18.08.2015   NUCLEAR CHEMICAL ENGINEERING

Physical Properties of TBP and Its Mixtures with Hydrocarbons, Water, and Nitric Acid

The general use of TBP as extractant in reprocessing nuclear fuel is due to its selectivity for the actinides, its reasonably good stability against radiolysis and reaction with nitric acid, its nonflammability, and its ready availability at low cost. Because its density is close to water’s and because of its high viscosity, for reprocessing TBP is diluted with a less dense, less viscous hydrocarbon. The diluents most inert to nitric acid and radiation are straight-chain paraffins. The diluent now usually chosen is a mixture of normal paraffins, mostly n-dodecane, because it is commercially available and provides a reasonable compromise between the desired low viscosity and high flash point. Maximum capacity of pulse columns is obtained at TBP concentrations between 20 and 30 v/o, the composition usually used in processing irradiated natural or slightly enriched uranium. TBP concentrations in the range of 2.5 to 7.5 v/o are used in processing fully enriched uranium or plutonium as one of the measures to avoid criticality.

Physical properties of pure TBP have been given in Table 4.5. Physical properties of n-dodecane and a 30 v/o solution of TBP in n-dodecane are summarized in Table 10.13.

When TBP and a hydrocarbon such as n-dodecane are mixed, a slight volume increase takes

Table 10.11 Concentrations in extracting section, uranium decontamination unit 2D

Stage number, n

1

2

3

Aqueous concentration, mol/liter

yE _ rE , E e f " 1 S+Fyn~l

HN03, Хн, п _

1.658[30] [31]

2.264

1.891

U02(N03)2,x§,n

0.01864*

0.2990

0.924

Ruthenium (Сі/liter), r|Ui„

0.1560*

0.1835

0.1570

Distribution coefficient HN03,DH „ (Fig. 10.14)

0.17

0.048

~0.026

U02(N03)2,Du,„ (Fig. 10.13)

7

1.41

~0.51

Organic concentration, mol/liter HN03,ygtn=DH,«xg,„

0.282

0.1087

0.0492

U02(N03)2, yi, n = — Du. n^u. n

0.1305

0.4216

0.47

Ruthenium

Distribution coefficient, DRu „ From Fig. no.:

10.9

10.8

10.8

Value

0.082

0.0026

0.0031

Organic concentration, Ci/Iiter

^Ru, n “^Ru, n*Ru»n

0.0128

0.00048

0.00049

* Given concentrations.

Table 10.12 Concentrations in scrubbing section, uranium decontamination unit 2D

Stage number, m 1_____________ 2_________________ 3^

Organic concentration, mol/liter

Ут = Уі + 1 “ 4)

E

HN03, Уц, т

ио2(мо3)2,Дт

0.02*

0.38*

0.0676

0.442

0.256

0.447

Ruthenium (Сі/liter), ><RUim Assumed distribution coefficient

0.0000174+

0.000302

0.0112

HN03,DH, m

0.055

0.060

0.044

0.042

U02(N03)2,DUim Aqueous concentration, mol/liter

0.90

0.90

0.93

0.97

HN03, xfi>m =’•

U02(N03)2, xfj m =9’U, m/-DU, m Distribution coefficient, from figures

0.364

0.333

1.536

1.609

0.422

0.422

0.475

0.456

HN03,DH, m (Fig. 10.14)

0.058

0.060

0.042

0.042

U02(N03)2, Du. m (Fig. 10.13) Ruthenium, D^u. m (Fig. 10.8) Aqueous ruthenium concentration, Ci/liter

JRu, m = ^Ru. m/^Ru. m

0.90

0.90

0.0090

0.00193

0.94

0.97

0.0040

0.076

place. For TBP contents between 15 and 45 v/o, the increase is about 0.2 percent of the volume of the separate constituents. In precise work it is thus necessary to specify whether v/o TBP is referred to the sum of the volumes of the separate constituents or to the mixture, as is done in this text. Then, the molarity of TBP is related to its volume percent by

The viscosity t? of mixtures of TBP and hydrocarbons is given within 20 percent by

log Vmix = v log r? TBP + (1 — u) log т? нс (Ю.6)

where и is volume fraction TBP.

The mutual solubilities of water and TBP-dodecane mixtures are given in Table 10.14. The volume change when water dissolves in TBP-dodecane mixtures is negligible.