Hideyuki Morita

Development of the Integrated IHX/Pump Component 1/4-Scale Vibration Testing

This report summarizes the evaluation method, the development schedule and the result of the test. A conceptual design study of the Japanese sodium-cooled fast reactor (JSFR) is in progress of “Feasibility Study on Commercialized Fast Reactor Cycle Systems.” In this study we have proposed a component which integrated IHX (Intermediate heat exchanger) with primary pump into one vessel (integrated IHX/Pump) as one of advanced concepts for the plant economy. By development this component, the amount of material (steel) of the primary cooling system can be reduced and the maintenance performance of IHX can be improved. In order to confirm its feasibility, it is important to avoid the resonant vibration caused by integrating of the pump into the static IHX and to prevent excessive wear-out of the heat exchange tubes caused by contact with the tube support plates. Therefore, the vibration evaluation method has been developed and a lot of examinations were carried out to confirm the feasibility of this concept. The pump is arranged at the center of the IHX and heat exchange tubes are arranged concentrically. This component consists of the multiple cylindrical layers. Tube support plates are installed and they support the tube bundle with 0.1–0.3mm gaps. The 1/4-scale model was selected for vibration tests. The first step test with an internal vibration exciter which simulated the pump was performed, and the test with the pump installed into IHX was done. This test model has been installed at Takasago R&D center of Mitsubishi Heavy Industries, Ltd. The vibration caused by the pump was measured. As a result of data analysis, the character of frequency response was acquired. The analysis code called as “FINAS” can directly handle the vibration behavior of complex multi-cylinders with fluid between the cylinders. The eigenvalue analysis and response analysis were performed using a detailed model and the results were compared with the test results. Vibration evaluation methods of the integrated IHX/Pump have been studied. The 1/4-scale vibration test was performed and the results were compared with the analysis.Copyright

Investigation on Buckling Behavior of Cylindrical Liquid Storage Tanks Under Seismic Excitation: 2nd Report — Investigation on the Nonlinear Ovaling Vibration at the Upper Wall

When a thin walled cylindrical liquid storage tank suffers a large seismic base excitation, buckling phenomena such as elephant foot bulge at the bottom portion and nonlinear ovaling vibration at the upper portion shows nonlinearity between the input and response level and suddenly occurs for the excessive input level, thus will be called as “nonlinear ovaling vibration” hereafter in this paper, may be caused. In the 1st report, the elephant foot bulge phenomena and the liquid pressure effects were investigated. In this 2nd report of the series of studies, the effect of nonlinear ovaling vibration phenomena were investigated based on the dynamic buckling tests using scaled models of thin walled cylindrical liquid storage tanks for nuclear power plants. The mechanism and the effect of vertical excitation and liquid sloshing were also studied and discussed.Copyright

Experimental Study on Free Standing Rack Loading Full Fuel Assembly

The spent fuel storage rack of a nuclear plant stores the spent fuel temporarily before it can be moved to a reprocessing facility. Therefore, the spent fuel storage rack must have a high tolerance against large seismic loads. So, the free standing rack is developed in Japan as other countries. The free standing rack structure incorporates the effect of the friction force on the spent fuel pool floor, and the fluid effect.Under earthquake condition, the free standing rack sliding and rocking motions are induced and the spent fuels rattle in the cells.In this paper, sliding and rocking motions of full-scale rack model having full loading fuel assembly subjected to the seismic excitation are studied. To develop an analysis evaluation method for rack motions, we carried out seismic test of a full-scale rack model using a shaking table, and obtained the fundamental data about the free standing rack.Copyright

Experimental Parameter Study on Free Standing Rack

The spent fuel rack of a nuclear plant stores the spent fuel temporarily before it can be moved to a reprocessing facility. Therefore, the spent fuel rack must have a high tolerance against big seismic loads. Sliding and rocking motions of full-scale rack model having full loading fuel assembly subjected to the seismic excitation are studied [1]. We carried out the seismic test of the free standing rack under some conditions. The distribution of the fuel assembly affects the sliding and rocking motions of the rack, and the outer plate reduces the rack response level by fluid effect. We made sure of them by seismic experiment using a shaking table.In this paper, sliding and rocking motions of full-scale rack model under some conditions are studied. To develop an analysis evaluation method of the rack sliding and rocking motions, we obtained the fundamental data about the free standing rack by seismic test using a shaking table.© 2012 ASME

Investigation on Buckling Behavior of Cylindrical Liquid Storage Tanks Under Seismic Excitation: 1st Report — Investigation on Elephant Foot Bulge

When a thin walled cylindrical liquid storage tank suffers a large seismic base excitation, buckling phenomena may be caused such as bending buckling at the bottom portion and shear buckling at the middle portion of the tank. However, the dynamic behaviors of the tanks is not fully clarified, especially those from the occurrence of buckling to some failures. In this study, bending buckling phenomena were focused which will be categorized as diamond buckling and elephant foot bulge. As ones of a series of studies, dynamic buckling tests were performed using large scale liquid storage tank models simulating thin walled cylindrical liquid storage tanks in nuclear power plants. The input seismic acceleration was increased until the elephant foot bulge occurred, and the vibrational behavior before and after buckling was investigated. In addition to the large scaled model tests, fundamental tests using small scaled tank models were also performed in order to clarify the effects of dynamic liquid pressure on the buckling threshold and deformation patterns.Copyright

Two-Phase Flow Induced Force Fluctuations on Pipe Bend

In this study, fluctuating force induced by both upward and horizontal gas-liquid two-phase flow on 90 degree pipe bend at atmospheric condition was investigated. First, the database comprised of dynamic force signals and two-phase flow parameters such as volumetric fluxes, area averaged void fraction and pressure fluctuations covering entire two-phase flow regimes was developed for both flow orientations. Then, study was conducted to develop a model which is capable of predicting the force fluctuation frequency and magnitudes particularly for the slug flow regime. The model was fundamentally developed from the local instantaneous two-fluid model which was applied to the control volume around the elbow test section. Main contribution of the force fluctuation of two-phase flow is from the momentum and pressure fluctuations for most of the flow regimes. For slug flow regime, however, water-hammer like impact was produced by the collision of liquid slug against the structure surface. In order to consider that effect, the liquid slug impact force model was developed. The model utilizes two-group interfacial area concentration correlation to treat the flow regime transition without an abrupt discontinuity. It was found that the newly developed model is capable of predicting two-phase flow induced force fluctuation and dominant frequency range with satisfactory accuracy for flow regimes up to churn-turbulent.Copyright

Evaluation of the Sliding Behavior of the Rack Using CAV Concept

The spent fuel taken out of a nuclear plant reactor is temporarily stored in spent fuel racks. This fuel will often have to be stored in the long periods before it can be moved to a reprocessing facility. Therefore, the spent fuel rack must have a large capacity with a high tolerance against big seismic loads. So, the free standing rack is developed as the optimal equipment meeting these requirements. The free standing fuel rack is installed on the floor in the spent fuel pool and it can have the simple structure, as it needs no supports on the floor or the wall of the spent fuel pool. The free standing spent fuel rack structure actively incorporates the effects of the friction force generated on the spent fuel pool floor, and the fluid effect. So, seismic analysis is performed by nonlinear dynamic time history analysis. In this study, we applied CAV concept (CAV: Cumulative Absolute Velocity) to evaluate of nonlinear rack response. And it was confirmed that the CAV concept using the low-pass filter is useful to evaluate the sliding and rocking behavior of the rack by simulation analysis.Copyright

The Ultimate Strength of Cylindrical Liquid Storage Tanks Under Earthquakes: Evaluation of Dynamic Buckling Behavior of Tanks Used in PWR Plants

The new seismic design guideline for nuclear power plants, which was established in September 2006 in Japan, requires the consideration of residual risk for earthquakes beyond the design base. Seismic Probabilistic Safety Assessment (PSA) is the current available method to evaluate the residual risk of the nuclear power plant. Since 2002, Japan Nuclear Energy Safety Organization (JNES) has been carrying out seismic capacity tests for several types of equipment whose malfunction would significantly affect core damage frequency. The primary purpose of those tests is to obtain seismic capacity data and use them to increase the reliability of the seismic PSA. In this study, some elastic-plastic analyses considering the dynamic buckling behavior were performed to evaluate previous seismic capacity test results. The study confirmed that response displacement, residual deformation of the elephant-foot bulge (EFB) and local strain of tank after the EFB occurred could be evaluated analytically. Besides, a 3D FEM elastic-plastic buckling analysis using kinematic hardening law could simulate the behavior in the early stage of the dynamic buckling. In addition to those analyses, dynamic response reduction factor (Ds) of the actual material tanks, and influence of different materials on the energy absorption and seismic capacity were evaluated by using previous seismic capacity tests results.© 2009 ASME

The Ultimate Strength of Cylindrical Liquid Storage Tanks Under Earthquakes: Seismic Capacity Test of Tanks Used in PWR Plants — Part 2, Static Post-Buckling Strength Tests

Since 2002, Japan Nuclear Energy Safety Organization (JNES) has been carrying out seismic capacity tests for several types of equipment which significantly contribute to core damage frequency. The primary purpose of this study is to acquire the seismic capacity data of thin walled cylindrical liquid storage tanks in nuclear power plants and to establish an evaluation procedure of the ultimate strength. As for the refueling water storage tank and the condensate storage tank which are used in PWR plants, elephant-foot bulge (EFB) is the typical buckling behavior of those tanks and the primary failure mode to be focused on. In the previous study, by conducting the dynamic and static buckling tests with aluminum alloy, it was confirmed that static buckling test represents dynamic buckling and post-buckling behavior in terms of energy absorption capacity. In this study, static buckling tests with actual material were performed in order to evaluate the ultimate strength of real tanks. Although the buckling mode did not differ among materials, tests with actual materials (steel, stainless steel) resulted higher seismic capacity compared to the aluminum alloy, and inner water leakage occurred from the cracks initiated at the secondary buckling on the EFB section.Copyright

The Ultimate Strength of Cylindrical Liquid Storage Tanks Under Earthquakes: Seismic Capacity Test of Tanks Used in PWR Plants — Part 1, Evaluation Method Verification Test

Since 2002, Japan Nuclear Energy Safety Organization (JNES) has been carrying out seismic capacity tests for several types of equipment which significantly contribute to core damage frequency. The primary purpose of this study is to acquire the seismic capacity data of thin walled cylindrical liquid storage tanks in nuclear power plants and to establish an evaluation procedure of the ultimate strength. As for the refueling water storage tank and the condensate storage tank which are used in PWR plants, elephant-foot bugle (EFB) is the typical buckling behavior of those tanks and the primary failure mode to be focused on. In the study, dynamic buckling tests were performed using scaled models of tanks. The input seismic acceleration was increased until the tanks reached the ultimate state at which internal water leaked from a crack on the sidewall. In addition, static buckling tests were performed in order to compare to the dynamic buckling tests and numerical simulation results. In the dynamic and static buckling tests, EFB occurred and internal water leaked at the EFB cross-section. Incremental deformation growth observed in the static buckling test was simulated by FEM, and analysis results showed a practically sufficient consistency in terms of out-of-plane displacement and local strain.© 2008 ASME