CN102623078A - A high-efficiency nuclear waste transmutation subcritical core based on hybrid energy spectrum - Google Patents

Abstract

A high-efficiency nuclear waste transmutation subcritical core based on mixed energy spectrum. From its center to the outside, there are outer neutron source area, transmutation area, moderation layer area, reflective layer area and shielding layer area. The moderator layer area and the reflector layer area are set so that the fast neutrons are fully moderated and then reflected back to the transmutation area to form a mixed energy spectrum. The mixed energy spectrum is used to simultaneously transmutate minor actinide nuclides (referred to as MA) and long-lived fission products (referred to as LLFP). The invention forms a mixed energy spectrum through a reasonable core structure layout, respectively sets a transuranium nuclide (abbreviated as TRU) fuel area and an LLFP fuel area according to the distribution of fast neutrons and thermal neutrons, and the two fuel areas use the same fuel The component form realizes simultaneous transmutation of MA and LLFP in the same core and the same transmutation zone. The core structure is simple, the neutron utilization rate is high, and it has the function of efficiently transmuting nuclear waste, and the liquid lead-bismuth alloy is used as the coolant to turn the transmutation zone The resulting fission energy is taken out of the core for production.

Description

A high-efficiency nuclear waste transmutation subcritical core based on hybrid energy spectrum

technical field

The invention belongs to the technical field of radioactive nuclear waste treatment, and in particular relates to a reactor core used for transmutation of high-level radioactive nuclear waste.

Background technique

Disposal of nuclear waste, especially the final disposal of long-lived nuclear waste is a worldwide problem, and currently no country has a definite disposal plan. With the rapid growth of the installed capacity of PWR nuclear power plants in my country, the accumulation of nuclear waste will increase rapidly. These nuclear wastes are long-lived and highly radioactive, posing long-term hazards to the human environment. How to minimize waste, minimize the volume and radiotoxicity of high-level radioactive waste generated by nuclear power plant operation, and safely dispose of high-level radioactive waste so that it can be reliably isolated from the biosphere for a long time and ensure the environmental safety of future generations is a matter of concern. One of the key issues affecting the sustainable development of nuclear energy and influencing public acceptance of nuclear energy.

At present, there are two kinds of spent fuel disposal schemes in the world, namely the "one-pass" method represented by the United States and the "closed cycle" method represented by France and other countries. The "one-pass" method is to store the spent fuel for cooling and then directly carry it into a deep landfill; the "closed cycle" method is to reprocess the spent fuel, recover the uranium and plutonium, and then solidify the remaining products before going to a deep landfill . Neither of these two methods has substantially dealt with high-level nuclear waste, and both have long-term radioactive risks, and there is a certain waste of resources. The "separation-transmutation" method is a new way of nuclear waste treatment, that is, the minor actinide nuclides (MA for short) and long-lived fission products (LLFP for short) in high-level radioactive waste are separated by chemical separation, and nuclear reactors are used to (such as reactors, accelerators) to convert long-lived nuclides into short-lived nuclides or stable nuclides. The existing research results show that MA is suitable for fast neutron transmutation and LLFP is suitable for thermal neutron transmutation.

The Accelerator Driven Sub-critical System (ADS) is currently an ideal device dedicated to the transmutation of radioactive nuclear waste, the effective use of nuclear resources and the generation of nuclear energy. The International Atomic Energy Agency (IAEA) included ADS in the new nuclear energy system, and called it "emerging nuclear waste transmutation and energy generation nuclear energy system". In the ADS transmutation system, the spallation neutrons produced by the spallation reaction and the fission neutrons produced by the fuel fission reaction belong to the fast neutrons, which are suitable for the transmutation of MA. In the existing conceptual design of ADS transmutation system, there are ATW plan in the United States, CDT plan in EU (based on MYRRHA/XT-ADS plan), OMEGA plan in Japan and HYPER plan in Korea for the transmutation of MA.

In Korea's HYPER project, the fast neutron spectrum core is used, and the function of simultaneous transmutation of LLFP is realized by setting LLFP fuel assemblies in the transmutation MA core. Graphite is used as the moderator layer in LLFP fuel assemblies. However, the thickness of graphite in LLFP fuel assemblies is limited, and the neutron moderation effect of the scheme using LLFP fuel assemblies in the HYPER plan is limited. Whether the expected purpose of transmuting LLFP can be achieved remains to be verified.

In Chinese patent CN 1945751B, China Institute of Atomic Energy discloses an accelerator-driven fast-thermally coupled subcritical reactor. The reactor forms an epithermal neutron energy spectral region in the fast neutron energy spectral region and thermal neutron energy spectral region, and utilizes the epithermal neutron energy spectral region to transmute LLFP. In this scheme, the fast neutron energy spectrum region adopts sodium (using aluminum simulation in the embodiment) as coolant, and the thermal neutron energy spectrum region adopts water (using polyethylene simulation in the embodiment) as moderator, and the fast spectrum region The fuel assembly in the thermal spectrum area adopts a different structural arrangement. In the same reactor, there are two different coolants and two different arrangements of fuel assemblies at the same time, which greatly increases the complexity of the system and puts forward higher requirements for the design and operation of the reactor. Moreover, a violent chemical reaction will occur when sodium and water are in contact, which will pose a serious safety hazard.

In Chinese patent 03152870.8, the Institute of Plasma Physics of the Chinese Academy of Sciences discloses a method for the production of subcritical nuclear waste and nuclear fuel based on neutron multiplication of fissionable materials, which can simultaneously realize the functions of transmutation MA, nuclear fuel multiplication and transmutation LLFP. However, in this method, there are few low-energy neutrons moderated from the fission fuel breeding region, and it is difficult to determine the transmutation effect of LLFP.

In the mixed energy spectrum supercritical water reactor proposed by the School of Nuclear Science and Engineering of Shanghai Jiaotong University, the concept of mixed energy spectrum is proposed, and it is used for production capacity and multiplication to improve the economic benefits of the reactor. The reactor of this scheme belongs to the fast neutron reactor, if it is used for nuclear waste transmutation, it will make the dynamic parameters of the reactor (Doppler coefficient, cavitation coefficient, delayed neutron share, etc.) affect the safety of the reactor. Therefore, this scheme is not suitable for nuclear waste transmutation.

Contents of the invention

The technical problem of the present invention is to overcome the deficiencies of the prior art, and provide a high-efficiency nuclear waste transmutation subcritical core based on the mixed energy spectrum, which forms a mixed energy spectrum in the transmutation region, according to the fast neutron and thermal neutron The TRU fuel area and the LLFP fuel area are respectively set for the distribution. The two fuel areas adopt the same form of fuel assembly, use the fast neutron transmutation MA in the mixed energy spectrum, and use the thermal neutron transmutation LLFP in the mixed energy spectrum to realize Simultaneous transmutation of MA and LLFP functions in the same transmutation zone of the same core, high neutron utilization rate, simple core structure, high-efficiency transmutation of nuclear waste, and the use of liquid lead-bismuth alloy as coolant to generate transmutation zone The fission energy can be taken out of the core for production.

The technical solution of the present invention: a high-efficiency nuclear waste transmutation subcritical core based on mixed energy spectrum, from the center to the outside is the outer neutron source area, the transmutation area, the moderation layer area, the reflection layer area and the shielding layer area; the external neutron source uses the spallation neutrons produced by the spallation reaction of high-energy protons hitting the target as the external source neutrons; the transmutation area is respectively set up with a TRU fuel area and an LLFP fuel area, and the two fuel areas use the same fuel Component form; the external neutron source drives the fuel in the transmutation region to undergo fission reaction, and produces fast neutrons. The fast neutrons leaked from the transmutation region undergo a moderation through the moderation layer region, and reflect back after reaching the reflection layer region. It passes through the moderator layer again for secondary moderation, and finally moderates into thermal neutrons and enters the transmutation area, so that the spallation neutrons provided by the outer neutron source area, the fast neutrons produced by the fission reaction, and the moderated and reflected neutrons Thermal neutrons form a mixed energy spectrum in the transmutation zone, using fast neutrons to transmute MA and thermal neutrons to transmute LLFP, realizing the function of simultaneously transmuting MA and LLFP in the same core and the same transmutation zone. High efficiency, simple core structure, high-efficiency transmutation of nuclear waste, and the use of liquid lead-bismuth alloy as a coolant to bring the fission energy generated in the transmutation area out of the core for production capacity.

A liquid lead-bismuth alloy spallation target is placed in the outer neutron source area, and a high-energy proton beam with an energy of 1GeV and an average current intensity of 10mA is used to bombard the liquid lead-bismuth alloy target material to generate neutrons of 10MeV. , as the outer neutron source driving the transmutation region.

The fast neutrons in the transmutation area are mainly distributed on the inside, and the thermal neutrons are mainly distributed on the outside. According to the distribution of fast neutrons and thermal neutrons, a TRU fuel area and an LLFP fuel area are respectively set up from the inside to the outside. The zone is 6-layer fuel assembly, and the LLFP fuel zone is 1-layer fuel assembly.

The moderator layer area is composed of a moderator layer component, and the main material is graphite.

The reflective layer area is composed of one layer of reflective layer components, and the main material is stainless steel.

The shielding layer area is composed of one layer of shielding layer components, and the main material is boron carbide.

The axial distribution of the moderator layer area, reflective layer area and shielding layer area are all arranged on the fuel rod.

The core uses a liquid lead-bismuth alloy as a coolant to take out heat from the core to generate energy.

The advantage of the present invention compared with prior art is:

(1) The structure of the high-efficiency nuclear waste transmutation subcritical core based on the mixed energy spectrum provided by the present invention has both fast neutrons and thermal neutrons in the same transmutation zone, and the fast neutrons are concentrated in the inner layer, and the thermal neutrons are concentrated in the inner layer. The subsets are concentrated in the outer layer, which can simultaneously transmute MA and LLFP, have high neutron utilization rate, and realize the purpose of high-efficiency nuclear waste transmutation.

(2) The structure of the high-efficiency nuclear waste transmutation subcritical core based on the mixed energy spectrum provided by the present invention is provided with a TRU fuel area and an LLFP fuel area in the same transmutation area, and the two fuel areas adopt the same fuel assembly form. The core structure is simple.

(3) Compared with the accelerator-driven fast-thermal coupling subcritical reactor disclosed in Chinese patent CN 1945751B, the present invention only has one transmutation zone, only one fuel assembly form is used, the structure is simple, and there is no safety of sodium-water reaction problems, higher security, and the ability to efficiently dispose of nuclear waste.

(4) Compared with the scheme of using LLFP fuel assembly in Korea's HYPER project, the present invention has graphite with sufficient thickness for neutron moderation, neutrons can be fully moderated, and LLFP transmutation effect is better.

(5) Compared with the production method of subcritical nuclear waste and nuclear fuel based on neutron multiplication of fissionable materials disclosed in Chinese patent 03152870.8, the TRU fuel and LLFP fuel of the present invention are in the same transmutation zone and have enough neutrons Entering the moderation zone and reflecting back, and graphite with sufficient thickness for neutron moderation, the LLFP transmutation effect is better, and the fission energy generated by the TRU fuel zone and the LLFP fuel zone can be taken out of the core through the coolant, and carried out production capacity.

(6) Compared with the hybrid energy spectrum supercritical water reactor proposed by the School of Nuclear Science and Engineering of Shanghai Jiao Tong University, the present invention utilizes the hybrid energy spectrum to carry out nuclear waste transmutation, fully utilizes the characteristics of fast neutrons and thermal neutrons, and further develops Advantages of hybrid spectrum.

Description of drawings

Fig. 1 is a radial arrangement diagram of the present invention;

Fig. 2 is an axial layout view of the present invention.

Detailed ways

As shown in Figure 1, the high-efficiency nuclear waste transmutation subcritical core based on the mixed energy spectrum provided by the present invention has the outer neutron source area 1, the transmutation area 2, the moderation layer area 3, Reflective layer area 4 and shielding layer area 5. The total height of the core is 3.8m and the diameter is 3.5m, among which the height of the active zone is 1m and the diameter is 1.22m. As shown in Figure 2, the outer neutron source region 1 runs through the entire core, and from the transmutation region 2 to the upper and lower ends of the axial direction, there are moderator region 3, reflector region 4, and shielding layer region 5 in sequence. The spallation neutron energy provided by the external neutron source is about 10 MeV. The external neutron source drives the fuel in the transmutation zone 2 to undergo fission reaction, and produces fast neutrons with an energy of about 500keV. The fast neutrons leaked from the transmutation zone 2 enter the moderator zone 3 for primary moderation, reach the reflector zone 4, reflect back, pass through the moderator zone 3 again for secondary moderation, and finally moderate into thermal neutrons Enter transmutation zone 2. In this way, the spallation neutrons provided by the external neutron source, the fast neutrons produced by the fission reaction, and the slowed and reflected thermal neutrons form a mixed energy spectrum in the transmutation zone 2, which can realize simultaneous The function of transmuting MA and LLFP has the function of efficiently transmuting nuclear waste, and the liquid lead-bismuth alloy is used as the coolant to bring the fission energy generated in the transmutation area out of the core for production.

Outer neutron source area 1: place a liquid lead-bismuth alloy spallation target with a diameter of 20 cm, and a target with a window or without a window can be selected. The high-energy proton beam produced by the high-energy high-current proton accelerator with an energy of 1GeV and an average current intensity of 10mA bombards the liquid lead-bismuth alloy target material to generate 10MeV neutrons as the exogenous neutrons driving the transmutation zone 2. The spallation target of the high-energy and high-current proton accelerator is used as the external neutron source, and neutrons with a harder energy spectrum can be obtained in the transmutation region 2, which is beneficial to the transmutation of MA. The use of liquid lead-bismuth alloy as the spallation target is mainly considered to have a high neutron yield, and at the same time it can be used as a coolant for the reactor.

Transmutation area 2: The transmutation area 2 is composed of 210 boxes of fuel assemblies, which are divided into 2 areas, which are 6 layers of TRU fuel assemblies and 1 layer of LLFP fuel assemblies, with a total of 7 layers of fuel assemblies. The arrangement of fuel assemblies in the transmutation zone 2 is determined according to the distribution of neutrons in this zone: in the inner layer of the transmutation zone 2, close to the outer neutron source zone 1, the density of fast neutrons in this zone is high, and the neutron energy spectrum is hard, which is suitable for For transmutation of MA, 6 layers of TRU fuel assemblies are placed; in the outer layer of transmutation zone 2, close to moderation layer zone 3, with high thermal neutron density, it is suitable for transmutation of LLFP, and 1 layer of LLFP fuel assemblies is placed. In this way, the characteristics and distribution of fast neutrons and thermal neutrons are fully utilized, and MA and LLFP are simultaneously transmuted in one transmutation zone 2, thereby achieving the purpose of transmuting nuclear waste with high efficiency. The fuel assembly adopts a hexagonal casing assembly, and each box assembly is composed of 271 fuel rods arranged in a triangle. The fuel assembly height is 3.8m, the assembly center distance is 175mm, the assembly clearance is 4mm, and the assembly wall thickness is 3mm. The outer diameter of the fuel rod is 6.7mm, the distance between the rods is 10mm, the thickness of the cladding is 0.5mm, and the distance between the pellet and the cladding is 0.1mm. The axial distribution of the moderator layer area 3, the reflection layer area 4 and the shielding layer area 5 are all arranged on the fuel rods.

Moderator layer area 3: The moderator layer area 3 is composed of one layer of hexagonal moderator layer components, the main material is graphite, and the structural material is stainless steel. The fast neutrons from the transmutation area 2 are moderated by graphite once, The neutrons reflected by the reflective layer area 4 pass through the graphite again for secondary moderation, and finally become thermal neutrons and return to the transmutation area 2, where the transmutation is located in the LLFP area of the transmutation area 2. Graphite has good moderation performance and is a solid material. Graphite is used as the material for the moderation layer, which has a simple structure and high engineering feasibility.

Reflective layer area 4: The reflective layer area 4 is composed of one layer of reflective layer components, the main material is stainless steel, and reflects back the neutrons leaked from the moderator area 3.

Shielding layer area 5: Shielding layer area 5 is composed of one layer of hexagonal shielding layer components. The main material is boron carbide and the structural material is stainless steel. It mainly shields the neutrons leaked from the reflection area 4 and reduces the neutrons to the core Neutron irradiation losses to peripheral components.

The structure of the high-efficiency nuclear waste transmutation subcritical core based on the hybrid energy spectrum provided by the present invention has both fast neutrons and thermal neutrons in the transmutation zone 2, and TRUs are distributed according to the distribution of fast neutrons and thermal neutrons The fuel area and the LLFP fuel area, the two fuel areas adopt the same fuel assembly form to realize the simultaneous transmutation of MA and LLFP in the same core and the same transmutation area. The neutron utilization rate is high, the core structure is simple, and it has high-efficiency transmutation The function of nuclear waste, and the liquid lead-bismuth alloy is used as the coolant to bring the fission energy generated in the transmutation zone out of the core for production.

Claims (6)

1. one kind based on the subcritical reactor core of efficient nuke rubbish transmuting that mixes power spectrum, it is characterized in that: neutron source region (1) outside said reactor core is followed successively by outside mind-set wherein, transmuting district (2), slowing down layer district (3), reflector region (4) and screen layer district (5); The outer source neutron of spallation neutron conduct that outer neutron source region (1) uses high energy proton bump target generation spallation reaction to produce; Transmuting district (2) uses higher chain product (being called for short TRU) and long-lived fission product (being called for short LLFP) as nuclear fuel; Outer source neutron drives the nuclear fuel generation fission reaction in the transmuting district (2); Produce fast neutron; The fast neutron that is let out by transmuting district (2) carries out slowing down one time through slowing down layer district (3), arrives reflector region (4) back reflection and returns, and passes through slowing down layer district (3) once more and carries out the secondary slowing down; Last slowing down becomes thermal neutron to get into transmuting district (2); Fast neutron that the spallation neutron that is provided by outer neutron source region (1) like this, fission reaction produce and slowing down and the thermal neutron that reflects form one and mix power spectrum in transmuting district (2), be provided with TRU fuel region and LLFP fuel region respectively, inferior actinium series nucleic of utilization fast neutron transmuting wherein (abbreviation MA) and thermal neutron LLFP according to the distribution situation of fast neutron and thermal neutron; Realize in the same transmuting of the same reactor core district purpose of the efficient transmuting nuke rubbish of transmuting MA and LLFP simultaneously; The function that possesses efficient transmuting nuke rubbish, and adopt the liquid lead bismuth alloy to take the fission energy that the transmuting district produces out of reactor core as cooling medium, carry out production capacity.

2. according to claim 1 a kind of based on the subcritical reactor core of efficient nuke rubbish transmuting that mixes power spectrum; It is characterized in that: a liquid lead bismuth alloy spallation target is placed in said outer neutron source region (1); The energy that adopts high energy high current proton precessional magnetometer to produce is 1GeV; The high energy proton bundle bombardment liquid lead bismuth alloy target material of the strong 10mA of average flow, the neutron of generation 10MeV is as the outer source neutron that drives transmuting district (2).

3. according to claim 1 a kind of based on the subcritical reactor core of efficient nuke rubbish transmuting that mixes power spectrum; It is characterized in that: the fast neutron in the said transmuting district (2) mainly is distributed in the inboard of transmuting district (2); Thermal neutron mainly is distributed in the outside of transmuting district (2); Distribution situation according to fast neutron and thermal neutron is provided with TRU fuel region and LLFP fuel region from inside to outside respectively, and the TRU fuel region is interior 6 grate firing material assemblies, and the LLFP fuel region is outermost 1 a grate firing material assembly.

4. a kind of subcritical reactor core of efficient nuke rubbish transmuting according to claim 1 based on the mixing power spectrum, it is characterized in that: said slowing down layer district (3) is made up of 1 layer of slowing down layer assembly, and slowing material is a graphite.

5. a kind of subcritical reactor core of efficient nuke rubbish transmuting according to claim 1 based on the mixing power spectrum, it is characterized in that: said reflector region (4) is made up of 1 layer of reflection horizon assembly, and reflecting material is a stainless steel.

6. a kind of subcritical reactor core of efficient nuke rubbish transmuting according to claim 1 based on the mixing power spectrum, it is characterized in that: said screen layer district (5) is made up of 1 layer of screen layer assembly, and shielding material is a boron carbide.

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