Nuclear safety
An International Forum on Chernobyl's Nuclear Safety Aspects was held in Vienna from 1 to 3 April 1996 under the sponsorship of the IAEA and the UN Department of Humanitarian Affairs. The Forum results were reported at the Chernobyl Conference. Some highlights follow:
Causes of the Accident: The available detailed information is sufficient to identify the causes of the accident and to take effective measures to prevent the repetition of such an event. It was confirmed that:
- there were significant deficiencies in the design of the
reactor - in particular of its shutdown system - and operating
procedures were severely violated at the time of the accident;
- there was a lack of safety culture in the organizations responsible for operation and for control: important safety weaknesses had been recognized long before the accident occurred but were not remedied.
Safety of RBMKs. Between 1987 and 1991, a first stage of safety upgrading was performed on all RBMK units of the Chernobyl type, which addressed the most serious problems identified, as follows:
- void reactivity effect has been reduced;
- the efficiency of the scram system has been increased;
- the operational organization has strengthened.
Issues beyond the scope of this first stage of upgradings still require more detailed attention entailing varying requirements corresponding to the different generations of RBMK reactors.
The Sarcophagus. Broad agreement was reached that there is a risk of partial or total collapse of the sarcophagus during its design lifetime (approximately 30 years). While even in the worst case of a complete collapse widespread effects would not be expected, the stabilization of the sarcophagus is a high priority safety issue.
The sarcophagus is currently safe from the point of view of criticality. However, configurations of fuel masses exist inside it which could reach a critical state when in contact with water. Although this potential criticality could not lead to large off-site releases, water entering the sarcophagus is a further significant safety issue.
Potential safety implications of the proximity of the sarcophagus to the remaining operating unit of Chernobyl need further investigation.