摘要：

Pressure-vessel-type supercritical water cooled reactors (SCWRs) have been developed at the University of Tokyo (UT) since 1989 and are studied in Japan , Europe and other countries. UT's concepts of the reactor are termed 'Super LWR' for thermal neutron spectrum and 'Super Fast Reactor (FR)' for fast spectrum respectively. Fast spectrum option is expected to be possible with the same plant system as of the thermal option. The fast reactor will produce higher power rating than the thermal one with the same reactor pressure-vessel size , since the moderator is not necessary, so that the unit capital cost will be reduced further. With the scope of developing an economical fast reactor system, a Japanese research project of the 'Super FR' had been conducted since December 2005 to March 2010. University of Tokyo, Kyushu University , Japan Atomic Energy Agency (JAEA) and Tokyo Electric Power Company (TEPCO) have participated in the project. It consisted of three subjects: (1) development of the Super FR concept, (2) thermal-hydraulic experiments and (3) materials developments. All items have successfully finished. The present paper will summarize the results of the project. (1) Development of the Super FR concept: The purpose of the concept development is to pursue the advantage of high power density of fast reactors over thermal reactors to achieve economic competitiveness of fast reactors. The concept of Super FR was developed mainly by numerical simulations at the University of Tokyo. The studies covered fuel and core design, plant control, start-up, stability, plant heat balance, and safety analysis. 3D neutronic thermal-hydraulic coupled calculations were used for the core design. A candidate core was successfully designed with keeping both overall and local void reactivity negative by updating the fuel and core configurations. Solid moderators (ZrH layer) in blanket assemblies enables the Super FR to have a negative void reactivity without adopting flat core configuration or other special devices. (2) Thermal-hydraulic experiments: To develop a thermal-hydraulic database for the design of the Super FR, thermal hydraulic experiments were carried out at Kyushu University and JAEA. The measurement of critical flow at depressurization, condensation of supercritical steam and the critical heat flux near the critical pressure have been made using a single tube and 7-rod bundles with surrogate fluid (HCFC22) at Kyushu University. Heat transfer tests with supercritical-pressure water were carried out at JAEA to verify the results obtained from the tests with HCFC22. A single heater rod and a 7-rod bundle including the grid spacer, which is the same as that in the Kyushu University for HCFC22, were tested. These results were used for validation of a CFD code, which was developed in this project, based on 3-D two-fluid model. (3) Materials developments Based on an advanced austenitic stainless steel (PNC1520) with high creep strength developed by JAEA for the sodium-cooled FBR, candidate materials for the fuel cladding of the Super FR were manufactured. Tensile tests, creep tests, corrosion tests, slow strain rate (SSRT) tests, high temperature irradiation tests were conducted and showed good results. Thermal insulations will be necessary for the Super FR due to large temperature difference in the reactor vessel. Requirements for the thermal insulator are low heat conductivity, low neutron absorption, and good thermal shock resistance and dimensional stabilities. As the candidate material, porous Yttria-Stabilized Zirconia (YSZ) of which heat conductivity was one-twentieth of Zirconia was developed. A new approach was developed to evaluate elution characteristic of stainless materials in supercritical-pressure water. Radioactivated specimen (SUS304) with a known radioactivity is used as a sample and set at an autoclave vessel in supercritical water loop system. The elution database was accumulated using this approach. Present study is the results of 'Research and Development of the Super Fast Reactor' entrusted to the University

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