Thermal hydraulic design of a salt-cooled highly efficient environmentally friendly reactor

Abstract

A 1 OOOMWth liquid-salt cooled thermal spectrum reactor was designed with a long fuel cycle, and high core exit temperature. These features are desirable in a reactor designed to provide process heat applications such as oil refinery needs of heat and electricity. The reactor uses the binary salt NaF-BeF₂ as the primary coolant, and uses U-Zr-H as fuel and to provide neutron moderation. Design options were studied under the constraints of maximum fuel temperature of 720[degree]C, and a vessel wall temperature similar to today's reactors (i.e. limited to 430[degree]C). The selected design achieves a core power density of 26.35 kW/1 and can achieve a 10 year core lifetime before refueling. The core has a pressure drop of 1.03 MPa, and uses a hexagonal lattice with small, 7mm outer diameter fuel pins. The pins are arranged in a tight 1.08 pitch-to-diameter ratio, and use wire wrap spacers and assembly ducts for mechanical support. Silicon carbide is used for cladding, and the fuel-clad gap is filled with a low-melting point liquid metal to act as a thermal bond between the fuel and the cladding. The core is encircled with two rows of reflector assemblies and one row of thermal shield assemblies. A layer of graphite provides thermal insulation to the reactor vessel.

(cont.) The primary coolant is coupled to a CO₂ power cycle via heat exchangers located above the core in the same vessel. The reactor vessel is 8.5m in diameter and 15.3m tall, which achieves the goal of a vessel that can be produced off-site and transported via barge, but not by truck or train. The intermediate heat exchanger is designed with 1 cm outer diameter tubing with internal helical ribs. The tubes are arranged in a square array with a pitch to diameter ratio of 1.2. With a core exit temperature of 570[degree]C, the supercritical CO₂ power conversion system achieves, according to previous studies at MIT, a net efficiency of 45.7%. A comparison is made to other integral medium reactors (i.e those with the heat exchanger and the core in the same vessel). This reactor has the advantage of low pressure and high thermal conversion ratio compared to the IRIS water cooled reactor.