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Safe, Small and Simple Reactors By Yoshi Sakashita, Toshiba Corporation. 1. Please provide a brief description of 4S/XIV. 4S “Super-Safe, Small and Simple” are sodium-cooled fast reactors with thermal ratings of 30 Megawatts (10 MW electricity) and 135 MW (50 MW electricity). Their remarkable feature is that there is no need for reactor refueling for 10 years or more—and not for 30 years for the 30 MW thermal reactor. The fundamental concept is enhanced proliferation resistance and safeguards that dramatically cut fuel handling outside of the reactors. Reactivity is controlled by reflectors located around the core, which reflect neutrons back into the core. They maintain criticality by gradually moving upward to compensate for fuel burnup. The reflectors provide the primary shutdown system, and diverse system is assured by a shutdown rod that provides an independent backup. Both use gravity to achieve scram. Critical testing of the 4S core has been conducted by CRIEPI (Central Research Institute of Electric Power Industry) and JAEA (Japan Atomic Energy Agency) using FCA (Fast Critical Assembly) at Tokai village in Japan [1]. The 4S fuel is a binary alloy of enriched uranium and zirconium. The alloy and cladding are bonded by sodium, the same material as the primary coolant, enhancing heat transfers between the alloy and the cladding. This metallic fuel technology was developed by ANL (Argonne National Laboratory, US) and INL (Idaho National Laboratory, US), and demonstrated in EBR-II and in FFTF [2]. Adoption of static components, such as electromagnetic pump (EM pump) as primary coolant circulators, reduces maintenance requirements within the Responses to questions by Newal Agnihotri, Editor of Nuclear Plant Journal. reactor vessel. Several EM pumps were tested [1], and 4S specific EM pump testing is underway at Toshiba’s sodium test loop in Japan. 4S employs three-step heat transportation. The reactor is a pool-type, enclosing the primary system components Yoshi Sakashita Yoshi Sakashita is a manager in the Nuclear Energy Systems & Services Division, Toshiba Corporation. He concurrently undertakes research, development and deployment of advanced reactors, and promotes the construction of new plants. He joined Toshiba in 1993, and most of his career to date has been devoted to nuclear core design, fuel design, safety analysis and project management, primarily for sodium-cooled fast reactors, such as Japan’s DFBR and Toshiba’s 4S. He has a BS in Nuclear Engineering and an MS in Electromagnetics, both from Osaka University. and coolant within the reactor vessel. The reactors coolant outlet temperature is 510 o C, and heat generated in the core is transported from the primary sodium to the IHTS (Intermediate Heat Transport System) secondary sodium via the IHX (Intermediate Heat exchanger). Heat is 34 http://subscribe.npjonline.com http://www.NPJOnline.com Nuclear Plant Journal, January-February 2009
transported form the secondary sodium to the water-steam system via a Steam Generator (SG). A double-wall heat transfer tube is adopted for sodium-water reaction in the SG, and there are monitoring systems to detect one-boundary failure of the tube. The double-wall tubes were tested at ETEC (Energy Technology Engineering Center) in California [1], and additional tests are underway at Toshiba sodium test loop. There are two independent decay heat removal systems. The RVACS (Reactor Vessel Auxiliary Cooling System) removes heat form the reactor passively, using natural air drafts and natural sodium circulation in the reactor. Its heat transfer characteristics were tested by CRIEPI [1]. The IRACS (Intermediate Reactor Auxiliary Cooling System) removes heat form the IHTS. In case of ATWS (Anticipated Transient without Scram), the reactor will become stable passively by negative reactivity coefficients and passive decay heat removal systems. The 4S is envisioned as a small, simple energy source with superior safety features allowing both passive shutdown and passive decay heat removal. Licensing and construction of the 4S is expected within a 10-year timeframe. 2. Are the project dates given in your response likely to be expedited due to energy crisis If authorities expedite the approval process, it might be possible to bring forward commercialization. There are two aspects to the current crisis. One is that government support for the nuclear industry may increase, in recognition of global warming. However, the financial crisis and demand suppression may be a disincentive to private sector investment in electricity and/or energy. 3. Does your reactor include a containment building If yes, please describe the characteristics of your containment building. The 4S has steel containment vessels that surround the reactor. The upper containment vessel is the “Top Dome” and the lower one is the “Guard Vessel.” [3] 4. What has Toshiba done in using nuclear energy in applications other than power production, including District Heating, Seawater Desalination and Transportation We are studying possible applications to process heating, desalination, and hydrogen production. For example, we demonstrated hydrogen production with a capacity of 1 m 3 /hr by applying steam reforming technology to dimethyl ether (DME) using a heat source of approximately 300 o C. We are also developing high-temperature steam electrolysis (HTE) technology using heat sources of 500 o C or higher, and the iodine-sulfur (IS) method, thermochemical water splitting cycle, using heat sources of 900 o C or higher. 5. Who are Toshiba’s partners in producing hydrogen utilizing nuclear energy Has a prototype already been (Continued on page 36) SEALS, ACTUATORS, GRIPPERS & PNEUMATIC SPECIALTIES FABRIC-REINFORCED FOR STRENGTH & STRUCTURAL INTEGRITY “Technical expertise, enthusiasm, creative problem solving, unmatched experience and follow-through… that’s Seal Master for sure!” DESIGN ASSISTANCE OFFERED – WWW.SEALMASTER.COM SEAL MASTER CORPORATION 368 MARTINEL DRIVE, KENT, OH 44240-4368 USA (800) 477-8436 / (330) 673-8410 • FAX (330) 673-8242 E-mail: info@sealmaster.com Serving the nuclear industry since 1974. © 2009 Seal Master Corporation Nuclear Plant Journal, January-February 2009 http://www.NPJOnline.com http://requestinfo.npjonline.com 35
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