Comparison of RIMPUFF, HYSPLIT, ADMS atmospheric dispersion model outputs, using emergency response procedures, with (85)Kr measurements made in the vicinity of nuclear reprocessing plant.

The Institut de Radioprotection et de Sureté Nucléaire (IRSN) performed a series of (85)Kr air sampling campaigns at mesoscale distances (18-50 km) from the AREVA NC La Hague nuclear reprocessing plant (North West France) between 2007 and 2009. The samples were collected in order to test and optimise a technique to measure low krypton-85 ((85)Kr) air concentrations and to investigate the performance of three atmospheric dispersion models (RIMPUFF, HYSPLIT, and ADMS), This paper presents the (85)Kr air concentrations measured at three sampling locations which varied from 2 to 8000 Bq m(-3), along with the (85)Kr air concentrations output by the dispersion models. The dispersion models made reasonable estimates of the mean concentrations of (85)Kr field measurements during steady wind conditions. In contrast, the models failed to accurately predict peaks in (85)Kr air concentration during periods of rapid and large changes in wind speed and/or wind direction. At distances where we made the comparisons (18-50 km), in all cases, the models underestimated the air concentration activities.

Estimation of seasonal correction factors through Fourier decomposition analysis--a new model for indoor radon levels in Irish homes.

Radon concentrations in homes have been shown to vary considerably with season. It is important to account for this by applying a correction factor to any home radon measurement of less than one year. To date, Irish radon measurement services have used correction factors based on data derived for the UK in the 1980s. In the absence of similar data for Ireland at the time, these were considered suitable for use due to the similarities between the climates, house types and lifestyles in the two countries. In order to better estimate the long-term radon concentration, measurements from 5640 Irish homes were used to derive a set of correction factors specifically for Ireland. These were generated by means of Fourier decomposition analysis and the new correction factors compared, using 95% confidence intervals, to those derived for the UK using the same analysis and to those currently in use for Ireland. In both cases, a significant difference was found between 10 of the 12 monthly seasonal correction factors. This paper presents the methods used in detail and the results of the analysis.

A comparative study of lognormal, gamma and beta modelling in radon mapping with recommendations regarding bias, sample sizes and the treatment of outliers.

Radon risk maps have been produced in many countries using non-geologically based techniques utilising the lognormal and gamma distributions to display point estimates of the probability, P(RL), that indoor radon levels will exceed a reference level. Recent work on updating radon maps in Ireland prompted an examination of various statistical issues associated with non-geologically based radon mapping techniques. The purpose of this paper is to compare existing techniques with a new theoretically unbiased model which uses the beta distribution to estimate P(RL). We examine this new beta based model and four existing models for bias using simulated test data sets. Producing confidence intervals for P(RL), we also analyse the relationship between sample size and estimation error for each model and finally we consider the effect of extreme values on estimation procedures. We demonstrate that, under the assumption of lognormally distributed data with outliers, a two stage approach to testing which first detects and removes outliers from the data and then applies the beta based method is most satisfactory from both a theoretical and empirical perspective.

The Castleisland Radon Survey-follow--up to the discovery of a house with extremely high radon concentrations in County Kerry (SW Ireland).

In July 2003, a house with a seasonally adjusted annual average radon concentration of 49 000 Bq m(-3) was identified near Castleisland in County Kerry (SW Ireland). The possibility that other houses with similar extreme radon concentrations could be present in the surrounding area triggered the setting up of a localised radon survey, the so-called 'Castleisland Radon Survey' (CRS). To this end, approximately 2500 householders living in four 10 x 10 km2 grid squares from the Irish grid closest to the town of Castleisland were invited to participate. Four hundred and eighteen householders responded to the invitation (17% response rate) and 383 home results were used for further analysis. In the 400 km2 encompassing the four studied grid squares, 14% of the homes were found to have a seasonally adjusted annual average radon concentration above the national reference level of 200 Bq m(-3) while 2% above 800 Bq m(-3). An average radon concentration of 147 Bq m(-3) was calculated. This can be compared with the average radon concentration of 98 Bq m(-3) calculated for the same four grid squares on the basis of 80 measurements carried out during the Irish National Radon Survey (NRS) which was conducted between 1992 and 1997. The fourth highest radon concentration (6184 Bq m(-3)) and three of the ten highest ever measured in Ireland were all identified during the CRS. This shows that localised and targeted radon surveys are an invaluable tool for the identification of homes at highest risk from high radon concentrations. Two of the four grid squares investigated during the CRS are currently designated as high radon areas (defined as areas where 10% or more of all houses are predicted to exceed 200 Bq m(-3)) as predicted by the NRS. A thorough statistical analysis of the CRS and NRS data was carried out and indicated that both datasets could be merged and used to refine the original NRS predictions. The results indicate that two of the four studied grid squares could potentially be redesignated. The practical feasibility and overall benefit of updating the Irish radon map in light of this analysis is described.

High radon concentrations in a house near Castleisland, County Kerry (Ireland)--identification, remediation and post-remediation.

In July 2003, a passive radon measurement carried out over a 3-month period in a house near Castleisland in County Kerry (South-West of Ireland) identified a seasonally adjusted annual average concentration of approximately 49 000 Bq m(-3). This is the highest radon concentration ever recorded in a house in Ireland. It is almost 250 times higher than the national reference level of 200 Bq m(-3) for homes and it gives rise to an estimated annual radiation dose of approximately 1.2 Sv to the occupants. This paper describes the identification of the 'Castleisland house' and gives information on the local geology, the levels of natural background radiation in the area and the follow-up actions taken to remediate the house as well as the efforts made to heighten awareness in the locality of the hazards from radon.