Safety integrity level fault tree

In order to determine the required safety integrity level, the expected number of demands on the overfilling protection is calculated in the first place. These demands stem from the operational level, which is modelled by the fault tree of Fig. 11.8. This fault tree is quantified with the data from Table 11.7. 

Dutuit, Y, Innal, R, Rauzy, A. and Signoret, J.-P. 2008. Probabilistic assessments in relationship with safety integrity levels by using Fault Trees, Reliab. Eng. Syst. Safety vol. 93 Issue 12, Dec. 2008. 

Safety integrity level (SIL) by fault tree analysis (FTA). 

FTA, fault tree analysis LOPA, layer of protection analysis NR, not recommended PFDavgt probability of failure on demand SIL, safety integrity level X, acceptable. ... 

Technical Report ISA-TR84.00.02-2002-Part 3 Safety Instrumented Functions (SIF)- Safety Integrity Level (SIL) Evaluation Techniques Part 3 Determining the SIL of a SIF via Fault Tree Analysis, June 2002. 

Dutuit, Y, Innal, F., Rauzy, A. Signoret, X-P. (2008). Probabilistic Assessments in Relationship with Safety Integrity Levels by Using Fault Trees. Reliability Engineering and System Safety 93 1867-1876. 

RAU 06] Rauzy A., Dutuit Y., Signoret J.P., Assessment of safety integrity levels with fault trees , ESREL 2006, Estoril, Portugal, 2006. 

Summary of key functional safety requirements, estimated demand rates and risk reduction factors together with target safety integrity levels (SILs), analyses and fault tree logic diagrams where appropriate. 

ABSTRACT Technological advancements in area of sensor-based online maintenance systems have made the possibility of repairing some failed safety support systems of Nuclear Power Plants (NPP) such as electrical supply, I C systems, ventilation systems. However, the possibility of repair during accident situation is yet to be included into PSA level-1. Therefore, this paper presents a scheme of PSA level-1 by implementing an integrated method of Repairable Event Tree (RET) and Repairable Fault Tree (RET) analysis. The Core Damage Frequency (CDF) is calculated from consequence probabilities of the RET. An initiating event of Decay Heat Removal (DHR) systems of ASTRID reactor is analyzed. The proportionate CDFs estimated with repair and without repair have been compared and found that the recoveries can reduce CDF. In sum, this paper attempts to deal with the possibility of repair of some safety systems in PSA and its impacts on CDF of the NPP. 

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