Criteria for confinement of radioactive debris of Chernobyl NPP fourth power unit

In 1986 a sarcophagus (the Shelter) was constructed above the Chernobyl NPP fourth unit that was destroyed by a beyond the design-basis accident. The Shelter confines radioactive debris with the total activity of long-lived radionuclides of about 20 MCi. The Shelter performs a confining function presently, however it does not meet standards for mechanical stability, structural integrity and reliability. During 16 years of operation, its condition has deteriorated. The international Shelter Implementation Plan being carried out at the destroyed power unit provides for the stabilization of the existing Shelter and creation of new safe confinement as the most important safety measures. This report deals with the safety criteria to be applied during the measures on confinement and reliable isolation of the radioactive debris of the ChNPP fourth unit.(author)