Burnable absorber-integrated guide thimble (BigT) – II: application to 3D PWR core design

Figures & data

Figure 1. Design concepts of BigT-AHR.

Figure 2. The representative BigT-loaded 17 × 17 fuel assembly lattice.

Figure 3. Fuel, BA and clustered bank rodding patterns of 1/8th reference AP1000 first core.

Table 1. AP1000 reactor core design parameters [4].

Parameter	Value
Reactor core rated power (MWt)	3400
System pressure (bar)	155.1
Core-averaged fuel temperature (K)	900
Core-averaged coolant temperature (K)	575
Active core characteristics
Equivalent diameter (cm)	304.0
Active fuel height (cm), cold	426.7
Core structure
Core barrel, ID/OD (cm)	339.7/349.9
Reflectors – top and bottom (cm)	25.4
Number of fuel assembly	157
Fuel assembly design	17 × 17
Number of fuel rod	264
Number of guide thimble	24
Number of instrumentation tube	1
Assembly pitch (cm)	21.5042
Pin pitch (cm)	1.2598
Fuel rod
Pellet radius (cm)	0.4096
Clad inner radius (cm)	0.4178
Clad outer radius (cm)	0.4750
Guide thimble and instrumentation tube
Inner radius (cm)	0.5613
Outer radius (cm)	0.6121
Control rod
Ag-In-Cd absorber radius (cm)	0.4331
SS-304 clad inner radius (cm)	0.4369
SS-304 clad outer radius (cm)	0.4839
Control rod (for BigT design)
B4C/Ag-In-Cd absorber radius (cm)	0.3230
SS-304 clad inner radius (cm)	0.3168
SS-304 clad outer radius (cm)	0.3638

Table 2. The reference assemblies and neutronically similar BigT-AHR configurations.

UO2 w/o	# FA's	Reference	BigT
2.35	49	No absorber	No absorber
2.35	4	28I	0.06 mm thick, 12˚ span
3.40	32	24P, 88I	0.14 mm thick, 88˚ span
3.40	8	24P, 44I	0.10 mm thick, 88˚ span
3.40	12	24P, 28I	0.09 mm thick, 88˚ span
4.45	32	112I	0.04 mm thick, 88˚ span
4.45	8	24P, 72I	0.12 mm thick, 88˚ span
4.45	4	12P, 88I	0.06 mm thick, 88˚ span
4.45	8	9P, 88I	0.06 mm thick, 80˚ span

Figure 4. The selected fuel assembly reactivity depletion patterns of the reference against the neutronically similar BigT-loaded designs.

Figure 5. Top view (top) and side view (bottom) of the high-fidelity Monte Carlo simulation AP1000 core model.

Figure 6. Reactivity depletion of reference core against the BigT-loaded AP1000 first core.

Figure 7. Burnup-dependent radial assembly-wise power peaks of the AP1000 first core designs.

Figure 8. Normalized assembly power of 1/8th reference (top) and BigT-loaded (bottom) AP1000 first cores.

Figure 9. Normalized pin power of 1/8th hottest assembly (central lattice).

Figure 10. Burnup-dependent axial power peaks of the AP1000 first core designs.

Figure 11. Normalized axial power distributions along active height at 0 (top), 255 (middle) and 490 (bottom) EFPDs.

Table 3. BOC shutdown margin estimations of the AP1000 first cores.

Reactivity effects	Reactivity worth at BOC (pcm)
	Reference by	Reference by	BigT by Serpent
Reactivity insertion (HFP to HZP)	Westinghouse [4] (0.433 cm Ag-In-Cd)	Serpent (0.433 cm Ag-In-Cd)	(0.323 cm Ag-In-Cd)
Total power defect (include void effects)	1890	1890	1890
Redistribution (adverse xenon only)	270	270	270
Rod insertion allowance	2000	2000	2000
(1) Total rod requirement	4160	4160	4160
Estimated rod worth (HZP)
All rods inserted	12690	13969 ± 12	10956 ± 12 (12383 ± 12)^**
All assemblies but one (highest worth) inserted	10490	10846 ± 12	9045 ± 13 (9848 ± 13)^**
(2) N-1 worth^*	9756	10086 ± 12	8412 ± 13 (9159 ± 13)^**
Shutdown margin
Calculated margin [(2)–(1)]	5596	5926 ± 12	4252 ± 13 (5,011 ± 13)^**
Required margin	1600	1600	1600

^*Consideration of 7% uncertainty.

^**Natural B₄C rods for ‘black’ control assembly.

Public version of AP1000 design control document revision 19. Pittsburgh, PA: Westinghouse Electric Company LLC; 2011. (Report no. APP-GW-GL-702).

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