Out-of-pile thermophysicalproperties of metallic fuel for fast reactors in India

Transcription

1 Out-of-pile thermophysicalproperties of metallic fuel for fast reactors in India JoydiptaBanerjee a$,santukaity a,k.ravi a,m.r.nair a,m.t.saify b, RajeevKeswani c,arunkumar d,g.j.prasad d a RadiometallurgyDivision, b AtomicFuelsDivision, c MetallicFuelsDivision, d NuclearFuelsGroup, Bhabha Atomic Research Centre(BARC), INDIA $ -joydipta@barc.gov.in

2 Background Metallic fuel designs under consideration for fast reactors Objectives of present study Experimental Details of instruments used and experimental parameters Results Various thermophysical properties Chemical compatibility studies Summary Outline

3 Background India has vast thorium reserves but modest uranium reserves Once-through fuel cycle cannot sustain India s Nuclear Power Program. Hence Closed fuel cycle option chosen for long term energy security Fastreactorstoplaysignificantroleatthesecondstage of Indian three stage nuclear power program. For speedy expansion of second stage, Metallic fuels, with high breeding ratio, are considered for future fast reactors in India.

4 Background (contd.) Metallic Fuel designs Primarily, two design concepts being considered for the metallic fuel development programme in India:- Sodium bonded pin with U-15 wt%pu-6 wt%zr alloy as fuel Mechanically bonded pin with U-15 wt%pu alloy as fuel, T91 T91 Na U-Pu-Zr U-Pu-Zr Zr U-Pu Sodium bonded U-Pu-Zr (~10%) ternary with T91 cladding [Conventional] Na Sodium bonded U-Pu-Zr(~6%) ternary with/without Zr linedt91 Mechanically bonded U-Pu ( < 15%) binary with T91

5 Objectives Out-of-pile characterisation of U-6wt%Zr and U-15wt%Pu alloy in terms of the followings:- XRD, Microstructures, Coefficient of thermal expansion, Specific heat, Thermal conductivity. Phase transformation studies, Hot-hardness Chemical compatibility studies with cladding material (T91 grade steel) by diffusion couple experiments.

6 Experimental Alloypreparation U-15Pu alloy was prepared by melting and casting route. U-6Zr alloy sample was prepared by injection casting route. XRD and Microstructural analysis The phase analysis of the fuel alloy was carried out using XRD with Cu Kαradiation. Thermal conductivity Thermal conductivity of U-6Zr alloy was determined by Transient Plane Source (TPS) technique upto973 K in argon. Specific heat Specific heat measurements were carried out using a heat flux type differential scanning calorimeter. Phase transformation studies The transformation temperature measurements were carried out using a differential thermal analyzer Dilatometry The expansion behavior of U-6Zr was studied using a high temperature vertical dilatometer under high purity argon atomsphere. Hot hardness Hot hardness measurements were carried out using a hot hardness tester with the help of a diamond Vickers pyramid indenter. Chemical compatibility with T91 cladding material For the diffusion couple experiment, a thin Zrfoil of thickness 100 µm was sandwiched between the alloy (3 mm thick disc) and T91 discs (0.5 mm thick disc).

7 Results XRD U-6Zr (021) (002) (111) U-15Pu (132) (131) (023) Intensity (a.u) (110) (112) θ (degree) Both show Single phase structure corresponding to α uranium No δ phase for U-6Zr / ζ phase for U-15Pu could be detected

8 Results (contd.) Microstructure U-6Zr U-6Zr Microstructure of U-6Zr alloy (a) As-cast: showing Widmanstatten morphology; (b) Water quenched from 1173 K: showing martensitic plates and prior γ grain boundaries(indicated by arrows).

9 Results (contd.) Microstructure U-15Pu Microstructure of as-cast U-15Pu alloy.

10 U-Zr Phase diagram (γ β + γ") (β α + γ") K (662 ºC) corresponds to eutectoid reaction: (β α + γ ) 968 K (693 ºC) corresponds to monotectoid reaction : (γ β + γ")

11 Results (contd.) Phase transformation (U-6Zr) martensiticto non-martensitic solidus (β α + γ") (γ β + γ") The peak at 843 K corresponds to martensitic to non-martensitic transformation (various heat treatments to support, is shown in Fig. b) The peaks observed at 943 K and 968 K corresponds to eutectoid reaction (β α + γ") and monotectoidreaction (γ β + γ") respectively. The peak at 1448 K indicates the solidus temperature.

12 Results (contd.) Solidus temperature βu (εpu, γu) αu βu For U-15wt%Pu composition:- 833 K (560 ºC) corresponds to : α(u) β(u) transition. 991 K (718 ºC) corresponds to : β(u) (εpu, γu) transition K (975 ºC) corresponds to: solidus temperature.

13 Heat flow (µv) αu βu 837 K 991 K (a) βu (εpu, γu) Results (contd.) Phase transformation (U-15Pu) Solidus temperature 1248 K Temperature (K) Temperature (K) DTAcurveofascastU-15Pualloyshowing: (a) Different phase transformation temperatures(fig(a)) The peak observed at 837 K corresponds to αu βuand The peak at 991 K corresponds to the β(u) (εpu, γu) transition. The peak at 1248 K corresponds to solidus. Heat Flow (µv) (b) Eutectic reaction temperature 948 K between the alloy and T91 grade steel. (Same at 995 K between U-6Zr and T91 is superimposed in Fig (b)) U-6Zr U-15Pu (b) 948 K 995 K U-6Zr/T91 U-15Pu/T91 Addition of Pu decreases eutectic temperatureby~50k

14 Results (contd.) Thermal Expansion U-6Zr (γ β + γ") (β α + γ") U-15Pu βu (εpu, γu) αu βu Thermal expansion curve obtained from the dilatometer for (a) U-6Zr and (b) U-15Pu alloy. The slope changes corresponds to phase transformations as observed in DTA. The average coefficient of thermal expansion ( K) : U-6Zr :18.28 x 10-6 K -1 U-15Pu:18.58 x 10-6 K -1

15 Results (contd.) Specific Heat Zr U U-6Zr U-6Zr U (a)specific heat data for U-6Zr alloy obtained as a function of temperature; Specific heat of U-6Zr alloy determined by additive methodandliteraturedataofu,zrarealsoshown. (b)thermal conductivity data of U and U-6Zr alloy obtained as a function of temperature together with literature data of U and U-Zr alloys.

16 Results (contd.) Hot Hardness U-6Zr U-15Pu (b) Hardness versus temperature plot for (a) U-Zr alloy, showing the transition point and (b) U-15Pu alloy, showing phase dependant hardness variation

17 Results (contd.) Hot Hardness U-15Pu T91 U-15Pu Hardness versus temperature plot for U-15Pu alloy, showing fuel is softer than T91 cladding at reactor operating temperature. Hence,claddamagewouldbeverylessincaseofPCMI.

18 Chemical compatibility capsules Fig. (a) Photograph of quartz encapsulated stainless steel tube containing diffusion couple-fixture assembly with Inconel 600 fixture shown in the inset Fig. (b) Schematic of the diffusion couple-fixture assembly used showing the details. (b)

19 Results (contd.) Chemical Compatibility SEM images obtained for(a) the inter-diffusion layer formed at the interface of U-6Zr/T91 couple after annealing at 973 K for 500 h,(b) Magnified micrograph of the interface, showing formation of the various layers and (c) the melted structure of U-6Zr/T91 diffusion couple after annealing at 1023 K for 100 h.

20 Results (contd.) Chemical Compatibility Microstructure of (a)u-15pu/zr/t91 diffusion couple annealed at 973 K for 500 h, (b)magnified view of the U-15Pu/Zrinterface and (c)magnified view of the Zr/T91 interface.

21 Summary Metallicfuelwithdesignsbasedona)sodiumbonded ternary and b) mechanical bonded binary fuel are being considered for future fast reactors in India. Work has been initiated encompassing various aspects e.g. fabrication of the sodium/ mechanical bonded fuel pin, studies on out-of-pile thermo-physical and thermodynamics properties of fuel alloys, fuel-clad chemical compatibility etc. Laboratory scale fabrication of U-15Pu and U-15Pu- 6Zr has been carried out and test irradiation is planned. This presentation shared the experience on the evaluationof thermophysical properties and fuel-clad chemical compatibility studies for U-6Zr and U-15Pu, at BARC, INDIA.

22 Thank you for your kind attention

23 Background (contd.) Indian three stage nuclear power program I II Pu, Dep. U III 233 U, Th Dep.U Nat.U PHWR Pu FBR 233 U Th- 233 U breeder Reactor Energy Thas radial blanket Th Three stage nuclear power program was conceptualized for judicious utilization of vast thorium reserves in India

24 Background (contd.) Indian 1 st Fast reactor fuel choices:- FastBreederTestReactor(FBTR)fuelwasinitiallybasedonfuelof Rapsodie, France e.g. 70%UO 2 (85% enrichedu)-30%puo 2 Unavailability of imported (enriched) U led to the consideration of plutoniumenrichedmixedoxidefuele.g.76%puo 2-24%UO 2. This fuel was not pursued further due to chemical compatibility issues with sodium coolant& cladding material Third choice was indigenous development of high Pu- (natural) U mixed carbide fuel. e.g. MarkIfuel :(U 0.30 Pu 0.70 )C and MarkIIfuel:(U 0.45,Pu 0.55 )C.

25 Fuel Merits Challenges Carbide High Density High Thermal Conductivity Proven operation exceeding 16 at.% burn up (FBTR, India) Oxide Large scale fabrication and irradiation experience worldwide Proven high burn up (~20 at.%) Verylow PCMI/ high creep High melting point Good chemical compatibility with clad & coolant Metal (U-Pu/ U-Pu-Zr) Background (contd.) High density & thermal conductivity High breeding ratio/ low doubling time No radiotoxic dust hazard (fabrication by melting-casting route) Amenable to remotization/ automation Integrated fuel cycle (proliferation resistant Pyrophoric Radiotoxic dust hazard Difficulty in fabrication conforming to stringent specification tolerance Radiotoxic dust hazard due to P/M route of fabrication For PuO 2 rich mixed oxide fuel :- Difficult to dissolve in HNO 3 Compatibility issues with Na coolant High oxygen potential (high noble FP) & Poor thermal conductivity Low melting point High swelling FCCI Generation of αcontaminated Na waste during pin bonding Large scale demonstration lacking of fabrication/pyroprocessing technology Metallic fuels are considered for future fast reactors in India for its high breeding ratio (speedy expansion of second stage)