The PSA is a widespread technique used for the design and operation phases of a nuclear plant, to identify and analyze every situation and the sequence of events that could cause serious damage to the core. A typical PSA comprises:

  • Acquire a thorough understanding of the system and the collection of a large volume of related information.
  • Identify initiating events and states of plant damage.
  • Modelling the major plant systems using event trees and fault trees ET/FT.
  • Evaluate the relationships between events and human actions.
  • Develop a database of the reliability of the systems and components of a specific plant.

The results of these analyzes can identify not only the strengths but also weaknesses with respect to the safety of the plant and, therefore, help prioritize and focus efforts on the items identified to improve the safety of installations.

The ISA methodology improves the conventional PSA:

  • Including the PSA as a particular case.
  • Dynamically generates the Event Tree (DET).
  • Defining a standard flow calculation.

Sequences obtained with the ISA involve a wide range of phenomena that BABIECA need be able to unify in a single process.

The main objectives of SCAIS are; automatically generate the ET associated with an initiating event and obtain the Damage Exceedance Frequency of a sequence given certain safety limits. These are the classical goals that you always have while using the methodology. After multiple applications made, we have seen that we can also perform:

  • Complete analysis taking into account parametric uncertainties and stochastic uncertainties.
  • Study SAMGs and EOPs where you can see the suitability of these methods to study the available time for the different actions.

Coupling Codes

Simulation of an accidental sequence involves phenomena of very different nature, such as thermal hydraulics, severe accident, operator actions, and many others, that are difficult to find in a single code. To integrate all these systems into a single process, the engine of the simulator has a communication layer capable of handling connections to any external or internal code, due to its standard calculation flow that any code based on time steps can follow.

With this feature you can:

  • Building a broad scope simulation system capable of dealing with phenomena that are found in a variety of sequences leading to core damage, by merging the modeling capabilities of various codes specific purpose.
  • Reuse inputs of the facilities developed by plants to carry out analysis of accidents, since different facilities may use different codes to simulate the same type of transient.

General Aspects

Babieca was developed in C + + language and allows easy integration of modules. To provide persistence to the system a PostgreSQL database is used where the generated outputs are stored and also SCAIS relevant coupled outputs from other codes are stored. The system has been developed to enable parallelization of calculation using the PVM paradigm. SCAIS has been fully developed with general programming standards and Open Source license. The inputs are generated for SCAIS language and XML with Xerces-c-managed labels.

The main features that can be distinguished in Babieca are:

  • Solve block diagrams;
  • manages the flow calculation;
  • discrete and continuous variables;
  • outputs and restarts.

The main class is BabiecaModule that is designed to manage the topology, events and temporal control of the simulation.

A topology is composed of modules representing parts of the system or physical mathematical tools. The modules are designed to perform specific calculations.

Among the modules found (some, not all);

  • PIPE; Module representing a unidimensional line
  • MIXRVI, MIXRCO – Modules for the inlet and outlet of the vessel.
  • UASG; This function computes the thermohydraulic properties of water using pressure and enthalpy
  • LOGATEHANDLER; Connecting gate systems to Dendros to open the ET branches.
  • CONVEX; Solve transfer functions of linear systems.
  • VMETODO; Solve differential systems by Runge Kutta method.
  • SNDCODE and RCVCODE. These two modules are inseparable and are responsibles for sending and receiving messages to communicate coupled codes.

Coupling boundary conditions or initial conditions

Coupling initial conditions

This type of coupling can be used when a particular code is out of its scope and new models from other codes available are needed. In this case the first code execution is suspended and transferred appropriate initial conditions ensuring consistency and continuity of the transition.

A typical example of this type of coupling is the transition of a plant code to a severe accident when these conditions have been met.

In Babieca this is achieved by allowing the modules to be active or inactive depending on their mode of simulation.

Boundary conditions

This type of coupling is used to build a comprehensive code from multiple codes with a more limited scope with which the computational power increases. Babieca also allows. This feature makes it easier to manage large topologies, because the user is able to convert a topology into a more user-friendly or have different characteristics and need to be in a different model.