Abstract
Molten Salt Reactors are Gen-IV reactors that use liquid fuel. Fluid fuel allows continuous removal of fission gases as well as batch fuel reprocessing. With these control mechanisms the system can be sustained within the desired operating temperature range and required power output. These methods rely on the presence of a chemical processing plant on-site that adds complexity. This also creates a risk of processing plant unavailability due to faults, emergency downtime or maintenance. The work considers variation of fuel salt flow rate in Molten Salt Reactors as a means of controlling reactor operation without using reprocessing. The analysis is performed using the Molten Salt Fast Reactor as an example. An extended version of the SERPENT Monte-Carlo transport code coupled with OpenFOAM generic platform were used for capturing delayed neutron drift, decay heat, gaseous fission product removal, calculating fuel salt velocity vectors and the fuel temperature distribution. The two models were coupled via a script that accounted for reactivity insertion between time steps and the changes caused in the fission power. Results confirm that, while operating at constant power, the difference between fuel inlet and outlet temperatures increase as the flow rate decreases. Burnup analysis has shown that while the average fuel temperature continues to reduce with time, the difference between inlet and outlet temperatures can be controlled by varying the flow rate while maintaining constant power. Finally, the variation in the fuel flow rate has been shown to extend the reactor operating time with no insertion of additional fissile inventory.
Highlights
Molten Salt Reactors (MSRs) are one type of the Generation IV reactors [1]
This study investigates if the MSR control can be performed by varying the parameters that are independent from fuel salt reprocessing, such as pump rate
At lower flow rates constant inlet temperature of 850 K leads to an increase in average core temperature, which causes the suppression of keff due to negative temperature coefficient, resulting in power reduction and a consequent reduction of the outlet temperature
Summary
Molten Salt Reactors (MSRs) are one type of the Generation IV reactors [1]. The concept originates from the Aircraft Reactor Experiment in Oak Ridge National Laboratory [2]. The MSR use molten salt as the fuel that, in majority of the designs [3]–[9], is circulated between the core and the heat exchangers. In the event of lack of fissile material or reprocessing plant down-time the temperature will be decreasing. The MSFR is a MSR design developed during the Safety Assessment of the Molten Salt Fast Reactor (SAMOFAR) project. The reactor includes a nonmoderated core of 1.25 m radius, 2.5 m height and 16 heat exchanger loops which allow the fuel salt to be transferred to the heat exchangers and to the reprocessing plant [11], [12], see Figure 2.1. The fuel salt composition is LiF-UF4-ThF4 with 22.5% of heavy nuclei, 3% U233, the salt density at 900 K was assumed to be 4.3 g/cm
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