Accurate Reactivity Feedback Calculations for TRIGA Cores

Transkript

1 Accurate Reactivity Feedback Calculations for TRIGA Cores M.Badea, C.H.M.Broeders, R.Dagan, A.Travleev Forschungszentrum Karlsruhe Institut für Reaktorsicherheit P.O.Box 3640, D Karlsruhe, Germany Topics Introduction Accurate generating new thermal data for hydrogen bound in zirconium hydride Calculation methods and results JAHRESTAGUNG KERNTECHNIK - Nürnberg May

2 Introduction The TRADE project utilises existing TRIGA reactor RC - 1 Cassacia in Italy; The experimental program of TRADE needs detailed information about the temperature feedback effects (also at higher temperature range between C); The prompt fuel temperature dependent reactivity feedbacks contain 2 components : * the resonance broadening in the fuel (Doppler effect); * the upwards flux spectral shift due to enhanced temperature of the bound hydrogen in the fuel (scattering effect). JAHRESTAGUNG KERNTECHNIK - Nürnberg May

3 TRIGA fuel assembly model * Fuel elements are cylinders of ternary alloy uranium-zirconium hydride with H-Zr ratio 1.7 and 20% enriched U -235 * Fuel cladding stainless steel AISI 304 * Two graphite cylinders at the top and the bottom of the fuel rod R Z Al plate Graphite reflector Fuel mixed with Zr-rod R H2O R Cladding R reflective boundary condition Z zero flux boundary condition JAHRESTAGUNG KERNTECHNIK - Nürnberg May

4 Cross section and scattering kernels generating ENDF/B library NJOY RECONR BROADR LEAPR THERMR ACER GROUPR MCNPX Specific library MCNPX TWODANT LEAPR module: -a central force lattice dynamics model -generate thermal neutron scattering data (conservation of momentum and energy transfer- sum rule ) -standard temperature input deck dense temperature grid with 10 K intervals THERMR module: -additional refinements for hydrogen scattering (instead of standard 59 energy points to use more (83 energy points) -increase the number of equi-probable energy points (20 30) JAHRESTAGUNG KERNTECHNIK - Nürnberg May

5 Calculation Methods Monte Carlo calculations with the continuos energy option for MCNPX code, beta version 2.5d; Deterministic multi-group calculation with KAPROS-E LINUX version 2.02 using the TWODANT code. Measurements TRIGA cores in Cassacia and Slovenia; were performed by increasing the power fuel; the temperature of the the averaged temperatures for the whole core were derived based on the measuring positions and the power shape of the core. JAHRESTAGUNG KERNTECHNIK - Nürnberg May

6 E : KAPROS C: MCNP-accurate dk/dt [pcm/ C] _ B:TRIGA-Slovenia Exp. Data D:MCNP average according to GA rep A:RC1 - Exp.Data Fuel Temperature [ C] The comparison of experimental and computational results for the reactivity feedback of the TRIGA core and the TRIGA fuel pin respectively JAHRESTAGUNG KERNTECHNIK - Nürnberg May

7 Additional sensitivities of the reactivity feedback Increasing the energy grid in NJOY from 59 to 83 points for the scattering law data reduced by about 1.5 pcm/degree keeping the shape of the reactivity curve. Additional study is mandatory for the optimized energy grid considering a new model in the LEAPR module; The increase of the number of equi-probable energy points (20 30) for the S(α,β) tables no trend was observed; The modified Doppler effect by using resonant dependent S(α,β) tables for heavy isotopes showed negligible reactivity feedback growth due to the relative small U238 concentration JAHRESTAGUNG KERNTECHNIK - Nürnberg May

8 The total cross section for hydrogen bound in zirconium for different energy points JAHRESTAGUNG KERNTECHNIK - Nürnberg May

9 -6,5-7,0 dk/dt (pcm/ 0 C) -7,5-8,0-8,5-9,0 ρ H2 O =1 ρ H2 O =0.98 ρ H2 O =0.95 ρ H2 O =0.92 KAPROS- Total effects -9, Temperature ( 0 C) Total reactivity feedback effect of TRIGA fuel pin as function of void level in the water coolant using deterministic codes JAHRESTAGUNG KERNTECHNIK - Nürnberg May

10 dk/dt (pcm/ 0 C) ρ H 2 O =1 ρ H 2 O =0.95 MCNPX Temperature (C) Thermal reactivity feedback effect of TRIGA fuel pin as function of void level in the water coolant using MCNPX JAHRESTAGUNG KERNTECHNIK - Nürnberg May

11 Conclusion The unique phenomenon of the TRIGA reactivity feedback growth around 125 C was shown to be directly connected to the treatment of the bound hydrogen cross section based on specific S(α,β) probability tables ; Preliminary results show that also between C the reactivity coefficient is sensitive to the improved S(α,β) probability tables; The overall core reactivity feedback is only slightly affected by the moderator density. Stochastic and deterministic calculations show the same trend. JAHRESTAGUNG KERNTECHNIK - Nürnberg May

12 OUTLOOK The differences between the 2-dimensional calculations and the experimental results need 3D calculations; A MCNPX new data set based upon an improved model for the bound hydrogen in zirconium hydride is currently under investigation; A TRIGA oriented energy group structure will be applied to study the scattering effects by deterministic codes in order to comply with the MCNPX and experimental results. JAHRESTAGUNG KERNTECHNIK - Nürnberg May

13 JAHRESTAGUNG KERNTECHNIK - Nürnberg May