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).
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Recent achievements and remaining challenges on pyrochemical reprocessing in CRIEPI
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.
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.