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The scintillator with optical fiber (SOF) dosimeter consists of a miniature scintillator mounted on the tip of an optical fiber. The scintillator of the current SOF dosimeter is a 1-mm diameter hemisphere. For a scintillation dosimeter coupled with an optical fiber, measurement accuracy is influenced by signals due to Cerenkov radiation in the optical fiber. We have implemented a spectral filtering technique for compensating for the Cerenkov radiation effect specifically for our plastic scintillator-based dosimeter, using a wavelength-separated counting method. A dichroic mirror was used for separating input light signals. Individual signal counting was performed for high- and low-wavelength light signals. To confirm the accuracy, measurements with various amounts of Cerenkov radiation were performed by changing the incident direction while keeping the Ir-192 source-to-dosimeter distance constant, resulting in a fluctuation of

The core melt accidents at Fukushima Daiichi Units 1-2-3 have occurred due to the tsunami of the Great East Japan Earthquake at March 11, 2011. Now a coolant of approximately 100t is injected into each Reactor Vessel (RPV) in order to cool the fuel debris, and a part of the coolant leaks out from the water. The contaminated water is collected, and it is stored in the contaminated water storage tanks more than approximately 1,000 and the total amounts of coolant exceeds 1,000,000 t. Although the contaminated water is purified by ALPS, it is still in high nuclear pollution density. According to the homepage of Nuclear Regulation Authority (NRA) in Japan, the storage tanks have been placed on the concrete bed without any anchor. Tokyo Electric Company (TEPCO) reported to NRA in 2015 that the design acceleration used for the overturning evaluation of the tanks have 0.3G. At the Fukushima Daiichi Power Station in the Great East Japan Earthquake, the maximum horizontal acceleration was 0.6G, the maximum vertical acceleration was 0.326 G at the time of the Great East Japan Earthquake. Even if an earthquake that is a fraction of this earthquake comes back, there is a possibility that this tank will fall over. The temporary special design guideline is adopted. These tanks have already stored the contaminated water for 6 years. However, it is thought that the more long term countermeasures is necessary for preventing the contaminated water from flowing out into the Pacific Ocean when another great earthquake will attack this area in future. In this paper, we propose a drastic structure to add a foundation without causing ground to the present tank. In the past, the member fastening the steel plate of the upper structure of the tank and the concrete of the lower structure is a foundation bolt, but this time it is a stud welded to the tank side plate. This made it possible to flexibly design and reinforce the foundation itself even after tank installation.

When flexible pipes are subjected to internal flow, the pipes lose stability by flutter and divergence in increasing the fluid velocity. In addition, they also lose stability when they are subjected to external annular axial flow. In this paper, the pipe is subjected to internal flow and external flow at the same time. The dynamic stability of a double wall pipe structure system subjected to an internal flow and an external flow simultaneously is thought to be one of the important pipe structures for the development of a piping system in the field of ocean mining, and in the field of fluid energy generation, and so on. In this paper, the pipe structures are assumed to be composed of the cantilevered elastic tube structure. For the analysis of the internal flow, the conventional inviscid stability analysis method is applied. For the analysis of the external annular axial flow, both the viscous solution using the Navier-Stokes equation of motion and the ideal fluid solution which viscous influence are added to are applied. Changing the flow direction and the fluid velocity as for the internal flow and the external flow, the dynamic stability of the double wall pipes is investigated and discussed. Moreover, changing the flow rate and the density of a fluid and a structure, these effects on the stability of double wall pipes are investigated.

The vibration-induced fatigue failure of small-bore piping is one of the common causes of failure trouble at nuclear power plants (NPPs). Therefore, the purpose of this study is to develop the measurement methods of vibration-induced stress for the screening to prevent from fatigue failure mechanism of small-bore piping. First, a measurement method using a single-mass model was introduced, and then, a measurement method using a two-mass model developed as an improved calculation model was proposed. These two kinds of models were validated by vibration tests using mock-up with small-bore branch piping. The results showed that the single-mass model could be used as the coarse screening. Additionally, the two-mass model was found to be suitable to the fine screening due to more accurate measurement of vibration-induced stress. Next, for small-bore piping with typical pattern configurations consisting of several masses and supports, the model considering the supports and the center of gravity being out of pipe centerline was developed and put into practical use. Finally, for the more complex small-bore piping with general piping configurations consisting of many bends, branches, or joints, the method based on the finite element analysis and using the measured values was developed. In the developed method, the differences between the natural frequency and the response acceleration obtained by the measurement and those values calculated using the analysis model are optimized to be enough small, and then, the vibration-induced stress is estimated by superposing the vibration modes of the small-bore piping with the static deformation representing the main piping vibration. In this study, the usability of the developed method was confirmed by the comparison with the numerical results without the measurement error, which were assumed to be the true values. The peak stress induced by vibration frequently occurs at the filet weld part between the small-bore piping and the main piping. The developed methods can be used for various weld geometries although the measurement method using strain gauges cannot be used for such weld parts. The failure possibility by vibration-induced fatigue can be evaluated by comparing the nominal stress measured by the methods in this study with the fatigue threshold stress divided by the stress concentration factor appropriate for the weld geometry.

To improve design and troubleshooting techniques of piping systems for operating power plants, it is necessary to investigate, by experiment and simulation, the behavior of fluid inside the piping system in detail. This study was conducted using full-scale piping system under conditions that could seriously threaten the plant operation, by matching pressure pulsations, acoustic resonance, and piping natural frequency. Although piping vibration is reported to influence fluid pressure pulsations, there were no such examples of influence in this experiment. Knowing that the opening ratio of the pressure control valve affects the boundary condition for acoustic resonance, experiment and simulation at different opening ratios were conducted. It has been suggested that the cases in which a valve partially open at 25% or less should not be taken as a closed end. This finding conflicts with such a widespread design assumption.

In this study, the influence of valve closing and opening operations to change inner pressure during pump operations on the pulsation boundary condition was investigated to improve the prediction accuracy of pressure pulsation. Vibration experiments were conducted by using an actual size mock-up piping system with 40 m long as found in nuclear power facilities. A drastic change in the boundary condition of the acoustic resonance by a slightly different valve opening ratio to set a different inner pressure was seen in the experimental results. The simulation results by using the method of characteristics showed that the boundary condition of the acoustic resonance changed when the valve opening ratio was changed slightly from 10 % to 15 %. This indicated that the boundary condition of the acoustic resonance had a pulsed change and changed even at the small valve opening ratio, which was approximately 15% though the design threshold value was 25 %. It was concluded that the boundary condition of the acoustic resonance was sensitive to a slight change of the valve opening ratio and this was one of the reasons why it is difficult to predict the pressure pulsation behavior including acoustic resonance accurately in actual plants.

Evaluation methodologies for the flow-induced vibration of an elastic beam subjected to an axial flow confined in a narrow passage are reported. In this paper, by using the analytical method already proposed by one of authors, a parameter study is performed on the dynamic stability of an elastic beam subjected to axial flow confined a narrow passage. The effects of support conditions of structures, structural damping, and fluid characteristics on the dynamic stability are clarified. Especially, paying attention on the vicinity of critical velocity, the effects of stabilization or destabilization on flutter and divergence are investigated by changing fluid viscosity and structural damping.

In this study, the applicability of a previously developed optimal seismic design methodology, which can consider the structural integrity of not only piping systems but also elasto-plastic supporting devices, is studied for seismic waves with various frequency characteristics. This methodology employs a genetic algorithm and can search the optimal conditions such as the supporting location and the capacity and stiffness of the supporting devices. Here, a lead extrusion damper is treated as a typical elasto-plastic damper. Numerical simulations are performed using a simple piping system model. As a result, it is shown that the proposed optimal seismic design methodology is applicable to the seismic design of piping systems subjected to seismic waves with various frequency characteristics. The mechanism of optimization is also clarified.

The evaluation methodologies for the flow-induced vibration of an elastic beam subjected to an axial flow in confined narrow passage are reported. One of authors has already proposed an analytical method using the Navier-Stokes equation for the dynamic stability of an elastic beam subjected to an axial flow confined in a narrow passage. In this paper, by using the proposed analytical methods, the numerical studies are performed taking three kinds of support conditions as parameters, that is, a cantilever fixed at the upstream side, a cantilever fixed at the downstream side, and a simple support beam at the both sides, respectively. Moreover, the parameter-studies are also performed concerning with a width of annular gap, viscosity of a fluid, and structural damping. And the effects of support conditions of a structure, structural damping, and fluid characteristics on the dynamic stability of an elastic beam due to an axial flow confined in a narrow passage are clarified for proposing a safety dynamic design guideline concerning axial flow-induced vibrations in industries.

The purpose of this study was to develop a novel scintillation dosimeter for in vivo dosimetry in Ir-192 brachytherapy via the pulse-counting mode. The new dosimeter was made from a plastic scintillator shaped into a hemisphere of diameter 1 mm and connected to the tip of a plastic optical fiber. The relationship between pulse counts and absorbed dose was derived based on the assumption that scintillation photons from the incident gamma ray are proportional to the absorbed dose. An equation for the conversion of pulse counts to water-equivalent dose was deduced wherein the pulse height spectrum from scintillation photons was assumed to be exponential. To confirm its accuracy, the dose rate distribution in a water phantom was measured by the present dosimeter and this was compared with Monte Carlo simulations, resulting in a discrepancy of less than 1.97%. It was found that the dosimeter has a wide dynamic range of linearity up to an order of magnitude of almost 10(3), including corrections for loss of counts due to pile-up.

Unstable vibration of multi-connected bodies supported by damper and spring systems moving in a narrow flow passage are reported. These vibration phenomena have been often observed in high-speed trains running through tunnels, cleaning robots going through pipings, medical machines in human blood vessels and core internals in nuclear reactor vessels. The equations of motion of multi-connected bodies are derived by Lagrangian method. The fluid forces acting on the multi-connected rigid bodies are obtained analytically on the basis of the Navier-Stokes equations applied to a narrow flow passage. The equations of coupled motion of the multi-connected bodies and fluid are derived. Using coupled equation, a stability analysis is performed. The critical velocities at the onset of the unstable behavior are estimated by plotting root locus. The flutter type instability and the divergence type instability are observed when the flow velocity increases. The variation of the coupled mode shape corresponding to the increment of the flow velocity is shown, and the relation between the coupled mode shape and unstable phenomena is discussed. Furthermore, the effect of the number of bodies and the pressure loss at the connecting points on the coupled mode and pressure distribution is investigated. The mechanism of occurrence of unstable phenomena is studied.

Vibration behavior and unstable phenomena of multi-connected bodies supported by damper-spring elements moving in a narrow flow passage are reported. These vibration phenomena have been often observed in high-speed trains running in tunnels, cleaning robots going through pipings and so on. The fluid forces acting on the multi-connected rigid bodies are obtained analytically on the basis of the Navier-Stokes equations applied to a narrow flow passage. The equations of coupled motion of the multi-connected bodies and fluid are derived. Using coupled equation, a stability analysis is performed. The effect of the flow velocity and number of bodies on the coupled mode is investigated. The influence of the boundary conditions of fluid pressure at connecting points is also investigated.

A syringe-type radiopharmaceutical being supplied by a manufacturer has a syringe shield and a plunger shield, whereas an in-hospital labeling radiopharmaceutical is administered by a disposable plastic syringe without the plunger shield. In cooperation with Nihon Medi-Physics Co. Ltd., we have produced a new experimental plunger shield for the disposable plastic syringe. In order to evaluate this shielding effect, we compared the leaked radiation doses of our plunger shield with those of the syringe-type radiopharmaceutical (Medi shield type). Our plunger shield has a lead plate of 21 mm in diameter and 3 mm thick. This shield is equipped with the plunger-end of a disposal plastic syringe. We sealed 99mTc solution into a plastic syringe (Terumo Co.) of 5 ml with our plunger shield and Medi shield type of 2 ml. We measured leaked radiation doses around syringes using fluorescent glass dosimeters (Dose Ace). The number of measure points was 18. The measured doses were converted to 70 microm dose equivalent at 740 MBq of radioactivity. The results of our plunger shield and the Medi shield type were as follows: 4-13 microSv/h and 3-14 microSv/h at shielding areas, 3-545 microSv/h and 6-97 microSv/h at non-shielding areas, 42-116 microSv/h and 88-165 microSv/h in the vicinity of the syringe shield, and 1071 microSv/h and 1243 microSv/h at the front of the needle. For dose rates of shielding areas around the syringe, the shielding effects were approximately the same as those of the Medi shield type. In conclusion, our plunger shield may be useful for reducing finger exposure during the injection of an in-hospital labeled radiopharmaceutical.

In this study, a vibration experiment with a reduced scale model of a large-size cylindrical water storage tank is performed in order to investigate the nonlinear vibration responses of the cylindrical tank when the beam-type and the oval-type vibrations are coupled. The sinusoidal sweep test is conducted by varying the input acceleration from smaller to larger input. As a result, the resonance frequency shifts to the lower frequency region and the response magnification factor becomes smaller as the input acceleration level becomes larger. Furthermore, when larger input is applied, the oval-type vibration has a subharmonic resonance of order one-half, and its displacement-amplitude grows up significantly. It can be assumed that the large amplitude of oval-type vibration generates a geometrical nonlinearity for the beam-type vibration.

The seismic-proof design of a large-scale cylindrical water storage tank has been an important issue for enormous earthquake. For enhancing its reliability, it is necessary to study the vibration behavior of the tank in more detail. This paper describes the results of a vibration test with a 1/10 reduced scale model of a large-scale cylindrical water storage tank, and also refers to the dynamic fluid pressure distribution and its influence on the seismic-proof design. Considering the differences between the experimental values and numerical design ones, it becomes obvious that there is a discrepancy between the positive and the negative pressures of the dynamic fluid pressure and that the dynamic fluid pressure depends on the acceleration magnitude. And it is suggested that such phenomena are caused by oval-type vibrations. They, however, have little effect on the seismic-proof design of the tank in the range of acceleration used in this study.

When slender pipes are subjected to internal flow, the pipes lose stability by flutter and divergence in increasing the fluid velocity. In addition, they also lose stability when they are subjected to external annular axial flow. In the development of a piping system in the field of ocean mining, and in the field of fluid energy utilization, and so forth, the double walled pipe structure system subjected to an internal flow and an external flow simultaneously is thought to be one of the important pipe structures. In this paper, the pipe structures are assumed to be composed of the cantilevered beam structure which shows the complicated dynamic behavior than the other supported conditions. For the analysis of the internal flow, the conventional inviscid stability analysis method is applied. For the analysis of the external annular axial flow, both the viscous solution using the Navier-Stokes equation of motion and the ideal fluid solution which viscous influence is added to are applied. Changing the flow direction and the fluid velocity of the internal flow and the external flow, and the specifications of modeling, the stability of the double walled pipes is investigated and discussed.Copyright © 2015 by ASME