Page 10 - Dynamics and Control of Nuclear Reactors

CHAPTER

1
Introduction

1.1 Introduction
The power level of a nuclear reactor at any time is expected to be as desired by the
plant operator. These plants undergo transients that are induced by operator actions,
by actions initiated by an automatic control system, or by a component failure.
Designers and operators must understand the transient behavior in order to achieve
desired operation and safety.
The first step is to understand the transient operation of a reactor that operates at a
low power level, so low that there are negligible increases in temperature because of
fission heating. Such a reactor is usually called a zero-power reactor. The power is
not actually zero, but is so low that significant heating does not occur, and temper-
ature related feedback effects are negligible. Many research reactors are zero-power
reactors.
A power reactor, on the other hand, operates at power levels high enough to cause
major temperature increases. The temperatures of reactor components change along
with reactor power during transients and these temperature changes, in turn, affect
reactor power (a feedback loop). Also, power reactors that contain a compressible
fluid undergo pressure changes during a transient. These pressure changes also affect
reactor power (another feedback loop).
Transients are usually accompanied by control actions. Control systems monitor
selected plant parameters (such as power, temperature, pressure, flow rate) and
change appropriate controllable actions (such as control rods and valve positions).
Creating a set of mathematical equations and parameters (coefficients) in those
equations to be used to analyze reactor transients is called modeling. Creating a solu-
tion to those equations is called system simulation.
Nuclear reactor simulations generally have one of three purposes: obtaining a
basic understanding of reactor behavior during transients, analysis of transients dur-
ing normal maneuvering and response during accident conditions, and operator train-
ing. Each of these functions has different requirements for the level of detail in
the model.
Reactor simulation efforts started in the early days of reactor operation. Early
simulation involved hand calculations and rudimentary calculators. Shortly thereaf-
ter, reactor simulation turned to computers for implementation, and simulation
technology matured as the capabilities of computer technology evolved. Analog
computers were used extensively in early simulations. These computers used
1
Dynamics and Control of Nuclear Reactors. https://doi.org/10.1016/B978-0-12-815261-4.00001-9
# 2019 Elsevier Inc. All rights reserved.