Publications
Advanced Nuclear Power Program
Comparison of Active and Passive Safety Systems in Advanced Light Water Reactors
R. Eul, K. Ahn, S-P. Kao, P. Hejzlar, and M.S. Kazimi
MIT-ANP-TR-111 (September 2006)
Abstract
This work compares the functional and economic advantages of active versus passive safety systems in advanced light water cooled nuclear reactors. Two types of reactors are reviewed: pressurized water reactors and boiling water reactors, and the important characteristics in the passive reactor example of each are compared to those of the more traditional active reactor.
Considering a simplified heat removal system that uses an isolation condenser for decay heat removal, the key variables affecting system performance are (1) natural convection and (2) a pump to provide the circulation to remove the core heat. It is found that the passive system is less certain in its performance than the active system, if the pump of the active system is tested at least once every five months. Further, a cost model analysis found that, while the passive system offers the benefit of fewer components to maintain, it suffers from a greater uncertainty regarding the time required for licensing due to more limited data on the reliability of its operation.
Fault tree analyses are performed for evaluating the system reliability and component importance measuring factors. The risk of an active Isolation Condenser System (ICS) was found to be sensitive to the frequency of inspection of pumps in the active ICS. But the passive ICS is associated with larger uncertainty about the circulation dynamics. Nevertheless, the risk of both ICSs is comparable.
Finally, a survey of nuclear energy experts with a variety of affiliations was conducted to determine the current professional attitude towards these two design options. Results show that reactors with passive safety systems are more desirable among the surveyed expert groups, the perceived advantages being an increase in plant safety coupled to a decrease in cost.
