6. Conclusion

.

). The

/s. The gas

conditions with a temperature of 80C and 7.533 Psi. Assuming 35% core damage and 20% burst release. The rest of mass is assumed to release along with the coolant with mixing rate wx = 0.01 s<sup>1</sup>

The mass concentration of tellurium is simulated for droplet sizes (100–1000 microns). The containment spray system is activated with the initiation of an accident with a constant flow rate

Simulation results showed that the droplet size is quite effective to reduce the airborne FPs. It has been observed that the concentration of airborne tellurium decreases with a decrease in droplet size (Figure 12). The peak concentration in Tellurium mass reaches to a maximum concentration at a longer time with the higher droplet diameter. The magnitude of maximum concentration has been found the approximately inverse square of droplet diameter (1/d<sup>2</sup>

containment spray system removal rate for iodine versus droplet diameter is depicted in Figure 11. The maximum removal rate has been found 452 s<sup>1</sup> with alkaline solution spray with a droplet size of 100 micrometers. The removal rate is found to decrease exponentially as the droplet diameter increases. 44.7 s<sup>1</sup> removal rate has been seen for 1000-micron diameter

phase and liquid phase coefficients play a vital role in absorption efficiency. Both gas- and liquid-phase mass transfer coefficients (KG and KL) decrease drastically with an increase in droplet size (Figure 13). However, the gas- and liquid-phase mass transfer coefficients (KG and

Figure 13. A comparison of gas-phase mass transfer coefficient (KG) and liquid-phase mass transfer coefficients (KL) for

elemental iodine constant pH = 5.0, T = 80C.

).

droplet size for pH 9.5 and alkaline spray solution with spray flow rate 0.35 m<sup>3</sup>

KL) are also related to the inverse square of droplet diameter (1/d<sup>2</sup>

of 0.2 m3

/s.

60 Numerical Simulations in Engineering and Science

This chapter has presented the numerical simulation of FP activity inside the reactor containment building under LOCA. The numerical simulation of in-containment FPs against the mixing rate, puff release, droplet diameter, spray pH value and spray performance has been simulated. The results indicate that the mixing rate of FPs in coolant significantly affects airborne FP activity inside the containment. The higher pH spray solution (9.5) and spray with sodium thiosulfate (Na2S2O3) have observed similar scrubbing properties. The droplet size is significantly important for removal of FP. There is a higher tendency of FP to interact with airborne particles (Figure 11) with, due to their higher values of liquid- and gas-phase mass transfer coefficients (KL and KG) (Figure 13). Therefore, the acceptance criteria of droplet size have been suggested between 600 and 800 microns, with pH value higher than 7.0 which delivers higher removal rate. The earlier the containment spray system has operated, the airborne concentration will be minimum (Figure 8). However, the delay operation caused the higher airborne concentration of radioactive mass. It has also been observed if the containment spray system is failed during in-vessel phase a regain will be caused in radioactive mass (Figure 9). Based on our work, we are suggesting 600–8500 microns mean droplet diameter containment spray system should be used to get maximum radiation hazard safety. Moreover, from our results, we can conclude that the spray system should be operated within 500 s after the accident and should be operated more than 3000 s (whole in vessel phase). The uncertainties in simulated results depend on generally available data in the literature.
