Yoshitaka Chikazawa

Development of Advanced Fuel Handling Machine for JSFR

The Japan Sodium-cooled Fast Reactor (JSFR) has adopted an in-vessel fuel handling system that consists of a single rotating plug, an upper inner structure (UIS) with a vertically penetrating slit, and a fuel handling machine (FHM) with a pantograph arm enhancing a compact reactor vessel design. Since the reactor vessel design depends on the in-vessel fuel handling system, the feasibility of the JSFR compact reactor vessel design is directly related to the feasibility of the new FHM. In this study, we have fabricated a full-scale mock-up of the JSFR FHM and performed tests in air. From the tests, the FHM mock-up shows sufficient performance in terms of positioning accuracy, motion speed, and stiffness to ensure durability for practical use in commercial plants. Structural analyses have been conducted to validate and improve the seismic analysis model and the positioning control of the FHM. The numerical results are in good agreement with the vibration and positioning tests, showing that there is a sufficient possibility that the model has enough performance to conduct seismic analysis and improve positioning accuracy.

Electromagnetic Pumps for Main Cooling Systems of Commercialized Sodium-Cooled Fast Reactor

An electromagnetic pump (EMP) has superior potential to improve the economic performance and ease of maintenance of sodium-cooled fast reactors. This study investigates the adequateness of a modular-type EMP system for large-sized (1,500MWe class) sodium-cooled fast reactors. A flow rate of over 500 m3/min is required for the main circulating pump of such reactors. There is concern that such a large EMP will cause flow instability. A modular-type EMP system can solve this issue since smaller EMPs are arranged in parallel and the flow rate of each EMP is reduced. Parallel-module EMP systems have been investigated as the primary and secondary circulating pumps. The results of the design study and electromagnetic analysis of the primary main pump confirmed that flow instability does not occur under all operational conditions. From a safety viewpoint, a reliable flow-coast-down system has been proposed, comprising an electric supply system with a permanent magnet synchronous motor and a reliable circuit breaker system. The modular-type EMP system is also effective for the secondary system, drastically simplifying the piping arrangement. The results of this study show that the modular-type EMP system is highly compatible with the main circulating pumps of large-sized sodium-cooled fast reactors, as well as the advantages gained from adopting this system.

A Feasibility Study on a Small Sodium Cooled Reactor as a Diversified Power Source

A conceptual design study of a small sized sodium cooled reactor with 165 MWe output with a metallic fuel, which aimed at the application for the diversified power supply has been carried out. A metal fuel core has been developed with 550°C core outlet temperature and 20 years core life time by utilizing the three zone core having different Zr contents in U-Pu-Zr of metal fuel. Major components in the nuclear steam supply system has been design and safety analyses has been performed to evaluate economical and safety potential of the concept. ATWS analyses show the passive safety feature of this concept adopting control rod driver-line (CRD) expansion reactivity and prolongation of electromagnetic pump (EMP) coastdown. Enhancing passive safety features, a improved upper inner structure enhancing CRD expansion and a reliable power source for EMP has been proposed. Though construction cost in first of a kind (FOAK) does not satisfy the economical goal, the present concept has potential for achieving the economical goal in Nth of a kind (NOAK) considering learning effect.

Experimental Demonstration of Flow Diodes Applicable to a Passive Decay Heat Removal System for Sodium-Cooled Reactors

In remote areas, a small power source with a capacity less than 50MW electricity without refueling is attractive since fuel transfer cost is high. In a previous 50MW sodium-cooled reactor study, a concept with a long-life core and a simple plant system without refueling was proposed. The 50MW plant decay heat removal system adopts direct reactor auxiliary cooling systems (DRACSs). To enhance passive safety features, the 50MW plant DRACSs adopt flow diodes instead of valves which need active signals to become activated. In this study, two full-scale flow diode models, Types A and B, were manufactured and water tests were conducted. The Type A flow diode is a conventional vortex flow diode and Type B is a modified vortex flow diode which provides easy maintenance. Under the test condition, the former showed good performance while the latter lacked sufficient performance. Then, flow diodes for the 50MW plant DRACSs were designed according to the experimental results. An optimized Type A flow diode and a modified Type B flow diode were evaluated and found to meet requirements of natural convection decay heat removal operation while maintaining a sufficient lowbypass flow during normal power operation.

Heat transfer experiments on fuel subassembly transfer pot for JSFR

Japan sodium-cooled fast reactor is going to adopt an advanced fuel handling system. As for ex-vessel spent fuel handling, a transfer pot with two fuel subassembly positions has been developed so as to shorten refueling period increasing plant availability. The pot is required to provide sufficient cooling capability in case of transportation malfunction. To evaluate cooling capacity of the transfer pot, a mockup pot has been fabricated and heat transfer experiments have been conducted on the mockup pot.

Acoustic Leak Detection System for Sodium-Cooled Reactor Steam Generators Using Delay-and-Sum Beamformer

A new acoustic leak detection system for sodium-cooled reactor steam generators using a delay-andsum beamformer is proposed. The major advantage of the delay-and-sum beamformer is that it could provide information on the acoustic source direction. An acoustic source of a sodium-water reaction is supposed to be localized, while the background noise of the steam generator operation is uniformly distributed in the steam generator tube region. Therefore, the delay-and-sum beamformer could distinguish the acoustic source of the sodium-water reaction from the steam generator background noise. In this paper, results of numerical analyses are provided to show the fundamental feasibility of the new method.

Development of argon gas cleaning for sodium-cooled reactor spent fuel

Japan sodium-cooled fast reactor (JSFR) is going to adopt an advanced fuel-handling system. From the viewpoint of spent fuel cleaning, a new dry-cleaning process instead of the conventional process with water rinse is under development. In this study, drain performance tests on the JSFR subassembly inner duct and dry-cleaning performance tests with a pin bundle model are summarized. Based on the experimental data of the inner duct and pin bundle model tests, residual sodium on the spent fuel subassembly after argon gas cleaning has been evaluated to be 400 g. Water alkalinity and purification performance have been evaluated and the JSFR water pool system has shown the capability to accept 400 g residual sodium on the spent fuel subassembly after argon gas cleaning.

Development of a Slim Manipulator Type Fuel Handling Machine for a Commercialized Fast Reactor

A seismic analysis has been performed showing that the seismic interaction between the UIS and the FHM can be avoided eliminating the internal clearance of bearing at the FHM arm joint. An angular contact ball bearing is suitable for the new FHM since it can eliminate gaps by preload pressure. A major problem of the FHM bearings is lubrication since the contact pressure between the steel rings and ball of the ball bearing is larger than that of the roller bearing used in the previous design. Additionally, FHM operating temperature is about 200 deg-C and normal grease is not applicable under argon gas with sodium vapor to prevent contamination of grease in the primary sodium coolant. An endurance test with 1/10 scale bearings in the air has been performed to show applicability of angular contact ball bearings to the FHM arm joint. The results with 20,000 cycle showed that bearings with combination of MoS{sub 2} coating steel rings and ceramics balls can be tolerable as the FHM operating condition. A full-scale bearing test in argon gas with sodium vapor has also been demonstrated to reveal bearing size and sodium vapor effects. (authors)

Demonstration of Under Sodium Viewer in Monju

Abstract Development of an inspection technique in opaque liquid-metal coolant is one of the important issues to ensure the safety of the liquid-metal fast breeder reactor (LMFBR). Performance tests of an under sodium viewer (USV), which was developed to detect an obstacle in the reactor vessel (RV) of the LMFBR Monju, have been carried out. Ultrasonic sensors and reflectors are located across the core inside Monju’s RV. The USV can detect an obstacle existing between the core top and the upper core structure bottom by identifying differences of echo signals. This paper describes the USV performance tests. In the tests, the reference echo signals under various conditions were accumulated, and the signal-to-noise ratio successfully exceeded the target value. Measured signals clearly differed with and without an obstacle. These experimental results show the performance of the USV for detecting an obstacle in a specified place.

Performance evaluation of eddy current flowmeter in Monju

ABSTRACT Measurement of the temperature and flow rate at each fuel subassembly outlet is an effective way for a liquid metal fast breeder reactor to detect a loss of coolant accident or reactivity-initiated accident in the early stage and to understand the reactor’s thermal hydrodynamic performance. Japan Atomic Energy Agency has developed the eddy current flowmeter in practical use and installed 34 of them in the upper core structure of fast breeder reactor, Monju. This report presents data obtained by using the flowmeters in Monju. We observed high linearity between each of the flowmeter’s signal intensity and the primary sodium’s flow rate under 10–100% flow rate condition. High linearity was also observed in a region of low velocity (approx. 0.25 m/s). The fluctuation of flow rate observed by the flowmeters was below 0.2 m/s which is 5% of the time-averaged velocity under a rated condition. These experimental results show that the eddy current flowmeter is an effective tool to detect the changes in relative flow rate.