Periodic Reporting for period 3 - R2CA (REDUCTION OF RADIOLOGICAL CONSEQUENCES OF DESIGN BASIS AND DESIGN EXTENDION ACCIDENTS)
Reporting period: 2022-09-01 to 2023-12-31
The R2CA 4 ½-year project, dedicated to the Reduction of Radiological Consequences of Accidents, was mainly intended to improve the methodologies for assessing the environmental radiological sources terms of accidents within design basis and design extension conditions. It focused on two main kinds of accidental scenarios (LOCA & SGTR) and covered a wide range of LWR concepts (PWRs, EPR, BWR & VVERs). More especially its main goals were:
• To provide more realistic evaluations of the radiological consequences (then the safety margins) of the two categories of selected accidental scenarios within the Design Basis (DBA) and Design Extension (DEC-A) domains for different kinds of LWR concepts by reducing the use of overly conservative assumptions (especially for DEC-A scenarios) and/or of decoupling factors.
• To increase the NPP safety levels through optimizations of their emergency operating procedures, the development of innovative methods (based on artificial intelligence) for anticipated diagnosis/prognosis of specific accidental situations and more accurate evaluations of the pro and cons of Accident Tolerant Fuels (ATF) promoted worldwide.
To meet these two general objectives, several specific actions have been scheduled which were:
• Make a review and collection of the existing experimental data that will be used to verify and calibrate the updated/improved models and/or advanced simulations tools developed during the project for LOCA and SGTR accidental transients within DBA and DEC-A conditions.
• Make a comparative assessment of the existing methodologies used in different countries to evaluate the radiological consequences experimental results as well as the assumptions/hypotheses, models and simulation codes that are applicable to evaluate the safety margins of the considered reactor models within DBA & DEC-A conditions, through the RC of bounding scenarios.
• To provide advanced simulation tools and calculation schemes for reducing the degree of conservatism in radiological consequences evaluations of LOCA and SGTR scenarios and deriving more realistic safety limits within the DBA & DEC-A domains.
• To propose recommendations towards a harmonization of the RC evaluation methodologies of LOCA and SGTR in DBA and DEC-A conditions and especially for a more realistic evaluation of their RC evaluations and then of the safety margins in different kinds of operating and foreseen reactors in Europe.
• To provide analytical rationales for the development/use of innovative measures, devices (including evaluations of some ATF concepts) and tools that could be used for the prevention/management of these accidents and/or for the development/use of AI based tool for anticipating their diagnosis.
• To provide more realistic evaluations of the radiological consequences (then the safety margins) of the two categories of selected accidental scenarios within the Design Basis (DBA) and Design Extension (DEC-A) domains for different kinds of LWR concepts by reducing the use of overly conservative assumptions (especially for DEC-A scenarios) and/or of decoupling factors.
• To increase the NPP safety levels through optimizations of their emergency operating procedures, the development of innovative methods (based on artificial intelligence) for anticipated diagnosis/prognosis of specific accidental situations and more accurate evaluations of the pro and cons of Accident Tolerant Fuels (ATF) promoted worldwide.
To meet these two general objectives, several specific actions have been scheduled which were:
• Make a review and collection of the existing experimental data that will be used to verify and calibrate the updated/improved models and/or advanced simulations tools developed during the project for LOCA and SGTR accidental transients within DBA and DEC-A conditions.
• Make a comparative assessment of the existing methodologies used in different countries to evaluate the radiological consequences experimental results as well as the assumptions/hypotheses, models and simulation codes that are applicable to evaluate the safety margins of the considered reactor models within DBA & DEC-A conditions, through the RC of bounding scenarios.
• To provide advanced simulation tools and calculation schemes for reducing the degree of conservatism in radiological consequences evaluations of LOCA and SGTR scenarios and deriving more realistic safety limits within the DBA & DEC-A domains.
• To propose recommendations towards a harmonization of the RC evaluation methodologies of LOCA and SGTR in DBA and DEC-A conditions and especially for a more realistic evaluation of their RC evaluations and then of the safety margins in different kinds of operating and foreseen reactors in Europe.
• To provide analytical rationales for the development/use of innovative measures, devices (including evaluations of some ATF concepts) and tools that could be used for the prevention/management of these accidents and/or for the development/use of AI based tool for anticipating their diagnosis.
To meet its objectives, the project was structured around 4 main work packages dedicated to reactor calculations (LOCA & SGTR within DBA & DEC-A conditions); improvements and/or developments of models/simulation tools and/or calculation chains for LOCA and SGTR accidental scenarios (dedicated to fuel performance, FP transport and behaviour); innovative work (including the development of new EOPs for SGTR scenarios, the development of a neural-network based tool for early diagnosis of abnormal configurations, and the performance of more realistic evaluations of some Accident Tolerant Fuels).
Main outcomes of the project are:
• A dedicated experimental database (covering DBA & DEC-A conditions) which includes reports and/or data of more than 200 tests from about 50 experimental series performed at different scales as well as NPP measurements. It covers the main phenomena expected in LOCA and SGTR transients from fuel thermomechanical behaviour to FP activity release and transport.
• Significant improvements of the modelling of LOCA & SGTR phenomena at different levels through:
o The upgrading/development of models further implemented in simulation tools.
o The updating/improvement of simulation tools at different scales (integral or more mechanistic codes) for most impacting processes in radionuclide releases.
o The enhancement of the coupling between simulation tools (i.e. between fuel performance and fission product release codes…).
o The updating/development of calculation chains or radiological consequence evaluation methodologies for predicting the environmental sources terms.
• The more realistic evaluations of the radiological consequences of a large variety of LWR concepts (8) and LOCA/SGTR scenarios (70) within DBA & DEC-A conditions. All calculation results were archived and formatted to be able later to easily create a database if required.
• The generic recommendations formulated to further harmonize at European level the methodologies for radiological consequence evaluations of LOCA & SGTR accidents within DBA & DEC-A conditions in LWRs.
• The optimization of some Emergency Operating Procedures for SGTR scenarios (in VVER 1000 & PWR 1300) to reduce the environmental releases through respectively the development of automatic safeguards algorithms and numerical algorithm optimization (by means of the SIMPLEX event-based method).
• The development of a prototype of an expert system based on neural networks for early detection of defective fuel rods in a core.
• Updated evaluations of some Accident Tolerant Fuel concepts (in particular Cr-coated Zr-based cladding materials, Hastelloy-n claddings…) using the tools improved during the project.
The main results of the project were presented at various international conferences (18 papers published in conference proceedings). 6 R2CA related papers were also published in peer-review journals and a special issue in Annals of Nuclear Energy initiated gathering 18 papers. Finally, 19 public technical reports were issued, uploaded on the R2CA public website and archived in Zenodo.
Main outcomes of the project are:
• A dedicated experimental database (covering DBA & DEC-A conditions) which includes reports and/or data of more than 200 tests from about 50 experimental series performed at different scales as well as NPP measurements. It covers the main phenomena expected in LOCA and SGTR transients from fuel thermomechanical behaviour to FP activity release and transport.
• Significant improvements of the modelling of LOCA & SGTR phenomena at different levels through:
o The upgrading/development of models further implemented in simulation tools.
o The updating/improvement of simulation tools at different scales (integral or more mechanistic codes) for most impacting processes in radionuclide releases.
o The enhancement of the coupling between simulation tools (i.e. between fuel performance and fission product release codes…).
o The updating/development of calculation chains or radiological consequence evaluation methodologies for predicting the environmental sources terms.
• The more realistic evaluations of the radiological consequences of a large variety of LWR concepts (8) and LOCA/SGTR scenarios (70) within DBA & DEC-A conditions. All calculation results were archived and formatted to be able later to easily create a database if required.
• The generic recommendations formulated to further harmonize at European level the methodologies for radiological consequence evaluations of LOCA & SGTR accidents within DBA & DEC-A conditions in LWRs.
• The optimization of some Emergency Operating Procedures for SGTR scenarios (in VVER 1000 & PWR 1300) to reduce the environmental releases through respectively the development of automatic safeguards algorithms and numerical algorithm optimization (by means of the SIMPLEX event-based method).
• The development of a prototype of an expert system based on neural networks for early detection of defective fuel rods in a core.
• Updated evaluations of some Accident Tolerant Fuel concepts (in particular Cr-coated Zr-based cladding materials, Hastelloy-n claddings…) using the tools improved during the project.
The main results of the project were presented at various international conferences (18 papers published in conference proceedings). 6 R2CA related papers were also published in peer-review journals and a special issue in Annals of Nuclear Energy initiated gathering 18 papers. Finally, 19 public technical reports were issued, uploaded on the R2CA public website and archived in Zenodo.
In the end, the project contributed to:
• Less conservative assessments of the radiological consequences in LOCA and SGTR accidental sequences within DBA and DEC-A conditions that could be further applied to anticipate NPP responses for other configurations (i.e. other types of fuel (ATF), fuel with increased burn-up or Pu content…) and/or to extend with confidence such evaluations to other NPP concepts such as Small Modular Reactor (SMR) for which realistic radiological source term assessments will be even more crucial due to their potential proximity to homes and population.
• 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.
• A compendium of recommendations for each of the transients considered (LOCA & SGTR), to facilitate a future harmonization of radiological impact assessment methodologies at a European level.
• An optimization of EOPs used in SGTR scenarios in some LWR concepts (i.e. timing, operator's actions) that could be implemented in existing NPPs to reduce their radiological consequences.
• The demonstration of the ability of a neural network-based expert tool to determine early and with confidence the presence of defective fuel rods in a core and thus reduce the risks and the economic impacts associated to their occurrence.
• A better evaluation of the Pro and Cons of some Accident Tolerant Fuel concepts (Cr-coated Zr-based cladding materials and Hastelloy-n claddings) using the updated tools.
• Less conservative assessments of the radiological consequences in LOCA and SGTR accidental sequences within DBA and DEC-A conditions that could be further applied to anticipate NPP responses for other configurations (i.e. other types of fuel (ATF), fuel with increased burn-up or Pu content…) and/or to extend with confidence such evaluations to other NPP concepts such as Small Modular Reactor (SMR) for which realistic radiological source term assessments will be even more crucial due to their potential proximity to homes and population.
• 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.
• A compendium of recommendations for each of the transients considered (LOCA & SGTR), to facilitate a future harmonization of radiological impact assessment methodologies at a European level.
• An optimization of EOPs used in SGTR scenarios in some LWR concepts (i.e. timing, operator's actions) that could be implemented in existing NPPs to reduce their radiological consequences.
• The demonstration of the ability of a neural network-based expert tool to determine early and with confidence the presence of defective fuel rods in a core and thus reduce the risks and the economic impacts associated to their occurrence.
• A better evaluation of the Pro and Cons of some Accident Tolerant Fuel concepts (Cr-coated Zr-based cladding materials and Hastelloy-n claddings) using the updated tools.