Page 11 - Dynamics and Control of Nuclear Reactors

2 CHAPTER 1 Introduction

electrical circuits to mimic reactor operation. Next came hybrid computers. They
used digital computations along with analog components. The digital components
handled computations that were not possible or practical with analog components.
As digital computers became more powerful and faster, they came to dominate reac-
tor simulation activities.
Computer simulations may be performed on personal computers for some appli-
cations. Some solve model equations and provide numerical and/or graphical results.
Other, more sophisticated personal computer simulations provide screen displays
that mimic actual reactor control room displays.
Simulators for operator training include full-scope simulators that duplicate the
control room for the reactor being simulated. The displays provide computed results
for all of the variables monitored in the actual plant and include capability for sim-
ulating all operator actions.
Reactor accident analyses involve very detailed models that are implemented on
large, high-performance computers. Simulations deal with large disturbances with
potentially large consequences. Analyses include major accident scenarios such as
loss of coolant and control rod ejection.
This book addresses modeling and simulation of nuclear reactors, both zero-
power reactors and power reactors. Modeling options include a wide range of pos-
sibilities, each with very different levels of complexity. Modeling and simulation is
not a “do it and be finished” activity. Reactor constituents change continuously dur-
ing operation and immediately at restart after refueling. These changes cause
changes in the quantities that determine the reactor’s dynamic behavior. So, there
is no such thing as model or simulation that defines the reactor at all times. Further-
more, even trying to evaluate the parameters needed in a model is complicated by
the need to know neutronic and heat transfer properties that depend on position in
the core and the burnup history of the fuel and are difficult to evaluate. The impor-
tance of simulation is to provide a way to understand what goes on in a reactor and
why it happens rather than a precise determination of reactor dynamic response
behavior for a specific disturbance on a specific day.
There is very little in the book that requires detailed knowledge of reactor phys-
ics, but familiarity with reactor physics at least at the introductory level is helpful.

1.2 System dynamics and control design
Power generating units (such as a nuclear power plants, fossil-fueled power plants,
etc.) and large industrial facilities are complex systems. The design of these systems
requires extensive analysis that uses dynamic models and simulation of their oper-
ation under various conditions. Because of mathematical methods developed over
the past two centuries and computer capability developed since the 1950s, powerful
techniques exist for analysis of dynamic systems and for design of control systems. It
is now possible to predict the way a system will respond to external disturbances
and to develop a control strategy that will cause the system to perform as desired.