Kosuke Aizawa

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.

Pressure Fluctuation Characteristics of Complex Turbulent Flow in a Single Elbow With Small Curvature Radius for a Sodium-Cooled Fast Reactor

A multi-elbow piping system is adopted for the Japan sodium-cooled fast reactor (JSFR) cold-legs. Flow-induced vibration (FIV) is considered to appear due to complex turbulent flow with very high Reynolds number in the piping. In this study pressure measurement for a single elbow flow is conducted to elucidate pressure fluctuation characteristics originated from turbulent motion in the elbow, which lead potentially to the FIV. Two different scale models, 1/7- and 1/14-scale simulating the JSFR cold-leg piping, are tested experimentally to confirm whether a scale effect in pressure fluctuation characteristics exists. A distinguishing peak can be seen in each power spectrum density (PSD) profile of pressure fluctuation obtained in and downstream of the flow separation region for both scaled models. When nondimensionalized, the PSD profiles show good correspondence regardless of scale model and even of Reynolds number simulated in this study.

Selector-Valve Failed Fuel Detection and Location System for Japan Sodium-Cooled Fast Reactor

The Japan Sodium-cooled Fast Reactor (JSFR) is studied as an advanced loop-type sodium-cooled reactor. A selector-valve (SV) mechanism is adopted in the design of JSFR for its failed fuel detection and location (FFDL) system. JSFR has only two FFDL units for 562 core fuel subassemblies to reduce construction cost by decreasing the reactor vessel diameter. Consequently, one SV-FFDL unit must handle about 300 subassemblies. Because of the large number of subassemblies per unit, it is predicted that the total duration for measuring all the fuel subassemblies becomes long. In addition, JSFR adopts an upper internal structure (UIS) with a slit above the core. In order to detect the fission products from the subassemblies below the slit, additional sampling nozzles for the FFDL are set in the UIS around the slit. In previous water experiments and numerical simulation, the sampling performance for the subassemblies under the UIS slit has been evaluated to be lower than those under the normal UIS position. In this paper, the outline of the FFDL system is shown, which can be applied to a large number of fuel subassemblies in a compact reactor vessel. The detection capability of the FFDL system was studied to achieve the design conditions. Operation modes and procedures of the FFDL system were also investigated.

Under-Sodium Endurance Experiment of Selector Valve in Failed-Fuel Detection and Location System of JSFR

A conceptual design study of Japan Sodium-cooled Fast Reactor (JSFR) is in progress in the Fast Reactor Cycle Technology Development (FaCT) project in Japan. In the design of JSFR, a selector valve mechanism is adopted for its failed-fuel detection and location (FFDL) system. Since JSFR has only two FFDL units for [approximately]600 fuel subassemblies due to its compact design of the reactor vessel, one FFDL unit must handle a much larger number of subassemblies than in previous designs. In addition, during the long plant life of 60 years, the wear length of the selector valve will become longer than those of past reactors. Therefore, the endurance of the selector valve becomes important. To demonstrate the manufacturability and endurance of the selector valve, a full-size mockup valve including coating to protect the sliding mechanism was manufactured, and an endurance experiment of the mockup model under high-temperature sodium was conducted. Dimensional inspections and seal performance showed manufacturability of the selector valve. The cross-section observation, hardness measurement, and chemical assay results after the endurance experiment showed that the coating layer on the sliding surface still remains. Thus, the endurance of the JSFR selector valve was demonstrated.

Water experiment and numerical simulation on failed fuel detection and location system of Japan sodium-cooled fast reactor (JSFR)

A conceptual design study of Japan sodium-cooled fast reactor (JSFR) is in progress as the “Fast Reactor Cycle Technology Development (FaCT)” project in Japan. A selector-valve type failed fuel detection and location (FFDL) system is applied to the JSFR design that has an upper internal structure (UIS) with a slit above the core and several sampling nozzles for the FFDL are set in the UIS around the slit to detect the fission product (FP) from the subassemblies below the slit. Therefore, mixing process in the UIS of complicated geometry should be known and appropriate arrangement of the sampling nozzles in the UIS is needed. A water experiment using a 1/5-scale model was carried out to investigate the mixing process in the UIS and concentration distribution of FP simulant. Experimental results showed that the sampling nozzles set in the UIS detected the FP simulant concentration within the criteria of FFDL signal detection, even in case of failed subassemblies under the UIS slit. In addition, identification of the failed fuel subassembly under the UIS slit was achieved by means of comparing concentration profiles in the UIS. Therefore, the suitable sampling nozzle arrangement was obtained for JSFR. A numerical simulation using a CFD code was carried out and the simulation method was validated based on the experimental data of the FP simulant concentrations. The simulation results showed that the simulation predicts the FP concentration distributions.

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.

Tagging-Gas Failed Fuel Detection and Location System for Sodium-Cooled Reactors

Failed fuel detection for the Japan Sodium-cooled Fast Reactor (JSFR) has been studied. The present JSFR design adopts a selector-valve (SV) failed fuel detection and location (FFDL) system. In this study, a tagging-gas (Tag) FFDL (Tag-FFDL) system has been investigated as an alternative. Although the identification performance of the Tag-FFDL system has been demonstrated in small and medium-sized reactors, the Tag-FFDL system has not been demonstrated yet in a large reactor like JSFR, which has 1500-MW(electric) power and 562 core fuel subassemblies. Major issues of the JSFR Tag-FFDL system are affected by high-burnup fuel and large cover gas volume. High-burnup fuel leads to a large change of the isotope ratio, which is important for the detection performance of the Tag-FFDL system. Since the cover gas volume in JSFR is larger than that in previous reactors, the tagging-gas concentration in the cover gas is lower than that in previous reactors. Thus, a requirement of the background value is more strict in JSFR. This study investigates whether two issues of the Tag-FFDL system for JSFR would be solvable. Tag gas isotope change in a high-burnup condition has been evaluated regarding transmutation and fission gas release. Taking into account tag gas isotope change due to the high-burnup conditions and large cover gas space, JSFR tagging gas has been designed. The investigation results showed that the JSFR FFDL system can provide an identification capability for 672 subassemblies, which is larger than the number of subassemblies in JSFR combining tagging-gas and burnup estimation. In addition, an allowable background concentration of natural Kr and Xe in the cover gas has been evaluated.

Pressure Measurement Test of Single Elbow Simulating Na Cooled Fast Reactor Cold-Leg Piping

Regarding the Japan Sodium-cooled Fast Reactor, a multi-elbow piping system is adopted for its cold-legs. Flow Induced Vibration (FIV) is considered to be caused by complex flow with very high velocity in the elbows. In this study, pressure measurement test of a single elbow flow is conducted to find out pressure fluctuation characteristic which is related to the elbow turbulent flow and lead potentially to the FIV. Two types of experimental loops, that is, 1/7 and 1/15-scale setup simulating the JSFR cold-leg pipings, are used for pressure measurement, and a distinguishing peak can be seen in the power spectrum density profile of pressure fluctuation obtained where flow separation occurs and at the downstream from it. This characteristics of pressure fluctuation is obtained from the two different scale experiments, and the scale effect is not found in terms of the pressure fluctuation.Copyright