# Safety of Nuclear Power Plants with Respect to the Fault Displacement Hazard
## 4 Baseline Information for Plant Response to Permanent Ground Displacement
### Studies Contributing to Understanding the Case of Plant Responses to PGD  
For the evaluation of the consequences of differential settlement, useful experiences have been gained from the linear and non-linear analysis performed for the case of liquefaction for Nuclear Power Plant Paks, Hungary [29]. Although the physical phenomena of liquefaction and PGD is differing, the differential settlement in both cases cause similar static demand on the structure.  
The differential settlement in the study for Paks Nuclear Power Plant was comparable with the \(\delta a\) in the JANSI-FDE-03 [22] study. Here, the normal operational loads and the loss-of-coolant accident have been combined with the loads due to differential settlement. The load case was considered as a beyond design basis one. Except for the earthquake loads, a \"ready to use\" methodology does not exist for the beyond design basis analysis and evaluations. Therefore, the analysis and evaluation procedure were developed on the basis of standards ASCE/SEI 43-05 [30], FEMA-356 [31], EC 8-3 [32; 33]. The ASCE/SEI 43-05 \"slightly damaged, LS-C\" and \"significant damages, LS-B\" damage levels were set for the ultimate acceptable condition of the structures. These are practically equivalent with the categories \"immediate occupancy, IO\" and \"life safety, LS\" according to FEMA-365. The starting point was to justify the IO criteria. For the containment, this assumption complies with the general integrity criteria of the IAEA Safety Guide NS-G-1.10 [34]. If all relevant structural components resist the loads of differential settlement and loss-of-coolant accident in compliance with IO level, the nuclear safety criteria are met. Moreover, it is also assumed that the structures provide reliable supports for systems and components. In case of an LS condition, focused analysis has been made for the proof of the integrity/stability of the entire building and demonstrating that the safety functions will not behindered. The FEMA-365 NC condition could also be allowed for non-supporting structural elements if the damages of these structural elements do not affect the safety functions. The damage limits for the evaluation of conditions developed on the basis of EC-2 [35], E-3 [36], E-7 [37] and FEMA-356 [38; 39; 40; 31] are presented for some structural elements in the Table 1.  
For the systems and components inside the buildings, the effect of tilt on the integrity and function have been analyzed. Specific analyses have been made for underground piping and for the lifelines at the interfaces between adjacent structures. Piping and equipment have been examined per safety class, according to ASME Section III Division 1 for Service Level D [39]. The examination of the strain of containment liner has been performed according to ASME Section III Division 2 Table CC-3720-1 (Factored category, Combined Membrane and Bending) [40].  
The findings of the Paks NPP case study [41] will be implicitly used below during the qualitative judgement of the failure modes caused by differential settlement.