The last phase of a nuclear power plant life cycle is the decommissioning process. The three stages of nuclear power plant decommissioning are defined by the International Atomic Energy Agency – safe storage with surveillance, restricted site use, and unrestricted site use. This article deals with the financial aspects of nuclear power plant decommissioning using a protection safe storage before their final liquidation. This alternative is possible in the world today. The authors propose a calculation method of safe storage with surveillance time and the related costs. This method can be used not only for nuclear power plants safe storage with surveillance, but also for their protective safe storage. The method used the primary optimization calculation with subsequent corrections and is applied using the sample of the Biblis A Nuclear Power Plant in the Federal Republic of Germany. Ways of increasing the accuracy of this method are discussed at the conclusion of the article.