NUCLEAR FUEL RECYCLING SYSTEM

SYSTEME DESTINE AU RECYCLAGE DU COMBUSTIBLE NUCLEAIRE

English Abstract

ABSTRACT OF THE DISCLOSURE

In the processes of nuclear fuel manufacture,
scrap material such as uncontaminated reject powder
and reject pellets, which would previously have been
reprocessed chemically in conversion of the uranium
values by dissolution into liquid form, is now mechanically
reduced by crushing in a substantially inert atmosphere
and converted to a slurry having between about 70 to 85
weight per cent solids, and then attrition milled
utilizing scrap sintered UO2 pellets as the reducing
medium. Grinding swarf generated during the centreless
grinding of UO2 pellets may also be recycled provided
it is sufficiently pure.

Claims

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined
as follows:
1. The method of producing nuclear fuel comprising
retrieved nuclear fuel material selected from the group
comprising substantially uncontaminated grinding swarf,
sintered pellets and green pellet forms, including the
steps of:
(1) crushing pelleted material to fine powder in
a substantially inert atmosphere;
(2) mixing with grinding swarf and liquid to
form a slurry having a content between about 70 to 85 weight
per cent solids;
(3) adding sintered UO2 pellets as grinding
media to the slurry within a wet mill and
(4) wet grinding the slurry with the pellets in the wet
mill, to a predetermined consistency.

2. The method as claimed in Claim 1 including
the steps of drying said ground slurry to a powder, and
recycling the powder for manufacture to pellet form.

3. The method as claimed in Claim 1 or Claim 2,
wherein said slurry solids content is about 85 weight
per cent.

4. The method as claimed in Claim 1 wherein said
slurry includes the addition of clean powder UO2.


5. The method as claimed in Claim 4 wherein
said clean powder is virgin UO2.







6. The method as claimed in claim 1, wherein the
first step includes adding liquid nitrogen during the crushing
to provide an inert atmosphere, whereby the temperature of the
material is significantly reduced, to provide enhanced crushing
action.

Description

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This invention is directed to a method of
recycling scrap nuclear material, and nuclear fuel
manufactured by the process.
In the manufacture of nuclear fuel for use in
nuclear reactors, the conditions of service to which the
fuel is subject within a reactor are so demanding that very
high manufacturing standards must be met, which leads
to a comparatively high volume of reject sintered pellet
material, and the need for recycling this reject fuel
material. In addition to pelleted material, the swarf
resulting from pellet grinding also requires to be
recycled. At present sueh nuclear fuel reeyeling generally
relies upon ehemieal dissolution of uranium values into
liquid form followed by purifieation, preeipitation and
eventual powder manufaeture.
In aecordanee with the present invention, suitable
serap material may be prepared meehanieally by erushing
and milling as a high solids eontent slurry, using serap
sintered UO2 pellets as the grinding medium, to provide
powder of aeeeptable density and purity for reeyeling in a
pellet produetion line. In order to optimize utilization of
the present fuel serap retrieval system, the grinding
wheels used in initially grinding sintered pellets require
to be sueh that they do not introduee eontamination
- into the proeess (e.g. use of diamond wheels) in order
to maintain the purity of the ensuing grinding swarf, for
retrieval through the subjeet meehanieal proeess.
The use of UO2 sintered balls as the grinding
media is shown in Canadian Patent No. 656,281, Moss,
dated January 22, 1963.

Thus there is provided a method of produeing
nuelear fuel from retrieved nuelear fuel material of high


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purity selected from the group comprising substantially
uncontaminated grinding swarf and powder and pelleted
fuel, including the steps of:

(1) crushing scrap pellets to a fine powder
(2) mixing with grinding swarf and clean
and virgin powder, and adding liquid to form a slurry having
a density in the range 70 to 85 weight per cent solids;
(3) adding sintered UO2 pellets as grinding

media, to the slurry in an attrition mill, and
(4) grinding the slurry and pellets in the
mill to a predetermined consistency.

The process can include green pellet forms in the material
being treated.
The resulting ground slurry is dried to a
cake and granulated. The dried granulated powder is
recycled to a fuel pelleting line in combination with virgin
feed stock. The virgin feed stock is usually subjected to
the milling process simultaneously with the recycled
material.
In carrying out the initial step of crushing the
scrap UO2 material which is highly oxidizable, the
spraying of liquid nitrogen for purposes of providing an
inert atmosphere also serves to reduce the temperature
of the UO2 significantly, to increase its brittleness and
reduce its reactivity, thereby significantly diminishing
wear on the hammer mill while providing a substantially inert

atmosphere.
The subject process offers large savings, both
in avoidance of needless dissolution reprocessing, and
in the fact that undue handling of reject nuclear fuel
by shipping it to a distant dissolution plant is avoided,
while the dried powder that the process yields is of

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excellent size distribution and purity for use in the
pellet making process.
The step of pulverizing pelleted material can
involve the use of jaw crushers and hammer mills in a
suitably inert atmosphere, preferably using liquid nitrogen
as referred to above, with unsintered (green) pellets being
added at the hammer mill stage of reduction.
The starting materials of this process may
include any of: grinding swarf, sintered scrap, green scrap
and clean or virgin powder.
The sintered scrap is subject to a jaw crusher
operation to reduce it to a powder. The powder then
passes to a hammer mill, operated generally in a liquid
nitrogen atmosphere to which any available green scrap
(non-sintered) is added. Available grinding swarf in a
substantially non-contaminated condition is added to the
crushed material and the mixture passed to a wet mill
utilizing reject sintered fuel pellets as the reducing
media, the slurry having a high solids content, normally
: 20 in the range 70 to 85 weight per cent solids, and including
virgin fuel powder (UO2). The milled material is dried
when a predetermined consistency has been achieved, and
processed into pellets.
The virgin UO2 powder is normally added as
a component of the slurry in the wet ball mill, so that
when dried, the ball mill product is in a suitable
condition for repelleting.
In the subject process, by selection of substantially
uncontaminated materials, together with steps to substantially
preclude oxidation of the material during processing, the
need for chemical recycling can be avoided, in large measure,

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and an end product of suitable purity and appropriate
particle size distribution obtained, to facilitate
repelleting.
Significant cost savings may be effected, both in
handling and in transportation, while the nuclear fuel
inventory also is reduced, with commensurate savings.