Bubelis, E.

Chen, X.-N.

Flad, M.

Perez-Martin, S.

Rineiski, A.

English

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KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz AssociationKARLSRUHE INSTITUTE OF TECHNOLOGY (KIT), INST. FOR NEUTRON PHYSICS AND REACTOR TECHNOLOGY (INR)www.kit.eduSIMULATION OF ULOF INITIATION PHASE IN ESFR-SMART WITH SIMMER-IIIX.-N. Chen, A. Rineiski, S. Perez-Martin, M. Flad, E. BubelisKarlsruhe Institute of TechnologyInternational Conference on Fast Reactors and Related Fuel CyclesFR22: Sustainable Clean Energy for the Future (CN-291) Vienna, Austria 19-22 April 20222 Introduction Euratom Project: ESFR-SMART since 2017  Core Performance Improvement:From positive void worth in CP-ESFR Working Horse Core to low/negative void worth in ESFR-SMART  Major question here: if power excursion can be initiated by sodium boiling in ULOF transientsOur Studies: Direct numerical simulations with SIMMER-IIIThermal hydraulic and neutronic space-time coupled calculation of ULOFMajor neutronic feedback effects are includedHope to find something new and useful3 Introduction ESFR-SMART Concept Design: P= 3600 MWth and Sodium Tin = 395 C and Tout = 545 C Fissile part is higher in the outer zone and the lower fertile part is shorter Hottest FAs are in innermost ring of the outer zone Boiling onset takes place there. The effective boiling void worth is negative. 4 SIMMER ESFR-SMART Model Geometric and thermal hydraulic model, where cover gas is modelled Neutronic feedback: Doppler and coolant feedback are automatically taken into account. Thermal expansion models for the core, axial and radial, and CRDL are included. 5 Neutronic Feedback CoefficientsParameter Unit SIMMER Reference(Serpent calculations)Keff 1.00937 1.00471Prompt Neutron Lifetime [s] 4.25E-07 4.74E-07Beta Effective [pcm] 347 362Doppler ConstantFissile 1500 K -> 1800 KFertile 900 K  ->  900 K[pcm] -808 -685Core Void Worth without Voided Gaps at Tcool 763.2 K[pcm] 1755Core Void Worth with Voided Gaps[pcm] 1727 1542Upper Gas Plenum + Plug      Void Worth[pcm] -41.3 -62Coolant Density Reactivity Coefficient[pcm/K] 49/110.8= 0.442 48/110.8 = 0.433 Axial Thermal Expansion Coefficient[pcm/K] -0.0715 -0.083Radial Thermal Expansion Coefficient[pcm/K] -0.711 -0.646Control Rod Drivelines Expansion Coefficient[pcm/cm] -423/14.5 -423/14.56 SIMMER ESFR-SMART ULOF Results ESFR-SMART CORE THERMAL HYDRALIC CONDITIONSCase No. Case Description Boiling Onset Power Excursion1 Axial Fuel-Driven and 1.53E-5 CRDL 42 s Yes at 102 s2 Axial Clad-Driven and 1.53E-5 CRDL 69 s Yes at 129 s3 Axial Fuel-Driven and 1.82E-5 CRDL 45 s Yes at 117 s4 Axial Clad-Driven and 1.82E-5 CRDL 73 s NoCase 4 Results7 SIMMER ESFR-SMART ULOF Results Case 4 Results8 SIMMER ESFR-SMART ULOF Results Case 4 Results: boiling void and reactivityt = 83 s t = 89 s t = 94 s9 ULOF Results with Power ExcursionCase 3:  Fuel driven ThmExp, boiling onset at 43 sPower excursion at 117 sCase 4: Clad driven ThmExp,  boiling onset at 69 sNo power excursion10 ULOF Results with Power ExcursionNormalized Power in Case 3 Thermal Energy Release, JThe power excursion generates about 100 GJ 11 ULOF Long Time Results (Case 4) • The boiling oscillation decays and finally disappears• Due to sodium boiling the pressure at the cover gas increases from 1 bar to 2.7 bar.• 1 bar   => boiling temperature   883°C (1156 K)• 3.2 bar=> boiling temperature 1027°C (1300 K)12 Conclusions• The thermal expansion model is included and the new CRDL model isdeveloped and used. • 4 ULOF cases with fuel/clad driven axial thermal expansion and twodifferent steel thermal expansion coefficients for CRDL are calculated. • Sodium boiling oscillations with a period of 10s are observed andexplained, which is decisive for, whether the prompt criticality can bereached.  • Power excursions are obtained in the first 3 cases, with about 100 GJ thermal energy release.• No power excursion in the last case with strongest negative feedback.• Long time calculation shows that the boiling oscillation can evendisappear finally, which suggests a higher initial cover gas pressure canprevent the sodium boiling here.Acknowledgement:ESFR-SMART: This project has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 754501.

Simulation of ulof initiation phase in ESFR-SMART with Simmer-III

https://publikationen.bibliothek.kit.edu/1000163993/151613800

Simulation of ulof initiation phase in ESFR-SMART with Simmer-III

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