Author: Henrik

Listen to episode 21 of the SSM podcast Strålsäkert where severe accident research is discussed. The APRI program is described as an important and crucial activity in order to keep the level of knowledge high.

In this episode it is descrided  what happens during a core melt accident in a nuclear reactor and it is discussed how research can be used to enhance reactor safety and minimize the risk for severe accidents with releases of activity to the environment. The chairman of APRI Patrick Isaksson is interviewed as well as professor Sevostian Bechta from KTH and professor Christian Ekberg at Chalmers. Listen directly on the web (Soundcloud) or in any of the many podcast apps.

APRI research contributed with crucial knowledge during construction of the EPR core catcher. This is stated in an extensive article published by Energiforsk where the first criticality of Olkiluoto 3 is highlighted.

In their latest newsletter Energiforsk published a thorough account of the complete EPR project, from the first agreement between Framatome and Siemens in 1989 until today when Olkiluoto 3 recently became the latest EPR reactor to reach criticality. EPR is a Gen 3+ reactor that builds on earlier German and French reactor designs. Many years of development has resulted in reinforced safety systems, increased independence between systems, functions and plant structures as well as some completely new safety concepts. One of the safety features that has drawn perhaps most attention is the so called core catcher which will manage a core melt in the event of a severe accident. The EPR core catcher is a special device below the reactor vessel that catchers the core melt, transforms it into a low-viscous material and transports it to a special chamber where it is cooled in a controlled way.

In the article, Energiforsk describes that several international research and development programs were started in order to construct the core catcher. Among these programs were COMAS (Corium on Material Surfaces), VULCANO (Versatile UO₂ Lab for Corium Analyzes and Observations) and ECOSTAR (Ex-Vessel Core Melt Stabilisation Research). Sweden also participated in this research through experiments at KTH. It is mentioned that as a part of the APRI program KTH launched the POMECO experiments (POrous MEdia COolability) that showed that the coolability of a core melt was enhanced between 50 and 600 percent if the core melt was cooled from the bottom as well as from the top. This turned out to be one of the key principles for the final design of the core catcher where water is added on top of the melt and flows through channels below the melt in the separate chamber used to assure an effective and well-controlled core melt cooling.

It is great to see that research teams funded by APRI can contribute with knowledge on a very advanced level that eventually can be applied on real reactor designs and enhance reactor safety. Read the complete article by Energiforsk here.

The APRI 10 project ended in december 2020 and the results from the project have been compiled in a Final Report now published as SSM Report 2022:02.

Since the early 90’s APRI has run severe accident research projects in 3 year cycles. Recently the final report for the APRI 10 project was published. The APRI 10 final report presents research results from KTH, Chalmers and international projects regarding:

• core degradation in the reactor vessel,
• vessel failure modes,
• coolability of corium in the containment,
• the steam explosion phenomenon,
• chemical phenomena in the containment and
• uncertainty quantification regarding challenges to the containment as the final barrier.

Coverage of international research has enabled knowledge exchange and provided the project with large amounts of data about accident phenomena important for severe accident sequences. In the long run this will provide a stable foundation that helps to predict, assess and manage potential accidents involvning core damage in Swedish reactors.

The APRI 10 Final Report can be found here, and will shortly be available through the SSM website as SSM Report 2022:02.