SSM perspective
Background
The Swedish Radiation Safety Authority together with the Swedish Power companies operating nuclear power reactors in Sweden have since early 1990’s provided financial support for severe accident research at KTH and Chalmers. The research was initiated almost directly after the installation of severe accident management system and strategy, as filtered containment venting system and preflooding of the containment, to further study and verify the assumptions that was made when the accident management strategy was developed. The research objectives has on a strategic level continuously been focused on reducing uncertainties in the different phenomena and contributing to a more physical understanding on the phenomena involved in the severe accident progression in a Swedish BWR.
Objectives of the project
The overall objective of APRI is to gain and improve knowledge in severe accident with a focus on the severe accident management as it is implemented in the current operating Swedish BWR’s and PWR’s and ultimately confirm the Swedish accident management as it is applied. The focus and orientation of the research are phenomena considered to be of risk importance for the Swedish accident management strategy. In the objectives for APRI-11, the study at KTH was focused on a few in-vessel phenomena and a continued research on ex-vessel core debris coolability. More specifically the following five topical areas have been investigated in APRI-11: i) in-vessel debris behavior, ii) vessel failure mode, iii) melt-coolant interactions, iv) ex-vessel corium-structure interactions, v) reactor applications and safety analyses. At CTH the research have been focused on the basic understanding of Tellurium chemistry during severe accident conditions.
Summary by the author
APRI-11 has provided an additional understanding of several phenomena and processes, including:
- Re-melting phenomena of core debris in the reactor vessel: this refers to the behavior of solid materials that may be present in the reactor during extreme conditions, specifically how they melt and interact with other materials.
- Failure modes in the reactor vessel: understanding the different ways in which the reactor vessel can fail which is crucial for the understanding of the ex-vessel behavior.
- Interaction between molten material and coolant: this involves studying how molten materials (like melted fuel) behave in contact with the coolant, which is crucial for the understanding of ex-vessel phenomena as steam explosion and debris coolability.
- Interaction between molten material and structures beneath the reactor vessel: this focuses on how molten materials affect the structural integrity of components located beneath the reactor, which is essential for the understanding of the conditions for steam explosion and debris coolability in the containment.
- Reactor applications and safety analyses: This refers to the study of practical applications for the Swedish reactors.
- Tellurium chemistry under severe accident conditions: this area of study concerns how tellurium behaves chemically during severe accident scenarios, providing data for model development. The results have been achieved through experimental investigations, model development, and simulations.
These methods allow for a comprehensive understanding of complex interactions and behaviors under various conditions.