CA1095481A

CA1095481A - Nuclear fuel grinding reduction

Info

Publication number: CA1095481A
Application number: CA285,137A
Authority: CA
Inventors: Adam Krawczyk; Harvey R. Lee; Arnold K. Koch
Original assignee: Canadian General Electric Co Ltd
Current assignee: General Electric Canada Co
Priority date: 1977-08-19
Filing date: 1977-08-19
Publication date: 1981-02-10

Abstract

ABSTRACT OF THE DISCLOSURE
The reduction of powered substance by mill grinding in a slurry may utilize passivated iron bodies such as balls or rods. In the case of nuclear fuels containing primarily uranium material the neutral to acidic reaction of the slurry may be countered by the use of ammonium hydroxide, by means of which the viscosity of the slurry is significantly reduced so that the loading of the mill can be increased by a significant multiplier, while the relative moisture content of the resulting reduced slurry also is correspondingly reduced, to facilitate the drying thereof.

Description

109~'~81 Case 2599 This invention is directed to a powder production system, and in particular to the reduction in particle size of a normally acid slurry of uranium oxide, using a grinding mill arrangement wherein mill loading is significantly increased, and energy requirement for milling and drying are significantly reduced.
In the preparation of fabricated sintered bodies from powdered starting materials the control of particle size plays a significant role in the quality of the final product, and the cost of preparing the powder in the desired particle size range contributes significantly to the final cost of the fabricated body. The cost of powder production includes a cost factor for reducing the particle size of the powder and a cost factor for drying the powder.
In the case of milling reduction of nuclear fuel material it has been found that the normal load or batch of powder which the reduction system can handle can be dramatically increased in the order of about 200 percent, i.e. by a factor of approximately 3, by reducing the viscosit~
of the slurry while maintaining the gross liquid content thereof substantially unchanged.
Reduction in slurry viscosity is effected by the use of ammonium hydroxide. In one instance, in an attrition mill utilizing balls of low carbon steel as the grinding medium, and incorporating a slurry circulation pump to recirculate the slurry through the mill, with an initial batch load of three hundred gallons of water and five thousand pounds of uranium oxide fuel, the viscosity of the slurry within the mill was such that the capacity of the pump was reached, and the concentration of uranium oxide thus limited.
By the addition of six gallons of ammonium hydroxide, a low cost, commercially available chemical the viscosity of the slurry ,~

1095-181 Case 2599 reduced dramatically, so that a further ten thousand pounds to twelve thousand pounds of uranium oxide could be added to the system, and still handled by the pump without overloading.
Owing to the fact that the quantity of liquid is virtually unchanged, the solid to liquid weight ratio of the slurry increases from approximately 166% to upwards of 500%. Thus, in drying the slurry the weight of water per pound of slurry diminishes from 0.375 pounds per pound to the range 0.167 - 0.15 pounds per pound.
The reduction in water per pound of slurry correspondingly diminishes slurry drying costs, generally in the same order of saving i.e. at least 50% saving.
A further effect of grind reducing the oxide as a more heavily concentrated slurry is that the efficiency of grinding is enhanced using the greater slurry density, to show a saving in grinding time in the order of 10% or better, per pound of slurry, which corresponds with an energy saving of 10% in the grinding section and 50% in the drier section, with corresponding reduction in plant size or utilization, of 10% in the grinder and 50% in the dryer.
A further and most significant benefit is the reduction of water consumption required to process the oxide fuel, the water consumption improvement also being by a factor of three. Thus 3000 pounds of water services 15,000 to 17,000 pounds of uranium oxide, as compared with the former require-ment of 3000 pounds of water servicing 5000 pounds of uranium oxide. While in the past the cost of water has ~een reglected, this is no longer the case in our present ecology.
The avoidance of iron contamination in the subject process does not form a part of the present invention, being C~na.~l~ n~6~r ~5~,~3 ~
dealt with in a copending~applicationAin the name of the present inventors. However, the use of ammonium hydroxide in , Case 2599 1O~5L~81 the manner taught herein has been found to contribute significantly to the passivation of iron in component parts of the mill system.
The weight of ammonium hydroxide used comprises 1 to 4 weight % of the total weight of the charge.
In the case of grinding nuclear fuel the use of ammonium hydroxide has the particular advantage that the subsequent processing step, that of heating the reduced slurry, has the particular advantage that the ammonium hydroxide is totally decomposed and driven off from the fuel.
The slurry concentration achieved comprises 65 to 80 weight percent of UO2 in the UO2 plus H2O mixture.
In the case of other slurries it is postulated that the presence of the ammonium ion may be the root cause of the viscosity reduction, in which case it may prove possible to achieve the benefits of the invention using sources of the ammonium ion other than ammonium hydroxide in the slurry. The pH value for which significant benefit of viscosity reduction is obtained appears to lie in the range pH 9 to 12, in the case of ammonium hydroxide.
Ammonium hydroxide can be generated in-situ, at least in the case of the aqueous slurry of nuclear fuel, by bubbling ammonium gas into the slurry.

Claims

Case 2599 The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. The method of producing a powder material of reduced particle size from a slurry using attrition by abrading within a mill, comprising:
the improvement of carrying out said abrading step in the presence of ammonium hydroxide to achieve a desired particle size distribution while reducing the viscosity of the slurry to permit enhanced utilization of the process.

2. The method as claimed in claim 1 including the step of reducing the relative weight of water present in said slurry.

3. The method as claimed in claim 2 including the step of heating said abraded slurry to decompose said ammonium hydroxide.

4. The method as claimed in claim 1, claim 2 or claim 3 wherein said powder material comprises uranium oxide.

5. The method as claimed in claim 1, claim 2 or claim 3 wherein said slurry material comprises a mixture of UO2 and other oxides of uranium and/or plutonium oxide or mixtures thereof where oxides of uranium are the major constituent.

6. In a process for abrading an aqueous slurry containing uranium oxide the improvement comprising introducing ammonium hydroxide whereby the viscosity of the slurry is reduced.

7. The process as claimed in claim 6 wherein said ammonium hydroxide is added in liquid form to said slurry.

8. The process as claimed in claim 6 wherein said ammonium hydroxide is generated in-situ.

9. The process as claimed in claim 6, claim 7 or claim 8 wherein the pH value of said slurry having ammonium hydroxide combined therewith is in the approximate range pH 9 to 12.

Case 2599

10. The process as claimed in claim 6, claim 7 or claim 8 including the step of heating said abraded slurry in order to disperse said ammonium hydroxide from the said components of the slurry.