Analysis of GDH blockage event at ignalina NPP

The paper presents analysis of the postulated blocking of coolant flow rate in Group Distribution Header event at Ignalina NPP. Two types of analysis-'best estimate' and 'partially-conservative' are performed. Best-estimate' approach is based on the best estimate codes with realistic boundary and initial conditions plus uncertainty analysis, while partially-conservative' approach - on the best estimate codes with conservative boundary and initial conditions plus conservative assumptions. The performed comparison of both calculations show that the peak fuel cladding temperatures for 'best-estimate' calculation taking into account the uncertainty analysis is slightly lower in comparison with partially-conservative' calculation. 'Partially-conservative' approach requires considerably less computational time. However, when with this methodology obtained results do not meet acceptance criteria (as it was in this particular case), the complete analysis by employing 'best-estimate' approach is necessary. (author)