CFD Applications for Predicting Flow Behavior in Advanced Gas Cooled Reactors

Abstract

Nuclear energy plays an important role as a key instrument of sustainable energy supply. The 2011 U.S. EIA Annual Energy Outlook 2011 predicts a 21% growth in total energy consumption with electricity consumption growth returning to historic levels. Nuclear power can play a vital role in significantly reducing carbon emissions in the energy sector. According to the Nuclear Energy Institute (2008), nuclear energy is the nation’s largest emissions-free source of power, providing more than 20 percent of the country’s electricity and accounting for nearly 70 percent of U.S. emission-free power generation in 2009. Nuclear power generation emits virtually no greenhouses gases, making it a reliable power source that can provide the necessary energy to supply our growing economy while protecting the environment and ensuring the availability of energy. Advanced nuclear reactor concepts offer potential benefits over existing reactor designs. In this work, Computational Fluid Dynamics (CFD) is applied to improve the understanding of the complex flow behavior in proposed nuclear reactor designs, such as the Very High Temperature Reactor (VHTR) and Gas Cooled Fast Reactor (GFR). The prismatic VHTR reference design, based on the General Atomics Gas Turbine Modular Helium Reactor (GTMHR), is illustrated in Figure 1. The power conversion system (PCS) is shown to the left of the reactor. Helium coolant flows through the annulus of the hot duct as it returns from the PCS and through the annulus of the reactor vessel wall to the upper plenum. The coolant then travels downward through the fueled portion of the reactor core and into the lower plenum. The heated coolant flows out of the lower plenum and through the center of the hot duct back to the PCS to complete the cycle. The core has an annular layout with an inner and an outer reflector as well as upper and lower reflectors (graphite blocks are shown in white in Figure 1). The GFR system features a fast neutron spectrum, helium-cooled reactor and closed fuel cycle. It can be operated at high temperatures, has a high thermal efficiency due to the high temperature reached by the coolant, and being chemically inert by nature, the coolant does not react with the structural materials in the core. The hot gases can be coupled to a directcycle helium turbine for electricity generation and/or to a heat exchanger where the process heat is used to produce hydrogen via high temperature steam electrolysis (O’Brien et al. 2007). Through the combination of a fast spectrum and full recycle of actinides, the GFR minimizes the production of long-lived radioactive waste. The GFR’s fast spectrum also