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

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

A method for the prediction of the dose rate distribution in a primary containment vessel of the Fukushima Daiichi Nuclear Power Station

We propose a method to predict the dose rate distribution in a primary containment vessel of Unit 1 of the Fukushima Daiichi Nuclear Power Station (1F) using numerical calculations and measured data

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

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

POSSIBLE ROLE OF TADPOLE OF RANA CHENSINENSIS AS AN INTERMEDIATE HOST OF ANGIOSTRONGYLUS CANTONENSIS

Tadpoles of Rana chensinensis became infected by exposure to the 1st stage larvae of Angiostrongylus cantonensis, and the larvae developed into the 2nd stage 12 to 16 days after the infection. It was suggested that the tadpole might act as an intermediate host of A. cantonensis

Revision of the JENDL FP Fission Yield Data

Some fission yields data of JENDL FP Fission Yields Data File 2011 (JENDL/FPY-2011) revealed inadequacies when applied to delayed neutron related subjects. The sensitivity analyses of decay heat summation calculations also showed some problems. From these results the fission yields of JENDL/FPY-2011 have been revised. The present report describes the revision of the yield data by emphasizing the sensitivity analyses

Status and future work of the NEA Working Party on international nuclear data Evaluation Cooperation

The Working Party on international nuclear data Evaluation Cooperation (WPEC) is a collaborative effort between the major OECD nuclear data projects: ENDF/B (USA), JENDL (Japan) and JEFF (Europe), and the IAEA-supported non-OECD projects CENDL (China) and BROND (Russian Federation). Nuclear data challenges and problems that are common to all projects are considered in various WPEC subgroups that are normally of limited time span. The achievements of these subgroups during the course of 2005/06 are reviewed in this paper. Among the recent accomplishments are improved criticality predictions through revised U evaluations, the completion of new cross-section standards, and the creation of a new fission product library. Problems that are currently being addressed are the processing and inclusion of covariance data in the libraries, improvements in decay data to assist in decay heat calculations, assembly of a well-structured High Priority Request List, validation of the new fission product cross-section library, and the assessment of nuclear data needs for GEN-IV