Fast Spectrum Systems Research Articles

The Development of SIMMER-III, An Advanced Computer Program for LMFR Safety Analysis, and Its Application to Sodium Experiments

SIMMER-III is a general two-dimensional, three-velocity-field, multiphase, multicomponent, Eulerian, fluid dynamics code coupled with a space-time and energy-dependent neutron transport kinetics model. The philosophy behind the SIMMER-III development was to generate a versatile and flexible tool, applicable for the safety analysis of various reactor types with different neutron spectra and coolants including the new accelerator-driven systems for waste transmutation. Currently, a three-dimensional version is also available, coined SIMMER-IV. The main backbone for analyses, however, is still SIMMER-III.SIMMER-III has proven especially well suited for fast spectrum systems such as the liquid-metal-cooled fast reactor where it is one of the key codes for safety analysis, including its application within licensing procedures. To serve especially the last purpose, the code must be made sufficiently robust and reliable and be tested and validated extensively. A comprehensive and systematic assessment program of the code has been conducted. This paper gives the major achievements of this assessment program.The SIMMER-III code handles by default liquid-metal-cooled fast reactor core materials - fuel, steel, coolant, control rod, and fission gas, in solid, liquid, and vapor states. The total of 27 density and 16 energy components are modeled in three velocity fields and one structure field in order that important fluid motions in a degraded core are simulated adequately. The spatial differencing method is based on Eulerian staggered mesh with a higher-order differencing scheme to mitigate numerical diffusion. An improved analytic equation-of-state model provides good accuracy especially at high temperature and pressure. Multiple flow-regime treatment is available over the entire void fraction range. An interfacial area convection model improves the flexibility of the code by tracing transport and history of interfaces and thereby better represents physical phenomena. A generalized and flexible code framework, along with improved numerical stability and accuracy, allows us to apply it to a variety of simple and complex multiphase flow problems.The code assessment program is an ongoing effort. Two major milestones have been achieved in the past by completing two assessment campaigns, Phase 1 and Phase 2: Phase 1 for fundamental code assessment of individual models and Phase 2 for integral code assessment for key phenomena relevant to liquid-metal-cooled fast reactor safety. Through this systematic code assessment program, comprehensive validation of the physical models has been conducted step-by-step. The assessment program has demonstrated that SIMMER-III is a state-of-the-art code with advanced models sufficiently flexible for simulating transient multiphase phenomena occurring during core disruptive accidents. This paper concentrates on the specifics of the code, mainly reflected in its application to sodium experiments related to the safety of liquid-metal-cooled fast reactors.

FAST: An advanced code system for fast reactor transient analysis

One of the main goals of the FAST project at PSI is to establish a unique analytical code capability for the core and safety analysis of advanced critical (and sub-critical) fast-spectrum systems for a wide range of different coolants. Both static and transient core physics, as well as the behaviour and safety of the power plant as a whole, are studied. The paper discusses the structure of the code system, including the organisation of the interfaces and data exchange. Examples of validation and application of the individual programs, as well as of the complete code system, are provided using studies carried out within the context of designs for experimental accelerator-driven, fast-spectrum systems.

A comparative physics study of alternative long-term strategies for closure of the nuclear fuel cycle

The appropriate management of radioactive waste arising from the nuclear fuel cycle is considered to be a key issue in the development of future, more sustainable nuclear energy systems. In this context, the partitioning and transmutation of actinides could play an important role through the achievement of very significant reductions in the actinide content and radiotoxicity of the high-level waste requiring geological disposal. The current paper reports on the results of a detailed physics study carried out to compare the pros and cons of alternative strategies for closure of the nuclear fuel cycle. Different long-term “steady-state” scenarios have been considered, involving the deployment, to varying degrees, of light water reactors (LWRs) and advanced fast-spectrum systems. The same nuclear data and calculation methods have been used throughout, so that a consistent and reliable comparison of the relative performance of the three basic fuel cycle options (once-through, plutonium recycle, and recycling of all actinides) has been made possible. In addition, with transmutation having been considered employing both critical and accelerator-driven fast-spectrum systems, the study has provided an evaluation of the advantages and disadvantages of these two different advanced system types.

Partitioning and transmutation studies at JAERI both under OMEGA program and High-Intensity Proton Accelerator Project

At the Japan Atomic Energy Research Institute (JAERI), active and comprehensive studies on partitioning and transmutation (P&T) of long-lived nuclear waste from the reprocessing processes of spent fuel has been carried out under the OMEGA program. Studies at JAERI include a design study of dedicated transmutation systems both of an MA burner fast reactor (ABR) and an accelerator-driven subcritical system (ADS), and the development of a high intensity proton accelerator as well as the development of partitioning process, nitride fuel fabrication/dry separation process technologies and nuclear data studies. During the course of studies, JAERI developed the concept of the double-strata fuel cycle, in which a dedicated system is used for transmutation. Comparing the various transmutation systems, such as thermal neutron spectrum or fast neutron spectrum systems, power reactors or dedicated systems, from the viewpoints of reactor physics, nuclear fuel cycle and socio-technical issues, it was concluded that the ADS is the best option for transmutation of minor actinide(MA). JAERI, therefore, decided to concentrate its R&D efforts on the development of ADS and related technologies. One of the goals of R&D is to provide a basis for designing demonstration facilities of ADS, aqueous partitioning process and nitride fuel fabrication and dry separation technologies. As the initial step toward this purpose, the construction of an ADS experimental facility is planned under the High-Intensity Proton Accelerator Project which JAERI and the High Energy Accelerator Research Organization (KEK) are jointly proposing since 1998. The paper discusses the some of the results of P&T studies and the outline of the High-Intensity Proton Accelerator Project under which ADS experimental facility will be constructed.

ACCELERATOR-DRIVEN SYSTEMS FOR NUCLEAR WASTE TRANSMUTATION

▪ Abstract The renewed interest since 1990 in accelerator-driven subcritical systems for transmutation of commercial nuclear waste has evolved to focus on the issue of whether fast- or thermal-spectrum systems offer greater promise. This review addresses the issue by comparing the performance of the more completely developed thermal- and fast-spectrum designs. Substantial design information is included to allow an assessment of the viability of the systems compared. The performance criteria considered most important are (a) the rapidity of reduction of the current inventory of plutonium and minor actinide from commercial spent fuel, (b) the cost, and (c) the complexity. The liquid-fueled thermal spectrum appears to offer major advantages over the solid-fueled fast-spectrum system, making waste reduction possible with about half the capital requirement on a substantially shorter time scale and with smaller separations requirements.