Integrated Risk Assessment for Complex Systems

Scientific Essay, 2018
13 Pages, Grade: 2



Dan Serbanescu


Risk analyses are now at the point of moving to new horizons and solve new challenges. The search for new methods and / or integrated ones to cope with these tasks is a high challenge. The Integrated Risk Assessment (INTGRPRA) is part of this process and one of the possible solutions to many of the identified problems presented in (Serbanescu, 2005).


The issues related to risk evaluation are becoming more and more important for an extended area of topics. However there is a series of paradoxes identified, which are generated by various myths circulating in the risk theories. They are related to the definition of the object for the risk analyses in complex systems (RACS), the use of appropriate to the model methods in order to support extending the area of application to topics like ageing, commission errors (which could be called nonlinear tasks) and the communication of results, connected in fact with the first two problems.

One possible approach proposed to solve the problems generated by these paradoxes and requiring a solution is to perform with priority the following (see also Appendix):

- Clarify the representation of the whole model of RACS
- Improve methods able to use the combined deterministic and probabilistic approaches
- Clarify definitions of risk for various components of the RACS (public, regulator, industry)


Consideration of risk as being associated with the theory of complex systems will contain in itself reference to the notion of randomness and entropy. On the other side this process is also related to the need to identify the boundaries of the system evaluated, the method to be used in finding out truth statements about this system and the subject performing this knowledge quest.

A representation of the complex system – the nuclear power plant for the purpose of the evaluation of their safety was referenced in (Serbanescu, 2004). The complex system was represented as a hierarchical structured one on three levels, of which the first one is related to the generic society targets and objects. The next levels go to subsystems related to the regulatory, design and concept subsystems and to the operation and detailed evaluation. The system is represented with a feedback connection to the previous levels, assuring self-regulation. (Figure 1(a)) (See also Appendix).

Abbildung in dieser Leseprobe nicht enthalten

Figure 1 RACS model
(Serbanescu D., 2005 , ICRESH 2005, Bombay (unpublished))

Each level is defined by elements of the subsystems composing the whole. The elements of the sets at each level are connected on vertical (from level to level and on horizontal (at a given level). The vertical structure is defined by a relationship of a type “Element X is requiring element(s) Y with the degree of certainty W”. Figure 1(b) shows that at each level there are uncertainties connected to the rules environment, which indicates on the high importance of the type of inferences to be used, usually grouped in a conventional manner into deterministic and probabilistic ones. The three levels with the defined relation between levels generate on the created structure a sigma algebra, for which a norm can be used. For the third level of detail, risk can be used as a norm for the sigma algebras defined as per (Serbanescu, 2004). The method is using the standard tasks for Probabilistic Risk Assessment (PRA), with the structure as per Figure 2. In case of new designs or for special type of reactors (gas cooled ones for instance) important adjustments have to be made to PRA. In addition to the specifics of some new designs (for which a full PRA level 3 is needed due to the absence of the Core Damage) there is also the need to perform extensive sensitivity model runs, which require an integrated model of internal and external events (INTGRPRA) for all sources of radioactivity and all modes of operation (vanGraan et al, 2005)

Abbildung in dieser Leseprobe nicht enthalten

Figure 2 PRA model to support the definition of sigma algebras
(Serbanescu D., 2005 , ICRESH 2005, Bombay (unpublished))

Integration of external and internal events into one PRA model will also be done considering the fact that various tasks use various sub-models and computer codes as shown in Figure 3 for a model used for licensing purposes and in Figure 4 for a model used for the design optimization purposes.

The methods used to evaluate the risk criteria are for the models above are as per (van Graan et al, 2005 and Serbanescu, 2004). In the licensing application, the risk norm is used.


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Dan Serbanescu (Author), 2018, Integrated Risk Assessment for Complex Systems, Munich, GRIN Verlag,


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