TIMODAZ Project
Thermal impact on the stability of the lining
TIMODAZ (Thermal Impact on the Damage Zone around a Radioactive Waste Disposal in Clay Host Rocks) is an international research project one of the participants in which is the Centre for Experimental Geotechnics. The aim of the research is to investigate the effects of long-term thermal load on lining stability; the concept behind the research i.e., to determine the “ideal” form of spent nuclear fuel transformation technology in the mid- to long-term, follows extensive global discussion on this theme. Any eventual spent fuel transformation technology would require the safe removal of spent fuel from deep underground disposal. The extreme long-term functioning of the lining around the disposal vessel is one of the premises for the safe removal of spent fuel canisters from the engineered barrier. The long-term effects of heat could well bring about a severe reduction in the stability of the lining caused either by deterioration in the strength properties of the lining material or by the occurrence of deformations resulting in a collapse in the shape of the lining.
The experiment will consist of two physical tunnel lining models which will simulate two extreme cases of the effects of temperature on lining stability:
1) An “in situ” experiment within the Josef gallery
2) An underground silo experiment at the CEG laboratory
“In situ” experiment
This experiment simulates a thermally loaded lining which is not permitted to deform towards the rock massif and which therefore will experience an increase in stress. The stress should not exceed the loading capacity of the lining. The same lining as in PRACLAY project is used.
Long-term continuous measurement performed on the fully-instrumented model will provide data on temperature distribution and changes in stresses in several locations - in the surrounding rock massif, on the rock-lining contact and also inside the lining segments. The specialised radon detection will be performed by cooperating experts from the CTU in Prague.
The heating system consists of plastic tube heating spiral with hot water circulating inside, heater tanks, pumps and unit for regulation of the water temperature. The heating spiral is fixed on the inner surface of the lining tube and covered by thermal insulation. Maximum temperature of the surface of the lining will not exceed 90°C.
It is possible to check on-line and to visualize all the data on web site of the experiment. Two web cameras monitor the experiment continuously. http://uef-josef.uef-josef.eu/misc/mereni/
Construction phase commenced in February 2008. The experiment was switched-on on 30th October 2008.
Number of participating European institutions: 14
Project budget: 3,948,585 Euro
Project duration: 48 months (commenced 10/2006)
A short drift in the renovated part of the Josef gallery (the West Čelina belt) was chosen for the construction and performance of the experiment (see first picture). The rock environment within which the experiment is being constructed consists of tuffites with a high compression strength (230 MPa). Thermal conductivity is in the range of 3.6 W/mK; specific density is approximately 2740kg/m3.
