The RTS-1 “Galileo Galilei” is an open pool research reactor light water moderated and cooled. It had a maximum thermal output of 5 MWth and an average thermal flux of 5 E+13 n/cm2sec. It became critical for the first time on April 1963 and it was definitely shutdown in March 1980. The reactor is situated at CISAM (Joint Centre of Studies and Military Application - Italian Ministry of Defence), S. Piero a Grado, Pisa, Italy, and its decommissioning is in progress. In this paper the strategy adopted to achieve the green status of the reactor site is discussed, with particular attention on the different steps to be done according to the national laws. Emphasis is placed on the characteristics of two different conditions required, namely Passive Protective Custody, which is a step necessary to allow the decay of the radioactive materials present into the plant to decrease the radiological risk to operate safely, and Unconditioned Release, in which all the materials can be released without radiological restrictions. Another aspect discussed in this paper is the effort spent on the determination of the radioisotopic abundance of the reactor components, the personal dose evaluation due to the necessary activities to achieve two different status of “Passive Protective Custody” and “Unconditioned Release” and the waste characterisation. The necessary authorisations to start decommissioning has been obtained as far as concern the removal of spent fuel and the dismantling of some experimental equipments.

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