Note: Descriptions are shown in the official language in which they were submitted.
J~i93
The presen-t invention relates to an apparatus for
storing heat-releasing radionuclide configurations, whl.ch when
required are enclosed in containers wi-th free coo].i.ng with
ambient air, and comprising subs-tantially a housing with charg-
ing passage, supply-air and spent-air ducts and.closed storage
cells provided wlth ceilings and containing ,to-~age racks
(storage blocks) wi-th horizontally arranyed or inclined storage
shafts as storage positions for the radionuclide configurati.ons
or for the containers with radioactive materials, cooling ai.r
flowing in the axial direction through the storage shafts.
Radioactive materials and radionuclide configurations,
as for example, burned-out nuclear fuel elements or vitrified
highly radioactive waste produce heat when disintegrating so
that constant cooling is required during this storage. This
requires that the continuous presence of a coo].ing medium is
assured and that no inadmissible amounts of radioactivity are
carried off with tlle cooling medium. These requirements are
satisfied, for example, by a storage depot cooled directly or
indirectly with ambient air.
Various plans have been proposed for the dry inter-
mediate storage of heat-releasing radionuclide configurations.
Thus, for example in German offenlegungsschrift No. 2,730,729
it has been proposed to store the containers with radioactive
waste in vertical shafts, through which air flows axially from
the bottom to the top, -the containers being stacked either
individually or multiply one above the other. In German Offen-
legungsschrift No. 2,906,629 the containers are stored in
horizontal shafts with cross flow from the outside in the
vertical direction, the containers bei.ng individually or multiply
arranged in tandem. A direct cooling system or an indirect
cooling system can be used in these two cases.
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3 i~ 6i93
German Offenlegungsschrift 2,837,839 describes the
storage of containers in horizontal storage blocks having later-
ally arranged cooling elements with cross flow in the vertical
dircction. The storaye of vertical storage containers having
Front--end shic]diny gatcs serv;ng sirnultaneously as cooling
clemcnts is a]so known (Nuclear Technology, Vol. 24, December
1974) and so is the storage horizontally with cross flow within
a closed space and emission of heat to the environment by means
of heat pipes (Atom and Strom, 26th annual publication (1980)4).
The main disadvantage of the storage described in
German Offenlegungsschrift No. 2,730,729 lies in the cooling
with laterally arranged heat exchangers (walls) and in the
flow direction thus required. The cell air emerging with maximal
temperature and velocity of flow from the laterally arranged
shafts irnpinyes on the flat ceiling and ;s thcn conducted hori-
~.ontally to tlle Jateral hcat cxchal~gers. Kinetic energy is
destroyed hy the flow impinging on the flat ceiling. Furthermore,
the ]-,orizontal flow to the heat exchangers is not promoted by
the external field of forces (gravitation)since the heated air
tends to rise upwardly.
A further disadvantage of the apparatus cited in
German Offenlegungsschrift No. 2,730,729 is that a distinct
co-ordination of the heat removed from the storage stack region
to one of the two heat exchangers is not possible.
The main disadvantage of the apparatus described in
German Offenlegungsschrift No. 2,837,839 and of that described
in "Nuclear Technology" is that for the heat flow from the
storage containers to the cooling elcment,steep temperature
gradients, which can result in thermal s-tresscs of the stored
material, are required. The fact that in the storaye concept
accordlng to German OEfenle~ungsscilrift No. 2,837,839 the cooling
elellle3lt cons;sts of a solid properly heat-collductillg material,
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~ 3f;~33
usually metal, resulting in high costs is particularly unfavour-
ahle. Furthermore, because of the heavy weight of the storage
hlocks with cooling elements,special structural requi.rements
must be met hy the storaye racks.
'l'he substantial disadvantages of the apparatus describ-
ed in "~tom and Strom" lie ;n that a distinct coordination of
the heat to be removed from the region of the storage racks
to one of the two heat exchangers is not possible and that no
practical experience exists with regard to the behaviour of
heat pipes in the radiation field. Furthermore, in this case,
the emission of heat also is lateral so that the conduction of
the flow is not optimal.
In the apparatus described in German Offenlegungs-
schrift No. 2,906,629 the fact that the ambient air is exposed
t~ t]lC' r~diation fi.eld of the rad;.oactive materials Wit]lOUt any
large-sca].e shielding measures also is a disadvantage.
In all the apparatus for the intermediate storage of
heat-producing radionuclide configurations with indirect cooling
due to free convective flow,substantial disadvantages have
resulted primarily with regard to an optimal conduction of flow
and thus also with regard to both optimal heat removal, and
shielding of theambient air against direct irradiation by radio-
active substances.
Therefore, the present invention provides an apparatus
for storing neat-releasing radionuclide configurations, which
are enclosed in containers when required, with free cooling by
means of ambient air, i.e., an apparatus comprising substan-
tially a housi.ng provided witll charging passage, supply air
and spent-air ducts and closed storage cells provided with
ceilings and conta.i.ning s-torage racks or storac3e blocks with
horizontally arranged or inclined storage shaEts as storac3e
posi.t.ions for the radionuclide conf:iguratiolls or Eor tlle colltaill-
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g~
ers with radioactive ma-terials, coo]ing air Elowinc~ -through
the storage shafts in the axial direc-tion. With this apparatus
an improvement of -the conduction of coo]ing air Llow should
be at-tained, -thus assuring a reliable heat removal.
Thus, according to the present invention the ceilings
of the storage cells are heat exchangers and within the s-torage
cells there are disposed at the openings of the s-torage shafts
vertical up-draft and down-draft chirnneys, which are separated
in space and function and are open in the region of -the storage
racks with respect thereto and are provided with ]ockable charg-
ing orifices with respect to the charging passage.
It is favourable to arrange a separate up-draft
chimney and down-draft chimney for each storage rack or to design
the charging passage as a common up-draft or down-clraft chimney
for two storage racks.
Furthermore, it is advantageous to incline the storage
cell ceiling in the direction of down--draft chimney; an angle
of ~ 15 has been found to be favourable for this purpose.
By providing both a separate up-draft chimney through
which the warmed air is passed to the storage cell ceiling,
which is designed as a heat exchanger, and a separa-te down-draft
chimney, a distinct separation o-f the functioll of the up-draft
chimney for the warmed cooling medium and that of tlle down--draft
chimney for the cooling medium cooled at the ceiling is at-~ained.
Both the up-draft chimney and the down-draft chimney are aligned
in the direction of -the field of gravity, i.e., vertically.
This is particular]y favourable wi-th regard to the e~tent of
the pressure losses and thus favourably affects the temperatuIe
level in the storage depot.
The installation of the heat exchan~er at -the point
of the higllest temperature withinthe cooling cycle, narnely above
-the storage racks, has been found -to be partic~larly favourable
3~,;93
for reasons of thermodynamics since the thermodynamic efficiency
of -the heat exchanger thus is at a maximum.
In order to protect more effectively the ambient air
~low~.ng through the heat exchanger ~ceiling) against the effect
of di,rect radiation from the stored material it is advantageous
to install be]ow the ceiling and laterally thereof baffles to
shield the ceiling against radiation. The construction of up-
draft chimney and down-draft chimney then is such -that effects
of scattered radiation are avoided.
The apparatus according to the present invention is
explained in greater detail by means of examples represented
diagrammatically in the Figures I to VI.
The apparatus comprises one or several storage cells
(15), norma],ly separated by charging passages (10) and housed
in a builc~ing. The storage cells (15) contain storage racks
(9) or storage blocks with storage shafts (2). The storage
containers (1) filled with the material for storage are put into
the storage shafts (2), which preferably are s],ightly inclined,
and continuously passed through them when required. Spacers
(12), which can simultaneously serve as ribs of the container
surface, are used for centering the storage containers (1) in
the storage shaft (2). Storage container (1) and storage shafts
(2) thus form a free f]ow space through which the cooling air
can flow in the axial direction. In circular storage containers
(1) and circular storage shafts (2) an annular c],earance (17)
results as a free flow cross section. Other suitable shaft
cross sections, for example, for rectangular storage conatiners,
are feasible. The arrangement of the storage shafts (2) is
optional but prirnarily horizontal, square or hexagollal (Fig. II).
The cooling air is warmed on passing through the ree flow
Cl`OSS sect;olls (17) along ~he heated storage con~aillers an~
storage shaft surfaces. The inside shaft surface is heated
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i93
secondarily by heat transport due to radiation of heat from the
storaye container surfaces. The warmed cooling air flows from
the storage shaft (2) into the vertical up-draft chimney (3),
whcrein it rises upwards.
The apparatus according to the present invention is
an indirectly cooled storage depot, in which the warmed cooling
air is passed to the ceiling (4), which preferably is slightly
inclined in -the direction of flow and is designed as a cooling
surface. Along said cooling surface the cooling air is cooled
to the inlet temperature of the storage shaft. On emerging from
the cooling duct (5) disposed along the ceiling (4) and formed
by the ceiling (4) and the storage block (9) and baffles (21)
the cooling air passes via the down-draft chimney (8) back to
the storage shafts (2). The ambient air, which sweeps over the
ceil,;~ng (4) as the e~texnal cooling air for tll~ coollng surace,
passes via a supply-air duct (7) to the ceiling (4), where it
is warmed. The ambient air thus warmed is returned to the
outside via a spent-air duct (6).
Up-draft chimney (3) and down-draft chimney (8) are
separated from the charging passage (10) and, when required,
from a removal passage (11), by limiting walls (14) containing
charging orifices (13).
If a continuous storage operation is not required,
then the removal passage (11) and the charging orifices in said
limiting wall are dispensed with.
Howcver, it is also possible to dispense with the
local separation between up-draft chimney (3) or down-draft
chimney (8) and charging passage (10) and to design the charging
pclssage directly as the up-draft chimney (3) or down-draft chim-
ncy (8) (Fig. V). The limiting walls (14) with the chargingorifices (13) are then dispensed with in this case as wcll.
3t~3
~ ecause of the inc1ina-tion of the ceiling (4) and of
-the storage shafts (2) a speciEic direction of -the amhient air
flow can be a-ttained.
The prerequisite of a spec:ific direction of the ambient
air flow can also be attained when the individual storage shaf-ts
(2) in the storage rack (~) and the cooling duc-t (5) are so
designed that the resistances to flow for the two direc-tions of
flow differ in exten-t. The resistance to flow in the desired
direction of flow must then be smaller than that for -the opposi-te
direction. This can be a-ttained by correspondingly desiyned
baffles (20) at the storage shaft orifices (18, 19).
The direction of flow in the outer cooling cycle can
also be selected by varying heights of both the supply-air
duct (7) and the spent-air duct (6) at the building.
It has been found that an angle of inclination of -the
ceiling of < 15 is advantageous. This is a:Lso desirable for
constructional reasons so that the heig]lt of the building will
not be higher than necessary.
For thermodynamic reasons it is recommended to provide
the ceiling (4), designed as a heat exchanger, with cooling
ribs ~22). By enlarging the heat-transmitting surface the
temperature level in the storage depot is lowered. Furthermore,
at a specific cooling performance -the space required for the
ceiling (4) is reduced.
The shie]ding of the ceiling by baffles (21) (for
example, by a suspended thick concre-te ceiling) prevents a direct
irradiation of -the ambient air in the outer cooling cycle. Dust
activation and irradiation of other substances, wllich get into
-the heat exchallger with the ambient air is thus limited to
minimal values.
~ laterials which cause the radiation dosac3e to weaken
are used for tIIe baffles (21). Suitable materials are, for
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i93
example, concrete, iron or ]ead. The radiation-shielding baffles
(21) are designed, for example, as suspended concrete ceilings.
This ceiling (21) can be disposed directly above the storage
rack (9). In the region of the up-draft chimneys (3) and down-
draft chimney (8) said ceiling (21) has ports (24) which permit
t}-le cooling air -to flow into and out of the cooling cluct (5).
Up-draft chimney (3) and down-draft chimney (8) are
so constructed that scattered radiation effects are avoided,
i.e., an unimpeded radiation from the radioactive material into
the up-draft chimney (3) and down-draft chimney (8) and propaga-
tion of radiation due to scattering on the limiting walls is
prevented.
The production of the ceiling (4) from a metallic
material (for example, steel) is particularly favourable since
metals usually have very good heat-conducting properties and the
res;.starlce fo heat transfer between the 1nner and outer cooling
cyclcs ls minilnized. For ~he same reason it is recolr~ended to
sub~ect the surface of -the meta]lic ceiling (4) to a treatment
~hich promotes heat transport by radiation (for example, by
eloxadizing, coat of black paint).
A protection against corrosion (for example, galvaniz-
ing, eloxadizing) assures that the ceiling (4) also corresponds
to the requirements over a lengthy period.
Circular storage shafts (2) and circular storage con-
tainers (1) have been found to be favourable costwise. Other
cross sections, as for example, square or hexagonal ones, are
of course also suitable.
The lockable charging orifices (13) in the limiting
walls (14) are particularly suitable since they permit a local
30 separation between storage cell (15), charging passac3e (10) and
removal passage (11). This is of great aclvantage witn rec~.lrd
to possible measures of intervention.
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3t:;93
Cross f]ow-impeding baffles (16) within the storage
racks (9) can favourably prevent the formation of a localization
of heat at the highcst point of -the s~orage rack and thus also
the possibility of hot-spot formations.
Because of the fact that the storage shaft walls are
heated due to heat transport by radiation from the surface of
the storage containers the air in the spaces between the storage
racks (9) is warmed and rises upwards, where it accumulates in
the upper region of the storage racks (9) so that the locali~a-
tion of heat is possible in said region.
Therefore, in order to avoid this, there are installedmetal sheets (16) disposed transversely in the spaces between
the storage racks (9) so as to prcvent the air from f]owing
upwards.
Of course, the apparatus according to the p2-esent
invention can also be designed as a multistage heat e~changer
system with several heat exchangers arranged in tandem (Fig. IV),
the ceiling (4) being of multistage design.
This means that on the ceiling (4) the heat produced
in the storage cell (15) is not passed directly to the ambient
air but it is passed to a further closed c~cle (23), ~hich then
passes the heat to the ambient air.
