By taking the output of thermal fluid ( u → and T) as the input of the 210Po molecule transfer, the 210Po concentration and flux in both the steady state and the dynamic state can finally be obtained. The flow field and the heat transfer field are coupled strongly, while the flow heat transfer field and the concentration field are coupled weakly. In order to provide the specific parameters in the multi-physical field, the multi-physics coupling frame was established and the causal link between each physics had been found out in Figure 3.
Multi-Physics Frame and Numerical Models Multi-Physics Frame Where P i, g a s is the partial pressure of i in cover gas, P i is the saturated vapor pressure of pure i, x i is the mole ratio of solute i in solvent LBE, P i, s a t is the saturated vapor pressure of solute i in solvent LBE, and J i, 0 is the evaporation rate of Po in vacuum, and because of the cover gas in the LFR, the evaporation rate of Po and PbPo is four orders of magnitude lower than that in vacuum. In China, the National Standard GB18871-2002 rules mention the ALI of 210Po as 8.3 × 10 4 Bq, and the exemption concentration as 10 4 Bq ( Mao, 2014), the National regulation on 210Po of RA, US, and CN are given in Table 1. And the ALI for ingestion and inhalation are 1.11 × 10 5 Bq and 2.22 × 10 4 Bq, respectively ( Nuclear Regulatory Commission 10CFR, 2017). NRC regulation of 10 CFR Part.20, the derived air concentration (DAC) of 210Po is settled as 1.1 × 10 5 Bq/m 3, while one DAC is equal to allowable maximum air concentration at the breathing rate of 1.3 m 3/h for 2,000 working hours per year. In NRB-99 of Russia, the occupational annual limit on intake (ALI) is settled as 6.70 × 10 3 Bq, and the safety permission of air concentration is below 2.7 Bq/m 3 ( Pankratov et al., 2004). In the purpose of the occupational safety and public health, ICRP and nuclear power countries have specified healthful working conditions and given the exposure limits of 210Po. However, during normal operation of the LFR, 210Po, a highly toxic element with strong volatility, will be produced in the LBE coolant, which will induce a new radioactive safety problem. Lead–bismuth eutectic (LBE) is selected as the primary coolant for the LFR due to its neutronic economic and good thermal hydraulic properties ( Dierckx et al., 2014).
In addition, even if the leakage rate of 210Po in the cover gas into the containment is maintained at 5‰ per day, due to the deposition of Po aerosol, the 210Po contamination on the inner surface of the containment is still below the radioactivity concentration limits.Īs one of the generation-IV (Gen-IV) nuclear power system, the lead-cooled fast reactor (LFR) is expected to be the first concept to achieve industrial demonstration ( Lorusso et al., 2018 Nuclear Power, 2019). Preliminary results indicate that during normal operation, most of the 210Po in the LBE exist in the form of PbPo, and around 10 –9 of 210Po could evaporate from the LBE into the cover gas, and then further leak into the containment. Considering the effects of nuclide decay, cover gas leakage, containment ventilation, and Po aerosol deposition, a comprehensive simulation was carried out to evaluate the sensitivity of those effects on the 210Po distribution in detail. In order to simulate the behavior of 210Po in an LFR, this work developed a multi-physics model of an LFR from the perspective of radioactive transport. Therefore, the radioactive safety caused by 210Po has become an important topic in LFR-related research.