  In sodium cooled fast reactor, Specific plant conditions are required for inspections of components that include sodium. Most characteristic constraint conditions for inspections of sodium components are “sodium drain” and “nitrogen gas (or Air) filling”. The compartment for sodium components usually is filled with purity-controlled nitrogen gas as countermeasure of fire by sodium leakage even if not plant operation state. It is necessary to reject sodium form each component and to replace nitrogen gas with air in the compartment in order to perform inspections with human access. That is one of major cause for longer inspection period on SFR.

As other factor, there are too many electric and measurement equipment for sodium heating. In order to realize more effective and rational inspection, it is necessary to take into account features of the plant.

  To solve the above problem, we proposed the concept of scheme to realize inspection rationalization based on “system based code”.

The SBC concept was proposed in the course of the research and development for Japanese fast breeder reactors in the 1990s. One of the key concepts is margin optimization, which provides a new framework intended to allow the optimum allocation of margins for the structural integrity of components encompassing various technical aspects in a plant life cycle, such as the material, design, fabrication, installation, and inspection, as well as the repair and replacement. By fully taking these technical characteristics into account, the SBC concept pursues improved reliability and economy while meeting the plant safety goals.

  The purpose of this scheme is to develop the plant specific maintenance plan by considering target reliability of each component based on plant level risk information , and to apply from the design stage of the plant. The scheme is constituted by following modules; target reliability evaluation, degradation mechanism assessment, maintenance strategy setting, additional test and/or monitoring setting, optimization and acceptance judgement on inspection plan.

Through these modules, the scheme develops the inspection plan. If not acceptable, it returns improvement requirements to plant design. In this scheme, the process is repeated until developed inspection program satisfies plant safety and economy goals according to owner criteria. This target also includes realize an acceptable inspection period.

  "ASME Code Case N-875" and "Boiler and Pressure Vessel Code, Section XI, Division 2 (RIM)" based on system based code were already developed as standards for inspection. One of the proposed scheme goals is to make a concrete way of necessary assessment method. Another is to provide several combinations of design and maintenance, and information for owner in order to choose the acceptable combination. In the beginning, we are working to develop the scheme that can be applied to sodium fast reactor as the main concept of next generation reactor.

  In this context, Primary piping of fast reactor was evaluated by the scheme. The primary piping was chosen because it is major significant component and the inspection needs pre-inspection preparation work by constraint conditions. As a result, design candidate (e.g. single and double wall piping) and inspection candidate (e.g. ultrasonic testing and continues monitoring) combinations along with benefit of each cases were provided.


Proposal of Inspection Rationalization Method and Application for Sodium Cooled Fast Reactor

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

POWER-ICONE - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.