Satoshi Obara

Bio: Satoshi Obara is an academic researcher from Japan Atomic Energy Agency. The author has contributed to research in topics: Creep & Structural material. The author has an hindex of 1, co-authored 1 publications receiving 6 citations.

Creep Strength Evaluation of Welded Joint Made of Modified 9Cr-1Mo Steel for Japanese Sodium Cooled Fast Reactor (JSFR)

Abstract: This paper describes a proposal of provisional allowable stress for the welded joints made of modified 9Cr-1Mo steel (ASME Gr.91) applicable to the structural design of Japanese Sodium cooled Fast Reactor (JSFR). For the early commercialization of the SFRs, economic competitiveness is one of the most essential requirements. One of the most practical means to reduce the construction costs is to diminish the total amount of structural materials. To meet the requirements, modified 9Cr-1Mo steel has attractive characteristics as a main structural material of SFRs, because the steel has both excellent thermal properties and high temperature strength. Employing the steel to the main pipe material, remarkable compact plant design can be achieved. There is only one elbow in the hot leg pipe of the primary circuit. However, in such a compact piping, it is difficult to keep enough distance between welded joint and high stress portion. In the welded joints of creep strength enhanced ferritic steels including ASME Gr.91 (modified 9Cr-1Mo) steel, creep strength may obviously degrade especially in long-term region. This phenomenon is known as “Type-IV” damage. Though obvious strength degradation has not observed at 550°C yet for the welded joint made of modified 9Cr-1Mo steel, it is proper to suppose strength degradation must take place in very long-term creep. Therefore, taking strength degradation due to “Type-IV” damage into account, the allowable stress applicable to JSFR pipe design was proposed based on creep rupture test data acquired in temperature accelerated conditions. Available creep rupture test data of welded joints made of modified 9Cr-1Mo steel provided by Japanese steel vender were collected. The database was analyzed by region partition method. The creep rupture data were divided into two regions of short-term and long-term and those were individually evaluated by regression analyses with Larson Miller Parameter (LMP). Boundary condition between short-term and long-term was half of 0.2% proof stress of base metal at corresponding temperature. First order equation of logarithm stress was applied. For conservativeness, allowable stress was proposed provisionally considering design factor for each region. Present design of JSFR hot leg pipe of primary circuit was evaluated using the proposed allowable stress. As a result, it was successfully demonstrated that the compact pipe design was assured. For validation of the provisional allowable stress, a series of long-term creep tests were started. In future, the provisional allowable stress will be properly reexamined when longer creep rupture data are obtained. In addition, some techniques to improve the performance of welded joints were surveyed and introduced.Copyright © 2010 by ASME

Design Study and R&D Progress on Japan Sodium-Cooled Fast Reactor

Abstract: This paper describes the progress of the design study and research and development (R&D) for the Japan Sodium-cooled Fast Reactor (JSFR) implemented in the “Fast Reactor Cycle Technology Development (FaCT)” project. A sodium-cooled fast reactor with an electric power of 1,500MWe is targeted for commercialization at around 2050, and a demonstration reactor assuming a power output from 500 to 750MWe is planned to start operation at around 2025. R&D on innovative technologies to achieve economic competitiveness and enhance reliability and safety is carried out for the commercialization. A compact reactor vessel without a vessel wall cooling system is pursued in consideration of the wall thickness enough to resist the severest seismic condition. A two-loop cooling system with shortened highchromium steel piping is a crucial feature, and studies on the hydraulics in the pipe elbow and the fabrication capability of the pipes are being carried out. A double-walled straight tube steam generator is investigated to...

Evaluation of JSFR Key Technologies

Abstract: Key technologies for Japan Sodium-cooled Fast Reactor (JSFR) have been evaluated. The ten technologies - high-burnup core, safety enhancement, compact reactor vessel, two-loop cooling system using ...

Comparison of JSFR design with EDF requirements for future SFR

Abstract: A comparison of the Japan sodium-cooled fast reactor (JSFR) design with the future French sodium-cooled fast reactor (SFR) concept has been done based on the requirements of Electricite de France (...