The Council of State, on the submission of the Ministry of Trade Industry and by virtue of Section 81, first paragraph, point 1 of the Nuclear Energy Act (990/87) given on 11 December 1987, has decided on the following:
Chapter 1
Scope and definitions
Section 1
Scope
In this decision general regulations relating to the safety of nuclear power plants equipped with a light water reactor are given.
Section 2
Definitions
In this decision:
- dose (more precisely, effective dose) shall refer to the weighted sum of the equivalent doses of tissues and organs subjected to radiation, where the equivalent dose denotes the product of the mean energy absorbed per unit mass in the tissue or organ and of the radiation weighting factor;
- dose commitment shall refer to the time integral of the dose rate reaching to a separately defined period of time;
- criticality accident shall refer to such an accident during which an uncontrolled chain reaction of fissions caused by neutrons arises;
- quality assurance shall refer to all planned and systematic actions necessary to provide adequate confidence that a component, plant or activity will satisfy given requirements;
- anticipated operational transient shall refer to a deviation milder than an accident from normal operational conditions which can be expected to occur once or several times during any period of a hundred operating years;
- accident shall refer to a deviation from normal operating conditions which is not an anticipated operational transient. Accidents are grouped into two classes:
- postulated accident means an event which serves as a design basis for the engineered safety systems of a nuclear power plant. The nuclear power plant shall withstand a postulated accident without severe fuel damages and without radioactive releases that would require extensive measures for restricting the exposure of the general public; and
- severe accident means an event during which a considerable part of the fuel in the reactor is damaged.
- probabilistic safety analysis shall refer to estimates and calculations based on experience and probabilistic methods which address the reliability of operation of nuclear power plant systems, potential accident sequences, reactor damage, accident propagation and releases of radioactive materials;
- safety functions shall refer to functions important from the safety point of view the meaning of which is to prevent the emergence or advancement of transient and accident conditions or to mitigate the consequences of accidents; the most important safety functions are reactor shutdown, residual heat removal from the reactor to the ultimate heat sink and the functioning of the containment building; and
- nuclear power plant shall refer to a nuclear installation equipped with a nuclear reactor which is intended for electricity generation, or if several such or other nuclear installations have been placed on the same site, the entity of installations formed by them.
Chapter 2
General principles
Section 3
General objective
The general objective is to ensure nuclear power plant safety so that nuclear power plant operation does not cause radiation hazards which could endanger safety of workers or population in the vicinity or could otherwise harm the environment or property.
Section 4
Safety culture
When designing, constructing and operating a nuclear power plant, an advanced safety culture shall be maintained which is based on the safety oriented attitude of the topmost management of the organisations in question and on motivation of the personnel for responsible work. This presupposes well organised working conditions and an open working atmosphere as well as the encouragement of alertness and initiative in order to detect and eliminate factors which endanger safety.
Section 5
Quality assurance
Advanced quality assurance programmes shall be employed in all activities which affect safety and relate to the design, construction and operation of a nuclear power plant.
Section 6
Demonstration of compliance with the safety regulations
If compliance with the safety regulations cannot be directly ascertained, fulfillment shall be demonstrated by the necessary experimental and calculational methods.
Nuclear power plant safety and the design of its safety systems shall be substantiated by accident analyses and probabilistic safety analyses. Analyses shall be maintained and revised if necessary, taking into account operating experience, the results of experimental research and the advancement of calculating methods.
The calculating methods employed for demonstrating the meeting of the safety regulations shall be reliable and well qualified for dealing with the events in question. They shall be applied so that the calculated results are, with a good confidence, less favourable than the results which are considered best estimates. Furthermore, analyses which picture the likely course of transients and accidents shall be conducted for the purpose of probabilistic safety analyses and for the development of emergency operating procedures.
Chapter 3
Regulations concerning radiation exposure and releases of radioactive materials
Section 7
Limitation of radiation exposure
Radiation exposure arising from the operation of a nuclear power plant shall be kept as low as reasonably achievable. A nuclear power plant and its operation shall also be designed so that the limits presented in this decision are not exceeded.
Section 8
Radiation safety of nuclear power plant workers
A nuclear power plant's design and operation shall be implemented so that radiation exposure to workers can be limited as separately enacted.
Section 9
Limit for normal operation
The limit for the dose commitment of the individual of the population, arising from normal operation of a nuclear power plant in any period of one year, is 0.1 mSv. Based on this limit, release limits for radioactive materials during the normal operation of a nuclear power plant are to be defined.
Section 10
Limit for an anticipated operational transient
The limit for the dose of the individual of the population, araising, as the result of an anticipated operational transient, from external radiation in the period of one year and the simultaneous radioactive materials intake, is 0.1 mSv.
Section 11
Limit for a postulated accident
The limit for the dose of the individual of the population, arising, as the result of a postulated accident, from external radiation in the period of one year and the simultaneous radioactive materials intake, is 5 mSv.
Section 12
Limit for a severe accident
The limit for the release of radioactive materials arising from a severe accident is a release which causes neither acute harmful health effects to the population in the vicinity of the nuclear power plant nor any long-term restrictions on the use of extensive areas of land and water. For satisfying the requirement applied to long-term effects, the limit for an atmospheric release of cesium-137 is 100 TBq. The combined fall-out consisting of nuclides other than cesium-isotopes shall not cause, in the long term, starting three months from the accident, a hazard greater than would arise from a cesium release corresponding to the above-mentioned limit.
The possibility that, as the result of a severe accident, the above mentioned requirement is not met, shall be extremely small.
Chapter 4
Design requirements for ensuring nuclear safety
Section 13
Levels of protection
In design, construction and operation proven or otherwise carefully examined high quality technology shall be employed to prevent operational transients and accidents (preventive measures).
A nuclear power plant shall encompass systems by the means of which operational transients and accidents can be quickly and reliably detected and the aggravation of any event can be prevented. Accidents leading to extensive releases of radioactive materials shall be highly unlikely (control of transients and accidents).
Effective technical and administrative measures shall be taken for the mitigation of the consequences of an accident. Counter-measures for bringing an accident under control and for preventing radiation hazards shall be planned in advance (mitigation of consequences).
Section 14
Technical barriers for preventing the dispersion of radioactive materials
Dispersion of radioactive materials from the fuel of the nuclear reactor to the environment shall be prevented by means of successive barriers which are the fuel and its cladding, the cooling circuit (the primary circuit) of the nuclear reactor and the containment building.
Section 15
Ensuring fuel integrity
The probalitity of significant degradation of fuel cooling or of a fuel failure due to other reasons shall be low during normal operational conditions and anticipated operational transients.
During postulated accidents, the rate of fuel failures shall remain low and fuel coolability shall not be endangered.
The possibility of a criticality accident shall be extremely low.
Section 16
Ensuring primary circuit integrity
The primary circuit of a nuclear reactor shall be designed so that the stresses imposed upon it remain, with sufficient confidence, below the values defined for structural materials for preventing a fast growth crack during normal operational conditions, anticipated operational transients and postulated accidents. The possibility of a primary circuit break due to other reasons shall be low, too.
Section 17
Ensuring containment building integrity
The containment shall be designed so that it will withstand reliably pressure and temperature loads, jet forces and impacts of missiles arising from anticipated operational transients and postulated accidents.
Furthermore, the containment shall be designed so that the pressure and temperature created inside the containment as a consequence of a severe accident will not result in its uncontrollable failure.
The possibility of the creation of such a mixture of gases as could burn or explode in a way which endangers containment integrity shall be small in all accidents.
The hazard of a containment building failure due to a core melt shall also be taken into account in other respects in designing the containment building concept.
Section 18
Ensuring safety functions
In ensuring safety functions, inherent safety features attainable by design shall be made use of in the first place. In particular, the combined effect of a nuclear reactor's physical feedbacks shall be such that it mitigates the increase of reactor power.
If inherent safety features cannot be made use of in ensuring a safety function, priority shall be given to systems and components which do not require an off-site power supply or which, in consequence of a loss of power supply, will settle in a state preferable from the safety point of view.
Systems which perform the most important safety functions shall be able to carry out their functions even though an individual component in any system would fail to operate and additionally any component affecting the safety function would be out of operation simultaneously due to repairs or maintenance.
A nuclear power plant shall have on-site and off-site electrical power supply systems. The execution of the most important safety functions shall be possible by using either of the two electrical power supply systems.
Safety systems which back up each other as well as parallel parts of safety systems shall be separated from each other so that their failure due to an external common cause failure is unlikely.
In ensuring the most important safety functions, systems based on diverse principles of operation shall be used to the extent possible.
Section 19
Avoiding human errors
Special attention shall be paid to the avoidance, detection and repair of human errors. The possibility of human errors shall be taken into account both in the design of the nuclear power plant and in the planning of its operation so that the plant withstands well errors and deviations from planned operational actions.
Section 20
Protection against external events and fires
The most important nuclear power plant safety functions shall remain operable in spite of any natural phenomena estimated possible on site or other events external to the plant. In addition, the combined effects of accident conditions induced by internal causes and simultaneous natural phenomena shall be taken into account to the extent estimated possible.
Structures, systems and components important to safety shall be designed and located, as well as protected by means of structural fire barriers and adequate fire fighting systems so that the likelihood of fires and explosions is small and their effect on plant safety insignificant.
Section 21
Safety classification
The functions important to the safety of the systems, structures and components of a nuclear power plant shall be defined and the systems, structures and components classified according to their safety significance.
The systems, structures and components important to safety shall be designed, manufactured, installed and operated so that their quality level and the inspections and tests required to verify their quality level are adequate considering any item's safety significance.
Section 22
Monitoring and control of a nuclear power plant
A nuclear power plant's control rooms shall contain equipment which provide information about the plant's operational state and any deviations from normal operation as well as systems which monitor the state of the plant's safety systems during operation and their functioning during operational transients and accidents.
A nuclear power plant shall contain automatic systems that maintain the plant in a safe state during transients and accidents long enough to provide the operators a sufficient time to consider and implement the correct actions.
There shall be an emergency control post at a nuclear power plant which is independent of the control room and the necessary local control systems by the means of which the nuclear reactor can be shut down and cooled and residual heat from the nuclear reactor and spent fuel stored at the plant can be removed.
Chapter 5
Operation of a nuclear power plant
Section 23
Technical Specifications and plant procedures
Technical and administrative requirements and restrictions for ensuring the safe operation of a nuclear power plant shall be set forth in the plant's Technical Specifications.
Appropriate procedures shall exist for the operation, maintenance, in-service inspections and periodic tests as well as transient and accident conditions of a nuclear power plant.
Section 24
Operation and maintenance
In all activities affecting the operation of a nuclear power plant and the availability of components, a systematic approach shall be applied for ensuring plant operators' continuous awareness of the state of the plant and its components.
The reliable operation of systems and components shall be ensured by adequate maintenance as well as by regular in-service inspections and periodic tests.
Section 25
Personnel
Nuclear power plant personnel shall be well suited for its duties, competent and well trained. Initial, complementary and refresher training programmes shall be established for the personnel.
For ensuring safety in all situations, competent personnel shall be available in a sufficient number.
Section 26
Monitoring releases of radioactive materials
Releases of radioactive materials from a nuclear power plant and their concentrations in the environment shall be effectively monitored.
Section 27
Operating experience and safety research
Operating experience from nuclear power plants as well as results of safety research shall be systematically followed and assessed.
For further safety enhancement, actions shall be taken which can be regarded as justified considering operating experience and the results of safety research as well as the advancement of science and technology.
Chapter 6
Miscellaneous provisions
Section 28
Nuclear power plants in operation
For the part of such a nuclear power plant for which an operating licence was issued before the entry into force of this decision (an operating nuclear power plant) the limit for the dose referred to in Section 11 is 100 mSv, unless the application of the provisions contained in Section 11, as such, is justified, considering the provisions of Section 27, second paragraph.
The provisions of Sections 12, 17 and 18 of this decision are applied to an operating nuclear power plant to the extent justified based on the provisions of Section 27, second paragraph, and taking into account the technical solutions of the nuclear power plant in question.
Section 29
Detailed regulations
Detailed regulations relating to the safety of a nuclear power plant are issued by the Finnish Centre for Radiation and Nuclear Safety.
Section 30
Entry into force
This decision enters into force on 1 March 1991.