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ALARA (As Low As Reasonably Achievable): An internationally used principle regulating the amount of radiation doses at nuclear power plants.

AVI: Regional State Administrative Agency

Activation product: A radioactive nuclide created by neutron radiation in the reactor.

Activity: The number of spontaneous nuclear disintegrations occurring in a given quantity of radioactive material within a certain time. The unit of radioactivity, the becquerel (Bq), equals one disintegration per second.

Aerosols: A gaseous medium containing solid or liquid particles. In the case of emissions or releases from a nuclear power plant, these particles may be radioactive.

Alpha-active element: A radioactive element that emits an alpha particle upon decomposing. An alpha particle consists of two protons and two neutrons.


BOD7ATU: The biological oxygen demand in wastewater.

BWR, Boiling water reactor: A light-water reactor in which water used as the coolant boils as it passes through the reactor core. The steam generated rotates the turbines.

Background radiation: Radiation emanating from natural sources, such as radon from the soil, radiation from space, and radioactive materials in the human body.

Base load power: An electricity production method that is reliable and produces evenly. The production of renewable energy methods fluctuates for example along weather conditions so besides them a reliable base load power production such as nuclear power is needed.

Becquerel (Bq): The unit expressing the activity of a radioactive substance. 1 Bq is equal to one spontaneous nuclear disintegration in the substance per second.

Beta-emitting substance: Radioactive material that emits negatively charged particles (electrons).


CO2: Carbon dioxide

Capacity factor: The figure depicting the production at a power plant; for example, for one year. The capacity factor is the energy produced in a year by a power plant as a percentage of the energy it would have produced had it been operating at full capacity for the entire year.

Carbon-14: Carbon-14 is a long-lived, naturally occurring, beta-emitting radioisotope created by cosmic rays in the Earth's atmosphere. It is also formed in a nuclear reactor when the oxygen in the coolant is activated. Carbon-14 then enters the atmosphere bound to carbon dioxide.

Climate change: Long-term change in global or local climate. In common language climate change means the permanent changes in the climate caused by human actions and greenhouse gas emissions. These changes occur for example in temperature, precipitation, or winds.

Consortium: A temporary merger of companies, formed for a particular business venture.

Control rod: A rod holding material that absorbs neutrons. It regulates the number of neutrons in the reactor core and thus the power of the reactor. A power plant reactor has a large number of control rods.

Controlled area: The area that contains or may contain radioactive materials; separated from other plant facilities. The doors to the controlled area are locked.

Conversion: The chemical transformation of one substance into another substance. In nuclear technology, conversion usually refers to the conversion of uranium oxide (U3O8) into uranium hexafluoride (UF6) for enrichment purposes, and the conversion of uranium hexafluoride into uranium dioxide (UO2) for the fuel manufacturing process.


DNV GL: DNV GL Business Assurance Finland Oy Ab acts as an independent third party in various inspection/assessment tasks. DNV's central fields of operation include services relating to the classification of ships and the certification of management systems.

Decibel, dB: Noise is measured by a decibel scale expressing sound intensity.

Dose rate: A dose of radiation per time unit (e.g. mSv/h) expressing the amount of radiation a person is exposed to within a certain period of time.


EIA, Environmental Impact Assessment procedure: The Environmental Impact Assessment (EIA) procedure is a procedure related to the granting of an environmental permit. It must be performed in the planning phase of a project if the project causes, or may cause, significant environmental impacts.

ELY center: Center for Economic Development, Transport and the Environment.

EMAS: Eco-Management and Audit Scheme is an environmental management system for the EU region. TVO's environmental management system is EMAS compliant.

Ecosystem services: Ecosystem services are the benefits people obtain from nature. These include provisioning services such as food and water; regulating services such as flood and disease control; cultural services such as recreational, and cultural benefits; and supporting services, such as nutrient cycling, that maintain the conditions for life on Earth.

Emission right: EU-wide carbon dioxide emission rights trading began in 2005. For the entire EU area, annual carbon dioxide quotas were specified for industry and energy plants emitting carbon dioxide. The target is to allocate cost-efficiently emission reduction measures to where their implementation is the most inexpensive. Plants that successfully and cost-efficiently reduce their emissions to a lower level than their quota allows may sell their spare emission rights in emissions trading. The plants for which the reduction of emissions is costly can purchase emission rights from the market.

Energy aspect: An element related to energy production and energy use that has an impact on the company's total use of energy, such as technology, organisational operations, and behaviour.

Environmental aspect: An element of an organisation’s activities, products or services that has or can have an impact on the environment. Significant environmental aspect means an environmental aspect that has or can have a significant environmental impact.

Environmental impact: Any change to the environment, whether adverse or beneficial, wholly or partially resulting from an organisation’s activities, products or services.

Environmental objective: An overall environmental goal, arising from the environmental policy, that an organisation sets itself to achieve, and which is quantified where practicable.

Environmental performance: The measurable results of an organisation’s management of its environmental aspects.

Environmental policy: The overall intentions and direction of an organisation relating to its environmental performance as formally expressed by top management including compliance with all applicable legal requirements relating to the environment and also a commitment to continuous improvement of environmental performance. It provides a framework for action and for the setting of environmental objectives and targets.

Environmental programme: A description of the measures, responsibilities and means taken or envisaged to achieve environmental objectives and targets and the deadlines for achieving the environmental objectives and targets.

Environmental target: A detailed performance requirement, arising from the environmental objectives, applicable to an organisation or parts thereof, and that needs to be set and met in order to achieve those objectives.

Euratom: A unit of the EU Commission that supervises nuclear material.


Fission: The splitting of one heavy atomic nucleus into two or more intermediate-mass nuclei, releasing neutrons and a considerable amount of energy in the process.

Fission products: The medium-heavy nuclei produced in nuclear fission. They are usually radioactive.

Foreign material: Materials that gets into a process or machine but doesn't belong there. Examples of foreign materials are loose parts of appliances such as bolts and nuts, tools, and rubbish. Foreign materials cause malfunction in machines and processes, such as jamming machines, clogging pipelines, and fuel leaks.

Fuel assembly: An element formed by fuel rods.

Fuel rod: A slender metal tube holding fuel pellets. The fuel inside the tube is generally uranium oxide compressed into pellets.


GRI (Global Reporting Initiative): Reporting guidelines for social responsibility that were approved by a meeting of the UN in Johannesburg in 2002. The reporting covers a company's financial, human, and environmental responsibility.

Gamma radiation: Electromagnetic radiation emitted during alpha and beta decay.

Gigawatt hour, GWh: A unit of electrical energy. One gigawatt hour equals one million kilowatt hours.

Gigawatt, GW: A unit of power. One gigawatt is one million kilowatts.


Half-life: The time it takes for the activity of a radioactive isotope to be reduced by half.


IAEA: International Atomic Energy Agency.

IEA: International Energy Agency. An intergovernmental organization founded by the OECD in 1974 that promotes international co-operation in the energy sector. It serves its member countries as a scientific expert organisation and as a supporting actor for the development of the whole sector.

INES (International Nuclear Event Scale): A seven-level scale used internationally to depict the seriousness of accidents and incidents at nuclear power plants. The lower levels (1-3) depict incidents that have weakened plant safety and the upper levels (4-7) accidents that could cause emissions into the environment that require protective measures against radiation.

ISO 14001 standard: Environmental management that is widely used in various parts of the world.

ISO 9001 standard: International standard for quality management systems.

Iodine: From the point of view of radiation safety, the most important isotope of iodine among fission products is iodine-131, which has a half-life of eight days.

Ion exchange resins: Substances used to remove impurities from water.

Isotope: Atoms of the same element differing from each other in the number of neutrons in their nucleus. Almost all natural elements occur as more than one isotope.


KAJ Store: Storage facility for intermediate-level waste.

KPA: Interim storage for spent fuel.


MTT: MTT Agrifood Research Finland.

MWth: Thermal power produced in a nuclear power plant.

ManSievert, manSv: The unit used to indicate the collective radiation dose received by a certain number of people.

Megawatt, MW: A unit of power. One megawatt equals 1,000 kilowatts, or one million watts.


Natura area: Protected areas selected on the basis of EU-wide nature conservation goals. In Natura areas, nature conservation is implemented so that the normal use of the area is limited as little as possible.

Noble gas: The name for certain gases rarely found in the atmosphere. The noble gases are helium (He), neon (Ne) argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).

Nuclide: A type of atom or nucleus with a specific number of protons and neutrons.


ONKALO: ONKALO is the name of the underground bedrock research facility for the final disposal facility for spent nuclear fuel.

Occupational accident: An accident that occurs at work or on the way home from work or vice versa and which causes an absence of at least one day.


PRA: Probabilistic Risk Assessment.

PWR, Pressurized water reactor: A light-water reactor with such a high reactor pressure that water used as the coolant does not boil in the reactor. The hot water is conducted from the reactor to a steam generator in which the water in the secondary circuit evaporates and the steam is led to rotate the turbine.

Power delivered to the owners (GWh): Electricity produced - (internal consumption at the plant + consumption in the plant area).


Radiation: Electromagnetic waves or particle radiation consisting of the smallest particles of matter.

Radioactive operating waste: Waste such as plastic, paper, and cloth generated during maintenance work at the power plant. The volume can be reduced by baling.


SAHARA (Safety As High As Reasonably Achievable): An internationally used principle emphasizing safety at a nuclear power plant.

STUK: Finnish Radiation and Nuclear Safety Authority. STUK is the authority that regulates the Finnish nuclear energy sector.

Screenings: The organic matter which accumulates on the screening plant's fine screen and traveling basket filters in cooling water intake. The screenings mainly consist of debris, algae, mussels, and fish carried with cooling water.

Sievert (Sv): A radiation dose unit indicating the biological effects of radiation. As it is a very large unit, millisieverts (1 mSv = 0.001 Sv) and microsieverts (1 µSv = 0.001 mSv) are more commonly used.


TEM: The Finnish Ministry of Employment and the Economy.

TW, terawatt: A unit of power. One terawatt equals one billion kilowatts.

TWh, terawatt-hour: A unit of energy. One terawatt-hour equals one billion kilowatt hours.

Transuranium element: An element with an atomic number greater than that of uranium (92). Transuranium elements are not found in nature, but are created from uranium for example in nuclear reactors under the influence of neutron radiation.

Tritium: Tritium is a hydrogen isotope with a nucleus consisting of one proton and two neutrons. The nucleus is called tritium.

Tukes: The Finnish Safety and Chemicals Agency.


Uranium: An element with the chemical symbol U. Uranium comprises 0.0004% of the Earth's crust. All uranium isotopes are radioactive. Natural uranium is mostly in the form of isotope U-238, which has a half-life of 4.5 billion years. Only 0.72% of natural uranium is in the form of isotope U-235, which can be used as a nuclear fuel.


VLJ repository: A repository for low and intermediate-level radioactive waste.

VTT: Technical Research Centre of Finland.


WANO: The World Association of Nuclear Operators.


YVL guide: Nuclear power plant guide.