Emilian L. Popov

STUDY OF FUKUSHIMA DAIICHI NUCLEAR POWER STATION UNIT 4 SPENT-FUEL POOL

A study on the Fukushima Daiichi nuclear power station spent-fuel pool (SFP) at Unit 4 (SFP4) is presented in this paper. We discuss the design characteristics of SFP4 and its decay heat load in detail and provide a model that we developed to estimate the SFP evaporation rate based on the SFP temperature. The SFP level of SFP4 following the March 11, 2011, accident is predicted based on the fundamental conservation laws of mass and energy. Our predicted SFP level and temperatures are in good agreement with measured data and are consistent with Tokyo Electric Power Company evaluation results.

Simulation of the flow rotation and mixing in the downcomer of a VVER-1000 reactor

Flow rotation and mixing in a VVER-1000 reactor is investigated using two system codes with three-dimensional fluid-dynamics modeling capabilities (RELAP5-3D and TRACE) and a computational fluid-dynamics (CFD) code (FLUENT). Coarse-mesh models were developed for the system codes, and their applicability is evaluated using the test data as well as the detailed CFD results obtained. Two different temperature zone mapping schemes for comparison with the measured data are proposed and discussed. The test is very informative when used to examine the real loop mixing taking place at a nuclear reactor. The results can be used to improve code input data for correct simulation of the phenomenon. Correctly predicting the flow mixing is very important in regard to the prediction of the local three-dimensional feedback effects depending on the vessel mixing in coupled three-dimensional neutron-kinetic/thermal-hydraulic safety analysis of reactivity insertion accidents such as the main steam line break accident.

VVER-1000 Model Assessment Using RELAP5-3D

Detailed thermal-hydraulic analysis of commercial power reactors requires modeling of complex multidimensional thermal, fluids, and neutronic behavior. One code that has three-dimensional (3-D) thermal-hydraulic and neutronic capabilities is RELAP-3D. A comparison of RELAP-3D predictions to experimental data obtained during start-up of the Kozloduy VVER-1000 nuclear power plant in Bulgaria is presented here. The experiment has distinguishable 3-D hydraulics effects that allow for code model verification and reasonable agreement with the experimental results obtained. The transient investigated was conducted at 29% reactor power, and it was initiated from a steady state where three out of four reactor coolant pumps were operating. The transient consisted of the start-up of the nonoperating pump. Simulation results were compared to both temperature and pump data from the experiment. Temperature predictions compared reasonably well to the experimental data; however, discrepancies existed between predicted and experimental pump head values.

Report on UQ Assessments to support SESAME wire-wrapped bundle experiment

This work assesses the influence of assumptions made when generating a mesh of a wire-wrapped geometry. The contact region between a wire and its adjacent pin is commonly modeled by either embedding the wire to the adjacent pin or trimming the wire so that a gap separates the wire from its adjacent pin. These models are referred to as closed-gap and open-gap approaches herein and are applied to two geometries. The first geometry consists of a single pin wire-wrapped subchannel. A polyhedral mesh and a hexahedral mesh are generated. The second and third geometries are a 7and 19-pin wire-wrapped bundles meshed with polyhedral elements only. Pressure drops are obtained with the STAR-CCM+ computational fluid dynamic (CFD) package. Sensitivity analyses of the mesh density, the mesh type, and the turbulent models are performed. Numerical results show that the best matches to the experimental data and to the Cheng-Todreas correlation are obtained with the combination of a hexahedral mesh, the shear stress transport (SST) turbulent model, and the open-gap approach. In the case of the 7-pin geometry, the best results are obtained with the open-gap approach and the SST turbulent model. The 19-pin geometry yields contradictory results to the 7-pin geometry results, and thus will require further investigations.

Dakota Uncertainty Quantification Methods Applied to the CFD code Nek5000

This report presents the state of advancement of a Nuclear Energy Advanced Modeling and Simulation (NEAMS) project to characterize the uncertainty of the computational fluid dynamics (CFD) code Nek5000 using the Dakota package for flows encountered in the nuclear engineering industry. Nek5000 is a high-order spectral element CFD code developed at Argonne National Laboratory for high-resolution spectral-filtered large eddy simulations (LESs) and unsteady Reynolds-averaged Navier-Stokes (URANS) simulations.

Modeling and Simulation of the ITER First Wall/Blanket Primary Heat Transfer System

Abstract ITER inductive power operation is modeled and simulated using a thermal-hydraulics system code (RELAP5) integrated with a 3-D CFD (SC-Tetra) code. The Primary Heat Transfer System (PHTS) functions are predicted together with the main parameters operational ranges. The control algorithm strategy and derivation are summarized as well. The First Wall and Blanket modules are the primary components of PHTS, used to remove the major part of the thermal heat from the plasma. The modules represent a set of flow channels in solid metal structure that serve to absorb the radiation heat and nuclear heating from the fusion reactions and to provide shield for the vacuum vessel. The blanket modules are water cooled. The cooling is forced convective with constant blanket inlet temperature and mass flow rate. Three independent water loops supply coolant to the three blanket sectors. The main equipment of each loop consists of a pump, a steam pressurizer and a heat exchanger. A major feature of ITER is the pulsed operation. The plasma does not burn continuously, but on intervals with large periods of no power between them. This specific feature causes design challenges to accommodate the thermal expansion of the coolant during the pulse period and requires active temperature control to maintain a constant blanket inlet temperature.

RELAP5 MODEL OF THE DIVERTOR PRIMARY HEAT TRANSFER SYSTEM

This report describes the RELAP5 model that has been developed for the divertor primary heat transfer system (PHTS). The model is intended to be used to examine the transient performance of the divertor PHTS and evaluate control schemes necessary to maintain parameters within acceptable limits during transients. Some preliminary results are presented to show the maturity of the model and examine general divertor PHTS transient behavior. The model can be used as a starting point for developing transient modeling capability, including control system modeling, safety evaluations, etc., and is not intended to represent the final divertor PHTS design. Preliminary calculations using the models indicate that during normal pulsed operation, present pressurizer controls may not be sufficient to keep system pressures within their desired range. Additional divertor PHTS and control system design efforts may be required to ensure system pressure fluctuation during normal operation remains within specified limits.

MEASURED AND CALCULATED HEATING AND DOSE RATES FOR THE HFIR HB4 BEAM TUBE AND COLD SOURCE

The High Flux Isotope Reactor at the Oak Ridge National Laboratory was upgraded to install a cold source in horizontal beam tube number 4. Calculations were performed and measurements were made to determine heating within the cold source and dose rates within and outside a shield tunnel surrounding the beam tube. This report briefly describes the calculations and presents comparisons of the measured and calculated results. Some calculated dose rates are in fair to good agreement with the measured results while others, particularly those at the shield interfaces, differ greatly from the measured results. Calculated neutron exposure to the Teflon seals in the hydrogen transfer line is about one fourth of the measured value, underpredicting the lifetime by a factor of four. The calculated cold source heating is in good agreement with the measured heating.