Nuclear data uncertainties are considered a main limiting factor in proving safety of advanced reactors. A reasonable amount of available information should be applied to sensitivity and uncertainty analyses for this, and this work considers the influence of usually omitted angular distribution uncertainties. A sensitivity and uncertainty analysis of MOX3600 is conducted using Serpent. The angular distribution influence is assessed by applying covariances of the state-of-the-art libraries. The sensitivity analysis shows that quantifying the influence of higher-order Legendre moment uncertainties on the eigenvalue and void reactivity is of minor importance for MOX3600. The uncertainty analysis shows the P1-coefficients for 238U and 16O introduce uncertainties to the eigenvalue similar to 56Fe and should be accounted for. A library comparison reveals TENDL-2021 and ENDF/B-VIII.0 introduce uncertainties of a few hundred pcm to the eigenvalue, and the data should be reassessed, while the other libraries give an uncertainty of several tens of pcm.

The paper presents an assessment of the effect caused by technological uncertainties on keff using the example of the test problem for a MET1000 fast sodium reactor with metal fuel. It is proposed to perform this assessment using nuclear sensitivity factors by random sampling or direct perturbation without requiring multiple calculations. The TSUNAMI-3D module of the SCALE program was used to analyze the sensitivity to nuclear data uncertainty. The obtained constant and technological uncertainties based on ENDF/B VII.1 equal 1.15 and 0.6

There is a rise in sensitivity and uncertainty analyses with respect to nuclear data, which are a basis for a neutron transport simulation. The analyses are primarily concerned with the state-of-the-art reactors, known as Generation IV. They provide assessments of nuclear data performance, key nuclear data, and their uncertainty influence on functionals such as the eigenvalue, reactivity coefficients, delayed neutron fraction, etc. In this work, recent advances in sensitivity and uncertainty analysis with corresponding transport codes are reviewed. Furthermore, the available results of the analyses are compared and discussed. As a result, this review summarizes current analyses performed for the advanced systems in recent years. The gaps in the Generation IV system analyses are noted including SCWRs, MSFRs of different types, and other systems. Besides, the gaps in nuclear data of state-of-the-art libraries are discussed. Based upon this, these gaps can become a part of analyses for identifying future nuclear data needs.

This paper analyzes the methods and technologies for assessing the method of formation, composition, characteristics and features of corium, which is a mixture of nuclear and structural materials of the nuclear reactor core, formed as a result of an accident accompanied by partial or complete core melting. The study is based on data from the study of corium formed as a result of the accident at the Fukushima Daiichi nuclear power plant, which are in the public domain and are the result of the work of many scientific organizations around the world. Corium research is one of the main issues in the framework of improving nuclear safety in the future and is one of the objectives of the successful procedure for eliminating the consequences of the accident at the Fukushima Daiichi nuclear power plant. Without a detailed analysis of the neutronic, materials science, gravimetric and other characteristics of the corium, as well as the creation of a complex model of the corium that combines these data, it is impossible to organize an efficient and safe process for removing nuclear materials from the damaged units of the Fukushima Daiichi nuclear power plant. The objective of this work is to combine the existing research results into a data set that allows modeling of the corium using neutronic calculation codes and includes such data as the size, density and morphology of corium samples and their approximate nuclide composition. Such modeling allows not only to perform tasks related to increasing the level of safety in the implementation of the procedure for eliminating the consequences of the accident at the Fukushima Daiichi nuclear power plant, but also to serve as an international benchmark for modeling a mixture containing nuclear materials.

Nuclear data are a main uncertainty source in neutron transport simulations making their consideration in reactor safety necessary. This arises anew with the state-of-the-art reactors known as Generation IV. Some of the reactors suggests providing the reactivity margin below the effective delayed neutron fraction excluding prompt criticality accidents, and the breeding ratio is the key factor in this. Consequently, assessing a degree of the breeding ratio accuracy is of interest. Therefore, in this work, the breeding ratio uncertainties are analyzed by performing a sensitivity and uncertainty analysis of the MET1000 and MOX3600 models with respect to nuclear data using SCALE. As a result, the breeding ratio uncertainties are obtained approximately equal to 2% as the main contributors are 239Pu(n, gamma), 238U(n, gamma), and 238U(n, n'). The uncertainty sources between the models are compared, and 16O preponderantly increases the total uncertainty not directly by its uncertainty but by its impact on the spectrum.

The new calculation code capabilities are applied in the current work as well as important fast reactor criticality parameters uncertainty assessment articles’ results based on different nuclear data libraries and covariance matrices. A comparative analysis of uncertainty estimations related to neutron reactions is presented for lead-cooled reactor models and sodium-cooled reactor models. For the models of advanced BN and BR fast reactors with three fuel types (UO2, MOX, MNUP), the multiplication factor uncertainty calculations are performed using 252-group covariance matrices based on ENDF/B-VII.1 library via the SCALE 6.2.4 code system. The main nuclear data uncertainty contributors in the multiplication factor are determined. Recommendations are formulated for improving the cross sections accuracy for several nuclides in order to provide more reliable results of fast reactor criticality calculations. Lead-cooled reactors have no operational history compared to light-water and sodium-cooled reactors. The experimental data insufficiency calls in the question about reliability of the simulation results and requires a comprehensive initial data uncertainty analysis for the neutron transport simulation. The obtained results support the idea that lead- and sodium-cooled reactors have close nuclear data sensitivity using one and the same computation tools, nuclear data libraries and fuel compositions. This makes it possible to use the accumulated data of benchmarks for sodium-cooled reactors in the safety determination of lead-cooled reactors.

Fuel debris removal is the most challenging part of damaged nuclear power station decommissioning. It is important to carry out nuclear safety calculations accurately and quickly enough. Here, it was clarified that modern codes based on the Monte Carlo method were capable of performing neutronic analysis with the same accuracy and without significant differences in the results. The benchmark calculations were performed using three codes: MVP, Serpent, and MCU. In this study, the comparison focused on multiplication factor, neutron fluxes and reaction rates relative difference, and calculation time of many fuel debris particles system. Then the calculation results were used when codes comparing. It was shown that the calculation results showed good agreement between all codes. It was assumed that minor differences in the thermal range of neutron fluxes can be caused by different thermal neutrons scattering treatment for all codes. The study also showed that solving such problems requires significant computing power and time. It has been proven that the statistical geometry model in the MVP and the explicit stochastic geometry model in the Serpent have the possibility to provide solutions with the same accuracy, but much faster.

• University NRNU MEPhI works on testing of the Proryv codes. • The objectives of independent testing include assessment of the code quality. • Complexes were identified: CONSYST-RF, CORNER, DOLCE VITA, ODETTA, MCU-FR, BPSD. • The models of the BN-600, BN-1200, BR-1200 and BREST-OD-300 cores were used.

As the burnup increases, the requirements of nuclear and radiation safety for spent nuclear fuel (SNF) at the subsequent stages of operation grow. The analysis and estimation of the required cooling time of the spent fuel assemblies (SFAs) of the VVER-1200 reactor for transportation in various types of transport containers (TUK-13 and TUK-141O) are performed. The estimates are based on the analysis of residual energy release and gamma-radiation intensity of SNF depending on the cooling time for different burnups. The data on the absorbed dose rate of neutron and gamma radiation from SNF after 4 and 5 yr of cooling are presented.

Accident at Fukushima Daiichi nuclear power plant led to increase of importance of safety justification for processes at post-accident facilities in nuclear industry. One of such processes is extraction of corium from reactors cavity. Recriticality of this process is defined by potential unacceptable accident. This paper introduces supporting code for neutron fluxes and reaction rates visualization in systems with complex geometry that can be used in modeling of corium removing works. Visualization code is based on Unreal Engine 4 game engine. Code allows observing neutronic functionals distribution in three dimensions. The reseach and provided implementation details help to understand the physical processes that take place as the accidents occur during corium removing works.

After the accident at the Fukushima Daiichi NPP, the attention of the scientific community is riveted on how the consequences are being eliminated. Removing corium – a lava-like resolidified mixture of nuclear fuel with other structural elements of the reactor – remains the most difficult task, the solution of which can take several decades. It is extremely important to exclude the occurrence of any emergency processes during the removal of corium. The purpose of this work was to solve a coordinated hydrodynamic and neutronic problem characterized by a large number of randomly oriented and irregularly located corium particles in water as part of the development of a benchmark for this class of problems. Monte Carlo-based precision codes were used to perform a neutronic analysis. The positions of corium particles were determined from the numerical simulation results. The analysis results obtained using the codes involved showed good agreement for all the states considered. It was shown that the modern neutronic codes based on the Monte Carlo method successfully cope with the geometric formation and solution of the problem with a nontrivial distribution of corium particles in water. The results of the study can be used to justify the safety of corium handling procedures, including its extraction from a damaged power unit.

National Research Nuclear University “MEPhI” (NRNU MEPhI) is the leading university of the consortium of reference universities of the State Atomic Energy Corporation Rosatom (ROSATOM), a regular supplier of young specialists of the highest level. Since 2014 NRNU MEPhI has been training graduates for responsibility centers of the project direction “Proryv”. University responds quickly to staffing challenges, and provides the project “Proryv” the personnel with relevant unique competencies. These competencies include the ability to apply the knowledge gained to develop a new technological platform for nuclear power with the involvement of uranium-238 and spent nuclear fuel reprocessing products in the fuel cycle. Obtaining such unique knowledge is impossible without the use of external resources, namely, the involvement of leading scientists and practitioners of ROSATOM for conducting classes with students, organizing practices in scientific centers and at nuclear fuel cycle enterprises. The article discusses the features of the organization of the educational process in this area.

The unified code CONSYST-2020 for neutron constants preparation and the ABBN-RF-2020 neutron data library are being testing as part of the new generation codes development for neutronic calculations of fast reactors with mixed nitride uranium-plutonium fuel (MNUP). Testing was carried out on prototype models of fast reactors with MNUP fuel. The errors of the multigroup, group and subgroup approximation are analyzed in comparison with the calculations performed using point-wise cross-sections libraries. The results obtained with point-wise cross-sections libraries are accepted in the final cross-verification as reference results. An assessment was made of the influence of approximations associated with averaging and preparing group cross-sections, and methodological errors determined by the selected spatial and angular computational grids. It was shown that the transition to the direct use of 299-group blocked constants reduces the error to 0.1 – 0.2%. The assessment of the efficiency of using the subgroup approximation shows the possibility of reducing the constant component of the error below 0.05%.

As part of the tasks to improve the nuclear safety of nuclear power plants, a new program code was developed. The CORIUMSITY program code developed, considered in this work, is intended to analyze the scenario in which an accident at a nuclear power plant is simulated with the melting of the core and the formation of the so-called “corium” - a mixture of nuclear and structural materials of the nuclear reactor core, formed as a result of thermal and mechanical impact during an accident. The CORIUMSITY program code, is intended to analyze several scenarios of different accidents, include an accident with reactor core melting. The functions of this code can help in solving many urgent nuclear safety problems. One of the main methods of operation of the CORIUMSITY code algorithms is the matrix exponential method, which consists in using a matrix function of a square matrix, in which as values are used indicators corresponding to nuclides from the CORIUMSITY code database. The program implements an iterative Euler method for solving the system of levels of nuclear fuel burnup. The CORIUMSITY code was verified with benchmark data to assess the accuracy of the calculation.

In this paper, the idea of modifying the benchmark by increasing effective multiplication factor value in the considered system without increasing the number of particles under consideration and fuel enrichment is discussed. The technology of data transmission, processing and comparison of the results of neutron-physical calculations using three modern codes developed in different countries and implementing the Monte Carlo method has been worked out. For the corium and water mixture parameters search, the method conventionally called the gradient descent method is used. The search method for areas of critical state corium slurry in water is described. This method can be used to justify nuclear safety in the corium extraction and transportation processes. The methodology is based on the combined use of 1-D and 3-D criticality calculations capabilities of the SCALE 6.2 program pack. Fall of corium particles in water simulation benchmark version is formulated. The possibility of using the algorithm to find the parameters of a corium and water mixture is demonstrated. This benchmark includes the critical state of corium slurry in water and assumes the use of regular structures in the formation of geometric models. The proposed version of the critical benchmark for the corium particles in water state contains 55% fuel.

The paper formulates the main problems associated with research on transmutation, which should be paid attention to by today’s young researchers. The processes of production of hazardous nuclides during transmutation in reactor facilities are considered. The goals of transmutation and the choice of nuclides to be transmuted are discussed. The concept of radiotoxicity is explained as a measure of the radiological hazard of radioactive nuclides, based on the maximum permissible concentration of nuclides according to the IAEA standards. The problem of the formation of secondary radioactive nuclides in nuclear fuel during generation of neutrons for transmutation is discussed. The advantages and disadvantages of various methods of transmutation in nuclear installations are considered: inclusion of transmutable nuclides in nuclear fuel in fast reactors, transmutation in specialized thermal and fast transmutation reactor installations and ADS systems. The problem of accumulation of highly radioactive actinides in a transmutation facility during long-term transmutation and the problem of a potential hazard of the transmutation facility itself are discussed. The unacceptability of application of common-type power reactors for the transmutation of long-lived fission products is demonstrated.

This paper describes the development of full-scale models of the BR-1200 reactor for the MCU-FR code with a homogeneous and heterogeneous description of fuel assemblies’ geometry. The correctness of the control rods efficiency calculation in a homogeneous model is analyzed. The control rods requiring heterogeneous modeling are defined.

In this work was carried out the simulation in the SCALE6 code of an experiment on the BN-600 reactor on irradiating of fuel assemblies, containing samples of mixed nitride uranium-plutonium fuel. A comparison of the results for SCALE6 on the results of other codes is presented. The results of an estimation of uncertainties in the calculated data connected with uncertainties of an irradiation of an experimental sample and used neutron cross-sections library. Discussion of possible differences between analytical and experimental results is given.