JAVYS, the Slovak Nuclear Decommissioning Company, the owner and operator of National Radioactive Waste Repository (NRR) at Mochovce, is planning the enlargement of the existing NRR. The enlargement consists of the construction of new structures (double rows) like the ones existing for Low and Intermediate Level Waste (LILW) and of a new facility for the disposal of Very Low Level Waste (VLLW). A VLLW disposal site is being planned in Mochovce where a LILW disposal site is already located. As a part of ongoing licensing process for this change in utilization of the NRR we have updated the already existing assessment of potential radiological impact to members of the public after closure of the site, both from the migration of leachate in groundwater from the site and from possible inadvertent intrusion into the site, including future residential development on material excavated for the construction of a road. The radionuclides from the groundwater reach the biosphere through a stream flowing into the lake. It is conservatively assumed that individual in the critical group uses biosphere of the lake (for irrigations, fishing and recreation). In the case of unintentional intrusion into the repository, the exposed group consists of a small number of workers who excavate or examine repository materials. The assessment is based on preliminary conceptual design for VLLW module, estimation of future volumes for the different waste classes and their radiological inventories and considers some common aspects and potential interactions between both disposal systems, such as radiological criteria, critical group definition, institutional period, site environment, total activity inventory.
In Slovakia, low and intermediate level radioactive wastes are disposed in a near-surface repository at Mochovce site. The repository, which was commissioned in September 2001, has a disposal capacity 22,320 m3. It is a vault-type concrete structure repository with reinforced concrete containers as the final waste packages. The Mochovce repository is designed to receive acceptable radioactive wastes from decommissioned A-1 power plant at Jaslovske´ Bohunice, operational waste from NPPs V-1 and V-2 at Jaslovske´ Bohunice site and NPP Mochovce, as well as institutional radioactive wastes. Generally, calculation endpoint of disposal facilities performance assessment is radiological impact on humans and environment. In that case, starting points of assessment are the waste activity concentrations and inventory activity. The acceptance of radioactive waste in Mochovce repository is one of the many elements that directly contribute to the safety of the disposal system. In Mochovce repository safety analysis, end points are both the concentration per package and total activity values. On the other hand, radiological protection criteria are the starting points of the calculation. This approach was developed and applied because the actual inventory that will be disposed of is highly uncertain. As a result of the accidents, the primary circuit was contaminated by fission products. Some auxiliary circuits and facilities were also contaminated. The complicated problem is the relatively high content of long-lived radionuclides (inclusive transuranic elements) in some waste streams. After two technological incidents at NPP A-1 uncertainties in waste inventory are large because of variability in the types of waste streams and variability in the quality and completeness of the waste characterization data. This paper presents the philosophy of safety analysis, development of scenarios, their modelling and approach that have been used to derive waste acceptance criteria, specifically limits of activity. The approach consists of the determination of radionuclides important for safety, the use of relevant safety scenarios, the setting of dose limits associated with scenarios, the calculation of activity limits and application of the simple summation rule. Finally, information is provided about short operation of the repository.
The calculations for performance assessment of the Mochovce Radioactive Waste Disposal Facility in Slovakia were made by means of modified computer codes MODEMO, NUCDSLB and LAKE. During recent years computer codes DUST-MS, MODFLOW/MT3DMS and BS for source term, ground water flow and transport of radionuclides through ground water and biosphere respectively were implemented in the framework of the performance assessment iterative process. This paper describes results of comparison of the both approaches for source term and groundwater flow.
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