Projects / Programmes
Thermal-Hydraulic Safety Analyses
January 1, 1999
- December 31, 2003
| Code |
Science |
Field |
Subfield |
| 2.03.00 |
Engineering sciences and technologies |
Energy engineering |
|
| 2.13.00 |
Engineering sciences and technologies |
Process engineering |
|
| 1.07.00 |
Natural sciences and mathematics |
Computer intensive methods and applications |
|
| Code |
Science |
Field |
| T160 |
Technological sciences |
Nuclear engineering and technology |
| T210 |
Technological sciences |
Mechanical engineering, hydraulics, vacuum technology, vibration and acoustic engineering |
| T200 |
Technological sciences |
Thermal engineering, applied thermodynamics |
| T140 |
Technological sciences |
Energy research |
| P240 |
Natural sciences and mathematics |
Gases, fluid dynamics, plasmas |
Researchers (21)
Organisations (1)
| no. |
Code |
Research organisation |
City |
Registration number |
No. of publicationsNo. of publications |
| 1. |
0106 |
Jožef Stefan Institute |
Ljubljana |
5051606000 |
90,753 |
Abstract
A number of issues dealing with Thermal-Hydraulic Safety Analyses was addressed The uncertainty of a small-break loss-of-coolant accident simulation in a two-loop pressurized water reactor was evaluated using the Code Scaling, Applicability and Uncertainty (CSAU) methodology.
The appearance and disappearance of bubbly flow regime in downward flow was studied with the RELAP5 thermal-hydraulic computer code. Subcooled boiling was studied with two different approaches: a two-dimensional Eulerian model, and a three-dimensional Lagrangian model, in which vapor bubbles are tracked individually. A two-fluid interface-tracking model was combined with a "classical" two-fluid model. The resulting model is suitable for problems, where fluids, which are initially separated by a continuous interface, disperse and mix, so that the interface cannot be tracked on the same length scale. Natural convection in a fluid with internal heat generation was modeled with a Large Eddy Simulation method. The simulation revealed that the Rayleigh-Taylor instability is the dominant mechanism, which causes the appearance of turbulent flow regime
Hydrogen stratification in a nuclear power plant containment atmosphere during a severe accident was simulated using the MELCOR and CONTAIN computer codes. To model steam explosions, a combined single-multiphase flow model of the premixing phase was developed and used to simulate isothermal premixing experiments, performed in other research centers.
Probabilistic Safety Assessment
Fault tree analysis was used to improve the requirements specification of safety software. Based on sets theory and first order logical predicates, the requirements specification is stated formally in gates and basic events of the fault tree. A house events matrix was also developed, which upgrades static fault tree analysis into a dynamic tool capable of modeling time requirements. These research activities belong to the framework of the international project "Allowed Outage Time for Test and Maintenance - Optimization for Safety", supported by the International Atomic Energy Agency.
A method was developed, which explicitly includes numerical and linguistic information into the assessment of a specific failure rate. The basis of the method is Bayes' theorem, whereas specific data about component operation are included in the model using fuzzy set theory.
Structural Safety Analyses
Major efforts were devoted to computational simulations of intergranular cracking, with intergranular stress corrosion cracking as observed in Inconel 600 steam generator tubes taken as an example. Detailed simulation models at the grain size level were developed. The random grain structure is represented by an incomplete random tessellation (Voronoi tessellation). The mechanistic consideration of forces and other processes responsible for the initiation and growth of cracks is handled via empirical models.
Most important scientific results
Final report
Most important socioeconomically and culturally relevant results
Final report
