Near-surface disposal (NSD) has been applied in several countries to dispose of low-level radioactive waste. The demo plant of this disposal type is planned to be constructed in Serpong Nuclear Area, Banten. An assessment of radiation exposure is necessary to ensure the safety requirement of the facility in order to support this program. This study aims to estimate radionuclide migration from the proposed NSD demo facility to the environment and the corresponding total human dose using AMBER mathematical modeling. The representative radionuclide,137Cs, was selected because of its high mobility in the environment and the relatively long half-life in the low-level waste inventory. The scenario considered in the modeling was the normal release to the environment through groundwater. Parameters such as initial radionuclide concentration, soil physical parameters of the study site, and disposal design were entered into AMBER software to be calculated using mathematical formulas. The results show that the radionuclide concentration value in the environment is below the safe limit recommended by the Environmental Supervisory Agency. Likewise, the maximum dose received by the community around the facility is 7.40×10-11 mSv/y, 550 years after the post-closure of the facility, which is also below the regulatory limit of 1 mSv/y for the public.

In order to support and complement the radioactive waste management facilities in Indonesia, BATAN will build a demonstration disposal facility in Serpong Nuclear Area (SNA). Demonstration disposal that will be built is Near Surface Disposal (NSD) type. Engineered vault for NSD is reinforced concrete. The calculations for determining the thickness of NSD concrete vault is based on the conceptual design as the result of the placement optimization of  demonstration disposal that takes into account the inventory of radioactive waste and environmental geology conditions of the site at Serpong Nuclear Area. The thickness of the vault in this paper is focused on its ability to withstand radiation from stored waste so that workers or people who are around the disposal facility is safe with maximum radiation dose limit rate of 0.3 μSv / h. The calculation is performed with the aid of MicroShield 7:02 and Rad Pro Calculator Version 3:26 software. From the calculation so that the dose rate at the outer surface of the vault to be 0.3 μSv / h, required walls made of concrete with a density of 2:35 g / cm3 is 62.8 cm thickness.

ABSTRAKRencana pembangunan dan pengoperasian fasilitas disposal demo di Kawasan Nuklir Serpong memerlukan pengkajian keselamatan untuk memberikan bukti ilmiah bahwa fasilitas tersebut aman bagi keselamatan manusia dan lingkungan. Hasil dari pengkajian keselamatan tersebut digunakan sebagai dasar pemberian izin lingkungan untuk pembangunan dan pengoperasian fasilitas tersebut. Salah satu data tapak yang diperlukan dalam pengkajian keselamatan adalah arah dan kecepatan aliran air tanah. Oleh karena itu dilakukan penelitian untuk mengetahui arah dan kecepatan aliran air tanah pada zona akuifer bawah calon tapak disposal demo di Kawasan Nuklir Serpong. Penelitian dilakukan dengan menggunakan perunut (tracer) Rhodamin WT. Perunut dilepas pada sumur bor  utama (SBU) dan dipantau pada lubang bor (sumur bor pantau) SBP-1 (A), SBP-2 (B), dan SBP-3 (C). Dari hasil analisis contoh air dan analisis keruangan diperoleh data arah aliran air tanah pada kedalaman 16 m ke arah N 240º E (barat-barat daya) dengan kecepatan antara 0,35 m/hari sampai dengan 0,48 m/hari. ABSTRACTPlan for construction and operation of demo disposal facility in Serpong Nuclear Area requires safety assessments to provide scientific evidence that the facility is safe for human and the environment. The result of the safety assessment is used also as a basis for granting environmental permits for the construction and operation of the facility. One of the site data requirements on the safety assessment is the direction and velocity of groundwater flow. Therefore, a study to determine the direction and velocity of groundwater flow at lower zone aquifer of demo disposal site candidate in Serpong Nuclear Area conducted. The research was carried out by using Rhodamin WT tracer. The tracer released in the main well (SBU) and monitored in SBP-1 (A), SBP-2 (B), and SBP-3 (C) boreholes. Based on the water samples and spatial analysis, groundwater data flow direction at a depth of 16 m towards N 240º E (west-southwest) with a velocity of 0.35 m/day up to 0.48 m/day obtained.

Near Surface Disposal (NSD) for Radioactive Waste that should be developed due to increment of the low level radioactive waste, need to be analyzed and evaluated related to the radiological impact of the environment. A research method applied is done by modeling the distribution of radionuclide releases process. Analysis related with the releases of radionuclide in water and soil is using PRESTO (Prediction of Radiological Effects Due to Shallow Trench Operations). The application scenarios selected in this safety assessment is the migrations of Co-60 and Cs-137 scenario through the shallow groundwater flow pattern in the NSD site. The SigmaPlot software is also used to determine the concentration equation in well water and river water. The final results showed the concentration of radionuclide in wells and streams below the provision. Radionuclide activity concentrations in well ranged from 10^-10Bq/m³ to 10⁰Bq/m³ and in the river ranged from 10^-15Bq / m³ to 10^-1Bq / m3. The impact of radioactive waste of radionuclide Co-60 and Cs-137 will decrease to the background radiation level at a distance less than 10m and penetrate into the saturated layer up to 4m. In this study, an equation have been obtained that can predict radionuclide concentration patterns based on the distance and the depth of the ground surface against to the facility operation time.