Recent achievements and remaining challenges on pyrochemical reprocessing in CRIEPI

Tsuyoshi Murakami, Koichi Uozumi, Yoshiharu Sakamura, Masatoshi Iizuka, Hirokazu Ohta, Takanari Ogata and Tadafumi Koyama

Central Research Institute of Electric Power Industry (CRIEPI)

Parts of this work are the results of “Development and improvement of electrorefining process”and “Development of engineering technology basis for electrometallurgical pyroprocess equipment”, “Application of electrochemical reduction to pyrochemical reprocessing for oxide nuclear fuel”, entrusted to CRIEPI by Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).

Integrated fuel cycle for closing actinide cycle with P&T scenario

U, PuU, Pu

HLLW

Metal fuelFBR Cycle

Spentoxide fuel

MOX, UO2

Reduced fuel

U-Pu, U

ElectrorefiningReductive extraction

Electroreduction

U, Pu, MA

PyropartitioningMA

LWRCycle

Fuel fabricationPUREX

Metal fuel FBRLWR

Enrichment

Fuel fabrication

U

U

U, Pu, MA, Zr

Spent metal fuel

High proliferation resistant

Pyrochemical reprocessing

Molten salts has a higher stability against the radiation than aqueous solvents

Suitable to treat short-cooled and high MA content fuels

Recent developments

Electroreduction

Electrorefining

Pyropartitioning

Postirradiation test of U-Pu-Zr-MA-RE fuel

Summary and remaining challenges

Outline

Recent developments of Electrorefining Process

Electrorefining process

Anode basketSolid cathode Liquid Cd cathode

LiCl-KCl melts 500℃

UU, Pu, MASpent metallic fuel

U3+ U3+ Pu3+

MAn+

Intrinsic proliferation-resistant feature due to inherent difficulty of extracting weapon-usable Pu.

(CRIEPI /JAEA joint program)

Process Optimization for high recovery ratio

Sequential electrorefining test of unirradiated U-Pu

Feasibility demonstration

Electrorefining test of U-Pu-Zr-MA-RE fuel irradiated at Phenix

Ar atmosphere Hot Cell dedicated for pyroprocess installed in JRC-ITU.

(CRIEPI /JRC-ITU joint program)

Material Balances of actinides and FPs

Anode/solid cathode pairLiquid Cd cathode with liquid Cdtransport system

Cd

The feasibility of these electrodes was demonstrated separately.

Engineering-scale equipments development

Recent developments of electroreduction process

Cathode basketPt anode

LiCl-Li2O melts 650℃

Oxide fuelO2 gas

MO2 + 4e- → M + 2O2-2O2- → O2 + 4e-

O2-

Electroreduction process

Total; MO2 → M + O2

LiCl salt bath is suitable for UO2 and MOX reductionHigh reduction rate

High current efficiency

- High Li2O solubility : 12 mol% at 650 0C

- Low Li metal solubility : 0.6 mol% at 650 0C

M; U, Pu

Rate determining step of electroreduction

The transport of O2- is the rate determining step in electroreduction.

The reduction causes a gap formation in the UO2 sample.(Density: UO2 =10.96 g/cm3, U =18.97 g/cm3)

The salt permeates into the gap and the O2- diffuses from the U metal/UO2interface to the bulk salt through the gap.

Porous oxide pellet in large mesh basket

Cathode structure applicable to practical use

UO2 pellets with 30.5% porosity fabricated from U3O8powder simulating voloxidation product.Pellets have channels so that salts easily permeate inside the pellets.

50 μm

Engineering Study: 100 g-scale UO2 Reduction

Cathode basket with 104 g of UO2 pellets

External appearance of cathode basket

Cross section of a reduced UO2 pellet

Electrolysis inLiCl-1wt%Li2O

Current: 15-1 ATime: 9.3 hr

The UO2 pellets were completely reduced within 10 hours

Engineering Study: 100 g-scale UO2 Reduction

Still cylindrical shape

Pretreatment U-Pu-MA,U metal

Electroreduction Electrorefining

Reducing oxide fuel into metal

Decladding by voloxidation and pelletization

Collecting actinide metal free from FPs

Spent oxidefuel

Preparing porous oxide pellet

Pyrochemical Reprocessing Flow for Spent Oxide Fuels

- Oxide reduction rate is enhanced.

-We do not need to handle fine powder in the subsequent processes.

- Reduction products can be easily separated from the cathode basket.

- Volatile FPs such as Cs and Te are separated, which is quite convenient for electroreduction process.

Advantages

Recent developments of pyropartitioning process

Denitration(nitrate oxide)

Salt treatment(FP/salt-Cl2separation)

Reductive-extraction(actinide/FPseparation)

HLLW (nitrate)

Chlorination(oxide chloride)

U, Pu, MA, FPH2O

U, Pu, MAMetal Fuel FBR Cycle

LiCl-KClCl2

FP

FP Waste

NOx

Fig. Steps of pyropartitioning process

FPs: 2000 µg/g

Pyropartitioning

U: 8400 µg/g

TRU: 600 µg/g Np-237: 105 µg/g, Pu-239: 54 µg/g, Am-243 + Cm-243: 66 µg/g

rare-earth: 870 µg/g, alkaline-earth: 290 µg/g, alkaline: 170 µg/g, noble metal: 260 µg/g, Tc-99: 15 µg/g

HLLW contains

Demonstration using genuine HLLW from PUREX

Denitration(nitrate oxide)

Salt treatment(FP/salt-Cl2separation)

Reductive-extraction(actinide/FPseparation)

HLLW (nitrate)

Chlorination(oxide chloride)

U, Pu, MA, FPH2O

U, Pu, MAMetal Fuel FBR Cycle

LiCl-KClCl2

FP

FP Waste

NOx

Air supply

Closed reactor with heater

Empty bottle HNO3

scrubber

NaOHscrubber

500oC

crucible

Gas outletgas outlet

Pyropartitioning (Denitration)

Fig. Steps of pyropartitioning process

Denitration(nitrate oxide)

Salt treatment(FP/salt-Cl2separation)

Reductive-extraction(actinide/FPseparation)

HLLW (nitrate)

Chlorination(oxide chloride)

U, Pu, MA, FPH2O

U, Pu, MAMetal Fuel FBR Cycle

FP

FP Waste

NOx

KOH scrubbers

cold traps

Cl2 monitor

Cl2 gas

Ar hot cell

Pyropartitioning (Chlorination)

Fig. Steps of pyropartitioning process

LiCl-KClCl2

Carbon crucible 650oC

- The mass of the calcinated material (7.32g) almost agreed with theoretical value (6.91g).

- Only 0.2 - 0.3% of Ru was detected in the scrubber solutions.

Chlorination product

- Actinide recovery ratio was 99-113% with respect to initial amount in HLLW.

- No actinide elements evaporated.- The evaporated material contained Mo,

Zr, Sn etc., as expectedly.

Results of denitration and chlorination

Denitration

Chlorination

Ann+ FPn+

An

Li+

Li

Cd-Li

Heater

Molten LiCl-KCl

MgOcrucible

Liquid Cd

in Ar hot cell

Stirrer

500oC

Denitration(nitrate oxide)

Salt treatment(FP/salt-Cl2separation)

Reductive-extraction(actinide/FPseparation)

HLLW (nitrate)

Chlorination(oxide chloride)

U, Pu, MA, FPH2O

U, Pu, MAMetal Fuel FBR Cycle

FP

FP Waste

NOx

Pyropartitioning (Reductive extraction)

Fig. Steps of pyropartitioning process

LiCl-KClCl2

0%

1%

10%

100%

1000%

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Amount of Li reductant added to system(vs necessry to reduce U + TRUs in init ial salt )

Reco

vere

d ra

tio in

Cd

phas

e

UNpPuAmCm

All of TRUs were recovered in Cd.

Results of reductive extraction

Equivalent amount of Li to reduce U + TRU in the initial salt

Rec

over

ed ra

tio in

Cd

phas

e (v

s. in

itial

am

ount

in H

LLW

)

Whole pyropartitioning process (denitration, chlorination, and reductive-extraction) was successfully demonstrated.

No mass loss of TRUs in all steps of pyropartitioning

Postirradiation test of U-Pu-Zr-MA-RE fuel

3 types of test fuel pins285 100 100 10

3 irradiation conditionsBurn-up: 2.5at%, 7at%, 10at%Maximum cladding temperature : 570 oC

Irradiation test of U-Pu-Zr-MA-RE fuel at PHENIX

Pin#1

Pin#2

Pin#3

Bond Na

U-19Pu-10Zr U-19Pu-10Zr

U-19Pu-10Zr

U-19Pu-10Zr-5MA

U-19Pu-10Zr-2MA-2RE

U-19Pu-10Zr-5MA-5REMA: Np, Am, CmRE: Ce, Nd, Y, Gd

1mm Angle=0°

Angle=180°

Angle=90° A

ngle=270°

Postirradiation test of U-Pu-Zr-MA-RE fuel

An example of optical metallography results for U-19Pu-10Zr-5MA-5RE (2.5 at% burnup).

The fuel morphology (microstructure characteristics) as a function of irradiation temperature is similar to that of conventional ternary fuels. The characteristic appearance of MA (and RE) inclusions were observed.

Summary and challengesElectrorefining process

Electroreduction process

Pyropartitioning process

Metal fuel irradiation test

Engineering-scale equipments were developed and their throughput were high enough for practical use.Electrorefining test using irradiated fuels will be carried out to confirm material balance of actinides and FPs.

~100g porous UO2 pellets were successfully reduced to U metal within 10 hours.

It is strongly required to develop an alternative anode material to Pt.

Pyropartitioning process was successfully demonstrated using genuine HLLW.

The postirradiated experiments for the low burnup fuel (~2.5at.%) was started. Quantitative examinations on the redistribution behavior of the fuel constituents and MA transmutation performance will be conducted.

Results : Chlorination-2

Element/Group Evaporated at denitration

Evaporated at chlorination

Chlorination product Total

U 0.0% 0.0% 113% 113%

Np 0.0% 0.0% 109% 109%

Pu 0.0% 0.0% 99% 99%

Am 0.0% 0.0% 113% 113%

Cm 0.0% 0.0% 105% 105%

Tc 0.0% 0.6% 82% 82%

Rare-earth FP 0.0% 0.1% 101% 101%

Alkaline-earth FP 0.0% 1.9% 106% 108%

Transition metal FP(Tc excluded) 0.0% 20.4% 23.7% 44%

Noble metal FP 0.1% 0.0% 128% 128%

Other FP(Sn, Sb, Te. Cd excluded)

0.0% 0.4% 102.0% 104%

Mass balances of elements at denitration and chlorination

Results : Reductive-extraction-1

- TRUs and U were completely removed from salt phase and recovered in Cd.

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

0 5 10 15 20 25 30 35 40 45 50

Amount of Cd-Li alloy added to system(g)

Con

cent

ratio

n in

sal

t (w

eigh

t fra

ctio

n)

U-238 Np-237 Pu-239Am-243 Cm-244 Nd-143Eu-153 Sr-88 Cs-133

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

0 5 10 15 20 25 30 35 40 45 50

Amount of Cd-Li alloy added to system(g)C

once

ntra

tion

in C

d (w

eigh

t fra

ctio

n)

U-238 Np-237 Pu-239Am-243 Cm-244 Nd-143Eu-153 Rh-103C

once

ntra

tion

in s

alt (

wei

ght f

ract

ion)

Con

cent

ratio

n in

Cd

(wei

ght f

ract

ion)

Amount of Cd-Li alloy added to system (g) Amount of Cd-Li alloy added to system (g)

1E- 2

1E- 1

1E+0

1E+1

1E+2

1E+3

1E+4

1E+5

1E- 2 1E- 1 1E+0 1E+1Disribution of U- 238

(= mole fract ion in salt / mole fract ion in Cd)

Dist

ribut

ion o

f nuc

lides

(= m

ole fr

actio

n in

salt/

mole

frac

tion

in C

d)

Np-237 Pu- 239Am-241 Cm-244Ce-140 Nd- 143Np（SF=2.12） Pu（SF=1.88）Am（SF=3.08） Cm（SF=3.93）Ce（SF=49） Nd（SF=45）

Separation behaviors of TRUs and rare-earth FPs vs. U were similar to previous data.

Results of reductive extraction

Distribution of U238 (= mole fraction in salt/mole fraction in Cd)

Dis

tribu

tion

of n

uclid

es (=

mol

e fra

ctio

n in

sal

t/mol

e fra

ctio

n in

Cd)

Procedure to make a porous oxide pellet

3 types of test fuel pins285 100 100 10

Irradiation test of U-Pu-Zr-MA-RE fuel at PHENIX

Pin#1

Pin#2

Pin#3

Bond Na

U-19Pu-10Zr U-19Pu-10Zr

U-19Pu-10Zr

U-19Pu-10Zr-5MA

U-19Pu-10Zr-2MA-2RE

U-19Pu-10Zr-5MA-5REMA: Np, Am, CmRE: Ce, Nd, Y, Gd

Cladding: 15-15Ti austenite steel, 6.55 mm OD.1at% = 10000MWd/t

Fuel smear density = 75%