The proposed study deals with the assessment of passive systems, implemented in reactor designs to extend the coping period in the event of adverse situations, involving the melting of the core, such as occurred at the Fukushima Daiichi plant. To the aim, the feasibility of a new in-vessel core melt retention (IVCR) strategy is investigated. This strategy is based on an original design of a core catcher made of batch of ceramic multi-layered pebble that, by profiting of the low thermal conductivity, is capable to retard the heat-up of the lower head of the vessel during the relocation of the corium (recognized as the “Achilles-heel” of the Gen. II or earlier PWR designs). The arrest of heat-up and eventual quenching is indeed the key to the survival of the RPV as the significant thermal and pressure loadings may cause a reduction of mechanical strength of the vessel, and even its failure. In doing that, issues evolving and caused by the corium relocation are investigated both analytically and numerically. Thermo-mechanical analyses are performed by means of FEM code, assuming firstly homogeneous pool condition. The heat transport to the hemispherical boundary is simulated through conduction, and, then, through a boundary layer created by the downward flow along the curved wall from the upper part of the pool. Results show that the heat-up of the vessel wall, in the long time period, may cause a thermal degradation of the vessel strength. Nevertheless, the adoption of the proposed core catcher solution extends the coping period: after 1 hr from the event initiating the maximum temperature reached by the vessel wall is below the allowed limit for which localized failure may appear
Innovative engineering safeguards to cope with corium relocation: Identification of loads and failure modes
Burgazzi L.
2019-01-01
Abstract
The proposed study deals with the assessment of passive systems, implemented in reactor designs to extend the coping period in the event of adverse situations, involving the melting of the core, such as occurred at the Fukushima Daiichi plant. To the aim, the feasibility of a new in-vessel core melt retention (IVCR) strategy is investigated. This strategy is based on an original design of a core catcher made of batch of ceramic multi-layered pebble that, by profiting of the low thermal conductivity, is capable to retard the heat-up of the lower head of the vessel during the relocation of the corium (recognized as the “Achilles-heel” of the Gen. II or earlier PWR designs). The arrest of heat-up and eventual quenching is indeed the key to the survival of the RPV as the significant thermal and pressure loadings may cause a reduction of mechanical strength of the vessel, and even its failure. In doing that, issues evolving and caused by the corium relocation are investigated both analytically and numerically. Thermo-mechanical analyses are performed by means of FEM code, assuming firstly homogeneous pool condition. The heat transport to the hemispherical boundary is simulated through conduction, and, then, through a boundary layer created by the downward flow along the curved wall from the upper part of the pool. Results show that the heat-up of the vessel wall, in the long time period, may cause a thermal degradation of the vessel strength. Nevertheless, the adoption of the proposed core catcher solution extends the coping period: after 1 hr from the event initiating the maximum temperature reached by the vessel wall is below the allowed limit for which localized failure may appearI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
