|dc.description.abstract||The Pebble Bed Modular Reactor (PBMR) is a graphite-moderated, helium-cooled reactor that uses
the Brayton direct gas cycle to convert the heat, which is generated in the core by nuclear fission.
The heat is transferred to the coolant gas (helium), and converted into electrical energy by means of
a gas turbo-generator.
The Pebble Bed Micro Model (PBMM) is a model that was developed to demonstrate the operation
of the closed, recuperative three-shaft Brayton cycle in order to gain a better understanding of its
dynamic behaviour and to demonstrate the control strategies that will eventually be used in the
PBMR. It is also used to demonstrate the ability of Flownex to simulate the integrated performance
of the cycle.
Flownex is a general-purpose thermal-fluid network analysis code. It solves the flow, pressure and
temperature distribution in large unstructured thermal-fluid networks and provides the engineer or
designer with essential information about the interaction between network components. Flownex
can handle a wide variety of network components such as pipes, pumps, orifices, heat exchangers,
compressors, turbines, controllers and valves. A complete Flownex model of the PBMM exists and
will be used throughout the entire project.
The start-up and shutdown sequences of the Pebble Bed Modular Reactor (PBMR) is characterised
by numerous checks and control actions that occur in a very specific order. This order of events and
continuous checking of important system parameters are intuitively based on rules that inherently
describe the safe and preferred operating region of the plant.
Presently most of the sequences and actions are performed by an expert who knows the system very
well. Some of the sequences and actions are controlled by simple controllers and are only activated
by the operator.
A need therefore exists to capture the different control events of the start-up and shutdown
sequences in a control model or method. A control model or method was developed to control the
start-up and shutdown sequence of the PBMM model in Flownex. The control method was
implemented in SIMULINK® as there is an existing interface between Flownex and SIMULINK®.
The control method directly controls the procedures of start-up and shutdown through the Flownex/
SIMULINK® interface. The most important system parameters are monitored and adjustments are
automatically made by the control method in response to system changes. A graphical user interface
allows a user to manually activate start-up and shutdown.
The aim of the project is to develop a controller that can control the PBMM through start-up as
well as shutdown. Special emphasis is placed on critical transitions and pressure considerations due
to the control of the start-up blower system rotational speed. The project establishes expertise in the
control of the start-up and shutdown sequence of the PBMM in Flownex.
Flownex was successfully used as a modelling platform to simulate the normal and dynamic
operation of the PBMM. Identification of start-up and shutdown was a result of investigating the
start-up and shutdown checklist documents as well as a detailed consideration of data captured by
the PBMM. A control method was implemented in SIMULINK® and controls start-up and
shutdown through the Flownex/SIMULINK® interface. A graphical user interface allows in time
system changes by a user. Data captured by the simulation model was evaluated against data
captured from the real system.||