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An analysis of uncertainties in inhalation and ingestion dose estimates arising from uncertainties in dosimetric and foodchain transfer data

Objective

COMPUTER CODES FOR EVALUATING THE RADIOLOGICAL IMPACT OF ACCIDENTAL ATMOSPHERIC RELEASES OF RADIOACTIVITY ARE INCREASINGLY USED TO GENERATE DATA WHICH FORM AN INPUT TO DECISIONS ON EMERGENCY PLANNING AND ON REACTOR DESIGN, SAFETY AND SITING. THE CEGB HAVE, OVER THE LAST 5 YEARS, DEVELOPED THE DETERMINISTIC NECTAR COMPUTER CODE AND ARE CURRENTLY PRODUCING, JOINTLY WITH UKAEA (SRD), A PROBABILISTIC RISK ASSESMENT CONSEQUENCE CODE CALLED CONDOR FOR USE WITHIN THE UK NUCLEAR INDUSTRY. A SUBSTANTIAL PROGRAMME OF WORK IS ALSO IN PROGRESS AIMED AT QUALITY ASSURING THE CODES. IN PARTICULAR, A PROGRAMME OF EXPERIMENTS AIMED AT PRODUCING DATA TO VALIDATE SOME OF THE MODELS INCORPORATED IN THESE CODES IS CURRENTLY IN PROGRESS. DOSE OR HEALTH EFFECT ESTIMATES MADE USING CODES LIKE NECTAR OR CONDOR NEED TO BE ACCOMPANIED BY ESTIMATES OF UNCERTAINTY IF THEY ARE NOT TO BE MISINTERPRETED. UNCERTAINTIES IN THE CODE PREDICTIONS ARISE PRINCIPALLY FROM THREE SOURCES:
A)UNCERTAINTIES IN MODEL INPUT PARAMETERS, ARISING FROM UNCERTAINTIES IN THE KMOWN TRANSFER PROCESSES.
B)MODEL BIAS, ARISING FRON INHERENT OVERSIMPLIFICATIONS OR PESSIMISMS IN THE MODEL SIMULATING A PARTICULAR TRANSFER PROCESS.
C)THE INHERENT VARIABILITY OF THE TRANSFER PROCESSES THEMSELVES. THE CONTRIBUTION FROM THIS SOURCE IS RELATIVELY SMALL FOR MACROSCOPIC AVERAGES (EG.POPULATION DOSE COMPUTATIONS) BUT CAN BE LARGE FOR CRITICAL GROUP INDIVIDUAL DOSE CALCULATIONS.
THIS RESEARCH PROPOSAL COVERS WORK AIMED AT QUANTIFYING UNCERTAINTIES IN INHALATION AND INGESTION DOSE ESTIMATES ARISING FROM UNCERTAINTIES IN THE DOSIMETRIC AND, WHERE APPROPRIATE, THE FOODCHAIN TRANSFER DATA, FOR A RANGE OF NUCLIDES THAT ARE IMPORTANT FOR THERMAL REACTOR ACCIDENT CONSEQUENCE ASSESMENTS.
It has been possible, perhaps for the first time, to couple directly time dependent food chain and internal dosimetry models. The resulting software package enables detailed uncertainty analyses to be carried out. In addition, the results of the uncertainty analyses were subjected to a sensitivity analysis both with respect to specified parameter correlations and to the statistical method employed.

Research has been conducted to determine the uncertainty in ingestion dose estimates arising from uncertainties in food chain transfer and in internal (human) dosimetry. The secondary objective was to estimate the sensitivity of these uncertainties to the statistical sampling method chosen.
THE WORK WILL BE SUB-DIVIDED AS FOLLOWS:
A) AN EFFICIENT AND COMPREHENSIVE COMPUTER MODEL WILL BE PRODUCED FOR BOTH FOODCHAIN TRANSFER AND METABOLIC TRANSPORT IN THE BODY FOR INTAKES VIA INHALATION AND INGESTION OF SINGLE PARENT NUCLIDES. THE FOODCHAIN COMPONENET OF THE TIME-DEPENDENT MODEL WILL BE SIMILAR TO THAT INCORPORATED IN THE NECTAR AND CONDOR CODES. IT IS EXTENSIVELY USED BY CEGB AND ITS CONTRACTORS AND HAS BEEN PUBLISHED WIDELY. A LITERATURE SURVEY WILL BE CARRIED OUT TO STUDY THE VARIABILITY OF ALL RELEVANT FOODCHAIN AND METABOLIC TRANSFER PARAMETERS. THE DATA WILL BE ANALYSED TO DERIVE PARTIAL CORRELATION AND REGRESSION COEFFICIENTS AND PROBABILITY DISTRIBUTION FUNCTIONS (PDFS), WHICH TOGETHER FORM THE INPUT TO THE COMPUTER MODEL.
B) THE PDFS INPUT TO THE COMPUTER MODEL WILL BE USED TO COMPUTE OUTPUT PDFS FOR DOSE INITIALLY USING A LATIN HYPERCUBE SAMPLING ALGORITHM DEVELOPED BY SANDIA NATIONAL LABORATORIES. THIS ALGORITHM HAS ALREADY BEEN SATISFACTORILY MOUNTED AND TESTED ON THE CEGB'S CENTRAL COMPUTING FACILITY. INHALATION AND INGESTION DOSES WILL BE CONSIDERED BOTH SEPARATELY AND TOGETHER. THE OUTPUT PDFS WILL BE ANALYSED TO OBTAIN QUANTITATIVE ESTIMATES OF UNCERTAINTY. A SENSITIVITY ANALYSIS WILL ALSO BE CARRIED OUT, FOR EXAMPLE, TO STUDY THE SENSITIVITY OF THE COMPUTED UNCERTAINTY TO DIFFERING TYPES OF INPUT PDFS IN SITUATIONS WHERE THE DATA BASE IS TOO SPARSE TO YIELD RELIABLE ESTIMATES OF THE PDF.
C) THE INFLUENCE ON THE RESULTS OF OTHER STATISTICAL APPROACHES (EG. RESPONSE SURFACE SAMPLING) BEING DEVELOPED ELSEWHERE WITHIN THE MARIA PROGRAMME WILL ALSO BE STUDIED, AS THESE BECOME AVAILABLE FROM CONTRACTORS.

THIS PROPOSAL IS CONCERNED WITH UNCERTAINTIES IN DOSE CALCULATIONS ARISING FROM UNCERTAINTIES IN INHALATION AND INGESTION DOSE-INTAKE DATA AND, FOR INGESTION DOSE, THE FOODCHAIN TRANSFER DATA. IT THUS REPRESENTS AN ADVANCE ON PREVIOUS WORK IN THAT, FOR INGESTION DOSE, UNCERTAINTIES IN TWO MODULES WILL BE CONSIDERED TOGETHER: WORK CARRIED OUT PREVIOUSLY BY KFK, NRPB AND CEGB HAS CONSIDERED ONLY ONE MODULE OF A CONSEQUENCE CALCULATION AT A TIME (ATMOSPHERIC DISPERSION OR FOODCHAIN TRANSFER). DUPLICATION OF EFFORT WILL BE AVOITED BY EXCHANGING INFORMATION WITH ALL RELEVANT MARIA CONTRACTORS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

National Power plc
Address
Kelvin Avenue
KT22 7SE Leatherhead
United Kingdom