Nuclear Research and Consultancy Group (NRG) is a Dutch institute that performs nuclear research for the government and private companies. It is the most important producer of radionuclides in Europe and maintains and operates the Petten nuclear reactor.The institute also offers services to medical, chemical, oil, and gas companies..
The reactor pressure vessel (RPV) is a fundamental and virtually irreplaceable component of nuclear power plants. With the prolongation of the operation of light water reactors (LWRs) beyond their original design life (40 years for western LWRs), assessing the aging of such material has been an important and widespread research and development topic (long-term operation). In the 1990s, a LYRA irradiation rig was developed and made operational at the High Flux Reactor (HFR) in Petten, The Netherlands. The LYRA facility, located at the HFR's Pool Side Facility (PSF), was been designed to carry out the irradiation programs of the European Aging Materials European Strategy (AMES) Network, with the purpose of studying the irradiation embrittlement of RPV steels. The irradiation rig was comprised of gamma shielding, which occupied both PSF-10 and PSF-11 and the irradiation capsule itself, which was placed in PSF-11. The LYRA capsule was a reloadable capsule. For each new irradiation campaign, a new sample holder was manufactured and placed inside the capsule. The last campaign conducted in the LYRA facility was the joint Joint JRC-NRG irradiation campaign LYRA-10. It was started in 2007 and concluded in 2018. In LYRA-10, more than 600 specimens made of model steels based on typical VVER-1000 RPV steels (both base and weld metal) and western pressurized water reactor RPV steels with systematic variations in Ni and Mn content, and to a smaller extent, Si content, were irradiated to high fluence (approximately 1.1 x 1024 nm-2, E > 1 MeV) to understand their role and synergetic effects on RPV embrittlement. This paper primarily describes the operational objectives and conditions of LYRA-10, reporting on the fluences and temperatures achieved during the campaign. With the complementary data (fluence and temperature) provided in this paper, post irradiation examination of the irradiated specimens was carried out through the Euratom-funded project STRUMAT-LTO, which ran from 2020 to 2024. LYRA-10 was the last irradiation campaign to use the LYRA facility. After completion of LYRA-10, the LYRA facility was decommissioned because of significant aging after more than 20 years of use.
Within the Swiss deep drilling campaign 2019-2022, a series of Jurassic (Dogger, Lias) claystone samples were mineralogically and geochemically characterised and used in small-scale transport experiments. The advectivediffusive transport experiments clearly showed a faster breakthrough of anions relative to neutral tracers, which agrees with the accumulation of anions in a relatively faster moving porewater fraction due to anion repulsion by negatively charged clay surfaces. Electroneutral tracers were not affected by the clay charge and thus evenly distributed in all porewater domains, including stationary ones, and were transported more slowly than anions. The experiments showed consistently a faster breakthrough of Br relative to Cl, which was intuitively not expected based on the equal charge and chemical behaviour of these ions. Simulations with a continuum finite volume model approach that considers electrostatic effects in clay accurately described the different breakthrough curves of charged and neutral tracers. Matching of breakthrough behaviour required a model explicitly considering heterogeneous flow, because the simple Fickian advection-dispersion equation failed to predict the experimental data of all tracers in a consistent way. The model indicated that although the exclusion behaviour of Cl and Br as a function of concentration and surface potential is the same, the effective retardation factor (and thus breakthrough) of each ion depends on the difference in concentration of initial in-situ porewater and that of the infiltrating solution. Heterogeneous flow, electrostatic interactions, and multicomponent transport are key processes governing solute transport in claystone cores under large hydraulic gradients. These mechanisms were therefore incorporated into the presented model, enabling successful simulation of the experimental data.
The European AMHYCO project aims at enhancing the understanding of H2/CO combustion risk within the containment of a light water reactor nuclear power plant during the in-and ex-vessel phase of a severe accident. The goal is to incorporate this knowledge into severe accident management guidelines (SAMG) and give recommendations for long-term operation upgrades. Based on a critical review of established methodologies and practices related to combustion risk assessment, as well as the identification of accident sequences where the containment integrity may get challenged, experimental investigations were conducted to close knowledge gaps related to combustion characteristics and the operation of passive autocatalytic recombiners under late phase conditions. To prepare the basis for the further assessment and refinement of existing SAMGs, systematic and detailed analyses of the most challenging scenarios and possible mitigative measures were conducted for three generic European pressurized water reactor (PWR) containment designs, namely KWU, Westinghouse, and VVER. For each reactor type, one Loss of Coolant Accident and one Station Blackout scenario were selected for detailed analyses with a variety of different numerical codes. Both scenarios cover a range of in-containment atmospheric conditions from potentially flammable at medium pressure to a steam-inerted atmosphere at high pressure, including the late phase with an active filtered containment venting system (FCVS). This paper outlines the employed methodology using a consecutive analysis chain consisting of three levels with increasing level of detail (system codes, 3D GOTHICTM and CFD) to assess containment pressurization,efficiency and/or options of individual mitigation measures regarding H2/CO combustion risk and equipment and instrumentation survivability. As a common basis, the system code nodalization schemes and 3D models are developed from detailed CAD geometries. On the basis, the paper summarizes the outcome of the work with a focus on the comparative assessment of the impact and effectiveness of mitigative measures (passive autocatalytic recombiner, containment sprays, FCVS) on the combustion risk in the accident. The analyses highlight that without combustible gas mitigation, containment atmospheres develop combustible pockets and may even become globally flammable, highlighting the need for control systems to preserve integrity. PARs proved effective across all scenarios in preventing large clouds with flame acceleration conditions, with their capacity mainly influencing depletion rates and timing. Oxygen removal by PARs also enables safe operation of containment and core cooling systems without increasing combustion risk in the late phase.
