(g) The reactor core isolation cooling system for boiling water reactors;
(h) The isolation condenser system for boiling water reactors.
3.6.7. For each of the engineered safety features, the detailed description of the design should, to the extent possible, include the items specified in Appendix II.
In describing the materials used in the components of an engineered safety feature, interactions of the materials with fluids that could potentially impair the operation of the engineered safety feature should be taken into account.
The description should cover the compatibility of materials used for engineered safety features with core coolant and containment spray solutions. All organic materials that exist in significant amounts within the containment building should be described, including plastics, lubricants, paints and coatings, electrical cable insulation, and asphalt.
Emergency core cooling systems and residual heat removal systems
3.6.8. This section should present relevant information on the emergency core cooling systems, residual heat removal systems and associated systems. The description should cover safety systems designed to cope with design basis accidents and safety features for design extension conditions, including design extension conditions with core melting. These systems can be related to the primary or secondary circuits or to the containment, depending on the reactor design (e.g. safety injection system, feedwater system, steam dump system, passive safety system). This section should provide relevant information on all the engineered safety features — both active and passive — in accordance with the general design aspects presented in chapter 3 of the safety analysis report in order to meet Requirement 52 of SSR‑2/1 (Rev. 1) [3]. Further recommendations are provided in SSG‑56 [28]. Relevant coolant storage tanks should also be described in this section. A description of the actuation logic (for protection systems) should be provided in chapter 7 of the safety analysis report.
3.6.9. This section should provide information on the emergency feedwater system (if not covered in chapter 10 of the safety analysis report) as an essential means of residual heat removal through the secondary side of the steam generators in the case of accident conditions in pressurized water reactors. The information provided should be linked to the general design aspects presented in chapter 3 of the safety analysis report and should demonstrate compliance with Requirement 51 of SSR‑2/1 (Rev. 1) [3] and the recommendations provided in SSG‑56 [28].
3.6.10. As with the emergency feedwater system, this section should describe the emergency steam dump system as another essential means for the removal of excessive or residual heat from the steam system under certain accident conditions (see Requirement 51 of SSR‑2/1 (Rev. 1) [3] and the recommendations provided
in SSG‑56 [28]). Alternatively, the description of this system can be included in chapter 10 of the safety analysis report.
Emergency reactivity control system
3.6.11. This section should provide information on the means of ensuring reactor shutdown (e.g. by injecting concentrated boron) in addition to those provided by the standard reactivity control system.
Safety features for stabilization of the molten core
3.6.12. This section should provide relevant information on safety features to stabilize the molten core as a necessary means of molten core solidification — either inside the reactor pressure vessel or in a dedicated molten core localization system — as a necessary precondition for protecting the containment basemat and ensuring containment integrity in the long term.
Containment and associated systems
3.6.13. The description of the systems in this section should include both primary and secondary containment systems. This section should present relevant information on the containment and associated systems that are implemented to contain the effects of accidents and to prevent the loss of containment integrity in all plant states, including design extension conditions with core melting. This section should describe how the containment and associated systems meet Requirements 54–58 of SSR‑2/1 (Rev. 1) [3] and comply with the recommendations provided in IAEA Safety Standards Series No. SSG‑53, Design of the Reactor Containment and Associated Systems for Nuclear Power Plants [29]. This section, in combination with chapter 15 of the safety analysis report, should provide a sufficient demonstration of containment integrity for all plant states and should provide the basis for the development of procedures, the specification of any necessary instrumentation, and of the necessary operator response and equipment response.
3.6.14. This section should describe both the concrete structures and the internal steel structures of the containment, including a demonstration of their performance. The containment systems to be covered in this section should include the following, as applicable:
(a) The containment heat removal systems or containment spray system and other active heat removal systems;
(b) The containment passive heat removal systems;
(c) The system for control of hydrogen and other combustible gases in the containment;
(d) The containment isolation system;
(e) The systems for protection of the containment against overpressure and underpressure;
(f) The containment annulus ventilation system;
(g) The containment ventilation system;
(h) The containment filtered venting system;
(i) The containment penetrations, airlocks, doors and hatches.
3.6.15. The maximum allowable leak rate for accident conditions should be specified in this section. In addition, the containment leakage testing system should be described. It should be demonstrated that the containment, containment penetrations and other containment isolation barriers allow for periodic leakage testing as part of the operational programmes. This section should provide sufficient basis for the development and implementation of an adequate testing programme for containment leakage (see Requirements 29 and 55 of SSR‑2/1 (Rev. 1) [3] and SSG‑53 [29]). The following tests should be considered, including information on the proposed schedule for performing pre‑operational and periodic leakage rate tests as well as relevant special testing requirements:
(a) Containment integrated leak rate test;
(b) Containment penetration leak rate test;
(c) Containment isolation valve leak rate test.
Habitability systems
3.6.16. This section should present relevant information on habitability systems.
Habitability systems are those engineered safety features that are provided to ensure that essential plant personnel can remain at their posts to take actions to operate the plant safely in operational states and to maintain acceptable conditions in the event of an accident. The relevant locations to be considered include control locations (i.e. control room, supplementary control room, and other emergency response facilities and locations), technical support centres and emergency centres. The description should include the available means of ensuring the habitability of such locations. Examples of these means are shielding, air filtration or purification systems, compressed air storage systems, and other provisions (e.g. adequate lighting) for the control of working conditions (see paras 3.9.12 and 3.9.18).
3.6.17. The habitability of control locations under design extension conditions with core melting should be addressed in this section of the safety analysis report. For remote sites, the description should include a demonstration of the habitability of these locations in the case of external hazards exceeding the design basis events combined with internal events.
Systems for the removal and control of fission products
3.6.18. This section should provide relevant information on the systems for the removal and control of fission products (if not already described as a part of the containment systems). The following specific information should be presented to demonstrate the performance capability of these systems:
(a) Considerations of the coolant pH and chemical conditioning in all necessary conditions of system operation;
(b) The effects on filter operability of postulated design basis loads due to fission products;
(c) The effects on filter operability of design basis release mechanisms for fission products.
Other engineered safety features
3.6.19. This section should present relevant information on any other engineered safety features implemented in the plant design that are not covered in any previous sections. Examples include the steam dump to the atmosphere and the backup cooling systems. The list of these systems to be described will depend on the type of plant under consideration. It should be decided whether certain systems (e.g. the auxiliary feedwater system) are described here or in chapter 9 of the safety analysis report, which deals with auxiliary systems in a much broader sense, or in chapter 10, which deals with steam and power conversion systems.
CHAPTER 7: INSTRUMENTATION AND CONTROL