Elsevier

Nuclear Engineering and Design

Volume 282, February 2015, Pages 93-105
Nuclear Engineering and Design

Three dimensional neutronic/thermal-hydraulic coupled simulation of MSR in transient state condition

https://doi.org/10.1016/j.nucengdes.2014.11.026Get rights and content

Highlights

  • Developed a three dimensional neutronic/thermal-hydraulic coupled transient analysis code for MSR.

  • Investigated the neutron distribution and thermal-hydraulic characters of the core under transient condition.

  • Analyzed three different transient conditions of inlet temperature drop, reactivity jump and pump coastdown.

Abstract

MSR (molten salt reactor) use liquid molten salt as coolant and fuel solvent, which was the only one liquid reactor of six Generation IV reactor types. As a liquid reactor the physical property of reactor was significantly influenced by fuel salt flow and the conventional analysis methods applied in solid fuel reactors are not applicable for this type of reactors. The present work developed a three dimensional neutronic/thermal-hydraulic coupled code investigated the neutronics and thermo-hydraulics characteristics of the core in transient condition based on neutron diffusion theory and numerical heat transfer. The code consists of two group neutron diffusion equations for fast and thermal neutron fluxes and six group balance equations for delayed neutron precursors. The code was separately validated by neutron benchmark and flow and heat transfer benchmark. Three different transient conditions was analyzed with inlet temperature drop, reactivity jump and pump coastdown. The results provide some valuable information in design and research this kind of reactor.

Introduction

The concept of MSR was first presented in the late 1940s for a purpose to develop a nuclear powered airplane (Rosenthal et al., 1970). As a liquid reactor molten salt reactor it has several advantages: Neutron economy, inherent safety, non-proliferation attributes and continuous refueling etc, which enable the transmutation in MSR and the possibility of continuous or in-batch reprocessing reduces the need of high initial fuel load and almost can eliminated the risk of rupture which may lead to radiation contamination of environment. MSR was chosen to be one of the six candidates for the generation IV reactor systems (GIF, 2002). Therefore, different new concept molten salt reactors have been worldwide studied and developed. Mitachi et al. (1995) proposed a small molten salt reactor (SMSR) for utilization of thorium and plutonium from light water reactors. Ignatiev (2003) developed a new molten salt reactor concept molten salt advanced reactor transmuter (MOSART), which was developed for burning plutonium and minor actinides, and also other molten salt reactor concept was developed.

The fuel in MSR was dissolved in the fluid salt and flowing with the fluid through primary loop thus the delayed neutrons precursors were drifted by the fuel flow. For the influence of fluid flow the neutron kinetics and thermohydraulics of MSR is different to the reactor with solid fuel and highly related each other, especially when transient analysis, which lead to conventional analysis methods for the reactors using solid fuels not being applicable for molten salt reactors and many investigations have been done about this. Křepel et al. (2007) developed a code: DYN3D-MSR and do some transients investigate about the 3D neutronics and parallel channel thermal-hydraulics of MSR, where space-dependant efforts are relevant, like local blockage of fuel channels or local temperature perturbations. Zhang et al. (2009) use neutron diffusion theory develops a code analyzed the relative power changes and the distributions of temperature, neutron fluxes and delayed neutron precursors during three transient conditions including rods drop transient, pump coast down transient and inlet temperature drop. Wang et al. (2006) applied SIMMER-III code studied the thermal hydraulics performance of the MOSART. Hoogmoed (2009) developed a coupled code investigated the steady state condition of TMSR-NM based on DALTON and HEAT codes. Aufiero et al., 2014a, Aufiero et al., 2014b use Monte Carlo method coupling with OpenFOAM did some three dimensional calculation about MSFR, but Monte Carlo method may need more computation.

Although many investigations have carried out by several authors and achieved many positive result, but the molten salt reactors and the objectives they focused on are usually different and most of them are two dimensional analyses or use point kinetics model to analyzing which was not accurate in transient analysis. Some three dimensional calculation are outer-coupling, which was difficult to extend. As a complex three dimensional structure, two dimensional analysis can’t accurate reflect the realistic condition of molten salt reactor and only give a approximate result of which. In this paper, developed a three dimensional coupled code for MSR and applied to MOSART, investigated some transient characteristics of reactor.

Section snippets

Simulation model of MSR

In present study a homogenous reactor concept MOSART (Ignatiev et al., 2007) was selected as the research objective, compared with other molten salt reactor which does not contain graphite or other structure elements in the core. Some principal design data for MOSART fuel circuit relevant in our study were given in Table 1. The systematic diagram of the MSR was shown in Fig. 1. In normal conditions mass flow rate of salt in the core is 10000 kg/s, average axial velocity of stream in the core is

Theoretical model

To develop a coupled code and solve with a same solver, a uniform theoretical model of physical and heat transfer must be established. The physical models and the thermo hydraulics model were expressed separately and uniform model were built.

Grid dependency

The sensitivities of the grid dependence are analyzed under the reactivity jump condition, two different uniform grid systems were used in this paper. The velocity distribution of the core in middle section of the height along the radius with 42 × 80 × 42 and 54 × 120 × 54 grids were shown in Fig. 3.

The profile shown that the difference between two grids is very little and consider about the conservation of the CPU time the 42 × 80 × 42 grid was used for simulation.

Validation of the calculation code

The code was separately validated by

Results and discussion

In this section analyzed the thermal-hydraulic characteristics and neutronics properties of MOSART in three kinds of transient conditions, inlet temperature drop transient, reactivity jump transient and pump coastdown. All of these three transient calculations start from the same initial steady state condition, and the distributions of neutron fluxes, delayed neutron precursors, temperature and velocity varies with time were shown in below.

Conclusion

In present work, a three dimensional neutronic model considering the flow effects of the fuel salt was established for the molten salt reactors, and solved by developing a microcomputer code coupling with a flow and heat transfer model in the core. The founded models and developed code are applied to analyze the transient characteristics of the MOSART. Three kinds of transient conditions including inlet temperature drop, reactivity jump and pump coastdown are analyzed. The results show that the

Acknowledgment

This work is carried out under the financial support of the National Natural Science Foundation of China (grant no. 91026023) and (grant no. 91326201).

References (19)

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