Safety

The safety of nuclear power plants is continuously controlled by a number of authorities such as the International Atomic Energy Agency (IAAE) based in Vienna, or the State Office for Nuclear Safety (SUJB). As can be proven by safety analyses, power plants are designed to be safer and more resistant. Owing to the fact that the approach to safety in nuclear energy resources is highly above standard, accidents at plants with radioactive contamination of surrounding areas or threat to the inhabitants are practically eliminated, as safety analyses confirm. On top of that, a nuclear power plant is designed so that it can resist earthquakes or airplane crashes.

 

Technical safety requirements at nuclear power plants

Power plants are designed so that the physical principles during the process of obtaining energy from an atomic nucleus counteract, as stated above, the development of adverse processes (so called inherent safety). Moreover, operational safety is controlled by a number of systems, which automatically ensure protection, i.e., without an external energy supply against potential development of an event (passive safety). Nuclear power plants are equipped with systems that automatically monitor operational parameters and automatically start and prevent an event from developing (active safety) in case any limit values are exceeded. There are several (3-4) backups of important systems. Special attention during tests and maintenance is given to the equipment with higher, so called safety classification.

Four physical barriers prevent leakage of radioactive substances into the environment – fuel matrix (pellet), fuel cover (i.e. zirconium tubes), steel components of the primary circuit with reactor and containment(s). All barriers are monitored online and tested on a regular basis. Several backup safety systems are always ready for protection of individual barriers.

Source: http://www.hsem.state.mn.us/

The same care that is devoted to monitoring the function of the four above described barriers against the leakage of radioactive substances is also devoted to three basic safety functions that are monitored and controlled at all times

• reactivity control (reactor power control),
• heat removal from the reactor active zone,
• prevention of leakage of radioactive substances, control of operating effluents and limitation of leakage during accidents.

Important facilities are equipped with the self-control system which in case of imminent malfunction starts an alarm and eventually activates the active safety system.

 

Organisational requirements for nuclear power plant safety

A nuclear power plant is protected against attack by a number of safety measures. The basic measure is a division of the plant site into several safety zones with restricted entry and active and passive safety systems. Entry into the plant is stricter than at an airport. Employees are checked to ascertain if they have consumed alcohol or psychotropic substances. The site is guarded by specially trained personnel.

The no-flight zone above the plant is approximately 4,000 m in diameter at a height of 1,500 m.

All operating manipulation with nuclear power plant equipment and other procedures are described in the operating instructions and a simulator is used to train employees on their knowledge. The plant management places great emphasis on employee safety relations, on so called safety culture. This practically includes using the complex training system, control over observance of rules, investigating events and looking for ways to prevent them, establishing conditions for common, dutiful and active observance of safety principles. The questions of safety, which are given much attention, are incorporated into the management and decision-making in the project stage and in the construction and operation of the nuclear power plant as well.

The procedures used to minimise the consequences of an accident for inhabitants are established in the so called emergency plan, which is regularly practiced in a simulated accident. Rescue squads and local authorities take part in these exercises as well.

 

Nuclear power plant resistance

Nuclear power plants are designed to be able to resist different types of external or internal hazards. The risk is eliminated by active measures as well as by the choice of locality (which can mitigate a risk of earthquake or floods).

External hazards

• Earthquake – the plant is able to shut down and finish cooling (it has a special certificate for such hazard)
• Extreme weather conditions – wind, snow, frost, warm weather, drought
• Airplane crash
• Threat from surrounding industrial objects and traffic (at Temelín e.g. pipe-line)
• Electromagnetic interference – the equipment is designed (shaded) so that it cannot be disturbed
• Sabotage – solved by security guard

Internal hazards

• Fire – usage of fire resistant and heatproof materials, consistently separated safety systems
• Water, steam, gas, chemical and toxic substance leakages – the projects prevent them from leaking into the environment and simultaneously protects personnel safety
• Breakdowns of pressurised parts, supports, constructions – critical equipment is protected
• Tear of rotating parts
• Falling or clashing loads
• Unfavourable operational situations
• Abnormal situations – situations outside the standard operational conditions and standard transient conditions
• Accident – important failure of one of the four barriers

 

Radiation protection

The radiation situation in technological facilities, in the reactor building rooms, at the plant site and in the surrounding areas is constantly monitored. Besides that, gas and liquid drain outlets of the plant are continuously measured and the environment is monitored. Measurements prove that the influence of the outlets from the nuclear power plant is a thousand times lower that other factors influencing man – it is, for example, the same as an increase in cosmic radiation influencing an inhabitant of a panel house who has changed living on the ground floor for the tenth floor.

For more information see the web pages of the National Radiation Protection Institute.

 

Survey of sources irradiating inhabitants – comparison with nucleus

Survey of sources irradiating inhabitants

	Number of deaths per TW of output per year
Natural background	76.8
Medical exposure	19.6
Nuclear weapons testing	3.5
Nuclear power plant	0.1

 

Effective doses from the natural environment in the Czech Republic

	Effective dose
	[µSv/year]
Cosmic radiation	380
Cosmogenic radionuclides	460
Primordial radionuclides (without radon)	240
Radon	1.270
Total	2.400

Effective doses from the natural environment

	Dose supply
	[µSv/year]
TV watching	10
A stay 50 m above the sea level (getting closer to cosmic radiation)	10
Jobs in mines	15
Consequences of nuclear weapons testing	30
Flight Paris–Chicago and back	60
X-ray of bowels (one examination)	4.000
X-ray of stomach (one examination)	2.400
X-ray of haunches (one examination)	1.700
CT examination	7.000
Stay in the Indian state of Kerala	17.000
Sunbathing on one of Brazil’s beaches	175.000
Natural background in Ramsar	400.000