72-hour self-sufficiency criterion shall means that the system to which the criterion is applied must be able to perform its function for a minimum of 72 hours so that for the first 24 hours no material replenishments (such as filling the water or fuel tank of the system) are needed, and for the following 48 hours provisions and material reserves exist at the plant site to arrange the necessary material replenishments for the system.

Accident shall refer to postulated accidents, design extension conditions and severe accidents. (Nuclear Energy Decree 161/1988)

Air conditioning systems shall refer to systems designed to manage the purity, temperature, humidity and movement of indoor air by treating supply air or circulating air.

Annual dose shall refer to the sum of the effective dose arising from external radiation within the period of one year, and of the committed effective dose from the intake of radioactive substances within the same period of time. (Nuclear Energy Decree 161/1988)

Anticipated operational occurrence shall refer to such a deviation from normal operation that can be expected to occur once or several times during any period of a hundred operating years. (Nuclear Energy Decree 161/1988)

Appropriate certification shall refer to the certification of a quality system based on auditing in which the accreditation of the certification body has been done against the requirements of standard EN ISO/IEC 17021 and the accreditation is covered by the Multilateral Agreements (MLA) or Mutual Recognition Arrangements (MRA) entered into by FINAS.

Auditing shall refer to a systematic, independent and documented process to objectively evaluate the audit evidence obtained to determine the extent to which the agreed auditing criteria are met. (SFS-EN ISO 9000:2015)

Authorised inspection body shall refer to an independent inspection organisation approved by the Radiation and Nuclear Safety Authority under Section 60 a of the Nuclear Energy Act to carry out inspections of the pressure equipment, steel and concrete structures and mechanical components of nuclear facilities in the capacity of an agency performing public administrative duties. (Nuclear Energy Decree 161/1988, in Finnish). Authorised inspection body and authorised inspection organisation have same meaning in YVL Guides.

Barrier shall refer to an engineered or natural structure or material used for achieving safety functions. A barrier may also be an aggregate formed by different structures and materials.

Baseline configuration shall refer to a configuration of a product, formally established at a specific point in time, which serves as reference for further activities. (ISO 10007)

Boiler shall refer to an assembly intended for the production of steam or the boiling of a liquid other than water to a temperature exceeding 100°C, including at least one piece of heated pressure equipment with the danger of overheating.

Break preclusion (BP) shall refer to the principle of using advanced technical and organisational procedures in piping construction, operations and maintenance in such a way that the LBB principle will be implemented and this may be credited for the nuclear power plant design and its provision against the consequences of a complete, instantaneous pipe break.

Certification body shall refer to a recognised third-party organisation under Article 24 of the Pressure Equipment Directive 2014/68/EU.

Nuclear waste other than spent nuclear fuel may, regardless of its radioactive nature, be reused, recycled, recovered and disposed of in accordance with the provisions of the Waste Act (646/2011) if the amount of radioactive substances within it does not exceed the clearance level provided by the virtue of section 7 q, subsection 1, paragraph 28. (Nuclear Energy Act 990/1987 27 c §)

Commission agreement shall refer to a written agreement containing the information referred to in Section 73 of the Private Security Services Act (1085/2015) and Section 17 of the Government Decree on Private Security Services (874/2016).

Competence development shall refer to a set of planned, target-oriented and structured actions designed to assess, maintain and develop individual and organisational competences.

Conceptual plan of in-service inspections shall refer to a conceptual plan required under Section 35 of the Nuclear Energy Decree (161/1988). It refers to a document describing the in-service inspections performed using non-destructive inspection methods throughout the entire life cycle of a nuclear facility, from design to decommissioning. The conceptual plan of in-service inspections contains a preliminary description of the risk-informed selection processes of inspection items, the selection criteria for inspection intervals, the inspection systems and their qualifications, and the methods used to report and assess inspection results and flaw indications.

Conditional core damage probability (CCDP) shall refer to the probability of core damage as a result of an initiating event.

Conditional large release probability (CLRP) shall refer to the probability of a large release due to an initiating event.

Construction plans for nuclear fuel, control rods and dummy elements shall refer to the written documentation defining the detailed requirements for the structure and manufacturing of fuel, control rods and dummy elements, and their inspections taking place during manufacturing.

Contributory factors shall refer to events or conditions that, together with the other causes, increase the probability of an event but will not cause the event alone.

Controlled state shall refer to a state where a reactor has been shut down and the removal of its decay heat has been secured. (STUK Y/1/2018)

Controlled state following a severe reactor accident shall refer to a state where the removal of decay heat from the reactor core debris and the containment has been secured, the temperature of the reactor core debris is stable or decreasing, the reactor core debris is in a form that poses no risk of re-criticality, and no significant volumes of fission products are any longer being released from the reactor core debris. (STUK Y/1/2018)

Correction shall refer to a action that is performed in order toeliminate observed detected nonconformity.

Corrective actions shall refer to actions intended to eliminate the cause of nonconformities and prevent the recurrence of nonconformities. (SFS-EN ISO 9001:2015)

Criticality shall refer to a state where the output and loss of neutrons, created in nuclear fission and maintaining a chain reaction, are in equilibrium so that a steady chain reaction continues. (STUK Y/1/2018)

Criticality accident shall refer to an accident caused by an uncontrolled chain reaction of nuclear fissions. (STUK Y/1/2018)

Damping ratio shall refer to the ratio of the actual damping coefficient (the ratio of the viscous damping force to velocity) for a single-degree-of-freedom oscillator to the critical damping coefficient (the maximum value of the damping coefficient at which periodically attenuating oscillation is possible). The damping ratio is usually expressed as a percentage.

Dangerous object shall refer such an object, copy of an object, or substance that may endanger or can be used to endanger the use of nuclear energy, the safety or security of persons at the site where nuclear energy is used, or the safety of persons participating in the treatment and transport of nuclear materials/ nuclear use items or nuclear waste. (STUK Y/3/2020)

Decommissioning shall refer to the dismantling of a permanently closed nuclear facility so that no special measures are required at the facility site due to radioactive materials originating from the dismantled facility. (Nuclear Energy Act 990/1987)

Derived air concentration shall refer to a radionuclide-specific maximum value for the average airborne activity concentration, under which 2,000 hours of work may be carried out annually without exceeding the dose limits.

Design bases shall refer to all requirements, definitions and bases for normal operational conditions and accidents that pertain to the design and operation of a plant, system and component. (Nuclear Energy Decree, 161/1988)

Design basis threat shall refer to a threat of unlawful action used as the basis for the planning and assessment of the nuclear security arrangements for which the licensee is responsible. (161/1988)

Design extension condition shall refer to:
a. an accident where an anticipated operational occurrence or class 1 postulated accident involves a common cause failure in a system required to execute a safety function;
b. an accident caused by a combination of failures identified as significant on the basis of a probabilistic risk assessment; or
c. an accident caused by a rare external event and which the facility is required to withstand without severe fuel failure.
(Nuclear Energy Decree 161/1988)

Disposal facility shall refer to an entierety comprising therooms for the disposal of the waste packages (emplacement rooms) and the adjoining underground and above-ground auxiliary facilities. (Nuclear Energy Decree 161/1988)

Disposal site shall refer to the location of the disposal facility and, after disposal has been completed, the area entered in the real estate register in accordance with Section 85 of the Nuclear Energy Decree, and the ground and bedrock under it.

Diversity principle shall refer to the backing up of functions through systems or components having different operating principles or differing from each other in some other manner, with all systems or components able to implement a function separately. (STUK Y/1/2018)

Dose constraint shall refer to a constraint on the individual radiation dose of a person other than a patient arising from ionizing radiation during a specific period of time, used to optimize radiation protection in radiation practices. (Radiation Act 859/2018)

Dose limit shall refer to the radiation dose arising from ionizing radiation which may not be exceeded during a specific period of time. (Radiation Act 859/2018)

Dose Registry shall refer to a file into which the dose information and identification information of the employees engaged in radiation work is saved.

Dual-use item shall, in the context of Finnish legislation, refer to a product, technology, service or other commodity that can, in addition to its civilian use or application, be used to develop or manufacture weapons of mass destruction or missile systems that can be used to guide them to their targets.

Effective dose shall refer to the weighted sum of the equivalent doses in tissues and organs exposed to radiation, where equivalent dose denotes the product of the mean energy imparted by radiation to tissue or to an organ, per unit mass, and a weighting factor specified for the radiation. Effective dose is presented as a formula in the Government Decree on Ionising Radiation (1034/2018).

Emergency exposure situation means a situation in which the consequences of a radiation safety incident require or may require special measures to limit or reduce the radiation exposure of persons participating in the emergency work or protective measures or the exposure of members of the public. (Radiation Act 859/2018)

Emergency planning zone shall refer to an area extending to a distance of approximately 20 kilometres from the nuclear power plant and for which authorities shall draft an external rescue plan referred to in Section 48(1)(1) of the Rescue Act (379/2011). (STUK Y/2/2018) [Repealed, decision STUK 2/0002/2024]

Emergency power machine shall refer to a diesel engine or gas turbine without a generator.

Emergency situation shall refer to an accident or event during which the nuclear power plant’s safety has deteriorated or is in the danger of deteriorating or requires enhanced preparedness to act in order to ensure plant safety; emergency situations are classified on the basis of their severity and controllability as follows:

• an alert is a situation where the safety level of a nuclear power plant needs to be ensured in an exceptional situation.
• a site area emergency is a situation during which the nuclear power plant’s safety deteriorates or is in the danger of deteriorating significantly.
• a general emergency is a situation during which there is danger of radioactive substance releases that may require protective measures in the vicinity of the nuclear power plant.

(STUK Regulation Y/2/2018)

Emergency worker means a person with a pre-determined task in an emergency exposure situation and who may be exposed to ionizing radiation in the course of the emergency work or protective measures in an emergency exposure situation. (Radiation Act 859/2018)

Equipment assembly shall refer to a uniform and functional entity consisting of several components.

Equipment for use of force shall refer to a firearm referred to in section 2 of the Firearms Act (1/1998) and a gas spray referred to in section 11 of said Act, plastic or steel handcuffs, a baton of at most 70 centimetres in length, a telescopic baton, a dog trained in the use of force referred to in section 7n, subsection 3, paragraph 1 of the Nuclear Energy Act, a projectile-launcher using compressed air, a stun gun, a restraint belt, and leg-irons.

Event notification shall refer to a written account provided by a security guard/employee containing the information listed in Section 8 of the Private Security Services Act (1085/2015) and Section 18 of the Government Decree on Private Security Services (874/2016).

Expected evolution shall refer to evolution where the disposal system performs as planned or where one or more long-term safety functions are assumed to degrade.

External events shall refer to exceptional situations or incidents occurring in the vicinity of a nuclear facility that could have a detrimental effect on the safety or operation of the plant.

Facility shall refer to a nuclear facility or any other location where nuclear materials are customarily used. Facility also refers to a nuclear facility or a location where the annual material flow or use will exceed one effective kilogram. (IAEA Safeguards Glossary, 2001 Edition, International Nuclear Verification Series No. 3)

(N+1) failure criterion shall mean the same as the single failure criterion. Single failure criterion (N+1) shall mean that it must be possible to perform a safety function even if any single component designed for the function fails.

(N+2) failure criterion shall mean that the most important safety functions necessary to bring the plant to a controlled state and to maintain it must be ensured in postulated accidents even if any individual component of a system providing the safety function is inoperable and even if any other component of a system providing the same safety function or of a supporting system necessary for its operation is simultaneously inoperable due to the necessity for its repair, maintenance or testing.

The floor response spectrum describes the maximum vibrations of single-degree-of-freedom oscillators with various natural frequencies and a particular damping ratio positioned in a certain area of a building. The calculation of the floor response spectrum involves an analysis, based on the dynamic behaviour of the frame structure, of the transfer of the vibration from an earthquake or other external source to the part of the building under examination where it strains systems, structures, and components. Depending on the design basis, the floor response spectrum is an acceleration, velocity or displacement spectrum or an energy response spectrum in accordance with their combination.

Functions important to safety shall refer to functions where the individual performing the function has a direct or indirect effect on the safety of the nuclear facility at the various stages of its life cycle.

Functional isolation shall refer to the isolation of systems from one another so that the operation or failure of one system does not adversely affect another system; functional isolation also covers electrical isolation and isolation of the processing of information between systems. (STUK Y/1/2018)

General equipment requirement specification shall refer to a document that includes general equipment group-specific design and quality control requirements for safety classes 1, 2 and 3. When an equipment is procured, the requirements set out in this document will be completed with site-specific requirements.

Genericinvestigation shall refer to an analysis or investigation using information concerning several similar events.

Helper in an emergency means a person other than an emergency worker who provides assistance in protective measures or participates in other work necessary for society in an emergency exposure situation. (Radiation Act 859/2019)

High level waste shall refer to waste that, because of its high level of activity, requires highly effective radiation protection arrangements when processed and usually also cooling. The activity concentration of such waste is usually more than 10 GBq/kg.

Instrumentation and control (I&C) equipment shall refer to a piece of equipment such as a measuring device, display unit, electronic card or I&C relay that is part of an instrumentation and control system.

Instrumentation and control (I&C) platform shall refer to a product that, by the use of pre-developed tools and software and electronic modules, enables the design, implementation and maintaining of an application-specific I&C system.

INES scale (International Nuclear and Radiological Event Scale) shall refer to the IAEA's international classification scale of nuclear facility events and radiological events used to estimate and illustrate the radiation and nuclear safety significance of events when communicating on them. The INES scale is not applied to events which have no influence on radiation or nuclear safety.

An information security management system consists of the policies, procedures, guidelines, and associated resources and activities, collectively managed by an organization, in the pursuit of protecting its information assets.

Tarkastuslaitos tarkoittaa laitosta, joka suorittaa tarkastuksia tuotteen, prosessin, palvelun tai asennuksen tai niiden suunnittelun tutkimiseksi ja sen vaatimustenmukaisuuden todentamiseksi. (SFS-EN ISO/IEC 17020:2012)

Inspection organisation approved by STUK shall refer to an inspection organisation that has been approved in accordance with Guide YVL E.12.

Instrumentation and control (I&C) system shall refer to a system that controls, adjusts or observes the operation of a nuclear facility or components thereof. Control may consist of automatic operation or relaying commands given by humans. The results of the observation may be processed by the I&C system or relayed to the operators of the facility.

Intermediate level waste shall refer to nuclear waste that, because of its high level of activity, requires effective radiation protection arrangements when processed. The activity concentration of such waste is usually 1 MBq/kg – 10 GBq/kg. (STUK Y/4/2018)

Internal events shall refer to events occurring inside a nuclear facility that may have an adverse effect on the safety or operation of the plant.

“Leadership” shall refer to a manager using their skills and capabilities to direct the operation of employees and groups and have an impact on their commitment, values and behaviour. “Management” shall refer to authorised actions to guide the organisation and ensure work performance.

The leak before break (LBB) shall refer to a principle where piping does not have identified failure mechanisms creating the possibility of complete break, and faults that are not detected during inspections may at most create a small, local leak the detection of which allows the plant to be brought into a state where there is no risk of complete break.

Licensee shall refer to the holder of a licence entitling to the use of nuclear energy. (Nuclear Energy Act 990/1987)

Long-lived waste shall refer to nuclear waste the calculated activity concentration of which after 500 years is above 100 MBq/kg in a disposed waste package, or above an average value of 10 MBq/kg in waste placed in one emplacement room.

Long-term safety shall refer to the safety of disposal after the closure of the disposal facility, taking account of radiation exposure on humans and the environment.

Long-term safety functions shall refer to functions achieved by the characteristics or processes of engineered and natural barriers that are intended to isolate the nuclear waste from the bedrock and the biosphere or to impede the migration of radionuclides.

Loss of coolability of the nuclear fuel shall refer to a scenario where nuclear fuel loses its coolable shape due to fuel failure or a deformation that exceeds the design basis, or where a flow cooling fuel rods is blocked due to impurities in the fuel assembly.

Low energy equipment shall refer to Safety Class 2 equipment with a design pressure of up to 20 bar(g) and a design temperature of up to 120 °C and to which the design, dimensioning and quality-control requirements of a corresponding equipment from Safety Class 3 can be applied with technical justifications without having a risk to lose the operability of the equipment.

Low level waste shall refer to nuclear waste that, because of its low level of activity, can be processed without any special radiation protection arrangements. The activity concentration of such waste is usually not more than 1 MBq/kg. (STUK Y/4/2018)

Management shall also refer to a person or group orienting and guiding the organisation. Management includes top and middle management.

Management system shall refer to a system that is used to establish policy and objectives and to achieve those objectives.

Mechanical components shall refer to, for example, internals of reactor pressure vessel, control rod drives, pumps, motors, filters, valve actuators, cranes, load lifting attachments, fuel handling equipment, final disposal canisters, fans, and air ducts.

Minimum system performance can be determined by making the following assumptions:

1. Consider the consequential effects of the initiating event (component failure, for example).
2. Furthermore, select the failure combination that is most detrimental to the functionality of the system in accordance with the failure criterion presented in requirement 442 of Guide YVL B.1. The single failure with the highest reactivity effect is also assumed to occur in the reactor scram system.
3. Determine the performance parameters for each functioning component, which conform to the acceptance limits of components in periodic tests.

Non-linear structural analysis shall refer to solving a partial differential equation group using the finite element method (FEM), for example. The non-linearity of a structure may be geometrical by nature, due to the behaviour of the material, or related to the boundary conditions. A geometrical non-linearity is created when the loads cause large displacements in relation to the dimensions of the structure; in this case, the distribution of stress in the non-deformed and deformed structure will vary greatly. The non-linearity of a material means that the constitutive equations of the material are not linear.

Normal operating conditions shall refer to the planned operation of a nuclear facility according to the operating procedures. Normal operating conditions also include testing, plant start-up and shutdown, maintenance and the replacement of nuclear fuel. (STUK Y/1/2018)
YVL Guides also use the term normal operation, which means the same as normal operating conditions.

Notified body shall refer to a notified body as referred to in Article 12 of the Pressure Equipment Directive (2014/68/EU).

Nuclear facility shall refer to the facilities used for the generation of nuclear energy, including research reactors, facilities for the large-scale disposal of nuclear waste, and facilities for the large-scale production, use, processing or storage of nuclear material and nuclear waste. However, nuclear facility shall not refer to:
a) mines or ore processing plants intended for the production of uranium or thorium, or premises and locations including their precincts where nuclear wastes from such facilities are stored or deposited for final disposal; or
b) facilities and premises that have been permanently closed and where nuclear waste has been disposed in a manner approved as permanent by the Radiation and Nuclear Safety Authority; or
c) premises or parts of a nuclear facility that have been decommissioned in a manner approved by the Radiation and Nuclear Safety Authority. (Nuclear Energy Act 990/1987)

Nuclear information shall refer to:
• software that has been specially designed or modified for the development, production or use of the goods referred to in Appendix A to the Nuclear Energy Decree
• technology which means special information, in written or other form, necessary for the development, production or use of the goods referred to in Appendix A to the Nuclear Energy Decree, and that is not generally available or not related to basic scientific research. This information takes the form of technical data or technical assistance. Technical data may take forms such as blueprints, plans, diagrams, models, formulae, tables, engineering designs and specifications, manuals and instructions written or recorded on other media or devices such as disk, tape, read-only memories. Technical assistance may take forms such as instructions, skills, training, working knowledge and consulting services and may involve the transfer of technical data. (Council Regulation (EC) No 428/2009) The Nuclear Energy Act shall apply to nuclear information which may have bearing on nuclear proliferation or which are subject to the obligations of Finland’s international treaties in the nuclear energy sector. However, a licence defined in the Nuclear Energy Act is only needed for nuclear information that are subject to a particular safeguards obligation (Nuclear Energy Act, Section 19 a).

Nuclear material shall refer to special fissionable materials and source materials, such as uranium, thorium and plutonium, suited for obtaining nuclear energy. (Nuclear Energy Act 990/1987, Section 3).

Nuclear power plant shall refer to a nuclear facility for the purpose of electricity or heat production, equipped with a nuclear reactor, or a complex consisting of nuclear power plant units and other related nuclear facilities located at the same plant site.

Nuclear use item shall refer to nuclear material and the substances, devices, equipment, nuclear information and agreements referred to in Sections 2(1)(5) and 2(2)(1) of the Nuclear Energy Act (990/1987). (Nuclear Energy Decree 161/1988)

Nuclear waste shall refer to a) radioactive waste in the form of spent nuclear fuel or in some other form generated during or as a result of the use of nuclear energy and b) materials, objects and structures which, having become radioactive during or as a result of the use of nuclear energy and having been removed from use, require special measures owing to the danger posed by their radioactivity. (Nuclear Energy Act 990/1987)

Nuclear waste facility shall refer to a nuclear facility utilised for the encapsulation of spent nuclear fuel or the processing of other nuclear waste for disposal, and to a disposal facility for spent nuclear fuel or other nuclear waste; however, nuclear facility shall not refer to permanently closed facilities where nuclear waste has been placed in a manner approved as permanent by the Radiation and Nuclear Safety Authority. (Nuclear Energy Decree 161/1988)

Obsolescence shall mean that a plant SSC fails to meet the new safety requirements or no longer represents the current technological development in terms of the assurance of safety. The lack of technical support or spare parts is also regarded as a manifestation of the obsolescence of a SSC.

Operational event shall refer to a failure, flaw or non-conformity in safety functions, systems, components, structures or an organisation’s activities that has a bearing on radiation safety or nuclear safety. Operational events also include emergencies and disturbances as well as events compromising radiation safety. Operational events also include events taking place during the construction phase. Note: Operational event is a wider concept, but in YVL Guides, it shall refer to events in STUK’s controlled area (radiation and nuclear safety).

The Operational Limits and Conditions (OLC)) set out the technical and administrative requirements for ensuring the plant’s operation in compliance with the design bases and safety analyses; the requirements for ensuring the operability of systems, structures and components important to safety; and the limitations that must be observed in the event of component failure.

Operator shall, depending on the context, refer to a licensee, licence applicant or some other user of nuclear energy (use of nuclear energy is defined in Section 2 of the Nuclear Energy Act) who is engaged in, or is planning to engage in, operations falling within the area of application of the Nuclear Energy Act.

As referred to in Section 2(1)(6) of the Nuclear Energy Act, ores containing uranium or thorium shall mean minerals in which:
1) the average content of uranium is higher than 1 kilogram per metric tonne; or
2) the average content of thorium is higher than 30 kilograms per metric tonne, except for monazite, or higher than 100 kilograms per metric tonne for monazite.
(Nuclear Energy Decree 161/1988, Sections 2 and 3(2)(3)).

Parametric studies shall, in the context of qualification, refer to experimental laboratory studies to establish the impact of various separate essential parameters. The testing organisation conducts them to support the technical justification without witness by a qualification body.

Pass/fail criteria for in-service inspection qualification shall refer to the qualification assessment criteria relating to the number of defects detected in a test piece, the accuracy of determining defect size and position, and other factors that are reported in an inspection qualification and that determine the acceptability of the inspection system.

Passive fire protection shall refer to structural fire protection arrangements, such as fire compartmentation together with the functional design and layout design of the facility, in order to ensure the facility’s safety during fire situations as far as possible without active fire fighting operations.

Performance target shall refer to a measurable or assessable characteristic of a barrier. The performance target shall include a criterion describing the characteristic which, when met, ensures the performance of a long-term safety function.

Physical separation shall refer to the separation of systems or components from one another by means of adequate barriers, distance or placement, or combinations thereof. (STUK Y/1/2018)

Postulated accident shall refer to a deviation from normal operation which is assumed to occur less frequently than once over a span of one hundred operating years, excluding design extension conditions; and which the nuclear facility is required to withstand without sustaining severe fuel failure, even if individual components of systems important to safety are rendered out of operation due to servicing or faults. Postulated accidents are grouped into two classes on the basis of the frequency of their initiating events: a) Class 1 postulated accidents, which can be assumed to occur less frequently than once over a span of one hundred operating years, but at least once over a span of one thousand operating years; b) Class 2 postulated accidents, which can be assumed to occur less frequently than once during any one thousand operating years. (Nuclear Energy Decree 161/1988)

Practical trials shall, in the context of qualification, refer to the assessment of non-destructive inspection by open and blind trials, witnessed by a qualification body and applying the inspection to test pieces containing defects. Laboratory tests performed as parametric studies that are not witnessed by a qualification body are not practical trials.

Pre-service inspection plan shall refer to an inspection plan the purpose of inspections of which is to provide basic comparative data for in-service inspections and obtain data supplementing manufacture and installation quality assurance about the original condition of the inspection items inspected within the in-service inspection scope.

Precautionary action zone shall refer to an area extending to a distance of approximately five kilometres from the nuclear power plant, where land use restrictions are in force. (STUK Y/2/2018)[Repealed, decision STUK 2/0002/2024]

Preliminary suitability analysis shall be used by the licensee to verify that a component is suitable for its intended location of use on the basis of its rated values. The qualification of the component is also inspected and designed. After the preliminary suitability analysis the requirement specification of the component isverified, and the procurement of the component may be started, if necessary.

Pressure equipment dossier shall refer to a document defined in Section 69 of the Pressure Equipment Act (1144/2016) containing all the protocols and other essential documentation pertaining to pressure equipment.

Pressure equipment subject to registration shall refer to pressure equipment to be registered under Section 51 of the Pressure Equipment Act (1144/2016).

Preventive actions shall refer to measures intended to eliminate the cause of potential deviations and prevent the occurrence of deviations. (ISO 9001)

Probabilistic risk assessment (PRA) shall refer to a quantitative assessments of hazards, probabilities of event sequences and adverse effects influencing the safety of a nuclear power plant. (Nuclear Energy Decree 161/1988)

Process is a set of interrelated or interacting activities which transforms inputs into outputs.

Product shall refer to a result of a process. Examples of products include a nuclear facility, plant modification, system delivery, single component or part thereof, plan or design, processed material, or information product. A service is not a product.

Products specific to a delivery batch shall refer to products (materials, parts, components) that have been allocated to a nuclear fuel delivery batch at the time of their manufacture. Other nuclear fuel products are not considered allocated to a delivery batch.

Project shall refer to a unique process consisting of a set of coordinated and controlled activities with start and finish dates, undertaken to achieve an objective conforming to specific requirements, including the constraints of time, cost and resources. (SFS-EN ISO 9000:2015) Projects include for example construction projects of new nuclear facilities or plant modification projects launched to implement extensive modifications.

Protection automation shall refer to I&C systems that control systems needed to manage postulated accidents and design extension conditions in order to reach a controlled state and maintain it. Protection I&C systems also include I&C systems that control systems needed for accident management during possible I&C common cause failures.

Pump shall refer to a mechanical component (hydraulic machine transferring liquid), which transfers liquid and produces head for it. In the context of Guide YVL E.9, a pump is considered to include the pump’s auxiliaries and other parts forming an integral part of the pump structure and operations, excluding electrical and I&C equipment, such as the electric motor driving the pump.

Qualification is normally used as a synonym for “validation” in YVL-guides. Qualification shall refer to confirmation, through the provision of objective evidence, that the requirements for a specific intended use or application have been fulfilled.

Qualification shall refer to a demonstrated ability to apply knowledge and skills.(SFS-EN ISO 9000:2015)

Qualification body shall refer to an independent expert body which plans, conducts, assesses and witnesses qualifications of non-destructive testing. (Nuclear Energy Act 990/1987)

Quality management shall refer to management with regard to quality. Quality management may include drafting of a quality policy and setting of quality targets as well as establishing processes to achieve said quality targets through quality planning, quality assurance, quality control and improved quality. (SFS-EN ISO 9000)

Quality management system shall refer to a management system to direct and control an organisation with regard to quality. (SFS-EN ISO 9000:2015).

Radiation safety incident means an event or situation that compromises or may compromise radiation safety and unplanned medical exposure. (Radiation Act 859/2018)

Rare event impairing long-term safety shall refer to a potential event significantly reducing the performance of barriers that has a very low probability of occurring but that may jeopardize long-term safety in case of occurrence. Such an rare event may be caused by geological phenomena, climatic phenomena or human action.

Repair shall, in the context of Guide YVL A.8, refer to restoring the operability of a faulty SSC

Representative person shall refer to an individual in the population group most highly exposed to a given radiation source (here to the radioactive substances contained in releases), whose radiation dose represents the doses received by such a population group (ICRP Publication 101). The representative person is equivalent to, and replaces, the previous term ‘average member of the critical group’.

Requirement specification for equipment service place shall refer to the equipment requirement specification prepared for the planned service place. The requirement specification for equipment service place supplements the general equipment requirement specification.

Reviewing the effectiveness of operating experience feedback shall refer to assessing the functionality of the process. Reviewing the effectiveness of measures defined based on events shall refer to procedures to ensure that measures bring about the pursued plant-related or operational changes and that those measures that are insufficient for achieving the pursued changes are observed and responded to.

Risk analysis shall refer to examinations, performed using systematic measures, in order to 1) identify threats, problems and vulnerabilities, 2) identify the reasons for them, and 3) assess and classify the consequences and related risks of undesirable situations. (STUK Y/3/2020)

Risk matrix shall refer to a diagram consisting of three or more failure potentials (Y axis) and four or more consequence categories (X axis) describing the conditional core damage probability.

Safe state shall refer to a state where the reactor has been shut down and is non-pressurised, and removal of its decay heat has been secured. (STUK Y/1/2019)

Safe state following a severe reactor accident shall refer to a state where the conditions for the controlled state of a severe reactor accident are met and, in addition, the pressure inside the containment is low enough that leak from the containment is minor, even if the containment is not leak-tight. (STUK Y/1/2018)

Safety case shall refer to documentation for demonstrating compliance with the long-term safety requirements.

Safety functions shall refer to functions important from the point of view of safety, the purpose of which is to control disturbances or prevent the generation or propagation of accidents or to mitigate the consequences of accidents (STUK Y/1/2018).

Safety-classified system/structure /component shall refer to a system, structure or component assigned to safety classes on the basis of its safety significance.

Security arrangements shall refer to the measures needed to protect the use of nuclear energy against illegal activities in the nuclear facility, its precincts other places or vehicles where nuclear energy is used. (Nuclear Energy Act 990/1987)

Security organisation shall refer to the work community consisting of the nuclear security officers of a nuclear facility.

Security plan shall refer to the account (preliminary security plan) presented in Section 35(6) of the Nuclear Energy Decree and the account presented in Section 36(7) of the Nuclear Energy Decree, as well as any changes to them.

Security standing order shall refer to a document referred to in Section 7 o of the Nuclear Energy Act.

Security zone shall refer to the safety zone referred to in Section 4 of Regulation STUK Y/3/2020.

Separation principle shall refer to physical separation and functional isolation. (STUK Y/1/2018)

Serially manufactured component shall refer to a component which has not been designed particularly based on the customer’s specification but it is procured from an existing product line of the manufacturer. Typically one is manufactured in large quantities, and can be used for other applications, too. Functionality, structure, dimensions, materials, manufacturing process and quality of the component do not essentially differ within and between production lots.

Service life shall refer to the period of time beginning from the commissioning of the SSC fulfilling its operability requirements and ending when the degraded operability is not restored to the required level anymore.

Severe accident shall refer to an accident in which a considerable part of the fuel in a reactor or the spent fuel in a fuel pool or storage loses its original structure. (Nuclear Energy Decree 161/1988)

Severe reactor accident shall refer to an accident in which a considerable part of the fuel in a reactor loses its original structure. (STUK Y/1/2018)

Short-lived waste shall refer to nuclear waste, the calculated activity concentration of which after 500 years is below the level of 100 MBq/kg in each disposed waste package, and below an average value of 10 MBq/kg in waste in one emplacement room.

Significant functions with respect to safety shall refer to functions in accordance with the Radiation and Nuclear Safety Authority Regulations STUK Y/1/2018 and STUK Y/4/2018. The licensee shall designate these functions and verify the competence of the persons performing these functions. Functions in accordance with Sections 7 i and 7 k of the Nuclear Energy Act (990/1987) are always considered significant functions with respect to safety. Approval of the individuals proposed to these functions shall be requested from STUK.

Site area shall refer to an area in use by nuclear power plant units and other nuclear facilities in the same area, and to the surrounding area, where movement and stay are restricted by the Decree of the Ministry of the Interior issued under Section 52 of the Police Act (493/1995). (STUK Y/2/2018)

Small-diameter piping shall refer to piping with DN ≤ 50.

Source material shall refer uranium that contains the mixture of isotopes in amounts occurring in nature, or uranium in which the relative quantity of isotope 235 has been reduced, thorium, and any of the materials specified above in the form of metal, alloy, chemical compound or concentrate. (161/1988, Section 3)

Spare part shall refer to a back-up part for an SSC that can be used to restore the reduced or lost operability to the required level.

Special processes shall refer to manufacturing processes, the results of which cannot be directly verified by means of a product inspection or testing after manufacture; instead, any shortcomings in the process may only appear later while the product is in use. Special processes include, for instance welding, forming and heat treatment.

Summary programme for in-service inspections shall refer to a summary programme required under Section 36 of the Nuclear Energy Decree (161/1988).

Supplier shall refer to an organisation or person manufacturing or providing a product or service. (SFS-EN ISO 9000:2015)

System in the context of information security shall refer to a system consisting of information processing equipment, data transfer equipment and software intended to intensify or facilitate a certain function or to make it possible. The system may be an information system, a communications system, an electrical or I&C system, or a communication system for security surveillance or emergency preparedness.

System/structure/component important to safety shall refer to systems, structures or components in safety classes 1, 2 and 3 and systems in class EYT/STUK.

Systems, Structures and Components (SSC) shall refer to mechanical, electrical, I&C or civil system, structure or component in safety classes 1, 2 and 3 or in class EYT/STUK (non-nuclear).

Test specimen shall refer to a piece manufactured for testing from a concrete, steel or reinforcement sample.

Testing organisation shall refer to an organisation performing testing activities requiring special competence. (Nuclear Energy Act 990/1987)

Third party shall refer to an individual or organisation that is independent of the individuals or organisations responsible for the design, manufacturing, supply, installation, procurement, ownership, operation or servicing of the item analysed.

Threat shall refer to a situation in which unlawful action against a nuclear facility, nuclear material, or nuclear waste is ascertained, or there is reason to suspect this. (STUK Y/3/2016)

Threat level shall refer to the classification made based on the severity and controllability of threats. Threat levels are the following:

• Normal situation (baseline preparedness), in which there are no observed security threats to the nuclear facility and security arrangements are carried out at the basic level and in basic preparedness.
• Elevated monitoring (elevated preparedness), in which a probable threat to the nuclear facility has been observed and security arrangements are stepped up from the basic level as planned.
• Threat (full preparedness), in which unlawful action against a nuclear facility or other action that endangers nuclear or radiation safety has been detected or there is reason to suspect this. Security arrangements are carried out at the most effective level and in full readiness.

Time limited ageing qualification or analysis shall refer to testing or calculational analysis to demonstrate the service life of SSC when retaining of the operability is limited in time as the integrity or functionality of the SSC will degrade with relation to duration of stressors acting on the SSC in operating conditions.

Transition temperature shift shall refer to transition temperature increase in ferritic steels caused by neutron irradiation. See also definition for “Radiation embrittlement”.

The trickle charge voltage for a set of accumulators shall refer to a voltage generated by a battery charger in order to maintain a charge level on a set of accumulators that exceeds the nominal voltage of the set of accumulators.

Type approval for building products shall refer to a voluntary approval procedure for building products in use in Finland that are legislated in the Decree on the Type Approval of Certain Construction Products. Type approval shows that a building product meets its required essential technical requirements with respect to the purpose of use stated by the manufacturer. A manufacturer who so wishes may apply for type approval for a building product subjected to the Decree on the Type Approval. Type approval is granted by a type organisation authorized by the Ministry of the Environment. Type approval requires certification of the production control. The type approval is mandatory for the building inspection authorities, which means that a type approved building product can be used in a construction work.

Unlawful action shall refer to an activity or measure that is aimed at directly or indirectly endangering the nuclear safety or radiation safety of a nuclear facility, nuclear material or nuclear waste. Deliberate or negligent activity that is punishable by law towards a nuclear facility, nuclear material or nuclear waste, or towards the persons working at a nuclear facility is considered unlawful action. (STUK Y/3/2016)

Use of nuclear energy shall refer to the operations laid down in Sections 2(1) and 2(2) of the Nuclear Energy Act. (Nuclear Energy Act 990/1987)
According to Section 2(1), the Act applies to:
1) the construction, operation and decommissioning of nuclear facilities;
2) mining and enrichment operations aimed at producing uranium or thorium;
3) the possession, manufacture, production, transfer, handling, use, storage, transport and import of nuclear material;
4) the possession, manufacture, production, transfer, handling, use, storage, transport, export and import of nuclear waste;
4 a) the disposal of nuclear waste in small-scale as opposed to large-scale
5) in cases to be provided for by Government decree, the possession, manufacture, assembly, transfer and import of the following material, devices, equipment, or information, should they prove pertinent to the proliferation of nuclear weapons or should the obligations under Finland’s international treaties in the field of nuclear energy have a bearing on them:
a) non-nuclear material, when its properties are particularly suited to creating nuclear energy;
b) devices and equipment intended or otherwise particularly suited for use in nuclear facilities;
c) devices and equipment intended or otherwise particularly suited for use in the manufacture of nuclear material or material referred to in item a);
d) equipment essential for the manufacture of the devices or equipment referred to in items a) and b)
e) nuclear information that is in written or some other physical form and not generally available
6) export and import of ores containing uranium or thorium, to be specified under Government decree.

According to Section 2(2) of the Nuclear Energy Act, the application of the Nuclear Energy Act shall be provided for by Government Decree, with respect to:
1) the conclusion and implementation of a private law agreement, for implementation outside Finland in regard of any of the activities referred to in this section (Section 2), with a foreign State, a foreign person or corporation, should the agreement prove pertinent to the proliferation of nuclear weapons or should the obligations under international treaties in the field of nuclear energy, to which Finland is a Party, have a bearing on the agreement; and
2) Nuclear fuel cycle-related research and development activities determined in Article 18(a) of the Protocol Additional (53/2004) to the agreement made on the implementation of Article III (1) and (4) of the Treaty on the Non-Proliferation of Nuclear Weapons between Austria, Belgium, Denmark, Finland, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Portugal, Spain, Sweden, the European Atomic Energy Community and the International Atomic Energy Agency.
(Nuclear Energy Act 990/1987)

User inspectorate shall refer to an inspection organisation as referred to in Article 16 of Pressure Equipment Directive 2014/68/EU.

Validation shall refer to confirmation, through the provision of objective evidence, that the requirements for a specific intended use or application have been fulfilled.

Valve refers to a mechanical component which is used to open or close a flow route or to control the flow. In the context of Guide YVL E.8, a valve is considered to include the parts forming an integral part of the valve structure and operations, excluding electrical and I&C equipment, such as the electric-motor actuator.

Ventilation shall refer to maintaining and improving the quality of indoor air by circulating it; in some rooms of a nuclear facility, ventilation systems are also used to limit the spread of radioactive substances.

Very low-level waste shall refer to nuclear waste whose average activity concentration of significant radionuclides does not exceed the value of 100 kBq per kilogram and the total activity does not exceed the values laid down in Section 6(1) of the Nuclear Energy Decree (161/1988).

Vital area shall refer to locations and premises within the protected area of a nuclear facility from which it is possible to conduct actions endangering nuclear or radiation safety that may lead to significant radiological consequences, for which reason these locations and premises must be placed under special physical protection.