PSI - Issue 28

Dmitry O. Reznikov et al. / Procedia Structural Integrity 28 (2020) 1360–1368 D.Reznikov, N.Makhutov,O.Yudina / Structural Integrity Procedia 00 (2019) 000–000

1363

4

where F U ( x ) is cumulative probability distribution function of the economic loss U ; f U ( x ) is the probability density function of the economic loss. The mathematical mean of the economic loss E { U } is the most commonly used economic risk index:

{ } U U I E U x f x dx       ( )

0

Risk based management is to be carried out in the presence of two competing groups of requirements aimed at ensuring economic efficiency and safety of the facility. In this regard two types of management strategies can be developed that use various risks as control parameters: 1) Some parameters of risk are used as limitations when the optimization problem is being solved. In particular the limitation on individual risk value is often imposed as risk acceptance criteria. That could be maximization of profit Π generated by the facility in presence of limitation on individual [ R i ] and/or societal risk [ I n ]

max N N I I 

[ ] max or Ri Ri  



[ ]

2) Criteria of the accessibility of individual and/or social risk are used as limitations of the optimization problem while economic risks are included directly/implicitly in the objective function. In other words economic risks are included in the functional that determines the total costs of the HIF life cycle (Makhutov and Reznikov, 2012; Shubinsky and Zamyshlyaev, A., 2015).

min Ri Ri 

C 

[ ]

where C Σ are the life cycle costs that include costs of design Cdes, construction C con , operation C op and decommissioning C dec of the facility in question, as well as expected losses E { U } from potential accidents at the facility during its life cycle: { } d es con op dec C C C C C E U       . The optimization problem should be solved in presence of limitations regarding the magnitude of risks which should not exceed the normative maximum allowed values established on the basis of classifying the facility into a certain category. This determines the groups of interrelated problems of assessment, regulation, and management of risks associated with the operation of the facility in question. Another distinctive feature of the risk management is that it is carried out in the presence of a high level of uncertainty. In this case, two fundamentally different types of uncertainties can be distinguished that determine the level of risks induced by HIFs: - Uncertainties associated with the limited knowledge about the complex processes taking place in the HIF and about the interactions between its components (type 1 uncertainties). - Uncertainties due to the natural variability of the HIF parameters and the random nature of the external impacts (type 2 uncertainties). In accordance with this, there are two basic ways to reduce uncertainties that form the basis of risk based management (Health and Safety Executive, 2002): - To reduce the uncertainties of the 1st type, a comprehensive research programs should be developed aimed at constructing more sophisticated and adequate mathematical models of HIF, allowing one to predict more accurately various scenarios of the HIF evolution and to exclude the most catastrophic scenarios by building protection barriers. - To reduce uncertainties of the 2nd type, a comprehensive monitoring should be carried out aimed at obtaining additional information about the HIF, and comprehensive systems for technical diagnostics should be created to reduce the level of uncertainty regarding the current state of the HIF (the degree of damage to critical components of