Elsevier

Nuclear Engineering and Design

Volume 319, 1 August 2017, Pages 163-175
Nuclear Engineering and Design

Three-dimensional hydrodynamic modeling of the second shutdown system of an experimental nuclear reactor

https://doi.org/10.1016/j.nucengdes.2017.04.024Get rights and content

Highlights

  • A CFD analysis was conducted for calculating the dynamics of the SSS of an experimental nuclear reactor.

  • The numerical model solves coupled dimensionally heterogeneous systems using dynamic boundary conditions.

  • The numerical model captures all the features of the physical phenomena.

  • Details of 3D CFD simulation and validation procedure are outlined.

  • The validated multiscale model points out that safety requirements are accomplished by the SSS of RA-10 project.

Abstract

A three-dimensional (3D) computational fluid dynamics (CFD) model is presented for the Second Shutdown System (SSS) of the experimental nuclear reactor RA-10 under design and construction by the Argentinian National Commission of Atomic Energy (CNEA). The RA-10 SSS consists on the drainage of the reflector tank surrounding the reactor core through a system of pipes in a limited amount of time solely by the action of gravity. The CFD model focuses on the 3D modeling of the reflector tank hydrodynamics and links the effects of the draining piping system through dynamics boundary conditions. The CFD model is first applied to a similar system, the RA-10 SSS Mockup, for which experimental data is available. Reasonable agreement is observed between the CFD model and the experimental observations for the RA-10 SSS Mockup. Finally, the validated CFD model is applied to the RA-10 SSS. The model results show that the performance of the RA-10 SSS meets the design requirements.

Introduction

The RA-10 is a new 30 MWth multipurpose nuclear Research Reactor (RR) currently under design and construction by the Argentinian National Commission of Atomic Energy (CNEA) (Blaumann et al., 2013). The main objective of RA-10 will be the production of radioisotopes for medical purposes. This reactor will also provide irradiation testing facilities with neutron fluxes of the order of 1014ncm2 to support CNEA programs on material sciences and on nuclear fuels design. The reactor irradiation facilities are located in the heavy water reflector tank surrounding the reactor core (see Fig. 1a).

The heavy water in the reflector tank plays a central role in diminishing the neutron losses by increasing neutron re-entrance to the reactor core. The drainage of the reflector tank provides a redundant and independent safety system by allowing neutron losses from the reactor core. This is called the reactor Second Shutdown System (SSS). The reactor First Shutdown System (FSS) is based on the insertion of control rods.

Safety requirements to the RA-10 SSS demand the reflector tank to be drained to half its volume in a limited amount of time (55% of its height after 15 s) solely by the action of gravity. A three-dimensional (3D) computational fluid dynamic (CFD) model of the RA-10 SSS has been performed in order to confirm that safety requirements are met. The RA-10 SSS is composed by three different subsystems (see Fig. 1b): the reflector tank, the drainage network subsystem and the pressure equalization subsystem.

The reflector tank drainage involves complicated 3D free surface hydrodynamics, which has to be modeled in detail. On the other hand, the flow through the drainage and pressure equalization subsystems can be simplified and described by zero-dimensional models. This decomposition and conceptualization strategy was proved to be effective in similar problems (Leiva et al., 2010, Leiva et al., 2011. The challenge in this modeling approach is to solve the coupled system (Buscaglia et al., 2005).

The hydrodynamic modeling of the RA-10 SSS implemented in this work focuses on the 3D CFD modeling of the reflector tank. The interaction between the reflector tank subsystem and the drainage and pressure equalization subsystems is made possible by implementing dynamic boundary conditions in the 3D CFD modeling using a weak-coupling technique. The 3D CFD model is first applied to the RA-10 SSS Mockup for which experimental data is available. The validated model is then employed to make predictions on the performance of the RA-10 SSS.

This work is organized as follows. Section (2) describes the main features of the RA-10 SSS. Section (3) presents the 3D CFD model of the reflector tank together with the strategy for connecting the different subsystems by dynamics boundary conditions. Section (4) presents validation results by comparing experimental observations to the 3D CFD model results of the RA-10 SSS Mockup. Section (5) presents the results of the 3D CFD model applied to the RA-10 SSS. Finally in Section (6), the conclusions are summarized.

Section snippets

General description of the RA-10 SSS.

The RA-10 SSS is mainly composed by three subsystems: the reflector tank, the discharge hydraulic net and the pressure equalization line. A simple diagram is shown in Fig. 1b. When the SSS is required to act, a manifold of six valves located in the discharge hydraulic net opens and the heavy water starts to drain solely by the action of gravity. The heavy water flows from the reflector tank through the discharge net to a storage tank located below the reactor core level. The pressure at the

Three-dimensional computational fluid dynamic model for the reflector tank

The reflector tank geometry is shown in Fig. 1a. All the irradiation facilities are housed inside the reflector tank, which generate a complicated geometry of the system to model. On the other hand, as the reflector tank drains, helium fills the system generating a free surface flow. In order to incorporate these features in the modeling process, the incompressible, isothermal, multiphase solver interFoam based on OpenFOAM(R) libraries Version 2.2.2 (Greenshields, 2013, Greenshields, 2013,

RA-10 SSS Mockup experimental data

The position of the free-surface has been measured in a local manner in the RA-10 SSS Mockup facility (Garnero, 2014, Rechiman et al., 2015. This information was used in the validation procedure of the 3D CFD model. The position of the interface was track on a vertical ruler along the depth of the RA10-SSS Mockup tank by using a video camera. It is important to point out that the time evolution of the system starts (t=0) when the free-surface cross the junction between the upper part of the

Results in the geometry of interest of RA-10 SSS

The validated 3D-0D CFD model was applied to the geometry of interest of RA-10 SSS. Two cases have been studied, the same two cases than for RA-10 SSS Mockup.

Fig. 8 shows the 3D time evolution of the free-surface. After the plug fall into the tank the wave motion vanish and the free-surface is nearly plannar. The draining with a nearly plannar surface continue until the gas first enter to discharge patch at t7.8s. A distortion of free-surface in the surrounding of discharge box occurs. Finally

Conclusions

In the present work we have presented and discussed the results of a free-surface 3D CFD model applied to two geometrical configurations, the RA-10 SSS Mockup geometry and the RA-10 SSS geometry.

There were two main objectives in this paper. The first one was to validate the 3D-0D coupled methodology by comparing our results with theoretical and experimental data available for the RA-10 SSS Mockup configuration. The second one was to present a detailed analysis of the SSS performance for the

Acknowledgments

The authors acknowledge support from RA-10 project and Comisión Nacional de Energía Atómica (CNEA). We thanks to CIMEC from Universidad Nacional del Litoral for their support when endeavoring the first steps with OpenFOAM. We would also like to thank all the contributors in CFD online and OpenFOAM community.

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