A novel approach termed front-controlled Probabilistic Risk Assessment (Front-PRA) is proposed by the INET researchers. It aims to address the “lack of gain” issue with PRA applications using the traditional PRA approach for advanced nuclear power plants (NPP). By shifting risk control points from core damage to certain early checkpoints, it boosts the perception of risk variations caused by routine operational and maintenance activities, and further exploits the practical value of PRA methodology to achieve a win-win outcome for both safety and economy.
Author: LIU Tao| INET news
January 16, 2026
Background
Against the backdrop of the global nuclear energy revival, advanced nuclear energy technologies face the dual challenges of demonstrating economic competitiveness while upholding their safety advantages. Traditional Probabilistic Risk Assessment (PRA), characterized by Core Damage Frequency (CDF) and Large Early Release Frequency (LERF), exhibits insensitive to most routine operational and maintenance (O&M) activities. Regulators and NPP front-line staff look forward to risk insights that inform day-to-day operation decisions. To address this gap, researchers from INET and Sanmen Nuclear Power Co., Ltd. propose a new PRA approach called Front-PRA. This approach refocuses the risk analysis and management from post-accident mitigation to proactive accident prevention, thereby unlocking the operational value of the excellent safety performance demonstrated by Generation III NPP.
Highlights
Front-PRA innovates by shifting risk control “upstream”. Unlike traditional PRA that typically ends at core damage, the new approach tracks early checkpoints prior to core damage occurrence — specifically, the Automatic Depressurization System (ADS) for the AP1000 NPP —, and introduces the ADS Triggering Frequency (ADS-TF) as a new metric for PRA modeling and related applications. The ADS-TF is about four orders of magnitude higher than the CDF estimate, making it far more sensitive to routine O&M events and delivering actionable insights for O&M decision-making. The pilot study in an AP1000 NPP demonstrates that by ranking SSCs (Structure, System and Components) according to their ADS-TF contribution, the new approach identifies more SSCs requiring routine O&M interventions that are overlooked by traditional CDF-based PRA.
The new approach also proposes a risk management framework incorporating traditional CDF and ADS-TF for AP1000 NPP. The framework features four zones (Red - Yellow - White - Green), effectively resolving the paradox wherein “safer NPPs having less O&M flexibility”.
To a certain extent, front-PRA is tailored for operating NPPs, aiming to strengthen nuclear safety by aligning with the “prevention first”philosophy. In case of AP1000, reducing ADS triggering also directly lowers core damage risk and enhances the defense-in-depth.
Implications
Front-PRA can be leveraged to support the maintenance effectiveness management programs. The proposed four-zone framework provides a balanced risk management tool that recognizes the safety advantages, reduces unnecessary maintenance activities and enables consistent risk insights. While currently piloted in an AP1000 NPP, the authors note that the approach is reactor-type independent. It can also be integrated into the typical PRA application tools such as Risk Monitors.
Link to access the full paper
https://doi.org/10.1016/j.nucengdes.2025.114703
