Consideration of human actions in combination with the probabilistic dynamics method Monte Carlo dynamic event tree

Abstract

The various accident sequences to be considered in the framework of a probabilistic safety analysis (PSA) for a nuclear power plant derive from interactions between the physical process, technical system functions, operator performance and stochastic influences along the time axis. Probabilistic dynamics methods have been developed to adequately account for these interactions. They can potentially cover the spectrum of event sequences which may actually evolve and achieve a realistic probabilistic safety assessment. The probabilistic dynamics method MCDET is a combination of Monte Carlo simulation and the discrete dynamic event tree (DDET) method. It was implemented as a module which can operate in tandem with any deterministic code simulating the system and process dynamics. MCDET was supplemented by a so-called Crew-Module which permits to simulate the dynamics of human actions depending on but also acting on the system and process dynamics as modelled in the deterministic code and on stochastic influences as modelled in MCDET. This paper presents the Crew-Module and gives an overview of the results which may be obtained from its combination with MCDET and a deterministic dynamics code.

Simulation-based dynamic probabilistic risk assessment of an internal flooding-initiated accident in nuclear power plant using THALES2 and RAPID

“…During a flood, actions taken to isolate the floodwater can have a significant impact on the event progression. Therefore, human reliability analyses (HRAs), such as IDAC 44 and Crew-module, 45 which evaluate the reliability of operator actions, must be implemented in any detailed analyses. The simplified human reliability model was used to couple thermal-hydraulic and the simple flood propagation analysis program.…”

Improved Modelling and Assessment of the Performance of Firefighting Means in the Frame of a Fire PSA

“…The estimators of the mean ( Ep ) and variance Var( Ep ) can also be applied to calculate well-known inequations from statistics such as those of Chebychev (Formula (6)) or Cantelli (Formula (7). These inequations can then be used to quantify the epistemic uncertainty of Ep in terms of conservative estimations, for instance, of a 95% interval or of the 5%-or 95%-quantiles:…”

“…Since MCDET can in principal be coupled to any deterministic dynamics code, the open source and freely available code FDS (Fire Dynamics Simulator) from NIST [6] was selected to be applied for fire simulation. What makes MCDET particularly useful for a fire safety analysis is its Crew Module which allows for considering human actions such as those applied for firefighting as a time-dependent process [7,8] which can interact with the process modelled by any dynamics code chosen to be combined with MCDET such as FDS.…”

“…In that application, MCDET 2 Science and Technology of Nuclear Installations was combined with the code MELCOR (version 1.8.5, [9]) for integrated severe accident simulation. In another application, MCDET was coupled to the thermal-hydraulics code ATHLET (mod 2.0, [10]) to assess the emergency operating procedure "Secondary Side Bleed and Feed" [7]. This procedure is to be employed in a pressurized water reactor (PWR) to achieve the protection goal of steam generator injection after the loss of feed-water supply.…”

Development of a software tool for the analysis and verification of emergency operating procedures through the integrated simulation of plant and operators actions

“…For the shake of comparison, we can highlight, among the nowadays more developed support tools, the ADS-IDAC and the MDET-Crew module (Mosleh and Chang, 2004;Kloos and Peschke, 2007). ADS-IDAC is a tool based on DDET simulation which has a cognitive model (IDAC) to simulate most of the cognitive aspects considered in the current HRA methodologies and the forthcoming second generation ones, for instance EoC, situation assessment and decision making.…”