Patent Description:
The world currently depends heavily on fossil fuels, this dependency creates severe effects on climate, warming and biosphere degradation. The only alternative known to man is nuclear power, and the only one capable of achieving the appropriate safety and fuel efficiency is fusion power.

For fusion power to be an adequate alternative, fusion reactors need to be cheaper and smaller than the devices currently being envisioned, those based on the ITER design and DEMO. There is a need for fusion energy devices that are less complex, cheaper, and faster to construct.

The current devices being envisioned derive themselves from the designs of the <NUM>, therefore these designs consider a minimum size with a major radius in the range of <NUM>-<NUM>. Therefore, the production costs of actual reactors are enormous, prognosticated to over several billion dollars, and the construction time set to several decades with current construction methods. In addition to that, the cost of produced electricity by any power plant is affected by the cost of said power plant, which is approximately proportional to the plant's volume, so bigger machines, even if working on fusion principles would still produce electricity at a higher cost than other smaller machines. For these reasons there is a need for a fusion reactor that is smaller in size but that also has a higher fusion-power-density.

Further, fusion reactors also involve other sources of high costs during operation. One of them are the plasma facing components (PFCs), these are the components that face the plasma in the reaction chamber. PFCs are subject to very high energy during operation and as such the materials need to be replaced frequently. Another cost is that of the fuel, fusion power plants use tritium, a very expensive hydrogen isotope, for which the cost of a single gram may be as high as <NUM>,<NUM> dollars.

Those working in model fusion power plants have had little success in overcoming these difficulties in a way that also allow for reduction of the overall size of the reactor. As an example, ITER rests on <NUM>-hectare platform and is over <NUM> meters tall. The follow-up reactor, DEMO, is expected to be even bigger with an increase in linear dimensions of about <NUM>%.

The prior art teaches solutions as detailed next, some of them are based on using liquid metal as a plasma facing component. To the best understanding of the inventors these methods present a number of deficiencies that make them unsuitable or insufficient to accomplish the long-term goals of reducing the overall size of fusion reactor and increase the fusion-power density whilst also maintaining low costs.

A review of trends in liquid metals as plasma facing components is "<NPL>. Specifically, Abdou notices that there are some possible advantages if concepts become realizable, including: high power density capacity, smaller and lower cost components and improvements in plasma stability and confinement. Abdou describes liquid metal mixtures in a liquid medium including Sn-Li mixtures, Pb-Li mixtures, and the molten salt FLiBe. Abdou also describes how to use these liquid metal mixtures and fashion them into a liquid wall, methods to push the liquid metal into the wall are described, including: gravitymomentum driven, which uses centrifugal force; electromagnetically restrained concept, in which current is injected to the flow so that a force field that pushes the flow to the wall is generated; and other methods that include pressure driving forces. Abdou notices in page <NUM> that it is not known whether the advantages are realizable into a single concept, and he then writes that even if just a subset of these advantages are achieved, a remarkable progress toward attractiveness of fusion energy systems would be accomplished. Therefore, there is a need for a solution that realistically implements said advantages into a single concept.

In <CIT> a fluidized wall for protecting fusion chamber walls is described. The fluidized wall is described in two ways, as being a liquid lithium metal waterfall or as being a waterfall of solid pellets of lithium-ceramic. The waterfall is described as forming a blanket that protects the structural materials of the chamber. Because the wall is described as using lithium it suffers from being a very poor neutron attenuator. Because the fluid is falling as a waterfall, additional complications from this configuration include open spaces in the waterfall and liquid density issues, which results in an uneven shielding. This is also true of the lithium-ceramic pebbles described.

Another material used for fusion reactor blankets is metal beryllium, having neutron multiplying properties. Pebbles created for this material have been described in, for example <CIT> Such pebbles may not be allowed to come in contact with liquid metal mixtures as they may react making the pebbles unsuitable for their neutron multiplying purpose.

Prior art document <CIT> discloses a liquid metal mixture comprising lithium and lithium hydride. Prior art document <CIT> discloses a liquid lithium first wall for a tokamak. Prior art document <CIT> discloses a liquid metal mixture first wall for a tokamak, the liquid metal mixture comprising liquid Li and suspended lithium-containing particles.

Thus, there remains a need for a solution to the fusion problem that addresses how to build a smaller, lower cost, and higher power density fusion reactors or their components, while still using readily available materials.

One embodiment addresses all or some of the drawbacks of known plasma confinement walls or components.

According to claim <NUM>, the invention provides a first wall adapted to cover an inner wall of a vessel, the first wall being made of a liquid metal mixture comprising at least lithium and lithium hydride, the first wall further comprising pebbles suspended in the liquid metal mixture, each pebble being a neutron attenuating pebble, a neutron multiplying pebble or a neutron attenuating and multiplying pebble.

The first wall further comprises pebbles suspended in the liquid metal mixture, each pebble being a neutron attenuating pebble, a neutron multiplying pebble or a neutron attenuating and multiplying pebble, the pebbles being for example sized between <NUM> and <NUM>.

In one embodiment, at least one of the pebbles have a core externally coated by an outer shell.

In one embodiment, the core is a hollowed core, for example filled with pores and/or the outer shell is a hollowed shell, for example filled with pores.

In one embodiment, at least some of the pebbles are located at an outer surface of the liquid metal mixture.

In one embodiment, the mixture further comprises lithium tritide and/or lithium deuteride.

In one embodiment, the mixture comprises between <NUM> and <NUM> % in molar content of lithium hydride, lithium tritide and/or lithium deuteride, and the width of the first wall is for example comprised between <NUM> centimeters and <NUM> centimeters; or the mixture comprises between <NUM> % and <NUM> % in molar content of lithium hydride, lithium tritide and/or lithium deuteride and the width of the first wall is for example comprised between <NUM> centimeters and <NUM> centimeters.

One embodiment provides a vessel comprising an inner wall, wherein said inner wall is covered with a first wall according to an embodiment.

One embodiment provides a first wall device adapted to form a first wall according to an embodiment, wherein the device comprises:.

In one embodiment, the flowing means comprises:.

The flowing means comprise means for adding pebbles to the liquid metal mixture, for example hatchings or access points in a first tube of the flowing means, and may be adapted to circulating the liquid metal mixture at high temperatures, for example at temperatures comprised between <NUM> and <NUM>.

In one embodiment, the vessel or the device further comprises electrodes located on the inner wall of the vessel, the electrodes being adapted to applying an electric current to the liquid metal mixture of the first wall.

In one embodiment, the vessel or the device further comprises means for generating a magnetic field inside the vessel.

In one embodiment, the vessel has substantially a shape of a torus.

In one embodiment, the vessel forms at least part of a plasma confinement vessel, a nuclear reactor vessel, or an isotopic separation chamber.

According to claim <NUM>, the invention also provides a method adapted to form a first wall according to an embodiment, wherein the method comprises injecting a liquid metal mixture to an inner wall of a vessel, the liquid metal mixture comprising at least lithium and lithium hydride. The method further comprises injecting pebbles in the liquid metal mixture before or during the injection step, each pebble being a neutron attenuating pebble, a neutron multiplying pebble or a neutron attenuating and multiplying pebble.

In one embodiment, the method further comprises:.

Advantages of an embodiment of the lithium hydride first wall device may be listed as: allow for much more compact first wall in a fusion reactor, the first wall may be as small as a few centimeters but usually between <NUM> to <NUM> or more; there is no need for a separate lithium breeding blanket because the first wall also acts as the breeding blanket, it is possible to modify the amount of attenuation or absorption of neutrons, so it is possible to test different configurations easily and to change on the fly the tritium breeding ratio. Therefore, it would be possible to construct smaller fusion reactors if the disclosed liquid first wall is used. Other advantages include the prolonged life-time of the solid parts of the reactor, including structural materials and normal-conducting or superconducting coils, improved safety and reduced maintenance and replacement costs in otherwise highly radioactive environments. Other technical advantages will become apparent to someone skilled in the art from the detailed description, figures, and claims. Moreover, while specific advantages have been enumerated above, different embodiments may include all, none or some of the advantages listed.

For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail.

Unless specified otherwise, the expressions "around", "approximately", "substantially" and "in the order of" signify within <NUM> %, and preferably within <NUM> %.

The following figures are not to scale. It should be noted that the drawings refer to an embodiment of the disclosed lithium hydride first wall, sometimes also referred simply as device, when no ambiguity in the text is anticipated. Other embodiments may be possible, and some are described in the figures as well. The actual dimension and/or shape of each of the components of the embodiment may vary. Only important details of the embodiment are shown, however one of ordinary skill in the art can appreciate how the overall device may be constructed, without undue experimentation. Some details have been omitted from the drawings, but the inventors believe that adding these details is unnecessary for the overall appreciation of the characteristics of the invention disclosed. Some characteristics of the embodiment appear exaggerated to facilitate understanding. The embodiments disclosed, and alternatives observed should not be considered as limiting the invention as defined by the claims.

A first embodiment of lithium hydride first wall device is shown in <FIG>. A pump <NUM> injects a liquid metal flow <NUM> (liquid metal mixture) by means of an outflow tube 104a (first tube) into a vessel <NUM>. The outflow tube 104a may be split in two or more so that the liquid metal flow <NUM> may flow over the inner wall (s) <NUM> of the vessel <NUM>. The liquid metal flow <NUM> may be filled with a plurality of pebbles <NUM>. The liquid metal flow <NUM> returns to the pump by means of an inflow tube 104b. The inflow tube 104b (second tube) may have a plurality of inlets to collect the liquid metal flow <NUM> flowing over the inner walls <NUM> of the vessel <NUM>.

A plurality of electrodes <NUM> may be disposed on the inner wall <NUM> of the vessel <NUM>. A magnetic field <NUM> (B) may be applied inside of the vessel <NUM>. The electrodes may apply a current of density j, resulting in a force of density jxB, which forces the liquid metal flow to stick to the solid wall.

According to an example, the vessel forms at least part of a plasma confinement vessel. In other examples, the vessel may form at least part of a nuclear reactor vessel, or of an isotopic separation chamber.

In the first embodiment, the pump <NUM> may be fashioned to allow for circulation of high temperature liquid metals. Operating temperatures may be between <NUM> and <NUM> in fusion reactor applications. The inflow 104a and outflow 104b tubes are also adapted to operate at these temperatures. The inflow tube 104a takes the liquid metal flow <NUM> pumped from the pump <NUM> and services it to the inner wall(s) <NUM> of the vessel <NUM> from the top. The inner wall(s) <NUM> of the vessel <NUM> is (are) covered with the liquid metal flow <NUM>. As the liquid metal <NUM> flows over the inner wall(s) <NUM>, an outer surface <NUM> on the opposite side of the wall(s) <NUM> is formed by the liquid metal flow <NUM>. In order to ensure that the inner wall(s) <NUM> of the vessel is (are) completely covered, it may be necessary to split the inflow tube 104a or accommodate for receptacles to divide the flow over the wall. The liquid metal flow <NUM> is collected at the bottom of the vessel <NUM> by receptacles that service the outflow tube 104b. The outflow tube 104b takes the liquid metal flow <NUM> back into the pump where it may then be recirculated.

In the first embodiment, the liquid metal flow <NUM> is primarily composed of a mixture of lithium and lithium hydride and may contain traces of other elements.

In said embodiment, the mixture of lithium and lithium hydride may be composed of at least <NUM>% and at most <NUM>% of lithium hydride, or at least <NUM>% and at most <NUM>%, this composition may be in the sense of molar content. Further, the mixture may contain lithium deuteride and/or lithium tritide. The content of the lithium hydride in the mixture allows for modification of the properties of the liquid metal flow <NUM>. Changing the molar content of lithium hydride in the mixture modifies the attenuation and absorption properties of the liquid metal flow <NUM>.

When the lithium hydride content in the mixture is between <NUM>% and <NUM>%, the width of the liquid metal flow <NUM> as measured from the inner wall(s) <NUM> of the vessel <NUM> may be between <NUM> and <NUM> to effect optimum attenuation or absorption as required by the fusion reactor application while also accomplishing tritium breeding at an acceptable rate. When the lithium hydride content in the mixture is between <NUM>% and <NUM>%, the width of the liquid metal flow <NUM> as measured from the inner wall(s) <NUM> of the vessel <NUM> may be between <NUM> and <NUM> to effect optimum attenuation or absorption as required by the fusion reactor application while also accomplishing tritium breeding at an acceptable rate. It should be apparent to anyone proficient in the art that adding lithium tritide and/or lithium deuteride to the mixture produces the same or similar results.

In the first embodiment, the vessel <NUM> may be shaped like a torus or in another similar shape. This shape would accommodate for fusion reactor applications. In such an embodiment, the inside of the vessel <NUM> is under the effect of a magnetic field <NUM>. In <FIG>, the magnetic field <NUM> is directed to the outside of the page. The magnetic field may be created by coils outside of the vessel <NUM> or some other appropriate method according to the application. The vessel <NUM> also contains a plurality of electrodes <NUM>. Each of the electrodes <NUM> may be placed in a different location on the vessel <NUM> and they may be placed all over the inner wall(s) <NUM> of the vessel <NUM>.

The first embodiment includes a plurality of pebbles <NUM>. The pebbles <NUM> are added to the liquid metal flow <NUM> prior to being loaded into the device or during operation. In order to add pebbles <NUM> during operation, adequate hatchings or access points may be placed in the inflow tubes 104a. Each pebble <NUM> may have a different function and two main varieties are identified in this first embodiment. A first variety have the function of attenuation of neutrons and are henceforth called neutron attenuating. A second variety are called neutron multiplying and have the function of multiplying the number of neutrons inside the liquid first wall. The two varieties and their functions can be combined in a single type of pebbles, containing both neutron attenuating materials and neutron multiplying materials, or materials that can simultaneously attenuate neutrons and multiply them, like lead.

<FIG> shows a cross sectional view of a pebble <NUM>. The cross-sectional view of <FIG> is common to both varieties described. Each pebble <NUM> is constructed out of a core <NUM>, and externally coated by an outer shell <NUM>. Pebbles <NUM> may be constructed in a similar way to packed-bed beads that are common in nuclear fission applications. The outer shell <NUM> may be a coating of silicon carbide (SiC), graphite or other material suitable for stopping corrosion or interaction between lithium and the core <NUM>. The core <NUM> may be of a different material according to the function of the pebble <NUM>. The core <NUM> of a neutron attenuating pebble <NUM> may be constructed with lead or other materials of high atomic number, suitable for attenuating high energy neutrons. The core <NUM> of a neutron multiplying pebble <NUM> is constructed out of beryllium or other materials known for being adequate neutron multipliers. In the first embodiment, pebbles <NUM> may be sized between <NUM> and <NUM>.

The core <NUM> may be filled by pores <NUM>, thus making it hollow, which enables making the pebble <NUM> lighter. Alternatively, or additionally to the presence of pores, the outer shell <NUM> may be an electrical insulator or a poor conductor, so that the pebble is not or less subject to electromagnetic forces. Therefore, the pebble will not be or be less pushed radially outward. Instead, the pebble may float on the liquid metal-facing side of the vessel, where it is most needed and most effective for attenuation and multiplication of high-energy neutrons.

To describe the operation of the disclosed liquid metal first wall, a fusion reactor application will be used. It should be apparent to someone skilled in the art that use in other applications might be profitable, for instance in the nuclear fission reactor field or even in the isotopic separation of elements field.

In the operation of the first embodiment as part of a fusion reactor, a pump <NUM> injects a liquid metal flow <NUM> to the inner wall(s) <NUM> of a vessel <NUM>. As said, the vessel <NUM> is shaped like a torus and as such is hollow in the inside. There are pebbles <NUM> of the neutron attenuating and neutron multiplying variety suspended in the liquid metal <NUM>. Said liquid metal is a mixture of lithium and lithium hydride and may contain lithium deuteride and/or lithium tritide. Injection is made from the top of the vessel <NUM>.

The liquid metal flow <NUM> may preferably be injected with a sufficiently high tangential velocity so that it may adhere to the inner wall(s) <NUM> by effect of a centrifugal force. Adherence to the inner wall(s) <NUM> is further maintained by the application of an electric current through the use of electrodes <NUM>. An electric current is made circulate inside the liquid metal flow <NUM> in the poloidal direction. A magnetic field <NUM> is also applied in the toroidal direction. The interaction of the current and the magnetic field <NUM> causes an electromagnetic force that pushes the liquid metal flow <NUM> further into the inner wall <NUM>.

As there are pebbles <NUM> suspended on the liquid metal flow <NUM>, the action of the centrifugal and electromagnetic forces creates a situation of artificial gravity resulting in the pebbles <NUM> floating to the outer surface <NUM> of the liquid metal flow <NUM>. This is due either to lower density (obtained by porosity) and/or to the outer shell <NUM> being an electrical insulator or a poor conductor, thus making the pebbles <NUM> at least partially immune to electromagnetic forces. The outer surface <NUM> of the liquid metal flow <NUM> is the one that faces the inside of the toroidal vessel <NUM>. In the fusion reactor, a fusion reaction takes place in the inside of the vessel <NUM>. Neutrons and other particles are ejected with high energy towards the outer surface <NUM> of the liquid metal flow <NUM>. Neutrons interact with the pebbles <NUM>, according to their function they result in attenuation of the neutrons or multiplication of the neutrons. Further, neutrons interact with the lithium and lithium hydride mixture in the liquid metal flow <NUM> resulting in further absorption and tritium breeding.

The liquid metal flow <NUM> is at a high temperature after this process. The liquid metal flow <NUM> is collected at the bottom of the vessel <NUM>. The outflow tubes 104b then take the collected liquid metal flow and service other devices. For instance, other embodiments may include a heat exchanger, separators, or combinations of such, so that energy may be extracted from the liquid metal flow <NUM>. Afterwards, the liquid metal flow is again serviced to the pump <NUM> and the process may continue.

The tritium breeding characteristics of the disclosed lithium hydride first wall depend on the composition and amount of pebbles <NUM> and the composition of the lithium hydride mixture in the liquid metal flow <NUM>. Therefore, by modifying the pebbles <NUM> or the composition the size of the liquid metal flow <NUM> may be modified and the size of a vessel <NUM> that uses the described lithium hydride first wall may be made smaller than what is currently being designed and constructed.

In an additional embodiment, the lithium hydride content in the liquid metal flow <NUM> is as high as <NUM>% or even further. In such an embodiment the width of the liquid metal flow <NUM> when measured from the inner wall <NUM> may be as low as few millimeters in order to achieve acceptable tritium breeding rates.

In another additional embodiment, the outflow tube 104b takes the liquid metal flow <NUM> and delivers it to another device. For instance, this other device could be a heat exchanger that would remove the heat from the liquid metal <NUM> and exchange it with a different fluid, this could be part of a power generation plant.

Claim 1:
A first wall adapted to cover an inner wall (<NUM>) of a plasma confinement vessel (<NUM>), the first wall being made of a metal mixture (<NUM>) comprising at least lithium and lithium hydride, the metal mixture (<NUM>) being liquid when in operation, the first wall further comprising pebbles (<NUM>) suspended in the liquid metal mixture (<NUM>), each pebble being a neutron attenuating pebble, a neutron multiplying pebble or a neutron attenuating and multiplying pebble.