Experimental Investigation of Decontamination Factor Dependence on Aerosol Concentration in Pool Scrubbing

Abstract

Because a pool scrubbing is important for reducing radioactive aerosols to the environment for a nuclear reactor in a severe accident situation, many researches have been performed. However, decontamination factor (DF) dependence on aerosol concentration was seldom considered in an aerosol number concentration with limited aerosol coagulation. To investigate an existence of DF dependence on the concentration, DF in a pool scrubbing with 2.4 m water submergence was derived from aerosol measurements by light scattering aerosol spectrometers. It was observed that DF increased monotonically with decreasing particle number concentration in a constant thermohydraulic condition: a gradual increase from 10 to 32 in the range of 1.3×1011 - 8.0×1011/m3 at the inlet and a significant increase from 32 to 77 in the range of 3.6×1010 - 1.3×1011/m3. Two validation experiments were conducted in the range with the gradual DF increase to confirm whether the DF dependence is a real pool scrubbing phenomenon. In addition, characteristics of the DF dependence in different water submergences were investigated experimentally. It was found that the DF dependence became more significant in higher water submergence. Significant DF dependence was observed in the condition of the water submergence higher than 1.6 m and the inlet particle number concentration less than around 1×1011 /m3. It is recommended to perform further analysis for the DF dependence mainly in such condition since it could make a difference to both experiment and model of the pool scrubbing.

The dependence of pool scrubbing decontamination factor on particle number density: modeling based on bubble mass and energy balances

“…The experiments analyzed in the present paper [3] were conducted with insoluble, monodispersed spherical SiO 2 particles (Nippon Shokubai Co., KE-S50, 0.5 µm in diameter, amorphous silica) without any surface modification. The particle diameter distribution of the SiO 2 aerosol was measured by the aerosol spectrometer at the test section inlet and outlet, confirming that the aerosol was monodispersed with a mode diameter of 0.5 µm and a geometric standard deviation of 1.2-1.3 for both locations [3]. The water depth in the test section was varied in five steps (0, 0.3, 0.8, 1.6 and 2.4 m) and the inlet particle number density n 0 stepwise between 6 ×10 9 and 9 ×10 11 m −3 .…”

“…As a result of this heating, however, the condensate water on the solid test particles is also lost before reaching the spectrometer, making infeasible the measurement of particle diameter after condensational growth. Measurement detail and uncertainty are described in [3].…”

“…The present study is concerned with pool scrubbing data obtained by Sun et al [3] for monodispersed 0.5 µm insoluble particles injected into low temperature ( � 284 K) water. Experimentally observed degradation in pool scrubbing performance (DF) at high particle number densities beyond ~1 ×10 11 m −3 is focused on.…”

“…In this study, the experimental results [3] are modeled by hypothesizing that the degradation is caused by limited particle condensational growth due to depletion of vapor supersaturation in the bubbles, as the results of vapor consumption and latent heat release by the condensation, both increasing with the particle number density. The depletion of vapor supersaturation has been suggested in the previous paper [3] as one of the possible explanations for the experimental results. Also, it is known to be one of the mechanisms limiting the maximum measurable particle number density for condensation particle counters (CPCs) based on condensational particle growth [7].…”

Experimental Study on Influencing Factors of Aerosol Retention by Pool Scrubbing

“…Dehbi et al (2001) conducted the POSEIDON-II experiment with 17 tests to study the effects of pool depth, steam mass fraction, and particle diameter on the DF in low-subcooling pools during the process of a single-hole injection. Sun et al (2019) studied the dependence of DF on the aerosol concentration in pool scrubbing with a single-hole injection. However, the thermal hydraulic characteristics of a single-hole injection and multihole injection are different, such as the steam condensation regime (Park et al, 2007), interaction of holes (Cho et al, 2004), and condensation oscillation characteristic (Hong et al, 2012).…”