NRPB - W34 Methods for Interpreting Monitoring Data Following an Accident in Wet Conditions

Synopsis

A non-technical summary of this report is available.

Procedures for interpreting monitoring data after an accidental release have been developed primarily by considering the situations that might arise if the accident occurs in dry conditions. However, as rain is an effective mechanism for locally enhancing the deposition of material from dispersing plumes, the extent of significant deposition following an accidental release in wet conditions could be much greater than for the same release in dry conditions. In addition, rainfall rates vary in time and space, leading to the possibility of a wet deposition pattern that could vary rapidly in space.

Following an accident, monitoring would be carried out to describe the deposition pattern around the nuclear site. This is aimed partly towards estimating doses to people near the site and identifying those areas where countermeasures are required, and partly towards building up a complete picture of the consequences of the release. Simple atmospheric dispersion models can assist in building up a picture of the consequences and directing monitoring effort. However, those currently used after an accident do not include a realistic description of the effects of variations in rainfall rate on the deposition pattern.

Options and problems associated with the use of monitoring data in wet conditions are discussed with particular attention paid to the use of such data to support model estimates of accident consequences.

Last reviewed: 4 August 2009