nuclear accidental events from level 0 of the International Nuclear Event Scale
(INES). Operating rates of and accidents at nuclear power plants in Japan and the
United States are classified by type and age, and the relationship between operating
rates and frequency of accidents is statistically analyzed. Kainou divided the causes
of accidents into two categories: force majeure (natural disasters such as earthquakes
and tornadoes, as well as man-made external factors such as terrorist attacks and
plane crashes) and manageable (problems caused by reactor design, human operational error, and mechanical failures that should have been discovered during
inspections). The conclusion is that Japan and the United States do not differ greatly
in terms of nuclear power plant utilization rates.
In Japan and the United States, only two types of reactor, pressurized and boiling
water, were in operation, so the type of machine was given little consideration. In
other countries, many other types of nuclear power plants are also in operation,
including Russian light water reactors and CANDU heavy water reactors, which
require more complex analysis. Causes of accidents were grouped into internal and
external causes. However, as became clear in the Fukushima Daiichi nuclear power
plant accident, if a natural disaster such as an earthquake occurs outside the site, it
should be possible to prevent problems occurring if appropriate countermeasures are
taken in advance. In the case of intrinsic causes, although problems such as machine
failure can be prevented by inspection, it is unreasonable to classify these as identical
to human-induced causes such as operational errors.
Then, accidents can be classified by five causes: design, manufacture, maintenance, operation, and under investigation. This allows analysis from the viewpoint
of inspection. The frequency of troubles caused by manufacturing and maintenance
tends to be higher than those resulting from other causes. Troubles caused by design
can include cracks that occur during service due to failure to consider fatigue,
mechanical and electrical resonance in the design, and stress corrosion cracking, a
phenomenon that was unknown at the time of design. Troubles caused by
manufacturing include deterioration of material properties due to defective joints
or excessive heat input and cracking during use due to impurities adhering to the
product during manufacturing. Thus, troubles caused in the design and manufacturing stages may be due to quality assurance issues such as procurement management
or by events related to phenomena that were not understood during the design and
manufacturing stages. Troubles caused by maintenance are due to errors in inspection and maintenance work performed at the power plant during service. Examples
include equipment failure due to errors in restoration following disassembly and
inspection, leaks that occur due to a foreign object biting into the valve, and wire
breakage due to loose screws. Troubles caused by operation are due to errors in
operation and monitoring at the power plant during service. For example, reactor
power can be reduced due to errors in switching the operation of equipment, and
reactors can be automatically shut down due to errors in the monitoring of instruments and operation information displays.
This analysis categorizes all occurrences of trouble as human-caused. While some
unanswered questions remain regarding troubles under investigation, troubles
caused by design, manufacturing, maintenance, and operations are all considered
11 Construction of an East Asia Nuclear Security System
201
(INES). Operating rates of and accidents at nuclear power plants in Japan and the
United States are classified by type and age, and the relationship between operating
rates and frequency of accidents is statistically analyzed. Kainou divided the causes
of accidents into two categories: force majeure (natural disasters such as earthquakes
and tornadoes, as well as man-made external factors such as terrorist attacks and
plane crashes) and manageable (problems caused by reactor design, human operational error, and mechanical failures that should have been discovered during
inspections). The conclusion is that Japan and the United States do not differ greatly
in terms of nuclear power plant utilization rates.
In Japan and the United States, only two types of reactor, pressurized and boiling
water, were in operation, so the type of machine was given little consideration. In
other countries, many other types of nuclear power plants are also in operation,
including Russian light water reactors and CANDU heavy water reactors, which
require more complex analysis. Causes of accidents were grouped into internal and
external causes. However, as became clear in the Fukushima Daiichi nuclear power
plant accident, if a natural disaster such as an earthquake occurs outside the site, it
should be possible to prevent problems occurring if appropriate countermeasures are
taken in advance. In the case of intrinsic causes, although problems such as machine
failure can be prevented by inspection, it is unreasonable to classify these as identical
to human-induced causes such as operational errors.
Then, accidents can be classified by five causes: design, manufacture, maintenance, operation, and under investigation. This allows analysis from the viewpoint
of inspection. The frequency of troubles caused by manufacturing and maintenance
tends to be higher than those resulting from other causes. Troubles caused by design
can include cracks that occur during service due to failure to consider fatigue,
mechanical and electrical resonance in the design, and stress corrosion cracking, a
phenomenon that was unknown at the time of design. Troubles caused by
manufacturing include deterioration of material properties due to defective joints
or excessive heat input and cracking during use due to impurities adhering to the
product during manufacturing. Thus, troubles caused in the design and manufacturing stages may be due to quality assurance issues such as procurement management
or by events related to phenomena that were not understood during the design and
manufacturing stages. Troubles caused by maintenance are due to errors in inspection and maintenance work performed at the power plant during service. Examples
include equipment failure due to errors in restoration following disassembly and
inspection, leaks that occur due to a foreign object biting into the valve, and wire
breakage due to loose screws. Troubles caused by operation are due to errors in
operation and monitoring at the power plant during service. For example, reactor
power can be reduced due to errors in switching the operation of equipment, and
reactors can be automatically shut down due to errors in the monitoring of instruments and operation information displays.
This analysis categorizes all occurrences of trouble as human-caused. While some
unanswered questions remain regarding troubles under investigation, troubles
caused by design, manufacturing, maintenance, and operations are all considered
11 Construction of an East Asia Nuclear Security System
201