NL8302294A - PELLETS FOR THE SORPTION OF HYDROGEN ISOTOPE AND METHOD FOR THE USE THEREOF. - Google Patents

Description

-1- I i j VO 4901

Pellets for the sorption of hydrogen isotope and method for the application thereof.

There are numerous instances where it is desirable or necessary to remove large amounts of hydrogen and / or isotopes thereof from a special environment. For example, it may be necessary to remove hydrogen from a natural gas stream in order to separate the hydrogen from other gas components, such as methane or other hydrocarbons.

Large amounts of gas are then treated at high gas flow rates. To separate the hydrogen, the gas mixture can be passed over a bed of hydrogen sorbent material or non-evaporable capture material. These materials are usually inert to hydrocarbons, so they are not sorbed. Most non-evaporable scavengers are metallic or have a metallic component, which becomes brittle on sorption of large amounts of hydrogen and forms a very fine powder. This very fine powder can be entrained in the gas stream and can be difficult to recover efficiently. Loss of the particles means loss of the recovered hydrogen. It is also well known that uncontrolled very fine metal particles in the environment present an explosion hazard. In addition, fine metal hydride particles in the gas stream have an abrasive action and can therefore destroy certain components such as valves 20 or pumps.

Fusion reactors convert mass into energy by connecting light atoms together. Numerous different nuclear fusion reactions are possible, but only a few are of practical value for energy production. These include the isotopes of hydrogen. Three isotopes of hydrogen are known, namely hydrogen, deuterium and tritium.

Fusion processes must be carried out at high temperatures to generate energy. The energy production process, which can take place at the lowest temperature and is thus easiest in practice, is the combination of a deuterium core with a core of tritium.

4

The products are energy-rich helium-4 (He), the normal isotope of helium (which is also called an alpha particle), and a more energy-rich free neutron. The helium core carries about one fifth of the total released energy and the neutron carries the other four fifths.

35 Deuterium can be easily extracted from plain water.

8302294 18 4 '-2- * Earth's surface waters are estimated to contain more than 10 tons of deuterium, an almost inexhaustible source. The tritium can be used

be widely prepared by bombarding enriched Li with 14 MeV

6 3 neutrons Li (η, α) H of a fission reactor.

5 To extract energy from the reactor, it is surrounded by a neutron absorbing "blanket". The neutrons release their kinetic energy in the form of heat to the "blanket", after which the heat can be used, for example, to drive conventional turbines to generate electricity.

10 The heat can be extracted from the "blanket" in many different ways. The "blanket" itself may consist of a liquid metal, which is continuously circulated through a heat exchanger and then returned to the "blanket" environment. Unfortunately, this involves pumping the liquid metal through strong magnetic fields and complex geometric structures. Alternatively, the "blanket" may be a solid neutron absorber, over which flows a liquid or gaseous coolant such as high pressure steam or a noble gas such as helium.

Since the tritium required as fuel for the reactor is expensive, the "blanket" itself can be used as a source of tritium.

When the "blanket" is lithium or an alloy of lithium with other elements such as hydrogen, deuterium, lead or lead and aluminum or other lithium-based compounds such as Li 2 SiO 2, the lithium of the "blanket" produces material tritium, when it is irradiated with neutrons, from the fusion reaction.

Although reference will be made repeatedly to tritium in the following description, it is understood that some amount of hydrogen and deuterium in the "blanket" will be formed by (nf p) and (n, d) reactions, and these will behave analogously like tritium.

Tritium has only a low solubility in the "blanket" material and therefore starts to diffuse rapidly from the solid or liquid culture material, creating a high partial pressure of tritium gas and considerable difficulties in containing the tritium, especially when the coolant is a liquid culture material. Some of these difficulties can be alleviated by using a solid lithium-based culture material only as 8302294 t * -3- culture material and using a noble gas as a coolant or flushing gas to drain the tritium as it becomes formed.

The tritium must then be separated in a pure form from the noble gas used as coolant or purge gas.

The mixture of tritium and noble gas can be passed through a purification chamber containing powdered trapping material only to sorb the tritium, since the noble gas is inert and not sorted. However, since the amounts of tritium involved are large, the trapping powder can easily become brittle and decompose into such a fine powder that it is difficult to safely manipulate the latter. When the purification chamber is damaged, particles of the very fine powder containing radioactive tritium can escape. If the powder accidentally ignites, radioactive powder can also be released into the environment. It is not possible to mix the capture powder with the lithium culture material, because then the same pulverizing effect and the resulting dangers can occur. Furthermore, it is difficult to completely separate the radioactive tritium-containing capture powder from the culture material, without using complicated and expensive processes.

It has been proposed to place the non-evaporable capture powder in trays between flat porous support plates, but this leads to a discontinuous process since the gas flow must be stopped periodically to remove the trays.

It is therefore an object of the present invention to provide a hydrogen isotope sorption pellet which prevents the escape of loose particles from a capture material and which can be used in a continuous process for the sorption of hydrogen isotopes in a gas stream .

Another object of the present invention is to provide a pellet for tritium sorption and a tritium recovery method in a fusion reactor technology free from any of the drawbacks of previous tritium recovery devices or methods.

Yet another object of the present invention is to provide a pellet for the sorption of tritium and a method of recovering tritium from a noble gas or rinse gas used as a coolant from a fusion reactor culture "blanket" .

These and other objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and the drawing, in which: Figure 1 is a schematic cross sectional view of a pellet for sorting hydrogen isotopes according to the present invention, Figure 2 is a schematic cross-sectional view of a noble gas purifier using hydrogen isotope sorting pellets of the present invention to remove hydrogen isotopes from a noble gas or purge gas from a fusion reactor culture "blanket", and Figure 3 is a schematic representation of a method of removing hydrogen from a hydrogen-rich zone.

The present invention provides a hydrogen isotope sorption pellet having a shell of porous sintered metal powder enclosing a non-evaporable capture material, at least a portion of the capture material consisting of a powdered capture metal.

The porosity of the metal shell is sufficient to allow sorption of hydrogen isotopes after activation of the non-evaporable capture material, while still preventing loose particles of capture material from escaping.

Each hydrogen isotope sorbent pellet preferably comprises a substantially spherical porous metal shell enclosing a non-vaporizable trapping material. The porous metal shell can be suitably formed by partial sintering of a metal powder placed around the capture material. Any metal can be used which is resistant to the working conditions and is available in powder form and which forms a cohesive porous mass when heated at a sufficiently low temperature so as not to cause damage to the non-evaporable capture material. Suitable include steel, iron, nickel and cobalt. A preferred metal is stainless steel. Another preferred metal is nickel because it is magnetic and its magnetic properties can be exploited when handling the pellets. The metal powder may have any diameter suitable for forming a porous shell and that diameter may suitably be from 5-200 µm, preferably from 40 to 120 µm. With smaller diameters it is more difficult to control the partial sintering process and the shell may be insufficiently porous to allow proper passage of hydrogen isotopes to the capture material. With larger diameters, the porosity is such that particles of trapping material can escape through the shell.

The outer diameter of the shell can be between 0.2 and 5 cm and is preferably between 0.3 and 1.5 cm, while the shell thickness can be about 0.5-2 mm.

The trap entrapped by the shell may be any non-evaporable trap capable of reversible sorption of hydrogen isotopes such as titanium, zircon, tantalum or niobium as well as alloys and / or mixtures of two or more of the above said metals, which do not substantially reduce the sorption capacity. The preferred non-evaporable scavengers are those comprising a sintered mixture of powdered zirconium or titanium and an anti-sintering agent. The zircon or titanium is present as a fine powder passing through a 79 mesh / cm screen and preferably through a 158 mesh / cm screen. The sintering inhibitor 20 can be selected from the group consisting of C, Zr-Al alloys and Ti-V-Fe or Zr-V-Fe alloys.

The Zr-V-Fe and Ti-V-Fe alloys are particularly useful when the capture material must be enabled to sorb hydrogen isotope at fairly low temperatures.

The antisintering agent is present as a powder which passes through a 24 mesh / cm screen and preferably through a 47 mesh / cm screen. The particles of the antisintering agent are also generally larger than the zircon or titanium particles.

In operation, the sorting pellets are placed in the gas stream containing the hydrogen isotope to be recovered. This can be, for example, a stream of natural gas containing hydrogen or the noble gas used as a coolant or the purge gas of a fusion reactor culture "blanket".

They can be activated by eg induction heating, prior to introduction into the gas stream or, if the capture material can be activated at low temperatures, the temperature of the gas may be sufficient to cause activation and sorption of hydrogen 8302294 V * -6- * isotope to take place.

The pellets can also be placed in the culture "blanket" in close spatial relationship with the culture material.

The sorting pellets can therefore be used for any application, in which large amounts of hydrogen and / or isotopes thereof must be sorted and the formation of fine capture metal particles and their release in a gas stream could be dangerous.

The hydrogen useful in the present invention includes all the isotopes of hydrogen and may be H 1, T 1, HD, HT or DT.

The invention is especially useful in heavy hydrogen, which means deuterium and / or tritium.

Figure 1 of the drawing shows a schematic cross-sectional view of a hydrogen isotope sorption pellet 10 having a substantially spherical shell 12 of a porous sintered metal powder, preferably stainless steel powder with a particle size between 5 and 200 µm and preferably between 40 and 120 µm. The diameter of the shell is between 0.2 cm and 5 cm and its thickness is between 0.5 and 2 mm. A non-evaporable capture material -14 is enclosed in the spherical shell 12 and comprises a sintered mixture of 20 zircon and an anti-sintering agent, which may be selected from the group consisting of C, a Zr-Al alloy and preferably an 84% Zr-16% Al (by weight) alloy or a Ti-V-Fe alloy or a Zr-V-Fe alloy and preferably an alloy, the composition of which is in percent by weight when plotted in a temar composition diagram 25 in weight percent Zr, weight percent V and weight percent Fe, is contained within a polygon, the vertices of which are defined as follows: i) 75% Zr - 20% V - 5% Fe ii) 45% Zr - 20% V - 35% Fe iii) 45% Zr - 50% V - 5% Fe.

The sorting pellet is prepared by mixing zircon powder and the anti-sintering agent, placing the mixture in a spherical shape, and heating other vacuum for several minutes at about 800-1200 ° C. After cooling to room temperature, the sintered bulb of trapping material is placed in a second larger spherical shape, which is coated with the metal powder to form the shell.

The second mold is then heated under vacuum at about the same temperature for a sufficient time to impart the required porosity to the spherical shell. The porosity of the shell must be sufficient to allow the sorption of hydrogen isotopes from a gas mixture after activation of the non-evaporable capture material, while the escape of loose particles of capture material due to the sorption of large amounts of hydrogen isotopes prevented.

Alternatively, the capture powder mixture can simply be mechanically compressed into a cohesive spherical shape and then dipped into a metal powder bath 10 mixed with a binder to form a shell. This pellet is then heated under vacuum to cause simultaneous sintering of the capture material and the shell.

Figure 2 shows a noble gas purifier 16.15 for removing tritium from helium in a fusion reactor. The noble gas purifier 16 comprises a gas supply 18, which is attached to a tritium sorption chamber 20, and a gas discharge 22. A feed funnel 24, which contains pellets 26, 26 *, etc., identical to the pellet 10 for the sorption of tritium, is also connected to the sorption chamber 20 by means of a non-metal pipe 25 and two valves 30 and 32. An induction heating coil 34 surrounds the pipe 25. A discharge 36 for the tritium absorbing pellet is also provided with two valves 38 and 40.

The tritium-absorbing pellet is passed through the sorption chamber 20 by suitable operation of the valves 30, 32, 38, 40. Wire meshes 42 and 44 prevent the pellets resp. end up in the gas supply 18 and the gas discharge 22. Hot helium from the reactor "blanket" mixed with tritium is passed through the sorption chamber 20 and the tritium comes into contact with the tritium absorbing pellets while being sorbed. When the temperature of the helium is insufficient to activate the trapping material of the tritium absorbing pellets, the induction heating coil 34 can be used to activate the material as the pellets pass through the non-metal pipe 28 before they enter the sorption chamber 20 enter.

After removing the pellets from the sorption chamber, they can be handled safely without loss of trapping material and they can be heated under vacuum to recover the sorted tritium.

Figure 3 shows a schematic representation 300 of a method in which pellets of the present invention are used to remove the hydrogen from a hydrogen rich zone 302. A source 304 of pellets of the present invention is provided and connected to the hydrogen rich zone 302 by means of a suitable connector 306, which is suitably adapted to allow a continuous flow of pellets to pass into the hydrogen-rich zone 302. The pellets come into contact with the hydrogen present in the hydrogen-rich zone. , where they sort the hydrogen. The pellets are removed from the hydrogen rich zone 302 by a second connector 308 leading to a pellet collector 310. The pellets can then be heated to remove the hydrogen.

The hydrogen rich zone may be a noble gas contaminated with heavy hydrogen, hydrogen rich meaning any percentage of heavy hydrogen which is desired to be removed from the noble gas.

Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications can be made within the scope and spirit of the present invention as described and defined in the following claims.

25 8302294

Claims (6)

Pellet for the sorption of hydrogen isotope, characterized in that the pellet comprises: 1. a spherical shell of porous sintered metal powder; and 5 2. a non-evaporable entrapment entrapped in the shell and comprising a powdered entrapment, the porosity of the metal shell being sufficient to permit the sorption of hydrogen isotopes from a gas mixture upon activation of the non-evaporable entrapment, while preventing the escape of loose particles of capture material. 2. Pellet for the sorption of tritium, characterized in that the pellet comprises: 1. a substantially spherical shell of porous sintered stainless steel powder, the shell having a diameter between 0.2 and 15. cm and a thickness from 0.5 to 2 mm, and the stainless steel powder has a particle size between 40-120 µm; and 2. a non-evaporable trapping material enclosed in the shell of stainless steel powder and comprising a sintered mixture of powdered zirconium and an anti-sintering agent selected from the group consisting of C, Zr-. Al alloys, Ti-V-Fe alloys and Zr-V-Fe alloys, the porosity of the stainless steel shell being sufficient to allow the sorption of tritium from a gas mixture of noble gas and tritium after activation of the non-evaporable capture material, while preventing the escape of loose particles of capture material due to the sorption of large amounts of tritium. 3. A method of sorbing hydrogen isotopes, characterized in that the hydrogen isotope is contacted with a pellet for sorbing the hydrogen isotope, which pellet comprises: 1. A shell of porous sintered metal powder; and 2. a non-evaporable entrapment, which is ingrained in the shell and comprises a powdered entrapment metal, wherein the porosity of the metal shell is sufficient to allow the sorption of hydrogen isotopes after activation of the non-evaporable entrapment, while the escape of loose particles of catch material is prevented. 8302294 5 -10- *! 4. A method of sorbing tritium from a mixture of noble gas and tritium in a fusion reactor, characterized in that the tritium is contacted with a pellet for sorbing tritium, which pellet comprises: 1. a substantially spherical shell of porous sintered stainless steel powder, the shell having a diameter between 0.2 and 5 cm and a thickness of 0.5 to 2 mm, and the stainless steel powder having a particle size between 40 and 120 µm; and 2. a non-evaporable trap material enclosed in the shell of stainless steel powder and comprising a sintered mixture of powdered zirconium and a sintering inhibitor selected from the group consisting of C, Zr-Al alloys and Ti-V-Fe or Zr-V-Fe alloys, the porosity of the stainless steel shell being sufficient to allow the sorption of tritium from the gas mixture of noble gas and tritium after activation of the non-evaporable capture material, while preventing the escape of loose particles of capture material due to the sorption of large amounts of tritium. 5. A method for removing heavy hydrogen from a 20. noble gas contaminated with heavy hydrogen, characterized in that the method comprises the following steps- 1. contacting the gas which is with heavy hydrogen contaminated with a pellet comprising: 1. a spherical shell of porous sintered metal powder; and ii) a non-perishable trapping material enclosed in the shell and comprising a powdered trapping metal, and 2. removing the pellets from the gas. 6. Method for removing hydrogen from a hydrogen-rich zone, characterized in that the method comprises the following steps: 1. passing pellets in a hydrogen-rich zone, the pellets comprising .- i) a spherical shell of porous sintered metal powder; and ii) a non-evaporable entrapment entrapped in the shell and comprising a powdered entrapment metal, 2. contacting the pellets with the hydrogen contained in the hydrogen-rich zone to sorb the hydrogen; 8302294 .1 -11- 3. removing the pellets from the hydrogen-rich zone; and 4. heating the pellets to remove the hydrogen. 8302294