26.08.2015   Advanced separation techniques for nuclear fuel reprocessing and radioactive waste treatment

Fuel dissolution

The reduction in particle size greatly accelerates the rate of dissolution. The higher oxidation state of the uranium reduces the nitric acid requirement

Table 8.2 Effect of uranium oxidation state on dissolution nitric acid requirements

Dissolution reaction(s)

HNO3

(M)

Reference

3UO2 + 8HNO3 ^ 3UO2 (N03)2 + 2NO + 4H2O

<10

9

UO2 + 4HNO3 ^ UO2 (NO3)2 + 2NO2 + 2H2O

>10

9

U3O8 + 7.35HNO3 ^ 3UO2 (NO3)2 + NO2 + 0.35NO + 3.65H2O

~8

19

UO3 + 2HNO3 ^ UO2 (NO3)2 + H2O

all

a

a Theoretical; in actual practice a very small amount of NOx is produced.

Table 8.3 Transition metal (TM) fission products in undissolved solids (UDS)

Fuel burnup, GWd/MT

18

23

31

Total UDS, wt%

0.026

0.18

0.20

Total UDS after voloxidation, wt%

0.28

0.37

0.59

% of TM elements in UDS

Zr

5a

Mo

20

Tc

50

Ru

44b

Rh

CO

CO

u~

Pd

99

a Zr is apparently from residual cladding fines.

b Prior to dissolution, 50% of Ru and Rh apparently was removed by volatilization during the voloxidation or dissolution process. Of the non-volatilized portion, 80-90% was in the UDS.

and reduces the amount of NOx evolved (see Table 8.2).919 When produced, UO3 powder dissolves readily in >0.3 M HNO3 acid with only trace levels of NOx generated.

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