Canadian Regulatory Perspective on the Design and Aging Management for Reactor Pressure Vessel (RPV) in Boiling Water Reactors (BWRs)

Abstract of the technical paper/presentation presented at:
28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28)

Prepared by:
S. Eom, H. Mazhar, K. Kirkhope, M. Hornof

Abstract:

In a Boiling Water Reactor (BWR), the RPV is a vertical, cylindrical pressure vessel that contains the reactor core and coolant and performs the role of a nuclear boiler that produces the steam used to generate electricity. The RPV in the BWR design performs several vital functions, including coolant circulation, heat transfer, and accommodating system pressure under different conditions. In addition, the RPV houses the detection systems that monitor crucial operating parameters (e.g., temperature, pressure, neutron flux and fluence) for tracking reactor conditions.

The RPV also offers structural support and radiation shielding for the reactor core. An essential component of nuclear reactor safety and performance, the integrity and functionality of the RPV are critical to the safe and effective operation of BWRs. Therefore, the probability of failure in the RPV must be extremely low, so it should be designed, operated, inspected, and regulated in accordance with stringent requirements commensurate with the importance to safety to ensure its structural integrity and functionality is maintained under very severe operating conditions.

CNSC REGDOC-2.5.2 establishes requirements and guidance for the design of new water-cooled reactor facilities, covering a wide range of topics including safety objectives, design principles, and specific technical requirements for structures, systems, and components (SSCs) to ensure the safe operation and protection of individuals and the environment. It is essential to consider aging effects in the RPV to ensure long-term structural integrity, safety, and regulatory compliance, by mitigating degradation caused by factors such as radiation, thermal, and pressure-induced stresses. Therefore, CNSC REGDOC-2.5.2 states that the design shall take due account of the effects of aging and wear on SSCs, which are important to safety. Additionally, REGDOC-2.6.3, “Aging Management,” sets out requirements and provides guidance for managing the aging of SSCs, including the RPV, in power reactor facilities throughout their life cycle, ensuring the ability of required safety functions and addressing physical aging.

The main objective of this work is to provide a comprehensive overview of the regulatory perspectives on the design, fabrication, inspection, material testing, and aging management considerations of BWR RPVs in accordance with the requirements outlined in CNSC REGDOC-2.5.2, “Design of Reactor Facilities” and REGDOC 2.6.2, “Aging Management”.

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