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 × 1024 n·m−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.