Failure of nuclear power plants may occur as a result of one or more failures of the
components and systems comprising the power plant. Typically, failure of the power plant as
defined previously requires a larger number of failure of individual components and
subsystems. Thereby a certain robustness of the systems is ensured and the power plants in
general thereby become safer.
Critical components in nuclear power plants are valves, and their malfunction may lead to loss
of core cooling, which in turn may have severe consequences such as core damage and even
meltdown. In Figure 1.26 an overview is given showing the distribution of valve failures in
various sub-systems of a boiling water nuclear power plant.
Other
14%Valve (check)
7%
Valve operators
16%
Turbine
4%
Solenoid
7%
Sensors
5%
Seals
6% Motors
4%Instruments
19%Condensor 2 %Control rod drives 2%
Filters 1%
Generator (diesel) 2%
Heat exchanges 1%Piping 2%
Pumps 3%
Radiations monitors 2%
Relays 3%Figure 1.26 Distribution of valve failures on the various subsystems of boiling water nuclear power
plants (Scott and Gallaher (1979)).
From Figure 1.26 it is seen that most valve failures take place in piping and instrumental
systems. Further investigations have shown that physical and human causes are equally
important. Leaks and natural failures are the major physical causes, whereas maintenance
errors and plant design errors are the causes of the majority of human errors.
Failures of Chemical Facilities
Chemical and petrochemical industries typically involve production, storage and
transportation of substances, which may be extremely toxic or flammable and explosive.
Failures in such facilities may thus have significant consequences for personnel, environment
and also economic losses may be incurred due to damages and loss of production.
In Figure 1.27 an overview is given illustrating the major causes of heavy losses in the
chemical industry. It is seen that maintenance failures together with poor design and layout of
equipment are the major causes of heavy losses.