Evaluation of decontamination technologies for portable radioactive effluent treatment implementation

Abstract

After Fukushima disaster (2011), IAEA (International Atomic Energy Agency) suggested stricter nuclear power plant’s design criteria, DEC (Design Extension Condition). DEC is a new acceptance criteria based on high radiation doses or radioactive releases. Many countries, including ROK (Republic Of Korea), have passed a law to use 100 TBq of Cs-137 release as a part of probabilistic risk criterion. In order to meet this new design criteria DEC, FCVS (Filtered Containment Venting System) is developed to mitigate containment failure accident scenario. However, according to the probabilistic risk assessment from SOARCA (State-Of-Art Reactor Consequence Analysis) report, bypass accidents such as SGTR (Steam Generator Tube Rupture) and ISLOCA (Inter-System Loss-Of-Coolant Accident) have high accident frequencies, and consequently Korean nuclear power plants may not meet the new reactor design regulation for DEC. All reactors should equip mitigation system corresponding to each accident scenario to mitigate the accident consequences. As a result, mitigating nor preventing all reactor’s severe accident scenarios is financially impossible because installation of mitigation system for every nuclear reactor requires more cost. However, if mitigation systems can be designed as portable treatment system, not all reactors should install this mitigation system, then it means portable treatment system can save the reactor design costs.

Investigation of potentially applicable filters on portable treatment system was conducted. Performances of HEPA (High-Efficiency Particulate Air) filter, cyclone separator and pool scrubber are evaluated under severe accident effluent condition. Based on the literature review and simulation results, pool scrubber is considered as a most acceptable filter for portable treatment system. New pool scrubbing code is developed to evaluate the performance of pool scrubber, since existing pool scrubbing codes have limitations in perspective of hydrodynamic part, Decontamination Factor (DF) calculation, and absence of bubble population. New pool scrubbing code contains several new hydrodynamic models, new DF calculation method based on prediction of bubble’s concentration according to the depth of pool by applying Martinez-Bazan’s bubble breakup model. This code is validated through compare simulation results with experiment data which is conducted by Peyres et al.

Pool scrubbing code results showed reasonable DFs with conservatively assumed conditions. To design portable treatment system with pool scrubber, it requires to consider about design constraints

pressure drop, capability of vehicle, maximum height and gas flowrate. Based on the analysis of several design constraints, performance evaluation is conducted in terms of the height, radius of pool scrubbers and number of pool scrubbers. Lastly, applicability of suggesting portable treatment system is discussed for actual nuclear power plant’s severe accident condition.