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Abstract
Accident tolerant fuels (ATFs) are new nuclear fuels developed in response to the accident at the Fukushima power station in March 2011. The goal of ATFs is to withstand accident scenarios through better performance compared to currently employed fuels (e.g., small-scale hydrogen generation). This paper targets a method for evaluating and comparing ATF performance from a probabilistic risk assessment (PRA) perspective by employing a newly developed combination of event trees and dynamic PRA methods. Compared to classical PRA methods based on event trees and fault trees, dynamic PRA can evaluate with higher resolution the safety impacts of physics dynamics and the timing/sequencing of events on the accident progression without the need to introduce overly conservative modeling assumptions and success criteria. In this paper, we analyze the impact on the accident progression of three different cladding configurations for two initiating events [a large break loss-of-coolant accident (LB-LOCA) and a station blackout (SBO)] by employing dynamic PRA methods. The goal is to compare the safety performance of ATFs (FeCrAl and Cr-coated cladding) and the currently employed Zr-based clad fuel. We employ two different strategies. The first focuses on the identification of success criteria discrepancies between the accident sequences generated by the classical PRA model and the set of simulation runs generated by dynamic PRA using ATF. The second one, on the other hand, directly uses dynamic PRA to evaluate the impact of timing of events (e.g., recovery actions) on accident progression. By applying these methods to the LB-LOCA and SBO initiating events, we show how dynamic PRA methods can provide analysts with detailed and quantitative information on the safety impact of ATFs.
Acronyms
| AC | = | = alternating current |
| ACC | = | = accumulator |
| ATF | = | = accident tolerant fuel |
| CD | = | = core damage |
| DC | = | = direct current |
| DEGB | = | = double-ended guillotine break |
| ECST | = | = emergency condensate storage tank |
| HPI | = | = high-pressure injection |
| KNN | = | = K Nearest Neighbor |
| LB-LOCA | = | = large break loss-of-coolant accident |
| LPI | = | = low-pressure injection |
| LPR | = | = low-pressure recirculation |
| LS | = | = limit surface |
| LTSBO | = | = long-term station blackout |
| PCT | = | = peak clad temperature |
| = | = probabilistic distribution function | |
| PORV | = | = pilot-operated relief valves |
| PRA | = | = probabilistic risk assessment |
| PWR | = | = pressurized water reactor |
| RCP | = | = reactor coolant pump |
| ROM | = | = reduced order model |
| RPV | = | = reactor pressure vessel |
| RWST | = | = refueling water storage tank |
| SBO | = | = station blackout |
| SG | = | = steam generator |
| SRV | = | = safety relief valve |
| TDAFW | = | = turbine-driven auxiliary feedwater |