CN1945751A - Accelerator driven fast-thermally coupled subcritical reactor - Google Patents

Abstract

The invention discloses an accelerator-driven subcritical reactor. From the center outward, they are the target area, the fast neutron energy spectrum area, the thermal neutron energy spectrum area, the reflective layer area, the shielding layer area, and the stainless steel shell. In particular, the protons accelerated by the accelerator in the target area scatter with the main target nucleus. The neutrons produced by the fission reaction are used as the neutron source; the fissile material used in the fast neutron energy spectrum region is natural uranium or low-enrichment uranium; the thermal neutron energy spectrum region uses uranium with an enrichment of 3 to 4%. UO ₂ ; naturally forms an epithermal neutron region in the fast neutron energy spectrum region and the thermal neutron energy spectrum region, transmutation LLFP. This type of subcritical reactor not only realizes fast-thermal coupling, transmutation MA, and LLFP, but also can produce energy, truly realizing the concept of an accelerator-driven clean nuclear energy system.

Description

Accelerator-driven fast-thermal coupled subcritical reactor

technical field

The invention discloses a device for irradiating and transmuting radioactive waste with neutrons, in particular to an accelerator-driven subcritical reactor.

Background technique

In the spent fuel of the reactor, there are a large amount of radioactive substances, which are highly toxic and have a long half-life, many of which can be as long as 10 ⁴ to 10 ⁷ years, which is extremely harmful.

There are two international plans to deal with these spent fuels. One is the so-called one-pass method led by the United States, that is, after a long period of storage and cooling, the spent fuel is directly buried in deep geological land as high-level radioactive waste; the other is the French one. After the spent fuel is stored for a short period of time, reprocessing is carried out to recover uranium and plutonium, and the uranium and plutonium, all other actinide nuclides (referred to as MA) and all fission products (including long-lived Fission products (LLFP for short) are solidified as high-level radioactive waste for deep geological burial. Although the latter option is much less risky than the former one, it still has long-term radiological risks and a certain waste of resources.

In the fifth issue of "Modern Physics Knowledge" in 1994, Yu Zhongqiang disclosed in the article "Energy Amplifier" a method to provide clean nuclear energy proposed by a group led by C. Rubbia, director of the Western European Nuclear Center and Nobel Prize winner. The new concept of the company: using the high-energy proton beam generated by the high-energy proton accelerator (energy 1-1.6GeV, average current intensity-7mA), a nuclear cascade process is formed in the material to produce a large number of neutrons, natural thorium ( ²³² Th) Capture neutrons and transform into fissile elements ²³³ U, and ²³³ U fissions to produce neutrons to maintain the chain reaction. They called this device an energy amplifier. After the device is started, the proportion of fission elements in natural thorium can reach a relatively stable soon, forming a long-term stable energy output. The device operates in a subcritical state and a relatively high neutron flux (~10 ¹⁶ cm ^-2 ·s ^-1 ) to ensure the stability and continuity of the value-added process and the equipment without criticality hazards. There are very few long-lived actinides in the waste, which greatly simplifies the disposal of nuclear waste, and does not produce weapon-grade nuclear fuel, avoiding the concern of nuclear proliferation. This kind of system, which uses the neutrons produced by the spallation reaction of the high-energy protons accelerated by the accelerator and the heavy target nucleus as the external neutron source to drive the subcritical reactor system, is called ADS internationally. However, the ADS system provided by this document is only a new concept, and there are great difficulties in technology and process, because according to the current accelerator technology, it is necessary to build a proton with an energy of 1-1.6GeV and an average current intensity of 150mA. Accelerators are not an easy task. The reactor technology with a neutron flux of the order of 10 ¹⁶ cm ^-2 ·s ^-1 is also a new subject. In addition, if ADS uses a thermal neutron subcritical reactor to generate nuclear energy, it is designed to burn all LLFP, but not MA; if ADS uses a fast neutron subcritical reactor to generate nuclear energy, it is designed to burn all MA, but LLFP cannot be burned completely, because the transmutation of MA depends on fast neutrons and the transmutation of LLFP depends on epithermal neutrons. In conclusion, both reactor types (fast neutron reactor and thermal neutron reactor) have their own advantages and disadvantages.

In addition, in Chinese patent 03152870.8, the Institute of Plasma Physics, Chinese Academy of Sciences discloses a method for subcritical nuclear waste treatment and nuclear fuel production based on neutron multiplication of fissionable materials, which occurs through fusion reactions or high-energy protons and target materials The spallation reaction produces exogenous neutrons, and these exogenous neutrons enter the long-lived radioactive actinide element processing area, undergo fission reaction with actinide elements in the actinide element processing area, and simultaneously produce fissionable plutonium-239 or uranium-233 therein The fission reaction produces a large number of new neutrons; some of these neutrons enter the fissionable fuel breeding zone, and undergo a neutron capture reaction with depleted uranium or natural uranium or natural thorium to generate fissionable plutonium-239 or uranium-233 to supply actinides Recycling of element processing area, or output for other purposes; neutrons leaked from the fission fuel breeding area enter the fission product processing area, and capture and react with radioactive fission products mixed in the neutron moderator, so that the long-term Fission products with high lifetime toxicity are converted into stable non-toxic or short-lived and low-toxic fission products. The heat generated in each zone is cooled by coolant, and the zones are separated by structural materials. The entire system is shielded by shielding materials. Compared with the concept proposed by Rubia et al., this technical solution is more detailed, but it is still only a concept, and there are the following problems: 1) The use of D-T fusion reactors in the outer neutron source production area or by high-energy proton spallation reactions Providing an external neutron source is not only costly, but also difficult to control and difficult to realize. 2) The fission product processing area utilizes the low-energy neutrons slowed down in the fission fuel breeding area to undergo a capture reaction with the fission products to process long-lived fission product waste. In fact, there are very few low-energy neutrons available in the fission product processing area, and it is difficult to determine whether the expected purpose can be achieved. In addition, the fission product treatment area can only be used to dispose of long-lived fission product waste, which cannot generate energy and wastes fuel.

Technical solutions

The present invention is based on the concept of clean nuclear energy provided by C.Rubbia, Institute of Plasma Physics, Chinese Academy of Sciences, etc., to provide a fast-thermal coupling that can simultaneously burn off MA and LLFP, and can also produce energy. subcritical reactor.

A fast-thermal coupling subcritical reactor comprises a target area, a fast neutron energy spectrum area, a thermal neutron energy spectrum area, a reflective layer area, a shielding layer area, and a stainless steel casing from the center to the outside. The key is that the target area uses the neutrons produced by the spallation reaction between protons accelerated by the accelerator and the main target nucleus as the neutron source; the fissionable material used in the fast neutron spectrum area is natural uranium or low-enrichment uranium; The neutron spectrum region uses low-enrichment uranium for energy production. At the same time, an epithermal neutron region is naturally formed between the fast neutron energy spectrum region and the thermal neutron energy spectrum region.

The fast-thermal coupling subcritical reactor provided by the present invention has a fast neutron subcritical reactor inside and a thermal neutron subcritical reactor outside, which makes up for the respective shortcomings of the two types of reactors. The MA is transmuted by a subcritical reactor, and the LLFP is transmuted by the epithermal neutron region formed by the coupling of the internal fast neutron subcritical reactor and the external thermal neutron subcritical reactor. In addition, the internal fast neutron subcritical reactor can also amplify the neutron source generated by the accelerator, so that the external thermal neutron subcritical reactor can obtain a neutron source that is stronger than a purely external neutron source to drive thermal neutron subcritical reactors to generate more nuclear power or to ease accelerator requirements. The fast subcritical reactor is used as the amplifier of the external neutron source, and the amplification factor is $A=\frac{\mathrm{sl}}{1-k},$ Among them, s is the intensity of the external neutron source, l is the lifetime of neutrons in the reactor, and k is the effective multiplication factor of the fast subcritical reactor. If natural uranium is used as the fast zone and k is about 0.5, the external source can be enlarged twice. If the power is constant, the requirement for the speed flow of the accelerator can be reduced by 1/2, which can greatly reduce the requirement for the accelerator. If low-enrichment uranium is used instead of natural uranium, the subcritical effective multiplication factor k _s can be increased, and the magnification of the external neutron source will be larger.

In a word, the fast-thermal coupled subcritical reactor provided by the present invention makes up the shortcomings of the fast neutron subcritical reactor and the thermal neutron subcritical reactor in the ADS in transmutation MA and LLFP respectively and has both power generation functions, 1/3 of the power generation can be used for the electricity consumption of the accelerator. At the same time, the requirement for ADS to use low-enrichment uranium has been fulfilled.

Description of drawings

Fig. 1 is a transverse sectional view of the device;

Figure 2 is a longitudinal sectional view of the device.

Example

The technical solutions of the present invention will be further explained below in conjunction with examples.

As shown in Figure 1, a fast-thermal coupled subcritical reactor consists of target area 1, fast neutron energy spectrum area 2, thermal neutron energy spectrum area 4, reflective layer area 5, and shielding layer area from the center to the outside. 6. Stainless steel shell7. A lead buffer area 8 is set in the middle. The coupling between the fast neutron energy spectral region 2 and the thermal neutron energy spectral region 4 forms the epithermal neutron energy spectral region 3 .

As shown in Fig. 2, the structure of each area is as follows.

Target area 1: Take out 7 elements in the center of fast neutron spectrum area 2 to form a cavity with a diameter of 40-60 mm, the best design is 50 mm as the target area, and the length of the neutron source lead target tube is 500 mm. If the energy produced by the high-energy high-current proton accelerator is 1GeV, the high-energy proton beam with an average current intensity of ~1mA bombards the lead target and will produce a neutron source of 1.2-1.9×10 ⁹ n/s.

Fast neutron energy spectrum area 2: All components are installed in a hexahedral aluminum block, the diameter of the aluminum block is 195-220mm, and the best design is 200mm. The grid pitch is 25mm, and the average neutron energy is 700KeV. The natural uranium or low-enrichment uranium fuel element has an outer diameter of 22mm, a core diameter of 20mm, a core length of 1000mm, a total length of 1035mm, and a density of 18.6g/cm ³ . The casing material is aluminum. The fuel elements are inserted in the aluminum parts, and the number of elements is 264.

Thermal neutron energy spectrum region 4: the thickness is 150mm, the fuel elements are inserted in the polyethylene moderator and arranged in a triangle. The fuel element uses UO ₂ with an enrichment degree of 3-5%. The outer diameter of the element is 8mm, the diameter of the core is 6.55mm, the length of the core is 700mm, and the density of the element is 10.4465g/cm ³ . The thickness of the fuel element cladding is 0.65mm, and the material is Zr-2 alloy. Each element core weighs 753g and has a pitch of 12mm. The number of components depends on the needs, so that K _eff is between 0.90 and 0.98.

Reflective layer area 5: the material is polyethylene, the density is 0.937g/cm ³ , the radial thickness is >15-25cm, and the axial thickness is >15-25cm.

Shielding layer area 6: boron-containing polyethylene, thickness > 25cm.

Stainless steel shell 7: 10cm thick.

At the same time, an epithermal neutron region 3 is naturally formed between the fast neutron energy spectrum region 2 and the thermal neutron energy spectrum region 4, transmuting LLFP.

In the technical scheme provided by the present invention, in the fast neutron spectrum region 2 except the fuel element, aluminum is used to simulate the sodium-cooled material in the fast region, and in the thermal neutron spectrum region 4, except the fuel element, polyethylene is used to simulate the moderator The material - water, the structure is simple and practical. It not only achieves fast-thermal coupling, transmutation of MA, LLFP, but also production capacity, and realizes the concept of accelerator-driven clean nuclear energy system (ADS) in the true sense.

Claims (3)

1. fast-thermal coupling subcritical reactor, therefrom mind-set is followed successively by target area (1), fast neutron spectrum district (2), thermal neutron spectrum district (4), reflector region (5), screen layer district (6), stainless steel casing (7) outward, it is characterized in that target area (1) uses the neutron of accelerator protons accelerated and the generation of main target nucleus generation spallation reaction as neutron source; The employed fissile material in fast neutron spectrum district (2) is natural uranium or low enrichment uranium; What thermal neutron spectrum district (4) used is that enrichment is 3～5% UO ₂Naturally form epithermal neutron district (3), transmuting LLFP in fast neutron spectrum district (2) with thermal neutron spectrum district (4).

2. according to claim 1 fast-the thermal coupling subcritical reactor, it is characterized in that the diameter of fast neutron spectrum district (2) is 195～220mm.

3. according to claim 1 and 2 fast-the thermal coupling subcritical reactor, it is characterized in that the element radical of thermal neutron spectrum district (4) is according to K _EffNeeds between 0.90～0.98 and deciding.

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