22.351 Thorium 1

Thorium as a Nuclear Fuel Course 22.251

Fall 2005 Massachusetts Institute of TechnologyMassachusetts Institute of Technology

Department of Nuclear EngineeringDepartment of Nuclear Engineering

Earth Energy Resources

22.251 Thorium 2

Electricity Generation Potential

Resources

Coal 190 bt 190 350 11027,000*

Oil 0.6 bt 1.2 Not to be used for Power Generation

Natural Gas 540 bm3 1 280 10 40

Hydroelectricity 84 GWe at60% CF

0.2/y Renewable 84 Renewable(60% CF)

UraniumPHWRFBR

60,000 t1.2195

34016,000

15350

3065

ThoriumThermal BreedersFBR

320,000 t360

1,00070,000

200,000350350

285820

Amount GWe-Yr CapacityGWe

No. of Years at CF 70%

Coal Equivalent in Billion T

Commercial Energy Resources in India

*50% Coal reserved for non electricity generation use Figure by MIT OCW.

Breeding U233 and Pu239: Comparison

22.251 Thorium 3

232Th + 1 Neutron Fertile

Fissile

Fertile

Parasite

Fissile

234U + 1 Neutron

236U + 1 Neutron

237NpChemically Separable

233U + 1 Neutron90% Fission10% Capture

235U + 1 Neutron80% Fission20% Capture

233Pa (27.4 Days)Beta Decay

(2.3 Days)Beta Decay

238U + 1 Neutron

240Pu + 1 Neutron

242Pu + 1 Neutron

243AmChemically Separable

239Pu + 1 Neutron65% Fission35% Capture

241Pu + 1 Neutron75% Fission25% Capture

239Np

Figure by MIT OCW.

η – Factor vs Neutron Energy

22.251 Thorium 4

0.10

1

2

Num

ber o

f neu

trons

per

neu

tron

abso

rbed

, η

3239Pu

233U

238U

235U

232Th

4

1eV 1keV 10 100 1MeV10 100

Incident neutron energy

Neutron Yield per Neutron Absorbed

Figure by MIT OCW.

U233 as a Fissile Material

233U 235U 239Pu 241Pu

σcapture, barns 46 101 271 368

σfission, barns 525 577 742 1007

α = σc/σf 0.088 0.175 0.365 0.365

η = νσc/σf 2.300 2.077 2.109 2.151

Effective β factor, pcm 270 650 210 490

22.251 Thorium 5

22.251 Thorium

Th232 vs. U238

232Th 238U

σcapture, barns 7.40 2.73

σfission (fast spectrum, 1-group), barns 0.01 0.05

IR (infinite dilution), barns 85 272

Fission cutoff, MeV 1.5 0.8

Neutrons per fission (νaverage) 2.3 2.75

Effective β factor, pcm (fast fission) 2030 1480

6

0.010.001 0.01 0.1 1.0

E-MeV

σ(n,y)U238σ-

Bar

ns

σ(n,y)Th232

σ(n,f)U238

σ(n,f)Th232

10

0.1

1.0

10

σx10(n,y)Th232

Figure by MIT OCW.

MA Production Comparison

22.251 Thorium 7

Minor Actinides

Np-237

U5 + U8(Reference cycle)

(grams per ton HM)

U5 + Th2(%)

U3 + U8(%)

U3 + Th2(%)

Am(241+242+243)

Cm(243 to 246)

360a

900b

KeyaDischarge burn-up bDischarge burn-up

: 30 GW d/t: 60 GW d/t

160a

470b

36220

Relative Production of Minor Actinides in Diverse Cycles

13

6.3 10-5

1.8 10-3

1.68 10-5

6.37 10-4

92107

0.040.28

0.010.14

2013

106117

111132

Diverse Fuel Cycles

Figure by MIT OCW.

22.251 Thorium 8

U232 decay chain

0

50

100

150

200

250

300

350

400

0 20 40 60 80 100 120 140 160 180 200

Time (years)

Dos

e Rat

e (r

em/h

our

@ 1

m)

~45 weeks ~130 Years

self-protection limit

Th-232

Ra-228

Ac-228

Th-228

Ra-224

Rn-220

Po-216

Pb-212

Bi-212

α

β

β,γ

α

α

α

α

β

β, 3.1 mγ, 2.6 MeV

γ 1.6 MeV

γ, 2.6 MeV*α 0.3 µs

α, 60.6 m 33.7%)

β, 60.6 m, 66.3%)

Tl-208 Po-212*

Pb-208

1.4 1010 y, no γ

6.7 y, no γ

6 h, γ 0.96 MeV

1.91 y, low energy γ

3.64 d, γ 0.24 MeV

56 s, γ 0.54 MeV

10.6 h, γ 0.3 MeV

0.15 s, no γ

U-232

α, 72 y low en. γ

*Relative to excited states Figure by MIT OCW.

22.251 Thorium 9

Power Density Effect

0.9080

0.9026

0.8877

0.8766 0.8694

0.8523

0.80

0.82

0.84

0.86

0.88

0.90

0.92

0 10000 20000 30000 40000 50000 60000 70000

Burnup, MWd/t

K -i

nfin

ity

20 MW/t 40 MW/t 60 MW/t

Pa-233

T1/2 = 27.4 days

σa ~ 40 b

22.351 Thorium

ASPECT DIFFERENCE VS. URANIUM

Mining

Enrichment

Fabrication

(a). Thorium is perhaps 3 times more abundant but much less is mined. Best resources are monazite sands in India and Brazil.(b). Because uranium is really mined for its U-235, a once-through cycle needs only about 1/10th as much Thorium.

(c). U-free Th preferred because of absence of Th-230.

(d). Tailings less of a problem because Rn-220 has a much shorter half-life than Rn-222.

(a). Must provide as U-235 or Plutonium (could be from dismantling weapons).

(b). Recycled U-233 contains U-232, U-234.

(a). Typically as ThO2 using processes similar to UO2 and PuO2 (which are incorporated to provide fissile enrichment).

Storage and Transportation

Direct Disposal

Reprocessing

Refabrication

Safeguards

(a). Pa-233 decay (T 1/2 ~ 27 days) creates more U-233 over first several months.(b). Similar fission product decay heat and gamma emission.

(a). ThO2 is stable in oxidizing environment ( unlike UO2 which forms U3O8).(b). Factor ~ 10 lower concentration of radiotoxic higher actinides.

(a). Solvent extraction (THOREX) similar to PUREX but same equipment has about half the processing rate, hence ~ 30% more expensive.(a). Need to shield against hard gammas from U-232 decay chain (Bi-212, Tl-208), hence more expensive even than recycled U or Pu.(b). Preferable to delay recycle of Th for ~ 15 years to decay Th-228; one year suffices for Th-234.

(b). U-232 chain gammas complicate handling.(a). Must denature to < 12% U-233 in U-238.

BACK END

FRONT END

_

Th in LWRs: Front and Back End Fuel Cycle Effects

10

Figure by MIT OCW.

22.351 Thorium

PARAMETER WITH TH/U-233 PRINCIPAL CAUSES NOTABLE EFFECTS

Moderator temperature coefficient (MTC)

Doppler coefficient

Xenon worth

Progressively negative withburnup

Lattice neutronics less sensitive to spectral hardening

Less effect of lattice design changes

More negative, less so with burnup

Th-232 effective resonance integral, while smaller than that of U-238, is more strongly increased by temper-ature; less Pu-240 buildup

Improved transient response to rapid severe reactivity, (hence power) increases

Slightly less U-233 has lower yield of I-135 + Xe-135, but higher direct yield of Xe-135

1. Reduces reactor control needed

2. Higher direct yield of Xe-135 increases stability against Xenon oscillations

Fission product poiso-ning

Slightly different 1. U-233 has a different yield mix than U-234 and lower σa than Pu2. Somewhat offset by higher thermal σa of Th-232 vs. U-238

Only slightly disadvantageous

Delayed neutron fracti-on, β

Decrease with burnup is slightly more than in all-U core

β of U-233 is considerably less than that of U-235, but comparable to that of Pu-239, Pu-241

1. Roughly same detrimental effect on accidents involving sudden large reactivity insertions2. More rapid power decrease during scram

Reactivity loss due to burnup

Appreciably less Higher η of U-233 produces more excess neutrons for increasing the conversion ratio

1. Less poison reactivity requirement at BOC2. Burnup prediction more sensitive to errors in reactivity prediction

Hot to cold reactivity difference

Smaller Smaller MTC outweighs larger fuel (Doppler) TC

No control modification needed to accom-modate use of Th

Control requirements Reduced overall; but rod worth a bit less at low burnup

Smaller change with burnup domi-nates other effects; lower σa than Pu-239, 241; increases poison worth

1. Can reduce (or eliminate) soluble or burn-able poison concentrations2. Easier to design long-cycle/high burnup cores

Local power peaking Somewhat less both assembly- and pin-wise

U-233 has smaller σf than Pu-239, 241, smaller local ∆ρ due to burnup

More thermal-hydraulic margin, easier to meet design constraints

Fertile capture product Pa-233 more important absorber than Np-239

Pa-233 has T 1/2 = 27 days vs.2.4 d for Np-239

1. Delays U-233 production

2. Both neutrons and U-233 are lost by captures in Pa-233

Predicted Effects of Th/233U on Pressurized Water Neutronics Compared to All-U Fueling 11

Th in LWRs: Neutronic Effects

Figure by MIT OCW.

Summary of Th Advantages and Drawbacks Advantages

• Robust fuel and waste form • Generates less Pu and higher actinides • U233 has superior fissile properties • Large resources

Drawbacks

• Requires initial investment of fissile material (U235/Pu) • Pa considerations • U232 issue and more complicated reprocessing • U233 is weapons usable unless denatured

1222.251 Thorium

History of Using Thorium in Power Reactors High Temperature Reactors

• PEACH BOTTOM (40 MWe) General Atomics, 1966 - 1972. • DRAGON experimental reactor (20 MWt; 1966-73) OECD­

EURATOM, England • Pebble-bed AVR in Jülich (15 MWe) BBC-HRB (1967 and 1989),

THTR (1984) 300MWe

Other Reactors

• ELK RIVER, is a 24 MWe BWR (1963–68) • INDIAN POINT, a 285 MWe PWR (1962–1980) • AHWR in India, plans to build 500MWe Fast Thorium Breeder

Reactor • SHIPPINGPORT Light Water Breeder Reactor

1322.251 Thorium

LWBR Shippingport

14

Images removed due to copyright restrictions.

Thorium Based Fuel Design Options For once-through fuel cycle

• Homogeneously mixed UO2 – ThO2

• Micro-heterogeneous ¾ Small scale spatial separation

¾ Minimal changes in core design

• Macro-heterogeneous ¾ Large scale spatial separation

¾ Different residence times for U and Th parts

1522.251 Thorium

22.251 Thorium 16

UO2 vs. Homogeneously Mixed U-Th

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

1.40

1.45

1.50

0 10 20 30 40 50 60 70

MWd/kg ihm

K-in

f

Homogeneous U-Th

All-U

K-inf = 1.03

22.251 Thorium 17

Homogeneous U-Th Fuel NU Utilization

1.05

1.80

5.26

2.62

4.85

4.42

3.50

5.07 5.24

5.265.275.26 5.165.064.97

4.90

0

1

2

3

4

5

6

2 3 4 5 6 7 8 9 10 Fissile isotope (U-235) content in mixture, %

Nat

ural

U U

tiliz

atio

n , M

Wd /

Kg

NU

U-Th Case All-Uranium Case

22.251 Thorium 18

Micro-Heterogeneous U-Th Fuel

UO2

ThO2 UO2

UO2 ThO2

Checkerboard

UO2

UO2

ThO2

ThO2

Duplex Axial

22.251 Thorium 19

K∞ vs. Burnup for Ax4 and Hom. Cases

0.90

1.00

1.10

1.20

1.30

1.40

1.50

0 10 20 30 40 50 60 70 Burnup, MWD/kg

K-in

finity

All Uranium

Homogeneous

Axially Heterogeneous

•Spectral Shift •Resonance ShieldingThe effect is due to:

0.80

0.70

0.60

22.251 Thorium 20

Breeding U233 (cont.)

0.30

0.40

0.50

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000

CR

Bu rnu p , M W D/ t

U-Th Ax4

All U

Homog. (UO2-35w/o ThO2-65w/o)

22.251 Thorium 21

Breeding U233

9.0E-01

5.0E+12

1.0E+13

1.5E+13

2.0E+13

2.5E+13

0 10000 20000 30000 40000 50000 60000 70000

Burnup, MWd/t

Rea

ctio

ns/

sec

Homogeneous Th capture RR

Homogeneous U233 fission RR

Ax4 Th Capture RR

Ax4 U233 fission RR

22.251 Thorium 22

Spectral Shift

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.0E-09 1.0E-07 1.0E-05 1.0E-03 1.0E-01 1.0E+01

E (MeV)

Φ(u

)

Ax4 (UO2) Ax4 (ThO2)

Mix

22.251 Thorium 23

233U, 235U and 238U Absorption Cross-Sections

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

5 6 7 8 9 10

E,eV

σ a , b

arn

U-233

U-235

U-238

22.251 Thorium 24

Reactivity Limited Burnup Comparison

13.00

10.42

-10.00

0.04 0.00 -0.47 -0.65

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

Duplex Axially Het. Un-denatured

Radially Het. Un-denatured

Axially Het. Denatured

Radially Het. Denatured

Homogeneous All-U

Dif

fere

nce

fro

m A

ll-U

, %

22.251 Thorium 25

Proliferation Resistance

Ax4 Ax4NU Seed Zone

Seed Zone

Blanket Zone

Hom All-U Weapon Grade

Ratio of SFS to super grade Pu 29.29 24.2 22.2 22.5 23.0 2.9

Decay Heat (Watts/kg Pu) 59.6 48.4 13.4 38.6 33.9 2.4

Critical massa (kg Pu) 21.2 20.5 22.4 21.25 21.4 16.45

Specific Activity (Curies/kg Pu) 1.87e4 1.79e4 2.04e4 2.05e4 1.76e4 4.39e2

Multiples of Critical Mass /GWe-year 3.3 3.9 1.3 5.2 10.8 --a Calculated for un-reflected spherical geometry, Pu metal in δ-phase (ρ = 15.9 g/cm3)

Macro Heterogeneous Th Fuel

Seed

Blanket

SBU Radkowsky Seed-Blanket Concept WASB

Whole Assembly Seed-Blanket Concept

2622.251 Thorium

Pu Production in Macro Het. U-Th Fuel

2722.251 Thorium

Blanket Normalized Power Share

22.251 Thorium 28

Thorium Blanket Power Share

0.38

0.39

0.40

0.41

0.42

0.43

0.44

0.45

0.46

0.47

0.48

0.49

0.50

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

burnup, days

Nor

mal

ized

Pow

er

18 Month cycle

18 Month cycle, Average

12 Month cycle, Average

Blanket Normalized Power Share

Economic Performance of Heterogeneous Once-Through Th Cycle

4.01173.97683.88873.79553.8926Levelized FCC, mills/kWh(e)

57,55856,48353,75354,27453,753PV Electricity Production

79,81978,32874,52075,26574,520 Direct Electricity Production, kWh(e)*106

189.0189.0190.8147.1137.5SWU Requirements, t SWU/Gwe-Y

5.42345.49125.44185.32735.0475NU Utilization, GWd(th)/t NU

199.0196.5198.3202.6213.8NU Requirements, t NU/Gwe-Y

482473300454.5300Average Cycle Length, FPD

2020204.5333.2"equilibrium" enrichment, (%U235)

RTF18 Oxide Seed

RTF18 Metal Seed

RTF12 Metal Seed

PWR18PWR12

2922.251 Thorium

Pu Disposition in Th • Possible in virtually any reactor type

• Pu destruction efficiency and destruction rate depend on neutron spectra

• Denaturing of Th with uranium is required in order to eliminate proliferation concerns about bred U233 – presence of U degrades Pu destruction efficiency and rates

• Compared to UO2, Pu-Th fuel has more negative Doppler and MTC but much smaller βeff and control materials worth

3022.251 Thorium

22.251 Thorium 31

Pu Destruction Rates

300

400

500

600

700

800

900

1000

1100

1200

1300

0.1 1.0 10.0 100.0

H/HM atom ratio

Pu

Bu

rnt,

Kg/

GW

Yea

r e

Comp. 1

Comp. 2

Comp. 3

Comp. 4

Comp. 5

Comp. 6

Comp. 7

Comp. 8

PWR

Undenatured cases

Denatured cases

Note: Each point has different corresponding discharge burnup

22.251 Thorium 32

Residual Pu Fraction

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0.1 1.0 10.0 100.0

H/HM atom ratio

Pu

res

idu

al /

Pu

init

ial

Comp. 1

Comp. 4

Comp. 5

Comp. 8

PWR

22.251 Thorium 33

BU1 vs H/HM: Th-Pu Hom. mix

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

0.1 1.0 10.0 100.0

H/HM atom ratio

BU

1 M

WD

/kg

15%

11%

9%

7%

PWR

Pu / HM mass %

22.251 Thorium 34

Fissile Uranium Ratio

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.1 1.0 10.0 100.0 H/HM atom ratio

Fiss

ile U

rani

um R

atio

7% (Comp. 5)

9% (Comp. 6)

11% (Comp. 7)

15% (Comp. 8)

PWR

Pu / HM mass %

22.251 Thorium 35

Homogeneous TRU-Th fuel: TRU Destruction Rate

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

0.1 1.0 10.0 100.0 H/HM atom ratio

Kg/

GW

Year

e

Comp. 9

Comp. 9 (noTh chain)

Comp. 10

Comp. 10 (no Th chain)

Comp. 11

Comp. 11 (no Th chain)

Reference Pin Cell

Homogeneous TRU-Th fuel: MA Destruction Rate Kg

/GW

Year

e200

100

0

-100

-200

-300

-400

Reference Pin Cell

Comp. 9

Comp. 9 (no Th chain nuclides)

Comp. 10

Comp. 10 (no Th chain nuclides)

Comp. 11

Comp. 11 (no Th chain nuclides)

0.1 1.0 10.0 100.0

H/HM atom ratio

22.251 Thorium 36

Homogeneous TRU-Th fuel: Residual TRU Fraction re

sidu

al /

initi

al, %

100.0

90.0

80.0

70.0

60.0

50.0

40.0

30.0

20.0

10.0

0.0

Composition 9

Reference Pin Cell

Composition 10

Composition 11

0.1 1.0 10.0 100.0 H/HM atom ratio

22.251 Thorium 37

Pu-MA-Th Fuel: Reactivity Coefficients DOPLER COEFFICIENT, pcm/K

Comp. No. Description

Reference H/HM Reference + 40% H/HM

BOL MOL EOL BOL MOL EOL

6 Pu-Th den. -4.32 -4.65 -5.04 -3.43 -3.78 -4.22

9 Pu-MA-Th den. -2.98 -3.02 -3.15 -2.63 -2.80 -3.02

12 MOX -2.92 -3.09 -3.20 -2.36 -2.57 -2.70

13 All-U -2.20 -2.93 -3.33 -1.82 -2.31 -2.75

MODERATOR TEMPERATURE COEFFICIENT, pcm/K

6 Pu-Th den. -49.05 -58.68 -73.47 -38.91 -50.40 -66.73

9 Pu-MA-Th den. -18.53 -17.69 -23.40 -29.57 -33.17 -44.86

12 MOX -40.63 -54.65 -73.78 -32.37 -46.92 -66.39

13 All-U -22.17 -51.62 -77.79 -2.21 -26.00 -50.07

VOID COEFFICIENT, pcm/%void

6 Pu-Th den. -128.0 -156.8 -198.3 -104.8 -142.9 -190.4

9 Pu-MA-Th den. -42.8 -41.4 -51.7 -70.8 -85.3 -115.8

12 MOX -104.8 -145.3 -200.7 -86.0 -130.8 -190.8

13 All-U -62.5 -145.7 -228.0 -10.8 -83.5 -164.8

SOLUBLE BORON WORTH, pcm/ppm

6 Pu-Th den. -1.95 -2.28 -3.02 -2.82 -3.60 -5.15

9 Pu-MA-Th den. -1.05 -1.03 -1.24 -1.73 -1.90 -2.24

12 MOX -1.96 -2.37 -2.76 -2.88 -3.70 -4.85

13 All-U 22-4.80 .351 Thorium -5.22 -6.23 -6.65 -8.15 38-11.90

22.251 Thorium 39

Homogeneous Pu-MA-Th Fuel: βeff vs. Burnup

2.0

2.5

3.0

3.5

4.0

4.5

0 200 400 600 800 1000 1200

Burnup, EFPD

β eff x

10 3

Pu-MOX Pu-Th Pu-Th (higher H/HM) Pu-Th den. Pu-Th den. (higher H/HM) TRU-Th TRU-Th (higher H/HM)