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The intention of the startup physics tests was to confirm design characteristics of the core loading and their compliance with safety analysis preconditions. The program of startup tests for the leading unit is usually composed in such a way that is is possible to study as much neutron-physical characteristics as possible in the safest condition of zero power. State-of-the-art safety analysis is including computer codes that use three dimensional neutron kinetics and thermohydraulics models. For the substantiation of such models, for its validation and verification there is a need in reactor experiments that implementing spatially distributed transients. We based on such statements when composing hot zero power physical startup program for the new VVER-1200 unit of Novovoronezh NPP. Several tests unconventional for VVER were developed for that program. It includes measuring the worth for each of control rod groups and measuring of single rod worth from the inserted groups – test that models rod ejection event in some sense.

During the last decades several new VVER-1000 units of different projects have been commissioned. At some of them similar initial fuel loadings were implemented. To determine experimentally neutron-physics characteristics of those units almost similar physical start-up test programs were performed and measurement equipment were also similar. The paper presents the analysis of some result of neutron-physics characteristics that were carried out during physics start-up of VVER-1000 units with similar initial fuel loading. The subject of analysis is an estimation of experimental uncertainties. An effort is made to consider individual test result as a single random realization of universal set. It is assumed the analysis of individual results spread helps to estimate general inherent uncertainty of experiment.