Research Programs

Publications:

1. Pagani, L.P., Apostolakis, G.E., and Hejzlar, P., “The Impact of Uncertainties on the Performance of Passive Systems,” Nuclear Technology , 149:129-140, 2005.
2. Pagani, L.P. and Apostolakis, G.E., “A Methodology for Developing a Probability Distribution for the Failure Enthalpy of High-Burnup Fuels via Simulation,” accepted for publication in Nuclear Technology .

Investigators

• Professor G.E. Apostolakis
• Dr. P. Hejzlar
• L. Pagani

Quantification of Safety Margins

The development of PSA has improved the traditional deterministic safety approach by quantifying the risk and determining its main contributors. Through the use of PSA, it has been possible to identify accident sequences and important safety components. But, while the impact of redundancy has been explicitly modeled and quantified, the role of safety margins is still not explicitly taken into account. This makes it difficult to have a more accurate estimation of risk and to evaluate quantitatively the impact of modifications on plant risk. The quantitative effect of these margins (individually or in combination) on the PSA, that is, their impact on the CDF and LERF (large early release frequency) is not known.

To further improve the value of PSA, considering its significance in decision-making, it is important to be able to quantify the safety margins and to evaluate their impact on the final results. By explicitly modeling safety margins, the results of this research will also help to improve PSA quality, as well as uncertainty and sensitivity analysis. This project employs the stress/strength interference theory from reliability theory and explores the possibility of quantifying the “stress” and the “strength” in two case studies: the passive cooling of a gas-cooled fast reactor, and the failure limit for high-burnup fuel in a PWR rod ejection accident.