In-containment source term: Key insights gained from a comparison between the PHEBUS-FP programme and the US-NRC NUREG-1465 revised source term

Numerical Simulation of Decontamination of Airborne Fission Products during In-Vessel Release Phase by Containment Spray

The containment spray system (CSS) has a significant role in limiting the risk of radioactive exposure to the environment. In this work, the optimal droplet size and pH value of spray water to prevent the fission product release have been evaluated to improve the performance of the spray system during in-vessel release phase. A semikinetic model has been developed and implemented in MATLAB. The sensitivity and removal rate of airborne isotopes with the spray system have been simulated versus the spray activation and failure time, droplet size, and pH value. The alkaline (Na2S2O3) spray solution and spray water with pH 9.5 have similar scrubbing properties for iodine. However, the removal rate from the CSS has been found to be an approximately inverse square of droplet diameter (1/d2) for Na2S2O3 and higher pH of spray water. The numerical results showed that 450 μm–850 μm droplet with 9.5 pH and higher or the alkaline (Na2S2O3) solution with 0.2 m3/s–0.35 m3/s flow rate is optimal for effective scrubbing of in-containment fission products. The proposed model has been validated with TOSQAN experimental data.

Radioiodine in the atmosphere after the Fukushima Dai-ichi nuclear accident

About 160 PBq of (131)I was released into the atmosphere during the accident at the Fukushima Dai-ichi Nuclear Power Plant. The chemistry of radioiodine is complicated, and it can be released in several different forms. In addition, the different physical forms, like molecular iodine, aerosol-form iodine, or organic iodine, would have all behaved differently once in the atmosphere, and would have been removed at different rates. These releases were detected by monitoring stations throughout Japan, and from these measurements, key insights can be made about the different chemical forms that were released, as well as the persistence of each in the environment.