U.S. patent application number 11/001012 was filed with the patent office on 2005-10-06 for spallation device for producing neutrons.
This patent application is currently assigned to COMMISSARIAT A L'ENERGIE. Invention is credited to Ritter, Guillaume.
Application Number | 20050220248 11/001012 |
Document ID | / |
Family ID | 8852338 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050220248 |
Kind Code |
A1 |
Ritter, Guillaume |
October 6, 2005 |
Spallation device for producing neutrons
Abstract
A spallation device for production of neutrons includes a solid
spallation target that produces neutrons by interaction with a
hollow particle beam propagating within a first chamber, a second
chamber containing the spallation target, and a leak tight
partition separating the first and second chambers.
Inventors: |
Ritter, Guillaume; (Aix en
Provence, FR) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
COMMISSARIAT A L'ENERGIE
Paris 15eme
FR
|
Family ID: |
8852338 |
Appl. No.: |
11/001012 |
Filed: |
December 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11001012 |
Dec 2, 2004 |
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10332703 |
Jan 13, 2003 |
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6895064 |
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10332703 |
Jan 13, 2003 |
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PCT/FR01/02215 |
Jul 10, 2001 |
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Current U.S.
Class: |
376/190 |
Current CPC
Class: |
H05H 6/00 20130101; Y02E
30/30 20130101; G21C 1/30 20130101; Y02E 30/40 20130101; H05H 3/06
20130101; G21G 4/02 20130101 |
Class at
Publication: |
376/190 |
International
Class: |
G21G 001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2000 |
FR |
00/09028 |
Claims
1-15. (canceled)
16. Spallation device for production of neutrons, comprising: a
solid spallation target configured to produce neutrons by
interaction with the particle beam; a first chamber containing the
spallation target; a mechanism configured to generate the particle
beam; a second chamber in which the particle beam will propagate
towards the spallation target, along a propagation axis; a leak
tight partition through which the particle beam can pass,
separating the first chamber from the second chamber and reaching
the propagation axis; and a heat transporting fluid configured to
circulate in the first chamber to cool the spallation target,
wherein the particle beam is hollow and surrounds the propagation
axis.
17. Device according to claim 16, wherein the particles are chosen
from the group comprising protons, deuterium nuclei, tritium
nuclei, helium 3 nuclei, and helium 4 nuclei.
18. Device according to claim 16, wherein radial distribution of
current density in the particle beam is approximately gaussian and
is offset from an axis of symmetry of the particle beam.
19. Device according to claim 16, wherein the mechanism configured
to generate the particle beam is configured to produce the hollow
particle beam.
20. Device according to claim 16, wherein the mechanism configured
to generate the particle beam is configured to produce the hollow
particle beam from a solid particle beam.
21. Device according to claim 16, wherein the spallation target
comprises plural successive elementary targets, each elementary
target comprising a conical plate provided with a central
drilling.
22. Device according to claim 16, wherein a space is provided
between the leak tight partition and the spallation target for
circulation of the heat transporting fluid.
23. Device according to claim 16, wherein the spallation target has
an axis of symmetry of revolution that is coincident with the
propagation axis.
24. Device according to claim 16, wherein the leak tight partition
is convex towards an inside of the first chamber.
25. Device according to claim 16, wherein the leak tight partition
has an axis of symmetry of revolution coincident with the
progagation axis.
26. Device according to claim 16, further comprising means for
guiding the heat transporting fluid at least towards the leak tight
partition, in the first chamber.
Description
TECHNICAL FIELD
[0001] This invention relates to a spallation device for the
production of neutrons.
[0002] The device is used in applications in all fields in which an
intense neutron source is necessary.
[0003] The invention is particularly applicable to basic physics,
medicine and transmutation of material.
STATE OF PRIOR ART
[0004] Note that spallation corresponds to the interaction of
particles, and particularly protons, output from an accelerator and
with the high energy equal to about 200 MeV or more, with nuclei of
a target.
[0005] This interaction produces neutrons, for example about 30
neutrons per 1 GeV incident proton when the target is made of
liquid lead. About 80% of these neutrons originate from evaporation
and the remainder originate from inter-nuclear cascades. The
spectrum of these neutrons has a peak at about 3.5 MeV.
[0006] A spallation target may be solid, or it may be liquid. It
may also be thick or thin.
[0007] A liquid spallation target forms its own heat transporting
liquid. It is usually composed of a heavy metal in the liquid
state, for example chosen among liquid lead, eutectics of lead,
bismuth and mercury.
[0008] This liquid target cools the last interface separating it
from the vacuum chamber, the particles that will interact with this
target circulate in the vacuum chamber, or from any other buffer
region inserted between this vacuum chamber and the target.
[0009] FIG. 1 shows a longitudinal diagrammatic sectional view of a
known spallation device comprising a spallation target 2 made of a
liquid heavy metal. This device also comprises the chamber 4 in
which the spallation target circulates. Reference 6 represents the
spallation region.
[0010] An inlet 8 of a cold heat transporting fluid (target) can
also be seen at one end of this chamber 4, and an outlet 10 of the
hot heat transporting fluid can be seen at the other end of the
chamber.
[0011] A vacuum chamber 12 can also be seen within which the
particle beam 14 travels, which will interact with the target in
the spallation region 6. This vacuum chamber is separated from the
chamber 4 by a first window 16 forming a diaphragm that is cooled
by water circulation.
[0012] A second convex-shaped window 18 can also be seen, which is
convex towards the inside of the chamber 4. This second chamber 18
extends from the first window 16 towards the inside of the chamber
and cooperates with the window 16 to form a leak tight partition,
delimiting a buffer region 20 or an intermediate region, in which a
vacuum has also been created.
[0013] This second window 18 forms a membrane cooled by the
spallation target 2.
[0014] The convex shape of this window is dictated by the need to
guide the fluid entering through the inlet pipe 8 towards the
spallation region 6, minimizing the stagnation zone n in which the
cooling is not efficient.
[0015] A grid 22 can also be seen that will direct flow from the
liquid target and arranged in the chamber 4, between the second
window 18 and the spallation region 6.
[0016] As can be seen, the spallation target and the second window
18 have a symmetry of revolution about an X-axis along which the
particle beam 14 travels.
[0017] In the example shown, this beam that passes through the
first and second windows and the grid 22 in sequence before
interacting with the liquid target in the spallation region 6, and
the flow of this liquid target in this region 6, are in the same
direction.
[0018] Now consider known spallation devices using solid spallation
targets.
[0019] This type of device comprises a window that will confine the
solid target to be aligned with particle beam acceleration means,
the target itself being intended to supply neutrons by spallation
and for example being in the form of boards, cones, bars, tubes or
microballs, and a heat transporting fluid that will cool the
spallation target. The nature of each of these devices is
determined by its thermal, hydraulic, mechanical and neutronic
properties.
[0020] For a solid target that will supply thermal neutrons, the
transporting fluid way be water. This is very difficult if not
impossible when the medium surrounding the spallation target has a
fast neutron, spectrum.
[0021] FIG. 2 shows variations in the current density D1 of a
particle beam, used with a known spallation target, as a function
of the distance R to the centre line of this beam.
[0022] This type of beam, for which the current density has a
distribution approximately in the shape of a notch (curve I) or a
bell (curve II), induces strong thermomechanical stresses in the
leak tight partition separating the spallation target from the
vacuum in which the beam is propagated, and also in the target when
the target is solid, due to a high current density gradient.
[0023] This particle beam has a peak on the axis of symmetry of the
target, in a zone in which the heat transporting fluid circulates
very little (see curve III in FIG. 2 which is the curve of
variations of the velocity V of the fluid as a function of R).
Consequently, there is a hot point on the leak tight partition that
limits the performances of the spallation target and can threaten
confinement.
[0024] In some spallation devices, including the device shown in
FIG. 1, the existence of this zone in which the heat transporting
fluid circulates very little on the centre line of the particle
beam, makes it necessary to install the grid 22 irradiated directly
by the beam and makes it possible to channel the flow so as to
limit the length of this zone in which the heat transporting flow
velocity is too low.
[0025] Like all elements placed on the centre line of the beam,
this grid is affected by irradiation from this beam and its
mechanical and thermal performances deteriorate during time.
However, this grid does not contribute to spallation and its volume
is such that if any damage occurs, this grid will in turn damage or
even destroy the spallation target, particularly by partial or
total closing off of heat transporting fluid circuits.
[0026] Cooling by high flow water circulation in the membrane 16
generally made of steel, controls temperature rises caused by the
passage of the beam.
[0027] In a target subjected to an intense beam, the presence of a
heavy material immediately behind the window 18 causes the window
18 to absorb part of the energy of the beam. This systematically
occurs with liquid targets.
[0028] Cooling of the window 18 is only possible on one face of the
window, and this window has to be cooled (or any other window) has
to be cooled by the liquid target itself.
[0029] There will be a hot point if the particle beam has a current
density peak at the point at which the velocity of the target
forming the heat transporting fluid is minimum.
[0030] Note also that spallation devices are also described in
documents [1] and [2], which like other documents mentioned
subsequently, are mentioned at the end of this description.
PRESENTATION OF THE INVENTION
[0031] The purpose of this invention is to overcome the
disadvantages mentioned above with known spallation devices and
more precisely to minimize thermomechanical constraints applied to
key components of these devices, and particularly the leak tight
partition separating the spallation target from a chamber in which
the vacuum is created and through which the particle beam passes
before it reaches the target.
[0032] Precisely, the purpose of this invention is a spallation
device for the production of neutrons, this device comprising:
[0033] a spallation target that will produce neutrons by
interaction with a particle beam,
[0034] a first chamber containing the spallation target,
[0035] means of generating the particle beam,
[0036] a second chamber in which the particle beam will propagate
towards the spallation target, along a line of propagation (which
obviously requires the creation of a low pressure, below 10.sup.-8
Pa in this second chamber),
[0037] a leak tight partition through which the particle beam can
pass, separates the first chamber from the second chamber and
reaches this propagation axis, and
[0038] a heat transporting fluid intended to circulate in the first
chamber to cool the spallation target,
[0039] this device being characterized in that the particle beam is
hollow and surrounds the propagation axis.
[0040] Preferably, the particles are chosen to be in the group
comprising protons, deuterium nuclei, tritium nuclei, helium 3
nuclei and helium 4 nuclei.
[0041] According to a preferred embodiment of the device according
to the invention, the radial distribution of the current density in
the particle beam in the transverse half-plane delimited by the
propagation axis is approximately gaussian and is offset from the
axis of symmetry of the beam. This arrangement is characterized by
a minimum current density on the centre line of the beam.
[0042] This type of current density in the beam minimizes
mechanical stress concentrations.
[0043] According to a first particular embodiment of the device
according to the invention, generation means are designed to
produce the hollow particle beam directly, in other words by
themselves.
[0044] According to a second particular embodiment, the generation
means are designed to produce the hollow particle beam starting
from a solid particle beam.
[0045] The spallation target in this invention may be solid.
[0046] In this case, according to a preferred embodiment of the
invention, the spallation target comprises several successive
elementary targets, each elementary target comprising a conical
plate in which there is a central drilling.
[0047] This type of elementary target has a shape well adapted to
the hollow beam and to the flow of the heat transporting fluid.
[0048] Preferably, if the spallation target is solid, a space is
provided between the leak tight partition and the spallation target
for circulation of the heat transporting fluid.
[0049] On the contrary, with this invention, it is possible to use
a liquid spallation target, this target then also forming the heat
transporting fluid.
[0050] In this case, according to a first particular embodiment of
the invention, the spallation target moves in the first chamber
along the propagation axis and along the direction of propagation
of the particle beam.
[0051] According to a second particular embodiment, if the
spallation target is liquid, the spallation target moves within the
first chamber along the axis of propagation and in the direction
opposite to the direction of propagation of the particle beam.
[0052] According to a preferred embodiment of this invention, the
axis of symmetry of the spallation target is coincident with the
propagation axis.
[0053] Preferably, the leak tight partition is convex towards the
inside of the first chamber.
[0054] In this invention, the leak tight partition preferably has
an axis of symmetry of revolution that is coincident with the
propagation axis.
[0055] Preferably, the device according to the invention also
comprises guide means for the heat transporting fluid at least in
the direction of the leak tight partition, in the first
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] This invention will be better understood after reading the
description of example embodiments given below, for guidance only
and in no way limitative, with reference to the attached drawings
on which:
[0057] FIG. 1 is a diagrammatic longitudinal sectional view of a
known spallation device that has already been described,
[0058] FIG. 2 diagrammatically illustrates the radial distribution
of the current density in a particle beam that is used in a known
spallation device,
[0059] FIG. 3 diagrammatically illustrates the radial distribution
of the current density in a particle beam that can be used within
this invention,
[0060] FIG. 4 is a diagrammatic view of a scanning device used to
obtain a hollow beam that can be used in the invention,
[0061] FIG. 5 diagrammatically illustrates the radial distribution
of the current density in a particle beam that arrives at this
scanning device,
[0062] FIG. 6 is a diagrammatic view of various systems of a
spallation installation,
[0063] FIG. 6A diagrammatically illustrates the possibility of
obtaining two different configurations for the flow of the heat
transporting fluid and the particle beam in a device according to
the invention with symmetry of revolution about the axis of the
incident particle beam,
[0064] FIG. 7 is a partial cross sectional view of a known conical
plate that can be used in the invention as an elementary spallation
target,
[0065] FIG. 8 diagrammatically illustrates a spallation target that
can be used in the invention and that is formed from a stack of
such elementary targets,
[0066] FIG. 9 shows the interposition of a part of the heat
transporting fluid between the target in FIG. 8 and the leak tight
partition separating this target from a vacuum chamber from which
the particle beam arrives, and,
[0067] FIGS. 10 to 12 are diagrammatic views of particular
embodiments of the spallation device according to the
invention.
DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS
[0068] In the examples of the invention described below, a hollow
particle beam also called an "annular particle beam" is used, in
which the radial current density distribution is approximately
gaussian. FIG. 3 diagrammatically illustrates variations of this
density D2 as a function of the distance R from the hollow
beam.
[0069] This is a means of solving the following two problems:
[0070] limiting the current density gradient to avoid excessive
internal mechanical stresses in key components of the spallation
device, and particularly the leak tight partition, and the
spallation target in the case of a solid target, and
[0071] moving the peak power away from the axis of symmetry of the
target to avoid cooling problems.
[0072] An annular distribution of the current density in the
particle beam can be obtained using magnetic optical means that are
placed on the input side of the leak tight partition.
[0073] FIG. 4 diagrammatically illustrates the generation of a
hollow particle beam. FIG. 4 shows a vacuum chamber 24 that
prolongs a particle accelerator, not shown, designed to form a
solid particle beam 26 and to accelerate this beam. This vacuum
chamber (that is provided with means not shown to create the
vacuum) forms an elbow at which there is a curvature magnet 28.
After this curvature magnet, there is a magnetic system 30 designed
to make high frequency rotary scanning to obtain a hollow particle
beam 32 with an axis denoted X, starting from the solid beam
26.
[0074] The vacuum chamber 24 terminates with a convex leak tight
partition 38.
[0075] This partition is on the output side of a buffer-partition
36, if there is one (in this case, cooperating with partition 38 to
delimit a zone reference 34 in FIG. 4) and inside the chamber 40
containing the spallation target.
[0076] The thickness and the material from which each of the
partitions 36 and 38 are made are obviously chosen such that the
beam 32 can pass through these partitions.
[0077] FIG. 5 shows variations of the current density D3 in the
solid particle beam 26 as a function of the distance R from the
centre line of the beam, at the exit from the curvature magnet 28.
It can be seen that the beam 26 is approximately gaussian.
[0078] After the scanning system 30, and particularly in the
spallation target, the particle beam becomes hollow, the
distribution of the current density in this hollow beam being shown
in FIG. 3.
[0079] The magnetic system 30 placed on the input side of the leak
tight partition 38, is located on the trajectory of high energy
particles that are backscattered by the spallation target. This is
why the system is preferably composed of materials that are not
very sensitive to radiation and activation. The curvature magnet 28
protects the particle accelerator from these high energy
backscattered particles.
[0080] Note that other devices according to the invention can be
made without any curvature magnet. In this case a vacuum chamber is
used which is approximately straight on the input side of the
magnetic scanning system 30.
[0081] The scanning possible with the system 30, preferably
satisfies the requirements mentioned in document (3).
[0082] In another example, instead of forming the hollow particle
beam from an accelerated solid beam, the hollow beam is formed from
the particle source and this hollow beam is then accelerated.
Further information about this subject can be found in document
[4].
[0083] Note now that it is possible to provide guide means in the
chamber 40, for example ribs, to channel cooling onto the leak
tight partition 38 in order to avoid the need to replace this
partition 38 too frequently.
[0084] Furthermore, in one device conform with the invention, it is
preferable that the spallation target should be cooled by forced
convection, regardless of whether the target is solid or
liquid.
[0085] Furthermore, in a device according to the invention, the
hollow particle beam may be input to the spallation target at any
angle, from above or below and either obliquely or
horizontally.
[0086] FIG. 6 diagrammatically illustrates several systems, all of
which form an example of a spallation installation using the
invention.
[0087] This installation comprises:
[0088] a system 42 that supplies the hollow particle beam and which
includes the curvature magnet 28 and the scanning system 30 in FIG.
4,
[0089] a spallation device 44 conform with the invention, onto
which the hollow beam is directed,
[0090] a system 46 comprising heat transporting fluid transport
circuits,
[0091] a heat exchanger system 48 that receives the hot heat
transporting fluid 50 from the device 44 and supplies the cold heat
transporting fluid to this device through the system 46,
[0092] a useful coverage system 54 comprising irradiation means or
nuclear fuel and/or isotopes to be transmuted and receiving
neutrons 56 produced by the spallation device,
[0093] a system 58 for cleaning circuits and for the treatment of
radioactive effluents that is connected to the heat transporting
fluid transport circuits system 46, and,
[0094] a system 60 for draining these circuits.
[0095] This drain system 60 is useful for starting, stopping and
maintenance operations in the installation and also during
accidents or incidents in this installation.
[0096] The system 58 is used to extract undesirable species from
the installation such as heavy radioactive contaminants and
radioactive gases, and particularly tritium.
[0097] In one device according to the invention, accelerated
particles are preferably lightweight (charged) particles such as
protons, deutons, tritons, helium 3 nuclei, and helium 4
nuclei.
[0098] For example, protons may be used with an energy Ep equal to
approximately 600 MeV to achieve a compromise between the neutronic
efficiency of spallation, damage occurring on the leak tight
partition and on other structures of the target, activation of the
accelerator by particles lost due to space charge phenomena and
activation of the spallation device, including biological shielding
and the earth.
[0099] Depending on the configuration, this energy Ep can be
adjusted within a range varying from 200 MeV to several GeV.
[0100] The intensity of the beam supplied by the accelerator is
determined by spallation neutron needs of users of the spallation
device, and for example varies between 0.5 mA and several hundred
mA.
[0101] Thus, in one device according to the invention with a
symmetry of revolution about the axis of the incident particles
beam, it is possible to obtain two different configurations for the
flow of heat transporting fluid and the particle beam (as shown in
FIG. 6A in which curve I represents the fluid velocity V and curve
II represents the current density D of the beam), due to the use of
an annular particle beam while maintaining symmetry of revolution
of the device about the axis of the beam.
[0102] Moreover, in one device conform with the invention using a
solid spallation target, it is possible to separate cooling of the
leak tight partition from cooling of the target, in which there are
more degrees of freedom to direct the heat transporting fluid.
[0103] In the invention, it is advantageous to use conical plates
in order to form a solid spallation target. An example of these
plates is shown diagrammatically in FIG. 7.
[0104] At the centre of each plate 62a, there is a recess 65
through which the heat transporting fluid can dissipate heat
generated in this plate.
[0105] A spallation target 63 is formed using several such plates
62 one after the other such that the resulting assembly 63 has a
symmetry of revolution about the X axis of the hollow particle beam
64, as shown in FIGS. 8 and 9.
[0106] The plates 62 are arranged one after the other such that the
solid angle perceived by an illuminated part of a plate facing the
region in which the source neutrons are used and facing the
partition 74 in FIG. 9 (backscattered neutrons) is occupied by a
non-illuminated portion of the plate and vice versa.
[0107] Thus, the source spectrum is degraded in this part of the
target before it reaches the useful region, so that damage can be
limited to structural materials when this damage is due to the
highest energy neutrons.
[0108] Furthermore, the quantity of backscattered neutrons is
minimized, so that the life of the partition 74 is increased (FIG.
9) and damage inflicted to the structures of the accelerator before
the target can be limited.
[0109] Note that the arrows 66 in FIG. 8 represent the heat
transporting fluid.
[0110] With reference to FIG. 7, it can be seen that the plates are
clad, and a hollow space 68 is provided between an elementary
spallation target composed of a conical plate 70, for example made
of tungsten, and the cladding 72 of this elementary target, for
example a steel or aluminium alloy cladding, in order to enable
expansion of the elementary target during use.
[0111] Note also that the thickness of the plates 70 varies from
one plate to another, to flatten the axial distribution of the
neutron source.
[0112] With a solid target like that shown in FIG. 8, there are
problems related to corrosion by the heat transporting fluid. For a
solid spallation target, water is preferably used as a heat
transporting fluid in the case of a blanket when thermal neutrons
are necessary, or liquid sodium in the case in which thermal
neutrons are not required. The technologies associated with these
types of fluid are controlled.
[0113] Spallation reactions on heat transporting liquids are
unwanted because they reduce the neutron efficiency of the
installation and contribute to general or localized activation of
circuits (by redepositions).
[0114] However, purification technologies for circuits contaminated
with unwanted species are known, both for sodium and for water.
[0115] Furthermore, heat transporting gases like carbon dioxide or
helium hardly react with the incident particles due to the low
density of these gases, which improves the efficiency without
hindering overall operation of the installation.
[0116] Thus, a solid spallation target has the advantage that it
confines radioactivity in this target (which is clad) and circuit
purification systems. The spatial layout of the elements of this
solid target is compatible with the handling system provided for
these elements.
[0117] Liquid spallation targets are preferably composed of
materials for which the atomic mass is high and which are pure or
are in eutectic form so that they are liquid at temperatures
compatible with the mechanical and chemical behaviour of the
structural materials used in the target and in the associated
circuits.
[0118] For example, mercury, lead and lead eutectics may be used.
The main advantage of a eutectic such as lead-bismuth with 45% by
mass of lead and 55% by mass of bismuth, apart from its low melting
temperature, is that its density does not change during its phase
change. Usually, it is preferred not to have any bismuth because
bismuth can easily be activated into polonium 210 and other long
life radioactive isotopes.
[0119] The cross sections of inelastic reactions of lead (n, xn)
particularly the (n, 2n) reaction for a neutron energy exceeding
6.22 MeV, is a means of maximizing the efficiency of the
source.
[0120] Mercury will be avoided in some devices due to its very
strong physical corrosivity. At ambient temperatures, static
mercury dissolves about 1 mm of steel per year.
[0121] Lead and lead alloys are also corrosive for steels, which is
the reason for preferring clad solid targets. Pure or alloyed
liquid lead can be used, while limiting corrosion effects, due to
control of the oxygen concentration in the liquid lead. Operating
conditions define an oxygen concentration interval above which the
lead and the impurities are oxidized and precipitate, and below
which lead corrodes steel. Steel is then dissolved in the circuit
and can be deposited in cold zones or in zones in which the
velocity of the heat transporting fluid is low. This type of
deposit can cause blockage of circuits.
[0122] Finally, materials used in the invention are transparent to
neutrons in the main spectrum of the target. Thus, pure or alloyed
lead may be suitable for fast or thermal spectrum targets even if
some isotopes naturally present would be worth extracting by
isotope separation due to their large neutronic capture cross
section.
[0123] Mercury and tungsten are better adapted to targets with
essentially fast spectra to the extent that these two elements are
more capable of capturing neutrons in the thermal range.
[0124] In the invention, the spallation target (that contains the
spallation region) is confined, and only allows source neutrons to
pass.
[0125] The structures included in this target are transparent to
neutrons, and in a nominal or degraded situation, enable the best
possible confinement of the materials. Any mechanical isolation
system for the spallation region thus defines the target.
[0126] Biological shielding for the public and persons operating
the spallation device is sized to comply with the regulations in
force.
[0127] The accelerated particles are stopped by the spallation
target so as to maximize the efficiency.
[0128] Neutronic shielding for which a device according to the
invention is provided, also provides a remedy to problems of
protection against charged particles.
[0129] The position of the spallation target in the system in which
it is installed (for example the core of a power nuclear reactor or
a transmutation reactor, the moderator of a nuclear reactor or a
network of elements that can generate tritium) is preferably
determined by maximizing the weighting factor .phi.* that is
defined in document [5].
[0130] We will now consider the advantages provided by the
invention.
[0131] The use of a spallation target with an annular particle beam
is an easy and efficient means of dissipating heat generated in the
leak tight partition or window separating the spallation target
from the closest vacuum zone to this spallation target (without any
complicated geometry and without needing the grid 22 in FIG. 1,
which is exposed to irradiation by the beam).
[0132] It is also possible to make a device conform with the
invention operate with a leaky flow or a frontal flow of the heat
transporting fluid, without using a flow of heat transporting fluid
to cool sensitive components in the device. All that is necessary
is to make the heat transporting fluid enter through a region not
affected by spallation.
[0133] These advantages apply mainly to the leak tight partition
which is the most highly stressed part of the system. This leak
tight partition must resist a very low pressure, usually of the
order of 10.sup.-9 Pa, on the side from which the particle beam
arrives, and the pressure of the heat transporting fluid on the
other side. The pressure of the heat transporting fluid is very
high, usually more than 5.times.10.sup.6 Pa when this fluid is
water or a gas, and is of the order of 10.sup.5 Pa when the heat
transporting fluid is a liquid metal.
[0134] Furthermore, the insertion of a layer of heat transporting
fluid between the leak tight partition and the spallation target is
a means of reducing the proportion of backscattered neutrons close
to this leak tight partition. This is due to a solid angle effect
and due to the fact that the heat transporting fluid diffuses the
neutrons.
[0135] FIG. 9 shows a diagrammatic longitudinal sectional view of
the leak tight partition or window 74 that is followed by a set 63
of conical blades 62 with central drilling, these blades being
aligned along the X direction of the device (propagation axis of
the particle beam).
[0136] The layer of heat transporting fluid that circulates between
the leak tight partition 74 and the conical plate 62 closest to the
leak tight partition, is symbolically shown by two arrows 66
closest to this partition. The arrows 76 show backscattered
neutrons. The arrangement of the blade 62 can reduce the quantity
of these neutrons towards the beam centre line in the direction of
the partition 74. FIG. 9 also shows the incident particles beam
64.
[0137] FIG. 10 is a diagrammatic longitudinal sectional view of a
particular embodiment of the spallation device according to the
invention.
[0138] In this example, the device forms part of the hybrid reactor
for transmutation or energy production, the spallation target 78 is
a liquid metal and forms the heat transporting fluid and the flow
of this fluid is leaking.
[0139] The core 80 (fissile part) of the reactor in which the
device was installed, can be seen. The plenum 82 can be seen on
each side of the core 80.
[0140] The chamber 84 in which the spallation target 78 is
circulated, and one end of the vacuum chamber 86 in which the
hollow particle beam 88 is propagated in the direction of the
spallation zone, can also be seen. This zone is delimited by the
chain dotted lines 90, within the chamber 84.
[0141] The end of the vacuum chamber 86 is formed by the convex
shaped leak tight partition 92, made for example of steel, which is
convex towards the inside of the chamber 84 and that allows the
beam 88 to pass through it.
[0142] The shape of the partition 92 is approximately hemispherical
to prevent mechanical stress concentrations.
[0143] The means 89 of generating the hollow beam are not shown.
Refer to the description of FIG. 4 for further information in this
respect.
[0144] The arrows 94 symbolically show circulation of the liquid
metal target. This circulation takes place along the axis of
propagation of the beam and along the direction of propagation of
the beam.
[0145] This X axis is the axis of symmetry of revolution of the
chamber 84 and the leak tight partition 92.
[0146] The ribs 96 fixed to the internal partition of the chamber
84 close to the leak tight partition 92, can also be seen. The
spacing between these ribs is sufficient to enable the particle
beam 64 to pass without any interference. These ribs form a flow
guide for the liquid target and therefore for the heat transporting
fluid.
[0147] This fluid guide improves turbulence, and therefore heat
exchanges at the leak tight partition 92.
[0148] The arrows 98 in FIG. 10 symbolize neutrons generated in the
spallation zone.
[0149] The installation in which the device in FIG. 10 is installed
is started progressively. The first step is to warm the heat
transporting fluid up to the operating temperature in successive
steps in a storage reservoir (not shown), and the heat transporting
fluid is then introduced into the circuits (not shown) provided for
its circulation. The pumps (not shown) are then installed, and
circulate the fluid. The next step is to start the particle
accelerator (not shown) at a very low intensity, and the power is
increased to minimize stresses on the various structures in the
installation.
[0150] The same procedure is used for stopping and for starting, in
the reverse order.
[0151] Activation of the liquid heat transporting fluid and the
residual power induced prevent the heat transporting fluid from
freezing. Regardless of the configuration, the spallation device is
sized such that the residual power, after a planned or accidental
stoppage, can be dissipated by passive means such as natural
convection.
[0152] The intensity of the accelerator is determined by neutron
application needs, once the increase in power is complete.
[0153] In the case of a reactor generating electricity or used for
transmutation, the reactivity and power (measured from data about
the heat transporting fluid input and output temperatures and
information from the neutronic control system) define the beam
intensity.
[0154] In the case of a neutron source to be used for fundamental
physics research or technological tests, the power extracted from
the spallation target is controlling.
[0155] FIG. 11 shows a longitudinal diagrammatic sectional view of
another particular embodiment of the device according to the
invention, once again using a liquid metal spallation target, but
with a frontal flow instead of a leaky flow for this liquid target
and therefore for the heat transporting fluid.
[0156] Therefore, this flow takes place in the direction opposite
to propagation of the particle beam 88.
[0157] The device in FIG. 11 is identical to the device in FIG. 10
except that the ribs 96 are eliminated and at the end of the
chamber 84, opposite to the end with the partition 92, the device
comprises a main tubular flow guide 100, the axis of which is the
axis of symmetry of revolution of the device (coincident with the X
axis of propagation of the particle beam 88), and openings 102 on
each side of this main flow guide.
[0158] The inside diameter of the particle beam is greater than the
outside diameter of this main flow guide.
[0159] The liquid spallation target (heat transporting fluid)
enters the chamber 84 through the flow guide 100 and openings
102.
[0160] FIG. 12 shows a diagrammatic longitudinal sectional view of
another particular embodiment of the device according to the
invention.
[0161] This device is identical to the device in FIG. 10, except
that it does not include ribs 96 and that the spallation target in
it is solid.
[0162] In the example shown in FIG. 12, the heat transporting fluid
flow 95 symbolized by the arrows 94 flows in the same direction as
the propagation of the particle beam 88.
[0163] The spallation target 63 comprises several conical
elementary targets 62 with central drilling, like the target in
FIG. 7. These targets 62 are identical to each other and arranged
one after the other in the chamber 84, along the X axis of
propagation of the beam which is also the axis of symmetry of
revolution of the spallation target and the leak tight partition
92.
[0164] The diameter common to the drillings 65 is less than the
inside diameter of the beam 88, and the targets 62 have a larger
common diameter that is more than the outside diameter of the beam
88.
[0165] Means, not shown, are provided to fix each elementary target
62 to the inside partition of the chamber 84.
[0166] The heat transporting fluid 95 circulates around the leak
tight partition 92, between the leak tight partition and the
elementary target 62 closest to this leak tight partition, and
between the other elementary targets 62.
[0167] Due to their conical shape, all these elementary targets can
also be used to guide the flow of heat transporting fluid.
[0168] The spallation region, delimited by lines 90 in FIGS. 10 and
11 and by the elementary end targets in the case in FIG. 12, is
advantageously arranged so as to maximize the neutronic efficiency
of the spallation device.
[0169] In the case of devices according to FIGS. 10 to 12, a
mechanical or magnetic pump can be provided to obtain forced
convection of the heat transporting fluid.
[0170] The following documents are mentioned in this description,
in the order shown below:
[0171] [1] U.S. Pat. No. 5,160,696 (C. D. Bowman)
[0172] [2] U.S. Pat. No. 5,774,514 (C. Rubbia)
[0173] [3] J. M. Lagniel, The various parts of the
accelerator--From the proton source to the 1 GeV beam, GEDEON
Workshop "Which accelerator for which DEMO?" pp. 1-24 Aix en
Provence (France), Nov. 25-26, 1999.
[0174] [4] U.S. Pat. No. 5,811,943 (A. Mishin et al.)
[0175] [5] M. Salvatores et al., Nuclear Science and engineering,
126, pp. 333-340 (1997).
* * * * *