1 Scope
This document specifies the basic requirements for the overall design of an energetic safety system pressurised water reactor nuclear power plant (hereinafter referred to as "nuclear power plant") to ensure that it can operate safely and reliably.
This document is applicable to newly built pressurised water reactor nuclear power plants with energy safety systems, and in-service pressurised water reactor nuclear power plants with energy safety systems may refer to the implementation.
2 Normative references
The contents of the following documents constitute essential provisions of this document through the normative references in the text. Among them, the date of the cited documents, only the date of the corresponding version applicable to this document; do not note the date of the cited documents, the latest version (including all the revision of the list) applicable to this document.
GB 6249 Environmental radiation protection regulations for nuclear power plants
GB 11806 Regulations for the safe transport of radioactive substances
GB 18871 Basic standards for ionising radiation protection and safety of radiation sources
3 Terminology and definitions
The following terms and definitions apply to this document.
3.1
safety system
A safety critical system for ensuring the safe shutdown of a reactor, the discharge of waste heat from the core and the consequences of anticipated operational events and design basis accidents.
[Source: HAF102-2016, Glossary].
3.2
active safety system
An energetic system used to ensure the safe shutdown of a reactor, to discharge waste heat from the core or to limit the consequences of anticipated operational events and design basis accidents.
[Source: GB/T35730-2017,3.3, with modifications]
3.3
pressurized water reactor nuclear power plants with active safety systems
Pressurized water reactor nuclear power plants with active safety systems for all safety functions within the design basis accident.
Note: Abbreviated as "energetic nuclear power plant".
[Source: GB/T35730-2017, 3.4, with modifications]
3.4
Safety function
To ensure that the facility or activity is capable of preventing and mitigating the radiological consequences of the normal operation of a nuclear power plant, anticipated operational transients and accidental operating conditions.
4 Design objectives for nuclear power plants
4.1 Nuclear safety design objectives
4.1.1 Basic safety objectives
Basic safety objective:To establish and maintain effective defences against radiological hazards in nuclear power plants in order to protect people and the environment from radiological hazards.
In order to achieve the basic safety objective, the following measures shall be taken:
a) Control of radiation exposure to personnel and the release of radioactive material to the environment during operation;
4.2 General economic objectives
Nuclear power plants need to be designed in such a way that the construction costs and whole life generation costs of nuclear power plants are sufficiently competitive in the market.
The main factors that need to be considered in the design of a nuclear power plant that have an impact on the economic objectives include the design life of the plant, the overall construction cycle of the plant, the average plant availability, the level of unplanned plant outages, the replacement cycle, and the optimisation of energy utilisation taking into account the environmental conditions of the site.
5 General design requirements for nuclear power plants
5.1 Longitudinal defence design
5.1.1 General requirements for the application of defence-in-depth design
Nuclear power plants should be designed with defence-in-depth measures to improve multi-level defence (inherent characteristics, equipment and protocols). In order to prevent possible harmful effects on people and the environment, a balanced safety concept of prevention and mitigation should be implemented to ensure that the consequences of an accident can be mitigated by taking appropriate mitigation measures to protect people and the environment in the event of a protection failure. Each separate effective level of defence is a fundamental part of the defence-in-depth of a nuclear power plant and should ensure that safety-related activities can be incorporated into a separate level of defence-in-depth.
The defence-in-depth concept and the principles of defence-in-depth application in design are in accordance with the requirements of the five levels of defence-in-depth specified in HAF 102.
5.1.2 Design for independence of defence in depth
The various levels of defence in depth should be as independent as possible from each other, so that the failure of one level of defence does not reduce the effectiveness of the other levels. In particular:
a) Safety facilities designed to mitigate the consequences of a core meltdown are, as far as practicable, independent of those designed to mitigate a design basis accident.
a) Safety facilities designed to mitigate the consequences of a core meltdown are, as far as practicable, independent of those used to mitigate the design basis accident.
5.2 Nuclear power plant operating conditions and safety analysis
5.2.1 Nuclear power plant operating conditions
Nuclear power plant operating conditions are classified as normal operation, expected operating events, design basis accidents and design extensions.
The specific principles and list of conditions for each category can be implemented in accordance with NB/T20035. At the same time, a set of design expansion conditions (including design expansion conditions that do not cause significant core damage and core meltdown design expansion conditions) should be derived based on engineering judgement, deterministic and probabilistic evaluation.
5.2.2 Deterministic safety analysis
A deterministic safety analysis shall be performed during design and shall cover all nuclear power plant operating conditions as specified in 5.2.1. The purpose of the deterministic safety analysis is to confirm that
a) the safety functions can be performed reliably;
b) the necessary structures, systems and components, in combination with operator actions, are sufficient to ensure that the release of radioactive material from the nuclear power plant is below acceptable limits and has a suitable safety margin.
Deterministic safety analyses are required to demonstrate that the radioactive barriers of a nuclear power plant maintain their integrity within the required limits. Deterministic safety analysis, when supplemented by probabilistic safety analysis, should also help to demonstrate that:
a) the source term and potential radiological consequences are acceptable under different nuclear power plant operating conditions;
b) that specific conditions leading to early releases or significant releases can be considered as "practically eliminated".
The specific analytical objectives, analytical methods, steep-edge effects and non-discretionary effects of different nuclear power plant conditions for definitive safety analysis. Analytical assumptions, treatment of steep-sided effects and uncertainties, and acceptance guidelines can be implemented in conjunction with the requirements for deterministic safety analyses in the guidelines.
The radioactivity acceptance criteria for different nuclear power plant conditions should meet the requirements of GB 6249 and realistic models and best estimation methods can be used to evaluate the design expansion conditions.
5.2.3 Probabilistic safety analysis
In the design of a nuclear power plant, a probabilistic safety assessment of the nuclear power plant should be completed in order to
a) provide a systematic analysis of the need for the design to properly consider all operating modes and all states of the nuclear power plant (including shutdown conditions) and to compare the results of the analysis with the risk guidelines that have been specified;
b) demonstrate that the overall design is balanced, without any - facility or hypothetical initiating events (hypothetical initiating events, which are based on
deterministic or probabilistic approach or a combination of both) would make an excessive or clearly uncertain contribution to the total risk, and to ensure that the depth of
The contribution of the first and second levels of defence in depth to nuclear safety should be ensured;
Confirmation that small deviations in plant parameters do not cause serious abnormalities in plant performance (steep edge effects);
d) provide a safety assessment of the probability of a severe core damage state and a significant release of radioactive material outside the plant that requires an early response from outside the plant (especially associated with early containment failure);
e) provide an assessment of the frequency and consequences of external hazards (particularly those external events specific to the nuclear power plant site);
f) Identify systems that may reduce the probability of core meltdown accidents or mitigate their consequences through design improvements or modifications to operating procedures;
g) Evaluation of the adequacy of emergency procedures for nuclear power plants.
h) Nuclear power plant designs may refer to NB/T 20037 (all parts) for probabilistic safety evaluation.
5.4 Reliability design requirements
Safety critical structures, systems and components shall be designed in accordance with the latest or currently applicable codes and standards; their design shall have been previously verified under equivalent conditions of use.
Single-failure criteria shall be applied to each safety combination included in the design of a nuclear power plant. The principles for the application of the Single Failure Criteria are as specified in GB/T 13626 and the requirements for the application of the Single Failure Criteria to safety critical fluid systems are as specified in NB/T 20402.
The design needs to consider the possibility of common cause failures in safety critical items to determine how the required reliability should be achieved with the principles of diversity, multiplicity and independence.
6 General design requirements for specialist areas
6.1 General layout requirements
A nuclear power plant building includes the nuclear island building. The turbine plant and the nuclear power plant supporting facilities plant. The nuclear island plant shall be divided according to function, including the reactor plant, fuel plant, nuclear auxiliary plant and electrical plant, etc.
The layout of the nuclear island should follow the following guidelines:
a) Highly radioactive areas should be as compact as possible;
b) The reactor plant should be located in the centre of the nuclear power unit;
c) Safety systems should be located as close as possible to the reactor building;
d) the area between the other nuclear island buildings and the reactor building needs to be as spacious as possible to allow for sufficient containment penetrations;
6.2 Reactor core design
6.2.1 Design margins
The reactor core and associated coolant systems, control and protection systems should be designed with appropriate margins to ensure that the specified acceptable fuel design limits are not exceeded and that radiation safety standards are met under any operational and accident conditions.
6.2.2 Reactor nuclear design
The nuclear design of the reactor shall provide for fuel assemblies within the core. It should provide sufficient residual reactivity and control means to determine the power distribution, fuel consumption distribution and reactivity coefficient of the core to meet safety requirements.
Adequate means should be available to detect the distribution of neutron injection rates in the reactor core and their variation.
The reactor core and associated cooling system should be designed to have a negative power reactivity coefficient under all operating and accident conditions, with the net effect of the instantaneous nuclear feedback inherent in the reactor compensating for the rapid increase in reactivity.
The minimum and maximum limits of the reactivity coefficient are a function of various parameters (e.g. power level, boron concentration. The reasonableness of the reactivity factor envelopes used for the analysis of various operating and accident conditions should be confirmed by appropriate studies.
The reactor core and associated coolant, control and protection systems should be designed in such a way that power oscillation conditions exceeding the specified fuel design limits are unlikely to occur or, if they do occur, can be reliably and rapidly monitored and suppressed.
The basic requirements for the nuclear design of the reactor core can be found in NB/T 20057.1.
6.3 Reactor coolant system pressure boundary design
The reactor coolant system and associated auxiliary, control and protection systems should be designed with sufficient margins to ensure that the design conditions of the reactor cooling system pressure boundary are not exceeded during any normal operation including anticipated operational events.
The reactor coolant system should be protected against overpressure in all modes of operation, with particular attention to overpressure protection in cryogenic watertight conditions.
The design, manufacture, installation and testing of the reactor coolant system pressure boundary should ensure that the probability of abnormal leakage, rapid crack expansion and overall rupture is extremely low.
The design needs to take into account all conditions of the reactor coolant system pressure boundary material in operating conditions including maintenance, test conditions and accident conditions, as well as any uncertainties in determining the initial condition and possible rate of deterioration of the component after the expected effects of many factors such as erosion, creep, fatigue, chemical environment, radiation environment and ageing.
The design, manufacture and arrangement of the components of the reactor coolant system pressure boundary should facilitate adequate inspection and testing of the pressure boundary at regular intervals throughout the life of the nuclear power plant.
Specific reactor coolant system designs can be found in NB/T20187.
6.4 Design of containment systems
6.4.1 Functional design requirements for containment systems
The containment system shall be designed to ensure or contribute to the following safety functions:
a) containment of radioactive material during operational and accident conditions;
b) radiation shielding during operational and accident conditions;
c) defence against external natural and external man-made events.
The reactor containment and associated systems provide an inherent containment barrier to
Foreword
2 Normative references
3 Terminology and definitions
4 Design objectives for nuclear power plants
5 General design requirements for nuclear power plants
6 General design requirements for specialist areas
