Modeled Concentrations in Rice and Ingestion Doses From Chronic Atmospheric Releases of Tritium

Abstract

The expansion of nuclear power programs in Asia has stimulated interest in the improved modeling of concentrations of tritium in rice, a staple crop grown throughout the far east. Normally, the specific activity model is used to calculate concentrations of tritium in the tissue water of edible plants to assess ingestion dose from chronic releases. However, because rice, like other grains, has much lower water content than most crops, the calculation must also account for organically bound tritium. This paper reviews ways to calculate steady-state concentrations of tritium in rice, including the methods of Canadian and United States regulatory models, and the assumptions behind them. Concentrations in rice and resulting ingestion doses are compared for the various methods, and equations for calculating concentrations are recommended. The regulatory models underestimate doses received from ingestion of rice contaminated with tritium since they do not account explicitly for organically bound tritium. The importance of including organically bound tritium is illustrated in a comparison of doses from rice, leafy vegetables and milk for an Asian diet. Dose factors from tritium for these foods are estimated to be 135, 47, and 20 nSv y(-1)/(Bq m(-3)), respectively. Assuming known air concentrations, tritium concentrations in rice, calculated with the recommended equations, are uncertain by less than a factor 2 when tritium concentrations in the rice paddy water are known, and by less than a factor of 2.3 when concentrations in paddy water are unknown.

Root uptake of radionuclides following their acute soil depositions during the growth of selected food crops

“…The values for potato are about the tubers after being peeled and those for cucumber are the weighted means for the two harvests. For a chronic HTO release, a specific activity model, which is based on the assumption that plant tritium will be in equilibrium with atmospheric tritium, is widely used (Diabaté and Strack, 1990;Peterson and Davis, 2000). This kind of model cannot be applied to an acute release of HTO (Choi et al, 2007a;Higgins, 1997).…”

14CO2 ACTIVITY IN AIR SAMPLES AND DILUTION FACTOR EVALUATION OF KAKRAPAR GUJARAT SITE, INDIA

“…14 C is an important radionuclide for reactors using heavy water because of larger production than the pressurized water reactor (PWR) and boiling water reactor (BWR) (Graven et al 2011). 14 C production is more in moderator (Joshi et al 1987; Peterson et al 1997). The reasons behind higher 14 C production and emission in a pressurized heavy water reactor (PHWR) compared to a light water reactor (PWR, BWR) are as follows: (a) average thermal neutron flux in PHWR is higher than LWR, so a large amount of D 2 O is present in high thermal neutron fluxes at PHWR, because of this large inventory of 17 O arises; and (b) isotopic abundance of 17 O in D 2 O used in PHWR is higher than in H 2 O at LWR (Sohn et al 2012).…”

Fate of HTO following its acute soil deposition at different growth stages of Chinese cabbage

“…For a routine chronic release of HTO, a specific activity model is generally employed on the assumption that plant tritium is in equilibrium with atmospheric tritium (Peterson and Davis, 2000). This practice does not need data on the parameters concerning a tritium transfer between an environmental medium and crop plants.…”