R01036: A probabilistic modelling suite for the marine environment
Tuesday 2 September 2003
This research project aims to develop a probabilistic model for use in the assessment of routine discharges of liquid radioactive waste.
Study Duration: April 2000 to February 2003
Contractor: The Centre for Environment, Fisheries & Aquaculture Science (CEFAS)
Background
Given the inherent variability of natural processes and the uncertainties involved in modelling, presenting modelling results as distributions of probable values would provide a fuller representation of reality than the single values of the deterministic models. This project had two main aims: to develop a probabilistic model or models for use in the assessment of routine discharges of liquid radioactive waste, and to use the model for a sensitivity analysis of the input parameters. It was proposed to create probabilistic versions of two deterministic marine dispersion models (WAT and ADO) to be used in assessing the impact of proposed radioactive discharges as part of the FSA’s prospective dose methodology.
Research Approach
Two methods of selecting random numbers from specified distributions for use in the model were evaluated for accuracy: Simple Random Sampling and Latin Hypercube Sampling. The latter was chosen as it provided smoother distribution predictions. Uncertain parameters were identified and the parameter distributions determined, for the entire UK coast, through consultation with CEFAS experts. The distributions were then propagated through the models using Monte Carlo analysis. An assessment of the Sizewell nuclear site was used as a case study for the new models and for comparison with a deterministic assessment of the site. The uncertainty due to the habits survey for this site was investigated.
Results and findings
Further work is needed on whether to include the entire distribution of values from habits surveys, to take account of the variability of the entire group (as done in this study) or only to include the variability relating to the highest food consumers and site occupiers, i.e. the critical group. The 95 percentile of the dose output distribution is recommended for use as an indicator of the upper bound of dose to the critical group. This value is higher than that obtained using the deterministic model but it takes into account all the uncertainties and variabilities in the calculation and excludes extreme outlying values. It is suggested that it may be helpful to present a range of values for possible dose, e.g. the 5 percentile for minimum dose, 50 for likely and 95 for maximum. Further development and validation of the probabilistic models is needed, and a standard probabilistic assessment procedure developed. This project complements project R01037: uncertainties in assessing doses to members of the public due to radioactive discharges to the marine environment.
Dissemination information
Final report is available from the FSA Library and Information centre. To obtain a copy, please contact the Enquiry Desk,
Dr. Elsie Widdowson Library and Information Services, Food Standards Agency (020 7276 8181/8182 or at library&info@foodstandards.gsi.gov.uk).
Contact: For any enquiries concerning this research project, please contact the relevant Programme contact or email science@foodstandards.gsi.gov.uk