Abstract of Meeting Paper

Society for Risk Analysis-Europe 1997 Annual Meeting

Potential Risks Realization At The Shelter Site 4 Chernobyl NPP. E. L. Belousov and V. I. Kupny, Scientific Centre for Radiation Medicine, Ukrainian Academy of Medical Science, Melnikova st. 3, Kiev 252051, Ukraine

Currently, the following initial events may be identified which may cause a radiation accident: seismic occurrences and their consequences; tornado; air crash, flood; accidents leading to buildings and premises flooding, fires, explosions caused by chemical reactions (e.g. explosion of radiolysis hydrogen), equipment elements and building structures degradation, in particular: changes of physical condition of nuclear-hazardous fissile materials.

The gravest consequences will be caused by a collapse and destruction of the roof which will result in disappearance of a barrier between heavily contaminated surfaces of the central hall and the atmosphere. A serious effect of the considered event may be a release of radionuclides contained in the dust which is accumulated on elements of the destroyed building structures and in a layer of dumped materials of the accident localization in the central hall.

The worst scenario of a hypothetical accident to be considered may be a simultaneous or successive effect upon the Shelter site of a tornado and earthquake (average annual probabilities are 0.000003 and 0.01 respectively) which, in the most pessimistic scenario, may lead to the spread out of the entire non-fixed dust from the Shelter. The aggregate activity which may be released from the Shelter is estimated, according to different sources, to attain 1.3 mnCi.

In any event, the following calculations result appears to be undoubted: the roof collapse may lead to serious consequences in the immediate neighbourhood to the Shelter - at the plot with the length and width of several hundred meters (including operating units).

The water leaking into the site may become a source of several types of hazards:

• when appearing on accumulations of fuel-containing masses the water leads to the increase of a coefficient of neutrons multiplication in the system;

• transporting the enriched uranium dissolved salts, the water also raises a potential hazard of the site for ground waters;

• the water destroys FCM and fosters the uncontrolled transfer of radioactivity along the Shelter's internal premises;

• the water represents a cause for the Shelter's building structures destruction acceleration.

Consequences of a spontaneous chain reaction will depend on the critical mass formation rate, amount of FCMS. The energy of "shells" spread may be large enough to cause an additional dust rise. The emergence of a SCR will not jeopardize the population but will be of danger to the personnel.

The impact of an air crash upon the Shelter will be similar to that of the Shelter’s roof collapse. The consequences of fire within the Shelter site are estimated as minor and capable of leading to a local radiation accident.

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