Method of producing high-purity metal member

A high-purity metal member is produced by charging raw material such as sponge zirconium into a cavity of a mold such as a hearth under a vacuum atmosphere; irradiating the material with electron beams to melt it at a limited area of the cavity while forming a molten metal pool and irradiating the pool with the electron beam thereby elevate the molten metal pool to evaporate away impurities therein; and shifting the mold relative to the electron beams to provide a high-purity metal member. The metal pool is limited in its size and irradiated high energy density electron beams so that the temperature is raised whereby the impurities are easily evaporated away. The mold may have an annular cavity. In case of high-purity sleeve formation, the electron beams are irradiated onto the raw material while rotating the mold so that melting and solidification appear in a circumferential direction to be repeated. The impurities are repeatedly exposed to the electron beams.

BACKGROUND OF THE INVENTION 
This invention relates to a method of producing high-purity metal members. 
More particularly, it relates to a method of producing members used for 
lining composite fuel cladding tubes in a nuclear reactor. 
The fuel cladding tubes used in a nuclear reactor must have an excellent 
corrosion resistance, be non-reactive and conduct heat well, have high 
toughness and ductility, and have a small neutron absorption 
cross-section. 
Zirconium alloys are widely used for fuel cladding tubes, because they meet 
these requirements. 
Fuel cladding tubes made of a zirconium alloy can function very well under 
steady conditions, but when a great change takes place in load of a 
reactor there is the danger that they are subject to corrosion or stress 
cracking, and resultant breakage, because of the corrosive action of 
iodine gas released from the nuclear fuel pellets contained in the tubes, 
or the stresses generated by the expansion of nuclear fuel pellets. 
In order to prevent such stresses or corrosion cracking in fuel cladding 
tubes, a barrier made of one of various metals is provided between each 
cladding tube and the nuclear fuel pellets therein. With cladding tubes 
made of a zirconium alloy, these tubes are lined with pure zirconium which 
acts as a metal barrier, which is disclosed in Japanese Patent Laid-Open 
Publication No. 54-59600/1979. This is because the pure zirconium lining 
is capable of remaining more flexible than zirconium alloys during neutron 
irradiation, and has the effect of reducing local strains produced in the 
zirconium alloy cladding tube to prevent stresses and corrosion cracking. 
Experiments performed by the present inventors, however, have disclosed 
that the zirconium liner must be of an extremely high purity to maintain 
sufficient flexibility during neutron irradiation. In particular, when 
used under high-burning conditions, such a zirconium liner must have the 
purity of crystal-bar zirconium, particularly its low oxygen 
concentration, to produce the above effects. When the purity is of the 
sponge zirconium order, a liner can not provide the desired effects, 
because the degree of hardening due to irradiation is too high. 
The crystal-bar zirconium can be obtained by iodinating sponge zirconium 
and subjecting the resulting iodide to chemical vapor deposition to form 
zirconium crystal bars. With this method, the reaction speed of the 
formation of zirconium by the thermal decomposition of zirconium iodide is 
extremely slow, and is therefore unsuitable for mass production. Thus, 
zirconium produced by this conventional method is very costly. 
A vacuum arc furnace, a resistance-heating furnace, an electron-beam 
furnace, a plasma-arc furnace, or the like, is generally used for melting 
metals such as Zr, Ta, Nb, Ti, W, or Mo. The melting method which has the 
best refining effect is an electron-beam method in which the metal is 
melted in a high vacuum. 
In the conventional electron-beam melting method, electron beams are 
applied to the metal material to melt it, and the molten metal which pools 
at the bottom of a crucible is drawn downward while being cooled. 
According to this method, low melting point impurity elements in the melt 
can be evaporated away, but impurities with low vapor pressures, such as 
oxygen, cannot be removed adequately. 
Japanese Patent Laid-open Publication No. 56-67788 (1981) discloses a 
method of forming a nuclear fuel cladding liner by the electron-beam 
melting method. The publication describes, at page 3, left column, lines 
19 and 20 and right column, lines 1 and 2, that a columnar ingot of 50 mm 
diameter, 500 mm length is formed by using a sponge Zr as a raw material 
and repeating electron beam melting of it twice in a vacuum atmosphere of 
3.0.about.8.0.times.10.sup.-5 torr. From this description, it seems to use 
a rod melting method wherein members to be melted or a columnar ingot is 
disposed over a cavity and irradiated with electron beams to melt it, and 
the molten metal drops into the cavity thereby to form a purified columnar 
ingot. The rod melting method requires very great energy density to refine 
the sponge Zr. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a method of producing high-purity 
metal members such as Zr members by effectively elevating molten metal 
temperature under a vacuum atmosphere so as to evaporate impurities away 
from the molten metal. 
Another object of this invention is to provide a method which is capable of 
continuously producing high-purity metal sleeves by effecting melting and 
solidification of a metal such as Zr, Ta, Nb, Ti, W, or Mo in a horizontal 
plane, while continuously degassing and refining. 
The present invention resides in a method of producing high-purity metal 
members comprising the steps of charging a raw material to be melted of an 
active metal such as zirconium, tantalum, niobium, titanium, tungsten, or 
molybdenum into a mold cavity under a high-vacuum atmosphere, irradiating 
the material on a solid member with a heat source with a high energy 
density, and melting and solidifying the material in the mold by 
relatively moving the molten portion to the heat source to continuously 
form high-purity metal crystals. 
According to an aspect of this invention, a commercially available metal 
powder containing a relatively large amount of impurities, for example 
sponge zirconium powder, can be charged into a sleeve-shaped or annular 
mold cavity under a vacuum atmosphere and irradiated with a heat source of 
a high energy density, such as electron beams, and melting and 
solidification of the material are repeated to appear in a circumferential 
direction while moving, in the circumferential direction of the mold 
cavity, the mold or the heat source to be directed to the material so as 
to effect repeated degassing and refining reactions and thus accumulate 
high-purity zirconium crystals. 
According to another aspect of the invention, sponge zirconium is charged 
into a hearth mold, and irradiated with electron beams to form a molten 
metal pool so that the molten metal is irradiated to raise its temperature 
as well as the raw material. The hearth mold is gradually shifted to form 
a zirconium member of high purity.

PREFERRED EMBODIMENTS OF THE INVENTION 
The principle of the degassing and refining reactions in an aspect of this 
invention will now be described taking a sleeve formation method for 
instance. 
FIG. 1 and FIG. 2 are a plane view and a longitudinally sectioned view for 
explaining the degassing and refining of zirconium by repeated melting and 
solidification of a material in an annular mold cavity. Reference numeral 
1 denotes a mold provided with an annular cavity 2 which is maintained 
under a high vacuum. The annular cavity may be a sleeve-shaped one. An 
irradiator 3 for irradiating a high energy-density heat source such as 
electron beams and a chute 4 for charging the material to be melted are 
provided above an opening 2a of the mold cavity 2, at suitable positions. 
A zirconium seed material 5 is laid on the bottom of the mold cavity 2. 
To produce a zirconium sleeve using the mold 1, the mold 1 is first rotated 
in the direction of the arrow a while a predetermined quantity of raw 
material 6 is continuously poured into the mold cavity 2 from the chute 4, 
and when the rotation of the mold has reached half-way, electron beams 3a 
are applied toward the bottom of the cavity 2. This operation is repeated 
to effect repeated melting and solidification of the material, so that a 
high-purity zirconium sleeve can be produced. 
The process of this invention will now be described in detail. An aspect of 
the present invention is characterized in that (1) the raw material is 
charged into a mold cavity 2 and is rotated therein relatively to a heat 
source directed to the material, and (2) the relatively rotating raw 
material 6 in the cavity 2 is irradiated at least one part thereof with a 
heat source so as to melt on a solid member. According to this process, 
the raw material melts each time it is exposed to a heat-source spot and 
then solidifies until it reaches the next irradiation site within one 
rotation of the mold 1. This repetition of melting and solidification 
increases the purity of the molten metal, and a layer of high-purity metal 
is accumulated in a ring shape. 
FIG. 3 is a section taken along the line III--III of FIG. 1, showing how 
the material solidifies just after passing an irradiation site of an 
electron beam 3a. A molten portion 7 thereof cools as temperature 
gradients are formed toward the mold 1 and the surface of a solidified 
layer 10, and high-purity crystals are produced from the inner surface of 
the mold 1 and the surface of the solidified layer 10 to form a columnar 
structure 11 orientated toward the center of the cavity where the 
temperature is highest. A melt with a high impurity concentration remains 
in the final portion of a melt pool 12, and this melt portion solidifies. 
In this way, a zirconium portion which has a high impurity concentration 
gathers at the surface, so that the zirconium portion with a high impurity 
concentration is repeatedly exposed to irradiation from the high energy 
density heat sources to melt and the mold cavity 2 is maintained at a high 
vacuum during this operation, so that the impurities in the zirconium are 
gradually evaporated away. 
FIG. 4 is a longitudinal section taken along the line IV--IV of FIG. 1, 
illustrating the condition at the completion of solidification of the melt 
pool 12 which has passed an irradiation heat source 3. In this stage, a 
new high-purity layer 13 (corresponding to the columnar crystal structure 
11 of FIG. 3) has been formed on the layer 10 which has been formed on a 
layer 9, formed on a layer 8, and a solidified layer 14 of a high impurity 
concentration is formed on this layer 13. More material (powder) 6 is 
supplied on top of this solidified layer 14 to enable the sequential 
formation of a sleeve-shaped laminate. 
Two or more independent heat sources of high energy density can be employed 
around the circumference of the mold to irradiate the raw material so that 
a molten portion produced by one of the heat sources is solidified by the 
time of irradiation with another heat source. 
As described above, the present invention provides a novel method of 
producing a metal sleeve by continuously laminating high-purity metal 
layers. 
Various different heat sources such as vacuum arcs, plasma beams, laser 
beams, electron beams, etc., can be used in this invention, but it is 
essential that the heat sources are capable of effecting irradiation under 
high-vacuum conditions and have a high energy density, so that electron 
beams are most preferred. The higher the energy density (output/beam area) 
of a heat source, the more desirable it is for evaporating away 
impurities. After examining the effect of energy density on the effective 
reduction of impurities in metals such as Zr, Ta, Nb, Ti, W, and Mo, the 
present inventors have determined that an energy density of at least 50 
W/mm.sup.2 is necessary to achieve the desired effect. 
EXAMPLE 1 
An embodiment of this invention will now be described with reference to 
FIGS. 5 and 6. 
In FIG. 5, a water-cooled upper mold 20 comprises mainly three parts, that 
is, an outer mold 21, an inner mold 22 and a base plate 23. The outer mold 
21 is water-cooled and has a cylindrical inner face. The inner mold 22 is 
water-cooled and has an outer cylindrical face. The outer mold 21 and the 
inner mold 22 are disposed coaxially with a spacing therebetween to form 
an annular cavity 24. The base plate 23 forms the bottom of the cavity 24. 
In the cavity 24, a seed metal member 25 of Zr is disposed. An electron 
gun 26 is provided over the cavity 24 to irradiate electron beams 26a on 
the seed metal member 25 and a material to be melted. A chute 27 is 
provided over the cavity 24 at a position angularly spaced from the 
electron beam passage to feed a raw material 28 to be melted into the 
cavity 24. 
As apparent by referring to FIG. 6, these parts are disposed in a vacuum 
chamber defined by a casing 30. The casing 30 comprises two separable 
parts, that is, an upper casing 31 and a lower casing 32. The upper and 
lower casings are airtightly joined at flanges 33. 
The mold 20 is provided with a mechanism for rotating about the axis 
thereof to make a relative rotational movement between electron beams 26a 
and a sleeve to be formed of a raw material 28 being fed into the cavity 
24, and a mechanism for drawing a solidified metal sleeve 29 downward. 
Namely, the outer mold 21 is supported by a cylindrical support 34 the 
lower end of which is provided with rollers 36 to roll on a rest 35 guided 
by a guide 37, secured to the rest 35. The upper portion of the support 34 
also is guided by roller 41 secured to the lower casing 32. The base plate 
23 is rigidly connected to a connector 43. The connector 43, which is 
ring-shaped and has an annular recess, is slidably inserted in a vertical 
groove formed in the support 34. In the recess, a roller 46 is disposed. 
The roller 46 is connected to a hydraulic cylinder 44 by a connecting rod 
45. The cylinder 44 actuates the base plate 23 upward or downward while 
allowing it to rotate. The inner mold 22 is supported by a ram 47 with a 
key-like projection 48. The ram 47 passes through the base plate 23 to 
move freely in a vertical direction, but not to rotate because of 
restriction of the key-like projection 48. 
The lower end of the ram 47 is rotably supported by a bearing 49 secured by 
the rest 35. The cylindrical support 34 is rotated by a motor 40 through a 
pinion 39 provided on the motor 40 and a ruck 38 secured to the support 
34. The rotation is transferred to the base plate 23 through the connector 
43 and to the rod 47 by the key-like projection 48. Thus, the mold 20 
comprising the inner mold 21, the outer mold 22 and the base plate 23 is 
to be rotated by the motor 40. The metal sleeve 29 of solidified metal 
layer is gradually lowered by means of the hydraulic cylinder 44 while 
allowing the mold 20 to rotate. 
The material being worked is supplied at appropriate timing through the 
chute 27. 
Using the apparatus described above, Zr sleeves were produced continuously 
according to the process of this invention. 
Commercially available zirconium sponge used in nuclear reactors was used 
as the raw material. Table 1 shows the various melt conditions, for the 
electron beam (output and energy density), rotational speed of mold and 
descending speed of ram (drawing-out speed), used in the production. 
TABLE 1 
______________________________________ 
Energy Rotational 
Descending 
Run Output density speed speed 
No. (kW) (W/mm.sup.2) 
(rpm) (mm/min) 
______________________________________ 
1 6.5 36.8 6 5 
2 9.0 51.0 6 5 
3 11.0 62.3 6 5 
4 27.5 155.7 6 5 
5 50.0 283.1 6 5 
6 50.0 283.1 1 5 
7 50.0 283.1 30 5 
8 50.0 283.1 60 5 
______________________________________ 
Note: 
The rotational speed is that of the mold and the descending speed that of 
the ram. 
Other production conditions were as shown in Table 2 below. 
TABLE 2 
______________________________________ 
Electron beam diameter 
15 mm.phi. 
Degree of vacuum 1 .times. 10.sup.-4 Torr 
Mold Water-cooled copper mold 
Material (powder) 50-100 mesh Zr 
Material feed rate 
130 g/min 
______________________________________ 
The sleeves produced under the conditions shown in Tables 1 and 2 had an 
outer diameter of 100 mm, an inner diameter of 70 mm, and a length of 500 
mm. 
Table 3 compares the results of analysis of impurities in the raw material 
powder and in a zirconium sleeve produced under the conditions of Run 5 in 
Table 1. 
TABLE 3 
__________________________________________________________________________ 
(unit: ppm) 
Element 
Material O H N Al B Cd C Cl Co Cr Fe Hf 
Mg Mn Mo Ni Si Sn 
__________________________________________________________________________ 
Raw material 
810 
7 24 
33 
&lt;0.3 
&lt;0.5 
100 70 
&lt;10 
140 1030 
79 
180 40 
&lt;10 
&lt;10 
&lt;30 
&lt;20 
Zr sleeve accor- 
121 
4 20 
&lt;25 
&lt;0.3 
&lt;0.5 
&lt;50 &lt;10 
&lt;5 
&lt;10 53 
75 
&lt;10 &lt;10 
&lt;10 
&lt;10 
&lt;10 
&lt;10 
ding to Run 5 of 
Table 1 
__________________________________________________________________________ 
As is apparent from the table, zirconium sleeves produced according to the 
process of this invention had greatly reduced contents of the impurity 
elements O, C, Cr, Fe, Cl, Mg, and Mn, compared with the raw material 
powder. As a result, the purity of the Zr was increased from 99.74% to 
99.96%. No significant difference was seen between the impurity 
distribution in the longitudinal direction and that in the diametrical 
direction of each sleeve, and the impurity distributions in both 
directions were substantially uniform. 
EXAMPLE 2 
Nb sleeves were produced using the apparatus of Example 1 (FIGS. 5 and 6). 
The raw material was commercial grade Nb ASTM R04210. 
The melting conditions were those of Run 4 in Table 1 and other production 
conditions were the same as those of Example 1. The produced Nb sleeves 
had an outer diameter of 100 mm, an inner diameter of 70 mm, and a length 
of 500 mm. 
Table 4 shows the results of analysis of impurities in the raw material 
powder and in the Nb sleeves of this invention produced under the 
conditions of Run 4 in Table 1. 
As is apparent from the table, the Nb sleeves produced according to the 
process of this invention had markedly reduced contents of the impurity 
elements O, C, Fe, Si, Ni, and Al in comparison with the raw material. The 
purity of the Nb was increased from 99.79% to 99.86%. 
TABLE 4 
__________________________________________________________________________ 
(units: ppm) 
Element 
Material 
O H N C Zr Ta Fe Si 
W Ni Mo 
Hf Al 
__________________________________________________________________________ 
Raw material 
250 
10 
25 
100 100 
1000 
100 
50 
100 
50 
50 
200 
50 
Nb Sleeve ac- 
10 
10 
20 
&lt;50 80 
900 
20 
40 
100 
&lt;10 
50 
100 
&lt;10 
cording to Run 
4 in Table 1 
__________________________________________________________________________ 
EXAMPLE 3 
In this Example, Zr sleeves were produced according to the process of this 
invention by rotating the mold itself. In the apparatus used in this 
example, as shown in FIGS. 7 and 8, the lower side of the cavity of a mold 
50 is closed and a ram 53 is attached securely to the bottom center of the 
mold 50. The ram 53 can rotate and also move vertically. Zr seed members 
51 are provided at the bottom of the mold cavity. An electron beam 
irradiator 3 and a chute 4 are provided above the opening of the mold 50. 
It must also be noted that the mold 50 is a split type which allows the 
easy removal of the produced sleeve, as shown in FIG. 8. When producing a 
Zr sleeve using this apparatus, the raw material is supplied onto the Zr 
seed members 51 in the mold cavity from the chute 4 while the ram 53 is 
rotating, and then the electron beam 3a is applied onto the charged 
material, so that high-purity solidified layers are piled up successively. 
According to this method, the mold 50 is pulled down by the ram 53 as the 
pile of solidified layers grows, and melting and solidification are 
repeated until the mold cavity is filled with solidified Zr layers. When a 
Zr sleeve 52 of a desired length has been produced, the split mold 50 is 
separated, so that the sleeve 52 could be removed. 
EXAMPLE 4 
Zr sleeves were produced under the production conditions of Runs 1-4 and 
6-8 of Table 1 in Example 1, and the relationship between oxygen content 
in the obtained Zr sleeves and melting conditions, that is, the energy 
density of the electrom beam and the rotational speed of the mold, was 
examined. 
FIG. 9 is a graph of the relationship between energy density of the 
electron beam and oxygen content on the results obtained according to Runs 
No. 1-8 and a raw material. As can be seen from the graph in which 
reference numerals correspond to Run No., the raw material is referred to 
as a numeral 9 A, B, C, D indicate characteristic curves showing the 
relationships between energy density of the electron beam and oxygen 
content at 6, 1, 30 and 60 rpm, respectively, it was found that an energy 
density of at least 50 W/mm.sup.2 is necessary for reducing the oxygen 
content of the Zr sleeves. It is also important to select an appropriate 
rotational speed for the mold. If the speed is too low, such as below 1 
r.p.m., solidified layers with high impurity concentrations will be formed 
and pile up. On the other hand, if the rotational speed exceeds 60 r.p.m., 
orientated solidification does not occur, and so high-purity layers are 
not formed in the lower part of the laminate. 
Another embodiment in which a hearth mold is used for forming a high-purity 
Zr ingot for fuel cladding liners will be described hereinafter referring 
to FIG. 10. 
The hearth mold 60 which is made of copper and cooled with water passing 
through a pipe 61 is disposed horizontally in a vacuum atmosphere. A raw 
material 62 of Zr sponge is charged into the hearth 60 and irradiated with 
electron beams 63, whereby the material 62 is melted at a limited area of 
the hearth to form a relatively small molten metal pool on the hearth. The 
hearth is shifted gradually horizontally in a direction of A so that a new 
molten metal pool 64 is formed and leaves solidified pure zirconium 65. 
Thus, high-purity zirconium bar ingot or rod having a shape similar to the 
cavity of the hearth 60 is formed. The melting can be repeated at least 
once. The bar ingots are remelted in a vacuum or inert gas atmosphere to 
form a columnar ingot for a liner of the composite nuclear fuel cladding, 
which will be described later. 
As a raw material, a Zr sponge or its melted material of an oxygen 
concentration of more than 400 ppm, total impurities other than oxygen of 
1000.about.5000 ppm is used in a form of powder, rod or sheet. 
In order to raise the purity of the zirconium sponge by electron beams, it 
was found that the energy density is the most important. And in order to 
effectively use the energy, it is necessary to dispose the raw material on 
the hearth and irradiate the material with electron beams to form a 
relatively small molten metal pool whereby the molten metal pool also is 
irradiated by the electron beams to raise the temperature of the molten 
metal pool surface to evaporate away the oxygen in a form of ZrO. 
In FIG. 11, a relationship between oxygen concentration of the zirconium 
and energy density of the beam during melting. One effect is that oxygen 
concentration is lowered at an energy density of more than 50 W/mm.sup.2. 
As for the vacuum atmosphere, higher vacuum is more preferable, however, 
since the evaporation pressure of Zr is 4.times.10.sup.-5 torr at a 
melting temperature of 2200 k, too high vacuum is not preferable because 
of large evaporation loss of the Zr. Therefore, the vacuum of 10.sup.-4 
.about.10.sup.-6 torr is preferable. 
Table 5 shows electron beam melting conditions using the hearth. 
TABLE 5 
______________________________________ 
Energy Melting 
Run Output Vacuum density 
energy 
No. (kW) (torr) (W/mm.sup.2) 
(J/mm.sup.3) 
______________________________________ 
10 0.9 4 .times. 10.sup.-5 
47.2 35.1 
11 1.2 2 .times. 10.sup.-5 
61.1 45.5 
12 2.9 2 .times. 10.sup.-5 
150.5 112.3 
13 1.4 4 .times. 10.sup.-5 
278.5 135.2 
______________________________________ 
Table 6 shows the analysis results of impurity elements in the raw material 
used in the examples 10 to 13 (Run No. 10 to 13). The raw materials of Run 
No. 10 to 12 are sponge zirconium of ASTM B-351-79 grade R60001, each of 
which is a rod of 8 mm diameter. The raw material of example 13 is powder 
of reactor grade zirconium. 
TABLE 6 
__________________________________________________________________________ 
(Unit: ppm) 
Run No. 
O H N Al B Cd C Co Cr Cu Fe Hf 
Mg Pb Nb Ni Si Sn W U 
__________________________________________________________________________ 
10,11,12 
580 
8 20 
&lt;25 
&lt;0.4 
&lt;0.4 
&lt;50 
&lt;10 
145 
&lt;10 
670 
79 
&lt;10 
&lt;10 
&lt;10 
&lt;10 
&lt;30 
&lt;20 
&lt;50 
&lt;1 
13 750 
8 13 
40 
0.5 
&lt;0.5 
&lt;50 
&lt;5 
99 
&lt;10 
517 
82 
25 
&lt;10 
&lt;10 
&lt;30 
22 
&lt;20 &lt;10 
&lt;1 
__________________________________________________________________________ 
Table 7 shows comparison of the hearth melting and rod melting by electron 
beams under vacuum atmosphere, with respect to the concentration of 
oxygen, nitrogen and hydrogen. 
TABLE 7 
______________________________________ 
Electron beam 
Electron beam 
hearth melting 
rod melting 
Melting times 
O N H O N H 
______________________________________ 
(Raw material) 
750 13 8 780 -- -- 
1 275 4 11.3 661 73 3.8 
2 223 2 3 540 9 1.3 
3 215 10 2.6 593 8 3.2 
4 131 19 4.7 537 19 3.0 
5 96 16 5.1 555 13 3.3 
6 42 15 3.9 -- -- -- 
______________________________________ 
As is apparent from Table 7, the electron beam hearth melting has a great 
effect of reducing oxygen amount in the sponge zirconium compared with the 
electron beam rod melting. In the electron beam hearth melting, Zr ingots 
of oxygen concentration less than 300 ppm can be obtained by melting once. 
FIG. 12 shows relationship between melting times and oxygen concentration 
of Run No. 11 and 13. In FIG. 12, curves 1 and 2 show Run Nos. 13 and 11, 
respectively. Both show that the oxygen concentration decreases as melting 
times increases. Run No. 13 is much greater in its decreasing extent than 
Run No. 11. The higher the energy density, the more the oxygen 
concentration decreases. 
When oxygen concentration decreases to about 210 ppm, its Vickers hardness 
becomes less than 100 (Hv), so that the zirconium bar purified by the 
electron beam hearth melting has a hardness equivalent to a crystal-bar 
grade Zr. 
A lot of Zr ingot pieces according to Run No. 13 were produced. The ingots 
were melted in an electron beam melting furnace to form a large scale 
ingot of 56 mm diameter and 300 mm length. The large scale ingot had the 
same oxygen concentration as in the ingot pieces, that is, about 200 ppm. 
According to a conventional method, a composite fuel cladding is formed. 
As an outer billet, a Zr alloy tube of outer diameter of 79.30 mm, inner 
diameter 34.55 mm, length 250 mm (the alloy comprises, by weight, 1.52% 
Sn, 0.11% Cr, 0.13% Fe, 0.05% Ni and balance Zr.) is formed. An inner 
billet is produced by reducing the above-mentioned Zr ingot into a pipe of 
outer diameter of 32.55 mm, inner diameter of 21.25 mm and length of 253 
mm. The inner billet is inserted into the outer billet to form a double 
pipe. The pipe is subjected to hot extrusion, cold rolling and annealing. 
An example of the scale of the finished pipe is inner diameter 10.81 mm, 
thickness 0.86 mm, and thickness of a liner 75 .mu.m. 
Ultra-sonic test and observation of the sectional area found that the liner 
and the outer pipe have no faults all over the length and a good metal 
joining done. The oxygen concentration of the liner is not changed. 
The process of this invention is capable of producing high-purity metal 
members on a mass-production basis and at a low cost, and thus the 
invention has the prominent effect of making it easy to produce nuclear 
reactor members and superconducting materials with a high reliability and 
quality.