Title: ANALYSIS OF THE THERMAL METHODS USED TO DETERMINE THE AMOUNT OF NUCLEAR FUEL IN THE SARCOPHAGUS
Authors: K.P.Checherov (The Russia Scientific Center "Kurchatov Institute", 1 Kurchatov Av., Moscow, Russia)

The heat sources in the unit 4 of the Chernobyl NPP are shown not to be merely accumulations of fuel-containing materials (FCM), but also to include electrical equipment, heating and hot water supply and other sources; it is further shown that, by comparison with non-nuclear sources of energy, they are a small or insignificant part of the energy releases within the Sarcophagus. Comparison of the various sources of energy release has revealed a number of characteristic features of the thermal status of the Sarcophagus:
1. in connection with the scaling down of operations in the period 1988-1992, the internal (non-nuclear) heat sources are clearly decreasing with time;
2. technogenic factors connected with switching the heating on and off are superimposed on the seasonal fluctuations in the thermal state of the Sarcophagus;
3. convective heat exchange between the Sarcophagus and the environment creates a thermal background on such a scale that switching on the equipment with a rating of approx. 100 kW (or an input of other sources at the same time) has a negligible effect on the thermal state of the Sarcophagus;
4. the task of accurate determining the amount of nuclear fuel, which is not the only or the main source of heat, and is in general a minor source, is extremely difficult.
An analysis has been made of the estimates of the amount of nuclear fuel within the Sarcophagus based on heat measurements. Error sources in these estimates are demonstrated. A definition is given of the conditions that must be satisfied for the adequate determination of the amount of nuclear fuel from the measurements [1].

Comments: Figs. 0, Refs. 3, Tabs. 3.