High Temperature Zr Cladding Oxidation, Hydriding and Embrittlement

Transcription

1 Nuclear Safety Institute Russian Academy of Science High Temperature Zr Cladding Oxidation, Hydriding and Embrittlement Presented by Mikhail S. VESHCHUNOV Nuclear Safety Institute (IBRAE) Russian Academy of Sciences Workshop on Fuel Safety, Safety Criteria and Changes in Fuel Design Characteristics During Operation Islamabad, Pakistan December 2013

2 Outline: Introduction: Mechanistic Code SFPR for Modelling Single Fuel Rod Performance under Various Regimes of LWR Operation, including Design Basis and Severe Accidents High Temperature Zr Cladding Oxidation High Temperature Zr Cladding Hydriding High Temperature Zr Cladding Embrittlement Zr Cladding Embrittlement under LOCA Conditions SFPR Code: Development Plan 2

3 Introduction: Mechanistic Code SFPR for Modelling Single Fuel Rod Performance under Various Regimes of LWR Operation, including Design Basis and Severe Accidents 3

4 SFPR code Single Fuel Rod Performance SVECHA code Mechanistic modeling thermomechanical and physicochemical behavior of a single LWR fuel rod Initially designed for SA regimes, extended to normal operation conditions Collaboration of IBRAE with IRSN (France), FZK (Germany) JRC/IE, US NRC. MFPR code Mechanistic modeling fission product release from irradiated UO 2 fuel Various regimes of reactor operation, including severe accidents (SA), and high burnups Collaboration of IBRAE with IRSN (France). 4 4

5 Single-Rod Code SVECHA Development and Assessment Objectives advanced mechanistic models for oxidation, hydriding and chemical interactions of LWR fuel rod materials and thermomechanical deformations of cladding and pellet, tightly coupled within the code initially designed for modeling single-rod tests Development Validation IBRAE with support of FZK, IRSN and JRC/IE in the framework of European projects: 4th FP (COBE & CIT Projects), 5th FP (COLOSS); ISTC Projects #1648 & #2936, bi-lateral projects QUENCH Rig (FZK: COBE & CIT), BOX Rig (FZK: COLOSS), AEKI Rod Degradation (COLOSS), QUENCH Bundle (FZK: ISTC), Phebus FPT0 and FPT1 interpretation (JRC/IE: SARNET) Applications after verification and subsequent simplification, specific separateeffect models were implemented in integral codes: ICARE2 (collaboration IRSN), SCDAP/RELAP (collaboration US NRC), SOCRAT (collaboration ATOMENERGOPROECT and ROSATOM) 5

6 Single Rod Code SVECHA Important features: Mechanistic simulation of clad multi-layered structure + core degradation (eutectic interactions, molten pool formation, oxidation and relocation, etc.) Initially designed for SA, the code inherited the mechanistic approach in application to normal operation conditions Coolant flow: H 2 O(l), H 2 O(g), O 2, Ar, H 2 Vertical Mesh Pellet Gap α-zr(o) Zr Cladding ZrO 2 6

7 High Temperature Zr Cladding Oxidation 7

8 Cladding Oxidation Kinetics ANL oxidation tests train assembly (from Yan et al., JNM, 2009) 8

9 Cladding Oxidation Kinetics Oxidation of Zry 4 alloy at temperatures of C: a) 700 C; b) 800 C; c) 900 C; d) 950 C 9

10 Cladding Oxidation Kinetics Post transition Oxidation of Zry 4 alloy at temperatures of C: a) 1000 C; b) 1050 C; c) 1100 C; d) 1200 C 10

11 Cladding Oxidation Kinetics Post transition oxidation (break away effect) Appearance of E110 alloy after steam oxidation for: a) 5s at 1000 C; b) 290s at 950 C; c) 400s at 1000 C 11

12 Cladding Oxidation Kinetics G K t 1/ n Oxidation rate exponent of Zr alloys with temperature (Baek eta., KAERI, JNM 335 (2004) 443) 12

13 Cladding Oxidation Kinetics L ox K ox t 1/ 2 Parabolic ZrO 2 scale growth according to literature sources 13

14 Cladding Oxidation Kinetics G ox K T t 1/ 2 Comparison of mass gain rates 14

15 Cladding Oxidation Kinetics Parabolic correlations G ox K T t 1/ 2 K A exp Q RT 15

16 Cladding Oxidation Model Simulates kinetics of fuel cladding oxidation and physicochemical interactions with fuel pellet (UO 2 /Zr/steam) Based on numerical treatment of oxygen diffusion through multi layered structure of the interaction system up to 7 layers Best estimate diffusion coefficients for ZrO 2, Zr(O) and Zr forzry 4 and Zr1%Nb (E110) Tightly coupled with cladding thermo mechanical module 16

17 Cladding Oxidation Model ci t v i ci ( r, t) r 1 ci rdi ( r, t) r r r Diffusion equation dr c c (1) (2) i i1 i (1) (1) (2) (2) ( ci ci 1) Di 1 Di ci vi ci 1vi 1 dt r r r r r r dr dt ( ) i (1) (2) i i 1 ivi i 1vi1 i i Flux matches BETA ALPHA OXIDE C C g C C C / r r r r 17

18 Cladding Oxidation Model Microstructural changes of Zry 4 during oxidation 18

19 Cladding Oxidation Model Boundary conditions Binary phase diagram Zr O, assessed in (Abriate et al., 1986) 19

20 1e-4 Cladding Oxidation Model Oxygen diffusion coefficient in oxide T,C D f,cm 2 /s 1e-5 - Zry-4 calc. from [6] 1e-6 - Zry-4 calc. from [7] by metallography - Zry-4 calc. from [7] by weight gain - Zr-1%Nb present work 5,4 5,8 6,2 6,6 7,0 7,4 7,8 8, /T, [K -1 ] Calculated oxygen diffusion coefficients in ZrO 2 for Zr1%Nb и Zircaloy 4 20

21 Cladding Oxidation Model Oxygen diffusion coefficient in alpha phase T,C e-6 D a,cm 2 /s 1e-7 1e-8 - Zry-4 calc. from [6] - Zry-4 calc. from [7] by metallography - Zry-4 calc. from [7] by weight gain - Zr-1%Nb present work 5,4 5,8 6,2 6,6 7,0 7,4 7,8 8, /T, [K -1 ] Calculated oxygen diffusion coefficients in Zr for Zr1%Nb и Zircaloy 4 21

22 Cladding Oxidation Model Isothermal conditions Analysis of KfK tests with Zry 4 ZrO 2 thickness (mm) Temperature : 1273 K 1373 K 1473 K 1573 K 1673 K 1773 K 1823 K 1873 K S. Leistikow, G. Schanz (KfK, 1978) Time (min) Calculation results for oxide thickness (solid lines) in comparison with experimental results (dashed lines) 22

23 Cladding Oxidation Model Isothermal conditions Analysis of RIAR tests with Zr 1%Nb Thickness of layers, m Zr(O), calc. T=1000 o C - -Zr(O), exper. - ZrO 2, calc. - ZrO 2, exper Time, s Thickness of layers, m T=1100 o C - -Zr(O), calc. - -Zr(O), exper. - ZrO 2, calc. - ZrO 2, exper Time, s Simulation of the Zr and ZrO 2 layers growth kinetics in the RIAR isothermal tests on Zr 1%Nb cladding oxidation in steam at 1000 and 1100ºC 23

24 Cladding Oxidation Model Isothermal conditions Analysis of RIAR tests with Zr 1%Nb T=1200 o C 35 T=1200 o C 35 Thickness of layers, m Zr(O), calc. - -Zr(O), exper. - ZrO 2, calc. - ZrO 2, exper. Weight gain, mg/cm Wt., calc. - Wt., exper Time, s Time, s Simulation of the Zr and ZrO 2 layers growth and weight gain kinetics in the RIAR isothermal tests on Zr 1%Nb cladding oxidation in steam at 1200ºC 24

25 Validation of Oxidation Model against transient oxidation tests Temperature, K FZK tests (P. Hofmann) 1000 Oxide thickness (m) Time, s 2,50E-04 2,00E-04 1,50E-04 1,00E-04 5,00E-05 modified standard exp Thickness, micrometer Temp. rate 0.25 K/s 1 K/s 5 K/s 10 K/s 0,00E Time (s) Temperature, K Conclusion: being developed on the base of steady-state isothermal oxidation tests, the model demonstrates good agreement with transient tests data owing to: mechanistic approach (diffusion equations, D(T(t)) ); coupling with Mechanical Deformation model (influence of oxide microcracking) 25

26 1E+020 Oxidation kinetics under steam starved conditions OXYGENFLUX 8E+019 6E+019 4E+019 Oxygen flux Boundary conditions 2E t, s TIME ZrO 2 -Zr -Zr Evolution of layer structure Mole fraction of water in H 2 O-H 2 gas mixtures in equilibrium with hypostoichiometric ZrO 2 (from Olander, 1994) 26

27 High Temperature Zr Cladding Hydriding 27

28 Zr H Equilibrium Phase Diagram 28

29 Hydrogen solubility in Zr Sieverts law Sieverts constant 29

30 Hydrogen solubility in Zr Experimental studies M. Steinbrueck (FZK, 2004) 30

31 Gaseous Hydriding Model Zr H 2 interaction kinetics Dissolution of hydrogen in Zr metal as neutral atoms: H 2 H 2 (g) = 2H ab (m) Zr Sieverts law: C Hydrogen transport: 2k H 2 D P H H 2 b C r H S P H P 2 tot H s P s P tot H 2 s K S P 1/ 2 H 2 s P H2 P H2 (s) P H2 (b) 2 Thin Zr layer: D L DH texp t = 0 L dc 2 kh C 2 H PH b 2 2 RT K H 2 dt S Zr (metal) H 2 (gas) r 31

32 Model Verification FZK tests on hydrogen uptake by Zry-4 cladding in H 2 atmosphere (M. Steinbrueck, 2004) Mass gain, mg H 2 on H 2 off - exper. - calcul. Temp Temperature, o C Mass gain, mg bar 0.2 bar Temp. - exp. - calc. 0.6 bar 0.2 bar Temperature, o C Time, s Time, s P H2 = 0/0.5 bar P H2 = 0.2/0.6 bar Uptake: C H t K S P 1/ 2 b 1 exp H2 1 exp 2t 2t Release: C H t C H,0 1 t 1 32

33 Hydrogen solubility in ZrO 2 Experimental studies Park and Olander, 1991: gaseous H 2 hydriding of ZrO 2 Conditions: T= C, P H2 10 bar Interpretation: H 2 (g) = 2H(ox) [H] P H2 1/2 Sieverts law (in agreement with observations) Results: H solubility: [H] 10-5, H mobility: 0 (strong trapping) Conclusion: ZrO 2 is impermeable for neutral H Wagner, 1968: H 2 O dissolution in Yt-stabilized ZrO 2 Conditions: T=900, 1000C, P H2O 10-2 bar Interpretation: H 2 O(g)+V O 2+ = 2H i + (ox) + O(ox) [H i+ ] P H2O 1/2 ; (in agreement with observations) Results: H solubility: [H i+ ]10-5, (P H P H2 (Park & Olander)!) H mobility: D H cm 2 /s. Conclusion: ZrO 2 is permeable for protons H + ZrO 2 ZrO 2 H 2 H 2 O Fundamentally different dissolution mechanisms (neutral H / protons H + ) 33

34 Hydrogen uptake model (1/2) Dissociation of water molecules in the gas phase: 2H 2 O(g) = O 2 (g) + 2H 2 (g) (1) Dissolution of oxygen in oxide: O 2 (g) + 2V O e - (ox/g) = 2O O (ox) (2) Dissolution of hydrogen in oxide as neutral atoms: H 2 (g) = 2H ab (ox) (3) Dissolution of hydrogen in oxide as protons: H 2 (g) = 2H ab+ (ox) + 2e - (ox/g) (4) Eq. (3) corresponds to Park & Olander s mechanism: gaseous H 2 hydriding of ZrO 2 : H 2 (g) = 2H ab (ox) Superposition of (1), (2) and (4) corresponds to Wagner s mechanism: dissolution of water molecules in oxide: H 2 O(g) + V O +2+ = 2H ad+ + O O (ox) H + V O 2+ O 2- (ox) H e - ZrO 2 O 2 (s) H 2 (s) gas H 2 O(g) H 2 (g) Wagner s mechanism of water molecules dissolution in ZrO 2 might be responsible for high hydrogen uptake during Zr oxidation in steam 34

35 Hydrogen uptake model (2/2) Mass action laws Solution P H2O (s) 2 = k P H2 (s) 2 P O2 (s) P O2 (s)c v2 C e4 = γp H2 (s) =C H+2 C 2 e C H = K S P H2 (s) 1/2 2(k 1/2 β 1/2 /γ)c H+3 /P H2O (s) + C H+2 γ 1/2 P H2 (s) 1/2 =0 C C H+ CH Charge neutrality condition 2C v + C H+ = C e P H2 /P H2O if P H2 << P H2O C H+ P H2 (s) 1/4 >> C H P H2 (s) 1/2 In steam atmosphere hydrogen is dissolved (and transported) in ZrO 2 mainly in the form of protons (with high mobility) 35

36 Hydrogen transfer in oxide phase C H () -Zr C H () C H+ (b) C H (b) -Zr ZrO 2 C H+ (s) C H (s) Steady-state approximation J O (ox) = D O (ox) C O /(t) J H (ox) = D H+ (ox) C H+ /(t) + D H (ox) C H /(t) Experimental data B.Cox, 1976 (review): H 2 dissolution in thin layers of ZrO 2 on Zr substrate, Results: * 1m, ZrO 2 becomes permeable for H. Model assumption Two different regimes of H (neutral) mobility in the oxide: > * 1m, D (ox) H << D (ox). H+ < * 1m, D H (ox) - finite value Schanz et al., 1984: Zry interactions with H 2 /H 2 O mixtures Conditions: T= C Interpretation: mass gain in the initial period can be attributed to the hydrogen absorption Moalem and Olander, 1991: Zry interactions with H 2 /H 2 O mixtures Results: similar to G.Schanz 36

37 KIT Tests on Hydrogen Uptake by Neutron Radography (M. Grosse et al.) Scheme of INRRO furnace

38 KIT Tests on Hydrogen Uptake by Neutron Radography (M. Grosse et al.)

39 H 2 Concentration (vol. %) Tests simulations KIT tests on hydrogen uptake by Zry-4 cladding during isothermal oxidation in steam (50 l/h Ar + 50 g/h H 2 O ) T=1373 K Experiment Calculation H/Zr atomic ratio (%) T=1373 K Experiment Axial position 1 Axial position 2 Axial position H/Zr atomic ratio (%) Time (h) T=1473 K Experiment Axial position 1 Axial position 2 Axial position 3 H/Zr atomic ratio (%) Time (s) Experiment Axial position 1 Axial position 2 Axial position 3 T=1673 K Time (s) Time (s)

40 Tests simulations KIT tests on hydrogen uptake by Zry-4 cladding during isothermal oxidation in steam (30 l/h Ar + 30 g/h H 2 O at 1473 K) H/Zr atomic ratio (%) Experiment bottom middle top Time (s)

41 . Hydrogen Uptake under normal operation conditions Coupling of 2 models: Hydrogen absorption mechanism; Mass transfer through 2-phase zone (hydrides in metal Zr) Predictions: Non-uniform distribution of hydrides (owing to oxygen concentration profile); Close to parabolic hydriding kinetics: M H t 9/16 t 3/8 t 1/ 2 Metallographic cut of the rod cladding 41

42 High Temperature Zr Cladding Embrittlement 42

43 Cladding Embrittlement Criteria Criterion 17% ECR (and T<1204C) 43

44 Cladding Embrittlement Criteria Criterion 17% ECR (and T<1204C) Chung and Kassner (ANL, 1980) 44

45 Cladding Embrittlement Criteria Chung-Kassner advanced criterion Capability to withstand the different loading modes depends on thickness of and oxygen distribution in -Zr layer: 1. Capability to withstand thermal shock during LOCA reflooding: calculated thickness of the cladding with 0.9 wt % oxygen should be greater than 0.1 mm. Oxygen, wt.% 130 mcm,1400c 2. Capability to withstand fuel 100 mcm,1400c 0.7 handling, transport and storage: calculated thickness of the 0.5 cladding with 0.7 wt % oxygen 0.3 should be greater than 0.3 mm mcm,1400c 200 mcm,1400c Radial direction, mm 100 mcm,1600c Low hydrogen content < 700 w. p.p.m.!! 45

46 Double side oxidation (interactions with UO 2 pellet) In the case of solid contact between pellet and cladding, Zry reduces UO 2 to form oxygen stabilized -Zr(O) (internal) and (U,Zr)-alloy. The external cladding interaction with oxygen or steam results in the formation of -Zr(O) (external) and ZrO 2. The internal and external -Zr(O) layers of the cladding grow with the same rates. Initially the reaction-layer growth obeys a parabolic rate law. After the disappearance of -phase, the cladding tube is completely embrittled and no more mechanically stable. 46

47 Diffusion Model for Double Side Oxidation 1000 Calc. расчет Exper. эксперимент T=1700 K 750 Расстояние от UO 2, мкм 500 -Zr ZrO 2 -Zr (U,Zr) (U,Zr)O (U,Zr)O 2 Time, s 1/ Время, с

48 Cladding Embrittlement due to Fuel Bonding Formation of Zr(O) layer at the inner surface of the cladding as a result of UO 2 /Zr chemical interaction ( bonding ) can lead to cladding embrittlement even in the absence of oxidation atmosphere at the outer cladding surface. 30 Oxygen content, wt % C outer oxidation UO2/Zr interaction Distance, mm Maximum extent of oxidation and fuel pellet interaction to remain intact under thermal shock. 48

49 Cladding Embrittlement Criteria Effect of hydrogen uptake 700 w.p.p.m. 49

50 Cladding Embrittlement Criteria Combined effect of oxygen and hydrogen uptake 50

51 Zr Cladding Embrittlement under LOCA Conditions 51

52 Observations in KIT Tests (Stuckert et al., 2012) Temperature escalation at different elevations and appearance of ballooned zones 52

53 Observations in KIT Tests (Stuckert et al., 2012) External and internal cladding oxidation Ballooning zone Non-deformed zone 53

54 Observations in KIT Tests (Stuckert et al., 2012) Secondary hydriding of cladding Increased microhardness at positions of hydrogen rich bands 54

55 Observations in ANL Tests (M. Billone et al., 2008) Post-test appearance Temperature and pressure histories 55

56 Observations in ANL Tests (M. Billone et al., 2008) Axial distribution of oxygen and hydrogen content for: OCL#22 sample held at 1204ºC for 1 s (left) ; OCL#17 sample held at 1204ºC for 120 s (right). 56

57 Observations in JAERI Tests (Uetsuka et al., 1981) 57

58 Modification of Gas Kinetics Module Ar ( k J i ) k = N ( k I i ) Processes: o Oxidation of clad outer surface and transport of gas mixture (H 2 O-H 2 -Ar) in channel H 2 O, H 2 H 2 O, H 2 Ar H 2 O H2O, H2 k= 1 H 2 O k = 0 o o Oxidation/hydriding of clad inner surface and transport of gas mixture in gap Flux matching at breach position H 2 58

59 Transport in gap: Q Q i z t q z t, 2 2 H O H O, u z, t D i dni dx Modification of Gas Kinetics Module x0 u i 2 ni ni Di i i, 2 t z z 0 n 0 n 0 i i i n ( ext ) i n u Q z t Oxidation (i = 1); hydriding (i = 2) n i z, t - concentrations of gas components (1 = H 2 O, 2 = H 2, 3 = Ar, 4 = ) 1 1 x n n i, i n i ni P t ntkt t, Dk ( P, T ), xi i ik D ( P, T ) Q H z t q z, tq z,,, 2 H t 2O H 2 -H 2 O sink (calculated by oxidation kinetics module with consideration of steam starvation) q H z, t -H 2 sink (calculated by hydriding kinetics module) 2 - gas net velocity, induced by: 1) pressure drop between inner and outer after breaching ( 38s); 2) gas thermal expansion (during temperature escalation); 3) gas advection due to H 2 uptake by cladding (Stefan flow) DiSd i K, K 50 V d cl where - best fit k, i - flux matching at breach position Veshchunov & Shestak, Proceedings QW 18&19, KIT (2012&2013) i i i 59

60 Simulation of QL0 Test (1/6) Temperature distribution Pressure equilibration Lower Middle Upper Temperature evolution at the burst position Cladding temperature axial distribution at the calculation time moments 40 s, 60 s and 80 s 60

61 Simulation of QL0 Test (2/6) Burst geometry Pellet Inner Clad. Outer Clad Axial distribution of rod dimensions at bundle elevations from 1150 to 850 mm 61

62 Simulation of QL0 Test (3/6) Gas partial pressures in gap Axial coordinate (mm) Gap gas components partial pressures axial distribution at the time moments 40 s, 60 s and 75 s 62

63 Simulation of QL0 Test (4/6) Internal oxidation Axial coordinate (mm) Specimen inner surface oxidation layers thicknesses axial distribution at the time moments 40 s, 60 s and 75 s 63

64 Simulation of QL0 Test (5/6) Cladding oxygen content due to double-side oxidation Axial distribution of total oxygen content at the calculation time moments 40 s, 60 s and 75 s 64

65 Simulation of QL0 Test (6/6) Cladding hydriding Axial distribution of cladding total hydrogen content at time 40 s, 60 s and 75 s. Exp. Rod #1 #7 #3 #14 Oxidation ~ 74 s ~ 71 s ~ 64 s ~ 32 s period Hydrogen (w.p.p.m.)

66 Simulation of ANL Test OCL #17(1/7) Temperature distribution Lower Middle Upper Time, s Temperature evolution at the burst position Cladding temperature axial distribution at the calculation time moments 60 s, 80 s and 200 s 66

67 Simulation of ANL Test OCL #17(2/7) Burst geometry Axial coordinate (mm) Axial distribution of rod dimensions 67

68 Simulation of ANL Test OCL #17(3/7) Gas partial pressures in gap Gap gas components partial pressures axial distribution at the time moments 60 s, 80 s and 200 s 68

69 Simulation of ANL Test OCL #17(4/7) Internal oxidation ZrO 2,Time1 ZrO 2,Time2 ZrO 2,Time3 Zr(O), Time1 Zr(O), Time2 Zr(O), Time Axial coordinate (mm) Specimen inner surface oxidation layers thicknesses axial distribution at the time moments 60 s, 80 s and 200 s 69

70 Simulation of ANL Test OCL #17(5/7) External oxidation Axial distribution of gap gas partial pressures (left) and of outer surface oxidation layers thicknesses (right) at the time moments 60 s, 80 s and 200 s 70

71 Simulation of ANL Test OCL #17(6/7) Cladding oxygen content due to double-side oxidation 6 5 Calc. 60s Calc. 80s Calc. 260s Exp. Hold 120s Axial coordinate from the burst position (mm) Axial distribution of total oxygen content at the calculation time moments 60 s, 80 s and 260 s 71

72 Simulation of ANL Test OCL #17(7/7) Cladding hydriding Axial distribution of cladding total hydrogen content at times 60 s, 80 s and 100 s in comparison with experimental measurements 72

73 SFPR Code: Development Plan The first version of the fuel performance code SFPR, designed by coupling of MFPR with the mechanistic thermo-mechanical module SVECHA, was released and tested in 2008 Validation (by IBRAE) and commercial applications to operation conditions of the new VVER-2006 reactor design (by ATOMENERGOPROECT) started in 2009 Implementation of SFPR module in the advanced version of the Russian integral best-estimate safety code SOCRAT (for LWRs), started in 2010 (Russian collaboration under IBRAE coordination) Extension to the Fast Reactor (FR) fuel and implementation in the new generation integral code EUCLID (developed under IBRAE coordination) for FR design and safety justification, within the new Russian Federal Target Program Nuclear Power Technologies of a New Generation for the years with a perspective to