ? Pu(NO3)4 + 2H2

so that the uranium and plutonium, when they are dissolved, will be in solution as either

UO2(NO3)2 or Pu(NO3)4. The nitric acid solution present in the dissolver at the end of the first

batch will remain in the dissolver, and additional nitric acid and mercury as a catalyst will be

added to dissolve the materials in the second batch. After dissolution of the second batch is

completed, the product solution will be processed as for TRR dissolution solutions in the past.

For the third batch, the three well insert will be removed from the dissolver port, and the EBR-II

bundle DU006 and the 18 TRR bundles will be loaded into the dissolver. NaOH will again be

used to dissolve the aluminum bundles and cladding, and the aluminum waste products will be

transferred to waste. It should be noted that the individual fuel slugs in the EBR-II bundle will

fall to the bottom of the dissolver as the aluminum in the bundle and cladding is dissolved. The

0.5 inch spacing of the slats at the outer bottom of the charging crib will restrict pieces of the

EBR-II fuel from escaping the inner annulus of the dissolver until most of the fuel has been

dissolved. After the aluminum solution has been removed from this third batch, nitric acid will

again be used to dissolve the U-Pu metal. At the start of batch 4, the three well insert is replaced

into the dissolver port, and the 21 TRR bundles are loaded into the four ports. Nitric acid and

mercury as a catalyst will be added to the solution remaining from the third batch to dissolve all

the materials of the fourth batch. When these materials are all dissolved, the product solution will

be processed as for TRR dissolution solutions in the past.

During each batch discussed above, nitric acid in excess of that required to dissolve the uranium

and estimated aluminum will be added to the dissolver to minimize the possibility of acid deficient

dissolver solution causing plutonium polymerization. After the nitric acid is added to the

dissolver, the solution is heated to its specified temperature range and maintained there until

dissolution is complete. During the dissolution, the specific gravity is monitored, and at the end

point, sampling is used to calculate the concentration of the uranium and plutonium that is

present. A material balance is then done to confirm the completeness of dissolution before

subsequent charges are made. In the event that a significant discrepancy (> 10%) exists between

the known mass of the material charged and the measured mass in the solution, the dissolver will

be probed using the probing device, and an additional dissolution cycle (without additional fissile

charges) will be made.

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