Recent extensions of FRAPTRAN-1.5 at Quantum Technologies AB

Transcription

1 Recent extensions of FRAPTRAN-1.5 at Quantum Technologies AB Lars O. Jernkvist Quantum Technologies AB, Uppsala Science Park, SE Uppsala, Sweden FRAPCON/FRAPTRAN Users Group Meeting, Zürich, Switzerland, September 18, 2015

2 Outline of presentation Quantum Technologies AB Recent extensions of FRAPTRAN High-temperature models for the cladding - Model for axial fuel relocation during LOCA Some errors in FRAPTRANs thermal solution Ongoing activities with FRAPTRAN-QT1.5

3 Quantum Technologies AB Independent company, offering consulting services in analysis, modelling and simulation of mechanical-material systems Located in Uppsala, Sweden Close cooperation with universities Most of the business is in nuclear fuel analysis and modelling The Swedish Radiation Safety Authority (SSM) is a major client Swedish nuclear fleet: 7 BWRs + 3 PWRs (40 % of electricity production is nuclear)

4 Quantum Technologies AB Our software for fuel rod thermo-mechanical analyses: FRAPCON (PNNL/NRC) - General steady-state analyses FRAPTRAN (PNNL/NRC) - Transients and LOCA SCANAIR (IRSN/SSM) - Reactivity initiated accidents HYDRA (QT) - Hydrogen/hydride behaviour and hydride-induced cracking in Zr- and Ti-alloys [1,2]

5 Recent extensions of FRAPTRAN Models implemented in our extended version of FRAPTRAN-1.5: Zircaloy and Zr-Nb cladding high-temperature behaviour [3,4] - Metal-water reactions - Metal phase transformation kinetics - Creep in a-phase, b-phase and mixed (a+b)-phase - Rupture criteria (8 different, proposed in literature) Fuel column axial relocation and crumbling [5-7] - Axial relocation of fragmented/pulverized fuel - Packing fraction of crumbled fuel - Effective thermal conductivity of crumbled fuel All models are designed for and used with the FE-based mechanical module

6 Example: High temperature creep model Creep in the mixed (a+b)-phase region is enhanced by inter-phase interface sliding; Ashby-Verrall s model for superplastic flow [8,9] is used in FRAPTRAN-QT1.5. A separate model for the metal phase composition is used, accounting for oxygen effects and phase transformation kinetics Creep of M5 cladding (1 MPa stress) a a+b b

7 Example: Phase transformation model Oxygen effects Kinetic effects Zircaloy-4, Forgeron et al., The model [10,11] is also used in the BISON program [12].

8 Example: Fuel relocation/crumbling model Consists of three submodels, fully integrated with FRAPTRAN Axial relocation of fragmented/pulverized fuel - Packing fraction of crumbled fuel - Effective thermal conductivity of crumbled fuel Emphasis is placed on thermal feedback effects from the relocation - Radial heat transfer equation solved by FRAPTRAN is changed as a result of fuel pellet stack collapse (fuel crumbling) and axial fuel relocation In the course of work, several errors were discovered in FRAPTRANs thermal analysis module. These are not yet reported to PNNL/NRC, but a memo + corrected source code is underway...

9 Errors in FRAPTRANs thermal solution Some of the most important errors: Temperatures are calculated by use of a finite difference (FD) method [13], where the spatial discretization is defined by weights (geometry dependent coefficients) associated to each radial node. - The weights set in FRAPTRAN are incorrect (implementation error). Leads to poor performance if a coarse radial discretization is used. The weights used in the FD method are calculated based on the original, un-deformed geometry of the fuel and cladding. - This does not work well for large (radial) deformations. May lead to significant temperature errors in e.g. analyses of ballooning. Observed and reported already in 2014 by K. Govers, SCK CEN.

10 Test case 1: Small deformations Simple analytical reference solution: - Steady-state conditions - Constant thermal conductivities for pellet and cladding - Constant heat transfer coefficients - Uniform heat source in pellet - No heat source in cladding Original version of FRAPTRAN-1.5 Fair results for 45 radial nodes in the pellet (nfmesh=45). Poor results for coarser discretizations, due to incorrect FD weights.

11 Test case 1: Small deformations After correction of FD weights: - Nearly perfect agreement with analytical solution, also with very coarse discretization QT version of FRAPTRAN-1.5 The FD method in HEAT-1 [13] is extremely efficient, when correctly implemented

12 Errors in FRAPTRANs thermal solution Some of the most important errors found: Temperatures are calculated by use of a finite difference (FD) method [13], where the spatial discretization is defined by weights (geometry dependent coefficients) associated to each radial node. - The weights set in FRAPTRAN are incorrect (implementation error). Leads to poor performance if a coarse radial discretization is used. The weights used in the FD method are calculated based on the original, un-deformed geometry of the fuel and cladding. - This does not work well in case of large (radial) deformations. May lead to significant temperature errors in e.g. analyses of ballooning. Observed and reported already in 2014 by K. Govers, SCK CEN.

13 Test case 2: Large cladding deformations Original version of FRAPTRAN-1.5 QT-version of FRAPTRAN-1.5 Cladding hoop strain 47 % In the QT- version, the FD weights are re-calculated for each time step in the solution, based on the deformed geometry

14 Ongoing activities with FRAPTRAN-QT1.5 Projects under contract or in cooperation with SSM: Assessment of cladding high temperature rupture criteria (LOCA) - Review of rupture data + criteria available in the open literature - Assessed with FRAPTRAN-QT1.5, using its models for high temperature creep, phase transformations, etc. - Report soon to be published through SSM Participation in IAEA CRP FUMAC - Simulation of Halden IFA-650.9/10 in-reactor LOCA tests - Simulation of Studsvik-NRC out-of-reactor LOCA test 192 Simulation of Halden IFA LOCA test - Test was interrupted just before cladding rupture - Axial fuel relocation was observed

15 References [1] Jernkvist & Massih, Comp. Mat. Sci. 85 (2014) pp [2] Jernkvist, Comp. Mat. Sci. 85 (2014) pp [3] Manngård & Massih, J. Nucl. Sci.Techn. 48 (2011) pp [4] Research report SSM 2013:24, Swedish Radiation Safety Authority, [5] Research report SSM 2015:37, Swedish Radiation Safety Authority, [6] Jernkvist et al., TopFuel-2015, Zürich, Switzerland, Sept , [7] Jernkvist & Massih, SMiRT-23, Manchester, UK, Aug , [8] Massih, J. Nucl. Sci. Techn., 50(1) (2013) pp [9] Research report SSM 2014:20, Swedish Radiation Safety Authority, [10] Massih, J. Nucl. Mat. 384 (2009) pp [11] Massih & Jernkvist, Modelling Simul. Mater. Sci. Eng. 17 (2009) [12] Hales et al., Report INL/EXT Rev. 1, Idaho National Laboratory, [13] Wagner, AEC R&D Report IDO-16867, Phillips Petroleum Company, 1963.