Object-Oriented Modelling for Integral Nuclear Reactors Dynamic Simulation
A. Cammi*, F. Casella§, M. E. Ricotti*, F. Schiavo§
Politecnico di Milano
* Department of Nuclear Engineering
via Ponzio 34/3, 20133 Milano, Italy
Phone: +39-02-2399 6325, Fax: +39-02-2399 6309, E-mail: marco.ricotti@polimi.it
§ Department of Electronics and Information
via Ponzio 34/5, 20133 Milano, Italy
Abstract - In recent years a renewed interest in the
study and design of innovative reactors has risen, as
demonstrated by the international R&D effort primed
by Generation IV and NERI programmes. In
particular, Integral Reactor concepts have been
proposed with new features in terms of plant
components and safety systems. The IRIS reactor is
one of these innovative projects. As far as the
investigation of the plant dynamics is concerned,
reliable and effective tools for the numerical
simulation of the accident transient behaviour are
certainly available, validated and well recognized. The
same consideration seems not straightforwardly
applicable for tools allowing the rapid evaluation of
different solutions in the design phase or for control
purposes. Recent advances in the field of objectoriented,
multi-physics, dynamic system modelling led
to the definition of the Modelica language,
representing a viable path to achieve the capital goals
of modularity, openness, efficiency, tool support. The
language definition is open-source and it has already
been successfully adopted in different fields of
engineering. This language has been adopted to set up
libraries (namely ThermoPower and NUKOMP) of
physical models and components, suitable for the
implementation of nuclear power plant simulators. In
the paper, a first version of the simulator for the IRIS
integral reactor is presented, together with some
preliminary results referred to the dynamic response
of the reactor to stepwise forcing functions.
I. INTRODUCTION
Dynamic simulation plays a key role in the design phase
of the main systems for nuclear reactors. This statement
applies with emphasis when the study of an innovative,
integral reactor is undertaken. Suitable dynamic models
must be set up in order to evaluate different design
solutions during the phase of concept development, to
simulate the behaviour of the reactor in nominal and
accident conditions as well as the control system strategy.
As far as the simulation for safety analysis purposes is
concerned, several codes have been developed and are
available nowadays (e.g. RELAP, TRAC, ATHLET,
CATHARE) while, on the contrary, modelling and
simulation tools for the Dynamics & Control task for
reactors and nuclear power plants are not at the same
level of development and are still required. The tools
have to demonstrate a sufficient level of accuracy so as to
represent a wide range of operating conditions and
transients, at a viable computational effort.
As a statement of general validity, the key features for an
optimal reactor system simulator appears to be: a)
Modularity: the system model should be built by
connecting the models of its components, which have to
be written independently of their boundary conditions; b)
Openness: the code of each component model should be
clearly readable, close to the original equations and easily
customised by the experienced user; c) Efficiency: the
simulation code should be fast; d) Tool support: the
simulation tool should be based on reliable, accurate,
tested and well-documented software.
Few simulation environments and tools fulfilling at once
all the above mentioned characteristics seem to be
currently available for nuclear applications. Recent
advances in the field of object-oriented, multi-physics,
dynamic system modelling led to the definition of the
Modelica language, representing a viable path to achieve
the above-mentioned goals. The language definition is
open-source and it has already been successfully adopted
in different fields, as automotive, robotics, thermohydraulic
systems, mechatronic systems.
In this frame, specific models for nuclear reactor
components have been developed, to be applied for the
dynamic simulation of the IRIS integral reactor albeit
keeping general validity for PWR plants. The IRIS
(International Reactor Innovative and Secure) project,
described in [Carelli, 2003] and [Carelli et al., 2004],
involves 21 organizations from 10 countries and refers to
the design of an innovative, light water reactor with a
modular, integral primary system configuration. This type
of reactor is designed to satisfy four key requirements:
enhanced safety, improved economics, proliferation
resistance and waste minimisation. IRIS is a pressurized
water reactor having a medium power size (up to 335
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