Abstract
ABSTRACTIgnalina NPP contains two Units with RBMK-1500 reactors. After shutdown, several Unit 1 systems and equipment were radiologically characterized and dismantled. The highest volume of reactor structures is attributed to the graphite stack of the reactor core, radiological characterization of which has not yet been performed. The stack can be visualized as a vertical cylinder 8 m high and 14 m diameter, made up of 2488 columns where each column is made up from several graphite blocks. The total mass of the graphite stack blocks is about 1700 tonnes. Therefore, the main goal of work reported in this paper was to estimate the inventory of14C and other key radionuclides in the irradiated graphite by a combination of activity measurements and full 3D reactor graphite stack neutron activation modeling. Obtained results show that, based on the combination of modeling and measurement techniques, the total inventory of14C in graphite stack is estimated at 3.22×1014Bq at 9 years after Unit 1 reactor final shutdown.14C activity is the highest among the analyzed radionuclides; the second highest is60Co (~6 times lower).
Highlights
The Ignalina NPP is located in the northeast part of Lithuania and contains two power units with an RBMK-1500 reactor in each unit
The highest volume of reactor structures is attributed to the stack of the reactor core, which is constructed from graphite blocks; the radiological characterization of this is of great importance
This paper presented preliminary studies of the experimental 14C, 3H, 36Cl, and 60Co activity measurements in several graphite sub-samples, attributed to the same sample of the GR-280 grade graphite bushing from the temperature channel of the Ignalina NPP Unit 1 RBMK-1500 reactor
Summary
The Ignalina NPP is located in the northeast part of Lithuania and contains two power units with an RBMK-1500 reactor in each unit. Earlier studies (Ancius et al 2005; Smaizys et al 2005; Narkunas et al 2010) revealed that the radiological inventory in irradiated RBMK-1500 reactor graphite could be dominated by the radionuclide 14C, estimations were based on conservative assumptions and lacked experimental activity measurement data. Within the EC 7th FP project CAST, one of the tasks was to estimate 14C inventory based on a combination of available activity measurements and full 3D reactor graphite stack neutron activation modeling. Results in relation to 14C, as well as 3H, 36Cl, and 60Co inventory estimations, are presented in this paper
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