Simultaneous Sampling of Indoor and Outdoor Airborne Radioactivity after the Fukushima Daiichi Nuclear Power Plant Accident

Abstract

Several studies have estimated inhalation doses for the public because of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Most of them were based on measurement of radioactivity in outdoor air and included the assumption that people stayed outdoors all day. Although this assumption gives a conservative estimate, it is not realistic. The "air decontamination factor" (ratio of indoor to outdoor air radionuclide concentrations) was estimated from simultaneous sampling of radioactivity in both inside and outside air of one building. The building was a workplace and located at the National Institute of Radiological Sciences (NIRS) in Chiba Prefecture, Japan. Aerosol-associated radioactive materials in air were collected onto filters, and the filters were analyzed by γ spectrometry at NIRS. The filter sampling was started on March 15, 2011 and was continued for more than 1 year. Several radionuclides, such as (131)I, (134)Cs, and (137)Cs were found by measuring the filters with a germanium detector. The air decontamination factor was around 0.64 for particulate (131)I and 0.58 for (137)Cs. These values could give implications for the ratio of indoor to outdoor radionuclide concentrations after the FDNPP accident for a similar type of building.

Novel method for estimation of the indoor-to-outdoor airborne radioactivity ratio following the Fukushima Daiichi Nuclear Power Plant accident

“…Radionuclide concentrations in indoor and outdoor air were measured simultaneously after the FDNPP accident at the National Institute of Radiological Sciences (NIRS) in Chiba Prefecture, Japan, located about 220 km south-southwest of the FDNPP (Ishikawa et al, 2014). The researchers captured the indoor-to-outdoor concentration ratios for I-131 and Cs-137 for the readily characterizable concrete buildings they instrumented.…”

“…Ishikawa et al (2014) deployed two sets of air sampling equipment after the FDNPP accident. The first set placed 1 m above the roof of a five-story concrete building at NIRS, and the second was located on a fifth-floor room of the same building, approximately 2 m above the floor.…”

“…The sampling filters were analyzed with a high-purity germanium detector (HPGe) of NIRS that had been inter-compared with Hirosaki University. Table 1 lists the data from Ishikawa et al (2014). The integrated measured indoor-to-outdoor concentrations of I-131 and Cs-131 were estimated as:…”

“…Ishikawa et al (2014) used the measured values in all available sampling periods, resulting in values of 0.48 and 0.72. The different sampling periods account for the difference between Ishikawa's and the results for this work, with the sampling period here chosen to correspond closely with data employed for development of the model.…”

“…From the data of the Chernobyl accident (Noguchi and Murata, 1988), gaseous iodine is the main component of I-131. Generally, researchers think that there would be almost no effect of decontamination for gaseous iodine (Ishikawa et al, 2014). It is reasonable when the gaseous I-131 concentration in outdoor air always is high in a long term.…”