Radiological Operational Safety Verification for LILW Disposal Facility

The successful implementation of radioactive waste repository program depends on scientific and technical aspects of excellent safety strategy as well as on societal aspects such as stakeholder acceptance and confidence. Monitoring is considered as key element in serving both ends. It covers all stages of the disposal process from site selection to institutional monitoring after the repository is closed. Basically, the purpose of the monitoring of radioactive waste disposal facility is not to reveal any increase of radioactivity due to the repository, but to provide reassurance and confirmation that the repository is fulfilling its passive safety purpose as an initial disposal concept and that long-term safety driven by regulatory requirements is ensured throughout the entire lifetime of disposal facility including post-closure phase. Five principal objectives of monitoring of geological disposal are summarized by IAEA-TECDOC-1208 as follows 1) Supporting management decisions in a staged programme of repository development: 2) Strengthening understanding of system behavior: 3) Societal decision making: 4) Accumulating an environmental database: 5) Nuclear safeguards (if repository contains fissile material, i.e., spent fuel or plutonium-rich waste) Based on the results of detailed studies of the above objectives and related phenomena, 6 categories of potential monitoring parameters are determined as follows: (1) degradation of repository structures, (2) behavior of the waste package and its associated buffer material, (3) near field chemical interactions between introduced materials, groundwater and host rock, (4) chemical and physical changes to the surrounding geosphere, (5) provision of an environmental database, and (6) nuclear safeguards. Typical monitoring parameters include temperature (heat), water level, pore-water and moisture content (groundwater), rock pressure, fractures, displacement and deformation (stress), water quality chemistry and dissolved component (chemistry). They can be measured using proven equipment and methods such as wireless and non-intrusive monitoring techniques. Directly accessing the waste packages for the purpose of monitoring could negatively affect the long-term performance of engineered barriers. One way to solve this problem is to build a pilot facility (demonstration facility) at another site set apart from the actual disposal site and implement monitoring there. The pilot facility proposed by the 'Expert Group on Disposal Concepts for Radioactive Waste' of Switzerland is a small-scale facility which is different from test facility (in-situ rock laboratory) in terms of representative amount of real waste. The pilot facility provides information to confirm the performance of the repository system, and also allows the early detection of any deviations from the expected evolution. National low-level waste management program of the United States published a report containing 16 key radionuclides that are judged by the NRC to most likely contribute significantly to the radiation exposures estimated from a performance assessment of a proposed commercial LLW disposal facility. They are 3H, 14C, 60Co, 59Ni, 63Ni, 90Sr, 94Nb, 99Tc, 129I, 137Cs, 237Np, 238U, 239Pu, 241Pu, 241Am, 242Cm. They are almost consistent with concentration limits of radionuclides for disposal of No. of Notices of the MOST: 2009-37 except gross alpha radioactivity (TRU) and 238U. Four radionuclides, such as 3H, 14C, 99Tc and 129I, are identified as special considerations by the NRC in terms of ensuring that performance objectives for long-term environmental protection are met for disposal of commercial LLW. They are very mobile in groundwater, and their main route to enter the human body is by either ingestion or inhalation