Tatsuyuki Maekawa

Large-scale hybrid monitoring system for temperature, strain, and vibration using fiber Bragg grating sensors

Fiber Bragg grating (FBG) sensor systems have been widely developed and the feasibility of their application to various fields has been demonstrated. However, from the viewpoint of the combination of highly multiplexed system and hybrid sensing of static parameter and dynamic parameter, investigations are not adequate yet. In this paper an interrogation technique for static and dynamic FBG sensors is developed. We demonstrated that the method could measure the temperature within 1?<C and detect a frequency signal up to 300Hz. We designed a multiplexing method and evaluated that the multiplexed FBG sensor system was able to monitor a maximum of 192 FBG sensors. As a result, we confirmed the applicability of the system for large-scale monitoring of temperature, strain and vibration.

Development of Hard X-ray and Gamma-ray Detector With Transition Edge Sensor for Nuclear Materials Analysis

We have designed and fabricated a hard X-ray and gamma-ray TES spectrometer for nuclear materials analysis. A superconducting tin (Sn) absorber is coupled to the TES film by using a gold (Au) bump post to improve the thermal contact between the absorber and the TES. To obtain a sufficient detection efficiency at the high energy photons near 100 keV, an 8-pixel array of TES microcalorimeters were developed. In this new device, the epoxy glue which is used to connect the absorber and the gold bump post was well controlled and hence the slow component of the decay time constant was improved from 7.82 ms to 4.46 ms compared to our old device. The energy resolution was 131 eV FWHM at 59.5 keV gamma rays, which is better than the limit of HPGe detectors (400 eV FWHM at 60 keV).

Multipoint radiation monitor using waveguide scintillators and optical fiber

A novel multipoint radiation monitor using waveguide scintillators and optical fiber connections is described. A new design of waveguide scintillator consisting of a scintillating material and a wavelength-shifting fiber (WLSF) has been deeveloped. The WLSF is embedded in the scintillator, and each end is fitted with an optical connector for connection to a transparent optical fiber. Multiple waveguide scintillators can be connected in a series, and the ends of the transparent optical fiber loop are terminated with a pair of photodetectors. This new technique for radiation monitoring dispenses with electric apparatus and improves noise resistance. Furthermore, it offers the advantages of multipoint measurement, meaning that the radiation incident on each scintillator is monitred by two photodetectors. We have examined the light output characteristics and time resolution of a prototype arrangement of waveguide scintillators and confirmed the feasibility of multipoint measurements in a system of five waveguide scintillators connected in series using a 200 m optical fiber loop.

Long Scintillation Detector Using Composite Light Guide for β-ray Survey Measurement

In this paper, we describe a new type of scintillation detector that can be inserted into long, narrow tubes used in nuclear power plants to measure radioactive contamination of their inner surfaces. The sensitive area of the detector needs to cover the entire circumference and extend along the longitudinal axis, and its performance must be equivalent to that of a conventional survey meter. To construct such a sensitive area, we bonded six long, thin plastic scintillator strips around a hexagonal center core. For the hexagonal center core, we proposed a novel light collection structure called a “composite light guide,” using a wavelength-shifting technique to maintain the counting efficiency while achieving better uniformity along the longitudinal axis. We conducted basic experiments, and also established a simple light propagation model of the composite light guide, focusing on the light intensity, and confirmed its effectiveness. Using this light propagation model, we determined the optimum design and incorporated it into the manufacture of a prototype detector. From tests of the prototype detector, we verified that its performance satisfied the design requirements and that the composite light guide functioned effectively.

Next Generation Technologies in the Digital I&C Systems for Nuclear Power Plants

In this chapter, overviews of digital technologies for instrumentation and control (I&C) systems and the main control room (MCR) of boiling water reactor nuclear power plants (BWR NPPs) are explained. Then, cutting edge fundamental technologies and future possibilities for the next generation I&C systems are described.

A rapid-detection method for radioactive cesium in the air

ABSTRACT We propose a method of rapidly detecting radioactive cesium floating in the air for the purpose of alerting people active in the ‘difficult-to-return zone’ of Fukushima to changes in airborne radioactivity. With this purpose in mind, we set requirement specifications and created a new system concept. The targeted detection limit was 30 Bq/m3 and the mandatory level of measurement time was 48 min with a target level of 12 min, and these periods are 10 times faster than those of conventional air monitors. The system consists of a conventional gamma-spectrometer with a novel shaped shield. The targeted peak region of the measured energy spectrum is analyzed. After the basic design and confirmation of feasibility, we perform some experiments in the normal environment of Yokohama city and the difficult-to-return zone of Fukushima. Using the results, we conducted the design improvement and performance evaluation. As a result, the system performance is found to satisfy requirements. We thus conclude that this system is a promising candidate for rapid detection of airborne radioactivity in the difficult-to-return zone of Fukushima.

Alpha Radioactivity Monitor Using Ionized Air Transportation for Large Size Uranium Waste: Part 1—Large Measurement Chamber and Evaluation of Detection Performance

We present an ionized air transportation type alpha radioactivity monitor to efficiently perform the clearance level inspection for large size uranium waste and its detection performance. In previous work, we developed a prototype monitor with an about 1000 mm cubic measurement chamber to measure the cut waste. However, in a survey of target waste, we found that it is desired to measure not only the cut waste but also the lengthy waste such as uncut cylinders. Therefore, we developed an alpha radioactivity monitor with a long and large measurement chamber (effective sizes: 500 mm x900 mm x3200 mm) for long and large cylindrically-shaped waste (maximum size: 300 mm in diameter and 3000 mm in length, weight: 10 to 200 kg). We aimed <1000 Bq as the target value of Alpha radioactivity Detection Limit (ADL), which is one-tenth of the clearance level (1 Bq/g) for 10 kg waste. The issue to size up the measurement chamber was to suppress the reduction in sensitivity of alpha radioactivity. To overcome this, we enhanced an air fan power and optimized an ion sensor design. Using this monitor, we measured and evaluated ADLs for several cases supposing the practical applications (long cylinders with a smooth surface, bump, or concavity and convexity, and pipes with several small diameters). The resulting ALD ranged from 60 Bq to 120 Bq and sufficiently satisfied the target ALD (<1000 Bq). In conclusion, this monitor has sufficient performance for the clearance level inspection for large uranium waste.Copyright

Development of a new CdTe area radiation monitor using the G(E) function method

We developed a small Area Radiation Monitor (ARM) prototype with high accuracy performance by combining a cadmium telluride (CdTe) detector with the G(E) function method. To obtain the measurement accuracy required for ARMs, we created a G(E) function based on detailed spectral responses. The accuracy of the derived dose rate and other expected requirements for practical applications were experimentally evaluated. The accuracy for a CdTe detector with dimensions of 5x5x5 mm3 was within 14% in the 60–300 keV range and within 10% in the 300 keV--1.8 MeV range, which was comparable to a large ARM with an ionization chamber. The accuracy for a CdTe detector with dimensions of 2x2x2mm3 was within 23% in the 60–300 keV range and within 14% in the 300 keV—1.8 MeV range, which was inferior to the 5x5x5 mm3 detector but higher than a small ARM using a silicon PIN photodiode.

α/β radiation detector using wavelength and delayed fluorescence discrimination

Abstract This paper describes a novel two-layer radiation detector for α/β simultaneous counting for dust radiation monitoring in nuclear power plants. For α/β discrimination, wavelength and delayed fluorescence discrimination techniques were newly developed. To establish the wavelength discrimination, we adopted a two-layer scintillator consisting of the plastic scintillator (NE-111A) and Y 2 O 2 S(Eu) whose emission spectra are quite different. To reject the mixed β signal in the α detection layer, we used the delayed fluorescence characteristics of Y 2 O 2 S(Eu) in the signal processing. We manufactured the detector and tested its feasibility and the detection performance for dust radiation monitoring. Finally, we concluded that the performance of this new α/β detector using the new discrimination methods is suitable for dust radiation monitoring.