Recent achievements and remaining challenges on pyrochemical reprocessing in CRIEPI

Transcription

1 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).

2 Integrated fuel cycle for closing actinide cycle with P&T scenario Fuel fabrication Electrorefining Reductive extraction U Enrichment U U, Pu LWR Cycle U, Pu LWR Spent oxide fuel Electroreduction MOX, UO 2 U-Pu, U Reduced fuel Spent metal fuel Metal fuel FBR Metal fuel FBR Cycle U, Pu, MA, Zr U, Pu, MA PUREX HLLW Pyropartitioning MA Fuel fabrication Pyrochemical reprocessing High proliferation resistant Suitable to treat short-cooled and high MA content fuels Molten salts has a higher stability against the radiation than aqueous solvents

3 Outline Recent developments Electrorefining Electroreduction Pyropartitioning Postirradiation test of U-Pu-Zr-MA-RE fuel Summary and remaining challenges

4 Recent developments of Electrorefining Process

5 Electrorefining process Solid cathode Anode basket Liquid Cd cathode U U 3+ U 3+ Pu 3+ MA n+ Spent metallic fuel U, Pu, MA LiCl-KCl melts 500 Intrinsic proliferation-resistant feature due to inherent difficulty of extracting weapon-usable Pu.

6 Feasibility demonstration Sequential electrorefining test of unirradiated U-Pu (CRIEPI /JAEA joint program) Process Optimization for high recovery ratio Electrorefining test of U-Pu-Zr-MA-RE fuel irradiated at Phenix (CRIEPI /JRC-ITU joint program) Material Balances of actinides and FPs Ar atmosphere Hot Cell dedicated for pyroprocess installed in JRC-ITU.

7 Engineering-scale equipments development Cd Anode/solid cathode pair Liquid Cd cathode with liquid Cd transport system The feasibility of these electrodes was demonstrated separately.

8 Recent developments of electroreduction process

9 Electroreduction process Pt anode Cathode basket O 2 gas O 2- Oxide fuel LiCl-Li 2 O melts 650 2O 2- O 2 + 4e - MO 2 + 4e - M + 2O 2- Total; MO 2 M + O 2 M; U, Pu LiCl salt bath is suitable for UO 2 and MOX reduction - High Li 2 O solubility : 12 mol% at C High reduction rate - Low Li metal solubility : 0.6 mol% at C High current efficiency

10 Rate determining step of electroreduction The transport of O 2- is the rate determining step in electroreduction. The reduction causes a gap formation in the UO 2 sample. (Density: UO 2 =10.96 g/cm 3, U =18.97 g/cm 3 ) The salt permeates into the gap and the O 2- diffuses from the U metal/uo 2 interface to the bulk salt through the gap. Cathode structure applicable to practical use Porous oxide pellet in large mesh basket

11 Engineering Study: 100 g-scale UO 2 Reduction 50 μm UO 2 pellets with 30.5% porosity fabricated from U 3 O 8 powder simulating voloxidation product. Pellets have channels so that salts easily permeate inside the pellets.

12 Engineering Study: 100 g-scale UO 2 Reduction Electrolysis in LiCl-1wt%Li 2 O Still cylindrical shape Current: 15-1 A Time: 9.3 hr Cathode basket with 104 g of UO 2 pellets External appearance of cathode basket Cross section of a reduced UO 2 pellet The UO 2 pellets were completely reduced within 10 hours

13 Pyrochemical Reprocessing Flow for Spent Oxide Fuels Preparing porous oxide pellet Spent oxide fuel Pretreatment Decladding by voloxidation and pelletization Electroreduction Reducing oxide fuel into metal Electrorefining Collecting actinide metal free from FPs U-Pu-MA, U metal Advantages - 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.

14 Recent developments of pyropartitioning process

15 Pyropartitioning U, Pu, MA, FP U, Pu, MA Metal Fuel FBR Cycle HLLW (nitrate) Denitration (nitrate oxide) Chlorination (oxide chloride) Reductive-extraction (actinide/fp separation) FP Salt treatment (FP/salt-Cl 2 separation) FP NO x H 2 O LiCl-KCl Cl 2 Waste Fig. Steps of pyropartitioning process Demonstration using genuine HLLW from PUREX HLLW contains U: 8400 µg/g TRU: 600 µg/g Np-237: 105 µg/g, Pu-239: 54 µg/g, Am Cm-243: 66 µg/g FPs: 2000 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

16 Pyropartitioning (Denitration) HLLW (nitrate) U, Pu, MA, FP Denitration (nitrate oxide) NO x H 2 O Chlorination (oxide chloride) LiCl-KCl Cl 2 Air supply gas outlet Gas outlet U, Pu, MA Metal Fuel FBR Cycle Reductive-extraction (actinide/fp separation) FP Salt treatment (FP/salt-Cl 2 separation) FP Waste crucible Closed reactor with heater 500 o C Empty bottle HNO 3 NaOH scrubber scrubber Fig. Steps of pyropartitioning process

17 Pyropartitioning (Chlorination) HLLW (nitrate) U, Pu, MA, FP Denitration (nitrate oxide) NO x H 2 O Chlorination (oxide chloride) LiCl-KCl Cl 2 Cl 2 gas U, Pu, MA Metal Fuel FBR Cycle Reductive-extraction (actinide/fp separation) FP Salt treatment (FP/salt-Cl 2 separation) Ar hot cell cold traps Carbon crucible 650 o C Cl 2 monitor FP Waste Fig. Steps of pyropartitioning process KOH scrubbers

18 Results of denitration and chlorination Denitration - The mass of the calcinated material (7.32g) almost agreed with theoretical value (6.91g). - Only % of Ru was detected in the scrubber solutions. Chlorination - Actinide recovery ratio was % with respect to initial amount in HLLW. - No actinide elements evaporated. - The evaporated material contained Mo, Zr, Sn etc., as expectedly. Chlorination product

19 Pyropartitioning (Reductive extraction) HLLW (nitrate) U, Pu, MA, FP Denitration (nitrate oxide) Chlorination (oxide chloride) NO x H 2 O LiCl-KCl Cl 2 in Ar hot cell Cd-Li Molten LiCl-KCl U, Pu, MA Metal Fuel FBR Cycle Reductive-extraction (actinide/fp separation) FP Salt treatment (FP/salt-Cl 2 separation) FP Waste Fig. Steps of pyropartitioning process Liquid Cd An n+ FP n+ An Li + Li MgO crucible Stirrer Heater 500 o C

20 Results of reductive extraction 1000% Recovered ratio in Cd phase Recovered rat io in Cd phase (vs. initial amount in HLLW) 100% 10% 1% U Np Pu Am Cm 0% Equivalent Amount of amount Li reductant of added Li tto o system reduce U + TRU (vs necessry in the tinitial o reduce salt U + TRUs in init ial salt ) All of TRUs were recovered in Cd. No mass loss of TRUs in all steps of pyropartitioning Whole pyropartitioning process (denitration, chlorination, and reductive-extraction) was successfully demonstrated.

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

22 Irradiation test of U-Pu-Zr-MA-RE fuel at PHENIX 3 types of test fuel pins Pin#1 U-19Pu-10Zr Bond Na Pin#2 U-19Pu-10Zr-2MA-2RE Pin#3 U-19Pu-10Zr U-19Pu-10Zr MA: Np, Am, Cm RE: Ce, Nd, Y, Gd U-19Pu-10Zr-5MA U-19Pu-10Zr-5MA-5RE 3 irradiation conditions Burn-up: 2.5at%, 7at%, 10at% Maximum cladding temperature : 570 o C

23 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). Angle=180 Angle=90 Angle=270 1mm Angle=0 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.

24 Summary and challenges Electrorefining process 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. Electroreduction process ~100g porous UO 2 pellets were successfully reduced to U metal within 10 hours. It is strongly required to develop an alternative anode material to Pt. Pyropartitioning process Pyropartitioning process was successfully demonstrated using genuine HLLW. Metal fuel irradiation test 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.

25

26 Results : Chlorination-2 Mass balances of elements at denitration and chlorination 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%

27 Results : Reductive-extraction-1 Concentration in salt (weight fraction) fraction) 1E-1 1E-2 1E-3 1E-4 1E-5 1E-6 U-238 Np-237 Pu-239 Am-243 Cm-244 Nd-143 Eu-153 Sr-88 Cs Concentration in Cd (weight fraction) fraction) 1E-2 1E-3 1E-4 1E-5 1E-6 1E-7 1E-8 1E-9 U-238 Np-237 Pu-239 Am-243 Cm-244 Nd-143 Eu-153 Rh Amount Amount of Cd-Li of alloy added to system(g) to system (g) Amount of of Cd-Li alloy added added to system(g) to system (g) - TRUs and U were completely removed from salt phase and recovered in Cd.

28 Results of reductive extraction Distribution of nuclides (= mole fraction in salt/mole fraction in Cd) Distribut ion of nuclides (= mole fraction in salt / mole fract ion in Cd) 1E+5 1E+4 1E+3 1E+2 1E+1 1E+0 1E- 1 Np- 237 Pu- 239 Am- 241 Cm- 244 Ce-140 Nd- 143 Np(SF=2.12) Pu(SF=1.88) Am(SF=3.08) Cm(SF=3.93) Ce(SF=49) Nd(SF=45) 1E- 2 1E- 2 1E- 1 1E+0 1E+1 Disribution of U- 238 (= mole fract ion in salt / mole fract ion in Cd) Distribution of U238 (= mole fraction in salt/mole fraction in Cd) Separation behaviors of TRUs and rare-earth FPs vs. U were similar to previous data.

29 Procedure to make a porous oxide pellet

30 Irradiation test of U-Pu-Zr-MA-RE fuel at PHENIX 3 types of test fuel pins Pin#1 Pin#2 U-19Pu-10Zr Bond Na U-19Pu-10Zr-2MA-2RE Pin#3 MA: Np, Am, Cm RE: Ce, Nd, Y, Gd U-19Pu-10Zr U-19Pu-10Zr-5MA U-19Pu-10Zr-5MA-5RE U-19Pu-10Zr Fuel smear density = 75% Cladding: 15-15Ti austenite steel, 6.55 mm OD. 1at% = 10000MWd/t

31