Note: Descriptions are shown in the official language in which they were submitted.
~: `
- This invention relates to containers for radio-
active materials, particularly for nuclear fuels, and is di-
rected to the special structure and composition thereof.
Nuclear fuel containers are necessarily of very
special construction involving considerations of gas and liquid
seals, pressure and temperature build-up, physical dimensions
as regards neutron flux, and enormous physical and heat
strength demanded by the A.E.C. prescribed drop and oil fire
tests, while maintaining container weight at a realistic level. ; ~;
Thus, in accordance with the present teachlngs,
a double containment pressure vessel for use in a container
for nuclear materials is provided. The vessel comprises ~wo
generally tubular vessels, each of which has a closed bottom
end and a flanged upper end. A closure head is bolted to
each flanged upper end and gas seal means is provided between
: .
each closure head and associated flanged upper end. One of
the vessels is nested within the other such that gas passage~
ways areprovided interconnecting the seal means of both ~ ~
vessels. ~ ~ ;
The present invention represents very advanced
improvements in container design and composition and in one ;~
of its broad embodiments can be defined as comprising a metal
housing, a pressure vessel and gamma shield assembly in said
housing, positioning means extending between said housing and
said assembly for spacing the same, and insulation essentially
filling the space bekween said assembly and housing and
comprising water beads encapsulated in plastic.
.
This novel basic system allows the use of the
more complicated structure and composition which is detailed
~ 30 below in the specification and drawings wherein certain ~
i dimensions are shown out of proportion fox purposes of clarity. ~ ~ ;
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Fig. 1 is a side elevation of the container;
Fig. 2 is a top view thereof;
Fig. 3 is a cross-sectional view taken along line
3-3 of Fig. 2;
Fig. 4 is an enlarged cross-sectional view of the
seal of Fig. 3;
Fig. 5 is an enlarged cross-sectional view of a
variation o the seal of Fig. 4, and
Fig. 6 is a cross-sectional view as in Fig. 3,
showing the double contair~ent version of the present con-
tainer.
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Referring to ~iys. 1-3, the container ge~lerally
designated 10 comprises a metal housing 12 in the general form
of an elongated cylinder having formed strengthening ribs 14,
bottom 16, and cover 18. This housing may be constructed
conveniently from two 16 gauge steel 55-gallon drums with the
bottom of the top drum cut out and the remclining flange 20
welded as at 21 to the curled rim 22 of the top of the lower
drum.
A first bar band 24 is welded to the top of housing
12 just below curled rim 26, a second bar band 28 is welded to
the housing near the bottom thereof, and a third bar band 30
is welded to the housing about one-fourth of the way down the ~;
housing. These bands are preferably of 1/4-inch thick steel,
1 3/4-~inches wide at 24, and 3-inches wide at 28 and 30. A
bar ring 32, designated herein as second bar ring for purposes
of claim clarity, preferably 1/4-inch by 1 1/2-inch steel rolled
edgewise, is welded to the inside of housing 12 at a position
which allows the cover 18 to snugly fit. Preferably, the weld ;;
of ring 32 penetrates through housing 12 into first bar band
24 to provide a very strong unitary structure. A first bar
ring 34, preferably 1/4-inch by 1 1/2-inch steel rolled edge-
wise, is welded to the upper surace of cover 18. Nuts 36 are
, ~ . , ~ . attached, preferably by tack welding, to the underside of ring
32 to receive bolts 38 inserted through mating apertures 40 and
42 in rings 34 and 32, respectively. A pair of lifting lugs 40,
preferably i/4-inch by 3-inches flat bar steel are welded to
band 30. In the construction of the present container, all
stainless steel welds should be by Tungsten Inert Gas Process
(TIG) and all carbon steel welds should be by TIG, Metal Inert
.
Gas or shielded arc.
- The pressure vessel and gamma shield assembly
-i generally designated 43 is preferably mounted on and spaced from
-2-
,
~ t~
the bottom 16 of the housing b~ a wooden cross of two pieces
44 and 46 of 2-inch by 4 3~4-inch white oak. Piece 44 is
broken away at one end to show that the insulation-later
described in detail extends to the bottom of the container.
Assembly 43 comprises the pressure vessel consisting of tube 48,
preferably 5-inch Schedule tSch.) 40, 304L stainless steel (SS)
pipe, welded closed at the bottom 50, preferably by 1/2-inch
by 5-inch diameter 304L SS., first flange 52, preferably 5-inch -
300 pound Slip-on Flange 304L SS., welded to the top of tube
10 48 at 53, closure head 54, preferably 5-inch - 300 pound Blind
Pipe Flange 304L SS... and a seal generally designated 56, shown
in detail in Fig. 4.
Head 54 is provided with a gas relief valve 58,
preferably a l/4-inch NPT Hoke Valve 316 SS, with 1/4-inch NPT
Pipe Cap 59, 304 SS., mounted in coupling 60, preferably a
1/4-inch NPT 300 pound Half Coupling, 304L SS., welded to head
54. A shroud 62, preferably 5-inch Sch. 40 by 2 1/2-inch pipe,
304L SS., welded to 54 protects Valve 58. This valve provides
a controlled release of any gas which may ~e produced from the -~
~; i:
nuclear materials contained in the conventional vented poly~
ethylene tu~e carried within tube 48.
The seal 56 is shown disproportionately large in
Fig. 4 for purposes of clarity and in the preferred embodiment
comprises a metal disc of about 11 gauge having two pairs of
concentric channels 64 and 66, and 68 and 70 in which elastomeric ¦
rings 72 and 74 are positioned. These rings are preferably ¦
molded into the channels and retained therein by connecting
webs 76 which are molded in and extend through suitably
- circumferentially spaced apertures in the disc joining the
adjacent channels in oppos~te sides of the disc. The rings are
o~ a temperature and ~hemical resistant material such as Viton
A of duPont, a copolymer of hexafluoropropyle~e and ~inylidene
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fluoride. A plurality of passageways 77 are provided through
the disc so -that each side of the seal may be pressure tested~
An aperture 78 in the metal disc connects -to the passageway 80
in head 54 communicating with valve 58. In Fig. 5, the seal is
modified whereby the separate metal disc is eliminated and two
eiastomeric rings 80 and 82 nest in channels 84 and 86,
respectively, cut into head 54. A plurality of conduits 88 or
their equivalent connect the sealing rings for pressure testing.
The structuré of seal 56 allows a seal test device
- 10 such as a gas source and pressure change detector to be connected
to port 90 to test the sealing of the pressure vessel at any
time. Port 90 normally is sealed by a 304 SS. pipe plug 91.
, The gamma shield as shown in Fig. 3 comprises
inner wall 92, preferably of about 11 gauge steel tubing,
outer wall 94, preferably of about 1/4-inch steel tubing,
bottom plate 96, preferably of about 11 gauge steel welded
to adjacent ends of said walls, a second flange 98, preferably
lap joint forged steel, weldea to the periphery 99 of the open ;~
end of inner wall 92 and having a leg 100 projecting substantially ~-
normally downwardly from the face 102 of flange 98 a distance
` between walls 92 and 94, and a lead shield 104 about 1/2~inch
thick poured into and essentially filling the space between
said walls. Bolts 106, preferably cadmium plated, and nuts 107
tack welded to flange 98 clamp the assembly together.
It is particularly noted that leg 100 of flange 98 ~-
is not welded to wall 94 and allows thereby sufficient cocking
' or tipping motion of the pressure vessel and flanges to alleviate
undue stress on bolts 106. This is quite important where the
container is dropped or positioned on its side.
The above assembly may be secured to the wooden end
' spacer beams 44 and 46 by concrete nails 108. Similarly, wooden
spacers 110, preferably four, equally spaced aro~md the outer
1 -4
i,
.,
wall 94 of about 2~inch by 6~inch white oak are nailed at 112
to bracke-ts 114 welded to wall g4.
A very important feature of the present invention
resides in -the insulation or neutron shield material generally
designated 116 which fills substantially the remaining interior ~ ;
of the housing. ~his material is a water-in-resin emulsion
type system which is poured into the housing and peroxide cured
or cross-linked. A suitable mold is used to form the resin
during cure to provide cavities 118 and 120 and bolt clearances
122. A separately formed and removable block 124 of this resin
provides insulation at the top of the container while giving
easy access to the pressure vessel. A plurality of pressure
relief holes 126 of about 3/16-inch in diameter are formed
through the housing at suitable positions throughout its surace
and are plugged with a plastic cement, preferably epoxy. The
function of these holes will become more apparent hereinafter.
This insulation is extremely important to the present
invention in forming a combination spacer, positioner, heat ~ ;
barrier, concussion cushion and neutron shield for the pressure
vessel (and polyethylene radioactive salt solution container
ox oxide container carried therein) and gamma shield assembly.
This particular form of insulation, which
decomposes under high temperatures to form steam and gaseous
proaucts such as CO and CO2, serves many functions and is
I quite unique in this application. For example, the hydrogen -
`j entrained in the water is a pri~cipal neutron absorber. The
heat transfer characteristics of the insulation are such that,
under normal conditions, the heat generated by radioactive decay
of plutonium uranium, americium, and other daughter and
ij 30 residue'ission products is effec~ively emitted from the
container, while, under abnormal conditions wherein, for
:, ~
~3 example, extreme heat from an oil fire impinges on the housing
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:... . . - :. - ., . , . . -
tji~
exterior, such heat is not transferred to the pressure vessel
and gamma shield assembly and its contents. In other words,
under normal conditions, the heat transfer coefficient of the
solid, non-porous insula~ion is just right for transferring the i,~i
heat from radioactive decay out of the vessel~ but when the
container is subjected to oil fire heat, for example, the heat
transfer coefficient is not such that destruc:tive heat will
transfer in. Durlng such an oil fire, the he.at barrier
characteristics of the insulation come into play and the steam
blanket limits the surface temperature, that is, the temperature
of the inter~ace between the housing and the insulation. In
other words, decomposition of the insulation serves to impose
automatically a maximum temperature dlfferential between the
housing and the gamma shield. The insulation also acts as a
large heat sink and this large mass o insulation provides
ade~uate water for the steàm blanket to exist for the extended
oil fire test.
The composition and preparation of the water extended resin
may be varied. U.S. Patent 3,256,219 to Guenther Will Zimmerstrasse, ;
2n II issued June 14, 1966 (Reissue 27,444) describes various types of
systems wherein the resin is made, for example, by polymerizing
methyl methacrylate in the presence of polystyrene acting as
emulsifier.
Another and preferred system, such as is shown in
Example II of said patent, is that obtained, for example,
from maleic acid reacted with a propylene glycol starting with
maleic anhydride and under conditions well known to the art of
"cooking" polyester resins to finally obtain an unsaturated
resin of a molecular weight of from about 1200 to about 5,~00
and having an acid number of from about 10 to about 100 or
~' higher. This resin is then dissolved in a suitable monomer
such as styrene to give a final polymerizable resinous system
- 6 -
composed of from about 30-70% by weight polyester and conversely
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- 6 a
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1~ 71~
from about 70-30% by wei~ht styrene. This system is readily
polymerized by free radical polymerization initiators such as
a large variety of peroxides, transition metal ions, and/or light
and if long storage o~ the unpolymerized resin is desirable,
such stabilizers as hydroquinone, the monomethylether of
hydroquinone, or methylene blue ~ay be added in about 50 - 200 ppm.
A large variety of peroxide decomposition promoters such as the
cobalt organic salts may be used in concert with the peroxides. ~ ~`
The system is placed, preferably, in a mixer such as a Hobart
dough mixer and the other components, preferably premixed,
are slowly fed thereto to give mix compositions such as the
following, expressed in weight percent:
40 polymerizable resinoùs system
24.3 water
25.9 ethylene glycol (antifreeze)
1.0 hydrogen peroxide
8.8 sodium tetraborate (neutron absorber)
This mix composition is maintained during mixing,
preferably, at a temperature of from about 80 to about 105F.
for a short time (1-2 minutes may be adequate) to form an emul-
s~on or gel which is then poured into the container housing and
allowed to cure. In some instances, it may be desirable to add
minor amounts of surfactants including those classed as
detergents, protective colloids, and wetting agents. These
may be from the categories of anionic, cationic, nonionic, or
amphoteric surfactants.
In the above exemplary mix compositions, a
particularly effective polymerizable resinous system is
prepared from, in parts by weight, about 18-22 isophthalic acid, `
3-8 maleic anhydriae, 45-55 styrene, 3-8 propylene glycol, and
10-20 diethylene glycol. The well-known peroxide decomposition
~ -7-
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lI357~tj'~
promoters such a5 cobalt neodec~nate and dimethyl aniline may
be premixed with this resinous s~stem.
It has been ound that the weight o~ the present
container may be minimized by employing a filled version of the
above composition in certain portions of the container. Fox
example, it has been found that the resin will cure properly and
retain the water in the presence of up to about 50% by weight,
15 to about 30% by weight being preferred, and about 20~30~ by
weight being most preferred, based on total insulation weight of ~ `
vermiculite homogeneously blended into the emulsion or gel. Such
filled insulation can be used in the lower portion of the
container, that is, below about the bottom of bolts 106.
As indicated above, the curable polymer composition
may be varied or certain applications; however, the above
exemplary composition is outstanding. Useful variations
include, in general, the thermosetting (cross-linking) resins
derived from monomers and/or polymers obtained by addition `
polymerization such as~
1. Unsaturated polyesters as described by
"Unsaturated Polyesters: Structure and Properties", by Herman
V. Boenig, Elsevier Publishing Company, New York, 1964, ~ ;~
exemplified by epoxy, polyurethanes and polysulfides.
~. Synthetic rubbers based OII butadiene, chloro-
prene and copolymers containing these monomeric constituents
and as generally described in "Vinyl and Related Polymers",
by Calvin E. Schildkneckt, John Wiley & Sons, New York, 1959
pp. 48 to 178.
3. Vinyl-type mixtures of monomers and polymers
which give the "water~borax mixture~ the suitable mechanical
~ 30 wet properties before polymerization and which contain at leas~ -
J 1~ by weight based on the material of the total mixture
containing polymerizable unsaturation of a multifunctional
-,:
~ -8- -
polymerizable cross-linking agent such as divinyl benzene,
dialkyl phthalate, ethylene diacrylate and others well known
to the art of cross-linked resins.
The polymerizable monomer may be varied and includes
compounds such as those of the formula
-
Rl ~ .
CH2 = C~ . ~:
R2
,
wherein, for example,
Rl is H, CH3, CH2CH2-, phenyl, Cl- or -CN;
O o . : ~
; R2 is H, ~CN, -C-OH, -C-OR3; wherein
R3 is alkyl, cycloalkyl, or aryl.
Variations in insulation composition may be
employed. For example, other neutron absorbers such as the
water soluble cadmium salts including cadmium nitrate may be
used. The amount of neutron absorbing nuclei may be varied
J, ~epending on its absorp~ion effectiveness. With sodium te-tra-
borate, between about 0.5 to 1.5% by weight of the boron atom ~;~
based on total insulation weight is preferred. Also, other ^`~
antifreeze materials such as methanol, glycerol or various
inorganic salts may find limited application in the present
invention but are not preferred. As mentioned above, up to
I about 50~ by weight based on total insulation weight of solid
siliciferous material may be employed to fill ~he desired amount
of insulation. This material includes many other materials
besides vermiculite including other forms of lightweight mica.
Lava, pumice and perlite are also useful. Up to about 35
based on total insulation wèight of chopped glass fiber
~: reinforcing may be employed. Such glass fiber is shown, for~ 30
example, in the aforemention patents, as well as U.5. Patents
~.
i 2,877,501 to Fiberfil Corporation issued March 17, 1959 and
3,516,957 to Eastman Kodak Company issued June 23, 1970. In this
~ ' ~ 9 ~
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regard, the locations within ~ ~
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the housing which can accommodate the filled insula-tion will
depend to a l~rge degree on the test stresses imparted thereto.
Filling does tend to e~brit-tle many plastic systems. For this
reason, the fiber glass rein~orcement offers an lmportant
solution.
The insulation components may vary in parts by
weight based on 100 parts of resinous system between, for
example, 50-150 parts water, 50-150 parts ethylene glycol,
0.5-10.0 parts peroxide catalyst, up to about 40 parts sodium
tetraborate, and up to about 250 parts of siliciferous filler
or glass fiber or mixtures thereof. A preferred range of
insulation components in parts by weight, based on 100 parts
of polymerizable resinous system, is 55-70 parts water, 55-75
parts ethylene glycol, 1.0-5.0 parts hydrogen peroxide, and
15-30 parts sodium tetraborate and 40-70 parts vermiculite.
A preferred adjunct to the insulation is a
temperature resistant epoxy, alkyd, polyamide or the like
sealing coating covering all exposed surfaces of the insulation
116 including block 124 and bolt clearances 122. This coating
prevents loss of water from the insulation, particularly
when the cover 18 is removed for any appreciable period of
time. Water loss is also prevented by the use of a gasket ~-
of suitable elastomeric or latex material between rim 26 and
cover 18. A particularly effective way of preventing water
` loss around bolts 38 is to weld a seal between the ~uts 36 and
ring 32, shorten bolts 38 and dead-end the threaded holes in
nuts 36 to form threaded caps.
As mentioned previously, pressure relief hole 126
are plugged with epoxy or other suitable adhesive~ This
plugging seals in the water, the loss of which could otherwise
be substantial since there should be at least about one 3/16 -
inch diameter hole per square foot of exteri-or surfacle area of
~ - ' ' ` '
.,,1 ' .
, .
1~7~
the houslng 12. These holes are essential in releasing the
enormous pressures built up within the housing during the one-
hour oil fire -testing, during which the resin plugs in holes
126 are burned or forced out~ The number of relief holes
should not be excessive, however, since main-taining a pressurized
steam blanket in the housing is an important aspect of the
shielding of the pressure vessel and gamma shield assembly from
the otherwise disastrous heat of the oil fire. Also, an
excessive number of relief holes would allow air to enter the
lO container during the heat test and actually burn the insulation, ;~ ;
particularly those portions thereof which have become partially
heat disintegrated. ~-
; Variations in structural materials of the container
may also be used. For example, the wood spacers llO and 44
and 46 may be of steel where extreme strength is needed, regard-
less of container weight, and aluminum could be used in certain
; instances.
The particular configuration shown for the housing
is quite preferred but variations are possible. For example,
20 the stxengthening ribs 14, rather than being formed in the
sheet metal, could constitute welded-on rolled bars similar to
24. Moreover, longitudinal stiffeners could be welded up the ~-
side of the housing to the ribs 14 to provide a very strong -~
J cage effect. The housing, rather than being two drUmswelded
together, could be a single rolled and welded steel sheet, with for ;
example, longitudinally extending strengthening ribs formed
therein. Also, the sealing rings 80 and 82 could be set into
grooves in flange 52 rather than in the head 54. Moreover, the
~ sealing rings could be of different cross-sectional shapes and
-~ 30 several could be used to give a surer seal. At least two sealing
~ rings are required, however, in order that the pressuriæed test
.- ~ .
gas can be fed therebetween.
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1~5 71~
A particularly effec-tive container for ~lutonium
solids and solutions is essentially as shown in FIG. 3 employing
however solid resinous material 116 (WEP) rather than vermiculite
filled WEP, a considerably thicker (one inch) lead shield 104,
steel spacers 110, a one quarter inch thick bottom plate 96
the diameter of which extends to adjacent the inside of housing
12, the positioning of bar band 28 such that the plane of plate
96 will be approximately at the middle of band 28, and the use
of a slab of solid WEP at the bottom of the container housing
in place of the wooden pieces 44 and 46. For assembling such
container, the slab is poured first and then bottom plate 96
is nailed to it. Also in this container, inner wall 92 is a
iittle shorter than outer wall 94 and is closed at the bottom
by a one quarter inch thick stainless steel plate which, in the
.
assembled container, is spaced from bottom plate 96, and lead
shielding i5 provided in the space. The solid WEP is fiber glass
reinforced and contains the ethylene glycol and borax.
In FIG. 6 a double-containment version of the
container for transporting plutonium solids is shown. The
numbering corresponds to the equivalent parts of FIGS. 1-5.
This container is much heavier than the others described herein ``~ ~ "
and preferably 11 gauge steel for example is used for the
~ housing 12. The cover 18 is thick steel which, in the embodi-
1i ment shown is 3/8 inch thick, 28 inches in diameter, and secured
by 20 equally spaced 5/8 inch cadmium or zinc plateh hex head
cap screws 38 to a heavy angle ring 128 wPlded around the top
of housing 12. The seal between cover 18 and ring 128 is pro~
vided in this embodiment by a 1/8 inch thick by 2 inch wide
neoprene strip gasket 130 of 40 to 50 Durometer att~ched with
suitable adhesive thereto. In this embodiment, the pressure
vessel comprises stainless steel pipe 132 welded at the bottom
7 to stainless steel disc 134. The top of pipe 132 is weLded to ~ --
,,, " ' . ~ ' '
-12-
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stainless steel socket flange 136, Blind flange 137 completes
~he assembly. The rad.iation shielding comprises ring 138,
tubing 140 welded thereto, bottom disc 142 welded to the bottom
of -tubing 1~0, all of stainless steel, steel tubing 144 welded
at the top to ring 138 and at the ~ottom to disc 146. Disc 146
is welded on last after molten lead 148 is .poured into the
inverted shield. The double contain~ent aspect arises from
the stainless steel pipe 150 welded to ring 138 and to the inside
of stainless steel slip-on flange 152, and blind flange 54.
The pressure vessel is contained with the container thus defined.
In order for gasses which may lead past the pressure vessel
seal to be released through the outermost valve 58, and the
pressure thus dissipated throughout a larger volume, shroud 154
is spaced from the metal portion of outer seal ring 56 by two
~iton A pads 156.This arrangement provides vent gaps 156
communicating with said outermost valve 58 through flange 54. ~ :~
Shroud 154, alternatively to or in conjunction with pads 156,
. ~ ~ , . .
may be pro~ided with suitable apertures to provide the desired
gas communication to outermost valve 58 and may be of a large ~;.
J 20 diameter as desired. In this embodiment, the bolt holes in . .
flanges 136 and 152 are threaded to eliminate the need for
separate nuts. Also, disc 146 is secured in place to precast .. .:
. ~ .
slab 160 by nails 108, thus eliminati.ng members 44 and 46. .
Steel channels 162 welded to the bottom of plate 164 provide
convenient means for fork-truck handling, and gussets 166
, provide strength and stability for the top-heavy container. ::~
I List handles 168 are secured to plug 124 by any suitable means.
~ In this embodiment of Fig. 6, a typical uncured
` WEP formulation comprises in percent by weight, 33.0 to 39.0
and preferably 36.0 resin, 19.0 to 24.0 and preferably 21.9 water,
20.0 to Z7.0 and pre~erably 23.3 ethylene glycol, 6.0 to 9.0
. and preferably 7.9 borax ~equivalent to 0.9 boron)~ 0.4 to 1.5 ;- ~.
'. ..
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and preferably 0.9 hydrogen peroxide or the equivalent thereof of
other peroxide curing agents, and 6.0 and 15.0 and preferably 10.0
chopped fibergla~s roving. It is particularly noted that the
positioning means between the housing and the pressure vessel and ;
gamma shield assembly is the solid WEP, and wooden or steel
members such as 110 are obviated.
The unusual construction of FIG. 6 cGntainer may be
expressed as a container for nuclear fuels comprising a metal ~:
housing, a pressure vessel. and gamma shield assembly in said
housing, positioning means extending between said housing and
said assembly for spacing the same, insulation essentially
filling the space between said assembly and housing and
comprising water beads encapsulated in plastic, wherein the : ~ -
positioning means is the insulation and the pressure vessel is
double containment comprising two generally tubular vessels, each .
.
of which has a closed bottom end and a flanged upper end, a ..
closure head bolted to the flanged upper end and gas seal means
between the head and flanged upper end, one of said vessels . . :
being nested within the other such that gas passageways are
20 provided interconnecting the seal means of both vessels. .
The invention has been described in detail with
reference to certain preferred embodiments ~hereof, but it will
be understood that variations and modifications can be effected
within the spirit and scope of the invention. ~ ~
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