ability of the core components to fulfil their safety functions adequately over the lifetime of the plant.
(d) Any significant subsystem component, including any separate provision for moderation and fuel location, with corresponding design drawings.
(e) The conclusions from a consideration of the effects of in‑service maintenance programmes on the fulfilment of safety functions, including surveillance and inspection programmes to monitor the effects of irradiation and ageing on the core components.
CHAPTER 5: REACTOR COOLANT SYSTEM AND ASSOCIATED
codes. The specific detailed stress analyses for each of the major components should be directly referenced so as to enable further evaluations to be made, if necessary.
3.5.5. This section should contain a description of, and a justification for, the design features that have been implemented to ensure that the performance of the various components of the reactor coolant system and of the subsystems interfacing with the reactor coolant system meets the safety requirements for design. The description should include the reactor coolant piping or ducting, the main steam line isolation system, the isolation cooling system of the reactor core, the main steam line and feedwater piping, the pressurizer relief discharge system, and the residual heat removal system, including all components (e.g. pumps, valves, supports). For pressurized water reactors, this should also include the reactor coolant pumps, the steam generators and the pressurizer. For boiling water reactors, this should include the recirculation pumps and the boilers.
3.5.6. A schematic flow diagram of the reactor coolant system and associated systems denoting all major components, principal pressures, temperatures, flow rates and coolant volume under normal steady state, full power operating conditions should be provided. An elevation drawing of the piping and instrumentation of the reactor coolant system and associated systems showing the principal dimensions of the reactor coolant system in relation to the supporting or surrounding concrete structures should also be provided.
Materials
3.5.7. A justification of the choice of materials used for the components of the reactor coolant system and associated systems should be provided, specifically for those forming the primary pressure boundary. The information provided should describe the corresponding material specifications, including the following:
(a) Chemical, physical and mechanical properties;
(b) Resistance to corrosion;
(c) Consideration of the effects of irradiation (e.g. in terms of waste management and potential for occupational exposure);
(d) Dimensional stability, strength, toughness, crack tolerance and hardness.
3.5.8. The properties and required performance of seals, gaskets and fasteners in the pressure boundary should also be described. This section should address applicable degradation mechanisms and fabrication challenges, including stress corrosion cracking and sensitization of welds; it should describe the precautions
implemented to protect against such degradation mechanisms and fabrication challenges, and the analysis performed to justify the adequacy of the chosen materials and processes.
Reactor coolant system and reactor coolant pressure boundary
3.5.9. This section should describe the measures implemented to ensure the integrity of the reactor coolant system throughout the lifetime of the plant, including those measures taken to prevent cold overpressurization. In addition, this section should provide information on the means of overpressure protection of the reactor coolant pressure boundary, including all pressure‑relieving devices (e.g. isolation, safety and relief valves). The provisions for coolant leakage detection should also be described.
3.5.10. This section should also provide a description of the scope of application of the leak before break concept, or the break preclusion concept, and its implementation in the piping of the reactor coolant system. The description should include the means of monitoring and an analytical demonstration of what is necessary to ensure limitation of the break size in the reactor coolant system. This section should also describe the implications of these concepts for the design of other systems or components (e.g. reactor internals) and for the scope of the postulated initiating events covered by the safety analysis provided in chapter 15 of the safety analysis report.
Reactor vessel
3.5.11. The reactor vessel design should be described in this section in sufficient detail to demonstrate that all the materials, fabrication methods, inspection techniques and load combinations conform to applicable regulations and to industrial codes and standards. The design information should include the reactor vessel materials, the pressure–temperature limits and the integrity of the reactor vessel, including considerations of the effects of embrittlement. Information on the neutron flux distribution and expected neutron fluence on the walls of the reactor pressure vessel, derived from the core characteristics, should be included (see paras 3.4.5 and 3.4.10).
3.5.12. Information should also be provided on the provisions to ensure the protection of the reactor vessel against seismic loads and surrounding environmental conditions, including the effects of pressurized thermal shocks and the behaviour of reactor vessel penetrations.
Reactor coolant pumps or recirculation pumps
3.5.13. This section should provide a description of, and a justification for, the design features that have been implemented to ensure that the performance of the reactor coolant pumps (pressurized water reactors) or recirculation pumps (boiling water reactors) meets the safety requirements for design. The description should provide information on the hydraulic parameters that ensure adequate cooling of the fuel and adequate flow coastdown characteristics of the pumps in the event of a pump trip so as to avoid undesirable thermohydraulic conditions. The information should present the provisions made to preclude rotor overspeeding and to address cavitation and possible vibration of the reactor coolant pumps and associated structures in the event of a design basis loss of coolant accident. The description should also address the performance of pump seals, including their performance under prolonged station blackout conditions.
The evaluation of pump and motor lubrication system failures (e.g. leaks of lubricant, loss of cooling) should also be included to help prevent the sticking of bearings in pumps and motors.
Primary heat exchangers (steam generators) in pressurized water reactors 3.5.14. This section should provide a description of, and a justification for, the design features that have been implemented to ensure that the performance of the steam generators meets the safety requirements for design. The description should include the internal structures of the steam generators and connections to feedwater and steam exits and drains, as well as access points for inspection and leak detection.
3.5.15. The description should provide information on the design limits for water chemistry, for the concentration of impurities and for levels of radioactive material in the secondary side of the steam generators during normal operation.
3.5.16. The potential effects of damage to the heat exchange tubes, and the design criteria to prevent this from occurring, should be specified, including the following:
(a) The operational states considered in the design of the steam generator tubes, and the accident conditions selected, together with the justification for this selection, to define the allowable stress intensity limits;
(b) The extent of tube wall thinning that could be tolerated without exceeding the allowable stress intensity limits defined in para. 3.5.16(a) above, under the postulated condition of a design basis pipe break in the reactor
coolant pressure boundary or a break in the secondary piping during reactor operation.
Reactor coolant piping
3.5.17. This section should provide a description of, and a justification for, the design features that have been implemented to ensure that the performance of the reactor coolant piping meets the safety requirements for design. The description should include the design, fabrication and operational provisions to control those factors that contribute to stress corrosion cracking.
Reactor pressure control system
3.5.18. This section should provide a description of, and a justification for, the design features that have been implemented to ensure that the performance of the reactor pressure control system meets the safety requirements for design. In addition to the pressurizer systems (i.e. pressurizer heaters and sprays in pressurized water reactors), these design features should include the depressurization systems, such as the pressure relief tank or pool (in pressurized water reactors) or wet well (in boiling water reactors); the pressure relief and safety valves; and associated piping.
3.5.19. A description of the reactor depressurization systems used for design basis accidents and those used for design extension conditions should be provided, including a clear demonstration of the independence of the levels of defence in depth that reflects the relevance of these systems.
Reactor coolant system component supports and restraints
3.5.20. This section should provide a description of, and a justification for, the design features that have been implemented to ensure the adequacy and integrity of supports and restraints.
Reactor coolant system and connected system valves
3.5.21. This section should provide a description of, and a justification for, the design features that have been implemented to ensure that the performance of the valves interfacing with the reactor coolant system meets the safety requirements for design. This description should include safety and relief valves, valve discharge lines, and any associated equipment.
Access and equipment requirements for in‑service inspection and maintenance
3.5.22. In this section, information should be provided on the system boundary that is subject to inspection. In particular, components and associated supports should be described, including all pressure vessels, piping, pumps, valves and bolting, with regard to the following:
(a) Accessibility, including radiation protection aspects, working conditions (e.g. temperature, hygrometry) and systems operability;
(b) Examination categories and methods;
(c) Inspection intervals;
(d) Provisions for evaluating the results of examinations, including evaluation methods for detected flaws and repair procedures for components that reveal defects;
(e) System pressure tests.
The programmes for in‑service inspection and maintenance and their implementation milestones should be described, and reference should be made to any applicable standards.
Reactor auxiliary systems
3.5.23. This section should provide a description of, and a justification for, the design features that have been implemented to ensure that the performance of the various connected or associated systems interfacing with the reactor coolant system meets the safety requirements for design. The systems described in this section should be selected so as to avoid repetition of the information in other chapters of the safety analysis report, in particular in chapters 6, 9 and 10.
3.5.24. The associated systems that should be covered in this section include the following:
(a) The chemical and inventory control systems for the reactor coolant;
(b) The reactor coolant cleanup system;
(c) The residual heat removal system;
(d) The high point vents of the reactor coolant system;
(e) The heavy water collection system for pressurized heavy water reactors;
(f) The moderator system and its cooling system for pressurized heavy water reactors;
(g) The reactor core isolation cooling system for boiling water reactors;
(h) The isolation condenser system for boiling water reactors.