ie 1.
on the site itself
0.3
-
2.
up to 20 km
3.
up to 30 km
<
0.5% of the fuel
1.5 2.0% of the fuel
-
1.0 1.5% of the fuel.
The size of the particles varied considerably, being from <1 micron (millionth of a metre) to 10's of microns.
On matters, relating to Stabilization of the Core Debris, the expert was Dr D Powers of Sandia National Laboratories. The core debris did not interact with the concrete base mat of the reactor. Nevertheless, it was suggested that for other reactor systems it would be useful to exchange ideas and research data on the development of refractory (ie high temperature) concretes.
Since the accident management procedures adopted appeared so successful more details were sought on the materials dropped on the reactor, where they went and the sequence in which they
About were dropped. The following further details were given. 5000 tons in all were dropped between the 27 April and 10 May, the bulk of it between 28 April and 2 May. First 40 tons of boron carbide were used to ensure that the chain reaction was definitely shut down. Then 800 tons of dolomite (limestone) were used because the CO2 generated when it decomposed in the heat would starve the graphite fire of oxygen. There followed 2400 tons of lead. The main purpose of this was to remove heat from the core region the idea being that it would melt, run down to the bottom of the debris and carry away. The covering material was clay and sand to act as a filter to stop fission products reaching the atmosphere.
Questions on the special building being constructed to entomb the remains of the reactor concentrated upon the criteria which would be used for its construction.
The final part of the session was devoted to finishing the work of Working Group 1. In particular Mr Frescura again addressed the issues of design for safety. Professor Kuglin
These included all gave an overview of procedures in the USSR. the main features of western practice. That is: an examination of a wide range of possible events associated with failures of individual components, from which a list is agreed with the licensing bodies. This is the same for all reactor types. Using this agreed list a volume of "technological justification for safety" is submitted and agreed. From this is derived working documentation.
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