Radiation hardness testing of an organic liquid scintillator detector for use in high dose rate accident response scenarios

Organic liquid scintillation detectors offer the advantage relative to many alternatives that they are sensitive to both fast neutrons and gamma rays, whilst radiation type can be discerned on the basis of pulse-shape discrimination. Mixed radiation fields of this type can arise in the context of reactor accidents via, for example, 137Cs (gamma) and 244Cm (neutrons). However, performance degradation of such scintillators, such as EJ-301, is a significant possibility that might limit the use of this technology in accident response applications. The premise behind the high dose rate testing of such a liquid scintillator described in this paper is for fuel debris characterisation at Fukushima Daiichi, which has expected dose rates of up to 1000 Gy/hr in close proximity to fuel debris. The tests carried out for this investigation involved using the 60Co gamma irradiation facility at the Dalton Cumbria Facility, Cumbria, United Kingdom to expose the detector to a similar dose rate to that which is estimated within the primary containment vessel for survivability tests. Radiation hardness tests have rarely been reported for such devices and it is expected that the performance will be dependent on the survival of the window of the photomultiplier tube rather than the liquid scintillant itself. A major advantage of the use of this detector is its physical size, due to the limitations on access into Fukushima reactors physical space is a premium. The research described in this paper presents the results of the dose rate exposure of the detector before signal was lost with the total dose observed providing information on any degradation affecting the performance of the device post-irradiatio

Development of ROV system to explore fuel debris in the Fukushima Daiichi Nuclear Power Plant

Instruments and Methods were developed to explore fuel debris at the bottom of the Primary Containment Vessel in the Fukushima Daiichi Nuclear Power Plant. A Remotely Operated Vehicle was designed to explore fuel debris and to investigate the distribution and surface profile of fuel debris at the bottom of the primary containment vessel using a sonar and a compact radiation detector. Several tests were carried out using various facilities to determined the capabilities of the sonar and gamma-ray detector to determine the feasibility of the devic

On the design of a remotely-deployed detection system for reactor assessment at Fukushima Daiichi

The premise behind this research is the design of a system that will allow fuel debris characterisation at Fukushima Daiichi. The precise location of the debris is not known for example as to whether it remains within the reactor pressure vessel or it has leaked through into the base of the pedestal below, additionally the state of the fuel is also in question as to whether this has corroded from within its encasing or if it is intact. The most likely scenario is a combination of all four of these situations. The flooding of the reactor floors immediately following the Fukushima accident adds an extra element of complexity for the detection system requiring it to be submersible and to hold any detector system in water tight confinement. The research carried out has involved extensive modifications to a previously-designed low-cost small-scale AVEXIS submersible inspection vehicle and the incorporation of a variety of radiation detectors. The latter has been designed to allow for mapping and determination of the situation that is present within the primary containment vessels. The challenges addressed with the detection system arise from the high dose rates that have been recorded around the reactor pressure vessels which can be as high as 1000 Gy/hr. In such a harsh environment not only will the radiation detectors struggle to operate but the components that make up the remote-operated vehicle are also likely to suffer radiation damage after only a relatively short period of time. The research presented here evaluates the components currently incorporated into the AVEXIS system in terms of their radiation tolerability as well as presenting the combination of detectors to be used in the remote probe for the investigation of the fuel debris

Inkjet printed dual band antenna for paper UAVs

A dual band antenna is inkjet-printed and then folded as part of a paper unmanned aerial vehicle (UAV). The patterns of the antenna are reproduced on a standard photo paper substrate using an off the shelf inkjet printer. Readily available cartridges with nanoparticle silver conductive ink are employed. A single-layer planar antenna is fed by coplanar waveguide (CPW). The geometry of the radiating element consists of a semicircle with a centered square slot. In order to examine the effect of bending on performance, the antenna is tested unfolded and then folded when integrated onto the airplane. Two configurations of the folded antenna on the plane are analyzed. The aim is to investigate the feasibility of fabricating foldable antennas for paper airplanes using low-cost inkjet printing techniques. The antenna operates at the existing 2.4 GHz and 5.2 GHz WLAN bands. Finite different time domain simulations compare well with measurement

Effect of protective coatings on the water absorption and mechanical properties of 3D printed PLA

This work aims to study the influence of protective coatings on the water absorption and mechanical properties of 3D printed polyꖖlactic acid (PLA) parts. The PLA parts were fabricated with different levels of the 3D printing process parameters, aiming to define samples with distinct strength and ductility/toughness characteristics. Water absorption tests following the standard ASTM D570�98 were performed on uncoated and coated PLA specimens. The effectiveness of two protective coatings based on acrylic and polyurethane varnish on reducing water absorption was evaluated. Both protective coatings have shown being effective on preventing water absorption by the PLA, with polyurethane presenting the best performance reducing water absorption by 38%. Tensile tests were carried out to determine the ultimate tensile strength, elastic modulus, yield tensile strength, fracture strain and toughness of specimens, before and after the application of protective coatings. The polyurethane protective coating also benefits the tensile properties of PLA parts, increasing the strength and ductility/toughness characteristics of specimens up to 24%

Effect of protective coatings on the water absorption and mechanical properties of 3D printed PLA

This work aims to study the influence of protective coatings on the water absorption and mechanical properties of 3D printed poly–lactic acid (PLA) parts. The PLA parts were fabricated with different levels of the 3D printing process parameters, aiming to define samples with distinct strength and ductility/toughness characteristics. Water absorption tests following the standard ASTM D570–98 were performed on uncoated and coated PLA specimens. The effectiveness of two protective coatings based on acrylic and polyurethane varnish on reducing water absorption was evaluated. Both protective coatings have shown being effective on preventing water absorption by the PLA, with polyurethane presenting the best performance reducing water absorption by 38%. Tensile tests were carried out to determine the ultimate tensile strength, elastic modulus, yield tensile strength, fracture strain and toughness of specimens, before and after the application of protective coatings. The polyurethane protective coating also benefits the tensile properties of PLA parts, increasing the strength and ductility/toughness characteristics of specimens up to 24%

A Remote-operated System to Map Radiation Dose in the Fukushima Daiichi Primary Containment Vessel

This paper describes the development of a submersible system based on a remote-operated vehicle coupled with radiation detectors to map the interior of the reactors at the Fukushima Daiichi nuclear power station. It has the aim oflocating fuel debris. The AVEXIS submersible vehicle used in this study has been designed as a low-cost, potentially disposable, inspection platform that is the smallest of its class and is capable of being deployed through a 150 mm diameter access pipe. To map the gamma-ray environment, a cerium bromide scintillator detector with a small form factor has been incorporated into the AVEXIS to identify radioactive isotopes via gamma-ray spectroscopy. This provides the combined system with the potential to map gamma-ray spectra and particle locations throughout submerged, contaminated facilities, such as Units 1, 2 and 3 of the Fukushima Daiichi nuclear power plant. The hypothesis of this research is to determine the sensitivity of the combined system in a submerged environment that replicates the combination of gamma radiation and water submersion but at lower dose rates

Compact viscometer prototype for remote in-situ analysis of sludge

On the Sellafield site there are a number of legacy storage tanks and silos containing sludge of uncertain properties. While there are efforts to determine the chemical and radiological properties of the sludge, in order to clean out and decommission these vessels the physical properties need to be ascertained as well. Shear behaviour, density and temperature are the key parameters to be understood before decommissioning activities commence. However, limited access, the congested nature of the tanks and presence of radioactive, hazardous substances severely limit sampling and usage of sophisticated characterisation devices within these tanks and therefore these properties remain uncertain. This paper describes the development of a cheap, compact and robust device to analyse the rheological properties of sludge, without the need to extract materials from the site in order to be analysed. Analysis of a sludge test material has been performed in order to create a suitable benchmark material for the rheological measurements with the prototype. Development of the device is being made with commercial off the shelf (COTS) components and modern rapid prototyping techniques. Using these techniques an initial prototype for measuring shear parameters of sludge has been developed, using a micro-controller for remote control and data gathering. The device is also compact enough to fit through a 75 mm opening, maximising deployment capabilities