Abstract
ABSTRACTThere are two units with RBMK-1500 type reactors at the Ignalina Nuclear Power Plant (Ignalina NPP) in Lithuania where graphite was used as a neutron moderator and reflector. These reactors are now being decommissioned, and Lithuania has to find a solution for safe irradiated graphite disposal. It cannot be disposed of in a near surface repository due to large amounts of14C (radiocarbon, carbon-14); thus, a deep geological repository (DGR) is analyzed as an option. This study had the aim to evaluate14C migration from the RBMK-1500 irradiated graphite disposed of in a potential DGR in crystalline rocks taking into account the outcomes of the research performed under the collaborative European project CAST (CArbon-14 Source Term) and to identify the potential to reduce the conservatism in the assumptions that was introduced in the lack of data and led in the overestimated14C migration. The information gathered during the CAST project was used to model14C transport in the near field by the water pathway and to perform uncertainty analysis. The study demonstrated that more realistic assumptions could reduce the estimated14C flux from the near field by approximately one order of magnitude in comparison with the previous estimations based on very conservative assumptions.
Highlights
The Ignalina Nuclear Power Plant (Ignalina NPP) in Lithuania has two RBMK-1500 type reactors and they are currently being decommissioned
There are two units with RBMK-1500 type reactors at the Ignalina Nuclear Power Plant (Ignalina NPP) in Lithuania where graphite was used as a neutron moderator and reflector
This study had the aim to evaluate 14C migration from the RBMK-1500 irradiated graphite disposed of in a potential deep geological repository (DGR) in crystalline rocks taking into account the outcomes of the research performed under the collaborative European project CAST (CArbon-14 Source Term) and to identify the potential to reduce the conservatism in the assumptions that was introduced in the lack of data and led in the overestimated 14C migration
Summary
The Ignalina Nuclear Power Plant (Ignalina NPP) in Lithuania has two RBMK-1500 type reactors and they are currently being decommissioned. Graphite in the RBMK-1500 type reactors was used as a neutron moderator and reflector. As a result of Ignalina NPP operation, about 3800 t of irradiated graphite (i-graphite) was generated (Poskas et al 2012). One of the key radionuclides in the i-graphite is 14C. Its long half-life (5730 yr) and the role in biological processes require appropriate treatment and disposal of i-graphite waste. The final decision on the i-graphite management route in Lithuania has not yet been taken; disposal in a deep geological repository (DGR) is considered as a potential solution
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