This report was prepared as a report of work sponsored by an agency of the United States Government. Desired target accuracies with associated benefits for the various aspects of the nuclear reactor and chemical processing plants were also given.
A Case for Advanced Simulation
Because of the high costs and long time involved in experimentation, simulation has become more established in the process of scientific research. In principle, we can hope to minimize the impact of uncertainties arising from the modeling of physical processes.
B Challenging Problems That Will Benefit from Advanced Simulation
It is quite difficult to perform an accurate cost/benefit analysis for advanced simulation, but the ultimate goal, as previously indicated, is to be able to design a system with greatly reduced margins of uncertainty, reduced number of tests support and shorter design development. the time.
B.1 Safety Case for Sodium Cooled Fast Reactor
In the case of an unprotected LOF accident, the initiator is assumed to be the total loss of offsite power associated with a reactor scram failure. As the flow rate through the core decreases, the exit temperature of the coolant increases.
B.2 Fuel and Structural Materials in Reactor Operating Conditions
In the end, all these uncertainties translate into ad hoc factors (eg hot channel factors for hot spot determinations) and safety operating margins that harm the overall economics of the plant. When radiation results are finally available, the new fuel under study may already be out of date due to considerations that may not be related to the fuel design itself.
B.3 Chemical Separation and Reprocessing Plant
In general, the throughput (cell current) is determined by the cell configuration, operating conditions (mixing, applied voltage), and the chemical condition of the electrorefinery. The use of a multi-stage centrifugal contactor is an important element in the development of the UREX+ processes.
C Characteristics of a Future Advanced Simulation Tool
The dissolved fuel is processed in a series of solvent extraction processes to separate different components of the fuel. The products of the solvent extraction are streams containing specific components of the fuel in acidic solutions.
A Background
Φ are typically obtained by fitting a wide range of experimental data, such as lattice parameters, sublimation, vacancy formation energies, elastic constants, and energy differences between BCC and FCC lattices. It also provides a benchmark for more macroscopic methods such as Kinetic Monte Carlo (KMC), Dislocation Dynamics and Chemical Transition State Rate Theory, which can be used for their verification.
![Fig. II.1 MD cell for UO 2 [from [17] K.Kurosaki et al (2001)]](https://thumb-ap.123doks.com/thumbv2/azdokorg/10975949.0/21.918.210.700.634.887/fig-ii-md-cell-for-from-kurosaki-2001.webp)
B Functional Requirements
The multi-scale aspect of the materials simulation problem can be presented by two main phases that can be identified for the atomistic simulation tasks. CPU time (sec/MD timestep) for three parallel algorithms on 1024 processors of the Intel Paragon for different problem sizes.
C Current Tools and Approach
Planning to test and purchase the VASP ab-initio software package which has a better interface than Wien2K. Additionally, these codes enable simulations of chemical reactions of nuclear fission gases with cladding materials.
D Proposed Future Approach
It will be necessary to study the effects of interfacial strains and microstructural constraints; comparison of the kinetics versus thermodynamics for amorphous vs. Incorporate electronic properties into the classical MD: the potential functions will be corrected "in-fly" during the work of the main MD code.
A Background
With advances in computational capability, deterministic transport methods have advanced to handle configurations from one to two to three dimensions, and the handling of angle and energy has also been refined. The ad-hoc assumptions in such methods are well suited to experiments and operating experience to obtain acceptable results for existing reactors.
B Functional Requirements
In general, it is believed that the main source of uncertainty should be attributed to the cross-sectional data used in solving the neutron transport equation. A possible target could be an uncertainty, resulting from the solution method, of 50 pc. for the multiplication factor, and 0.2% for the energy distribution.
C Current Tools and Approach
This is the case of the Canadian code DRAGON [38] used to deal with specific CANDU problems. In the field of Monte Carlo codes, Los Alamos MCNP [46] is the widespread reference.
D Proposed Future Approach
Incorporating multiresolution into a new code would allow economy by allowing the level of approximation to vary over phase space; it should not be uniform but rather varied according to the physics of the problem. Finally, it can be expected that with advanced high-fidelity simulation that can be achieved with the proposed improvements in the solution of the neutron transport equations to be implemented in the next five years, it will be possible to achieve a level of uncertainty that comes only from methodological approximation, of 50 pcm on the eigenvalue, 0.5%.
A Background
B Functional Requirements
Various other simulations of nuclear power plants require models of thermal-hydraulic components that extend beyond the core, including the reactor vessel (especially for pool reactors), heat exchangers, steam generators, steam dryers, heat removal shutdown systems, and the spent fuel pool. The simultaneous solution of the Navier-Stokes equations in conjunction with the energy and species conservation equations lends itself to easy integration with chemical kinetics models such as CHEMKIN to optimize spent fuel reprocessing.
C Current Tools and Approach
Conjugate heat transfer to solve the energy equation between solid and fluid domains simultaneously. Quantifying the accuracy and uncertainty of the current generation of CFD software is not a trivial task and the results are application dependent.
D Proposed Future Approach
Current generation CFD tools with computational meshing conventions that allow accurate representation of realistic geometries typically use semi-implicit discrete solvers for transient simulation. All current generation commercial CFD tools are very sensitive to user specification of time step size.
A Background
B Functional Requirements
The K2 slump factor was developed to account for as-built configurations and is based on the difference between the structural information available to the analyst and the actual build configuration. The K3 slump factor was developed to account for material degradation and is based on the effect of material property degradation on the failure stress and structural load of the component.
C Current Tools and Approach
These reductions usually have values from 1 to 2 depending on the overall stress state of the material. SAP 2000: Finite element program for linear and nonlinear analysis of reinforced concrete and steel structures for general structural analysis of frame-type structures.
D Proposed Future Approach
Below is a brief description of the coupling of the structural mechanics code and the thermal-hydraulic (CFD), fuel behavior and neutronic codes. The fuel behavior code would provide the resulting internal forces of the fuel pins in the structural mechanics simulation.
A Background
The interconnection of three sets of input parameters in a formal system of equations provides a general representation of the difficult problem of fuel structure modeling. These load data are the results of the general solution of the equation system mentioned above.
B Functional Requirements
In addition to errors in material properties and thermomechanical model approximations, errors in reactor operating conditions can cause additional uncertainties in the calculated integral parameters. As shown in the table, codes 1-2 are D codes and each code has its own structural analysis approximations.
![Table 1. Summary of mechanistic fast reactors fuel performance codes [67].](https://thumb-ap.123doks.com/thumbv2/azdokorg/10975949.0/57.918.147.763.146.809/table-summary-mechanistic-fast-reactors-fuel-performance-codes.webp)
D Proposed Future Approach
Estimates from these detailed 3-D calculations, combined with high fidelity estimates of the operating parameters are expected to reduce the uncertainties in the FCCI estimates. However, given the uncertainties in the operating parameters, and the possible lack of experimental measurements to validate some of the detailed models, a 10% uncertainty would be more realistic for some of the parameters.
A Background
B Functional Requirements
C Current Tools and Approach
Not only are there limitations on the turbo-machinery side, but CFD tools for designing two-phase heat transfer devices such as steam generators are also limited. Not only are there opportunities for improvements in plant simulations, but also in AI diagnostics and control algorithms.
C Proposed Future Approach
For the development of turbomachines, the following specific data needs must be achieved by simulation alone. For the precooler (PC) and intercooler (IC), the following specific data requirements must be achieved by simulation alone.
A Background
Heat production in the fuel is quantified by models of decay heat production, fission rate and heat release. The release of heat from the fuel is limited by the thermal conductivity of the fuel material and the thermal resistance represented by the fuel/cladding interface, the cladding conductivity, and limitations of convective heat transfer at the cladding/coolant interface.
B Functional Requirements
At the cladding/coolant interface, the heat transfer capability is determined by the properties of the coolant and the flow rate. Uncertainties in the analysis must be quantified to a degree that meets a confidence level set by the regulator.
C Current Tools and Approaches
Beyond design basis failure analyzes (BDBA) are usually performed with "best estimate" modeling assumptions, that is, without considering uncertainties. For liquid metal fast reactors, the three most notable BDBA scenarios are 1) the unprotected transient overpower accident (UTOP), where one or more control rods are assumed to retract and the reactor scram system fails, 2) the unprotected loss-of-flow accident (ULOF), where it is assumed that the coolant pumps stop working and the reactor scram system fails, and 3) the unprotected heat sink accident (ULOHS), where normal heat rejection to the flow cycle is lost , and the reactor scram system fails. The SASSYS-1 calculation path is optimized for analysis of design basis accidents (DBA) and expected transients without scram (ATWS), and the SAS4A path is used to assess the consequences of severe accidents involving coolant boiling, cladding failure and fuel melt.
D Proposed Future Approach
From the regulator's perspective, the new capability should be seen as an evolutionary development of existing software, providing continuity with current practice. The new approach will replace certain components of the current hot channel technique with deterministic modeling, taking advantage of the performance of modern computer hardware to enable a more comprehensive analysis of the operating conditions and situations of reactors now limited by the imposing overly conservative uncertainty factors.
A. Aqueous Processing
A.1 Background
Plant operations must be scaled based on process stream volumes, processing times, and space requirements for specific equipment.
A.2 Functional Requirements
A.3 Current Tools and Approach
Third, the Aspen Tech packages are designed for the wide range of unit operations encountered in the chemical process industries and are therefore not optimized for a unique application such as a reprocessing plant. If this behavior is expected, adding additional extraction stages may result in the required decontamination.
A.4 Proposed Future Approach
At a more fundamental level, changes in the chemical structure of the extractant molecules can be computerized to achieve higher selectivity for specific elements. Such calculated structures can then be synthesized and tested in the laboratory to achieve the desired improvement in product selectivity and quality and be incorporated into new extraction processes.
B. Pyrochemical Processing
B.1 Background
Oxide ions are transferred to the cell anode and oxidized to produce oxygen gas, which is released from the cell. The cathode containing the base metals is transferred from the oxide reduction cell to the electrorefiner where it serves as the anode of the electrochemical cell.
B.2 Functional Requirements
In this electrolytic process, the spent fuel oxide is placed in the cathode of the cell, and when current is applied to the cell, the metal ions in the metal oxide are reduced to form the base metal, and oxide ions are released into the molten salt. LiCl – Li2O. Numerous opportunities exist for the use of advanced simulation tools for the pyrochemical treatment of spent advanced burner reactor fuel.
B.3 Current Tools and Approach
B.4 Future Tools and Approach
This simulation tool will allow the design of advanced fuel handling sheets, provide guidance for completing experimental flowsheet demonstration activities, and ultimately lead to the development of optimized flowsheets for pilot-scale evaluation. In close coordination with process flow sheet simulation, a tool will be developed for a virtual spent nuclear fuel treatment facility (eg, AFCF) based on pyrochemical processes.
A Background
In this case, the calculation of correlations between the design and the experiments allows you to determine how representative the latter is of the former, and therefore, to optimize the experiments and reduce their number. In the case of the Monte Carlo methodology [99], several runs of the same problems are performed with different random input values, taken within the specified uncertainty range and associated distribution law, and then finally the final results are statistically combined. in order to determine the mean value and associated standard deviation.
B Functional Requirements
Furthermore, if necessary (e.g. in security analysis), the link between the different fields should be covered by the sensitivity analysis capability. Due to the nature of the sensitivity evaluation (generally performed to first order approximation), the sensitivity coefficients may be calculated with a level of accuracy that is not the same as that of the high-fidelity calculation.
C Current Tools and Approach
The biggest disadvantage of the additional methodology is, as previously pointed out, related to the number of additional functions that must be calculated if there are a large number of objective parameters. Also inconvenient is the fact that the additional solution must be coded directly inside the code.
D Proposed Future Approach
Nevertheless, the adjustment procedures in advanced modern simulations, such as adaptive mesh refinement and iterative linear algebra with finite tolerance, make sensitivity calculations much less accurate. To address this one can use a modified PDE technique [121] which gives the same sensitivity results in the limit, but does not differentiate through the fitting procedures and results in much more robust sensitivity estimates.
A Background
While the ultimate motivation and most of the headlines are reserved for scientific and engineering results, some of the most complex problems and the greatest overall gains in efficiency come from sophisticated applications of these fundamental enabling technologies. Of course, designing a class of codes that efficiently utilizes state-of-the-art computing resources (ie, 100,000+ processors) for simulating first-principles physics requires a significant investment in supporting HPC tools.
B Functional Requirements
C Current Tools and Approach
D Proposed Future Approach
Rimpault, "Algorithmic Features of the ECCO Cell Code for Treating Heterogenous Fast Reactor Subassemblies", Intl. Nimal, «A Survey of TRIPOLI-4», Proceedings of the 8th International Conference on Radiation Shielding, Arlington, Texas, VSA, 24-28 April 1994, pp.
