Development of System Based Code (1) Reliability Target Derivation of Structures and Components

Abstract

The present paper describes a new method for determining the target value of structural reliability in the framework of the System Based Code (SBC) by considering the safety point of view. This new method utilizes analysis models of a probabilistic safety assessment (PSA), and the reliability target is derived from (1) the proposal to a quantitative safety goal that was published by the nuclear safety commission (NSC) of Japan; (2) the quantitative safety design requirements on the core damage frequency (CDF) and the containment failure frequency (CFF) that were determined in the Fast Reactor Cycle Technology Development (FaCT) project by Japan Atomic Energy Agency (JAEA). This method was applied to determine the reliability target of the structures and components which constitute the reactor cooling system in the Japan sodium-cooled fast reactor (JSFR). The risk from the reactor is shown by the sum of combination of various elements in the PSA analysis model. Those elements include dynamic failures and static failures of the structures and components, and human errors. However, the present study focuses on the sequences including the static failure, and the probability of dynamic failures and human errors in those sequences is conservatively assumed as a unity. It was confirmed that the present method combined with the PSA analysis model for internal initiating events is applicable to determine the reliability target associated with a random failure of the structures and components, and also confirmed that the method related to seismic initiating events can derive the target value of the occurrence frequency at which any of the important structures and components fails due to an earthquake.

Structural Materials and Code Development for Japanese Sodium-Cooled Fast Reactors

“…The System Based Code (SBC) concept was proposed by Asada [2] and extensively studied not only in JSME [2][3][4][5] but also in ASME [13] as a new framework that would realize the most adequate allocation of margins to various technological aspects of plant design and operation. The SBC concept consists of three parts: 1) design to target reliability that must be met throughout the service life, 2) margin exchange among the various technical areas of concern such as design, inspection, fabrication, and fitness for service, and 3) expand technical options by the timely adoption of newly developed technologies that are not in current codes and standards.…”

“…As to the framework of code requirements that allows to fully take advantage of structural materials for fast breeder reactors, the System Based Code (SBC) concept, the concept currently being extensively elaborated for the application to next generation reactors, can be utilized [2][3][4][5]. The SBC concept was proposed based on the recognition that existing codes and standards structure had become unnecessarily rigid in the long history of development and through a number of revisions.…”

Development of System Based Code (2) Application of Reliability Target for Configuration of ISI Requirement

“…In the new method (14) , the reliability target is derived using PSA analysis models from a proposal for a quantitative safety goal published by the Nuclear Safety Commission of Japan (15) , and quantitative safety design requirements on the core damage frequency and the containment failure frequency (CFF) determined by the Fast Reactor Cycle Technology Development project conducted by Japan Atomic Energy Agency (16) .…”

“…Two reliability targets for the reactor vessels can be selected for failure related to the risks arising from internal initiating events (14) . The first target is 2.0 × 10 −6 /year, which is the target value for a primary coolant boundary failure of the reactor vessel.…”

“…The other is to use the reliability of existing components and structures as reliability targets. We have proposed a new method to determine the reliability targets for the structures and components in FBR plants by using analysis models based on a PSA (14) , from the viewpoint of safety. In this study, we investigate the effectiveness of the probability of failure as an index and the reliability targets derived using the new method based on the SBC concept.…”