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5 e PRESENT STATUS OF THE INVESTIGATION OF
=

AQUEOUS SOLUTIONS SUITABLE FOR USE
IN A THORIUM BREEDER BLANKET ]

M. H. Lietzke
W. L. Marshall

P. S. BAKER, ORNL/CO

 
  
 

 

LD 13 EXENYY FROML DOR 1579 S#VIEW ORL

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OAK RIDGE NATIONAL LABORATORY

OPERATED BY

CARBIDE AND CARBON CHEMICALS COMPANY

A DIVISION OF UNION CARBIDE AND CARBON CORPORATION

(T3

POST OFFICE BOX P
OAK RIDGE. TENNESSEE

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- ORNL 1711

 

This document consists of 13 pages

Copy 4f'of 179 copies Series A

Contract No W-T4tO5-eng-26

PRESENT STATUS OF THE INVESTIGATION OF AQUEOUS SOLUTIONS

SUITABLE FOR USE IN A THORIUM BREEDER BLANKET

M H Lietzke and W L Marshall

DATE ISSUED

MAY 19 1954

OAK RIDGE NATIONAL LABORATORY
Operated by
CARBIDE AND CARBON CHEMICALS COMPANY
A Division of Union Carbide and Carbon Corporation
Post Office Box P
Ozk Ridge, Tennessee

 

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Present Status of the Investigation of Aqueous Solutions Suitable for Use

1n a Thorium Breeder Blanket,

 

M H ILietzke and W L Marshall

Oak Ridge National Laboratory
Oak Ridge, Tennessee

Abstract

 

The present report summarizes the work that has been done in the search
for an aqueous solution suitable for use in a thorium breeder blanket  Some
of the work has been previously reported in HR P and Chemistry Division
Quarterly Reports, but data concerming the basic nitrate system and the
phosphate-mitrate system are reported here for the first time, It has been
felt desirable to summarize all the work in this report so that an

overall-picture may be had of the exploratory work that has been done to date
Thorium Nitrate=ljJater System

 

The system thorium mitrate-=water has been studied by Templeton(l) from

20° ¢ to 160° ¢ and by Marshall, Gill, and Secoy(z) from 20° ¢ to 211° ¢

above 130° C mitrogen oxides are liberated and basic thorium oxade 1s preci=
pitated However, in a closed system the vapor phase appears to equilibrate
with the liquid phase, and the system in this form does not show precipitation
until a temperature of about 230o ¢ 1s reached for systems containming 80-90%
thorium nitrate by weight The experimental data indicate that a solutaon of
thorium nitrate containing 1000 g Th/1l wall be stable in the temperature range
120° ¢ to 230° ¢ and that solutions containing lower concentrations of thorium

will be stable from room temperature to the 100-230° ¢ Trange,

Effect of Excess Nitric Acid on the Thorium Nitrate-Water Systems

 

Marshall and Secoy(B) investigated the effectiveness of excess mitric
acid 1in preventang hydrolysis of thorium nitrate solutions at high tempera-
tures, Solutions with NO3/Th ratios of 3 95, 5.47, and 6 65 were prepared
1n concentrations that varied from 20 to LOO g Th/l, The first mole of
excess nitrate caused the greatest elevation in precipitation temperature,
while the vapor phase coloration was much greater per unit change of mitrate
after the imtial four moles were added to the thorium, Crystalline solids
appeared 1n the concentrated regions, the composition of which may have
corresponded to acid salts The crystalline compounds were reversible in
solubility over the time of the experiments as contrasted to the apparent
irreversibility in the solubility of the hydrolysis products Solutions
containing 400 g Th/L with N03/Th ratios of 5e47 and 6 65 were stable to

temperatures between 300 and 340° Ce
 

-3 =

Effect of Excess Base on the Thorium Nitrate-gater System

 

A series of experiments was performed by Lietzke and Marshall to determine
whether solutions in which the thorium had been partially hydrolyzed would be
stable at higher temperatures, The partial hydrolysis was accomplished 1in two
ways (1) by the addition of L10H to a stoichiometric thorium nitrate solution,
and (2) by precipitating thorium hydroxide and dissolving the precipitate
in less than the stoichiometric amount of mitraic acad,

Table 1 shows the results obtained with thorium nitrate solutions that
had been partially hydrolyzed by the addition of InOH The effect of fluoride
both on the partially hydrolyzed and on the stoichiometric thorium mitrate

solutions 1s also shown The rate of heating i1n each case was 2,5° C/mine

Table 1

Precipitation Temperatures of Thorium Nitrate Solutions to Which Iathium

 

Hydroxade and Iathium Fluoride Have Been Added,

 

 

Thoriunm _
Concentration N0§/Th OH /Th F~/Th Observations

 

Loo g Th/1 L 1,8 0 Cloudy at 210° ¢, abundant
ppt at 2380 Ce

 

 

 

 

b 1.8 1 Abundant ppte between 180°
and 188° ¢

L 1 1 Ppt at 225° C.

Ly 0 1 Some particles at 260° ¢,

much cloudiness at 26L4° C,

 

L 0 1.8 Cloudy ppt at 2L8° C.

 

 

 

 

 

None of the precipitates redissolved upon cooling to room temperature.
 

-l -

The second method of preparing partially hydrolyzed thorium mitrate

solution consisted i1n precipitating thorium hydroxide from diluted aliquots

of thorium nitrate solution by saturation waith ammonia gas  The thorium

hydroxide was washed by centrifugation and decantation, then dissolved in

sufficient concentrated nitric acid to give a N03/Th ratio of 2 2, The thorium

concentration was varied from 200 g Th/1 to 1000 g Th/l, Table 2 summarizes the

data obtained upon heating these solutions at temperatures of 70° ¢ and 80° Ce

Table 2

Precipitation Temperatures of Thorium Nitrate Solutions With a Hydroxyl

 

Number of 1 8

 

 

 

 

 

 

 

 

 

Thorium Concentration Tempo ° ¢ Observations
200 g/1 70 No ppte 1n 2L hrs,
80 Ppte after 3 hrs
400 g/1 70 Ppte 1n 2l hrse
530 g/1 70 No ppt in 24 hrs.
80 Cloudy after 3 hrs.
Ppt after 2L hrs,
800 g/1 70 No ppte 1n 2l hrs,
80 Cloudy after 2L hrs
Ppt after L8 hrs,
1000 g/1 70 Ppt after 1} hrs,

 

 

 

In all cases the precipitates did not redissolve upon cooling to room

temperature, When HF was added to the solutions to give a F/Th ratio of

1,0 precipitation occurred upon standing at room temperature The precipi-

tate would not redissolve upon heatinge
 

ThO,=H3P0) ~Ho0 System

 

The marked solubilaity of ThOs or Th3(POh) in concentrated phosphoric
acid and the low neutron cross-=section of phosphorus favor the consideration
of the Th02“H3P0h system as a possible breeder blanket solutlon(h),

Although apparently stable phosphate solutions containing up to 1100 g Th/1

with PO)/Th ratios of 5 to 7 could be prepared, the high viscosities of these
solutions leave considerable doubt as to their applicability. However, solutions
containing a Poh/Th ratio of 10 with a total Th concentration of 40O g/l are
stable at 250°-300° ¢ and have a viscosity little higher than that of
concentrated phosphoric acid,

A series of experiments was performed(s) in an effort to lower the
viscosity of the thorium phosphate solutions containing the Poh/Th ratios of
5 to 7 without at the same time decreasing the thorium concentration. It
was found that some concentrated hydrofluoric acid can be added to the
concentrated H3P0), mixture but that precipitation occurs before any signifi-
cant improvement in properties becomes evident, dissolving ThFh 1n H3PO),
appears to give a simlarly viscous mixture at PO)/Th ratio of 5. Solutions
in HoPO3F seem to act simlarly to those in H3PO), with no improvement in
solubility or viscosity. Adding HpS0) to HBPOh”ThB(POh)h mixtures lowers
the solubility under otherwise similar conditions and appears to offer no

advantages,

The Th0p-H3PO),~HNO3 System

 

Table 3 summarizes data obtained by Marshall in a study of the

thorium=phosphate-nitrate systems
 

-6 =
Table 3

Thermal Phase Stability of the Th02=H3POh—HNO3 Systen

 

 

 

Molarity | Molarity | Molarity | Mole Ratio After 1 1/2 weeks at
H4PO), HNO4 ThO) Th/P0),/N03 125-150° ¢
560 S0 560 1/1/1 Completely solid (white)
540 5,0 265 1/2/2 n m "
540 540 1,67 1/3/3 Ca 95% u n
10,0 5.0 500 1/1/2 Completely " 0
10,0 50 25 1/2/4 Ca, 607 n "
10,0 5.0 1 67 1/3/6 Ca 1% " n
Te5 205 265 1/1/3 Completely "
765 265 1,25 1/2/6 Cao 90% n "

 

 

 

 

 

From the data in Table 3 1t appears that the Tho?"HBPOh"HNOB system 1s
stable at elevated temperatures only in the presence of concentrated H3PO), e
Tn all cases the precipitates dad not redissolve upon cooling to room

temperature

Thorium Systems Involving S0) and F‘(S)

 

Prelimnary results on dissolving Th(OH)), 1n an HF-HpS80) mixture, containing
one HF and one and one half HpS0), molecules per molecule of Th(OH)h indicated
a "solubility" of about 200 g Th/l. (There was evidence for the presence of
a colloid,) Immediate dissolution occurred followed by slow precipitation.
Changing the F“/Sohz/Th(IV) ratios while maintaimng stoichiometric neutrality
showed no improvement in solubility. It was also found to be impossible to
prepare similar solutions containing higher concentrations of thorium (LOO and

600 g Th/1l)s The pH of all the supernatant solutions indicated that some
 

-7 =

hydrolysis occurred during the precipitation A solution made up to contain
50 g Th/1 as the nitrate plus one mole of HF, one of HNO3s and one and one half
of HpS0), per mole of thorium showed some precipitation on standing a few days.

No hydrolysis would be expected to occur in this solution,

Thorium Systems Involving 5°h=s Seohz, L1+, and Mg**,

 

A large mumber of exploratory tests with various combilnations of thorium
sulfate or thorium selenate with lithium and magnesium salts of the same anions
have indicated

(1) The addition of the lithium or magnesium salt increases the solubility
of the thorium salt at 25° ¢ but not to a very great extent, The maxamum
ampunt of thorium that can be kept in solution 1s of the order of 100-150 g Th/1l,

(2) 1In all cases thorium selenate 1s more soluble than the sulfate,
but not sufficiently more so to compensate for the higher neutron cross=section
of selenium,

(3) At temperatures above 100° ¢ the solubality of the Th salts decrease
rapidly The formation of precipitates and their dissolution at room
temperature are both slow, There 1s a strong possibility that the "solutions®
at 250 C are actually metastable and that, in time, mich of the thorium would
precipitate

(4) At L3° ¢ a solution of thorium sulfate may be prepared containing
19 g Th/1000 g Hy0 This 1s the maximum solubility of thorium sulfate in

water.
 

-8 =

Conclusions
(1) of the systems investigated only two, the Th(N03)h'¥ excess HNO3
and the ThyPO))), * H4PO) with a PO),/Th ratio of 10, have both the necessary
thermal stability and desirably low vaiscositye
(2) From the standpoint of neutron capture cross=-section the ThB(POh)3 -
H3PO), system 1s perhaps satisfactory 1In the case of the Th(No3)h system
A

separated le 1sotope would have to be used, Ekwv?ffl w f !
{

(3) There 1s no present evidence that corrosion in the mitrate system ‘l

would be intolerable However, the phosphate system attacks both Ti and Zr
at relatively low temperatures and no satisfactory container 1s yet known
for this system A more thorough study of the corrosion properties of the
solutions should be made,

(4) The radiation decomposition of mitrate (including the products
formed under varying conditions) appears to be the most important unknown
concerning the nitrate system, A preliminary experiment by Bidwell of
Los Alamos using a uranyl phosphate = H3PO), solution containing enriched U235
in the:}ITR showed no gross decomposition of phosphate 1om.

(5) whenever hydrolytic phenomena seem to be responsible for precipitation
1n thorium systems the time factor 1s very important. Solutions which seem to
be stable at higher temperatures on short time heatipg usually show precipl=
tation upon being held at much lower temperatures for a longer period of time.

(6) on the basis of the rather extensive survey that has been made 1t
seems unlikely that amy thorium systems other than the two mentioned will be
found that satisfy both the thermal stability and low neutron capture cross-
section requirements, However this statement camnot be made with certainty

unless a thorough phase study 1s made of some of the systems investigated,
 

-9 -
References
(1) C Templeton, AECU-=1721 (1950).

(2) W L Marshall, J S Gill, ¢ H Secoy, H ReE Quarterly Progress Report
for Period Ending Nove 30, 1950, ORNL-925, p 279

(3) W Lo Marshall and C He. Secoy, HeReP Quarterly Progress Report for
Period Ending Oct. 31, 1953, ORNI~1658, pp. 93-96.

(4) P A Agron and W L Marshall, Chem Div Semiannual Progress Report
for Period Ending June 20, 1953, ORNL-1587, pp 90-93.

(5 P A Agron et al, HR P Quarterly Progress Report for Period Ending
July 3]-, 1953, 0RNL"16059 PPe 128-130,