Post-Closure Safety Analysis of Nuclear Waste Disposal in Deep Vertical Boreholes

Abstract

Isolation of spent nuclear fuel assemblies in deep vertical boreholes is analyzed. The main safety features of the borehole concept are related to the repository’s great depth, implying (a) long migration distances and correspondingly long travel times, allowing radionuclides to decay, (b) separation of the repository from the dynamic hydrological cycle near the land surface, (c) stable geological and hydrogeological conditions, and (d) a geochemically reducing environment. An integrated simulation model of the engineered and natural barrier systems has been developed to examine multiple scenarios of the release of radionuclides from the waste canisters, the transport through a fractured porous host rock, and the extraction of potentially contaminated drinking water from an aquifer. These generic simulations include thermal effects from both the natural geothermal gradient and the heat-generating waste, the influence of topography on regional groundwater flow, moderated by salinity stratification at depth, and the role of borehole sealing. The impact of these processes on the transport of select radionuclides is studied, which include long-lived, soluble, sorbing or highly mobile isotopes along with a decay chain of safety-relevant actinide metals. The generic analyses suggest that a deep vertical borehole repository has the potential to be a safe option for the disposal of certain waste streams, with the depth itself and the stable hydrogeological environment encountered in the emplacement zone providing inherent long-term isolation, which allows for reduced reliance on a complex engineered barrier system.

Forecast of 241Am Migration from a System of Deep Horizontal Boreholes

“…SNF and HLW are proposed to be disposed of in boreholes with a diameter of 0.2-0.8 m at a depth of up to 5 km, where the lower part with waste is from 1 to 3 km. This disposal option has been known for more than 65 years [14]; this concept has been repeatedly refined [15][16][17][18][19][20][21][22][23][24][25][26][27], although it has been noted [12,13,[23][24][25] that borehole disposal facilities cannot solely be used for the disposal of the entire range of HLW and SNF accumulated.…”

“…The GDF long-term safety is determined by the inventory of radionuclides that will be released from the repository into the biosphere. It can be estimated by modelling the migration of radionuclides [27,[31][32][33][34][35][36][37][38][39][40][41][42]. Disposal of waste in horizontal boreholes has a number of advantages over disposal in vertical boreholes of the same length.…”

Borehole RW Disposal Concept and Prospects of its Implementation in Russia

“…Организации по обращению с отходами и научные учреждения разных стран периодически проводят обзор и анализ осуществимости различных концепций удаления радиоактивных отходов (РАО) и отработавшего ядерного топлива (ОЯТ) в геологическую среду . На сегодня в мировой литературе между собой сравниваются, по крайней мере, три концепции геологической изоляции РАО: шахтные хранилища (ШХ), глубокое скважинное захоронение (ГСЗ/Deep Borehole Disposal) и захоронение в латеральных глубоких скважинах (ЛСЗ/Disposal in Horizontal Drillholes) [1][2][3] . ГСЗ подчас представляется как социально более приемлемая альтернатива ШХ, консенсус в отношении перспективности которой начал складываться еще 1960-х годах [4] .…”

Storage and Disposal Options for Nuclear Waste

“…These parameters can also be calculated using computational simulation. Oettingen [5] validated the NFCSS burnup system developed by the IAEA. In this work, data from the destructive analysis of the 254 PWR fuel samples from 15 reactors were used.…”