ELEMENTS,

CONVERSION OF NUCLEAR ENERGY INTO HEAT AND DEVICE THEREFOR (EMBODIMENTS)

This invention refers to nuclear chemistry of heavy chemical elements, nuclear power engineering, more specifically, to a method for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat, and a device to accomplish the same by exposing a deeply under-critical target to a beam of accelerated heavy charged particles, said target dimensions being sufficient to fully absorb such beam.

The invention is suitable for other purposes as well including, without limitation, irradiation and deactivation of various materials and substances, production and separation of isotopes, nuclear doping.

Separation of isotopes of various elements and particles by energies is currently under quite active studies. Thus, for example, known in the art are methods of separation of alkali metal isotopes (RF Patent No. 2129909 B01D59/34), ytterbium isotopes (RF Patent No. 2119816 B01D59/00, B01D59/34, C01G57/00, 1998), mercury isotopes (RF Patent No. 2074018 B01D59/34, C01G13/00).

Known in the art is isotope separation by ionization to process materials for nuclear fuel (RF Patent No. 2189273 B01D59/00, published in 2000) wherein the components having the energy within the first range and/or equal to the first energy level are partially separated from the components having the energy within the second range and/or equal to the second energy level and a chemical material interacting with the components is introduced into plasma.

A method and a device for separation of charged particles by energies (RF Patent No. 2187171 B01D59/00, 2000) is of great applied relevance for nuclear engineering. These solutions are aimed at separating charged particles, for example, at a stage of isotope separation by energies, together with the other prior art solutions which were developed when looking for ways to separate isotopes, implement controlled nuclear and thermonuclear fusion, generate charged particle beams by ion-beam and electron-beam devices and control the charged particle beams in acceleration apparatus.

According to RF Patent No. 2119688, G21F9/00 of 1997, "Method for Silicon Deactivation", and Patent Application No. 2000124650 of 2000, "Method for Neutron Transmutation Doping of Silicon", a secondary neutron flux originating from a nuclear power plant reactor core is suggested to be used for deactivation, etching and doping of silicon monocrystals.

RF patent No. 2267826, G21G1/02 of 2001 , "Method for Incineration of Transuranic Chemical Elements and Nuclear Reactor Therefor" describes a method and a device using a weakly subcritical (k~l) core of the nuclear reactor where long-lived radionuclides of heavy elements are placed. Additional neutrons required for criticality (k=l) of the core are injected from an external source such as a proton accelerator with energy of 1 GeV with a lead or lead-bismuth target as proposed therein. However, this prior art engineering solution does not allow any significant increase in the efficiency of conversion of nuclear energy into heat due to conceptually insurmountable restrictions inherent in the method based on proton beams. Moreover, it also does not remove the sources for production of an unacceptably high amount of long-lived radionuclides or risks relating to production of materials suitable for nuclear terrorism.

In RF patent No. 2238597, G21C1/30 dated 2003 "The Method for Conversion of Nuclear Energy into Heat", it is proposed to use a relativistic proton beam to trigger nuclear cascade processes in a deeply under-critical target made of heavy chemical elements (lead, bismuth, thorium and depleted uranium, as well as their combinations), with the target content employed concurrently as fuel and heat transfer medium. The inventors noted an increase in probability of a deeper splitting of target nuclei with a rise in energies of accelerated particles. However, this engineering solution suffers from similar shortcomings as noted above, which are due to the use of a relativistic proton beam, and does not address the issues associated with the utilization of the beam of secondary neutrons produced in the proposed target and leaving the target.

The closest prior art is the invention according to RF patent No. 2413314 dated 2008, "Method and System for Conversion of Nuclear Energy into Heat". This solution employs the acceleration of a beam of heavy charged particles (e.g. multiple-charged ions of uranium, thorium, bismuth and lead isotopes) up to an energy causing the origination of a flux of cascade nucleons in a deeply under-critical core used as a target, to which such a flux is directed and the condition of which is monitored with, if necessary, replacement of its content. To raise the intensity of the said flux, the core is proposed to be made, in part or in full, of spent nuclear fuel. The device for this method comprises an accelerator of relativistic multiple-charged ions, a unit for beam transportation and introduction onto the target to couple the accelerator and the target, the latter being normally placed in a strong case, often cylindrically shaped. The excess of heat produced in the reactor (target) is removed with the help of a subsystem comprising first and second circuit coolant, heat- into-electricity conversion units with the function of a heat transformer.

The claimed advantages of the said prototype, however, are accompanied by several disadvantages related to incomplete utilization of accelerated ion beams for increasing the efficiency of conversion of nuclear energy into heat, recycling of long-lived radionuclides, including plutonium and minor actinides (neptunium, americium and curium).

The herein proposed invention eliminates the above disadvantages of the prior art inventions and the prototype.

The object of this invention is to increase the efficiency of conversion of nuclear energy into heat and recycling of a wide range of long-lived radionuclides.

Long-lived radionuclides in this case are those with a half-life longer than 15 years. The technical effect of the invention consists in an increased efficiency of conversion of nuclear energy into heat, recycling of a wide range of long-lived radionuclides, and production of materials suitable for further use.

The technical effect of the method for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat is achieved as follows. A relativistic ion beam is produced and accelerated, the beam is directed to a regularly refreshable material of a deeply under-critical target, which results in fission of target nuclei, the flux of secondary particles is produced, including neutrons, the secondary particles are arranged to split the nuclei of isotopes of heavy chemical elements, which, in its turn, results in release of nuclear energy, the condition of the target of a size ensuring the transfer of the beam's kinetic energy and that of the secondary particles to the target is monitored, and the duration of accumulation and replacement of nuclear fission products is determined. The aforesaid relativistic ion beam is accelerated to an energy level at which at least two generations of nuclear multifragmentation products are produced by means of fission of the target material, and nuclear energy is released within a time interval that exceeds the duration of the accumulation and replacement of the fission products by a material prepared for exposure. The flux of secondary particles is recycled and the exposed material is cooled down and forwarded for recycling as work material for extraction of materials suitable for further use according to the claimed method. The technical effect in the device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat is achieved as follows. In the first embodiment of the device, which comprises a relativistic ion beam accelerator, a unit for beam transportation and introduction onto the target, a deeply under-critical target made of heavy chemical elements suitably enclosed in a fire-, radiation- and corrosion-resistant case with an open upper end, and a heat transformer unit, all arranged in series, the target case, according to the invention, has a conical or spherical shape relative to the energetic axis of the device and is connected through pipelines to the heat transformer and through a pipeline and shutoff gear to a backup unit that allows its replenishment and is located above the target. As a result, the simplest and hence more reliable design of the device for conversion of nuclear energy into heat is provided. In the second embodiment of the device, which comprises a relativistic ion beam accelerator, a unit for beam transportation and introduction onto the target, a deeply under- critical target made of heavy chemical elements, suitably enclosed in a fire-, radiation- and corrosion-resistant case with an open upper end, and a heat transformer unit, all arranged in series, the target case, according to the invention, is made of two sections consecutively disposed relative to the unit for beam transportation and introduction onto the target, the lateral surface of the sections relative to the energetic axis of the device has a similar cylindrical or conical shape, the base part of the first section, that can be easily replaced and fixed, is made planar or spherical, the second section is connected through pipelines to the heat transformer and through a pipeline and shutoff gear to a backup unit that allows its replenishment and is located above the target. This embodiment of the device is distinguished in that along with power production it offers the possibility to concurrently transmute, under a relativistic ion beam, radioactive waste with a prevailing portion of long-lived radionuclides into radioactive waste with predominantly short-lived radionuclides through potential replacement of the target's first section formed of radioactive waste and/or actinides and/or spent nuclear fuel.

In the third embodiment of the device, which comprises a relativistic ion beam accelerator, a unit for beam transportation and introduction onto the target, a deeply under- critical target made of heavy chemical elements suitably enclosed in a fire-, radiation- and corrosion-resistant case with an open upper end, and a heat transformer unit, all arranged in series, the target case, according to the invention, is made of three sections consecutively disposed relative to the unit for beam transportation and introduction onto the target, the lateral surface of the sections relative to the energetic axis of the device has a similar cylindrical or conical shape, the base part of the first section that, can be easily replaced and fixed, is made planar or spherical, the base parts of the second and third sections are spherical and separated from each other to a distance equal to the difference of their radii, wherein the third section of the target case is connected through pipelines and shutoff gears to the second section and a backup unit, respectively, with the second section connected through pipelines to the heat transformer, while the design of the backup unit allows its replenishment and the said unit is located above the third section of the target. This embodiment features, in addition to the advantages of the second embodiment, the possibility to achieve the utmost power production through increasing the portion of fissile radionuclides in the second section of the target.

The features of the claimed method and device will be better understood by reference to the accompanying drawings of Figures 1 - 13 and Table 1.

In the drawings:

Fig.l displays the first six stages of an avalanche process of multifragmentation of

238

uranium target nuclei, triggered by a multiple-charged U ion with energy of 1 GeV per nucleon.

Fig.2 presents a general view of the device for irradiation of isotopes of heavy chemical elements, conversion of nuclear power into heat, which comprises a single- section conical target, to implement the method proposed herein.

Fig. 3 displays a sectional view of the proposed device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat.

Fig.4 depicts a general view of the device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat, which uses a single-section spherical target to implement the method proposed herein.

Fig.5 presents a sectional view of the said device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat.

Fig. 6 displays a general view of the device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat, wherein a two-sectioned cylindrical target with a cylindrical first section is used.

Fig. 7 provides a sectional view of the said device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat. Fig. 8 displays a sectional view of the device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat, wherein a two-sectioned cylindrical target is used, the base part of the target's first section being spherical.

Fig.9 provides a sectional view of the device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat, wherein a two-sectioned conical target with a frustum-like first section is used.

Fig.10 presents a sectional view of the device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat, wherein a two-sectioned conical target and spherical base parts of both sections are used.

Fig. 11 shows a general view of the device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat, wherein a three-sectioned cylindrical target is used, with the first section made cylindrical, the second and third ones having a spherically shaped base part.

Fig.12 presents a sectional view of the same device for irradiation of isotopes of heavy chemical elements, conversion of nuclear energy into heat.

Fig. 13 shows a diagram of the nuclear fuel cycle closed on long-lived radionuclides.

Table 1 contains a list of long-lived radionuclides.

The proposed method is based on the results obtained in the course of a systematic

3 study into power aspects of multifragmentation of radionuclide nuclei (ranging from H to 251

Cf) when exposed to a relativistic beam of heavy particles (ranging from neutrons, protons, deuterons to multiple-charged uranium ions). The effect of nuclear multifragmentation has been known for a long time ("Experimental Nuclear Physics", in two volumes, K.N. Mukhin, Moscow, Energoatomizdat Publishing House, 1993, ch.l l, para 73). Yet, no systematic calculations for power aspects of nuclear multifragmentation as a result of, among other factors, fragments of such decay have been carried out. The effect of power release from decay of target nuclei by fragments of the second and further generations has not been discovered or investigated.

This work has been performed by the authors who used their own computer program based on the method for calculation of energies of nuclear reactions in targets made of various chemical elements and exposed to relativistic ion beams (Physical values. Handbook. I.S. Grigoriev, E.Z. Melikhov. Moscow, Energoatomizdat Publishing House, 1991), as well as an array of estimated nuclear data on mass defect values for neutron and 3288 nuclides, which is provided on the site of the Brookhaven National Laboratory (http://www.nndc.bnl.gov/nudat2/). Results of the calculations are supposed to be corroborated with experimental data.

The bottom line of the carried out work is the discovery of significant features, more specifically, advantages of power characteristics of nuclear multifragmentation of long- lived radionuclides, including actinides, when the target is exposed to relativistic heavy particles (with release of nuclear energy and absorption of kinetic energy of the relativistic particles), which demonstrates a positive contribution of electrically charged nuclear fragments to a rise in the efficiency of energy release. As a result, the authors propose a novel way for practical utilization of the said effect to address the challenges and problems of power engineering, environment and public health.

238

Thus, for example, inelastic collision between a U relativistic multiple-charged uranium ion and a ^C nucleus causes multifragmentation thereof accompanied by an escape of (as follows from the calculations) approximately 30 fragments, including neutrons, and transfer of projectile particle kinetic energy to such fragments. A possible

238

outcome of hitting a U nucleus with a relativistic neutron is a collapse of the former accompanied by an escape of (as follows from the calculations) not more than 30 fragments through any of the channels with energy release. The high-energy fragments having the charge and mass comparable with a chlorine nuclide or higher (up to palladium

238

inclusive) cause U nuclei fission accompanied by an escape of (as follows from the

137 calculations) not more than 33 fragments and energy release. For Cs multifragmentation accompanied by a similar transfer of kinetic energy of a similar relativistic particle to a plurality of escaping fragments, the number of such fragments may be as large as 35.

Similar results were obtained for high-energy products of multifragmented target nuclei fission, which hit in turn subsequent nuclei causing fission thereof. Electrically charged nucleus fragments and neutrons thus formed carry not only the projectile particle energy but also the energy frequently released from multifragmentation and when such fragments and neutrons further collide with the target nuclei, another generation of secondary particles is generated whereby an avalanche process of particle material fission is triggered.

238

Fig.l illustrates the first six stages of the process of multifragmentation of U

238

nuclei, triggered by a 32-charged U ion with an energy of 1 GeV per nucleon with the appearance (as the first generation) of six electrically charged fragments of comparable masses and 39 neutrons taken as an example:

238

1. Collision of an accelerated U ion against a target nucleus.

2. Appearance of high-energy first-generation fragments with release of 194 MeV (~ 12

3* 10 implementation options).

3. Separation of first-generation fragments.

4. Collisions of the first-generation fragments against target nuclei.

5. Appearance of high-energy second-generation fragments with release of -190 MeV

g

(calculated) (over 2* 10 implementation options).

6. Separation of second-generation fragments. Fig. 1 characterizing the method proposed herein shows that each neutron and electrically charged fragment of the first generation may bring into existence, as follows from the calculations, at least 10 high-energy fragments and cause a release of approximately 190 MeV. The flux particle in this case gives rise to at least two generations of fragments thereby destructing (as follows from the calculations) more than 450 target nuclei and causing a release of a nuclear energy of approximately 194 + 45 * 193 MeV = 8.7 GeV. When the third generation of such fragments is produced, the number of destructed nuclei, as follows from the calculations, increases to 4500 and an energy of approximately 194 + 450 * 190 MeV = 86 GeV is released.

Thus, an avalanche process of nuclear fission is triggered and starts escalating, including, among other factors, under the effect of electrically charged fragments of decayed nuclei with energies that exceed the Coulomb barrier of the nuclei along the trajectories of such fragments, with their subsequent destruction.

Such tracking of a sequence of events associated with probable behavior of the other

238 nucleus fragments of the first generation, specifically, from 6-fragment destruction of U nuclei, leads to similar, so-called loop-shaped chains, i.e., the chains closed to the fragments having a similar mass and charge and giving rise to such sequences of target nuclei destruction acts. The said sequences of various sizes naturally occur when the target nuclei are split into any other number of fragments from a plurality of options allowed by the laws of conservation of energy, momentum, electrical and baryonic charges and implemented in such process.

Thus, when such destruction processes take place, a plurality of the loop-shaped sequences of target nuclei destruction events comparable in power occur. In other words, to ensure practically acceptable power of a plurality of such sequences initiated in a target by relativistic particles of the flux, the said particles must, other things being equal, acquire the energy sufficient for the purpose. In this case, any particle in the flux is capable of utilizing a very large number of the target nuclei, which, correspondingly, causes a substantial reduction in the requirements for accelerator current intensity. The significance of the said effect of multiplication of decay of target material nuclei is as follows.

Firstly, by adequately placing and exposing various materials (including the long- lived radionuclides listed in Table 1 to relativistic beams of heavy charged particles in the target section facing the beam, one can achieve their practically complete recycling through a multiple recycling process on the respective irradiated target material by means of coupled radiochemical regeneration and refabrication.

Secondly, radioactive waste recycling products (for both separated waste, i.e. that with a predominant portion of long-lived radionuclides, and non-separated (and/or chemical) waste, as well as spent nuclear waste from research, industrial and power reactors) may find application in diverse fields of national economy after such recycling products are cooled down and radiochemically or otherwise converted. It is due to that the aforesaid products are chiefly stable and neutron-deficit nuclides. As known, the latter ones (in their vast majority) differ from neutron-excessive ones, which are produced in fuels of existing reactor types, by sizably lower half-life values.

Thirdly, under conditions of full absorption of the flux of secondary neutrons in the respective target section, fissile radionuclides are produced with a respective rise in power production in the target and conversion into electric power, in particular for compensation of the electric power spent for the acceleration of the particle beam. The excess of power so produced can be taken off by other power consumers.

The proposed device comprises an accelerator, a deeply under-critical target, a unit for beam transportation and introduction onto the target, a heat transformer, and a backup unit.

Reference numbers in the figures denote the following:

1 - relativistic ion beam accelerator;

2 - unit for beam transportation and introduction onto the target;

3 - target; 4 - backup unit;

5 - heat transformer;

6 - target makeup pipeline;

7 - backup unit shutoff gear;

8, 9, 10, 11 - coolant pipelines;

12 - first section of the target;

13 - second section of the target;

14 - third section of the target;

15 - pipeline for makeup of the target's second section with material of the third section;

16 - shutoff gear for the target's third section.

The beams of relativistic heavy ions are generated with the help of a backward travelling wave linear accelerator 1 (BTWLA, see A.S. Bogomolov, T.S. Bakirov, "Ion Accelerators for Industrial Use", Moscow, Kuna, 2012, 87 pp.) with achieving an energy of accelerated multiple-charged ions of not less than 100 MeV per nucleon. Exceeding the said energy level by multiple-charged ions allows using them practically in full for triggering the afore-mentioned diversity of nuclear processes.

The distance from the unit for beam transportation and introduction onto the target, wherefrom the beam is directed immediately onto the target section adjacent to the unit, to the target is derived from the condition of minimization of negative impact of the ionizing radiation of the irradiated material from the said section upon the unit for beam transportation and introduction onto the target.

The material of a single-section target 3 and a first section 12 of two- and three- sectioned targets is formed of radioactive waste, other substances that contain long-lived radionuclides intended for direct destruction, including small actinides (plutonium and minor actinides), and/or spent nuclear fuel in the form of a low-melting U-Fe type eutectic. Such materials can initially be in a solid or liquid phase. The thickness of the layer of these materials along the beam trajectory is derived for the single-section target 3 from the condition of complete absorption therein of not only the primary beam, but also the flux of secondary particles, including neutrons. The layer thickness and the accelerator beam intensity determine the capability for full melting of the material of such a target. The thickness of the first section 12 in the case of two and three -sectioned targets is derived from the condition of conversion of a greater part of primary particles in the beam into a secondary flux with the formation (in this section) of a prevailing amount of neutron- deficit fission products. Due to release of nuclear energy even in the case of a relatively deep nuclear multifragmentation, the temperature of the material in the first section 12 rises to values sufficient for at least partial melting of the material. The duration of the exposure to the beam (with accumulation of nuclear fission products) of the first section 12 in a two or three -sectioned target is normally determined numerically, proceeding from the necessity to achieve an appropriate portion of decayed target material with, yet, keeping a sufficient strength of the respective case. Once a specified irradiation dose is reached, the material of the section is replaced with new (prepared) one with subsequent cooling-down and handover of the exposed material to a radiochemical enterprise as stock for fabrication of next-in-turn batches of materials with radionuclides meant for burnout under the accelerator beam device. In this context, it should be noted that a service life of the proposed device can be achieved which is incomparably longer than the time needed for accumulation of nuclear fission products not only in the target's first section, but also in the target as a whole.

The material of a second section 13 of the target (see Figs 6 - 10 and 12) is fabricated mainly of actinides, including depleted and/or regenerated uranium and/or spent nuclear fuel with absolute adherence to the requirement of deep under-criticality. In this target section, the greater part of energy is released from all kinds of destruction giving way to nuclear energy release. Therefore, the material of the second section is fabricated as a low-melting U-Fe type eutectic that, once exposed to an intense flux of particles, reaches its melting point and its melt is then used as a primary coolant to remove heat from the target via pipelines 8 - 11 (see Figs 6 - 12). Along with removal of excess heat from the target, the pipelines provide also the homogenization of the target material through factual mixing. A similar eutectic is used for conversion of the material of a third section 14 into a liquid phase (see Figs 11 and 12) in the case of a three-sectioned target meant to utilize the

232 flux of neutrons that lost their capacity (in the second section 13) to destruct Th and/or U nuclei with reproduction of fissile nuclides. Such an eutectic in all the three sections and all the three embodiments may be replaced with a liquid salt melt of respective chemical elements or their compositions.

The amount of material in the third section 14 of the three-sectioned target is taken with a sufficient surplus that allows timely compensation of inevitable decrease in the material in the second section 13 due to not only the transition of the material into a liquid phase after the heating, but also as a result of a prolonged burnout under a beam. For this purpose, an appropriate amount of the molten material from the third section 14 of the target is supplied from a heated backup unit 4 (see Figs 11 and 12) placed above the third section of the target at the natural head level, via a makeup pipeline 6 and a shutoff gear 7. The same function is performed by the backup unit 4 in embodiments of the device with single and two-sectioned targets (see Figs 2-10). Out of there, via the makeup pipeline 6 and the shutoff gear 7, decreases are compensated in the level of material in those sections of the target where the greater part of heat is released. In this connection, it is worth noting that the main position of shutoff gear ('closed') is shown in Figs 1 - 12.

To compensate the material decrease in the second section 13 of the three-sectioned target, a required amount of exposed material enriched with fissile nuclides from the third section 14 of the target is supplied from the case of the third section 14 by means of the pump forming part of a shutoff gear 16, via a pipeline 15 (see Figs 11 and 12).

The device operates as follows.

238

In a steady-state operation mode, an accelerator beam 1 of multiple-charged U ions with an average current of ~ 1 mA and an energy of ~ 1 GeV per nucleon is directed, with the help of a unit for beam transportation and introduction onto the target 2, onto either the target 3 of the device with a single-section target (see Figs 2 - 5) or the first section 12 of the two or three -sectioned target (see Figs 6 - 12).

In the case of the single- section target 3 (Figs 2 - 5) with a conical or spherical case and the material fabricated of radioactive waste and/or actinides and/or spent nuclear fuel, the beam of primary particles generates a flux of secondary particles, first generations of which also destruct target nuclei. In the bottom part of the target 3, the secondary flux of particles is utilized. Wherein nuclear energy is released, which is converted into heat in the target. The decrease in the target material is compensated from the backup unit 4 via the pipeline 6 fitted with the shutoff gear 7. Excessive heat is removed from the target 3, via the pipelines 8, 9, 10, 11 to a heat transformer 5, where it is converted into electric power.

In the second embodiment of the device, it has a two-sectioned target (Figs 6 - 10) with the case whose lateral surface has cylindrical or conical shape. Also, the base part of the first section 12 is made planar or spherical, the contents of the first section is identical to that of the target as per the first embodiment, whereas the second section 13 is filled with actinides and/or spent nuclear fuel with strict adherence to the condition of deep under-criticality. The primary beam generates a flux of secondary particles in the first section, thereby making nuclei of the material therein neutron-deficit. The flux of secondary particles in the second section provides the greater part of energy release and is utilized similarly to the case of a single-section target. The decrease in the target material is replenished from the backup unit 4 via the pipeline 6 fitted with the shutoff gear 7. Excessive heat from the second section 13 is removed via the pipelines 8, 9, 10, 11 to the heat transformer 5 where it is converted into electric power.

In the third embodiment of the device (see Fig.12) where the target is made three- sectioned, the lateral surface of the sections is cylindrical or conical, the base part of the first section is made planar or spherical, the base parts of the second and third sections are spherical and separated from each other to a distance equal to the difference of their radii. The distance between the cases of the second and third sections is derived from the condition of full absorption in the third section of the flux of secondary neutrons leaving the second section. In the third section, complete utilization of the neutron flux is ensured. The third section of the target is coupled by means of the pipelines and the shutoff gear to the second section and the backup unit respectively. The first section 12 and the second section 13 are filled with the same materials as the respective sections of the above two- sectioned target, while the material of the third section 14 is fabricated from depleted

238 232

and/or regenerated U and/or Th. The second section ensures energy release, in the third section 14 the secondary flux of neutrons that lost their capacity to destroy U 232

and/or Th nuclei through converting them into fissile radionuclides is recycled.

The aforesaid purposes of the device (generation of heat and electric power, utilization of long-lived radionuclides) allows the development of an exhaustive plurality of relevant closed cycles based on long-lived radionuclides, including production of heat and electric power through release of nuclear energy, on chemical waste.

As an example, the diagram of a nuclear fuel cycle closed by long-lived radionuclides is provided in Fig.13. According to the diagram, practically all spent nuclear fuel and radioactive waste, including that containing plutonium and minor actinides that are produced in such a fuel cycle, are fed to a coupled recycling cycle comprising the proposed device, a storage facility to cool down irradiated materials, radiochemical processing, a production facility for preparation of materials with long-lived radionuclides (and/or chemical waste) for exposure. In this case, such materials include also those

232 238

containing Th and/or U, which are used for, among other purposes, reproduction of fissile nuclides within the device. Products of the long-lived radionuclide recycling process are heat and electric power that are in demand in not solely the nuclear fuel cycle, but also beyond its limits.

The above recycling cycle can involve radioactive waste from mining, hydrometallurgical and other production facilities, depleted uranium produced in the

235

course of uranium enrichment (by U isotope), spent nuclear fuel, regenerated uranium, plutonium and minor actinides, as well as radioactive waste from radiochemical production facilities.

The diagram presented in Fig.13 is applicable to formation of all types of nuclear fuel cycles (U, U-Pu, Th-U and so on) closed on long-lived radionuclides, for feasible combinations, using fast-neutron reactors or not, with involvement of other types of devices and production facilities that inevitably produce radioactive waste, with total refusal, on principle, from burial of such waste, which is practiced nowadays. It should be noted that the above recycling cycle has a self-consistent value as well when its input includes not only spent nuclear fuel, radioactive waste coupled with its reprocessing, thorium, uranium, plutonium and minor actinides, but also radioactive waste of other nature, for instance, that produced in the course of dismantling of nuclear reactors and/or similar facilities with service life expired or decommissioned for whatever other reasons.

In a similar way, closed cycles are formed for any industries on respective chemical waste fed as input of a recycling cycle similar to the cycle depicted in Fig.13 and using the proposed recycling device, yet adapted for predominant burnout of chemical elements forming the bulk of waste in the given industry. In such a case, the industry will receive heat and electric power for its needs and the adjacent nuclear fuel cycle will provide the above mentioned consumables and assembly parts for the recycling cycle.

Thus, a full-scale implementation of the proposed method and device for conversion of nuclear energy into heat will allow achieving not only logical completeness and environmental consistency of existing types and modifications of nuclear fuel cycles and those in the process of design in full compliance with applicable IAEA requirements (unlimited amount of fuel stock, invariability of the Earth's radiation background, inviolability of the non-proliferation regime, inherent safety of nuclear power facilities), but also developing, in a purposeful and consistent manner, a deeply under-critical environmental-friendly power engineering capable of ensuring, among other aspects, adequate justification of human activities in industrial sphere as a whole, including its nuclear segment.

Table 1

List of long-lived radionuclides

Ag-

438(9) 58 Po-209 102(5) 88 Bk-247 1380(250) 108m

Sn-

43.9(5) 59 Ra-226 1600(7) 89 Cf-249 351(2) 121m

Sn-126 2.30(14)+5 60 Ac-227 21.772(3) 90 Cf-251 898(44)

Note: LLR - long-lived radionuclide;

1.387(12)+6 - (1.387 ± 0.012) * 10 ⁶