WO2022077250A1 - 基于等离子体的乏燃料干法后处理方法 - Google Patents

基于等离子体的乏燃料干法后处理方法 Download PDF

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WO2022077250A1
WO2022077250A1 PCT/CN2020/120792 CN2020120792W WO2022077250A1 WO 2022077250 A1 WO2022077250 A1 WO 2022077250A1 CN 2020120792 W CN2020120792 W CN 2020120792W WO 2022077250 A1 WO2022077250 A1 WO 2022077250A1
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spent fuel
plasma
puf
dry
gas
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PCT/CN2020/120792
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English (en)
French (fr)
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陈明周
刘夏杰
黄文有
周江
陆杰
李晴
杨武
张子炜
魏欢饴
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中广核研究院有限公司
中国广核集团有限公司
中国广核电力股份有限公司
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Priority to EP20957031.6A priority Critical patent/EP4060681A4/en
Priority to CN202080033494.7A priority patent/CN113795894A/zh
Priority to GB2207525.3A priority patent/GB2606640A/en
Priority to PCT/CN2020/120792 priority patent/WO2022077250A1/zh
Publication of WO2022077250A1 publication Critical patent/WO2022077250A1/zh

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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
    • G21C19/42—Reprocessing of irradiated fuel
    • G21C19/44—Reprocessing of irradiated fuel of irradiated solid fuel
    • G21C19/48—Non-aqueous processes
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/28—Treating solids
    • G21F9/30—Processing
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G43/00—Compounds of uranium
    • C01G43/01—Oxides; Hydroxides
    • C01G43/025—Uranium dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G43/00—Compounds of uranium
    • C01G43/04—Halides of uranium
    • C01G43/06—Fluorides
    • C01G43/063—Hexafluoride (UF6)
    • C01G43/066—Preparation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G56/00—Compounds of transuranic elements
    • C01G56/004—Compounds of plutonium
    • C01G56/005—Oxides; Hydroxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G56/00—Compounds of transuranic elements
    • C01G56/004—Compounds of plutonium
    • C01G56/006—Halides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B59/00—Obtaining rare earth metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
    • C22B60/02—Obtaining thorium, uranium, or other actinides
    • C22B60/0204—Obtaining thorium, uranium, or other actinides obtaining uranium
    • C22B60/0208—Obtaining thorium, uranium, or other actinides obtaining uranium preliminary treatment of ores or scrap
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
    • C22B60/02—Obtaining thorium, uranium, or other actinides
    • C22B60/0204—Obtaining thorium, uranium, or other actinides obtaining uranium
    • C22B60/0213—Obtaining thorium, uranium, or other actinides obtaining uranium by dry processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
    • C22B60/02—Obtaining thorium, uranium, or other actinides
    • C22B60/0295—Obtaining thorium, uranium, or other actinides obtaining other actinides except plutonium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
    • C22B60/02—Obtaining thorium, uranium, or other actinides
    • C22B60/04—Obtaining plutonium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/001—Dry processes
    • C22B7/002—Dry processes by treating with halogens, sulfur or compounds thereof; by carburising, by treating with hydrogen (hydriding)
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
    • G21C19/42—Reprocessing of irradiated fuel
    • G21C19/50—Reprocessing of irradiated fuel of irradiated fluid fuel, e.g. regeneration of fuels while the reactor is in operation
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/02—Treating gases
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies

Definitions

  • the invention relates to the technical field of nuclear power fuel, in particular to a plasma-based dry post-processing method for spent fuel.
  • the spent fuel contains U, Pu and other transuranic elements (TRU, transuranium In addition to elements), it also contains alkali metal (AM) elements, alkaline earth metal (AEM) elements, platinum group elements, etc. as fission products (FP, fission products).
  • TRU transuranium In addition to elements
  • AM alkali metal
  • AEM alkaline earth metal
  • FP fission products
  • Japan's Hitachi has proposed a FLUOREX process (US7, 445, 760 B2) that combines fluorination volatilization and water reprocessing.
  • the process is divided into two steps: “dry” and “wet”: It is converted into UF 6 and separated from Pu, FP, etc., and at the same time, the non-volatile form of Pu is controlled; the non-volatile U, Pu, FP, etc. are converted into oxides, which are then dissolved in nitric acid and separated by the water method PUREX process.
  • Pu is kept in a non-volatile form, and then recovered by the water method, which avoids the problem of low Pu yield in the original fluorination volatilization method.
  • the fluorination volatilization step can remove more than 90% of the U in spent fuel, which greatly reduces the burden of the subsequent PUREX process by first separating a large amount of uranium.
  • the above process still has a water method link, the generation of high-level waste liquid is unavoidable, and the economy of the "dry” and "wet” combined process is worth verifying.
  • the dry post-processing technology in the full sense mainly includes fluorination volatilization method and metal melt extraction method. Has the following advantages:
  • the fluorination volatilization method is based on the special properties of uranium, plutonium and neptunium to form volatile hexafluorides, while most of the fission products (lanthanides) and ultra-plutonium elements present in spent fuel form non-volatile trifluorides. This property creates several processes based on the fluorination of spent fuel by strong fluorinating agents such as BrF3 , BrF5 , ClF3 , NF3 and even pure F2.
  • thermochemical reprocessing technology In the field of reprocessing, fluorination volatilization is considered as a promising advanced thermochemical reprocessing technology, which can be used not only for the treatment of spent fuel from light water reactors, but also for spent fuel that is difficult to reprocess by wet processes.
  • Fuel including: spent oxide fuel from Generation IV reactors - fast reactors, and advanced oxide fuel types (e.g. fuels with inert matrices and/or high burnup, high plutonium content and very short cooling times) , Nitride, carbide, alloy and other types of spent nuclear fuel are pre-oxidized to oxides.
  • the fluoride volatilization method can be divided into molten salt fluorination method and gas direct fluorination method.
  • gas direct fluorination method the gas flame fluorination technology is the only method that is not based on molten salts and uses only simple fluorinating agents and adsorbents. Able to achieve the required performance and yield, recover the amount of fissionable material to a set quality, and generate a minimum amount of radioactive waste, improve industrial and nuclear safety, and greatly reduce the negative impact on the environment.
  • the technical problem to be solved by the present invention is to provide a plasma-based dry post-processing method for spent fuel.
  • the technical solution adopted by the present invention to solve the technical problem is to provide a plasma-based dry post-processing method for spent fuel, comprising the following steps:
  • the spent fuel powder is fully mixed and reacted with the plasma containing F atoms in the plasma reactor to form a product including volatile fluoride and non-volatile fluoride;
  • the gas-solid two-phase flow is filtered to remove the solid product wherein, then through condensation, adsorption, desorption and rectification, the mixed gas containing UF 6 and PuF 6 is obtained;
  • step S1 the spent fuel powder is transported into the plasma reactor through a nozzle under the action of a carrier gas of an inert gas.
  • the particle size of the spent fuel powder is less than or equal to 200 ⁇ m.
  • the plasma containing F atoms is formed by transforming a fluorinated medium; the fluorinated medium includes CF 4 , NF 3 , F 2 , HF, BrF 3 , BrF 5 , ClF 3 and SF 6 one or more of the gases.
  • the plasma containing F atoms is formed by the fluorinated medium through gas discharge transformation and then input into the plasma reactor; or, the plasma containing F atoms is produced by the A fluorinated medium is transformed in the plasma reactor.
  • the plasma containing F atoms is generated by at least one of high voltage discharge, direct current arc discharge, high frequency discharge, microwave discharge and laser ionization.
  • step S2 when the fluorination medium is F 2 , the chemical reaction formula of UO 2 and U 3 O 8 in the spent fuel powder reacting in the plasma reactor is as follows: (2):
  • PuF 4 produced according to formula (3) reacts with enough F 2 to promote the reaction of formula (4) to proceed to the right end, so that PuO 4 is completely converted into PuF 6 ;
  • the chemical reaction formula for the reaction of the minor actinides in the spent fuel powder in the plasma reactor is as follows:
  • NpF 4 produced according to formula (8) reacts with enough F 2 to promote the reaction of formula (9) to proceed to the right end, so that NpF 4 is completely converted into NpF 6 .
  • the temperature of the reaction zone in the plasma reactor is greater than 2000K; the temperature of the wall of the plasma reactor is controlled below 950K.
  • step S5 includes: treating the mixed gas of UF 6 and PuF 6 by a dry method or a wet method to obtain a mixed oxide of UO 2 and PuO 2 , HF; or,
  • Step S5 includes: separating UF 6 and PuF 6 of the mixed gas; treating UF 6 by dry method or wet method to obtain UO 2 and HF; treating PuF 6 by dry method or wet method to obtain PuO 2 and HF .
  • step S5 includes: subjecting the mixed gas of UF 6 and PuF 6 to electromagnetic separation to obtain U, Pu and F 2 ; or,
  • Step S5 includes: separating UF 6 and PuF 6 of the mixed gas; subjecting UF 6 to electromagnetic separation to obtain metals U and F 2 ; subjecting PuF 6 to electromagnetic separation to obtain metals Pu and F 2 .
  • the spent fuel dry reprocessing method further comprises the following steps:
  • step S6 recovering the solid product obtained by the separation of step S3 and step S4.
  • the plasma-based dry post-processing method for spent fuel of the present invention avoids the generation of a large amount of radioactive waste liquid, and solves the problem of needing to store and process a large amount of waste liquid, compared with the traditional water chemical processes such as dissolution, precipitation, filtration and other operating procedures;
  • the fluorine atoms of the plasma react with U, Pu and other components in the spent fuel.
  • the plasma has the effect of a wider temperature range and stronger activity of the fluorinating agent, realizing the complete conversion of Pu into PuF 6 , solves the problem of separating Pu from the fission product fluoride, promotes the separation of U and Pu from the fission product, improves the recovery rate, and simplifies the process.
  • the method of the invention has a wide range of applications, is suitable for processing spent fuel of fast neutron reactors, thermal neutron reactors and other types of advanced reactors, and is suitable for various types of spent fuels, including oxides, nitrides, carbides and metals Wait. Simple process flow and less secondary waste; compared with other fluorination methods, the reaction rate is higher and the temperature is easier to control (control the reaction rate by controlling the atomic density of the reactant by the discharge power; component control, ions, electrons and neutrals The atomic temperature is controlled separately) to achieve the maximum conversion of Pu, which is conducive to the formation of a closed nuclear fuel cycle structure.
  • FIG. 1 is a schematic flowchart of a plasma-based dry post-processing method for spent fuel according to an embodiment of the present invention.
  • a plasma-based dry post-processing method for spent fuel includes the following steps:
  • the spent fuel after removing the cladding can be processed by but not limited to mechanical processing, and it is ground into powder, that is, spent fuel powder.
  • the particle size of the spent fuel powder is preferably ⁇ 200 ⁇ m.
  • the spent fuel powder can be transported into the plasma reactor through the nozzle under the action of the carrier gas; the carrier gas adopts an inert gas, which does not chemically react with the transported material (spent fuel powder).
  • spent fuel powder can also be sent to the plasma reactor by mechanical conveying (such as a screw conveyor).
  • the spent fuel powder is fully mixed and reacted with the plasma containing F atoms in the plasma reactor to form a product including volatile fluoride and non-volatile fluoride.
  • the plasma containing F atoms is formed by the transformation of a fluorinated medium, which can be preliminarily transformed from a fluorinated medium by gas discharge and then input into the plasma reactor; or, the plasma containing F atoms is formed by the fluorinated medium in the plasma transformed in the bulk reactor.
  • the plasma containing F atoms may be generated by at least one of high voltage discharge, direct current arc discharge, high frequency discharge and microwave discharge.
  • the plasma containing F atoms may be generated by at least one of high voltage discharge, direct current arc discharge, high frequency discharge, microwave discharge and laser ionization.
  • the fluorinated medium as the plasma includes one or more of CF 4 , NF 3 , F 2 , HF, BrF 3 , BrF 5 , ClF 3 and SF 6 gases.
  • the temperature of the reaction zone in the plasma reactor is greater than 2000K.
  • the wall temperature of the plasma reactor is controlled below 950K (or 550°C) to reduce the risk of corrosion.
  • the elements contained in spent fuel powder include uranium (U), plutonium (Pu), lanthanide (Ln) and less actinide (Np, Am, Cm) and so on.
  • U uranium
  • Pu plutonium
  • Ln lanthanide
  • Np actinide
  • U uranium
  • Pu plutonium
  • Ln lanthanide
  • Np actinide
  • U forms UF 6 (non-volatile fluoride)
  • Pu eventually forms PuF 6 (non-volatile fluoride)
  • most of the fission products such as Sr, Ba, Y, Cs and lanthanides
  • fission products such as Sr, Ba, Y, Cs and lanthanides
  • a small number of fission products such as Nb, Ru, Te, Mo, I, and minor actinides
  • the chemical reaction occurring in the plasma reactor is described in detail below by taking F 2 as the fluorinated medium as an example.
  • the fluorinated medium is other fluorine source gas, the reaction mechanism is the same.
  • the fluorinated medium reacts with UO 2 and U 3 O 8 in the atomic state of F in the plasma reactor, and the reaction rate is higher, so the above formulas (1) and (2) are respectively as follows (1.1), (2.1) ):
  • PuF 4 produced according to formula (3) reacts with enough F 2 to promote the reaction of formula (5) to proceed to the right end, so that PuO 4 is completely converted into PuF 6 .
  • the chemical reaction formula for the reaction of the minor actinides in the spent fuel powder in the plasma reactor is as follows:
  • NpF 4 produced according to formula (8) reacts with enough F 2 to promote the reaction of formula (9) to proceed to the right end, so that NpF 4 is completely converted into NpF 6 .
  • equations (7) to (11) are actually as follows (7.1) to (11.1):
  • the product is rapidly cooled at a cooling rate of 10 4 K/s-10 9 K/s to form a gas-solid two-phase flow and a solid product.
  • step S2 the product obtained in step S2 is passed through the rapid cooling area, and the product is rapidly mixed with the cold gas flow in the rapid cooling area or through the cooling method of the aerodynamic nozzle, so that the cooling rate is 10 4 K/s-10 9 K/s
  • the cooling rate is 10 4 K/s-10 9 K/s
  • the solid products mainly include fluorination products of minor actinides such as LnF 3 , AmF 3 , CmF 3 gas and the like.
  • the gas-phase substances in the gas-solid two-phase flow include gaseous fluorination products such as UF 6 and PuF 6 in the above-mentioned formulas (1) to (11); the solid products also included are fluorination products of secondary actinides such as LnF 3 , AmF 3 , CmF 3 gas, etc.
  • the solid products (such as LnF 3 , AmF 3 , CmF 3 , etc.) in the gas-solid two-phase flow are first separated from the gas phase by filtration.
  • Filtration uses fine-pore filter equipment, such as sintered metal filters or combinations with other filters.
  • Condensation, adsorption, desorption and rectification are performed on the gas phase.
  • the purpose of condensation is to separate the fluorinated products of U, Pu and Np from other fluorinated products, and the condensation temperature is lower than 350K.
  • the adsorption adopts a fluoride adsorbent, such as NaF or MgF 2 , and the adsorption temperature is 300K-400K. After adsorption, the temperature can be increased to 600K-700K to achieve desorption.
  • NpF 6 contained in the gas phase is removed by adsorption, thereby obtaining a mixed gas containing UF 6 and PuF 6 .
  • the mixed gas is recovered and processed to form oxides, and the method can be as follows: the mixed gas of UF6 and PuF6 is processed by dry method or wet method to obtain the mixed oxide of UO2 and PuO2 , HF .
  • UF 6 and PuF 6 of the mixed gas process UF 6 by dry or wet process to obtain UO 2 and HF; process PuF 6 by dry or wet process to obtain PuO 2 and HF.
  • the separation of UF 6 and PuF 6 can adopt the heating method, and PuF 6 is volatilized and separated from UF 6 .
  • UF 6 and PuF 6 react with water vapor to directly generate UO 2 , HF and PuO 2 , HF, respectively.
  • the reaction is as follows:
  • the mixed gas is recovered and processed to form a metal
  • the method can be as follows: the mixed gas of UF 6 and PuF 6 is processed by electromagnetic separation to obtain an alloy of U and Pu and F 2 .
  • the UF 6 is subjected to electromagnetic separation to obtain metals U and F 2 ; and the PuF 6 is subjected to electromagnetic separation to obtain metals Pu and F 2 .
  • the electromagnetic separation treatment can be realized by using the prior art, and reference may be made to WO 97/34685 and the like.
  • the recovered oxides and HF, metals and F 2 can be sent back to the relevant sections for reuse.
  • the above-mentioned mixed oxides of UO 2 and PuO 2 recovered after the treatment are supplemented with uranium (usually depleted uranium oxides), and then passed through the nuclear fuel processing section to form mixed oxide fuel (MOX fuel).
  • uranium usually depleted uranium oxides
  • MOX fuel mixed oxide fuel
  • HF and F2 can be used as fluorine sources back into the plasma reactor.
  • dry post-processing method of spent fuel of the present invention further comprises the following steps:
  • step S6 recovering the solid product obtained by the separation of step S3 and step S4.
  • the solid products separated in steps S3 and S4 mainly include fluorination products of minor actinides such as LnF 3 , AmF 3 , CmF 3 and the like.
  • Recycling treatment includes stabilization treatment or consumption treatment of solid products, and after stabilization treatment, products that are convenient for storage or disposal are formed; consumption treatment is to apply solid products to fast neutron reactors, etc.

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Abstract

本发明公开了一种基于等离子体的乏燃料干法后处理方法，包括以下步骤：S1、将脱去包壳后的乏燃料加工成乏燃料粉末，送至等离子体反应器中；S2、乏燃料粉末与含F原子的等离子体充分混合并发生反应，形成产物；S3、将产物进行急速冷却，形成气固两相流和固态产物；S4、将气固两相流过滤去除固态产物，再经过冷凝、吸附、解吸和精馏，得到混合气体；S5、将混合气体进行回收处理，形成对应的氧化物或金属。本发明通过等离子体的氟原子与乏燃料中的U、Pu等反应，相较于火焰氟化工艺，等离子体具有温度范围更宽、氟化剂活性更强的效果，实现Pu完全转化成PuF6，解决了从裂变产物氟化物中分离Pu的问题，促使U和Pu与裂变产物分离，提高回收率，简化工艺。

Description

基于等离子体的乏燃料干法后处理方法 技术领域
本发明涉及核电燃料技术领域，尤其涉及一种基于等离子体的乏燃料干法后处理方法。
 背景技术
核电厂中，乏燃料中除含有U、Pu等超铀元素（TRU，transuranium elements）以外，还含有作为裂变产物（FP， fission product）的碱金属（AM）元素、碱土类金属（AEM）元素、铂族元素等，采用适当的工艺对乏燃料进行后处理，将U、Pu与乏燃料分离不但能够回收可裂变材料，提高经济效益，还会大大减少随后需要处理的乏燃料的体积。
经过半个多世纪的发展，以普雷克斯（PUREX）流程为代表的水法后处理工艺日趋完善。但是，随着乏燃料后处理规模的扩大，水法工艺的主要缺陷也变得越来越突出：使用液态酸溶解乏燃料，产生大量放射性水溶液和有机盐溶液，并由此积累了需要存储的大量高放废物（HLW）。高放废液需要进行复杂的处理：先脱水，然后转化为微溶性化合物（玻璃）形态，或者其他更易于储存的固体形态。对于这样使用水溶液和有机溶液的乏核燃料后处理工艺，其规模的增加越来越难以满足生产中的工业安全和核安全要求。另一方面，面对新型反应堆的乏燃料，水化学工艺存在显著局限性：无法处理先进氧化物燃料，包括惰性基质燃料、高燃耗燃料以及Pu含量高、冷却时间短的燃料。
日本日立公司提出了将氟化挥发法与水法后处理流程相结合的FLUOREX流程（US7, 445, 760 B2），该流程分“干”、“湿”两步：首先将乏燃料中的U 转化为UF 6与Pu、FP等分离，同时控制Pu为不可挥发的形态；未挥发的U 和Pu、FP等转型成氧化物，然后用硝酸溶解后，采用水法PUREX流程进行分离处理。FLUOREX流程中将Pu保持为不可挥发的形态，然后采用用水法工艺回收，避免了原有氟化挥发法中Pu收率低的问题。氟化挥发步骤可以除去乏燃料中90％以上的U，该流程因首先分离了大量的铀而使后续的PUREX流程负担大为减轻。但是，上述流程仍然存在水法环节，高放废液的产生不可避免，并且“干”、“湿”组合流程的经济性值得验证。
完全意义上的干法后处理技术主要包括氟化挥发法和金属熔融萃取法。具有如下优点：
（1）不存在材料辐射分解问题，可处理燃耗深、冷却时间短的乏燃料；
（2）减少了水法工艺所必需的固态——水溶液——固态转换环节，精简了工艺和设备；
（3）废物量少，并且主要形式是固态，更易于储存、处理和处置；
（4）由于不存在中子慢化材料，缓解工艺设备的临界问题，也降低了成本；
（5）与水法工艺相比，干法运行所需的物料体积缩小了，工艺设备可以小型化；
（6）可直接回收合金材料。
氟化挥发法是基于铀、钚、镎形成挥发性六氟化物的特殊性质，而乏燃料中存在的大多数裂变产物（镧系元素）和超钚元素则形成非挥发性三氟化物， 这种性质形成了基于乏燃料被强氟化剂（如BrF 3、BrF 5、ClF 3 、NF 3甚至纯F 2）的氟化的几种工艺。
在后处理领域，氟化挥发法被认为是一种有前途的先进热化学后处理技术，不仅可以用于处理轻水堆的乏燃料，还可以用于处理湿法工艺难以进行后处理的乏燃料，包括：第四代反应堆——快堆的氧化物乏燃料，以及先进氧化物燃料类型（例如：具有惰性基质的燃料和/或高燃耗，钚含量高且冷却时间极短的燃料），氮化物、碳化物、合金等类型的乏核燃料被预氧化为氧化物。
根据介质类型的不同，氟化物挥发法又可以分为熔盐氟化法和气体直接氟化法。在所有已知的干法高温化学后处理过程中，只有气体直接氟化法——气体火焰氟化技术是唯一一种不基于熔盐的方法，仅仅使用简单的氟化剂和吸附剂就能实现所需的性能和产率，回收可裂变材料的量达到设定的品质，并产生最少量的放射性废物，提高工业安全性和核安全性，大幅降低对环境的负面影响。此外，由于几乎所有可裂变材料（UF 6、PuF 6）直接参与大多数工艺和操作环节，不涉及外部加入的稀释剂、溶剂等，因此工艺过程中使用的设备及其布置方式可以非常紧凑。
然而，直接氟化法需要克服的两个问题：一是氟化时温度较高，时间较长，氟化气体（F 2或者HF）对设备腐蚀严重；二是化学平衡在钚的氟化温度下平衡常数很大，PuF 6本身的稳定性较差，在氟化的同时分解，PuF 4造成气路堵塞，降低钚的回收率。为了解决这些问题，需要提高氟化反应的速率，并采取适当的冷却措施，从动力学上防止PuF 6热分解。
在火焰氟化乏燃料的过程中，由于乏燃料中存在裂变产物，并且处理时间短，其中的成分转化为六氟化物的过程不能完全实现，这些组分以较低价氟化物的形态残留在炉渣中。基本上，这些氟化物的粉末都是在收集容器中收集的，但是至多20％沉积在反应器的壁上。为了从反应器中清理炉渣，必须拆卸反应器，操作复杂且难。
 技术问题
本发明要解决的技术问题在于，提供一种基于等离子体的乏燃料干法后处理方法。
 技术解决方案
本发明解决其技术问题所采用的技术方案是：提供一种基于等离子体的乏燃料干法后处理方法，包括以下步骤：
S1、将脱去包壳后的乏燃料加工成乏燃料粉末，送至等离子体反应器中；
S2、所述乏燃料粉末在所述等离子体反应器中与含F原子的等离子体充分混合并发生反应，形成包括挥发性氟化物和不挥发性氟化物的产物；
S3、将所述产物在10 4K/s-10 9K/s的冷却速率下进行急速冷却，形成气固两相流和固态产物；
S4、将所述气固两相流进行过滤去除其中的固态产物，再经过冷凝、吸附、解吸和精馏，得到含UF 6和PuF 6的混合气体；
S5、将所述混合气体进行回收处理，形成对应的氧化物或金属。
优选地，步骤S1中，所述乏燃料粉末在惰性气体的载气作用下通过喷嘴输送至等离子体反应器中。
优选地，步骤S1中，所述乏燃料粉末的粒径≤200μm。
优选地，步骤S2中，所述含F原子的等离子体通过氟化介质转化形成；所述氟化介质包括CF 4、NF 3、F 2、HF、BrF 3、BrF 5、ClF 3及SF 6气体中一种或多种。
优选地，步骤S2中，所述含F原子的等离子体由所述氟化介质通过气体放电转化形成后再输入所述等离子体反应器中；或者，所述含F原子的等离子体由所述氟化介质在所述等离子体反应器中转化形成。
优选地，所述含F原子的等离子体通过高压放电、直流电弧放电、高频放电、微波放电和激光电离中至少一种产生。
优选地，步骤S2中，当氟化介质为F 2时，所述乏燃料粉末中的UO 2和U 3O 8在所述等离子体反应器中发生反应的化学反应式如下式（1）、（2）：
             UO 2+3F 2→UF 6+O 2                 （1）
             U 3O 8+9F 2→3UF 6+4O 2            （2）
    所述乏燃料粉末中的PuO 2在所述等离子体反应器中发生反应的化学反应式如下式（3）至（5）：
              PuO 2+2F 2→PuF 4+O 2               （3）
             PuO 2+3F 2→PuF 6+O 2               （4）
             PuO 4+F 2↔PuF 6                     （5）
其中，根据式（3）产生的PuF 4再与足够的F 2反应，促使式（4）的反应向右端进行，使PuO 4完全转化为PuF 6；
所述乏燃料粉末中的镧系元素在所述等离子体反应器中发生反应的化学反应式如下：
             2Ln 2O 3+6F 2→4LnF 3+3O 2            （6）
所述乏燃料粉末中的次锕系元素在所述等离子体反应器中发生反应的化学反应式如下：
             NpO 2+3F 2→NpF 6+O 2                 （7）
             NpO 2+2F 2→NpF 4+O 2                 （8）
             NpF 4+F 2↔ NpF 6                        （9）
             2Am 2O 3+6F 2→4AmF 3+3O 2           （10）
             2Cm 2O 3+6F 2→4CmF 3+3O 2           （11）
其中，根据式（8）产生的NpF 4再与足够的F 2反应，促使式（9）的反应向右端进行，使NpF 4完全转化为NpF 6。
优选地，步骤S2中，所述等离子体反应器中反应区的温度大于2000K；所述等离子体反应器的器壁温度控制在950K以下。
优选地，步骤S5包括：将UF 6和PuF 6的混合气体通过干法或湿法处理，得到UO 2和PuO 2的混合氧化物、HF；或者，
步骤S5包括：将所述混合气体的UF 6和PuF 6分离；将UF 6通过干法或湿法处理，得到UO 2和HF；将PuF 6通过干法或湿法处理，得到PuO 2和HF。
优选地，步骤S5包括：将UF 6和PuF 6的混合气体通过电磁分离处理，得到U、Pu以及F 2；或者，
步骤S5包括：将所述混合气体的UF 6和PuF 6分离；将UF 6通过电磁分离处理，得到金属U和F 2；将PuF 6通过电磁分离处理，得到金属Pu和F 2。
优选地，所述乏燃料干法后处理方法还包括以下步骤：
S6、将步骤S3和步骤S4分离得到的固态产物进行回收处理。
 有益效果
本发明的基于等离子体的乏燃料干法后处理方法，较于传统水化学工艺溶解、沉淀、过滤等操作流程，避免产生大量放射性废液，解决了需要存储、处理大量废液的难题；通过等离子体的氟原子与乏燃料中的U、Pu及其他成分反应，相较于火焰氟化工艺，等离子体具有温度范围更宽、氟化剂活性更强的效果，实现Pu完全转化成PuF 6，解决了从裂变产物氟化物中分离Pu的问题，促使U和Pu 与裂变产物分离，提高回收率，简化工艺。
本发明的方法应用范围广，适用于处理快中子堆、热中子堆以及其他类型先进反应堆的乏燃料，并且适用于多种类型的乏燃料，包括氧化物、氮化物、碳化物以及金属等。工艺流程简单，二次废物少；相对于其他氟化方法，反应速率更高、温度更容易控制（通过放电功率控制反应物原子密度，从而控制反应速率；分成分控制，离子、电子和中性原子温度分别控制），实现Pu的最大程度转化，有利于形成闭式核燃料循环结构。
 附图说明
图1是本发明一实施例的基于等离子体的乏燃料干法后处理方法的流程示意图。
 本发明的实施方式
参考图1，本发明一实施例的基于等离子体的乏燃料干法后处理方法，包括以下步骤：
S1、将脱去包壳后的乏燃料加工成乏燃料粉末，送至等离子体反应器中。
其中，对脱去包壳后的乏燃料的加工可以采用但不限于机械加工方式，将其研磨成粉末，即为乏燃料粉末。乏燃料粉末的粒径优选≤200μm。
乏燃料粉末可以在载气作用下通过喷嘴输送到等离子体反应器中；载气采用惰性气体，不与输送物料（乏燃料粉末）发生化学反应。当然，乏燃料粉末也可以通过机械输送（如螺旋输送机）送到等离子体反应器中。
S2、乏燃料粉末在等离子体反应器中与含F原子的等离子体充分混合并发生反应，形成包括挥发性氟化物和不挥发性氟化物的产物。
其中，含F原子的等离子体通过氟化介质转化形成，其可以预先由氟化介质通过气体放电转化形成后再输入等离子体反应器中；或者，含F原子的等离子体由氟化介质在等离子体反应器中转化形成。
在等离子体反应器外部，含F原子的等离子体可以通过高压放电、直流电弧放电、高频放电和微波放电中至少一种产生。在等离子体反应器中，含F原子的等离子体可以通过高压放电、直流电弧放电、高频放电、微波放电和激光电离中至少一种产生。作为等离子体的氟化介质包括CF 4、NF 3、F 2、HF、BrF 3、BrF 5、ClF 3及SF 6气体中一种或多种。
等离子体反应器中反应区的温度大于2000K。等离子体反应器的器壁温度控制在950K（或550℃）以下，降低被腐蚀风险。
通常，乏燃料粉末中含有的元素包括有铀（U）、钚（Pu）、镧系元素（Ln）和次锕系元素（镎Np、镅Am、锔Cm）等等。经过与等离子体反应，其中U形成UF 6（不挥发性的氟化物），Pu最终形成PuF 6（不挥发性的氟化物），大部分裂变产物（如Sr、Ba、Y、Cs和镧系元素）形成不挥发性的氟化物，少部分裂变产物（如Nb、Ru、Te、Mo、I和次锕系元素）形成挥发性氟化物。
下面以F 2作为氟化介质为例对等离子体反应器中发生的化学反应进行详细说明，当氟化介质为其他的氟源气体时，反应机理同理。
 当氟化介质为F 2时，乏燃料粉末中的UO 2 、U 3O 8在等离子体反应器中发生反应的化学反应式如下式（1）、（2）：
           UO 2（s）+3F 2（g）→UF 6（g）+O 2（g）         （1）
           U 3O 8（s）+9F 2（g）→3UF 6（g）+4O 2（g）     （2）
实际上，氟化介质在等离子反应器中以原子状态F与UO 2 、U 3O 8发生反应，反应速率更高，因此上式（1）、（2）分别如下式（1.1）、（2.1）：
          UO 2（s）+6F（p）→UF 6（g）+O 2（g）           （1.1）
          U 3O 8（s）+18F（p）→3UF 6（g）+4O 2（g）      （2.1）
    乏燃料粉末中的PuO 2在等离子体反应器中发生反应的化学反应式如下式（3）至（5）：
           PuO 2（s）+2F 2（g）→PuF 4（s）+O 2（g）       （3）
           PuO 2（s）+3F 2（g）→PuF 6（g）+O 2（g）       （4）
           PuO 4（s）+F 2（g）↔PuF 6（g）                       （5）
其中，根据式（3）产生的PuF 4再与足够的F 2反应，促使式（5）的反应向右端进行，使PuO 4完全转化为PuF 6。
实际上，氟化介质在等离子反应器中以原子状态F与PuO 2发生反应，反应速率更高，因此上式（3）至（5）分别如下式（3.1）至（5.1）：
           PuO 2（s）+4F（p）→PuF 4（s）+O 2（g）       （3.1）
           PuO 2（s）+6F（p）→PuF 6（g）+O 2（g）       （4.1）
           PuO 4（s）+2F（p）↔PuF 6（g）                     （5.1）
乏燃料粉末中的镧系元素在等离子体反应器中发生反应的化学反应式如下：
          2Ln 2O 3（s）+6F 2（g）→4LnF 3（s）+3O 2（g）      （6）
对应原子状态的F，式（6）实际如下式（6.1）：
         2Ln 2O 3（s）+12F（p）→4LnF 3（s）+3O 2（g）     （6.1）
乏燃料粉末中的次锕系元素在等离子体反应器中发生反应的化学反应式如下：
           NpO 2（s）+3F 2（g）→NpF 6+O 2（g）                  （7）
           NpO 2（s）+2F 2（g）→NpF 4（s）+O 2 （g）         （8）
           NpF 4（s）+F 2（g）↔ NpF 6（g）                           （9）
           2Am 2O 3（s）+6F 2（g）→4AmF 3（s）+3O 2（g）           （10）
           2Cm 2O 3（s）+6F 2（g）→4CmF 3（s）+3O 2（g）           （11）
其中，根据式（8）产生的NpF 4再与足够的F 2反应，促使式（9）的反应向右端进行，使NpF 4完全转化为NpF 6。
对应原子状态的F，式（7）至（11）分别实际如下式（7.1）至（11.1）：
           NpO 2（s）+6F（p）→NpF 6+O 2（g）                    （7.1）
           NpO 2（s）+4F（p）→NpF 4（s）+O 2 （g）           （8.1）
           NpF 4（s）+2F（p）↔ NpF 6（g）                           （9.1）
           2Am 2O 3（s）+12F（p）→4AmF 3（s）+3O 2（g）      （10.1）
           2Cm 2O 3（s）+12F（p）→4CmF 3（s）+3O 2（g）       （11.1）
上述式子中，“（s）”和“（g）”分别表示固态和气态，“（p）”表示等离子体态；固态的氟化产物（如LnF 3 、AmF 3 、CmF 3）为不挥发性氟化物，其他气态的氟化产物为挥发性氟化物。
S3、将产物在10 4K/s-10 9K/s的冷却速率下进行急速冷却，形成气固两相流和固态产物。
其中，将步骤S2获得的产物通过急速冷却区域，产物在急速冷却区域内通过与冷气流急速混合或者通过气体动力学喷嘴的冷却方式，使冷却速率为10 4K/s-10 9K/s，同时伴随流速变化，初步实现气相与固相的分离，得到气固两相流和固态产物。
固态产物主要包括次锕系元素的氟化产物如LnF 3 、AmF 3 、CmF 3气等。气固两相流中气相物包括有如上述式（1）至（11）中的气态的氟化产物，如UF 6和PuF 6；还夹杂的固体产物有次锕系元素的氟化产物如LnF 3 、AmF 3 、CmF 3气等。
S4、将气固两相流进行过滤去除其中的固态产物，再经过冷凝、吸附、解吸和精馏，得到含UF 6和PuF 6的混合气体。
该步骤中，先通过过滤将气固两相流中的固态产物（如LnF 3 、AmF 3 、CmF 3等）从气相物中分离出来。过滤采用细孔过滤设备，例如烧结金属过滤器或者与其他过滤器的组合等。
对气相物进行冷凝、吸附、解吸和精馏处理。其中，冷凝的目的在于实现U、Pu、Np的氟化产物与其他氟化产物分离，冷凝温度低于350K。吸附采用氟化物吸附剂，例如NaF或者MgF 2，吸附温度为300K-400K，吸附后在温度升高至600K-700K可以实现解吸。在上述的吸附、解吸中，气相物中所含的NpF 6被吸附除去，从而得到含UF 6和PuF 6的混合气体。
S5、将混合气体进行回收处理，形成对应的氧化物或金属。
作为一种选择，将混合气体回收处理形成氧化物，方法可如下：将UF 6和PuF 6的混合气体通过干法或湿法处理，得到UO 2和PuO 2的混合氧化物、HF。
或者，将混合气体的UF 6和PuF 6分离；将UF 6通过干法或湿法处理，得到UO 2和HF；将PuF 6通过干法或湿法处理，得到PuO 2和HF。UF 6和PuF 6的分离可采用升温方式，PuF 6挥发从UF 6中分离出来。
在上述的选择中，优选采用干法处理：UF 6和PuF 6分别与水蒸气反应分别直接生成UO 2 、HF和PuO 2 、HF。以UF 6为例，反应如下：
         UF 6(g)+H 2(g)+H 2O(g)→UO 2+6HF(g)
作为另一种选择，将混合气体回收处理形成金属，方法可如下：将UF 6和PuF 6的混合气体通过电磁分离处理，得到U和Pu的合金以及F 2。
或者，将混合气体的UF 6和PuF 6分离；将UF 6通过电磁分离处理，得到金属U和F 2；将PuF 6通过电磁分离处理，得到金属Pu和F 2。
电磁分离处理可采用现有技术实现，可参考WO 97/34685等。
经过回收出来得到的氧化物和HF、金属和F 2，分别可送回至相关工段进行再使用。例如，上述经过处理回收的UO 2和PuO 2的混合氧化物，补充铀（通常是贫化铀氧化物）之后，经过核燃料加工工段，形成混合氧化物燃料（MOX燃料）。HF和F 2可作为氟源再返回等离子反应器中使用。
进一步地，本发明的乏燃料干法后处理方法还包括以下步骤：
S6、将步骤S3和步骤S4分离得到的固态产物进行回收处理。
步骤S3和步骤S4分离得到的固体产物主要包括次锕系元素的氟化产物如LnF 3 、AmF 3 、CmF 3等。
回收处理包括对固态产物进行稳定化处理或消耗处理，稳定化处理后形成便于存放或处置的产物；消耗处理即将固态产物应用于快中子反应堆等。
以上所述仅为本发明的实施例，并非因此限制本发明的专利范围，凡是利用本发明说明书及附图内容所作的等效结构或等效流程变换，或直接或间接运用在其他相关的技术领域，均同理包括在本发明的专利保护范围内。

Claims (11)

  1. 一种基于等离子体的乏燃料干法后处理方法，其特征在于，包括以下步骤：
    S1、将脱去包壳后的乏燃料加工成乏燃料粉末，送至等离子体反应器中；
    S2、所述乏燃料粉末在所述等离子体反应器中与含F原子的等离子体充分混合并发生反应，形成包括挥发性氟化物和不挥发性氟化物的产物；
    S3、将所述产物在10 4K/s-10 9K/s的冷却速率下进行急速冷却，形成气固两相流和固态产物；
    S4、将所述气固两相流进行过滤去除其中的固态产物，再经过冷凝、吸附、解吸和精馏，得到含UF 6和PuF 6的混合气体；
    S5、将所述混合气体进行回收处理，形成对应的氧化物或金属。
  2. 根据权利要求1所述的乏燃料干法后处理方法，其特征在于，步骤S1中，所述乏燃料粉末在惰性气体的载气作用下通过喷嘴输送至等离子体反应器中。
  3. 根据权利要求1所述的乏燃料干法后处理方法，其特征在于，步骤S1中，所述乏燃料粉末的粒径≤200μm。
  4. 根据权利要求1所述的乏燃料干法后处理方法，其特征在于，步骤S2中，所述含F原子的等离子体通过氟化介质转化形成；所述氟化介质包括CF 4、NF 3、F 2、HF、BrF 3、BrF 5、ClF 3及SF 6气体中一种或多种。
  5. 根据权利要求1所述的乏燃料干法后处理方法，其特征在于，步骤S2中，所述含F原子的等离子体由所述氟化介质通过气体放电转化形成后再输入所述等离子体反应器中；或者，所述含F原子的等离子体由所述氟化介质在所述等离子体反应器中转化形成。
  6. 根据权利要求5所述的乏燃料干法后处理方法，其特征在于，所述含F原子的等离子体通过高压放电、直流电弧放电、高频放电、微波放电和激光电离中至少一种产生。
  7. 根据权利要求4所述的乏燃料干法后处理方法，其特征在于，步骤S2中，当氟化介质为F 2时，所述乏燃料粉末中的UO 2和U 3O 8在所述等离子体反应器中发生反应的化学反应式如下式（1）、（2）：
                 UO 2+3F 2→UF 6+O 2                   （1）
                 U 3O 8+9F 2→3UF 6+4O 2               （2）
        所述乏燃料粉末中的PuO 2在所述等离子体反应器中发生反应的化学反应式如下式（3）至（5）：
                     PuO 2+2F 2→PuF 4+O 2               （3）
                 PuO 2+3F 2→PuF 6+O 2                 （4）
                 PuO 4+F 2↔PuF 6                    （5）
    其中，根据式（3）产生的PuF 4再与足够的F 2反应，促使式（4）的反应向右端进行，使PuO 4完全转化为PuF 6；
    所述乏燃料粉末中的镧系元素在所述等离子体反应器中发生反应的化学反应式如下：
                 2Ln 2O 3+6F 2→4LnF 3+3O 2            （6）
    所述乏燃料粉末中的次锕系元素在所述等离子体反应器中发生反应的化学反应式如下：
                 NpO 2+3F 2→NpF 6+O 2                  （7）
                 NpO 2+2F 2→NpF 4+O 2                  （8）
                 NpF 4+F 2↔ NpF 6                        （9）
                 2Am 2O 3+6F 2→4AmF 3+3O 2             （10）
                 2Cm 2O 3+6F 2→4CmF 3+3O 2             （11）
    其中，根据式（8）产生的NpF 4再与足够的F 2反应，促使式（9）的反应向右端进行，使NpF 4完全转化为NpF 6。
  8. 根据权利要求1所述的乏燃料干法后处理方法，其特征在于，步骤S2中，所述等离子体反应器中反应区的温度大于2000K；所述等离子体反应器的器壁温度控制在950K以下。
  9. 根据权利要求1所述的乏燃料干法后处理方法，其特征在于，步骤S5包括：将UF 6和PuF 6的混合气体通过干法或湿法处理，得到UO 2和PuO 2的混合氧化物、HF；或者，
    步骤S5包括：将所述混合气体的UF 6和PuF 6分离；将UF 6通过干法或湿法处理，得到UO 2和HF；将PuF 6通过干法或湿法处理，得到PuO 2和HF。
  10. 根据权利要求1所述的乏燃料干法后处理方法，其特征在于，步骤S5包括：将UF 6和PuF 6的混合气体通过电磁分离处理，得到U、Pu以及F 2；或者，
    步骤S5包括：将所述混合气体的UF 6和PuF 6分离；将UF 6通过电磁分离处理，得到金属U和F 2；将PuF 6通过电磁分离处理，得到金属Pu和F 2。
  11. 根据权利要求1-10任一项所述的乏燃料干法后处理方法，其特征在于，所述乏燃料干法后处理方法还包括以下步骤：
    S6、将步骤S3和步骤S4分离得到的固态产物进行回收处理。
PCT/CN2020/120792 2020-10-14 2020-10-14 基于等离子体的乏燃料干法后处理方法 WO2022077250A1 (zh)

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