5.3. Mixing rate (wx) effect on in-containment FPA

The delayed core released fraction (1-fx)(exp -wxt) for various values of mixing rate wx which contributes to airborne volumetric activity through coolant has been simulated. The volumetric activity of 131I inside the containment for various values of mixing rate wx from 0.005 to 1.0 s<sup>1</sup> has been numerically simulated. It has been observed that a slight change in the value of wx results in astonishing variation in airborne activity. The results are shown in Figure 7. For wx = 1.0 s<sup>1</sup> , highest magnitude has been observed with a shift of peak toward lower timescale value. However, the 131I has been observed to reduce almost linearly with mixing rate 1.0 s<sup>1</sup> (Figure 7). The in-containment volumetric concentration of 131I increases and then starts decreasing gradually for mixing rate value from wx = 1.0 to 0.03 s<sup>1</sup> ; however, it remains constant for mixing rate 0.005 s<sup>1</sup> . This is because of trivial mixing of iodine in the coolant. A higher magnitude of 131I activity has been observed with higher mixing rate.

### 5.4. Fission product activity with spray system

The primary purpose of the spray system is to mitigate the FP exposure to the environment and to maintain the containment integrity. In this work, we have studied the effect of the spray system in mitigating the radioactive masses (gaseous and particles) released during in-vessel release phase. During loss of coolant accident, the temperature and pressure inside the containment start raising. It reached to 80 pressure and reached to 7.533 psi within few minutes. The simulation has been carried out by assuming the containment temperature at 80C and pressure at 7.533 psi and the spray with pH 5.0 and 9.5 and the alkaline spray. The spray system is found to have minimum effect on noble gasses and reduces iodine and other radioactive particles effectively. The spray system is started at 100, 500, 1000, and 1500 s after the release time. The effect of spray system activation time on noble gasses and iodine is shown in Figure 8.

Figure 8. Radioactive noble gasses and iodine release during in-vessel release phase with mixing rate wx = 0.01 s<sup>1</sup> .

5.3. Mixing rate (wx) effect on in-containment FPA

ing gradually for mixing rate value from wx = 1.0 to 0.03 s<sup>1</sup>

5.4. Fission product activity with spray system

magnitude of 131I activity has been observed with higher mixing rate.

wx = 1.0 s<sup>1</sup>

mixing rate 0.005 s<sup>1</sup>

Figure 7. 131I activity (g/cm3

56 Numerical Simulations in Engineering and Science

The delayed core released fraction (1-fx)(exp -wxt) for various values of mixing rate wx which contributes to airborne volumetric activity through coolant has been simulated. The volumetric activity of 131I inside the containment for various values of mixing rate wx from 0.005 to 1.0 s<sup>1</sup> has been numerically simulated. It has been observed that a slight change in the value of wx results in astonishing variation in airborne activity. The results are shown in Figure 7. For

) for 131I as a function of time (s) for various values of wx.

value. However, the 131I has been observed to reduce almost linearly with mixing rate 1.0 s<sup>1</sup> (Figure 7). The in-containment volumetric concentration of 131I increases and then starts decreas-

The primary purpose of the spray system is to mitigate the FP exposure to the environment and to maintain the containment integrity. In this work, we have studied the effect of the spray system in mitigating the radioactive masses (gaseous and particles) released during in-vessel release phase. During loss of coolant accident, the temperature and pressure inside the containment start raising. It reached to 80 pressure and reached to 7.533 psi within few minutes. The simulation has been carried out by assuming the containment temperature at 80C and pressure at 7.533 psi and the spray with pH 5.0 and 9.5 and the alkaline spray. The spray system is found

, highest magnitude has been observed with a shift of peak toward lower timescale

. This is because of trivial mixing of iodine in the coolant. A higher

; however, it remains constant for

Figure 9. Iodine with containment spray system failures during in-vessel release phase with mixing rate wx = 0.01 s<sup>1</sup> .

The iodine concentration first increases exponentially in containment and immediately starts reducing with the activation of the spray system. This is because of computation between the continuous source of radioactive iodine (Pi) coming from reactor pressure vessel (RPV) and removal of iodine with the containment spray system (Figure 8). The volumetric iodine starts reducing exponents after the activation of the spray system. The droplet size has been assumed 800 microns for the simulation. However, the noble gasses are observed to be unaffected with a spray system. The response of airborne iodine to the failure of the spray system is depicted in Figure 9.

Figure 9 indicates that the premature failure of the system (t = 100 s) does not affect the airborne iodine concentration. The slight decrease in airborne iodine concentration is seen if the spray system is failed or malfunctions at 500 s. However, the spiracles are operated for a longer period, for example, 1000–1500 s during the in-vessel phase. The airborne concentration of iodine is reduced significantly. The failure of the system at 1000 and 15,000 s caused the regaining of airborne iodine (Figure 9).

### 5.5. Droplet diameter and pH effect on in-containment FPA

The droplet collection efficiency of spray also depends on the containment atmospheric temperature, pressure and spiracle pH value. The affect of spray water pH value and an alkaline spray has been simulated. The results are depicted in Figure 10. The results showed that the higher pH spray solution (pH 9.5) and alkaline solution (Na2S2O3) have similar removal characteristics for airborne iodine. The iodine removal rates of Boric (pH 5.0), NaOH (pH 9.5) and alkaline solution with different droplet sizes are shown in Figure 11.

Figure 11. Droplet removal rate for iodine at pH 5.0, 9.5 and with alkaline spray solution (Na2S2O3).

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Figure 12. Tellurium inventory during in-vessel release phase with mixing rate wx = 0.01 s<sup>1</sup>

.

The removal rate has been seen to decrease exponentially with the increase in droplet size for an alkaline solution (Figure 11). However, for a spray solution with pH value 5.0, the removal rate decreases in a linear manner. The in-containment volumetric mass under the atmospheric

Figure 10. Response of radioactive iodine for spray pH value during in-vessel release phase with mixing rate wx = 0.01 s<sup>1</sup> .

Numerical Simulation of Fission Product Behavior Inside the Reactor Containment Building Using MATLAB http://dx.doi.org/10.5772/intechopen.70706 59

Figure 11. Droplet removal rate for iodine at pH 5.0, 9.5 and with alkaline spray solution (Na2S2O3).

The iodine concentration first increases exponentially in containment and immediately starts reducing with the activation of the spray system. This is because of computation between the continuous source of radioactive iodine (Pi) coming from reactor pressure vessel (RPV) and removal of iodine with the containment spray system (Figure 8). The volumetric iodine starts reducing exponents after the activation of the spray system. The droplet size has been assumed 800 microns for the simulation. However, the noble gasses are observed to be unaffected with a spray system. The response of airborne iodine to the failure of the spray system is depicted in

Figure 9 indicates that the premature failure of the system (t = 100 s) does not affect the airborne iodine concentration. The slight decrease in airborne iodine concentration is seen if the spray system is failed or malfunctions at 500 s. However, the spiracles are operated for a longer period, for example, 1000–1500 s during the in-vessel phase. The airborne concentration of iodine is reduced significantly. The failure of the system at 1000 and 15,000 s caused the regaining of

The droplet collection efficiency of spray also depends on the containment atmospheric temperature, pressure and spiracle pH value. The affect of spray water pH value and an alkaline spray has been simulated. The results are depicted in Figure 10. The results showed that the higher pH spray solution (pH 9.5) and alkaline solution (Na2S2O3) have similar removal characteristics for airborne iodine. The iodine removal rates of Boric (pH 5.0), NaOH (pH 9.5)

The removal rate has been seen to decrease exponentially with the increase in droplet size for an alkaline solution (Figure 11). However, for a spray solution with pH value 5.0, the removal rate decreases in a linear manner. The in-containment volumetric mass under the atmospheric

Figure 10. Response of radioactive iodine for spray pH value during in-vessel release phase with mixing rate

Figure 9.

wx = 0.01 s<sup>1</sup>

.

airborne iodine (Figure 9).

58 Numerical Simulations in Engineering and Science

5.5. Droplet diameter and pH effect on in-containment FPA

and alkaline solution with different droplet sizes are shown in Figure 11.

Figure 12. Tellurium inventory during in-vessel release phase with mixing rate wx = 0.01 s<sup>1</sup> .

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 of 0.2 m3 /s.

6. Conclusion

able data in the literature.

Acknowledgements

financial support.

Author details

References

(KAU), Jeddah, Saudi Arabia

Khurram Mehboob\* and Mohammad Subian Aljohani

\*Address all correspondence to: khurramhrbeu@gmail.com

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 avail-

Numerical Simulation of Fission Product Behavior Inside the Reactor Containment Building Using MATLAB

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61

This article was funded by the deanship of scientific research (DSR) at King Abdul Aziz University, Jeddah. The author, therefore, acknowledges with thanks DSR for technical and

Department of Nuclear Engineering, Faculty of Engineering, King Abdul Aziz University,

[1] Rahim FC, Rahgoshay M, Mousavian SK. A study of large break LOCA in the AP1000

reactor containment. Progress in Nuclear Energy. 2012;54:132-137

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> ). The 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 droplet size for pH 9.5 and alkaline spray solution with spray flow rate 0.35 m<sup>3</sup> /s. The gas 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 KL) are also related to the inverse square of droplet diameter (1/d<sup>2</sup> ).

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.
