## 6 Discussion
### Deterministic and Probabilistic Method for the Safety Assessment of Radwaste Disposal  
The techniques for the evaluation of the evolution of nuclide geochemistry include two types of method: deterministic methods and probabilistic methods. The input parameters for deterministic and probabilistic methods should reflect the concentration of the adsorption or total dissolution of the nuclide of interest and the concentration of the released nuclides (e.g., high or low Kd values, the adsorption capacity, and the released concentration value). Because deterministic methods use point estimation to represent input parameters (e.g., chemical component concentration, equilibrium constant, temperature, pH and pe), using average values to represent these parameters may lead to the underestimation of the calculated nuclide concentrations, while the use of upper bound estimates would result in overly conservative estimates of the simulation scenarios. Meanwhile, probabilistic methods use the estimation of a probability density function (PDF) to estimate the scenario development profile, and can generate parameter distributions and uncertainties (e.g., the distribution of Kd and chemical equilibrium constants). Both the aleatory uncertainty and epistemic uncertainty associated with the long-term safety assessment of radioactive waste disposal often exist in engineering practice. However, the difficulty in dealing with the probability distributions of the parameters included in the long-term safety assessment of radioactive waste disposal can mean that there is no reasonable probabilistic safety assessment for radioactive waste disposal. A general method for safety assessment can be achieved through the statistical processing of the measured parameters. The aleatory uncertainty is quantified as a probability distribution. Additionally, based on expert judgment, the epistemic uncertainty is quantified as a probability distribution [61; 62; 63; 64]. [PERSON] [62] proposed the modified transfer factor to establish the Kd value probability distribution function for the evaluation and application of Kd, including the following: (1) a surface area normalization transfer factor (f\({}_{\text{A}}\)), (2) a mechanical damage transfer factor (f\({}_{\text{m}}\)), (3) a cation exchange capacity transfer factor (f\({}_{\text{CEC}}\)), and (4) a groundwater chemical transfer factor (f\({}_{\text{chem}}\)). Because the first three transfer factors--f\({}_{\text{A}}\), f\({}_{\text{m}}\) and f\({}_{\text{CEC}}\)--are defined as the ratios of variables that have either normal or log-normally distributed uncertainty ranges, the transfer factors themselves also have log-normally distributed uncertainty ranges. The term f\({}_{\text{chem}}\) is a groundwater chemistry transfer factor that relates the theoretical value of the distribution coefficient under the application conditions, K\({}_{\text{d(app)}}\), to the theoretical distribution coefficient value for a reference groundwater, K\({}_{\text{d(ref)}}\). The f\({}_{\text{chem}}\) = K\({}_{\text{d(app)}}\)/K\({}_{\text{d(ref)}}\). Because it contains uncertainty and spatially variable (usually non-random) variables, there is no reason to make it a lognormal distribution. However, f\({}_{\text{chem}}\) can be estimated from the functional relationship between the ionic strength and f\({}_{\text{chem}}\), and then the convolution is performed between the probability density function of Kd and the probability density function of f\({}_{\text{chem}}\). Thus, the uncertainty range of the conditional Kd value corresponding to the specific hydrochemical characteristics of groundwater is obtained [65]. With the development of safety assessment techniques for radioactive waste repositories, the demand for support for the modeling of adsorption data is increasing. In the future, it is expected that the experimental determination of radionuclide Kd will still be the main means for the estimation of the adsorption characteristics of the whole repository system.