I
L. J. MU INS, J. A. LEARY, and W. J. M RAMAN Los Alamos Scientific Laboratory, University of California, Los Alamos, N. M.
Reprocessing Plutonium Reactor Fuel
Removal of Fission Product Elements by Slagging The original preparation of reactor fuel from mineral ores is mainly the adaptation of old techniques. Quite the opposite is true of techniques used to handle and reprocess spent fuel. N e w chemical processes must be invented to separate unused fuel from fission products. Here is one of them
OXIDE
and halide slagging are two of the simpler methods proposed for the purification of spent reactor fuels (3,5-7, 70-73). I n these methods, elements which form more stable oxides or chlorides than the fissile material are removed from the fuel. A consideration of the standard free energies of formation listed in Table I shows that the following reactions should proceed satisfactorily in the direction indicated, assuming reactants and products to be in their standard states:
+ 3MgO --+ 2La + 3hfgC1, --+ 2La
+ 3Mg 2LaC13 + 3Mg
La,03
Although the reactants and products in a slagging process normally would not be in their standard states, their brhavior can be estimated qualitatively from the standard thermodynamic quantities. Thus, lanthanum (or any other fission product more electropositive than magnesium) should be removed from the molten fuel by forming a compound which concentrates in an immiscible slag phase. T h e by-product, magnesium, may be removed from the molten metal phase by vacuum melting, and the slag may be separated from the fuel by standard physical means.
Table 1. Standard Free Energies of Formation of Compounds in Order of Increasing Stability (8) (Kcal. per gram atom of anion) -AF”, - AF’, Oxides 1700’ K. Chlorides 1000° K. CsnO TeOz Ru02 Rb2O RhzO
TCOZ
KzO Sb203 In0 MoOi FeO
NbO Zr02 Mgo UOZ PUZO8
SrO yzo8
Ndz08 Cez01 La203
... 2 2
PdClz TcCL MoCla NbC13 TeCI:
6 7 8 12 17
16 20 23 25 32 36
BiCh AgCl SbCh FeCb SnCln CdCL
18 19 22 27 28
64 90 92 95 96
InCl UC1a ZrC12 MgC1z PuC13
34 53 56 58 59
101 105 106 108
Y C18 NdC13 CeCL LaCb NaCl
62 63 66 67 77
LiCl CSCl RbCl KCl SrCh BaC12
79 81 81 82 82 84
0 0
108
The composition of a t\ pica1 plutonium-rich fuel after 10% burnup is shoivn in Table 11, where the fission products have been grouped into five classes according to predicted chemical behavior. This composition was calculated from plutonium-239 fast neutron fission yields ( 4 ) because the ultimate application of plutonium as a fuel probably will be in fast breeder reactors. I n such applications. extremely high decontamination of specific fission product elements is not required, because the neutron capture cross sections a t high energy are generally low and do not have high resonance peaks.
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Table II. Composition of Iron-Plutonium Fuel after 10% Burnup Weight R after Irradiation Pu Fe A. Rare gases B. Alkali and alkaline earth elements C. Rare earths D. Refractory and “noble” metals E. “Well” elements [Cd to I]
VOL. 52, NO. 3
135 days 365 days 87.65 87.65 2.53 2.53 1.33 1.32 1.51 1.45
2.71 3.81
2.74 3.83
0.49
0.46
MARCH 1960
227
TANTALUM THERMOCOUPLE SHEATH 8 EXTENSION ROD
-A
ll
F
B-
c
4
STOPPER ROO
-G
WATER COOLED CURRENT CONCENTRATOR
A
FlSSlUM MELT
ARGON
MAGNESIA CRUCIBLE
VACUUM
INDUCTION COIL
C D
MAGNESIA LINER
ll
PYREX VACUUM
E-COPPER MOLD
A
t
E
F
L
TANTALUM DASH-POT STIRRER a THERMOCOUPLE SHEATH SLlOlNG SEAL TEFLON STOPPER QUARTZ TUBE TANTALUM CRUCIBLE TAPEREO PLUG FOR SAMPLING PORT
G SAMPLING PORT H METAL PHASE I
SALT PHASE
I
H
Various slag compositions were equilibrated with fissium melts in this halide slagging setup
4
Oxide slagging in magnesia was done in this equipment. For zirconia runs the water-cooled concentrator was omitted and a quartz vacuum envelope was used
Rare gas fission products, A, are removable by vacuum melting. The reactive elements, B, should be removable by chloride slagging, but probably are not all removable by oxide slagging. However, these are volatile a t temperatures of -1700’ K. that normally are
Table 111. Composition of Fissium and Liquated Fissium Alloys Fissium Alloy Concentration, Wt. % Element Alloy Liquated alloy
Pu
91.47 2.56 0.81 0.87 1.31 1.05 1.93
Fe Zr Mo Ru Ce
La
95.21 2.54 0.003 0.036 1.22
