Extension of NCRP 129 to short-lived radionuclides.

NCRP 129 contains dose conversion factors for 200 radionuclides that allow one to estimate the maximum dose to an individual based on the concentration of the radionuclide in the soil and the way in which the land is used. The methodology of NCRP 129 has been extended to be applicable to 28 common short-lived radionuclides and their progeny, and dose conversion factors were obtained for these radionuclides. In addition to applying the NCRP 129 calculational methodology to these radionuclides, holdup times from harvest or slaughter until consumption have been incorporated into the decay correction equations used to determine the maximum annual dose due to the significance of the holdup time with respect to the dose from short-lived radionuclides. These holdup times were included in the Monte Carlo sampling regimen used in NCRP 129. A test using emission rates proportional to those of the Chernobyl event indicated that areas of high dose, where rainout occurs, more than doubled in areas where short-lived radionuclides from this study were included.

Internal exposure from the ingestion of foods contaminated by 137Cs after the Chernobyl accident. Report 1. General model: ingestion doses and countermeasure effectiveness for the adults of Rovno Oblast of Ukraine.

The Chernobyl accident, which occurred in April 1986, resulted in the atmospheric release of about 70--100 PBq of 137Cs. This paper examines the doses to the adult population of the northern part of Rovno Oblast, Ukraine, from ingestion of 137Cs. Fallout of 137Cs in these regions was lower than in other regions of Ukraine. However, the transfer of 137Cs from soil to milk in the region considered is high (up to 20 Bq L-1 per kBq m-2) and results in the predominance of internal doses compared to those from external exposure. Numerous measurements of 137Cs soil deposition, 137Cs milk contamination, and 137Cs body burden have been made in the area and form the basis of a general model of internal exposure from the ingestion of foods contaminated by 137Cs. This paper has two main purposes. The first is to develop the general phenomenological description of the process leading to internal exposure from the ingestion of 137Cs contaminated foods in the situation where different countermeasures are realized. The second is to apply the model for the adult population of the northern part of the Rovno Oblast (first report) for the limited time period of up to six years after the accident. The doses actually received by the adults are estimated to be four to eight times smaller than the doses calculated for the situation without countermeasures.

Uncertainties in predicted radionuclide body burdens and doses from discrete stochastic source terms.

Expressions are derived in three cases for the expectation and uncertainty of body burdens and doses calculated from a linear model of environmental transport and human metabolism in terms of expectation and uncertainty in inputs of discrete, stochastic random variables. Three cases are compared to determine the relationship of the expectations and uncertainties under varying assumptions. In the constant input case, the input is selected randomly at the outset of the simulation period [O,T] from the distribution to which the population is exposed and then is held constant throughout [O,T]. In the two time-varying cases, random and autoregressive, it was assumed that N discrete stochastic exposures to the input were made uncorrelated and partially correlated, respectively. Each exposure was constant during each time interval of length T/N. The expectation values of the body burdens and doses in the constant input case were identical to those in the random case and the autoregressive cases for stationary inputs. The uncertainties of the body burdens and the doses in the constant input case were identical in the limit of rapid metabolism to those of the random case and the autoregressive cases for stationary inputs. In the limit of slow metabolism, the uncertainties of the body burdens and the doses in the constant input case were N1/2 and (3N/4)1/2, respectively, greater than those in the random case and were ((1 + alpha)/[(1 - alpha)N])1/2 and (4(1 + alpha)/[3(1 - alpha)N])1/2, respectively, greater than those in the autoregressive case for stationary inputs and autocorrelation coefficient alpha. That is, increasing the number of sampling periods decreases the uncertainty and increasing the autocorrelation increases the uncertainty. In an example application for ingestion of 137Cs at Bikini Island, a weak form of both slow and rapid metabolism limits apply and give the result that the uncertainty of the body burden in the constant input case is 18 times greater than the random case. For alpha = 0.5, the uncertainty of the body burden in the autoregressive case is 1.7 times greater than the random case. The smooth transition of the autoregressive case from the random case to the constant input case is shown as alpha increases from 0 (random) to 1 (constant).