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Technical Papers

Dynamic PRA Methods to Evaluate the Impact on Accident Progression of Accident Tolerant Fuels

, , , &
Pages 389-405 | Received 28 Feb 2020, Accepted 07 Jul 2020, Published online: 21 Oct 2020
 

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

PDF=

= 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

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