Periodic Reporting for period 3 - AMHYCO (TOWARDS AN ENHANCED ACCIDENT MANAGEMENT OF THE HYDROGEN/CO COMBUSTION RISK)
Reporting period: 2023-10-01 to 2025-03-31
The main objective of the AMHYCO project was to propose innovative enhancements in the way combustible gases are managed in case of a severe accident in currently operating reactors.
The specific objectives of the AMHYCO project were:
• SO1: To experimentally investigate phenomena that are difficult to predict theoretically such as H2/CO combustion and PARs (Passive Autocatalytic Recombiners) behaviour under realistic accidental conditions, tconsideringtheir interaction with safety systems.
• SO2: To improve the predictability of analysis tools Including Lumped Parameter (LP), 3D and Computational Fluid Dynamic (CFD) codes – used for explosion hazard evaluation inside the reactor containment and providing support to Severe Accident Management Guidelines (SAMGs) design and development.
• SO3: To help improve the SAMG for both in-vessel and ex-vessel phases with respect to combustible gases risk management, using theoretical, simulation and experimental results.
The project has achieved all of the three objectives through: 1) analysis of experimental results and provision of a experimental database on H2/CO combustion and PARs (Passive Autocatalytic Recombiners) behaviour (SO1); 2) numerical simulations that learned from the WP3 experimental results (SO2); and 3) issuing of lessons learned and recommendations to the SAMGs developers in WP5 for the three technologies involved: PWR-W, PWR-KWU and PWR-VVER (SO3).
The specific objectives of the AMHYCO project were:
• SO1: To experimentally investigate phenomena that are difficult to predict theoretically such as H2/CO combustion and PARs (Passive Autocatalytic Recombiners) behaviour under realistic accidental conditions, tconsideringtheir interaction with safety systems.
• SO2: To improve the predictability of analysis tools Including Lumped Parameter (LP), 3D and Computational Fluid Dynamic (CFD) codes – used for explosion hazard evaluation inside the reactor containment and providing support to Severe Accident Management Guidelines (SAMGs) design and development.
• SO3: To help improve the SAMG for both in-vessel and ex-vessel phases with respect to combustible gases risk management, using theoretical, simulation and experimental results.
The project has achieved all of the three objectives through: 1) analysis of experimental results and provision of a experimental database on H2/CO combustion and PARs (Passive Autocatalytic Recombiners) behaviour (SO1); 2) numerical simulations that learned from the WP3 experimental results (SO2); and 3) issuing of lessons learned and recommendations to the SAMGs developers in WP5 for the three technologies involved: PWR-W, PWR-KWU and PWR-VVER (SO3).
In WP1 ‘Critical review’, a critical review of the available literature regarding (1) PAR efficiency under ex-vessel conditions, (2) existing PWR SAMGs regarding containment risk management (3) H2/CO combustion and the available engineering correlations for combustion risk estimation, and (4) equipment and instrumentation surveillance under severe accident conditions has been performed. A public deliverable (D1.1) reviewed by externals, has been published. One conference paper for NURETH2025 is under preparation.
In WP2 ‘Selection of severe accident sequences’, the two main tasks have been achieved successfully. On one hand, the PWR-W, PWR-KWU and PWR-VVER generic models have been developed, being documented extensively in the public deliverable D.2.1. On the other hand, a broad number of severe accident sequences for the three types of reactor have been performed with Lumped Parameters (LP) codes such as MELCOR, ASTEC or COCOSYS. As a consequence, an outstanding database on H2/CO scenarios of interest for the three types of PWR containments (KWU, W and VVER) have been developed. The sequences were documented in the public deliverable D2.2 together with the lessons learned. Several conference papers were published (see “publications”) and two journal papers are under preparation.
In WP3 ‘Experimental investigations’, the experiments on flammability limits and turbulent flames were done for the data that had a clear knowledge gap in the literature or no data available at all. For the second task, the PAR experiments in the REKO facilities have been performed to validate numerical PAR models. The public deliverables D3.1 and D3.2 were issued. Several journal and conference papers have been already published and some more are under preparation.
In WP4 ‘Full containment analysis’, new simulation models from the generic containment database of WP2 were created for three different modelling approaches: LP, 3D and CFD. Afterwards, a significant amount of sequences for LP codes were performed, investigating the impact of safety systems such as containment sprays, fan coolers, filtered venting systems and PARs was investigated regarding combustion risk in the containment. Very valuable lessons learned were taken from the 3 approaches comparison, which have been documented in D4.2 (restricted) and D4.3 (public). Additionally, relevant work was done to create better estimations of the combustion risk in the late phase of accidents learning from the WP3 experimental combustion data. This work has been documented in D4.1. From this WP, one journal paper was published, several conference papers were issued and other ones are under preparation.
The WP5 ‘Enhancement of severe accident management guidelines’ was designed as the interface from academic research and numerical simulations into industrial application. During its work, the results of these preceding work packages were reviewed, the applicability to existing European pressurized water reactor types (PWR-W, PWR-KWU, PWR-VVER) confirmed, and the results presented in a language commonly used in the industrial framework. The main outputs of this WP were: 1) enhanced technical accident management (AM) measures based on results achieved in the project; 2) a translation into practical AM measures in which human error is minimized as far as possible; and 3) recommendations for long term operation (LTO) upgrades to comply with the proposed AM measures above.
In WP6 ‘Dissemination, communication, education and training’, many activities took place: workshops with PhD students, students mobility programme, defences of PhD thesis, AMHYCO students being awarded for their work, participation at many events and conferences. From the start of the project, AMHYCO was present at 23 scientific conferences, had 49 conference proceedings/papers and presentations, and 5 peer-review journal papers (2 additional papers are currently under review and 10 are under preparation).
In WP2 ‘Selection of severe accident sequences’, the two main tasks have been achieved successfully. On one hand, the PWR-W, PWR-KWU and PWR-VVER generic models have been developed, being documented extensively in the public deliverable D.2.1. On the other hand, a broad number of severe accident sequences for the three types of reactor have been performed with Lumped Parameters (LP) codes such as MELCOR, ASTEC or COCOSYS. As a consequence, an outstanding database on H2/CO scenarios of interest for the three types of PWR containments (KWU, W and VVER) have been developed. The sequences were documented in the public deliverable D2.2 together with the lessons learned. Several conference papers were published (see “publications”) and two journal papers are under preparation.
In WP3 ‘Experimental investigations’, the experiments on flammability limits and turbulent flames were done for the data that had a clear knowledge gap in the literature or no data available at all. For the second task, the PAR experiments in the REKO facilities have been performed to validate numerical PAR models. The public deliverables D3.1 and D3.2 were issued. Several journal and conference papers have been already published and some more are under preparation.
In WP4 ‘Full containment analysis’, new simulation models from the generic containment database of WP2 were created for three different modelling approaches: LP, 3D and CFD. Afterwards, a significant amount of sequences for LP codes were performed, investigating the impact of safety systems such as containment sprays, fan coolers, filtered venting systems and PARs was investigated regarding combustion risk in the containment. Very valuable lessons learned were taken from the 3 approaches comparison, which have been documented in D4.2 (restricted) and D4.3 (public). Additionally, relevant work was done to create better estimations of the combustion risk in the late phase of accidents learning from the WP3 experimental combustion data. This work has been documented in D4.1. From this WP, one journal paper was published, several conference papers were issued and other ones are under preparation.
The WP5 ‘Enhancement of severe accident management guidelines’ was designed as the interface from academic research and numerical simulations into industrial application. During its work, the results of these preceding work packages were reviewed, the applicability to existing European pressurized water reactor types (PWR-W, PWR-KWU, PWR-VVER) confirmed, and the results presented in a language commonly used in the industrial framework. The main outputs of this WP were: 1) enhanced technical accident management (AM) measures based on results achieved in the project; 2) a translation into practical AM measures in which human error is minimized as far as possible; and 3) recommendations for long term operation (LTO) upgrades to comply with the proposed AM measures above.
In WP6 ‘Dissemination, communication, education and training’, many activities took place: workshops with PhD students, students mobility programme, defences of PhD thesis, AMHYCO students being awarded for their work, participation at many events and conferences. From the start of the project, AMHYCO was present at 23 scientific conferences, had 49 conference proceedings/papers and presentations, and 5 peer-review journal papers (2 additional papers are currently under review and 10 are under preparation).
AMHYCO results addressed both expected impacts listed in the NFRP-02:
1) In the AMHYCO project, several outcomes that could help covering vulnerabilities of the operating plants under severe accidente conditions were produced. In the first place, a new PAR correlation has been created, called “AMHYCO correlation”, which helps to simulate better the late phase of the severe accident compared with the most used approach before AMHYCO. In the second place, new correlations have been proposed for the estimation of combustion risk in H2/CO/O2/diluents mixtures, which allow to understand better the associated risk to different severe accident scenarios. In the last place, valuable lessons learned have been taken from the numerical simulations that have built an useful database to be able to give feedback to the actual Severe Accident Management Guidelines.
2) As a result of the experimental and numerical work done in the project, specific recommendations to improve the nuclear safety of the current Generation II and III fleet has been made for the Severe Accident Management Guidelines and the long term operation manteinance plan. Valuable feedback has been made regarding the actuation and manteinance of safety systems such as the PARs, the Filtered Containment Venting System, the Containment Spray System and the Fan Coolers.
Moreover, the project increased the knowledge transfer to younger generations and brought the industry community closer to investigations of hypothetical severe accidents. Through dissemination activities the general public was informed about how the nuclear industry manages the combustion risk in severe accidents with safety measures. Finally, the project also had an environmental impact since the improvement in managing the combustion risk will lower the probability of containment integrity failure and therefore, minimize the potential radiological release in case of a severe accident with combustion risk.
1) In the AMHYCO project, several outcomes that could help covering vulnerabilities of the operating plants under severe accidente conditions were produced. In the first place, a new PAR correlation has been created, called “AMHYCO correlation”, which helps to simulate better the late phase of the severe accident compared with the most used approach before AMHYCO. In the second place, new correlations have been proposed for the estimation of combustion risk in H2/CO/O2/diluents mixtures, which allow to understand better the associated risk to different severe accident scenarios. In the last place, valuable lessons learned have been taken from the numerical simulations that have built an useful database to be able to give feedback to the actual Severe Accident Management Guidelines.
2) As a result of the experimental and numerical work done in the project, specific recommendations to improve the nuclear safety of the current Generation II and III fleet has been made for the Severe Accident Management Guidelines and the long term operation manteinance plan. Valuable feedback has been made regarding the actuation and manteinance of safety systems such as the PARs, the Filtered Containment Venting System, the Containment Spray System and the Fan Coolers.
Moreover, the project increased the knowledge transfer to younger generations and brought the industry community closer to investigations of hypothetical severe accidents. Through dissemination activities the general public was informed about how the nuclear industry manages the combustion risk in severe accidents with safety measures. Finally, the project also had an environmental impact since the improvement in managing the combustion risk will lower the probability of containment integrity failure and therefore, minimize the potential radiological release in case of a severe accident with combustion risk.