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Seminari didattici del ciclo « Historia Magistra Vitae »
Seminario su Rifiuti urbani e radioattivi: tecniche innovative di trattamento
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