10-IEMPT Mito, Japan 1

The 10th OECD/NEA Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation

October 6-10, 2008Mito, Japan

Development of Nitride Fueland Pyrochemical Process for

Transmutation of Minor Actinides

Y. Arai1), M. Akabori1), K. Minato1) and M. Uno2)

1) Japan Atomic Energy Agency (JAEA)2) Osaka University

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Content of Presentation

(1) Introduction of nitride fuel cycle development for transmutation of minor actinides (MA)

(2) Progress of thermal property measurements on nitride fuel• Thermal expansion, thermal conductivity, and so on • MA nitrides and their solid solutions• Burnup simulated nitrides• ZrN or TiN-containing nitrides

(3) Progress of pyrochemical process for treatment of spent nitride fuel• Electrochemical behavior of nitrides in LiCl-KCl melt• Formation of nitrides from electrodeposits in cathode

(4) Summary

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Double-Strata Cycle Concept and Nitride Fuel

Fuel Fabrication

Reprocessing

Repository

LWR/FBR

U, Pu

U, Pu

2nd StrataTransmutation

Cycle

U, PuMA, FP

Short-lived FP

1st StrataCommercial Cycle

MA, FP

• Each fuel cycle pursues safety and economy of the fuel cycle independently.

• Performance of the commercial power-generation fuel cycle is not disturbed by MA.

• Hazardous MA are confined in the dedicated transmutation fuel cycle with a small throughput.

Double-strata fuel cycle concept

Nitride fuel for MA transmutation• High thermal conductivity,

high melting point and high heavy metal density

• Mutual solubility among actinide mononitrides

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R&D Activities on Nitride Fuel and Pyrochemical Process

Flowsheet for MA transmutation fuel cycle

N-15

HLLW from Commercial Fuel Cycle

Partitioning

MA(+Pu) Nitride

Transmuter (ADS)

Spent Fuel

Molten Salt Electrorefining

MA(+Pu) Electrodeposits

Nitride Formation in liq. Cd

N-15

Preparation of MA bearing nitrides by carbothermic reduction

Measurement of thermal properties on MA nitrides and burnup simulated nitrides

Molten salt electrolysis for treatment of spent nitride fuel

Formation of nitrides from electrodeposits in cathode

Irradiation behavior of U-free nitride fuel

N-15 related issues

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Preparation of Nitride Fuel for ADS

Nitride fuel for ADS is a so-called U-free fuel. In this case, MA are contained as a principal component and a diluent material such as ZrN is added in place of U. A composition of nitride fuel proposed by JAEA is (MA0.24Pu0.16Zr0.6)N. There are two routes for preparation of nitride fuel for ADS.

One is the carbothermic reduction of MA oxides partitioned from HLLW, and the other is the nitride formation of MA and Pu recovered in liquid Cd cathode by pyrochemical reprocessing.

1) MA partitioned from HLLW

(MA oxide + carbon) sphere

MA nitride sphere

2) (MA + Pu) in liquid Cd cathode

(MA + Pu) nitride powder

(MA,Pu,Zr)N fuel for ADS ZrN

Sol-gel method

Carbothermic reduction

Nitridation/distillation combined reduction

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Thermal Expansion of MA Nitrides and Their Solid Solutions

• Thermal expansions of MA nitrides and their solid solutions were measured from room temperature to 1478K by high temperature X-ray diffractometry.

• Average thermal expansion coefficients of the solid solutions could be approximated by the linear mixture rule of respective mononitrides.

Ref. M. Takano, et al (2008)

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Heat Capacity of NpN and AmN

• Heat capacities of NpN and AmN were measured from 374 to 1071K by drop calorimetry and compared with literature values for UN and PuN.

• Heat capacities of actinide mononitrides had similar temperature dependence, although that of AmN was slightly smaller than those of UN, NpN and PuN.

Ref. T. Nishi, et al (2008)

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Thermal Conductivity of NpN and AmN

• Thermal diffusivities of NpN and AmN were measured from 473 to 1473K by laser flash method, from which thermal conductivities were derived.

• Thermal conductivities of actinide mononitrides decreased with the atomic number of actinides, although they had similar temperature dependence.

500 1000 15000

5

10

15

20

25

30

NpN

PuN (Arai et al.)

UO2 (Ronchi et al.)

AmN

Ther

mal

con

duct

icvi

ty (W

m-1K

-1)

Temperature (K)

UN (Arai et al.)

500 1000 15000

2

4

6

AmN : on heating : on cooling

: on heating : on cooling

Ther

mal

diff

usiv

ity (1

0-6m

2 s-1)

Temperature (K)

NpN

Ref. T. Nishi, et al (2008)

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Thermal Conductivity of Burnup Simulated Nitrides

200 600 1000 1400 18000

10

20

30

120

150

UN [This work] UN+M o 7.1 m ol% [This work] UN+M o 1.6m ol% [This work] U

0.973N d

0.027N [This work]

U0.878

N d0.122

N [This work]

M o(Handbook) (U,Nd)N+M o (L) [This work] (U,Nd)N+M o (H) [This work]

Therm

al condu

ctivity,

κ 0 (W m

-1 K

-1)

Tem prature, T (K)

• Thermal conductivity of UN+Mo : Almost independent of Mo content• Thermal conductivity of (U,Nd)N : Decrease with Nd content• Thermal conductivity of (U,Nd)N+Mo : Decrease with Nd content but

independent of Mo content

Ref. M. Uno, et al (2007)

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Thermal Conductivity of Nitrides with Diluent Materials

• Thermal conductivity of (U0.4Zr0.6)N : ≅ UN

• Thermal conductivity of 0.4UN+0.6TiN: >UN

Ref. M. Uno, et al (2007)

250 650 1050 1450 18500

10

20

30

40

50

60

70

80

250 650 1050 1450 18500

10

20

30

40

50

60

70

80

UN+TiN [This work] UN+TiN [This work] UN+TiN [Schulz　Eq.]

Therm

al conductivity, κ

0 (W m

-1 K

-1)

U N [This w ork]

U0.4Zr

0.6N [This w ork]

ZrN (100 % T.D.) [Basini] ZrN (70 % T.D .) [Basini] ZrN (89.2 % T.D.) [Hedge]

TiN [literature]

Tem prature, T (K)

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Electrochemical measurement in LiCl-KCl-UCl3: CV and EMFPotential-controlled electrolysis using liquid Cd cathode

UN in UN+Mo and (U,Nd)N: Dissolution in LiCl-KCl at the similar potential as pure UN and recovery of U in liquid Cd cathodeMo in UN+Mo: Remain in anode undissoved NdN in (U,Nd)N: Dissolution but Nd almost stay in the salt phase

Comparison of CV before and after the electrolysis for UN+Mo and (U,Nd)N

Ref. T. Satoh, et al (2007)

Molten Salt Electrolysis of Burnup Simulated Nitrides

(U,Nd)N

Cur

rent

/ m

A UN+Mo

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Molten Salt Electrolysis of Nitrides with Diluent Materials

Electrochemical measurement in LiCl-KCl-UCl3: CV and EMFPotential-controlled electrolysis using liquid Cd cathode

UN in (U,Zr)N: Dissolution in LiCl-KCl at more positive potential (~by 1V) than pure UN and recovery of U in liquid Cd cathode UN in UN+TiN: Dissolution in LiCl-KCl at the similar potential as pure UN and recovery of U in liquid Cd cathode

Comparison of CV before and after the electrolysis for (U0.4Zr0.6)N

-1.2 -0.8 -0.4 0.0 0.4 0.8Potential / V vs. Ag/AgCl

Cur

rent

/ m

A

120

0

-40

40

80(U0.4Zr0.6)N

BeforeAfter

Ref. T. Satoh, et al (2008)

100

50

0

-50

(B)

(A)

UN

(U0.4Zr0.6)NZrN

-1.2 -0.8 -0.4 0.0 0.4 Potential / V vs. Ag/AgCl

Cur

rent

/ m

A

(U0.4Zr0.6)N

Comparison of CV between UN, (U0.4Zr0.6)N and ZrN

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AmN Formation Behavior in Molten Cd

10 20 30(deg.)

Inte

nsity

(arb

. uni

t)

Reference AmN(by carbothermic reduction)

Products of reaction

＊＊

××

××

Am-Cd alloy(Cd+AmCd6)

▼

▼

▼ ▼▼

▼▼▼

▼：Cd□：Am2O3

□ □▼ □ □ ▼

▼

＊：Pt holder×：W holder

2θ

Appearance of AmN powder after heating the product in vacuum at 723K

(1) Electrolysis of AmN in LiCl-KCl-AmCl3 melt with liquid Cd cathode(2) Nitridation/distillation combined reaction of the electrodeposits

in N2 stream at 973K(3) Vacuum heating at 723K for removal of residual Cd

Prepared by carbothermic reduction of AmO2 Prepared by solid-solid reaction of AmN and CdCl2

Constituted by Cd and AmCd6

Ref. H. Hayashi, et al (2008)

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Nitride Pellet Preparation from Pyrochemical Process

(U,Pu)N pellet in Mo crucible before electrolysis

Liquid Cd cathode in Al2O3crucible after electrolysis

U-Pu-Cd in Y2O3 crucible before nitridation/distillation combined reaction

(U,Pu)N powder obtained by nitridation/distillation combined reaction

(U,Pu)N pellet prepared by sintering in flowing Ar-H2atmosphere at 2023K

Single phase of (U,Pu)NDensity: ~84%TDO2 impurity: 0.1~0.2wt%

Ref. Y. Arai, et al (2008)

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For demonstrating technical feasibility of nitride fuel cycle for transmutation of MA, fundamental study has been carried out continuously by use of MA, Pu and burnup simulated nitrides.

Thermal properties, such as thermal expansion, heat capacity and thermal conductivity, of MA nitrides and burnup simulated nitrides have been almost clarified. Measurements on MA nitrides with a diluent material such as ZrN or TiN are ongoing.

As for pyrochemical process for the treatment of spent nitride fuel, molten salt electrolysis and actinide-renitridation process have been investigated. Material balance of actinides throughout the process is to be clarified in a laboratory scale.

Further study shall include the preparation of thermal and thermodynamic database on MA nitride fuel cycle in addition to ongoing experimental study, which will contribute to the progress of design study and evaluation of fuel behavior.

Summary

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Part of this study was carried out within the task “Technological development of a nuclear fuel cycle based on nitride fuel and pyrochemical reprocessing” entrusted from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.

Acknowledgement