Natural circulation cooling into the MYRRHA reactor

SCK•CEN Mentor

Keijers Steven, skeijers@sckcen.be, +32 (0)14 33 34 53

Expert group

Nuclear Technology Engineering

SCK•CEN Co-mentor

Van Tichelen Katrien , kvtichel@sckcen.be , +32 (0)14 33 80 06

Introduction

MYRRHA (Multi-purpose HYbrid Research Reactor for High-tech Applications) is a multifunctional research nuclear reactor, conceived as an accelerator driven system (ADS), able to operate in sub-critical and critical modes. It consists of a proton accelerator of 600 MeV, a spallation neutron source and a nuclear core with MOX fuel, cooled by liquid lead-bismuth eutectic.
MYRRHA will be a flexible fast spectrum irradiation facility for material development, study of transmutation of high level nuclear waste and the production of radioisotopes for medical and industrial applications.
This thesis focus on safety aspects of the reactor system during postulated incidents in which the coolant pumps fail or are not available.  In these conditions the cooling of the reactor is assured by natural circulation.
Several heat sources and heat sinks are present in the system and should be quasi balanced in all conditions to meet the temperature criteria on the different components.
The main heat source is the decay heat of the fuel assemblies. These fuel assemblies can be into the core of the reactor, into the in-vessel fuel storage or a combination of the two positions depending on the operational state of the system.  
Another heat source is the decay heat of Polonium formed during operation within the coolant.
The heat sinks are the primary heat exchangers and/or a back up system formed by the reactor vault cooling system.
The different positions of heat sources and sinks create different natural circulation cooling flow patterns into the lead bismuth.

Objective

The goal of this master thesis is to investigate the possibility to build a representative mock up which allows the investigation of different natural circulation flow patterns.
At first the phenomena important for the natural circulation cooling shall be identified and quantified with relevant non-dimensional numbers. Based on these numbers a simplified mock up shall be sketched which allows a flexible positioning of heat sources and sinks.
Finally, a CFD model of the mock up shall be constructed to make an evaluation of the flow patterns and the stability with respect to the relative positions of the sources and sinks.
An in-depth investigation of the different modelling options (boundary conditions, turbulence, mesh), geometry and properties (porosity, power) should allow to estimate the key parameters of the natural circulation cooling and to generate a stability map of the installation.

Scientific approach
-literature study on natural circulation in pool type reactors (recent updates)
-determining relevant non-dimensional numbers and sketch a representative mock up based on scaling  
-modelling the designed mock up within a general purpose CFD code (ANSYS CFX or Fluent)
-investigating the key parameters for the positioning of the heat sources and sinks
-analyzing the results
-evaluation of the safety significance
-reporting of the work performed.
Required experience
This thesis requires some experience with computational fluid dynamics. Insight into physics and thermal hydraulics

The student should have affinity to computer work, be persistent and precise.

The minimum diploma level of the candidate needs to be

Academic bachelor

The candidate needs to have a background in

Mathematics , Physics , thermal hydraulics