阅读说明：本技术 一种快堆混合铀钚燃料成分控制的设计方法 (Design method for component control of fast reactor mixed uranium plutonium fuel ) 是由 胡赟 徐李 杨勇 张坚 单浩栋 霍兴凯 曹攀 陈仪煜 于 2020-11-24 设计创作，主要内容包括：本发明涉及一种快堆混合铀钚燃料成分控制的设计方法,所述方法包括以下步骤：步骤(1)、堆芯设计计算,计算求得混合铀钚燃料中的钚当量设计值；确定混合铀钚燃料的钚当量目标值；并根据上述钚当量目标值计算混合铀钚燃料中Pu和U成份(如混合铀钚氧化物燃料MOX中的PuO-2粉末和UO-2粉末)的质量份额；步骤(2)、挑选出钚当量值与步骤(1)中钚当量设计值接近的所需数量的原料；步骤(3)、将挑选出的原料进行钚原料混丰,得到混丰后的Pu原料粉末；步骤(4)、制备混合铀钚燃料芯块/芯体。本发明提供的设计方法能够解决钚同位素成分差别对使用铀钚混合燃料快堆堆芯设计参数特别是组件功率分布影响问题。(The invention relates to a design method for controlling components of fast reactor mixed uranium plutonium fuel, which comprises the following steps: step (1), calculating reactor core design, and calculating to obtain a plutonium equivalent design value in the mixed uranium plutonium fuel; determining a plutonium equivalent target value of the mixed uranium plutonium fuel; and calculating the Pu and U components of the mixed uranium plutonium fuel (e.g. PuO in mixed uranium plutonium oxide fuel MOX) based on the plutonium equivalent target value 2 Powder and UO 2 Powder) mass fraction; step (2) of selecting a required number of raw materials having a plutonium equivalent value close to the designed plutonium equivalent value in step (1); step (3), performing plutonium raw material mixing on the selected raw material to obtain mixed Pu raw material powder; step (4) of preparing a mixed uranium plutonium fuelCore block/core body. The design method provided by the invention can solve the problem that the difference of the plutonium isotope components influences the reactor core design parameters of the fast reactor using the uranium plutonium mixed fuel, particularly the power distribution of the assembly.)

1. A design method for controlling the composition of a fast reactor mixed uranium plutonium fuel is characterized by comprising the following steps:

step (1), core design calculation, which specifically comprises the following steps:

A. determining nominal components of the Pu material used by the reactor core raw material, namely the plutonium isotope type of the Pu material and the mass percentage of each plutonium isotope, using the nominal components as reactor core design input, and calculating the plutonium equivalent weight factor of each plutonium isotope; calculating to obtain a plutonium equivalent design value of the Pu material according to the mass percentage of each plutonium isotope and the plutonium equivalent weight factor thereof;

B. b, based on the core design input determined in the step A, performing core design calculation of the mixed uranium plutonium fuel, and determining a plutonium equivalent target value of the mixed uranium plutonium fuel; calculating the mass shares of Pu materials and U materials in the mixed uranium plutonium fuel according to the plutonium equivalent target value;

step (2) of calculating the plutonium equivalent value of the Pu raw material in each minimum plutonium raw material container in the plutonium raw material stock according to the isotope type and mass percentage of the Pu raw material in each minimum plutonium raw material container in the plutonium raw material stock, and selecting a required number of raw materials having plutonium equivalent values close to the plutonium equivalent design value set in step (1);

step (3), performing plutonium raw material mixing on the selected raw material to obtain a mixed Pu material;

and (4) calculating the mass fractions of Pu and U in the mixed uranium plutonium fuel according to the target plutonium equivalent value of the mixed uranium plutonium fuel determined in the step (1) B and the plutonium raw material component obtained after mixing in the step (3), and mixing the Pu and U obtained in the step (3) according to the mass fractions to prepare a mixed uranium plutonium fuel pellet/core.

2. A design method for controlling the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 1, characterized in that: the Pu material is PuO₂Powder; the U material is UO₂And (3) powder.

3. A method of designing a control of the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 1 or claim 2, characterised in that: the calculation method of the plutonium equivalent weight factor is shown in formula (1):

wherein W_iPlutonium equivalent weight factors representing different nuclides;representing the effective fission cross-section of the g-th group of the i-th nuclide; phi is a_gA neutron spectrum representing the corresponding region; g represents the number of clusters used in the core physics calculations.

4. A method of designing a control of the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 1 or claim 2, characterised in that: the calculation method of the plutonium equivalent weight factor is shown in formula (2):

wherein the content of the first and second substances,representing the product of the number of fission neutrons and the fission cross section of the ith nuclide in the g group; phi is a_gA neutron spectrum representing the corresponding region; g represents the number of clusters used in the core physics calculations.

5. A method of designing a control of the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 1 or claim 2, characterised in that: the calculation method of the plutonium equivalent weight factor is shown in formula (3):

wherein the content of the first and second substances,representing the product of the number of fission neutrons and the fission cross section of the ith nuclide in the g group;showing the effective absorption cross section of the g group of the i nuclide; phi is a_gA neutron spectrum representing the corresponding region; g represents the number of clusters used in the core physics calculations.

6. A design method for controlling the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 2, characterized in that: the calculation method of the plutonium equivalent weight factor is shown in formula (4):

where k represents the effective core growth factor and Ni represents the mass of the i-th nuclide.

7. A design method for controlling the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 2, characterized in that: in step (1), the mass fractions of Pu and U in the mixed uranium plutonium oxide fuel are calculated based on the following formula (5):

formula (5);

wherein E_MOXA plutonium equivalent target value for the mixed uranium plutonium oxide fuel;

f_i ^Uand f_i ^PuNormalized isotope mass compositions of uranium and industrial plutonium, respectively;

W_i ^Puand W_i ^UPlutonium equivalent weight factors of each plutonium isotope and uranium isotope respectively;

M_Pu、M_U、respectively corresponding to U, Pu atom or UO₂、PuO₂Molecular mass;

for PuO in mixed uranium plutonium oxide fuels₂Mass content of (a).

8. A design method for controlling the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 2, characterized in that: the specific method for mixing plutonium raw materials in the step (3) is as follows:

assuming that N tanks of PuO are required for the preparation of mixed uranium plutonium oxide fuels₂Powder raw materials, according to the actual conditions of the production line, each batch of the PuO with at most K tanks₂The concrete operation steps of mixing and enriching the powder by taking the raw materials of a K tank (K is less than or equal to K/2) as a group are as follows:

A. taking an absolute value of the difference between the plutonium equivalent value of all stock raw materials and the plutonium equivalent design value in the step (1), and intercepting the N tank raw material with the minimum absolute value as a primary screening result;

B. sorting the raw materials subjected to primary screening from high to low according to plutonium equivalent, equally dividing the raw materials into N-N/k groups according to k raw materials, and rounding N: the plutonium equivalent of the n-th group of raw materials is the largest, the plutonium equivalent of the n-1-th group of raw materials is the second, … … and the plutonium equivalent of the 1-th group of raw materials is the smallest;

C. mixing the n group of raw materials with plutonium equivalents in descending order with the 1 st group of raw materials in ascending order, mixing the n-1 group of raw materials with plutonium equivalents in descending order with the 2 nd group of raw materials in ascending order, and so on to form m groups of raw materials, wherein if n is an even number, m is n/2; if n is an odd number, m ═ n + 1)/2;

D. if the m groups of raw materials meet the target requirement of mixing, ending the mixing operation; if the number of the raw materials is not equal to the number of the raw materials, dividing the m group of raw materials into 2 parts, if n is an odd number, obtaining n groups of raw materials after 1 mixing without dividing, recalculating the plutonium equivalent of the n groups of raw materials, and sequencing from high to low; then repeating the process of the step C until the rich requirement is met;

after the mixing of the parameters according to the plutonium equivalent for many times, the PuO with uniform plutonium equivalent can be obtained₂And (3) powder.

9. A design method for controlling the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 1, characterized in that: the method further comprises the steps of: and (3) preparing the mixed uranium plutonium fuel pellets prepared in the step (5) into mixed uranium plutonium fuel elements and components, and feeding the mixed uranium plutonium fuel elements and components to a reactor.

10. A design method for controlling the composition of a fast reactor mixed uranium plutonium fuel as claimed in claim 1, characterized in that: in the step (1), the target plutonium equivalent value of the mixed uranium plutonium fuel is a plutonium equivalent value of the mixed uranium plutonium fuel for balancing the reactor core when the reactor core reaches an equilibrium state.

Technical Field

The invention belongs to the technical field of nuclear power design, and particularly relates to a design method for component control of a fast reactor mixed uranium plutonium fuel.

Background

Fast neutron reactors (fast reactors for short) are nuclear reactors in which fast neutrons initiate a chain fission reaction. The fast reactor has the obvious characteristics of being capable of proliferating nuclear fuel and transmuting long-life nuclear waste, and is a main reactor type of a fourth generation nuclear energy system. In order to effectively utilize natural uranium resources and improve fuel multiplication capacity, the most typical fast reactor fuel is mixed uranium and plutonium fuel. The mixed uranium plutonium fuel may be in the form of a mixed uranium plutonium oxide fuel (MOX, such as the driver fuels for french phoenix, ultra-phoenix fast, and russian BN-800 fast, etc.), a mixed uranium plutonium zirconium ternary alloy fuel, a mixed uranium plutonium nitride fuel, or other fuel types. MOX fuel is the most mature fuel at present, and has the most abundant irradiation tests and application experiences on the reactor; a great deal of off-pile and on-pile researches on U-Pu-Zr ternary alloy fuel on the American EBR-II pile are carried out, and the U-Pu-Zr ternary alloy fuel is close to a mature fuel model selection; uranium plutonium nitride fuels are still under development.

Regardless of the fuel type used, mixed uranium plutonium fuels use plutonium as the major fissile material and uranium as the fertile material. The plutonium mainly uses industrial plutonium recovered by reprocessing of pressurized water reactor or fast reactor spent fuel as driving fuel, and the uranium can be depleted uranium or uranium in nature recovered from spent fuel. The ratio of plutonium to uranium in the fuel is an important parameter in the design of mixed uranium plutonium fuels, and needs to be designed and determined according to the requirements of the residual reactivity of the core design and power distribution. Meanwhile, the fast reactor industry first recovers plutonium by post-processing from spent fuel of a pressurized water reactor, the composition of the plutonium isotope depends on the enrichment degree, specific burnup and cooling time of the pressurized water reactor fuel, and the isotope composition of the plutonium isotope greatly differs with fuels with different enrichment degrees, different burnup levels and different cooling times.

Due to the obvious difference of nuclear characteristics and the obvious difference of the isotopic composition of plutonium, industrial plutonium loaded from different sources often has great influence on the neutron physical characteristics of the reactor core. If industrial plutonium with different components is directly loaded without changing the ratio of the plutonium to uranium, the physical characteristic parameters of neutrons in the reactor core are influenced to a certain extent, such as power distribution, residual reactivity, control rod value, burnup reactivity loss, relevant reactivity effect and the like.

Some of the core parameters may be adjusted by core loading or operating cycles, etc. For example, the plutonium component affects the residual reactivity of the core and can be adjusted by adjusting the number of fuel assembly charges. The major factor that is highly influenced and cannot be adjusted by conventional means is the core power distribution. Direct use of plutonium from different sources can result in significant changes in component power, affecting the outlet coolant temperature profile, and possibly even exceeding fuel cell line power limits, affecting reactor safety.

Therefore, research needs to be carried out to provide a design method for controlling the components of the fast reactor mixed uranium-plutonium fuel, so as to solve the problem that the difference of the components of plutonium isotopes affects the design parameters of a reactor core, particularly the power distribution of assemblies.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a design method for controlling the components of a fast reactor mixed uranium plutonium fuel, which puts forward plutonium equivalent control target requirements on different process stages of fast reactor mixed fuel preparation through a plutonium equivalent design method so as to effectively reduce the influence of loading uranium plutonium mixed fuels prepared from different industrial plutonium sources on reactor core design parameters.

In order to achieve the above purposes, the invention adopts the technical scheme that:

a design method for controlling the composition of a fast reactor mixed uranium plutonium fuel, the method comprising the steps of:

step (1), core design calculation, which specifically comprises the following steps:

A. determining nominal components of the Pu material used by the reactor core raw material, namely the plutonium isotope type of the Pu material and the mass percentage of each plutonium isotope, using the nominal components as reactor core design input, and calculating the plutonium equivalent weight factor of each plutonium isotope; calculating to obtain a plutonium equivalent design value of the Pu material according to the mass percentage of each plutonium isotope and the plutonium equivalent weight factor thereof;

B. b, based on the core design input determined in the step A, performing core design calculation of the mixed uranium plutonium fuel, and determining a plutonium equivalent target value of the mixed uranium plutonium fuel; calculating the mass shares of Pu materials and U materials in the mixed uranium plutonium fuel according to the plutonium equivalent target value;

step (2) of calculating the plutonium equivalent value of the Pu raw material in each minimum plutonium raw material container in the plutonium raw material stock according to the isotope type and mass percentage of the Pu raw material in each minimum plutonium raw material container in the plutonium raw material stock, and selecting a required number of raw materials having plutonium equivalent values close to the plutonium equivalent design value set in step (1);

step (3), performing plutonium raw material mixing on the selected raw material to obtain a mixed Pu material;

and (4) calculating the mass fractions of Pu and U in the mixed uranium plutonium fuel according to the target plutonium equivalent value of the mixed uranium plutonium fuel determined in the step (1) B and the plutonium raw material component obtained after mixing in the step (3), and mixing the Pu and U obtained in the step (3) according to the mass fractions to prepare a mixed uranium plutonium fuel pellet/core.

Further, the Pu material is PuO₂Powder; the U material is UO₂And (3) powder.

Further, the calculation method of the plutonium equivalent weight factor is as shown in formula (1):

wherein W_iPlutonium equivalent weight factors representing different nuclides;representing the effective fission cross-section of the g-th group of the i-th nuclide; phi is a_gA neutron spectrum representing the corresponding region; g represents the number of clusters used in the core physics calculations.

Further, the calculation method of the plutonium equivalent weight factor is as shown in formula (2):

wherein the content of the first and second substances,representing the product of the number of fission neutrons and the fission cross section of the ith nuclide in the g group; phi is a_gA neutron spectrum representing the corresponding region; g represents the number of clusters used in the core physics calculations.

Further, the calculation method of the plutonium equivalent weight factor is as shown in formula (3):

wherein the content of the first and second substances,representing the product of the number of fission neutrons and the fission cross section of the ith nuclide in the g group;showing the effective absorption cross section of the g group of the i nuclide; phi is a_gA neutron spectrum representing the corresponding region; g represents the number of clusters used in the core physics calculations.

Further, the calculation method of the plutonium equivalent weight factor is as shown in equation (4):

where k represents the effective core growth factor and Ni represents the mass of the i-th nuclide.

Further, in step (1), the mass fractions of Pu feedstock and U feedstock in the mixed uranium plutonium oxide fuel are calculated based on the following formula (5):

formula (5);

wherein E_MOXA plutonium equivalent target value for the mixed uranium plutonium oxide fuel;

f_i ^Uand f_i ^PuNormalized isotope mass compositions of uranium and industrial plutonium, respectively;

W_i ^Puand W_i ^UPlutonium equivalent weight factors of each plutonium isotope and uranium isotope respectively;

M_Pu、M_U、respectively corresponding to U, Pu atom or UO₂、PuO₂Molecular mass;

for PuO in mixed uranium plutonium oxide fuels₂Mass content of (a).

Further, the specific method for mixing plutonium raw materials in the step (3) is as follows:

assuming that N tanks of PuO are required for the preparation of mixed uranium plutonium oxide fuels₂Powder raw materials, according to the actual conditions of the production line, each batch of the PuO with at most K tanks₂Mixing powders with K tank (K is not more than K/2) as a groupThe specific operation steps are as follows:

A. taking an absolute value of the difference between the plutonium equivalent value of all stock raw materials and the plutonium equivalent design value in the step (1), and intercepting the N tank raw material with the minimum absolute value as a primary screening result;

B. sorting the raw materials subjected to primary screening from high to low according to plutonium equivalent, equally dividing the raw materials into N-N/k groups according to k raw materials, and rounding N: the plutonium equivalent of the n-th group of raw materials is the largest, the plutonium equivalent of the n-1-th group of raw materials is the second, … … and the plutonium equivalent of the 1-th group of raw materials is the smallest;

C. mixing the n group of raw materials with plutonium equivalents in descending order with the 1 st group of raw materials in ascending order, mixing the n-1 group of raw materials with plutonium equivalents in descending order with the 2 nd group of raw materials in ascending order, and so on to form m groups of raw materials, wherein if n is an even number, m is n/2; if n is an odd number, m ═ n + 1)/2;

D. if the m groups of raw materials meet the target requirement of mixing, ending the mixing operation; if the number of the raw materials is not equal to the number of the raw materials, dividing the m group of raw materials into 2 parts, if n is an odd number, obtaining n groups of raw materials after 1 mixing without dividing, recalculating the plutonium equivalent of the n groups of raw materials, and sequencing from high to low; then repeating the process of the step C until the rich requirement is met;

after the mixing of the parameters according to the plutonium equivalent for many times, the PuO with uniform plutonium equivalent can be obtained₂And (3) powder.

Further, the method further comprises the steps of: and (3) preparing the mixed uranium plutonium fuel pellets prepared in the step (5) into mixed uranium plutonium fuel elements and components, and feeding the mixed uranium plutonium fuel elements and components to a reactor.

Further, in the step (1), the target plutonium equivalent value of the mixed uranium plutonium fuel is a plutonium equivalent value of the mixed uranium plutonium fuel for balancing the core when the core reaches an equilibrium state.

The design method for controlling the components of the fast reactor mixed uranium plutonium fuel has the following advantages:

1. the actual industrial production of the mixed uranium plutonium fuel such as MOX fuel is a complex process, the design method provided by the invention can be used for performing plutonium equivalent control in two links in the production process of the mixed uranium plutonium fuel such as MOX fuel, and effectively controlling the influence of plutonium component change on the power distribution of a reactor core so as to minimize the influence on the performance of the reactor core.

2. The design method provided by the invention can solve the problem of influence of neutron physical design parameters, particularly component power distribution change, of the reactor core caused by the composition difference of industrial plutonium isotopes in the design of fast reactor cores (including critical and subcritical reactor cores) of mixed uranium plutonium fuels. By the plutonium equivalent design method, plutonium equivalent control target requirements are put forward to different process stages of fast reactor mixed fuel preparation, so that the influence of loading of uranium plutonium mixed fuel prepared from industrial plutonium of different sources on reactor core design parameters can be effectively reduced.

Drawings

Fig. 1 is a schematic flow chart of a design method for controlling the composition of a fast reactor mixed uranium plutonium fuel provided in embodiment 1 of the present invention;

FIG. 2 shows PuO of a design method for controlling components of fast reactor mixed uranium plutonium fuel provided in embodiment 1 of the present invention₂Schematic diagram of powder mixing method.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

The invention provides a design method for controlling components of fast reactor mixed uranium plutonium fuel, wherein the mixed uranium plutonium fuel comprises a plurality of mixed uranium plutonium oxide fuels (PuO)₂And UO₂Blends) and also PuN and UN, PuC and UC, U-Pu-Zr, etc., the method of the invention is applicable to any uranium plutonium blended fuel.

Example 1

In this example, the method of the present invention is specifically described by taking a mixed uranium plutonium oxide fuel (MOX) as an example, and as shown in fig. 1 and 2, the method includes the following steps:

the method comprises the following steps of (I) calculating the design of a reactor core:

A. determination of core feedstock utilization of PuO₂Nominal composition of the powder, i.e. PuO₂The kinds of industrial plutonium isotopes of the powders and the mass percentages of the respective industrial plutonium isotopes are used as a stackInputting core design, and calculating plutonium equivalent weight factors of all industrial plutonium isotopes; calculating and obtaining the PuO according to the mass percentage of each industrial plutonium isotope and the plutonium equivalent weight factor thereof₂Plutonium equivalent design value of the powder;

in a mixed uranium plutonium fuel fast reactor,²³⁹pu is the major fission nuclide and can be used²³⁹Pu is used as a target Pu equivalent weight kernel, and equivalent processing is carried out. Isotopic plutonium equivalent weight factors can be defined in a number of ways: for example, the following 3 types of reaction cross sections are adopted, specifically see formulas (1) to (3); alternatively, reactive value equivalence, i.e., based on k, can also be employed_effThe sensitivity coefficient of (a) is weighted, see equation (4):

wherein W_iPlutonium equivalent weight factors representing different nuclides;representing the effective fission cross-section of the g-th group of the i-th nuclide; phi is a_gA neutron spectrum representing the corresponding region; g represents the number of clusters used in the core physics calculations. The calculation method corresponds to fission reaction rate equivalence, has the effect of ensuring fuel fission heating equivalence, and aims to ensure that various isotope components of actinide in uranium-plutonium mixed fuel are subjected to neutron spectrum conditions so as to obtain the fuel fission heating equivalence²³⁹Pu nuclides are used as a reference and are converted according to an equivalent principle.

Wherein the content of the first and second substances,representing the product of the number of fission neutrons and the fission cross section of the ith nuclide in the g group; phi is a_gA neutron spectrum representing the corresponding region; g represents the energy group used for the physical calculation of the coreAnd (4) counting.

Wherein the content of the first and second substances,representing the product of the number of fission neutrons and the fission cross section of the ith nuclide in the g group;showing the effective absorption cross section of the g group of the i nuclide; phi is a_gA neutron spectrum representing the corresponding region; g represents the number of clusters used in the core physics calculations.

Where k represents the effective core growth factor and Ni represents the mass of the i-th nuclide.

The calculation result shows that the plutonium equivalent weight factor calculated by the formula (1) can effectively control the power distribution deviation caused by different plutonium components (the maximum relative deviation is less than 3%, and the requirement of component power change is met), and meanwhile, the deviation of parameters such as residual reactivity, fuel consumption reactivity loss and the like is small. Therefore, it is reasonable to select formula (1) to calculate the plutonium equivalent weight factor.

B. B, based on the core design input determined in the step A, performing core design calculation on the mixed uranium plutonium oxide fuel to determine a plutonium equivalent target value of the mixed uranium plutonium oxide fuel; and calculating the PuO in the mixed uranium plutonium oxide fuel based on the following formula (5) based on the above plutonium equivalent target value₂Powder and UO₂The mass fraction of the powder; and the plutonium equivalent target value of the mixed uranium plutonium oxide fuel is the plutonium equivalent value of the mixed uranium plutonium oxide fuel for balancing the reactor core when the reactor core reaches a balanced state.

Formula (5);

wherein E_MOXA plutonium equivalent target value for the mixed uranium plutonium oxide fuel;

f_i ^Uand f_i ^PuNormalized isotope mass compositions of uranium and industrial plutonium, respectively;

W_i ^Puand W_i ^UPlutonium equivalent weight factors of each plutonium isotope and uranium isotope respectively;

M_Pu、M_U、respectively corresponding to U, Pu atom or UO₂、PuO₂Molecular mass;

for PuO in mixed uranium plutonium oxide fuels₂Mass content of (a).

(II) screening and mixing raw materials: according to the PuO of each tank in the industrial raw material warehouse₂Calculating the isotope type and mass percentage of the powder raw material, and calculating the PuO of each tank₂And (3) selecting a required number of raw materials having a plutonium equivalent value close to the designed plutonium equivalent value in the step (i).

Mixing the selected raw material with plutonium to obtain the mixed PuO₂Powder; the specific method for mixing plutonium raw materials comprises the following steps:

assuming that N tanks of PuO are required for the preparation of mixed uranium plutonium oxide fuels₂Powder raw materials, according to the actual conditions of the production line, each batch of the PuO with at most K tanks₂The concrete operation steps of mixing and enriching the powder by taking the raw materials of a K tank (K is less than or equal to K/2) as a group are as follows:

A. taking an absolute value of the difference between the plutonium equivalent value of all stock raw materials and the plutonium equivalent design value in the step (1), and intercepting the N tank raw material with the minimum absolute value as a primary screening result;

B. sorting the raw materials subjected to primary screening from high to low according to plutonium equivalent, equally dividing the raw materials into N-N/k groups according to k raw materials, and rounding N: the plutonium equivalent of the n-th group of raw materials is the largest, the plutonium equivalent of the n-1-th group of raw materials is the second, … … and the plutonium equivalent of the 1-th group of raw materials is the smallest;

C. mixing the n group of raw materials with plutonium equivalents in descending order with the 1 st group of raw materials in ascending order, mixing the n-1 group of raw materials with plutonium equivalents in descending order with the 2 nd group of raw materials in ascending order, and so on to form m groups of raw materials, wherein if n is an even number, m is n/2; if n is an odd number, m ═ n + 1)/2;

D. if the m groups of raw materials meet the target requirement of mixing, ending the mixing operation; if the number of the raw materials is not equal to the number of the raw materials, dividing the m group of raw materials into 2 parts, if n is an odd number, obtaining n groups of raw materials after 1 mixing without dividing, recalculating the plutonium equivalent of the n groups of raw materials, and sequencing from high to low; then repeating the process of the step C until the rich requirement is met;

after the mixing of the parameters according to the plutonium equivalent for many times, the PuO with uniform plutonium equivalent can be obtained₂And (3) powder.

(III) according to the PuO calculated in the step (I)₂Powder and UO₂The mass fraction of the powder is that of the PuO obtained in the step (II)₂Powder with UO₂Powder mixing, namely preparing a mixed uranium plutonium oxide fuel pellet; the mixed uranium plutonium oxide fuel pellets are further processed into mixed uranium plutonium oxide fuel elements and assemblies and fed to a reactor.

Example 2

Calculation of first furnace core fuel design of certain MOX fuel fast reactor

Taking a certain 60 ten thousand kilowatt sodium-cooled MOX fuel fast reactor as an example, the reactor core of the reactor is designed to have a rated thermal power of 1500 MW. The reactor uses MOX fuel, wherein the industrial plutonium comes from the post-treatment reclaimed material of the pressurized water reactor spent fuel, and the uranium is depleted in uranium. Liquid metal sodium is used as the coolant. The reactor core in a balanced state is loaded 348 boxes of MOX fuel assemblies, and the MOX fuel assemblies are divided into an inner region, a middle region and an outer region according to different enrichment degrees. Since industrial plutonium in MOX fuels is intended to be industrial plutonium in pressurized water reactor spent fuel recovered from a reprocessing plant, a balanced core design is developed based on the nominal plutonium component given by the reprocessing plant, and the plutonium-uranium component ratio in MOX fuels in each zone, i.e., the nominal MOX fuel component of the balanced core, is determined.

The plutonium equivalent weight factor is calculated by using the formula (1), and the weight factors of different nuclides in different fuel regions, which are defined based on different plutonium equivalents, are obtained under the neutron spectrum of the balanced reactor core, and are shown in table 1. The main actinide relative ratio in the MOX new fuel is obtained²³⁹And the weighting factor of the Pu nuclide is used for equivalent calculation of the plutonium equivalent in different subsequent links.

TABLE 1 plutonium equivalent weight factor for different nuclei

The source of industrial plutonium in MOX fuel of the first reactor core of the reactor core is different from that of the balanced reactor core, and the nominal composition of the industrial plutonium used for designing the first reactor fuel and the balanced reactor core is compared in a table 2.

Table 2: isotopic composition of industrial plutonium

According to the MOX fuel components of the balanced reactor core, calculating to obtain that the plutonium equivalent values in the MOX fuel in the inner region, the middle region and the outer region are respectively 19.7%, 22.2% and 25.3%, namely the target plutonium equivalent values designed for the first furnace reactor core fuel. PuO in MOX fuel of first furnace reactor core calculated according to formula (2) based on industrial plutonium nominal component and plutonium equivalent target value₂The mass contents of (A) are shown in Table 3, wherein the equilibrium core MOX fuel PuO is also given₂Comparison of mass content of (a). It can be seen that the PuO in MOX fuel is different in the case of different plutonium isotopes₂Should be different, the greater the change in the plutonium composition, the greater the PuO₂The greater the change in mass fraction.

TABLE 3 PuO in MOX Fuel₂In mass fraction of

Thus, MOX fuel components in different core states are obtained by a plutonium equivalent design method, and even if industrial plutonium from different sources is used, it is ensured that the module power does not deviate significantly from the equilibrium core reference state.

Example 3

The case was chosen for a certain million kilowatt sodium cooled MOX fuel core. In order to flatten the core power distribution, the fuel assemblies are divided into an inner region, a middle region and an outer region according to different enrichment degrees, and the number of the fuel assemblies loaded in the three regions is 211, 156 and 174 respectively. The reactor core control rod system consists of 30 control rods, including 2 regulating rods, 3 passive safety rods, 9 safety rods and 16 compensating rods. When designing the reactor core, the PuO is considered₂The plutonium isotope composition of the powder is of a determined value (i.e. nominal value), and the enrichment of the fuel in the inner, middle and outer zones is adjusted by varying the PuO₂Powder and lean UO₂The proportion of the powder. The design values of the industrial plutonium isotope composition of the first reactor core fuel are shown in table 4, and the fuel component is the target component of the mixing.

TABLE 4 Industrial plutonium isotope composition used for first furnace core design

And under the neutron energy spectrum corresponding to the case reactor core, calculating the weight factor according to the formula (1). The plutonium equivalent weight factor obtained by calculation is shown in table 5. Converting 5 plutonium isotopes according to a plutonium equivalent weight coefficient during mixing, and enabling all the isotopes to be equivalent to²³⁹Pu. The mixing problem is simplified by the processing mode. The plutonium equivalent target calculated from the components in table 4 and the weighting factors in table 5 was 0.8234.

TABLE 5 plutonium equivalent weight factor for reference cores

Due to the lack of data from the actual reprocessing plant, it is assumed that the industrial plutonium used by MOX fuel comes from the reprocessing of spent fuel recovered plutonium from a bay nuclear power plant, and also that the fuel enrichment and specific fuel consumption of the bay nuclear power plant are shown in table 6, with cooling times of 1-9 years. Calculated by different spent fuel plutonium²³⁹Pu and²⁴¹the Pu content varies. These PuOs were combined₂The powder feedstock composition data were summarized as a pooled plutonium feedstock pool.

TABLE 6 enrichment and specific burnup of typical fuel assemblies for pressurized water reactor

When the composition of each of the plutonium isotopes in the plutonium feedstock is equivalent to the above-mentioned plutonium equivalent by the weighting factors shown in table 5, the equivalent plutonium equivalent calculation results of the plutonium feedstock are obtained, and a comparison of the plutonium equivalent values corresponding to the nominal plutonium components used for core design shows that the plutonium in the feedstock is significantly different in composition from itself and also significantly different from the plutonium used for core design, and therefore it is necessary to perform a blending operation in accordance with the designed target plutonium equivalent.

Mixing and enriching according to the method. In the scheme, the MOX fuel of the first reactor core needs 3 tons of PuO₂Powder, PuO after recovery if assumed after work-up₂The storage specification of (2) is 1500 kg/can. Selecting a raw material which is as close as possible to the target plutonium equivalent and is worth 1500 cans of plutonium. Puo after supposition of richness₂And a powder having an equivalent plutonium equivalent within 1% of the equivalent plutonium equivalent of the design value. The results are shown in Table 7.

As can be seen from the results, after the mixing based on the plutonium equivalent, the absolute standard deviation of the plutonium equivalent of the raw plutonium can be reduced by 2 to 3 orders of magnitude, that is, the uniformity of the raw plutonium can be significantly improved, and the deviation from the target plutonium equivalent can be reduced.

TABLE 7 analysis of the results of the mix

The above-described embodiments are merely illustrative of the present invention, which may be embodied in other specific forms or in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. The scope of the invention should be indicated by the appended claims, and any changes that are equivalent to the intent and scope of the claims should be construed to be included therein.