A method for making a delayed light photon ACE format database

Abstract

The application discloses a kind of production methods of delayed photon ACE format database, first, the fission yield sublibrary and decay sublibrary of evaluation nuclear database are used to calculate the delayed photon production cross section;The delayed photon energy distribution can be obtained by processing the decay photon spectrum into the form of equal-probability energy band;To ensure that the average energy of the delayed photon obtained by calculation is the same as the average energy of the delayed photon given in the evaluation nuclear database, the delayed photon production cross section is corrected;Finally, the delayed photon production cross section, the delayed photon energy angle distribution information is stored in the ACE format database.The application proposes a kind of production method of delayed photon ACE format database, and the method has the advantages of high calculation accuracy and fast calculation speed in Monte Carlo program.

Description

Technical Field

[0001] This invention relates to the field of photon nucleus data processing and computing technology, specifically to a method for creating a slow-release photon ACE (ACompact ENDF) format database. Background Technology

[0002] Monte Carlo programs require data on photons produced after neutron nuclear reactions when performing neutron-photon coupled transport calculations. Besides transient photons released through radiative trapping, inelastic scattering, and fission reactions, photons are also released during the decay of excited-state fission products; these are called slow-emission photons. Slow-emission photons have a significant impact on nuclear reactor power distribution and photon irradiation damage.

[0003] Currently, Monte Carlo programs handle slowed-light luminescence in several ways. OpenMC assumes that the energy spectra of transient and slowed-light luminescence produced by fission in equilibrium are similar. It amplifies the transient luminescence yield of each fission cycle according to the slowed-light luminescence energy ratio to account for the effect of slowed-light luminescence. However, there is a significant difference between the fission slowed-light luminescence and transient luminescence spectra, so directly correcting the transient luminescence yield introduces some error. MCNP uses its built-in decay database to consider the effect of slowed-light luminescence. This database stores the decay relationships between radionuclides and uses 25 energy bars to describe the slowed-light luminescence spectrum. However, this method suffers from low computational accuracy and slow speed.

[0004] To address the aforementioned issues, this invention proposes a method for creating a slow-light ACE format database, which offers advantages such as high computational speed and high computational accuracy. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to propose a method for creating a slow-emitting electron ACE format database. The method of the present invention has the advantages of fast calculation speed and high calculation accuracy when considering slow-emitting electrons in Monte Carlo programs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for creating a slow-photon ACE format database includes the following steps:

[0008] Step 1: Calculate the slowed photon generation cross section based on the fission yield sub-library and decay sub-library of the evaluation kernel database;

[0009] During the long-term steady-state operation of a nuclear reactor, the production and decay rates of fission products and their decay products are approximately equal, i.e., decay equilibrium. Therefore, the production of slow-emitting electrons is independent of time. The yield of slow-emitting electrons at any given time is the total number of slow-emitting electrons released by fission products and their decay products when they return to the ground state. That is, fission products immediately complete the decay process after the fission reaction occurs. Based on the above decay equilibrium concept, the slow-emitting electron production cross-section is calculated using the following formula:

[0010] σ delay,i (E)=σ f,i (E)Y i (E) Formula (1)

[0011] In the formula:

[0012] σ delay,i (E)——Slow photon production cross section of fission nuclide i, unit: number·barn;

[0013] σ f,i (E)——Fission cross section of fission nuclide i, unit: barn;

[0014] Y i (E)—— Slow-light photon yield of fission nuclide i, in units of: particles;

[0015] E – Incident neutron energy, unit: MeV;

[0016] The fission cross section was obtained from the evaluation nuclear database after resonance reconstruction and linearization. The slow-emitting electron yield of fission nuclide i was calculated using the following formula:

[0017]

[0018] In the formula:

[0019] y i→p (E)——Independent fission yield of fission product p produced by fission nuclide i, in units of: p;

[0020] —The decay branching ratio of nuclide p to daughter nucleus p1;

[0021] D p — Decay photon yield of nuclide p, in units of photons;

[0022] — Decay photon yield of nuclide p1, in units of photons;

[0023] p—Identifier for fission products;

[0024] p1—Identifier of decay products of fission products;

[0025] Among them, the decay photon yield D of nuclide x x The following formulas are used for calculation: Formula (3) is used when the photon energy spectrum is a discrete energy spectrum, and Formula (4) is used when the photon energy spectrum is a continuous energy spectrum.

[0026]

[0027] In the formula:

[0028] D x — Decay photon yield of nuclide x, in units of photons;

[0029] k — the decay reaction channel number that releases photons;

[0030] NSP – The number of reaction channels that produce decaying photons;

[0031] A k —The normalized coefficient of decay reaction channel k that releases photons;

[0032] m—Discrete photon energy point identifier;

[0033] NER—Number of discrete photon energy points;

[0034] γ k,m (E γ — The decay photon yield at the m-th discrete energy point in the k-th decay reaction channel, in units of photons;

[0035] γ k (E γ — The energy spectrum of continuous decay photons in the k-th decay reaction channel, in units of photons / MeV;

[0036] E γ — Decay photon energy, unit: MeV;

[0037] Step 2: Calculate the slow-release photon energy distribution according to the form of an equal-probability energy pool;

[0038] An equal-probability energy grid divides the energy range of a slow-emitting particle into N energy intervals, with each interval having an equal probability of falling within it. These N intervals constitute the N energy grids. When storing slow-emitting particle energy distribution data using the equal-probability energy grid format, N+1 boundary point energies are required. The boundary point energies are calculated using the following formula:

[0039]

[0040] In the formula:

[0041] E bound,i —Energy at the i-th energy point, unit: MeV;

[0042] P(E) — Decay photon energy spectrum, unit: photons / MeV;

[0043] i — Energy point identifier;

[0044] N – Number of energy units;

[0045] Although the decay photon energy in the decay sub-database of the JEF-2.2 evaluation nuclear database can reach up to 12.7 MeV, the energy of slowed photons is actually mostly concentrated in the range of [4.7 MeV-6 MeV]. If the energy of the last energy point is set to 12.7 MeV, the energy of slowed photons will be overestimated. Therefore, the energy of the last energy point is set to 6 MeV, that is, slowed photons above 6 MeV are ignored.

[0046] Step 3: Correct the slow-light emission cross section using the average energy of slow-light emission given in the evaluation kernel database;

[0047] The evaluation nuclear database provides the average energy of slowed photons released after fission of fissile nuclides. The total slowed photon production cross-section of fissile nuclides is corrected to ensure that the average slowed photon energy calculated using fission yield and decay data is consistent with the average slowed photon energy provided in the evaluation nuclear database. The corrected slowed photon production cross-section is calculated using the following formula:

[0048]

[0049] In the formula:

[0050] —Modified slow-photon generation cross section, unit: barn;

[0051] Q delay —Evaluate the average energy of slowed photons released after fission of fission nuclides given in the nuclear database, in MeV;

[0052] Q delay,cal —The average energy of slowed photons, calculated using fission yield and decay data, in MeV;

[0053] Step 4: Create an ACE database containing slow-emitting photons by adding a photon-generating reaction channel to the ACE database;

[0054] The slow-photon generation cross section and the instantaneous-photon generation cross section are added together and stored in the GPD (Photonproduction data) array of the ACE database; the slow-photon energy distribution is stored in the DLWP (Photonproduction energy distributions) array of the ACE database; since all decaying photons are isotropic, the slow-photon angular distribution is stored in the ANDP (Photonproduction angular distributions) array of the ACE database according to the isotropic distribution; finally, the processed data is output in ACE format to obtain the slow-photon ACE format database.

[0055] Compared with the prior art, the present invention has the following advantages:

[0056] (1) Existing technologies either directly amplify the transient luminescence yield or use the yield of 25 groups of slow luminescence to consider the influence of slow luminescence, which cannot accurately describe the energy spectrum of slow luminescence and has the problem of low calculation accuracy. This invention uses the form of equiprobable energy groups to describe the energy spectrum of slow luminescence. Since there are many equiprobable energy groups, the energy spectrum of slow luminescence can be accurately described, and therefore the calculation accuracy is higher than that of traditional methods.

[0057] (2) Compared with using a decay particle database, the database made using this invention does not require traversing the decay chain of each fission product during Monte Carlo calculations, which can save calculation time and improve calculation efficiency. Attached Figure Description

[0058] Figure 1 This is a flowchart of the method of the present invention.

[0059] Figure 2 It is a spherical shell filling 233 Comparison of photon flux at time U.

[0060] Figure 3 It is a spherical shell filling 235 Comparison of photon flux at time U.

[0061] Figure 4 It is a spherical shell filling 238 Comparison of photon flux at time U.

[0062] Figure 5 It is a spherical shell filling 239 Comparison of photon flux at Pu. Detailed Implementation

[0063] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0064] This invention discloses a method for creating a slow-photon ACE format database, which involves adding a photon generation reaction channel to the slow-photon data into the ACE (ACompact EndF) format database. Figure 1 As shown, the present invention includes the following steps:

[0065] Step 1: Calculate the slowed photon generation cross section based on the fission yield sub-library and decay sub-library of the evaluation kernel database;

[0066] During the long-term steady-state operation of a nuclear reactor, the production and decay rates of fission products and their decay products can be approximated as equal, i.e., decay equilibrium. Therefore, the production of slow-emitting electrons can be considered independent of time. The yield of slow-emitting electrons at any given time can be considered to be the total number of slow-emitting electrons released by fission products and their decay products when they return to the ground state. In other words, fission products are assumed to complete their decay process immediately after the fission reaction occurs. Based on this decay equilibrium concept, the slow-emitting electron production cross-section is calculated using the following formula:

[0067] σ delay,i (E)=σ f,i (E)Y i (E) Formula (1)

[0068] In the formula:

[0069] σ delay,i (E)——Slow photon production cross section of fission nuclide i, unit: number·barn;

[0070] σ f,i (E)——Fission cross section of fission nuclide i, unit: barn;

[0071] Y i (E)—— Slow-light photon yield of fission nuclide i, in units of: particles;

[0072] E – Incident neutron energy, unit: MeV;

[0073] The fission cross section can be obtained from the evaluation nuclear database after resonance reconstruction and linearization. The slow-light luminescence yield of fission nuclide i is calculated using the following formula:

[0074]

[0075] In the formula:

[0076] y i→p (E)——Independent fission yield of fission product p produced by fission nuclide i, in units of: p;

[0077] —The decay branching ratio of nuclide p to daughter nucleus p1;

[0078] D p — Decay photon yield of nuclide p, in units of photons;

[0079] — Decay photon yield of nuclide p1, in units of photons;

[0080] p—Identifier for fission products;

[0081] p1—Identifier of decay products of fission products;

[0082] Among them, the decay photon yield D of nuclide x x The following formulas are used for calculation: Formula (3) is used when the photon energy spectrum is a discrete energy spectrum, and Formula (4) is used when the photon energy spectrum is a continuous energy spectrum.

[0083]

[0084] In the formula:

[0085] D x — Decay photon yield of nuclide x, in units of photons;

[0086] k — the decay reaction channel number that releases photons;

[0087] NSP – The number of reaction channels that produce decaying photons;

[0088] A k —The normalized coefficient of decay reaction channel k that releases photons;

[0089] m—Discrete photon energy point identifier;

[0090] NER—Number of discrete photon energy points;

[0091] γ k,m (E γ — The decay photon yield at the m-th discrete energy point in the k-th decay reaction channel, in units of photons;

[0092] γ k (E γ — The energy spectrum of continuous decay photons in the k-th decay reaction channel, in units of photons / MeV;

[0093] E γ — Decay photon energy, unit: MeV;

[0094] Step 2: Calculate the slow-release photon energy distribution according to the form of an equal-probability energy pool;

[0095] An equal-probability energy grid divides the energy range of a slow-emitting particle into N energy intervals, with each interval having an equal probability of falling within it. These N intervals constitute the N energy grids. When storing slow-emitting particle energy distribution data using the equal-probability energy grid format, N+1 boundary point energies are required. The boundary point energies are calculated using the following formula:

[0096]

[0097] In the formula:

[0098] E bound,i —Energy at the i-th energy point, unit: MeV;

[0099] P(E) — Decay photon energy spectrum, unit: photons / MeV;

[0100] i — Energy point identifier;

[0101] N – Number of energy units;

[0102] Although the decay photon energy in the decay sub-database of the JEF-2.2 evaluation nuclear database can reach up to 12.7 MeV, the energy of slowed photons is actually mostly concentrated in the range of 4.7 MeV-6 MeV. If the energy of the last energy point is set to 12.7 MeV, the energy of the slowed photons will be overestimated. Therefore, the energy of the last energy point is set to 6 MeV, that is, slowed photons above 6 MeV are ignored.

[0103] Step 3: Correct the slowed-light generation cross section using the average energy of the evaluated slowed-light electrons given in the evaluation kernel database;

[0104] The evaluation nuclear database provides the average energy of slowed photons released after fission of fissile nuclides. The total slowed photon production cross-section of fissile nuclides needs to be corrected to ensure that the average slowed photon energy calculated using fission yield and decay data is consistent with the average slowed photon energy given in the evaluation nuclear database. The corrected slowed photon production cross-section is calculated using the following formula:

[0105]

[0106] In the formula:

[0107] —Modified slow-photon generation cross section, unit: barn;

[0108] Q delay —Evaluate the average energy of slowed photons released after fission of fission nuclides given in the nuclear database, in MeV;

[0109] Q delay,cal—The average energy of slowed photons, calculated using fission yield and decay data, in MeV;

[0110] Step 4: Create an ACE database containing delayed photons by adding a photon generation reaction channel to the ACE (A Compact EndF) database; add the delayed photon generation cross section to the instantaneous photon generation cross section and store it in the GPD array of the ACE database; store the delayed photon energy distribution in the DLWP array; since all decaying photons are isotropic, store the delayed photon angular distribution in the ANDP array according to the isotropic distribution; finally, output the processed data in ACE format to obtain the delayed photon ACE format database.

[0111] The fission yield sub-library and decay sub-library in the evaluation kernel database used in steps 1 and 3 are only applicable to the method of creating the slow-luminescent ACE format database in this invention, and there are no restrictions on the source and use of the evaluation kernel database.

[0112] Validation of the ACE format database of slow-release phosphors

[0113] To verify the accuracy of the slow-photon ACE format database, the database was constructed using both the method of this invention and the multi-group form normalized slow-photon yield method. Neutron and photoatomic data were evaluated using the ENDF / B-VII.0 nuclear database, while fission and decay data were evaluated using the JEF-2.2 nuclear database. 233 U、 235 U、 238 U、 239 The ACE database of slow-emitting photons for the four common fissile nuclides (Pu) was used to calculate a one-dimensional spherical shell problem using a Monte Carlo program. The shell had an inner diameter of 10 cm and an outer diameter of 19.9 cm, and the materials were the four fissile nuclides mentioned above. The center of the shell was a 14.1 MeV isotropic neutron source. The flux of 123 photon groups in the energy range [0.3679 MeV, 10 MeV] at the shell was statistically analyzed, and the results were compared with those obtained using a conventional decay particle database. To ensure consistency with the evaluation nuclear database used, the slow-emitting photon yields of 25 groups for each radionuclide calculated using NECP-Atlas based on the JEF-2.2 evaluation nuclear database were used to replace the corresponding parts in the decay particle database. The calculation results are as follows: Figures 2-5 As shown:

[0114] from Figures 2-5It can be seen that the calculation results using the multi-group form to describe the energy distribution of slow-photon are in good agreement with the results calculated using the decay particle database. Furthermore, both the multi-group database and the traditional decay particle database average the discrete photon yield within each energy group when describing the energy distribution of slow-photon, thus smoothing out fluctuations in the energy distribution. Using the database of this invention can more accurately describe the fluctuations in the energy spectrum of slow-photon; therefore, the method of this invention has higher calculation accuracy than traditional methods.

[0115] The computation time using the traditional decay particle database and the database of this invention is shown in Table 1.

[0116] Table 1 Comparison of Calculation Time

[0117]

[0118] Traditional decay particle databases store the slow-emission yield of each radionuclide, requiring a step-by-step traversal of the decay chain during Monte Carlo simulations, resulting in long execution times. The database of this invention, however, takes only about a quarter of that time.

Claims

1. A method for creating a delayed-emission ACE format database, characterized in that: Includes the following steps: Step 1: Calculate the slowed photon generation cross section based on the fission yield sub-library and decay sub-library of the evaluation kernel database; Step 2: Calculate the slow-release photon energy distribution according to the form of an equal-probability energy pool; Step 3: Correct the slow-light emission cross section using the average energy of slow-light emission given in the evaluation kernel database; Step 4: Create an ACE database containing slow-emitting photons by adding a photon-generating reaction channel to the ACE database; Step 2 involves the following process: The equal probability energy range is divided into... N There are several energy ranges, and the probability of a slow-release photon falling into each energy range is equal. N The interval is N When storing slow-photon energy distribution data in the form of an energy bounding system with equal probability, it is necessary to obtain... N +1 boundary point energy, which is calculated using the following formula: Official (5) In the formula: ——No. i Energy point energy, unit: MeV; — Decay photon energy spectrum, unit: photons / MeV; —Energy point identifier; —Quantity of energy zones; Although the decay photon energy in the decay sub-database of the JEF-2.2 evaluation nuclear database can reach up to 12.7 MeV, the energy of slowed photons is actually mostly concentrated in the range of [4.7 MeV-6 MeV]. If the energy of the last energy point is set to 12.7 MeV, the energy of slowed photons will be overestimated. Therefore, the energy of the last energy point is set to 6 MeV, that is, slowed photons above 6 MeV are ignored. The specific process of step 4 is as follows: add the slow photon generation cross section and the instantaneous photon generation cross section together and store them in the GPD array of the ACE database; store the slow photon energy distribution in the DLWP array of the ACE database; since all decaying photons are isotropic, store the slow photon angular distribution in the ANDP array of the ACE database according to the isotropic distribution; finally, output the processed data in the ACE format to obtain the slow photon ACE format database.

2. The method for creating a slow-photon ACE format database according to claim 1, characterized in that: The specific process of step 1 is as follows: During the long-term steady-state operation of the nuclear reactor, it is approximately assumed that the production rate and the disappearance rate of fission products and their decay products are equal, i.e., decay equilibrium. Therefore, the production of slow-emitting electrons is independent of time. The yield of slow-emitting electrons at any given time is the total number of slow-emitting electrons released by fission products and their decay products when they return to the ground state. That is, after the fission reaction occurs, the fission products immediately complete the decay process. Based on the above idea of ​​decay equilibrium, the slow-emitting electron production cross-section is calculated using the following formula: Official (1) In the formula: — fission nuclides i The cross-section of slow-emitting photons, in units of particles per barn; — fission nuclides i The fission cross section, in barn; — fission nuclides i The yield of slow-emitting electrons, in units of: particles; —Incident neutron energy, unit: MeV; The fission cross section was obtained from the evaluation nuclear database after resonance reconstruction and linearization, and the fission nuclides were... i The yield of slow-release photons is calculated using the following formula: Official (2) In the formula: — fission nuclides i Generate fission products p Independent fission yield, unit: units; —Nucleotides p decaying daughter nuclides p decay branching ratio of 1; —Nucleotides p Decay photon yield, in units of: units; —Nucleotides p Decay photon yield of 1, unit: number; —Identifier for fission products; —Identifiers of decay products of fission products; Among them, nuclides x decay photon yield The following formulas are used for calculation: Formula (3) is used when the photon energy spectrum is a discrete energy spectrum, and Formula (4) is used when the photon energy spectrum is a continuous energy spectrum. Official (3) Official (4) In the formula: —Nucleotides x Decay photon yield, in units of: units; —The decay reaction channel number that releases photons; —The number of reaction channels that produce decaying photons; —The decay reaction that releases photons k The normalized coefficient; —Discrete photon energy point identifier; —Number of discrete photon energy points; ——No. k decay reaction channel, first m Decay photon yield at discrete energy points, in units of photons; ——No. k The energy spectrum of continuous decay photons in a decay reaction channel, unit: photons / MeV; — Decay photon energy, unit: MeV.

3. The method for creating a slow-photon ACE format database according to claim 1, characterized in that: Step 3 is as follows: The average energy of slowed photons released after fission of fissile nuclides is given in the evaluation nuclide database. The total slowed photon production cross section of fissile nuclides is corrected to ensure that the average slowed photon energy calculated using fission yield and decay data is consistent with the average slowed photon energy given in the evaluation nuclide database. The corrected slowed photon production cross section is calculated using the following formula: Official (6) In the formula: —Modified slow-photon generation cross section, unit: barn; —Evaluate the average energy of slowed photons released after fission of fission nuclides given in the nuclear database, in MeV; —The average energy of slowed photons, calculated using fission yield and decay data, in MeV.

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