Maddalena Casamirra

Fuzzy modelling of HEART methodology: application in safety analyses of accidental exposure in irradiation plants

This study refers to the results obtained by Fuzzy Fault Tree analyses of accidental scenarios that entail the potential exposure of operators working in irradiation industrial plants. For these analyses, the HEART methodology, a first generation of the Human Reliability Analysis method, has been employed to evaluate the probability of human erroneous actions. This technique has been modified on the basis of a fuzzy set concept to more directly take into account the uncertainties of the so-called error-promoting factors, on which the method is grounded. The results also allow us to provide some recommendations on procedures and safety equipment to reduce the risk of radiological exposure.

Decay Heat Removal and Transient Analysis in Accidental Conditions in the EFIT Reactor

The development of a conceptual design of an industrial-scale transmutation facility (EFIT) of several 100 MW thermal power based on accelerator-driven system (ADS) is addressed in the frame of the European EUROTRANS Integral Project. In normal operation, the core power of EFIT reactor is removed through steam generators by four secondary loops fed by water. A safety-related decay heat removal (DHR) system provided with four independent inherently safe loops is installed in the primary vessel to remove the decay heat by natural convection circulation under accidental conditions which are caused by a loss-of-heat sink (LOHS). In order to confirm the adequacy of the adopted solution for decay heat removal in accidental conditions, some multi-D analyses have been carried out with the SIMMER-III code. The results of the SIMMER-III code have been then used to support the RELAP5 1D representation of the natural circulation flow paths in the reactor vessel. Finally, the thermal-hydraulic RELAP5 code has been employed for the analysis of LOHS accidental scenarios.

TREEZZY2, a Fuzzy Logic Computer Code for Fault Tree and Event Tree Analyses

In conventional approach to reliability analysis using logical trees methodologies, uncertainties in system components or basic events failure probabilities are approached by assuming probability distribution functions. However, data are often insufficient for statistical estimation, and therefore it is required to resort to approximate estimations. Moreover, complicate calculations are needed to propagate uncertainties up to the final results. In our work, in order to take account of the uncertainties in system failure probabilities, the methodology based on fuzzy sets theory is used both in fault tree and event tree analyses. This paper just presents our work in this issue, which resulted in a computer program named TREEZZY (TREE fuZZY).

Dry deposition models for radionuclides dispersed in air: a new approach for deposition velocity evaluation schema

In the framework of a National Research Program funded by the Italian Minister of Economic Development, the Department of Energy, Information Engineering and Mathematical Models (DEIM) of Palermo University and ENEA Research Centre of Bologna, Italy are performing several research activities to study physical models and mathematical approaches aimed at investigating dry deposition mechanisms of radioactive pollutants. On the basis of such studies, a new approach to evaluate the dry deposition velocity for particles is proposed. Comparisons with some literature experimental data show that the proposed dry deposition scheme can capture the main phenomena involved in the dry deposition process successfully.

Analysis of Protected Accidental Transients in the EFIT Reactor With the RELAP5 Thermal-Hydraulic Code

The European Facility for Industrial Transmutation (EFIT) is aimed at demonstrating the feasibility of transmutation process through the Accelerator Driven System (ADS) route on an industrial scale. The conceptual design of this reactor of about 400 MW thermal power is under development in the frame of the European EUROTRANS Integrated Project of the EURATOM Sixth Framework Program (FP6). EFIT is a pool-type reactor cooled by forced circulation of lead in the primary system where the heat is removed by steam generators installed inside the reactor vessel. The reactor power is sustained by a spallation neutron source supplied by a proton beam impinging on a lead target at the core centre. A safety-related Decay Heat Removal (DHR) system provided with four independent inherently safe loops is installed in the primary vessel to remove the decay heat in case of loss of secondary circuits heat removal capability. A quite detailed model of the EFIT reactor has been developed for the RELAP5 thermal-hydraulic code to be used in preliminary accidental transient analyses aimed at verifying the validity of the adopted solutions for the current reactor design with respect to the safety requirements, and confirm the inherent safety behavior of the reactor, such as decay heat removal in accidental conditions relying on natural circulation in the primary system. The accident analyses for the EFIT reactor include both protected and unprotected transients, on whether the reactor automatic trip, consisting in proton beam switch off, is actuated or not by the protection system. In this paper, the main results of the analyses of some protected transients with RELAP5 are presented. The analyzed transients concern the Protected Loss of Heat Sink (PLOHS), in which the DHR system plays a key role in bringing the reactor in safe conditions, and the Protected Loss of Flow (PLOF) transients with partial or total loss of forced circulation in the primary system.Copyright

Safety analysis in the LBE-Cooled XADS plant through an integrated use of HAZOP, FAULT TREE and thermalhydraulic transient analyses

A detailed description of possible accidental scenarios, with their frequency of occurrence and their consequences, taking into account both internal and external causes that might contribute to them, can be attained by using the most important risk analysis methodologies (HAZard and OPerability studies, HAZOP; Event Tree, ET; Fault Tree, FT; etc.). As it is known, the Fault Tree methodology is aimed at the evaluation of the frequency of an undesired accidental event (Top Event, TE), and is used to describe this one as a combination of primary events identified, for example, by a HAZOP analysis [1]. However, the classic HAZOP analysis, while allowing to perform an exhaustive study of the examined plant process, generally doesn’t permit to reconstruct the sequences that might bring the plant to the identified accidental events [2].