Preliminary Neutronics Analysis for IB Shielding Design on FNSF (Standard Aspect Ratio)

1. Preliminary Neutronics Analysis for IB Shielding Design on FNSF (Standard Aspect Ratio) Haibo Liu Robert Reed Fusion Science and Technology Center, UCLA August 19th, 2009

2. Objective • To maximize the TBR of the FNSF design with an effective IB shielding of a given thickness. Approach: • Within a 50-cm IB shielding, the damage rates are kept below the allowable limits by investigation of various IB configuration/material choices, type of magnet insulators, etc.

3. How to Achieve Shielding Effectiveness IB total thickness: 50cm Case1: FW(2cm) + PbLi(7cm) + Reflector(5cm) + Shield(36cm) Case2: FW(2cm) + Be(5cm) + Reflector(5cm) + Shield(38cm) Case3: FW(2cm) + PbLi(2cm) + struc(0.5cm) + Be(5cm) + struc.(0.5cm) + PbLi(5cm) + Reflector(5cm) + Shield(30cm) Case4: FW(2cm) + PbLi(2cm) + struc.(0.5cm) + Be(3cm) + struc.(0.5cm) + PbLi(5cm) + Reflector(5cm) + Shield(32cm) Case5: case3 IB + Full Coverage OB Shield: 5%Water + 5%SS + 25%B4C + 65%W

4. Model and Code Reflective Boundary Model: based on GA FDF design and the VNS design of Ho&Abdou(1996) 3D Calculation: MCNP XS Library: FENDL/MC-2.1 Normal magnet is used. FNSF parameters assumed Elongation: 2 Aspect Ratio A: 3.5 Major Radius R: 2.5m Neutron Wall Load: 2MW/m2 Peak Inboard Fluence: 6 MWa/m2 A DCLL blanket (83.4cm) is used on the outboard in all calculations. Vacuum Boundary Reflective Boundary 20o Model (CAD Model Generated by MCAM)

5. TFC Magnet Case PFC VV OHC Magnet Case IB OB PFC Components Description

6. IB Design Cases IB total thickness: 50cm Case1: FW(2cm) + PbLi(7cm) + Reflector(5cm) + Shield(36cm) Case2: FW(2cm) + Be(5cm) + Reflector(5cm) + Shield(38cm) Case3: FW(2cm) + PbLi(2cm) + struc(0.5cm) + Be(5cm) + struc.(0.5cm) + PbLi(5cm) + Reflector(5cm) + Shield(30cm) Case4: FW(2cm) + PbLi(2cm) + struc.(0.5cm) + Be(3cm) + struc.(0.5cm) + PbLi(5cm) + Reflector(5cm) + Shield(32cm) Case5: case3 IB + Full Coverage OB Plasma Side 1-D Diagram of IB Design Cases Shield: 5%Water+5%SS+ 25%B4C+65%W PbLi: 90%enriched 6Li FW: 40%FS+60%He Reflector: 100%FS

7. Difference Between Case3 and Case5 Case5 – Full OB Coverage Case3

8. Radial Dimension and Materials Composition ** one of five cases * organic insulator

9. Design Limit for Damage Rates • Limit dose for epoxy insulator ~109 Rads (10 MGy) • Limit fast neutron fluence for epoxy insulator ~ 5×1021n/m2 • Limit dose for ceramic insulator Generally ~1012 Rads but > 1012 Rads for MgAl2O4(spinel) • Limit fast neutron fluence for MgAl2O4 ~2×1026 n/m2 • Limit VV He production rate 1 He appm Copper Magnet Electrical Resistivity Change • ∆ρtrans = KNiCNi + KZnCZn, where KNi = 11.2 nΩm, KZn = 3.0 nΩm, and CNi & CZn are atomic percentages. • ∆ρrad,def≈ A(1-e-B·DPA), where A is the saturation resistivity change. A=1.2 nΩm for pure copper and 1.6 nΩm for DS and Cu-Cr-Zr copper alloys at 100oC. B=100. The electrical resistivity of pure copper is 17.1 nΩm at 20oC.

10. TBR and Peak VV He appm Tritium Breeding Ratio Peak VV He appm • Case3, with a sandwich IB configuration, has larger IB TBR and the total is 1.04. The TBR can be further increased to 1.24 by extending the OB to the divertor region. But does it feasible from the engineering point of view of FNSF? • The peak VV SS helium production rate for all the cases are below the reweldability limit of 1appm. The maximum is 0.33 He appm from Case5.

11. Peak Insulator Dose Peak Insulator Dose with Epoxy Insulator Peak Insulator Dose with Spinel Insulator The epoxy insulator doses for all the cases are much higher than 109 rads. The ceramic insulator is suggested to be used in the FNSF design for its much higher dose limit. The dose in spinel insulator case5 is 4.7×1010rads. If the epoxy insulator is preferred, the IB shielding thickness has to be increased.

12. Peak Fast Neutron Fluence and DPA OHC Peak Fast Neutron Fluence OHC Peak DPA • The maximum OHC peak fast neutron fluence is from spinel insulator Case5, which is 8.6×1019n/cm2, higher than the result of epoxy insulator case5. • The maximum OHC peak copper DPA is also from spinel insulator Case5, which is 0.05DPA.

13. Peak Magnet Electrical Resistivity Change OHC Resistivity Change with Epoxy Insulator OHC Resistivity Change with Spinel Insulator The resistivity change for two kinds of insulators are about 1.2 nΩm, about 7% increase to the total copper electrical resistivity. The DPA-induced electrical resistivity increase in magnet pushes its resistivity almost to the saturation value of 1.2 nΩm for pure copper. The transmutation induced resistivity change is very small because of the low neutron fluence.

14. IB Nuclear Heating Rate Case1 IB Nuclear Heating Rate Case3 IB Nuclear Heating Rate The peak nuclear heating rate in Case3 is about 14 w/cc in the FW-FS, about 23 w/cc in the 1st PbLi layer, which occurs before the beryllium multiplier layer, and this could be because of the effect of the neutron multiplication and reflection from the beryllium. In Case1, the PbLi layer heating rate is also increased along the IB depth because of the reflective neutron induced gamma from the FS reflector.

15. Summary Five FNSF IB cases with 50cm IB thickness have been calculated. Taking into account the high damage rate, ceramic insulator is suggested to be used in FNSF. The MgAl2O4 could be a good choice based upon its good mechanical and electrical properties. For getting tritium self-sufficiency, the Case5, PbLi & Be & PbLi sandwich IB design with full OB coverage, is confirmed better choice. The TBR from Case5 is 1.24, which is larger than the other cases. The DPA-induced increase in magnet electrical resistivity is the dominant part of the total increased resistivity under the low neutron fluence.

16. Thank you for your attention!