Periodic Reporting for period 2 - R2CA (REDUCTION OF RADIOLOGICAL CONSEQUENCES OF DESIGN BASIS AND DESIGN EXTENDION ACCIDENTS)
Berichtszeitraum: 2021-03-01 bis 2022-08-31
R2CA, a 4-year collaborative project initiated in September 2019 in the frame of the Horizon-2020 Program of the European Commission, is dedicated to the Reduction of Radiological Consequences of Accidents within design basis (DBA) and design extension conditions (DEC-A). It gathers 17 organizations from 11 countries around best-estimate evaluations of radiological consequences (RC). The project addresses a broad scope of LWR designs from Gen II, III and III+ through the analyses of bounding scenarios of Loss Of Coolant Accidents (LOCA) and Steam Generator Tube Rupture (SGTR) transients.
Its main motivations are to increase the level of Nuclear Power Plant (NPP) safety through the performance of more realistic evaluations of the radiological consequences of Design Basis Accidents and to strengthen the assessments of NPP safety levels considering situations more severe than those currently integrated in plant designs (DEC-A domain).
More explicitely the overall objectives of the project are:
- To perform more realistic evaluations of the radiological consequences of explicit DBA and DEC-A accidental scenarios (LOCA & SGTR) through reduction of some conservatisms used in safety analyses;
- To elaborate updated calculation methodologies for their evaluations and provide recommendations for the harmonization of these methodologies;
- To improve the accident management procedures and derive rationales for the optimization of the EP&R actions;
- To develop innovatives measures, devices and tools for an anticipated diagnostic of accidental scenario and for the management or mitigation of these accidents;
- To evaluate some promising Enhanced-Accident Tolerant Fuel (E-ATF), focussing on the near-term concepts
Its main motivations are to increase the level of Nuclear Power Plant (NPP) safety through the performance of more realistic evaluations of the radiological consequences of Design Basis Accidents and to strengthen the assessments of NPP safety levels considering situations more severe than those currently integrated in plant designs (DEC-A domain).
More explicitely the overall objectives of the project are:
- To perform more realistic evaluations of the radiological consequences of explicit DBA and DEC-A accidental scenarios (LOCA & SGTR) through reduction of some conservatisms used in safety analyses;
- To elaborate updated calculation methodologies for their evaluations and provide recommendations for the harmonization of these methodologies;
- To improve the accident management procedures and derive rationales for the optimization of the EP&R actions;
- To develop innovatives measures, devices and tools for an anticipated diagnostic of accidental scenario and for the management or mitigation of these accidents;
- To evaluate some promising Enhanced-Accident Tolerant Fuel (E-ATF), focussing on the near-term concepts
The project activities have started by performing reviews on methodologies and simulation tools currently used by R2CA partners for fission product release evaluation. In addition, was also identified and collected in a database the available experimental data which will be used to verify and validate the improvements of the corresponding tools in LOCA and SGTR bounding scenarios within DBA and DEC-A domains.
These first activities allowed the strengths/weaknesses of the different tool capabilities used in the project and to identify more clearly the development needs.
In WP2 dedicated to reactor calculations, a simple tool for the evaluation of the radiological consequences to different groups of population from the calculated releases from the facility to the environment was provided. Also the first set of calculations, using the existing simulation tools and assumptions/hyptoheses currently used in Safety Studies, was finalised. In total, about 48 scenarios (LOCAs or SGTRs, within DBA or DEC-A conditions, 8 different reactor concepts) have been performed. The second set of reactor calculations using the upgraded calculation chains (benefiting from WP3 & WP4 work within the project) was also initiated.
Regarding WP3 dedicated to the R&D work performed for LOCA-related phenomena, several clad burst models were implemented in some of the codes as well as model adaptation for mainly Zr-based alloys (for plastic deformation, high-temperature creep and crystallographic phase transition). At the same time, refined approaches for the whole core description were elaborated. Meanwhile, a higher degree of mechanistic modelling was implemented in fuel performance codes by their coupling with mesoscale codes describing the behaviour of Fission products at the fuel grain level. Finally, the models for Fission Product transport/in-containment behaviour were also re-assessed upon selected tests of the R2CA experimental database within the boundary conditions representative of DBA and DEC-A conditions.
Regarding WP4 dedicated to the R&D work performed for SGTR-related phenomena, code capabilities were also enhanced with new physico-based models, external functions or user’s driven coefficients. These developments covered Iodine/Caesium peak releases from fuel to gap-primary coolant occuring during power transients and iodine transport from primary-to-secondary in the failed Steam Generator such as partitioning, steaming phenomena. For clad secondary hydriding, within normal operation conditions, also both simple models for H2 uptake at low temperatures in Zircaloy-based materials and a multi-physical model simulating all the phenomena from water ingress to hydride blister formation were developed.
In WP5 dedicated to innovation, preliminary concepts of accident management strategies were built for cover lift-up in VVERs. A current study was also initiated using the Downhill-SIMPLEX method to find a functional dependency between accident management parameters and the critical safety function of interest (such as i.e. timing of iodine activity release) in order to optimize the procedures in cases of SGTR in accordance with the defined safety goals. Meanwhile, an innovative approach using Artificial Neural Network (ANN) was developed to make predictions for clad defect detection. Finally, regarding ATFs some evaluations have been performed focusing on Cr-coated Zr4 clads.
In parallel to the technical work, the design of material to support project dissemination and communication activities has been finalized. A project brochure and a poster are available; social network accounts have been created. Education and training needs have been collected including lists of mobility (7), master thesis/post doc (7). Training sessions on SCIANTIX, TRANSURANUS and DRACCAR tools were organized. Three Newsletter have been issued and about 20 R2CA related papers that have been published in journal or were presented in international/national conferences. A special issue on R2CA gathering open-access papers was also initiated.
These first activities allowed the strengths/weaknesses of the different tool capabilities used in the project and to identify more clearly the development needs.
In WP2 dedicated to reactor calculations, a simple tool for the evaluation of the radiological consequences to different groups of population from the calculated releases from the facility to the environment was provided. Also the first set of calculations, using the existing simulation tools and assumptions/hyptoheses currently used in Safety Studies, was finalised. In total, about 48 scenarios (LOCAs or SGTRs, within DBA or DEC-A conditions, 8 different reactor concepts) have been performed. The second set of reactor calculations using the upgraded calculation chains (benefiting from WP3 & WP4 work within the project) was also initiated.
Regarding WP3 dedicated to the R&D work performed for LOCA-related phenomena, several clad burst models were implemented in some of the codes as well as model adaptation for mainly Zr-based alloys (for plastic deformation, high-temperature creep and crystallographic phase transition). At the same time, refined approaches for the whole core description were elaborated. Meanwhile, a higher degree of mechanistic modelling was implemented in fuel performance codes by their coupling with mesoscale codes describing the behaviour of Fission products at the fuel grain level. Finally, the models for Fission Product transport/in-containment behaviour were also re-assessed upon selected tests of the R2CA experimental database within the boundary conditions representative of DBA and DEC-A conditions.
Regarding WP4 dedicated to the R&D work performed for SGTR-related phenomena, code capabilities were also enhanced with new physico-based models, external functions or user’s driven coefficients. These developments covered Iodine/Caesium peak releases from fuel to gap-primary coolant occuring during power transients and iodine transport from primary-to-secondary in the failed Steam Generator such as partitioning, steaming phenomena. For clad secondary hydriding, within normal operation conditions, also both simple models for H2 uptake at low temperatures in Zircaloy-based materials and a multi-physical model simulating all the phenomena from water ingress to hydride blister formation were developed.
In WP5 dedicated to innovation, preliminary concepts of accident management strategies were built for cover lift-up in VVERs. A current study was also initiated using the Downhill-SIMPLEX method to find a functional dependency between accident management parameters and the critical safety function of interest (such as i.e. timing of iodine activity release) in order to optimize the procedures in cases of SGTR in accordance with the defined safety goals. Meanwhile, an innovative approach using Artificial Neural Network (ANN) was developed to make predictions for clad defect detection. Finally, regarding ATFs some evaluations have been performed focusing on Cr-coated Zr4 clads.
In parallel to the technical work, the design of material to support project dissemination and communication activities has been finalized. A project brochure and a poster are available; social network accounts have been created. Education and training needs have been collected including lists of mobility (7), master thesis/post doc (7). Training sessions on SCIANTIX, TRANSURANUS and DRACCAR tools were organized. Three Newsletter have been issued and about 20 R2CA related papers that have been published in journal or were presented in international/national conferences. A special issue on R2CA gathering open-access papers was also initiated.
Expected results of the project are:
- Less conservative assessments of the radiological consequences in LOCA and SGTR accidental sequences within DBA and DEC-A conditions
- An updated knowledge and new validated numerical tools in support to the integration of DBA and DEC-A accident risks (i.e. radiological consequences of releases into environment) in the design phase of future Nuclear Power Plant concepts
- Harmonization of the methodologies used in Safety Analyses for the evaluation of the radiological consequences of LOCA and SGTR accidental scenarios within DBA and DEC-A conditions
- Innovative actions to reduce the radiological consequences of some accidental scenarios (i.e. timing, operator's actions..) and optimize the accident management procedures (including the use of Artificial Neural Network) to be used in the reactor designs
- A better evaluation of the Pro and Cons of near-term ATF concepts
- Less conservative assessments of the radiological consequences in LOCA and SGTR accidental sequences within DBA and DEC-A conditions
- An updated knowledge and new validated numerical tools in support to the integration of DBA and DEC-A accident risks (i.e. radiological consequences of releases into environment) in the design phase of future Nuclear Power Plant concepts
- Harmonization of the methodologies used in Safety Analyses for the evaluation of the radiological consequences of LOCA and SGTR accidental scenarios within DBA and DEC-A conditions
- Innovative actions to reduce the radiological consequences of some accidental scenarios (i.e. timing, operator's actions..) and optimize the accident management procedures (including the use of Artificial Neural Network) to be used in the reactor designs
- A better evaluation of the Pro and Cons of near-term ATF concepts