Civil Engineering Reference
In-Depth Information
Chapter 5
Safety and Risk of Light Water Reactors
Abstract
This chapter starts with the goals of protection for LWR plants. These
are: safe shutdown of the LWR plant, assurance of core cooling and safe and intact
containment structures. The safety concept of LWRs is based on multiple contain-
ment structures and engineered safeguard components. The staggered in depth
safety concept relies on accident prevention, accident limitation or accident miti-
gation and severe accident management. LWR plants must be designed and built on
the design basis concept. Sequences of events exceeding the design basis must be
counteracted by beyond design accident management measures. Probabilistic
safety analyses supplements these guidelines and assures frequencies of occur-
rences per year for a severe accident with core melt of 10
-5
to 10
-7
per year.
Most countries issued an Atomic Energy Act establishing the legal frame for the
peaceful utilization of nuclear power. The chapter continues by describing thermo-
dynamic and neutron physics design of a LWR core as well as the stable behavior of
PWRs when controlled by movement of control elements or of BWRs when
controlled by the speed of the recirculation pumps, and moving control elements.
The mechanical design of the pressure vessel is of high importance. It follows the
guidelines of the ASME Boiler and Pressure Vessel Code. This is accompanied by
quality assurance and in-service inspections. Also the mechanical design of the
reactor containment follows similar guidelines. The chapter ends by discussing the
different design basis accidents which must be analyzed prior to licensing of the
LWR plant.
5.1
Introduction
The purpose of reactor safety is the protection of personnel in nuclear reactors as
well as the protection of the environment of these plants and of the population.
Failures leading to radioactivity releases must be excluded in the design of the
