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

Haibo Liu Robert Reed

Fusion Science and Technology Center, UCLAAugust 19th, 2009

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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.

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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

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Model and Code

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 assumedElongation: 2Aspect Ratio A: 3.5Major Radius R: 2.5mNeutron Wall Load: 2MW/m2

Peak Inboard Fluence: 6 MWa/m2

A DCLL blanket (83.4cm) is used on the outboard in all calculations. 20o Model

(CAD Model Generated by MCAM)

Reflective Boundary

Reflective Boundary

Vacuum Boundary

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Magnet Case

Magnet Case

TFC

IB

OHC

OB

PFC

PFC

VV

Components Description

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IB Design Cases

IB total thickness: 50cmCase1: 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

1-D Diagram of IB Design Cases

Shield: 5%Water+5%SS+ 25%B4C+65%WPbLi: 90%enriched 6LiFW: 40%FS+60%HeReflector: 100%FS

Plasma Side

case1

case2

case3/5

case4

IB 50 ( D im ens ion in cm )

F W

L iP b R eflectorS hie ldB e

S tructure

2

2

2

2

7 5 36

5 5 38

2 5 5 5 30

2 3 5 5 32

Insulator

O H C

V V

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Case3 Case5 – Full OB Coverage

Difference Between Case3 and Case5

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Radial Dimension and Materials CompositionComponent Radial thickness (cm) Composition

TFCCoil 106 60%Copper+25%Water+15%insulator

Insulator 0.2 40%Epoxy+60%Al2O3

Case 7 100%SS316L(N)-IG

OHCCoil 7.8 60%Copper+25%Water+15%insulator

Insulator * 0.2 40%Epoxy+60%Al2O3

VV Void 2 -

Inboard (Case3**)

Shielding 30 5%Water+5%SS+25%B4C+65%W

Reflector 5 100%FS

PbLi 5 100%PbLi (90%enriched)

Struc. 0.5 100%FS

Be 5 100%Be

Struc. 0.5 100%FS

PbLi 2 100%PbLi (90%enriched)

FW 2 40%FS+60%He

SOL 5 void

Plasma 132 Neutron Source

SOL 5 void

Outboard DCLL TBB 83.4 From Dr. Youssef (DEMO)

** one of five cases * organic insulator

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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.

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0.0

0.2

0.4

0.6

0.8

1.0

1.2

Tri

tium

Bre

ed

ing

Ra

tio

case1 case2 case3 case4 case5

IB OB Total

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.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

VV

Pe

ak

He

ap

pm

case1 case2 case3 case4 case5

VV

6MWa/m2

TBR and Peak VV He appm

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0

1

2

3

4

5

6

7

Insu

lato

r D

ose

(1

010

rad

s)

case1 case2 case3 case4 case5

neutron gamma total

6MWa/m2

0

1

2

3

4

5

6

7

Insu

lato

r D

ose

(1

010ra

ds)

case1 case2 case3 case4 case5

neutron gamma total

6MWa/m2

Peak Insulator Dose with Epoxy Insulator Peak Insulator Dose with Spinel Insulator

Peak Insulator Dose

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.

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0

1

2

3

4

5

6

7

8

9

OH

C P

ea

k F

ast

Ne

utr

on

Flu

en

ce (

10

19 n

/cm

2 )

case1 case2 case3 case4 case5

epoxy spinel

6MWa/m2

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

Pe

ak

OH

C D

PA

case1 case2 case3 case4 case5

epoxy spinel

6MWa/m2

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.

Peak Fast Neutron Fluence and DPA

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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.

Peak Magnet Electrical Resistivity Change

0.01

0.1

1

OH

C r

esi

stiv

ity c

ha

ng

e (nΩ

m)

case1 case2 case3 case4 case5

trans. defect

6MWa/m2

0.01

0.1

1

OH

C r

esi

stiv

ity c

ha

ng

e (nΩm

)

case1 case2 case3 case4 case5

trans. defect

6MWa/m2

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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.

0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14

Nu

cle

ar

He

atin

g R

ate

(w

/cc)

Depth in IB (cm)

Case12MW/m2 NWLFW-FS

PbLi

Reflector-FS

Shield-SS

0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14

16

18

20

22

24

Nu

cle

ar

He

atin

g R

ate

(w

/cc)

Depth in IB (cm)

Case32MW/m2 NWL

FW-FS

PbLiBe

PbLi

Reflector-FS

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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.

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Thank you for your attention!