Feldmann, H.

Gabrielli, F.

Hoefer, A.

Pauli, E. M.

Sanchez-Espinoza, V. H.

Stakhanova, A.

English

KITopen

Impact of Realistic Fuel Inventories onthe Radiological Consequences of aSevere Accident Scenario in a GenericKONVOI Plant by means of the ASTECCodeF. Gabrielli1, A. Stakhanova1, V.-H. Sanchez-Espinoza1, E.-M. Pauli2, A. Hoefer2, H. Feldmann21 Karlsruhe Institute of Technology2 Framatome GmbHMotivation Evaluation of source term (ST) and fission product (FP) dispersion during a severe accident(SA) in NPPs is one of the major objectives of the nuclear reactor safety research programat KIT. Main goal → supporting the emergency and management teams during such abnormalevents → a reliable evaluation of the source term is mandatory. Reference codes to be employed for assessing a database of STs during SA scenarios fordifferent NPPs → Realistic fuel inventories, ST evaluation (ASTEC), U&S and STprediction (FSTC+MOCABA algorithm), FP dispersion (JRODOS). Activities triggered by the KIT/Framatome joint participation to the EU H2020 MUSA andGerman WAME projects. The amount of FPs initially loaded in the core is one of the main parametersaffecting the in-vessel and ex-vessel accident progression as well as the ST. Large mass of FPs loaded → larger decay power → larger in-vessel degradation → largerFP release from the vessel to the containment and then to the environment.KIT Strategy for Source Term Analyses (1/2) https://www.ites.kit.edu/english/294.php European reference Accident Source Term EvaluationCode (ASTEC), developed by IRSN and co-developed by KITsince 2020 → SA scenario analyses and ST evaluations. ASTEC results employed to analyze the FP dispersion in theenvironment by means of the Java based Real-Time On-Line Decision Support system (JRODOS, KIT).Source TermKIT Strategy for Source Term Analyses (2/2) 12…NST Training Database Development of in-house Fast Source Term Code (FSTC) → Uncertainty Quantification (UQ) of theASTEC ST results + training database for Source Term prediction → Monte Carlo-based Bayesian inference model (MOCABA algorithm fromFramatome GmbH embedded)A. Stakhanova, et al., 2022, Uncertainty and Sensitivity Analysis of the ASTEC Simulation Results of a MBLOCA Scenario in aGeneric KONVOI Plant Using the FSTC Tool, ERMSAR2022, May 19-22, Karlsruhe.E.-M. Pauli, et al, 2022, Prediction of the Radiological Consequences of a Severe Accident Scenario in a Generic KONVOINuclear Power Plant, ERMSAR2022, May 19-22, Karlsruhe.ASTEC+UQASTEC+UQ+MOCABAASTEC Model of a Generic KONVOI NPP Significant improvement and extension of the original generic ASTEC input deckavailable in the code release. All the calculation modules activated → analysis of theSA scenario from the initiation up to the basematrupture. SOPHAEROS module for element- and isotope-wiseFP transport and behavior from the core to theenvironment. Heat exchange (convection, conduction, and radiation)and oxidation models. Main models governing the in-vessel and ex-vessel(relocation to the cavity after the lower head vesselrupture+MCCI) behaviour of the molten material.A. Stakhanova, et al., 2022, Uncertainty and Sensitivity Analysis of the ASTEC Simulation Results of a MBLOCA Scenario in a Generic KONVOI Plant Using the FSTC Tool, ERMSAR2022, May 19-22, Karlsruhe.Plant rooms (11 volumes) Operating rooms (9 volumes, white) Annulus (3 volumes, light yellow)Fuel Inventory Library of fuel inventories for an equilibrium cyclewith 328 effective full power days computed. Core is loaded with 193 Fuel Assemblies (48 UFAs, 6 batches; 81 U-Gd FAs, 6 batches; 64 MOXFAs, 4 batches). Depletion calculations, the ORIGEN-ARP tool hasbeen used, employing the ORIGEN reactorlibraries for an 18x18 FA design embedded inSCALE 6.2.3. Two initial fuel inventories employed:• Beginning of Cycle (BOC)• End of Cycle (EOC)Element VolatilityActivity @BOC (Bq)Activity @EOC (Bq)Xe Noble Gas 1.502E+19 1.678E+19Kr Noble Gas 4.323E+18 4.576E+18I Very Volatile 4.311E+19 4.726E+19Cs Very Volatile 3.718E+19 7.702E+20TeModerately Volatile2.258E+19 2.547E+19SrModerately Volatile1.104E+19 1.393E+19BaModerately Volatile5.492E+20 6.913E+20Ru Less Volatile 1.298E+19 1.541E+19La Less Volatile 2.236E+19 2.465E+19Ce Less Volatile 1.662E+19 1.895E+19Scenarios MBLOCA (12”) and SBLOCA (2”)1. Medium (12’’) and small (2’’) break of the cold leg at t=0 s2. Reactor scram, if the primary pressure < 132 bar or containment overpressure > 30 mbar3. Admission to turbine and closure of the main feed water pumps into the steam generator;4. Emergency Core Cooling System (ECCS) activated if two of the following three conditions are fulfilled containment overpressure >30 mbar, RCS pressure <110 bar or pressurizer liquid level< 2.30 m5. Main Coolant Pumps are coasted down and the pressure regulation in the pressurizer is switched off6. Activation of the Emergency Feed Water System (EFWS) when the liquid level of one SG falls <4.50 m7. HPIS (SBLOCA) and LPIS (MBLOCA) activated (T_gas in the primary > 650 °C) up to the tanks are empty → severe accident8. Activation of the Extra Borating System when the pressurizer water level <2.30 m9. When the horizontal erosion reaches 4.4 m radius, water from SUMPF flows into the cavity and the spalt MBLOCA (12”) and SBLOCA (2”) + Station Black Out (SBO)• AC loss @t=0 s• As above but no 4 – 8 actions (namely only accumulator discharge available)MBLOCA Scenarios: QuicklookBOC EOCPhenomenon MBLOCA MBLOCA+SBO MBLOCA MBLOCA+SBOFPs Release (s) 644 644 434 44420/50 tons relocated to the LP (h) 4.6 0.5 -/- 0.2/0.470/90 tons relocated to the LP (h) 4.6 0.8/0.9 -/- 0.5/0.6LPV Failure (h) 5.7 1.6 1.5 0.8Basemate Rupt. (h) 93.2 7.8 4.3 5.0Total H2 In-vessel/Containm. (kg) 938/1820 731/2124 638/1987 825/2270Final Aerosols in Cont. (kg) 184 135 100 145 Significant effect of the composition of the fuel inventory on the accident progression. Significant effect of scenarios on the mass of aerosols in the containment.SBLOCA Scenarios: QuicklookBOC EOCPhenomenon SBLOCA SBLOCA+SBO SBLOCA SBLOCA+SBOFPs Release (s) 11056 1133 10619 142620/50 tons relocated to the LP (h) 6.6 0.5/0.7 6.0 0.570/90 tons relocated to the LP (h) 6.6 -/- 6.0 -/-LPV Failure (h) 8.5 1.3 6.8 1.0Basemate Rupt. (h) 102.2 48.5 77.8 6.0Total H2 In-vessel/Containm. (kg) 865/2241 741/2790 862/2095 546/1652Final Aerosols in Cont. (kg) 1159 144 1032 544 Significant effect of the composition of the fuel inventory on the accident progression. By comparison with MBLOCA results, huge effect of scenarios on the mass of aerosols in the containment.Containment and Annulus Pressure Containment Higher pressures in EOC conditions. Long term higher pressures w/o SBO. In SBLOCA (EOC), pressurecontainment up to about 9 bar No containment rupture modeled(WAME project). Annulus Pressure in the annulus decreasesdue to the release to the environmentMBLOCAMBLOCA SBLOCASBLOCAContainmentAnnulusTotal activity in the Plant MBLOCA scenarios → about 1% of the initial activity of the fuel inventory transported to the containment. SBLOCA scenarios more severe• SBLOCA+SBO (@EOC) → about 3% of the initial activity in the vessel transported to the containment in thelong term.• SBLOCA @EOC → max. activity release to the containment about 15-20% (no SBO) and 70% (+SBO) ofthe initial activity.• The release to the containment is almost twice as high for a fuel inventory at EOC as for a fuelinventory at BOC.Xe Mass in Containment and Environment Noble gases almost completelytransported to the containment. Largest release at higher fuelburn-up in SBLOCA scenarios. (SBLOCAs and MBLOCA+SBO)Release with fuel at EOC is abouttwice than at BOCMBLOCAMBLOCA SBLOCASBLOCAContainmentEnvironmentXe-wise isotopes in the Containment and Environment SBLOCA results shown Element- and isotope wiseresults stored in the database:• Dose rates in Containmentand Annulus• Activity in the containment,annulus, and environmentXe133Xe135Xe133 Xe135ContainmentEnvironmentI Mass in the containment: Total and Aerosols Release strongly dependenton:• Scenario• Initial core inventory SBLOCA+SBO (@EOC) Total: Up to 75% of the initialinventory Aerosols: up to 60% of theinitial inventoryMBLOCAMBLOCA SBLOCASBLOCACs Mass in the containment: Total and Aerosols Release strongly dependenton:• Scenario• Initial core inventory SBLOCA+SBO (@EOC)• Total: Up to 55% of theinitial inventory• Aerosols: up to 20% of theinitial inventoryMBLOCAMBLOCA SBLOCASBLOCAConclusion and Outlook Platform of reference codes (ASTEC, FSTC, JRODOS) for the analysis of the radiological impact ofsevere accidents assessed at KIT, triggered by the KIT/Framatome joint participation to EU and Nationalprojects. ASTEC results for selected SA scenarios in a generic KONVOI NPP showed large effect of the initialamount of FPs in the core both on the accident progression and on the ST. Evaluation of realistic fuel inventories and employment in integral codes modelling is mandatory toperform reliable evaluations ST evaluations → final goal: supporting the emergency and decision teamsduring severe accidents. Source term databases from ASTEC results + UQ currently under assessment for generic KONVOIand VVER-1000 NPPs. Rather solid basis of understanding in view of the planned ASTEC analyses at KIT of SA scenarios ingeneric Small Modular Reactors (SMRs).• Evaluation of the fuel inventories challenging because of the rather heterogeneous core arrangementsin these systems → insights from the EU H2020 McSAFER project• Employment of innovative materials, e.g. Accident Tolerant Fuels (ATFs)

Impact of Realistic Fuel Inventories on the Radiological Consequences of a severe accident scenario in a generic KONVOI plant by means of the ASTEC Code

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Impact of Realistic Fuel Inventories on the Radiological Consequences of a severe accident scenario in a generic KONVOI plant by means of the ASTEC Code

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