Breeding Capability of Moltex's Stable Salt Reactor

Naoyuki Takaki, Takumi Iida Department of Nuclear Safety Engineering

Contents

•Recent movement in Japan

•Why breeder ?

•Moltex’s Stable Salt Reactor • Pin cell analysis • Full core analysis

•Conclusions

2

New strategic energy plan

• On July 3rd 2018, the Japanese Cabinet approved the “5th Strategic Energy Plan” that will guide the national energy policy going forward to 2030 or beyond.

• Referring to renewable energy as a core power source, it also continues to position nuclear power as an important base-load power source and maintains the current figures of share (20-22%) in FY2030 for Japan’s energy mix.

3

4

Renewable

Nuclear

LNG

Coal

Oil

Geothermal Biomass Wind Solar Hydro

Energy mix targeted in 2030

5

6

It refers to “molten salt reactor” for the first time in Chapter 3 “Promotion of technology development”

溶融塩炉

（Yoyu En Ro） Molten Salt Reactor

New strategic energy plan • Technical challenges to be pursued

• LWR technology improvement

• Innovation is necessary to improve safety, reliability and efficiency of nuclear energy

• To promote this with strategic flexibility, the Cabinet shows visions and keeps watching on SMR and MSR developments progressing in US and EU.

• This movement was driven by some representatives of the Liberal-Democratic Party stirred up by some enthusiastic thorium evangelists.

• This seems to affect decisions by Ministries (finance, industry, education) for building budget for MSR studies.

7

8

• International forum on MSR was held at members hall of the Liberal-Democratic Party on June 2018.

• Presentaters invited from ThorCon, Elysium Industry and SINAP

• >200 participants from nuclear Industry

• 2010/6-2016/9 Working Group on “Utilization of Thorium fuel in LWRs and FBRs” （Shinsuke Yamanaka, Osaka University）

• 2013/6-2018/3 Specialists committee on “Spreading out of molten salt technology to nuclear energy” (Michio Yamawaki, University of Tokyo)

• 2018/8- Specialists committee on “Thorium nuclear energy system” (Naoyuki Takaki, Tokyo City University)

9

Activities in Atomic Energy Society of Japan

• Members： > 40 （Manufacturers, Utilities, Universities, Institues） • Purposes:

1. Following up on world trend 2. Comparison between Uranium and Thorium system from scientific and engineering view points 3. Proposal for how Japanese strategy for thorium R&D including MSR ought to be

Contents

•Recent movement in Japan

•Why breeder ?

•Moltex’s Stable Salt Reactor • Pin cell analysis • Full core analysis

•Conclusions

10

Why breeder ?

11

0

10

20

30

40

50

60

70

80

90

100

0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3

Res

ou

rce

uti

lizat

ion

fac

tor

[%]

Conversion ratio / Breeding ratio

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15

Res

ou

rce

uti

lizat

ion

fac

tor

[%]

Averaged burnup [%]

0.1

0.5

1

2

5

Recovery loss [%]

Recovery loss

1 [%]

3[%]

5[%]

Breeder

JSFR

Monju

Converter

Burner

CR>1 Averaged burnup : 7%

CR<1 U-235 enrichment: 5% Burnup: 5%

Breeding with closed cycle is essential for maximizing resource utilization and minimizing wastes,

regardless of U or Th, solid or liquid.

Stable Molten Salt Reactor (SSR)

12

Core specifications of SSR

13

Nuclides Pu-238 Pu-239 Pu-240 Pu-241 Pu-242 Np-237 Am-241 Am-243 Cm-244

(wt%) 2.2 47.0 23.2 10.7 6.5 5.6 3.1 1.3 0.4

TRU composition (LWR SF, 45-49GWd/t、 4years cooling)

Methods

14

Pin cell calculation for parametric survey Full core calculation for core performance evaluation

Then

Continuous energy Monte-Carlo code MVP-2.0

Burnup calculation code MVP-burn

Nuclear data library JENDL-4.0

Burnup performance

0,95

0,96

0,97

0,98

0,99

1

1,01

1,02

1,03

1,04

1,05

0 20 40 60 80 100 120 140 160

k-in

f

Burnup [GWd/t]

Reference core (SSR) Pu enrichment： 30wt%

Burnup performance

16

0,95

0,96

0,97

0,98

0,99

1

1,01

1,02

1,03

1,04

1,05

0 20 40 60 80 100 120 140 160

k-in

f

Burnup [GWd/t]

Reference core (SSR) Pu enrichment： 30wt%

Cl-37 enriched core Pu enrichment： 27wt%

Modifications: 1.Chlorine composition : Natural → Enriched Cl-37 (to reduce absorption)

Z

18

17

16

Burnup performance

17

0,95

0,96

0,97

0,98

0,99

1

1,01

1,02

1,03

1,04

1,05

0 20 40 60 80 100 120 140 160

k-in

f

Burnup [GWd/t]

Reference core (SSR) Pu enrichment： 30wt%

Cl-37 enriched core Pu enrichment： 27wt%

Cl-37 enriched + Na cooled core Pu enrichment： 15wt%

Modifications: 1.Chlorine composition : Natural → Enriched Cl-37 (to reduce absorption) 2.Coolant material : Fluoride salt → Sodium

(to mitigate spectrum softening)

Z

18

17

16

18

Reference core (SSR) Pu enrichment： 30wt%

Cl-37 enriched core Pu enrichment： 27wt%

Cl-37 enriched + Na cooled core Pu enrichment： 15wt%

Neutron Spectrum and scattering contributers

1,E+10

1,E+11

1,E+12

1,E+13

1,E+14

1,E+15

1,E+16

1,E+01 1,E+02 1,E+03 1,E+04 1,E+05 1,E+06 1,E+07

Neu

tro

n f

lux

[n

eutr

on

/cc/

sec]

エネルギー [eV]

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,E+01 1,E+02 1,E+03 1,E+04 1,E+05 1,E+06 1,E+07

∑s

[a.u

.]

エネルギー [eV]

冷却塩全体

F-19

Na-23

K-39

K-40

K-41

Zr-90

Zr-91

Zr-92

Zr-94

Zr-96

19

1,E+10

1,E+11

1,E+12

1,E+13

1,E+14

1,E+15

1,E+16

1,E+01 1,E+02 1,E+03 1,E+04 1,E+05 1,E+06 1,E+07

Neu

tro

n f

lux

[n

eutr

on

/cc/

sec]

エネルギー [eV]

Reference core (SSR) Pu enrichment： 30wt%

Cl-37 enriched core Pu enrichment： 27wt%

Cl-37 enriched + Na cooled core Pu enrichment： 15wt%

Neutron Spectrum and η (neutron reproduction factor)

(JENDL-4.0)

Performances

20

0,4

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

0

20

40

60

80

100

120

140

160

Reference core(SMSR)

Cl-37 enrichedcore

Cl-37 enriched + Na cooled

core

Co

nve

rsio

n R

atio

Bu

rnu

p [

GW

d/t

]

Burnup[GWd/t]

Conversionratio*

-20

-15

-10

-5

0

5

10

15

20

-100

-80

-60

-40

-20

0

20

40

60

80

100

Reference core(SMSR)

Cl-37 enrichedcore

Cl-37 enriched + Na cooled

core

MA

pro

du

ctio

n [

kg/G

Wt/

y]

Pu

bre

edin

g ga

in [

kg/G

Wt/

y]

Pu breeding[kg/GWt/y]

MA production[kg/GWt/y]

Full core analysis

21

Fuel assemblies (574) Radial blankets assemblies (288) Control rods assemblies (57) SUS shielding (60cm)

Thermal output 3530MWth

Equivalent core diameter 535cm

Core height 154.5cm

Thickness of axial blanket (upper / lower)

45cm / 45cm

No. of fuel assemblies 574

No. of fuel pins/assembly 61

No. of radial blanket assemblies

288 (with 3 layers)

Assembly pitch 21.3cm

Equivalent core diameter 535cm

Thickness of wrapper duct 0.5cm

22

Breeding & burnup performance

Pu enrichment [wt%] Pu enrichment [wt%]

Bre

ed

ing

rati

o (

at B

OC

)

Ach

ieva

ble

bu

rnu

p

(G

Wd

/t)

UCl3/NaCl ratio ○ 100 / 0 △ 70 / 30 × 40 / 60

• UCl3/NaCl ratio in blanket region was parameterized (40%→100%)

• Pu: 30%, UCl3/NaCl: 40% → BR: 0.84, BU: 26GWd/t

• Increase in UCl3/NaCl ratio → Not effective to improve BR

• Reduction in Pu enrichment → Effective to improve BR → But degrading BU

23

Why SSR cannot breed ?

• Fluoride salt causes spectrum dip in critical energy range for breeding

• Cl-35 (76%) in Chloride salt works as parasitic absorber (and produces Cl-36 as long-lived activation products > 4kg/GWt/year)

• Static salt reactor has smaller fuel volume ratio

• Any fuel salt contains less fuel material than solid fuel (per volume)

• Smaller actinide inventory in core means →＊ less fertile → smaller fissile production → less fissile → needs higher enrichment → less fertile＊ → large leakage effect → needs higher enrichment → less fertile＊

Conclusions

• Separated salt (fuel/coolant) type reactor has advantages to limit circulation area of highly activated materials

• However, it shows difficulty in breeding due to less HM inventory with large neutron leakage effect

• If thorium is used for this fast spectrum reactor, worse result estimated

• Combination of “molten salt fuel + liquid metal coolant” required for further consideration

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