INFLUENCE OF DOSE-RATE ON TL RESPONSE OF HEAVILY IRRADIATED ROCK-SALT

The effect of high absorbed doses of gamma radiation on rock salt has been studied, in the framework of the 4th R&D programme of the Commiss ion of the European Communities 'Management and Storage of Radioactive Waste'. To fulfil the objectives of the aforementioned research, the Gamma Irradiation Facilities of the Joint Research Centre of the Europ ean Communities were used. These facilities operate with spent fuel wh ich allows dose rates up to 200 kGy.h(-1). Several experiments have be en performed so far, at dose rates of 4, 15 and 50 kGy.h(-1). Irradiat ions were performed under a controlled temperature of 100 degrees C an d total doses ranging from 20 kGy to 1223 MGy. The irradiated rock sal t was studied by thermoluminescence (TL). As expected, there was an in crease in the TL response with increasing dose. In addition, the tempe rature onset of the glow curve was shifted to higher temperatures with increasing dose. At doses around 800 MGy, the glow curve started abov e 430 degrees C, hindering its evaluation with a standard commercial T L reader. For the same absorbed dose, the TL response was higher in sa mples subjected to lower dose rate irradiations. This phenomenon was a lso detected with optical absorption spectroscopy measurements perform ed in the same samples. The results agree with the predicted concentra tion of radiation-induced defects present in the rock salt obtained by modelling.