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Section 4.5.3, Design principles and requirements

The application should describe the design principles and requirements that cover the processes for the overall design of the facility, and the operation and interaction of all of the SSCs to be addressed. To ensure that the reactor facility will be reliable, robust and maintainable, the applicant should ensure that the design:

·       conforms to high quality levels

·       is informed by recent developments in knowledge and technology

·       is resistant to the effects of common-cause events and, to the extent practicable, to severe accidents

When aspects of the design are based on conservative deterministic principles, such as those outlined in international codes and standards or in regulatory documents, the application should describe the use of such principles. If the design of the reactor facility does not fully comply with a specific deterministic principle in a regulatory document, the applicant should demonstrate that the overall level of safety is not impaired.

The application should identify the criteria used for determining the level of acceptable risk, and should show that the criteria meet general safety objectives and concepts in accordance with section 4 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

The application should describe the decision-making methodology (for example, cost/benefit, best available technology, and so on) that was used to select the design option.

Safety objectives and goals

The safety objectives and goals are described in detail in REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

The application should describe how the safety objectives and goals have been met in the design of SSCs, and should demonstrate that these objectives and goals are in accordance with sections 4.1 and 4.3.3 of REGDOC‑2.5.2 [9].

Where there is some duplication of information requested in various sections, the application may include cross-references to detailed information in other sections as appropriate.

Safety objectives include general nuclear safety objectives, radiation protection objectives, technical safety objectives and environmental protection objectives. Safety goals include qualitative and quantitative safety goals, core damage frequency, and small and large release frequencies.

Design authority

The application should demonstrate that the design authority is established in accordance with section 5.1 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

The application should identify the design authority responsible for the overall design. If the design authority has been transferred from another organization, the applicant should provide the formal relationships (including roles and responsibilities) and the prerequisites that had to be met prior to the transfer.

Applicable regulations, codes and standards

The application should demonstrate that the design envelope of the reactor facility is established in accordance with section 7.2 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

The application should include declarations of the design's compliance with the codes and standards used. The applicant should evaluate these documents for their applicability, sufficiency and adequacy, and provide the results in the application. If necessary, the standards used should be supplemented with additional requirements that should also be identified in the application.

The applicant should provide an assessment, such as a gap analysis, if the codes and standards differ from those used in Canada. The application should include information pertaining to cases where requirements contained in any of the applicable regulations or codes and standards are not met.

The application should include an assessment of the safety significance of any deviations from applicable codes and standards. Where necessary, a separate and complete justification should be provided for each deviation. This justification should include all information necessary to assure the CNSC that any deviations will not negatively affect the facility's overall level of safety. This justification should be included wherever applicable in the licence application or in documents referenced in the licence application.

Safety assessment and engineering evaluation

The applicant should demonstrate that a systematic process has been applied throughout the design activities to ensure that the design meets all relevant safety requirements, and that the design process of the reactor facility has followed proven engineering practices. For systems important to safety, this includes:

·       failure modes and effects analysis

·       assessment of vulnerability to single failures, crosslinks, common cause and common mode failures

·       assessment of system reliability and equipment function in the anticipated environment

·       as applicable, assessment of seismic events

The applicant should ensure that the reactor facility design meets all other applicable safety and regulatory requirements.

The application should summarize compliance with applicable design requirements (with reference to the original reports), including technical information on:

·       material strength

·       overpressure protection

·       corrosion resistance

·       environmental qualification

·       reliability assessment

·       resistance to electromagnetic and radiofrequency interference

·       verification and validation of software

This section should provide the following information for each system that is credited, or that supports a credited system, in the safety analysis:

·       an assessment of the functional capability of the system that is directly credited in the safety analysis, including but not limited to:

·       timing of system operation

·       minimum system performance envelope to meet safety analysis assumptions

·       ability of the system to perform over the lifetime of the reactor facility

·       ability of the system to perform in any abnormal environmental conditions in accident scenarios for which the system is credited

·       a demonstration that the physical separation, the electrical and/or fluid isolation devices and the environmental qualification requirements (or any other special protective measures) provide sufficient capacity to deliver the credited functions reliably

Identification of plant states and operational configurations

The application should identify all plant states and operational configurations in accordance with:

·       REGDOC‑2.4.1, Deterministic Safety Analysis [24]

·       section 7.3 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9]

For operational states (normal operation and anticipated operational occurrences (AOOs)), the information should cover configurations such as start-up, normal power operation, shutting down, shutdown, refuelling and any other normal operating configuration. The application should identify the key parameters and unique characteristics of each operational configuration, including the specific design provision for maintaining the configuration. The application should also provide the permissible periods of operation at different conditions (for example, power level) in the event of a deviation from normal operating conditions.

Design envelope

The application should include a cross-reference to the design envelope for the reactor facility, which includes all plant states and configurations. The applicant should demonstrate that the design authority has established the design envelope.

Defence in depth

The applicant should describe the approach taken to incorporate the defence-in-depth concept into the design of the reactor facility. The design approach adopted should ensure that multiple and (to the extent practicable) independent levels and barriers for defence are present in order to provide protection against AOOs and accidents including DBA and severe accidents. For more information, see sections 4.3.1 and 6.1 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

The application should describe the selection of the main barriers, with particular emphasis placed on SSCs important to safety. The application should describe any proposed operator actions to mitigate the consequences of events and to assist in the performance of important safety functions.

Safety functions

The application should describe how the fundamental safety functions have been incorporated into the design of the reactor facility, in accordance with section 6.2 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9]. The application should provide information on the SSCs used to perform necessary safety functions at various time intervals following a PIE.

The application should also identify and provide a description of any additional safety functions; for example, heat removal from irradiated fuel in fuel handling and storage systems.

Safety classification of structures, systems and components

The application should describe the approach adopted in the design for the safety classification of the SSCs. The approach should be in accordance with section 7.l of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9]. It should include criteria for deciding on the appropriate design requirements for each class, such as:

·       appropriate codes and standards to be used in the design, manufacturing, construction, testing and inspection of individual SSCs

·       in accordance with the appropriate sections of REGDOC‑2.5.2 [9]:

·       system-related characteristics, such as the degree of redundancy, diversity, separation, and reliability (section 7.6)

·       environmental qualification (section 7.8)

·       seismic qualification (section 7.13)

·       availability requirements for particular SSCs for on demand duty and for reliability for the prescribed mission time

·       quality assurance requirements

Design for reliability

The application shall include the basis for reliability targets that meet the requirements in section 7.6 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9] and REGDOC‑2.6.1, Reliability Programs for Nuclear Power Plants [27].

The description of the reliability program should include the following:

·       methods used for reliability assessment

·       how aging-related considerations are taken into account

·       selection criteria for the reliability assessment input data and subsequent updates, based on testing, surveillance and other experience

The applicant should demonstrate that all SSCs important to safety have been designed with sufficient quality and reliability to meet the design limits. The applicant should provide a reliability analysis for each of these SSCs. In accordance with the appropriate sections of REGDOC‑2.5.2 [9], the application should include considerations of:

·       common-cause failures (section 7.6.1)

·       single-failure criterion (section 7.6.2)

·       fail-safe design (section 7.6.3)

·       allowance for equipment outages (section 7.6.4)

·       shared systems (section 7.6.5)

Human factors

The application should describe how the facility design takes into account human factors. It should describe the systematic process that has been followed, for all systems, to incorporate considerations of human factors into the specification, definition and analysis of requirements; design activities; and verification and validation activities.

The application should describe the interfaces of human factors in design with other areas (for example, as inputs to the development of operating and other procedures and training). The application should also describe the considerations of human factors that apply to the design of specific SSCs, including:

·       human-machine interfaces for all plant states

·       instrumentation, displays and alarms provided to monitor system operations

·       physical location, accessibility and usability of equipment that is operated, tested, maintained or monitored

·       physical interlocks, and indication of bypassed or inoperable status

The application should include a list of human factors analyses and activities that were used in developing the design. The applicant should demonstrate that human factors engineering and human-machine interface considerations have been applied to all operational states and accident conditions, and for all  locations within the reactor facility where such interactions are anticipated.

The applicant should also provide a human factors engineering program plan.

For additional information on human factors design requirements, refer to:

·       REGDOC‑2.5.1, General Design Considerations: Human Factors [21]

·       CSA N290.12‑14, Human factors in design for nuclear power plants [28]

·       section 7.21 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9]

Radiation protection

The application shall include a description of the design approach adopted that demonstrates the facility design meets the requirements of the Radiation Protection Regulations and the radiation protection objectives and dose acceptance criteria in accordance with sections 4.1.1 and 4.2.1 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

The information submitted shall demonstrate that, over the lifecycle of the nuclear facility and in all operational states, radiation doses within the reactor facility or any planned release of radioactive material are kept below regulatory limits and are as low as reasonably achievable (ALARA).

Robustness against malevolent acts

The information submitted should demonstrate that the design includes considerations of both physical protection concerns and transportation routes, in accordance with the requirements of:

·       the Nuclear Security Regulations

·       REGDOC‑1.1.1, Site Evaluation and Site Preparation for New Reactor Facilities [26]

·       section 7.22 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9]

The application should describe both the general design approach and the approach and provisions followed to ensure the physical protection of the reactor facility (including control areas) against internal and external sabotage. These measures should take into account the selection of specific materials, the physical separation of redundant systems, the performance requirements of the equipment, and the use of barriers to segregate redundant safety trains.

The description of the design approach should include:

·       rules followed to establish the scope of threats

·       justification for the specification of vital areas and the anticipated loads (for example., impact forces, blast pressure waves, internal induced vibrations, fires and missiles) on SSCs and buildings

·       methodology used for assessing the vulnerability of the reactor facility, along with the measures selected to address these vulnerabilities and their consequences

The application should also describe the provisions for protecting the capability of:

·       monitoring and control of reactor facility parameters

·       emergency management and response

·       mitigation and recovery measures to ensure the safety of workers and the public

Note: Applicant submission and resultant review correspondence related to this topic is considered to be prescribed information under the NSCA and must be submitted in a secure manner. Refer to REGDOC‑2.12.3, Security of Nuclear Substances: Sealed Sources and Category I, II and II Nuclear Material [4] and the Treasury Board of Canada Secretariat Policy on Government Security [5] for further details on handling, submitting and transmitting assets considered security-sensitive.

Safeguards in the design and design process

With respect to the design and design process, the information submitted should demonstrate that the design and design process comply with the obligations arising from the safeguards agreement between Canada and the International Atomic Energy Agency (IAEA). For additional information on safeguards, see section 4.13.

Design changes

The application should describe the provisions being established for control and implementation of design modifications such that the reactor facility is maintained and modified within the limits prescribed by the design, analysis and (once established) licensing basis.

The application should also describe the processes for maintaining the design basis, taking into account new information, operating experience, safety analyses, resolution of safety issues or correction of deficiencies.

The application should describe how design changes are assessed, addressed and accurately reflected in the safety analyses or analysis of record prior to implementation.

Feedback into the design and design process from operating experience and safety research

The application should describe how lessons learned from the operation of other facilities or results of new research have been incorporated into the submitted reactor facility design in accordance with section 5.5 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

With respect to the design and design process, the application should describe how feedback from operating experience (OPEX) and safety research takes into account:

·       changes in design due to recent advances in material properties

·       improved methods of construction and fabrication

·       considerations related to improvement in reliability and in the operability and maintainability of the reactor facility

·       considerations on the current safety approach

·       the understanding of important phenomena governing behaviour of the reactor facility

·       methods and tools used in design and analysis

Operability and maintainability

The application should describe how, in general, the design process and its outputs support the design for system and equipment operability and maintainability in accordance with sections 7.3.1 and 7.14 of REGDOC‑2.5.2, Design of Reactor Facilities: Nuclear Power Plants [9].

Control of foreign material

The application should demonstrate that the design provides for the detection, exclusion and removal of all foreign material and corrosion products that may have an effect on safety.

Other safety functions

The application should specify, describe and explain the appropriateness of any other safety requirements or criteria that have been respected in the design to reduce the effect of failures and enhance the safety of the design. The description should include, but not be limited to:

·       adequate safety margins

·       simplified design

·       passive safety features

·       gradually responding systems

·       fault-tolerant reactor facility and systems

·       operator-friendly systems

·       leak-before-break concepts

·       fail-safe design

Decommissioning

The application shall describe considerations and design provisions that will facilitate future reactor facility decommissioning and dismantling activities.

The application should also describe considerations and provisions for storage of radioactive waste after the end of commercial operation.

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