5.2. Puff release (fx) effect on in-containment FPA

told = t(j-1); yold = y(j-1,:)'; k1= feval(diffeq,told, yold);

54 Numerical Simulations in Engineering and Science

ytemp(n) = yold(n) + h2\*k1(n);

k2= feval(diffeq,told+ h2, ytemp);

ytemp(n) = yold(n) + h2\*k2(n);

k3= feval(diffeq,told +h2, ytemp);

ytemp(n) = yold(n) + h\*k3(n);

k4= feval(diffeq,told+h, ytemp);

y(j,n)= yold(n)+h6\*(k1(n)+k4(n))+h3\*(k2(n)+k3(n));

5. Some results from numerical simulation

The core inventory for typical 1000 MW PWR has been evaluated by ORIGEN 2.2 code which is used by our model as a subroutine. A 35% core damage has been considered and 20% (fx) as the puff release. While the rest of radioactive mass release along with coolant

of time is depicted in Figure 5. The volumetric radioactive mass found to increase during

Figure 5. In-containment FP inventory during in-vessel release phase with mixing rate wx = 0.01 s<sup>1</sup>

. The FP release inside the containment building as a function

.

5.1. Volumetric fission product inventory

with mixing rate wx = 0.01 s<sup>1</sup>

for n= 1:neq

for n= 1:neq

for n= 1:neq

for n= 1:neq

end

end

end

end end end

> The LOCA is due to the uncontrolled leakage from coolant piping (hot leg or cold leg). The coolant burst release generates the immediate escape of radioiodine into containment with the rapture. The volumetric activity of 137Xe inside the containment has been simulated for various values of instantaneous burst release (i.e., fx = 10–70%) of total activity inside the core. The simulation results are depicted in Figure 6. The results indicated that with the higher percentage of instantaneous release (fx = 50–70%), the activity in containment slightly increased and then decreased linearly.

> However, a less fraction of burst release (fx = 10–30% of total activity), the activity inside the containment first increases and then starts decreasing after approaching to the maximum value. As the value of fx decreases, the peak shifts toward higher timescale. The peak becomes more prominent with small values of fx. This happens due to competition between fx term in the initial condition and (1-fx)(exp -wx) term in source term (Eq. (4)). The behavior of 137Xe for various values of instantaneous release (fx) with mixing rate wx = 0.01/s explains the clearer picture of airborne Xenon (Figure 6).

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

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

http://dx.doi.org/10.5772/intechopen.70706

57

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>

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

.

.

Figure 7. 131I activity (g/cm3 ) for 131I as a function of time (s) for various values of wx.
