Note: Descriptions are shown in the official language in which they were submitted.
The invention relates to a method of storing irradiated
fuel assemblies before reprocessing thereof, and apparatus for
performing the method.
It has become known heretofore to store burned up or
irradiated fuel assemblies in water-filled spent-fuel containers
or pits until the reprocessing thereof can be undertaken, after
an adequate decay period for the decay power or heat thereof has
expired. With increasing numbers oE nuclear power plants and
the operating periods thereof, spent fuel assemblies accumulate
to an ever increasing extent and must be stored in the aforedes-
cribed manner. It is readily apparent that the storage capacity
necessary therefor must be continuously expanded, which is not
only accompanied by an ever increasing space requirement but pri-
marily also a requirement for suitable purifying or cleaning equip-
ment Eor the container or pit water, as well as cooling devices
for removing the decay power or heat of the spent fuel assemblies.
It is self-evident that, in this regard, as in other aspects of
reactor engineering or technology, redundant operational, measur-
ing and monitoring systems must be installed which, in the course
of time, calls for an exceptionally great and costly technical
expenditure. Furthermore, electrical energy is consumed and weak-
ly radioactive waste is produced in a by-no-means inconsiderable
amount in the course of removing the heat and keeping the coolant
pure and clean.
It is accordingly an object of the invention to provide
a method and apparatus for storing burned-up or irradiated fuel
assemblies wherein the aforedescribed expense is kept consider-
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ably lower than heretofore.
With the foregoing and other objects in view, thereis provided in accordance with the invention, an apparatus for
storing burned-up nuclear reactor fuel assemblies comprising:
a water container for holding irradiated fuel assemblies unloaded
from a nuclear reactor, and associated with the water container
a packing station for encapsulating the burned-up reactor fuel
assemblies removed from the water container in gas-tight capsules
and a gas-tight dry storage chamber comprising a gas-tight contain-
ment having an interior defined by a radiation-shielding surround-
ing a support structure for the gas-tight capsules containing
the burned-up reactor fuel assemblies and a coolant gas contained
i~ the interior, cooling pipe means embedded in the radiation-
shielding of the gas-tight containment, a cooling medium flowing
through the cooling pipe means for assisting the conduction of
heat from the interior of the containment through the radiation-
shielding and the containment, and means for radiation-shielding
and gas tightly closing an opening in the gas-tight containment
for loading and unloading the capsules containing the burned-up
fuel assemblies.
This means that the irradiated or burned-up fuel assem-
blies need not spend the entire decay period thereof in the water-
filled spent-fuel pit or container, but rather only a consider-
ably shorter period i.e. about 1/10 of the period spent heretofore,
and that they can then be stored in the dry storage chamber or
container because the residual decay heat has by then become so
little that it can be removed by radiation or convection cooling
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with gases. As a result, the storage e~pense of burned-up or
irradiated fuel assemblies can be reduced considerably without
compromising the reliability or safety of the storage facility.
In addition to the provision of an active component
in the form of the cooling pipe means embedded in the shielding,
a passive component in the Eorm of surface-enlarging elements
disposed on the interior surface of the radiation-shielding may
also be provided to assist in transEer of heat.
The dry storage chamber may have an access opening that
is closed by a double rotating cover.
Preferably, a drying device is associated with the water
container for drying the burned-up reactor fuel assemblies removed
from the water container before encapsulating in gas-tight cap-
sules in the pac~ing station.
The apparatus preferably includes, in combination with
the dry storage container, sluice and manipulating devices for
transporting ~he fuel assemblies from a water-filled spent-fuel
container through the drying and packing
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devices to a location within the dry storage container.
Although the invention is illustrated and described herein as
embodied in storage of irradiated fuel assemblies, it is nevertheless not
intended to be limited to the details shown, since various modifications and
structural changes may be made therein without departing from the spirit of
the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be best under-
stood from the following description of specific embodiments when read in
connec~ion with the single figure of the drawing which is a diagrammatic
view of apparatus for performing the method of storing irradiated fuel
assemblies in accordance with the invention.
Referring now to the drawing, there are shown, in the figure
thereof, fuel assemblies 2 stored in a water-filled spent-fuel container 4
which is provided, for this purpose, with a non-illustrated inner support
structure which, due to the geometrical shape thereof and/or due to absorber
materials introduced therein reliably prevents the fuel assemblies stored
therein from becoming critical. The container water is provided with non-
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illustrated purifying or cleaning devices as well as cooling devices. In thisway, initially present and still very great decay heat is removed and can,
under certain conditions, be further used also for other technical purposes.
This liberated decay heat of the fuel assemblies decreases with increasing
storage time so that, beginning with a given point of time, water cooling by
the inventive method of the instant application, is no longer necessary.
At this juncture, it should also be noted that the fuel assemblies
2 provided also with so-called bearing bushings or capsules, can be deposited
in the storage container or pit 4. After decay or decrease of the decay heat
to a value removable by dry cooling, the fuel assemblies 2 are remotely
handled, for example, individually removed from the storage container 4 with
the aid of a crane installation S, ~1 or with non-illustrated manipulating
equipment and inserted into a drying device 5. Due to the remaining decay
heat as well as due to gas, such as air or nitrogen, for example, fed in
through a line 52 and discharging ~hrough a line 53, the container water ad-
hering to the fuel assemblies 2 is dried up. Then, after taking off the cover
51, the fuel assemblies 2 are removed from the drying chamber 5,and, also again
remotely handled are delivered to a packing station 6 closed off from ~he
outside. The fuel assemblies are inserted into canisters 3 which are gas-
tightly closed by a cover 31. The interior space of the thus-closed canisters
3 is advantageously filled with an inert gas. The thus-pac~ed fuel assemblies
2 are then, again remotely handled delivered into a dry storage container 7
wherein the closed canisters 3 containing the fuel assemblies 2 are inserted
into a support structure 35 which can be constructed similarly to that in the
wet fuel assembly-storage pit 4. The support structure 35 thus serves as the
mechanical holder or support for the fuel element canisters 3 inserted therein
as well as for preventing a distribution or arrangement thereof that would
become critical. When the decay heat of these inserted fuel assemblies 2 has
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also become so little that no water cooling is necessary anymore, the radio-
active radiation thereof is nevertheless great enough that the dry storage
chamber 7 has to be surrounded by radiation shielding 71. Cooling pipes 72
are embedded in the shielding 71 and are traversed by a coolant passing
through union fittings or connection pieces 78 and 7~. Natural circulatory
flow produced in the interior of the dry storage chamber 7 absorbs the heat
from the fuel assemblies 2 and surrenders it to the shielding 71. The inner
wall surface of the shielding 71 can be provided with surface-enlarging
elements such as ribs 80 or the likel for e:~ample, so that heat transfer is
thereby improved or facilita~ed.
In addition, cooling gas can be introduced through a line 76 into
the storage chamber 7, and discharged therefrom through a line 77. This heat
carrier i.e. either the coolant flowing through the cooling coils 72 or this
cooling gas, can be used again for heating up the drying apparatus 5 so that
only a part thereof has to be discharged and can possibly also be used further
as process heat.
Non-illustrated sluices or locks can be provided for introducing
the fuel assemblies 2 into the drying storage chamber 7, or also, as shown in
the figure, a double rotating plug or cover 74, 73 as is generally known from
nuclear power plant technology. A blower 75 for effecting improved circula-
tion of the volume of cooling gas and thereby cooling of the fuel assembly
canisters 3, can additionally be provided on the plug or cover 73.
The closure for this dry storage container 7 must obviously be of
gas-tight construction, and also the radiation shielding 71, as well, must be
provided with at least an outer dense skin in order to prevent external
contamination due to possibly damaged or faulty canisters 3.
Naturally, this dry storage container 7 and also the intermediate
station for performing the method according to the invention are provided with
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non-illustrated monitoring devices of conventional construction so that any
distuTbances that might possibly occur can be detected in time and suitably
remedied.
Of course, other possible constructions for the apparatus accord-
ing to the invention are conceivable, such as~ for example, the outer dense
skin and the shielding can be so disposed that the heat at the fuel assemblies
carried by natural convection to the outer structure passes through the latter
by heat conduction and is discharged by natural convection to the outside.
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