A Prelude on Nuclear Safety Research Report - Envision a Nuclear-Free Homeland
The institute of nuclear energy research is the top research institute on nuclear science and engineering in Taiwan over past four decades. Our current national energy policy is to develop green energies, mitigate the release of greenhouse gases and gradually set up the circumstances for a Nuclear-free Homeland. In the meantime, we have to make sure the integration of any infrastructures of nuclear power plant before and after stopping running, to develop technologies needed for the safe decommissioning procedure, and to plan the radioactive wastes intermediate storage and final disposal strategies.
All these efforts aim at reaching the expected target of planned energy policy. Therefore, in the fiscal year of 2016, INER had engaged in research including the safety issues about the operation and maintenance of nuclear power plant, the technologies to execute the TRR decommissioning project, and the optimum spent nuclear fuel storage strategy and its final disposal safety assessment method. Valuable results have been achieved.
In the aspect of assuring the operational safety of nuclear power plant, a risk assessment method, named as Level-2 PRA, has been established to evaluate the nuclear facilities safety when it comes to the severe accident condition. This method updated the source term data of the three operating nuclear power plants and used these results to strengthen the last component of defense in depth and to specifically evaluate the adequacy of the Emergency Planning Zones (EPZ) of the plants. Furthermore, an advanced fuel lattice design automation technique for BWR has been developed. This is a feasible method that can accomplish a high quality BWR lattice design with reduced resolution time for fuel lattice design optimization.In the aspect of enhancing the equipment maintenance convenience, we have developed a methodology to determine the extreme thermal and radiation conditions to be suffered by the equipment during the Design Basis Accident. This technology has been applied to the Kuosheng Nuclear Power Plant to establish the conditions, including temperature, pressure, humidity, and radiation, to be withstood in the environmental qualification of the safety-related electrical and instrumental equipment installed in the Reactor Auxiliary Building. The conditions are revised and relaxed reasonably, without compromising safety margin, to facilitate the equipment procurement and maintenance to save time and cost. In addition, we used centrifuge test to understand the phenomena of pile group in liquefying soil under a ground motion. This technology helps us deploy solutions to construction work, such as anti-tsunami walls and offshore wind turbine, to prevent from the possible demolition of pile foundation in soften ground caused by earthquake. Furtherly, the weld quality is also an important issue for the equipment maintenance. We have established a rapid safety assessment method for cylindrical shell weldments with multiples through-wall cracks. It can assist the engineers to evaluate core shroud rapidly with limited data. In another case about the weld, INER has integrated welding process of gas tungsten arc welding (GTAW) and laser beam welding to solve the problems of induced cracks. This technology can be widely applied to nuclear and petrochemical industries to increase the operational safety and production efficiency. INER also keeps Seismic Testing Laboratory on the cutting edge of innovation. Not only the test skills have been used to elevate the opportunity of choosing local industrial products as replacing items, but also the analysis technology about the seismic research has been developed.
With regard to nuclear facility decommissioning, we have acquired plenty knowledge and techniques through the implementation of TRR decommissioning. The major missions in phase I (2004~2017) have been achieved mostly, including the dismantling of wet storage tank, emergency cooling tower, and the cleaning of spent fuel pool. To improve the feasibility and safety of nuclear facilities decommissioning, a computerized 3D digital model has been developed in INER. It can offer a visualized 3D digital model for the work, such as segmentation, waste inventory, radiation dose distribution etc. During the fulfilment of a decommissioning project, the spent fuel usually shall be removed to another storage site with either wet storage or dry storage. We have developed an apparatus for verifying the integrity of the confinement boundary of spent nuclear fuel dry storage canister in operation. With this apparatus and the proposed method, it can effectively verify the integrity of the confinement boundary and detect the damage of the confinement boundary in early phase to avoid the leakage of any radionuclides.
Besides, in the aspect of spent nuclear fuel disposal, INER is developing safety assessment methods. With a set of reference case information and referring to KBS-3 vertical disposal concept of Sweden, a safety case was documented through the international technology exchange with SKB. Also, in order to understand the evolution of engineered barrier system (EBS), we used the finite difference method to simulate the thermo-mechanical coupling effect to EBS by FLAC3D under the heating effect of the canister. The result helps to develop a three dimensional numerical method that modeled with T-M coupling, which the calculation results were compared with the international case study to verify its correctness. This technology will be used to understand the stability under the thermal effect furtherly. Furthermore, to construct a specific biosphere concept model in Taiwan for the long-term safety assessment of spent nuclear fuel disposal, INER adopted the reference biosphere concept which has been developed as part of IAEA BIOMASS. FEPs list and international interaction matrix were also used to identify the exposure pathways and groups. Last but not the least, a stage dataset for biosphere dose assessment was established, which will be beneficial to the work of engineering design of the disposal facility and the safety assessment.