Technical specification (TS) establishes the limits and conditions for the safety operation of Nuclear Power Plants. These limits and conditions have been originally based on engineering judgments and determinist analysis. Regulatory bodies are encouraging the use of Probabilistic Risk Assessment (PRA) to support a risk-informed regulatory framework, in particular for evaluating changes to TS seeking for an improvement in NPP safety. However, in spite of regulatory guides require that all sources of uncertainty be indentified and analyzed such that their impacts are understood, it is only recently when some guidance is being proposed on the systematic treatment of uncertainties associated with the use of the PRA in risk-informed decision making of LB changes. However, no specific guidance has been proposed yet for the treatment of uncertainties in analyzing TS changes. This paper presents an approach for the evaluation of the risk impact of changes to an Allowed Outage Time (AOT), which is part of the Limiting Condition for Operation (LCO) in TS, using a level I PRA including treatment of uncertainties. It is provided also a case study that focuses on an AOT change of the Accumulators System of a Nuclear Power Plant.