Efforts are on worldwide to develop technology for ultimate disposal of heat emitting radioactive waste in suitable geological formations in the depth range of 500–700 m in specially planned and built Geological Disposal System (GDS). In India, granitic rocks are being evaluated for establishing their efficacy in providing long term isolation and confinement to these wastes against release to Biosphere. Present paper presents a study on the time dependent near-field evolution of the heat field introduced by emplacement of 20 nos. of high level long lived heat emitting radioactive waste canisters in single disposal tunnel module of granite hosted conceptual GDS. For this Finite Difference Method (FDM) based model of a disposal tunnel of 20 m (Height) × 10 m (Width) × 49 m (Length) size located in a granitic rockmass has been developed and analyzed. Additionally, in the second case representing Far-field model, time dependent thermal distribution in complete GDS (2 km height × 3 km length) has been simulated to estimate the spread of thermal field due to emplacement of 10,000 heat emitting canisters in disposal pits. Jalore Granite (JG) forming a part of Sankra pluton of Rajasthan have been considered as host rock for such GDS. These canisters are emplaced in disposal pits with layers of Bentonite Clay (BC)—Granite (G) based mixtures with spacing of 2.5 m between two Cylindrical Thermal Source (CTS) simulating canister. The both FDM based models are analyzed for time dependent buildup of temperature around these CTS with BC-G based mixture. The study reveals that with spacing of 2.5 m and BC-G mixture having Bentonite and Granite as 70–60% and 30–40% respectively produces maximum temperature of 92.21 °C within the clay barriers at 2.7 years after positioning of CTS in disposal pits. The temperature built up steadily reduces below 50 °C by 200 years. The maximum temperature of 79.13 °C has been recorded in granite rockmass. Therefore, it is established that selected BC-G mixture with CTS pitch distance of 2.5 m is suitable especially in terms of maximum desirable temperature and thermal stresses for hosting such GDS.