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Trattamenti pirometallurgici per lo spent fuel Dr. Giorgio De Angelis – ENEA ENEA, Sede Centrale, 6 Luglio 2017

Processi idrometallurgici: il processo PUREX

Diagramma di flusso del riprocessamento pirometallurgico del combustibile metallico

Processi pirometallurgici: trattamento del combustibile metallico

Schema di cella elettrolitica per l’elettroraffinazione di PuN;

Pasticca di PuN nel cestello forato di molibdeno prima dell’elettrolisi

Elettroriduzione del combustibile a nitruro

Esperienze sono state condotte in scala laboratorio per dimostrare la fattibilità del processo, utilizzando nitruri di uranio, nettunio e plutonio. A seguito del passaggio di corrente, all’elettrodo anodico si verifica la seguente reazione:

AN A3+ + 3e- + ½ N2, dove A sta per U, Np, o Pu.

Al catodo, tenendo conto che l’elettrodo Ag/AgCl viene usato come elettrodo di riferimento, la reazione complessiva è:

AN + 3AgCl ACl3 + ½ N2 + 3Ag

Processi pirometallurgici: trattamento del combustibile a nitruro

Elettroriduzione del combustibile ad ossido

Processi pirometallurgici: trattamento del combustibile ad ossido (metodo americano)

Sequenza di operazioni per il riprocessamento elettrolitico di combustibile UO2 e PuO2

Processi pirometallurgici: trattamento del combustibile ad ossido (metodo russo)

Pin

Casting

Melting

Consolidation Immobilization

Crucible Mold

Crucible

Salt Waste (Cs, Sr, RE) Metal Waste

Duct Clad, NM

Disassembly

and

Chopping

TRU

Spent

Salt

New

Fuel

Gas waste, (T, Xe, Kr) Spent

Fuel

Zr

Salt, Cd

U - salt

U – TRU

- Cd - salt

Cathode

Processing

Electrorefining

TRU

Extraction

TRU: Pu, Np, Am, Cm

RE: Rare Earth

NM: Noble Metal

Pyroprocessing of metal fuel: general flow-sheet

U, Pu, MA, AL,

ALE, RE

U, Pu, MA, RE, Zr,

NM

LiCl-KCl-U/PuCl3

Bi pool

Ar atm

U

Spent

Fuel

U, Pu, MA

FP Gas

(Kr, Xe)

Solid iron

cathode

Bi cathode

Power

supply

Power

supply

Bi cathode

Pyroprocessing of metal fuel: electrorefining step

Vantaggi della PIROMETALLURGIA

• radiation stability of molten salts

(allowing processing of spent fuels of high radioactivity);

• absence of neutron moderator such as water;

• low waste production;

• non-proliferation requirements.

Processi pirometallurgici

Pyrel III pilot plant

Main body of Pyrel III pilot plant

Heating system of Pyrel III plant

Components of Pyrel III plant

Strip heater of Pyrel III plant

Components of Pyrel III plant

Zirconia crucible, cover and guide-tubes

Components of Pyrel III plant

Crane used for insertion of flange and guide-tubes

Components of Pyrel III plant

Components of Pyrel III plant

Manometers, vacuum pump, and posting box

Direct transportation from FDB to SSC

Electrorefining experiments

La La La3+

LiCl-KCl

Ar

Bi

La3+

La3+

Galvanostat (left) and screen (right)

Electrorefining experiments

Trend of temperatures before, during, and after an experimental campaign

Electrorefining experiments

Typical trend of the potentials recorded during an experiment of direct transportation of Lanthanum from FDB to SSC (Ecell: cell potential; Ea: anode potential; Ec: cathode potential)

Electrorefining experiments

Cathode deposit after an experiment with lanthanum metal

Electrorefining experiments

Solid cathode with deposit at the end of an experiment (left); detail at the stereomicroscopy of the cathode deposit, showing high porosity (right)

Electrorefining experiments

FDB before (left) and after (right) experimental campaigns

Electrorefining experiments

Gas Trapping System

Improvements to Pyrel III: Gas Trapping System

Venturi tube

Trap (left) inside the steel shroud as seen from the top (middle) and from the bottom (right)

Improvements to Pyrel III: Gas Trapping System

Detection of chlorine and carbon anidride (top), and nitrogen (bottom) generated by pyro experiments and transferred outside the glove-box through GTS

Improvements to Pyrel III: Gas Trapping System

Conditioning of molten salts

• Sodalite (aluminosilicate containing chlorine, )

• SAP (xSiO2 – yAl2O3 – zP2O5)

SODALITE synthesis from Zeolite 4A

Zeolite 4A

Na12(AlSiO4)12 . nH2O

Sodalite

SODALITE synthesis from Zeolite 4A: INL Process

Beds of zeolite pellets in series for the cleanup of spent salts

Al2Si2O7 . 2H2O --- NaOH

NaAlSiO4

LiCl-KCl

Melting

Freezing

Crushing

Simulated Waste Salt NaAlSiO4

Mixing

Pressing

Ar glove-box

Air

773 K

room temp.

Heating

Mixing

Nepheline

Kaolinite

SODALITE synthesis from kaolinite

Heating

Green pellet

Synthesized sodalite

pellet (13 mm F)

Crushing

Surface

analyses

Structural

analyses

Leach

tests

Air

Ar glove-box

1.073 K

SODALITE synthesis from kaolinite

SODALITE synthesis from kaolinite

Reference composition of chloride salt wastes

Percentage of components in the mix

SODALITE synthesis from kaolinite

Argon-atmosphere glove-box

Oven with graphite crucible inside the glove-box

SODALITE synthesis from kaolinite

700°C

700°C Synthesis of NEPHELINE

Kaolinite

+ NaOH

SODALITE synthesis from kaolinite

Mixing and grinding of Nepheline with LiCl-KCl

SODALITE synthesis from kaolinite

Preparation of pellets

molten salt – nepheline (F 13 mm)

SODALITE synthesis

SODALITE synthesis

XRD of SODALITE synthesized from NEPHELINE

NS-100

NE

NS-100

NE

FTIR of SODALITE synthesized from NEPHELINE

SODALITE synthesis

SAP synthesis

SAP synthesis

SAP synthesis

SAP matrix

SAP matrix

Leach tests on SAP samples

ENEA activities on Pyroprocessing

• PYROREP, EUROPART, ACSEPT, SACSESS European Programmes (V, VI, and VII FP)

• National programme «Ricerca di Sistema Elettrico», financed by Economical Development Ministry

• NEA/OECD Working Group on Separation Chemistry