Spent Nuclear Fuel Dry Cask Storage
Development of Software for Numerical Analysis of Fuel Temperature States and Heat- and Mass-Transfer Processes in RBMK-1000 SNF Casks at the Main Steps of Preparing Fuel to Dry Long-Term Storage, Numerical Studies
Tech Area / Field
- ENV-RWT/Radioactive Waste Treatment/Environment
- FIR-DEC/Decommissioning/Fission Reactors
- FIR-FUC/Fuel Cycle/Fission Reactors
- FIR-MOD/Modelling/Fission Reactors
- FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors
- INF-SOF/Software/Information and Communications
3 Approved without Funding
Research Institute of Technology, Russia, Leningrad reg., Sosnovy Bor
- Lawrence Livermore National Laboratory, USA, CA, Livermore
Project summaryLong-term storage of nuclear spent fuel (SNF) that is not to be reprocessed is a very challenging problem for Russia. A special concern is given to the RBMK SNF in at-reactor fuel storage pools and wet storage facilities at NPP sites. These storage rooms are now filled over their original design capacity and the storage capabilities are expected to be fully exhausted in Russia within years 2006-2008. This situation aggravates the problem of safety ensuring and is a hazard to the environment in NPP vicinities.
With the lack of well-founded data on the possibility for SNF wet long-term storage and taking into account the best world (Germany, France, the USA, and Japan) practices of SNF management, the Russia’s Minatom has launched a project for development of dual-purpose casks. The project has motivated work on SNF dry cask storage and transport technologies.
In the past 7 years the Special Mechanical Engineering Design Office (KBSM) with its business partners have developed a group of metal-concrete casks (MCC) which meet SNF safe storage and transport requirements existing in Russia and related IAEA standards.
In parallel with designing of casks, work is underway on a technology for preparing RBMK-1000 SNF to dry storage in casks. Based on the design features of RBMK-1000 assemblies and their decay storage under water, a technology for preparing fuel to dry cask storage should involve the following steps: spent assembly cutting; cask charging with SNF; cask sealing and drying; bringing the parameters of gas atmosphere in the cask internal cavity to the level specified for SNF long-term storage.
It is proposed to carry out RBMK SNF cutting and casking in special-purpose rooms at NPP sites. These rooms will be adjacent to the SNF fuel storage facilities and provided with several safety barriers in respect of the environment. The rooms and plant-specific technologies for RBMK-1000 NPPs are being developed with reference to each storage facility design, site characteristics, etc. The development of the projects for the Leningrad NPP and Kursk NPP is in the finalizing phase.
Since the existing technology for cutting spent assemblies before loading them into casks does not involve procedures for removing water from the assembly structures, some liquid is sure to enter the MCC internal cavity. Therefore, after loading fuel into MCC, installing and sealing the inner cap, the cask internal cavity with SNF will be dried by evacuation through a specially designed valve unit. Using vacuum pumping for drying casks being prepared to dry long-term storage is a world-wide practice.
The problem of changeover to SNF dry long-term storage was not defined at the governmental level in Russia until recently. Thus, now there is a deficiency of up-to-date software needed to provide mathematical support for the main steps of preparing fuel to dry long-term storage in casks. The existing domestic computer codes are designed to calculate the fuel and cask body temperature states under normal and accident long-term storage conditions and are not able to model the main steps of SNF preparation to dry cask storage.
Since 1999, Alexandrov NITI scientists and researchers have been carrying out experiments and numerical analyses in support of the possibility for drying RBMK-1000 SNF casks using vacuum pumping. A group of NITI members have designed a small-scale experimental set-up for simulating the process of drying a single flask. Also, they have developed methods and algorithms to compute the SNF MCC vacuum drying effects at specified process parameters and, based on the estimates obtained, support the proposed concept as such. However, the results of these studies are not sufficient for adequate representation of the procedure for preparing SNF MCC to long-term storage, because the existing mathematical models for approximate estimates take no account of the process equipment effect and the influence of the spent assembly cutting and casking routine. The problem at hand is to model in full the main steps of SNF preparation to dry cask storage and re-define the basic process parameters (moisture content, pressure in the cask maintained by means of evacuation, etc.) on the basis of knowledge world-wide gained to date in the field.
In the light of what is mentioned above the authors propose the following activities to be carried out under the project:
- development of software for analyzing the RBMK-1000 SNF temperature state in the process of fuel loading into MCC and for evaluating the amount of residual moisture in the cask at the moment when drying is started;
- development of software for numerically analyzing the processes of drying the cask internal cavity, taking into account the casking routine effect and effect of the vacuum drying equipment;
- development of software for analyzing the temperature states of fuel, structures, and cask body and the atmospheric conditions in the cask internal cavity during dry long-term (~ 40-50 years) cask storage of RBMK-1000 SNF;
- numerical analysis of heat- and mass-transfer processes at the main steps of RBMK-1000 SNF preparation to dry cask storage.
The project results such as special-purpose programs for calculating heat-and mass-transfer in RBMK-1000 SNF casks at the main steps of preparing fuel to dry long-term cask storage and during storage will be used in support of domestic technologies for spent fuel management, specifically, timely transfer of RBMK-1000 SNF from wet storage facilities into casks for future dry storage. The use of computer codes providing the physical validity of calculated results will contribute to saving the cost of large- and full-scale experiments and, consequently, the total work cost.
Positive results of the project activities can be used in:
- designing indigenous versatile software to simulate loading and drying technologies for different types of SNF casks, thus making it possible to significantly reduce research costs;
- numerical analyses of new cask types for SNF storage and transport.
The project objective is to resolve an important national problem – provide software support to the safety justification of technologies for RBMK-1000 SNF changeover to dry long-term cask storage. Also, the project responds to the main ISTC purposes such as:
1. Providing weapons scientists the opportunity to re-orient their talents to peaceful activities (NPP SNF management) pertaining to environment protection and nuclear safety.
2. Integration of weapons scientists and engineers into international scientific community through information exchange with collaborators and participation in international meetings and conferences on SNF management problems.
3. Improvement in the competitiveness of Russian-designed program products through implementation of the project and learning the world best practices in the area, including research activity under the market economy conditions.
The estimated project duration is eighteen months.
Within the first six months, the authors plan to:
- develop physical-mathematical models and algorithms and write programs for modelling the RBMK-1000 SNF casking process;
- carry out a numerical simulation and analysis of the fuel temperature state and the amount of residual water in the cask for different modes of fuel loading.
During the remainder of this project year, it is planned to:
- develop physical-mathematical models and algorithms and write programs for modelling the RBMK-1000 SNF cask drying by evacuation;
- carry out a numerical simulation and analysis of various regimes for drying the RBMK-1000 SNF cask internal cavity, taking into account the effect of loading routine;
- develop algorithms and write programs for modelling the conditions of RBMK-1000 SNF dry cask long-term storage;
- carry out a numerical analysis of the atmospheric parameters in the cask internal cavity and the temperature states of the fuel and cask body both after drying and injection of an inert gas into the internal cavity and during dry long-term storage.
Consistent with the main ISTC purpose, i.e. integration of Russian scientists and engineers into the international scientific community, the following scope of cooperation with foreign institutions is proposed:
- information exchange in the course of project implementation;
- conduction of joint seminars, meetings, workshops, and consultations;
- consultations on intellectual property rights and commercial application of project results;
- other possible ways of collaboration.
The project will be executed on a step-by-step basis according to the Technical Schedule. By convention each project task is pided into three main steps: theoretical development of a mathematical model, implementation of the model in programs, and carrying out numerical analyses. It is planned to develop three program packages (PP) for modelling the steps of RBMK-1000 SNF preparation to dry cask long-term storage: PP for calculation of the temperature conditions at the step of spent assembly cutting and casking, PP for modelling SNF cask drying by using vacuum pumping, and PP for calculation of heat transfer in the cask during long-term storage.
To adequately represent the temperature conditions, all of the key heat transfer effects related to the above-mentioned SNF management procedures will be accounted for: transient heat conduction, heat transfer by radiation, heat transfer by convection, and heat- and mass-transfer in multi-component mixtures.
The program packages for simulating heat- and mass-transfer processes associated with spent fuel preparation to dry cask storage will be developed on the basis of existing programs, methods, and algorithms such as:
- codes for calculating transient heat conduction effects in complex geometries, using the finite element method;
- codes for calculating the angular coefficients of radiation in complex geometries, using the Monte-Carlo method;
- methods for calculating the interfacial heat- and mass-transfer;
- methods for calculating heat- and mass-transfer in a multi-component mixture;
- programs and methods developed in the course of previous numerical studies on SNF MCC drying.
The successful completion of the project is assured by high-level qualifications and expertise of the scientific personnel in the project. NITI researchers and engineers have gained essential experience both in the field of numerical simulations of reactor plants of different types, including simulations on powerful DEC computer systems, and in the area of heat- and mass-transfer investigations for SNF casks (since 1999).
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