The TOCATTA-χ model for assessing 14C transfers to grass: an evaluation for atmospheric operational releases from nuclear facilities

Impacts of 14C discharges from a nuclear fuel reprocessing plant on surrounding vegetation: Comparison between grass field measurements and TOCATTA-χ and SSPAM14C model computations

“…Carbon substrate variations due to storage and remobilisation processes and from the recycling of senescing shoot and root were not considered either; nor were the carbon fluxes associated with root N uptake and exudation processes. These and other simplifications were made in the conceptual model and are fully described by Aulagnier et al (2013).…”

“…Once this is done, the 14 C activity concentration in grass is derived from the simulated 14 C activity concentration in the substrate pool of grass using a moving average. As mentioned by Aulagnier et al (2013), the 14 C activity concentration in the carbon flux leaving the substrate pool to be allocated to growth is the substrate 14 C activity concentration. By averaging the substrate 14 C activity concentration, it is basically hypothesized that the old, ageing structural dry matter is going to be gradually replaced by structural "fresh" matter and that this newly created structural matter has been fed by the net primary production of the previous days.…”

“…By averaging the substrate 14 C activity concentration, it is basically hypothesized that the old, ageing structural dry matter is going to be gradually replaced by structural "fresh" matter and that this newly created structural matter has been fed by the net primary production of the previous days. The averaging period can thus be regarded as a mean turnover time and its relationship to the mode of management of the grass field (see discussion in Aulagnier et al, 2013). If we neglect the radioactive decay process, we have the following equation to describe the 14 C activity in grass, [ 14 C] Grass :…”

“…The main equations for estimating the weight, input and output fluxes of dry matter, stable carbon and 14 C in the sap compartment are derived from a simplified version of the PaSiM process-based model (Riedo et al, 1998) that have been adapted to model radiocarbon. The details of the calculation of the different rates associated with each process are described by Aulagnier et al (2013).…”

“…For the calculation of the Photosynthetically Active Radiation (denoted PAR, in W m À2 ) absorbed by the plant canopy, which has been reduced to a single layer, we have used the same empirical equation as in Aulagnier et al (2013); however, in our application we have neglected the effect of clouds, as the inclusion of cloud effects would potentially reduce the PAR. Other simplifying assumptions have been made to compute the radiation scheme (see Aulagnier et al, 2013).…”