It is very important to estimate the flow and deformation behaviour of fresh concrete at the stages of mixing, transporting, placing, consolidating etc. to obtain good performance of concrete works. However, analytical methods to predict the behaviour of fresh concrete are not well established, and there are few theoretical studies to clarify the properties of fresh concrete subjected to vibration1,2
Jet pumps are key components to feed cooling water into reactor core in boiling water reactor. Inside condition of jet pumps is high flow condition. Therefore, jet pumps have risk of damages by flow-induced vibration, especially, the leakage-flow-induced vibration at the slip joint between the inlet mixer and the diffuser in extended power uprating condition with increasing core flow rate or particular operating condition such as single loop operation that increases differential pressure of the slip joint. To mitigate the risk of the leakage-flow-induced vibration, slip joint extension which can be installed on the top of diffuser was developed (See Figure 1). Self-excited vibration is treated as negative damping i.e. unstable state. It is well-known that the leakage flow through divergent gap flow passage causes the negative damping. However, the configuration of the gap flow passage of the slip joint with slip joint extension is complicated flow passage which consists of convergent, divergent and parallel flow passage region. To addition to this, the leakage flow direction in normal or power uprating condition is opposite to in abnormal operating condition such as single loop operating. Therefore, it is necessary to identify the optimum configuration of gap flow passage of the slip joint extension to suppress leakage-flow-induced vibration for various operating conditions. To achieve this goal, the gap flow passage of the slip joint extension was determined using transfer matrix method based on the leakage-flow-induced vibration theory. The effect and characteristic of vibration suppression for the slip joint extension was confirmed by fundamental tests that simulated the slip joint configuration.
Jet pumps in Boiling Water Reactor (BWR) have risk of damages by Flow-Induced Vibration (FIV) for when increasing the core flow rate for power uprating. Especially, the vibration by leakage flow at the slip joint between an inlet mixer and a diffuser can cause serious damage on jet pumps. It is one of the obstructive factors for power uprating. Another problem is crud deposition on the inside surface of the inlet mixer and nozzle. Thus fouling causes performance degradation of jet pumps. To reduce the risk of an FIV problem, the gap flow passage of the slip joint was modified based on the leakage-flow-induced vibration theory. The effect and characteristic of vibration suppression for the improved design was confirmed by fundamental tests that simulated the slip joint configuration. To mitigate crud deposition, a sol-gel ceramic coating process using ZrTiO4, which generates electrostatic repulsion force to crud, was developed. The effect of the coating was confirmed by experiments using test pieces. These techniques for mitigating damage due to FIV and fouling were applied to inlet mixers of jet pumps for replacement in the actual BWR plant.
The reactor concept considered in this paper has a mid/small power output, a compact containment and a simplified BWR configuration with comprehensive safety features. Compact Containment BWR (CCR) is being developed with matured BWR technologies together with innovative systems/components, will provide attractiveness for the energy market in the world due to its flexibility in energy demands as well as in site conditions, its high potential in reducing investment risk and its safety feature facilitating public acceptance. The flexibility is achieved by CCR’s mid/small power output of 400 MWe class and capability of long operating cycle (refueling intervals). The high investment potential is expected from CCR’s simplification/innovation in design such as natural circulation core cooling with the bottom located short core, top mounted upper entry control rod drives (CRDs) with ring-type dryers and simplified safety system with high pressure resistible primary containment vessel (PCV) concept. The natural circulation core eliminates recirculation pumps as well as needs for maintenance of such pumps. The top mounted upper entry CRDs enable the bottom located short core in RPV. The safety feature mainly consists of large water inventory above the core without large penetration below the top of the core, passive cooling system by isolation condenser (IC), high pressure resistible PCV and in-vessel retention (IVR) capability. The large inventory increases the system response time in case of design base accidents including loss of coolant accidents. The IC suppresses PCV pressure by steam condensation without any AC power. Cooling the molten core inside the RPV if the core should be damaged by loss of core coolability could attain the IVR. CCR’s specific self-standing steel high pressure resistible PCV is designed to contain minimum piping and valves inside with reactor pressure vessel (RPV), only 13m in diameter and 24m in height. This compact PCV makes it possible to fabricate and perform pressure-test at the factory and transport to the construction-site as a module. Basing on CCR design concept of simplification and compact, reactor building layout design has been carried out. Layout design has been performed taking into account module construction, reduced system and components and compact PCV. As a result, CCR’s reactor building, specific volume to power output value is almost equal to ABWR one. Module fabrication and construction method is promising technology from the points of construction duration shortening and construction cost reduction. Electrical equipment are piled up to multi-layer and connected and tested at the factory and transported to the construction-site in one module. Other equipment rooms and areas are also built into the various pre-fabricated module types in CCR construction. The construction of the CCR by the large module is planned to achieve only 24-month construction period from bedrock inspection to commercial operation. The CCR has possibilities of attaining both economical and safe small reactor by simplified system and compact PCV technologies with advanced construction.
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