Projects / Programmes
Steam explosions in sodium cooled fast reactors
| Code |
Science |
Field |
Subfield |
| 2.13.01 |
Engineering sciences and technologies |
Process engineering |
Multi-phase systems |
| Code |
Science |
Field |
| T160 |
Technological sciences |
Nuclear engineering and technology |
| Code |
Science |
Field |
| 2.03 |
Engineering and Technology |
Mechanical engineering |
Generation IV reactors, sodium cooled fast reactor, nuclear safety, severe accident, vapour explosion, multi-phase flow, thermo-dynamical tables, heat transfer, solidification, numerical simulation, MC3D code
Researchers (1)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
29182 |
PhD Mitja Uršič |
Process engineering |
Head |
2013 - 2015 |
265 |
Organisations (1)
| no. |
Code |
Research organisation |
City |
Registration number |
No. of publicationsNo. of publications |
| 1. |
0106 |
Jožef Stefan Institute |
Ljubljana |
5051606000 |
90,706 |
Abstract
One of the important issues in core melt progression during a severe accident in an innovative sodium cooled fast reactor (SFR) is the likelihood and the consequences of a vapour explosion. A vapour explosion may occur when the hot core melt comes into contact with the liquid sodium. A strong enough vapour explosion in a nuclear power plant could jeopardize the containment integrity and so lead to a direct release of radioactive material to the environment.
The purpose of the project is to investigate the potential of strong vapour explosions in SFR. Namely, previously performed experiments showed that vapour explosions could occur in SFR. These experiments revealed also an important effect of the sodium sub-cooling on the behaviour of the melt-sodium interaction. The vapour explosion probability and efficiency for a higher sub-cooling is lower than for a lower sub-cooling. The physical properties of sodium, which strongly affects the melt-sodium heat transfer, and the melt solidification, which strongly affects the energy efficiency during the explosion, are identified as the reason for the observed behaviour.
Current fuel-coolant interaction (FCI) computer codes do not model the physical properties of sodium and do not model the melt solidification in enough detail. Therefore the first objective of the postdoc project is to enable the modelling of the melt-sodium interaction with FCI codes. We will:
· Propose the use of adequate sodium thermo-dynamic tables.
· Model adequately the heat transfer between the melt and sodium. The focus will be on the heat transfer modelling during the film boiling regime, which is generally agreed to be the initial condition for a vapour explosion, and the transition regime, which strongly affects the melt solidification.
· Use the solidification influence modelling approach, which we have developed in the frame of the doctoral thesis.
· Incorporate proposed models and tables into FCI code and validate them on experimental data.
The second objective of the postdoc project is to assess the potential of strong vapour explosions during melt-sodium interactions. Therefore we will:
· Perform analyses of integral FCI experiments with the improved MC3D code.
· Perform a sensitivity study with which the relevance of sodium physical properties and melt solidification on the vapour explosion phenomenon will be assessed.
· Use the results of the sensitivity study to estimate the potential of strong vapour explosions in SFR.
By improving FCI codes we will obtain simulation tools, which will enable realistic simulations of FCI experiments with sodium and in future more realistic simulations of reactor conditions and consequently a more reliable estimation of the vulnerability of SFR to vapour explosions.
Significance for science
The purpose of the project was to investigate the potential of strong vapour explosions in sodium cooled fast reactors. Namely, one of the important issues in core melt progression during a hypothetical severe accident in an innovative sodium cooled fast reactor is the likelihood and the consequences of a vapour explosion. A vapour explosion may occur when the hot core melt comes into contact with sodium. A strong enough vapour explosion in a nuclear power plant could jeopardize its integrity and thus lead to radioactive material release to the environment. Previous performed experiments showed that vapour explosions could occur in sodium. However, the analysis of sodium experiments with the current fuel-coolant interaction codes developed with the focus on water is not directly applicable. Evidently, the applicability of the current fuel-coolant interaction codes for the fuel-sodium interaction must still be assessed because the physical properties of sodium are very different from those of water. The analyses of the modelling approaches in the fuel-coolant interaction codes have shown that especially the modelling of heat transfer in the transition boiling regime must be improved. With the help of the experimental data analyses we have proposed a modelling approach for the transition boiling regime. The developed heat transfer modelling approach was incorporated in the advanced fuel-coolant interaction code and validated. The computer code was used to simulate and analyse integral experiments and to assess the potential of vapour explosions in sodium. The analyses of experimental results highlighted the importance of the melt solidification and the sodium vapour pressure curve on the strength of the vapour explosion. The results of the project present a step towards an improved risk assessment of vapour explosions in sodium cooled fast reactors. The results of the project present a scientific contribution in the field of vapour explosion research related to nuclear safety. The results importantly contribute to improved understanding, modelling and interpretation of integral experiments.
Significance for the country
The results of the project improve our understanding of the vapour explosions phenomenon. Therefore the research contributes to creating, keeping and improving of our own technical knowledge and enhances the independence on foreign expertise in support of safe Krško nuclear power plant operation and helps the regulatory body in the inspection of Krško nuclear power plant operation and maintenance. All this contributes to the increase of the competitive position of Slovenia. A tight cooperation with foreign researchers within the project improves the possibilities for the participation in international projects related to the innovative reactors.
Most important scientific results
Annual report
2013,
2014,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2013,
2014,
final report,
complete report on dLib.si
