Numerical study of initiating phase of core disruptive accident in small sodium-cooled fast reactors with negative void reactivity

Figures & data

Figure 1. Conceptual design of SAS4A.

Figure 2. General physical phenomena during the initiating phase. The red and blue frames indicate positive and negative reactivity respectively. In the large/medium SFRs, the physical phenomena that cause the positive and negative reactivities described in the upper part of the figure occur. In the small SFRs, the physical phenomena that cause the negative reactivities described in the lower part of the figure occur.

Figure 3. Core layout and channel arrangement for SAS4A code.

Table 1. Comparison of main specifications with typical medium SFR.

Items (Unit)	Small SFR	Medium SFR
Thermal power (MWth)	100	714
Number of fuel subassembly	79	198
Fuel smear density (%TD)	87	80
Coolant void reactivity ($) *	−3.7	3.9 (4.9)**

Note: * Values in the row are the sum of positive and negative values.

**Values in brackets in the Medium SFR column are the sum of positive values only.

Figure 4. Axial distribution of void coefficient of reactivity of representative SAS channel.

Figure 5. Normalized coolant inlet flow rate in ULOF.

Figure 6. Control rod withdrawal reactivity in UTOP.

Table 2. Uncertainty considered in uncertainty case.

Reactivity	Uncertainty
Doppler reactivity	30% uncertainty of the reactivity coefficient is considered.
Axial expansion reactivity	30% uncertainty of the reactivity coefficient is considered.
Coolant void reactivity	30% uncertainty of the reactivity coefficient is considered.
Cladding motion reactivity	The friction factor between the molten steel and the sodium vapor is increased by a factor of 10.
Fuel motion reactivity	Fuel failure criteria (areal fuel melt fraction) is increased or decreased (50% or 0%).

Figure 7. Transition of total reactivity and normalized power under ULOF reference condition.

Figure 8. Transition of reactivity under ULOF reference condition.

Figure 9. Transition of the total reactivity for the uncertainty cases of Doppler reactivity, axial expansion reactivity, and coolant void reactivity in ULOF.

Figure 10. Transition of the total reactivity for the uncertainty cases of cladding motion and fuel motion in ULOF.

Figure 11. Transition of total reactivity and normalized power under UTOP reference condition.

Figure 12. Transition of reactivity under UTOP reference condition.

Figure 13. Transition of the total reactivity for the uncertainty cases of Doppler reactivity, axial expansion reactivity, and coolant void reactivity in UTOP.

Figure 14. Transition of the total reactivity for the uncertainty cases of the failure criteria in UTOP..

Figure 15. Transition of the total reactivity for the parametric cases of the coolant void reactivity in ULOF.

Figure 16. Transition of reactivity in ULOF coolant void reactivity 0$ case.

Figure 17. Transition of the coolant void and the cladding motion reactivity for the parametric cases of the coolant void reactivity in ULOF.

Figure 18. Transition of the total reactivity for the parametric cases of the coolant void reactivity in UTOP.