Early faecal excretion of inhaled plutonium

Report of the Japan Health Physics Society ad hoc working group for the Plutonium intake accident

This paper describes an overview of the radiation protection response to the Plutonium intake accident that occurred at the Plutonium Fuel Facility of the Oarai Research and Development Center of the Japan Atomic Energy Agency on 6 June 2017. In the hood of the analyzing room at the Plutonium Fuel Facility five workers were checking a storage container of fast reactor nuclear fuel material. Around 11:15 a.m., vinyl bags inside the fuel material container containing Plutonium and enriched uranium burst during the inspection work. All the workers heard the bang, which caused misty dust leakage from the container. This event caused significant both skin and nasal α-contamination for three workers and just skin α-contamination for one worker. Decontamination was conducted in the shower room. Then the five workers were transferred to the Nuclear Fuel Cycle Engineering Laboratory to evaluate inhalation intake of Plutonium etc in the lungs. The maximum values of 2.2 × 104 Bq for 239Pu and 2.2 × 102 Bq for 241Am were estimated by the lung monitor. Based on these results, injection of a chelate agent was conducted for prompt excretion of Plutonium etc. The next morning, the five workers were transferred to the National Institute of Radiological Sciences for treatment including decontamination of their skin and measurement by a lung monitor. At that time no obvious energy peak was confirmed for Plutonium. The Japan Health Physics Society launched an ad-hoc working group for Plutonium intake accident around the middle of June to survey issues and to extract lessons for radiological protection. The authors, who are the members of the ad-hoc working group, here report the activity of the working group.

AN ACCIDENT OF INTERNAL CONTAMINATION WITH PLUTONIUM AND AMERICIUM AT A NUCLEAR FACILITY IN JAPAN: A PRELIMINARY REPORT AND THE POSSIBILITY OF DTPA ADMINISTRATION ADDING TO THE DIAGNOSIS

This article introduces the first accident of internal contamination with plutonium (Pu) or americium (Am) in Japan for which treatment was carried out. An accident of internal contamination with Pu and Am occurred at a Pu research facility at Oarai-town of Ibaraki prefecture in Japan. A plastic bag containing these radionuclides ruptured when five workers were inspecting a storage container in a hood. As a consequence, these workers were internally contaminated with Pu and Am. Although contamination on the body surface was observed in all five workers, a positive nasal swab was detected in only three of them. A chelating agent, calcium diethylenetriaminepenta-acetate (CaDTPA), was administered to all of them including the two workers without a positive nasal swab. However, bioassay detected a significant amount of Pu and Am in urine after administration of DTPA in these two workers, whereas the levels of these nuclides were below minimum detectable levels in urine before the administration. Since the prevalence of adverse reactions in DTPAs is low, the present results suggest that administration of DTPA can be used for the diagnosis of internal contamination even when a nasal swab is negative or contamination around body orifices is not detected.

Individual monitoring for internal contamination with plutonium compounds at JAEA-NCL

This paper provides an outline of an individual monitoring programme for internal contamination with Pu compounds and some of the knowledge obtained from experience of inhalation incidents that occurred over the past few decades at the Japan Atomic Energy Agency, Nuclear Fuel Cycle Engineering Laboratories (JAEA-NCL). Most of the incidents resulted in minor exposure doses, being an average of 0.1 mSv at a mixed oxide plant and 1.5 mSv at a reprocessing plant. Only two incidents involving three workers resulted in exposure over the regulatory dose limits of that time. The maximum exposure dose, an effective dose equivalent of 90 mSv, was assessed for a worker involved in the incident that took place at the reprocessing plant in 1993. Only faecal measurements have been used in final dose assessments because alternative monitoring data have rarely been available. Further investigations on the physicochemical properties specific to Pu compounds in workplaces have therefore been needed to improve not only the accuracy of internal dose assessments but also the nasal swab method useful in deciding medical intervention.

Characterisation of nasal swab samples by alpha spectrometry

A positive nasal swab taken at a radiation emergency, when properly collected and analysed, is a good indication of a potential inhalation intake. It may be expected to be a useful method for early dose assessment in cases of accidental inhalation of an alpha emitter. To improve the first estimation of intake activity, the quality of a nasal swab measurement was experimentally investigated. Alpha spectrometry was used to examine the experimental nasal swab samples involved with a plutonium solution or particles. Also, a numerical simulation analysis on the alpha spectrum using advanced alpha-spectrometric simulation was made to characterise the experimental results. It was observed that the alpha energy spectrum had a quite different shape among samples, and it was characterised by the type of contaminant. This could be the second advantage of using alpha spectrometry in addition to nuclide identification. The absorption of alpha radiation within the experimental nasal swab sample was different between the types of contaminants. For a quantitative discussion, the absorption for a swab sample must be determined for each type of contaminant. This new finding could be very useful for first responders. A nasal swab sample measured using an alpha spectrometer will give more useful information during the first response of an emergency.