Preliminary Study on Static and Dynamic Stability of Canister for High-level Radioactive Nuclear Waste Disposal Based on Discrete Element Method
Received date: 2022-12-17
Revised date: 2023-04-06
Online published: 2023-09-20
Canister for high-level radioactive waste is a core part in nuclear waste disposal barrier,and its static and dynamic stability during transportation,installation,and deep buried operation is of great importance.A silicon carbide(SiC) material based canister was proposed in this paper.The material has remarkable chemical stability,but its brittleness may be the key to restrict it application.In oder to investigate the static and dynamic stability of this canister,series of numerical simulations were performed using discrete element method,considering the physical nature of rock blocks and characteristics of interactions between rock and canister.The tensile strength characteristics of SiC was first investigated via specially designed lab and numerical tests.Comparison with analytical results has proved the reliability of adopted numerical method.The influence of disposal depth and horizontal to vertical stress ratio was then investigated.The dynamic loading behaviour pattern and basic failure mode of canister under free fall and rock impact were investigated,and the influence of rock fragmentation was mainly considered.The results show that the silicon carbide material is relatively brittle,with tested tensile strength between 150 MPa and 200 MPa,compared to its very high compressive strength.The tensile strength of silicon carbide was chosen 150 MPa for safety reason in later analysis.However,this value of 150 MPa is higher than the tensile or even compressive strength of ordinary rocks.The canister can survive under 1 200 m depth,horizontal to vertical stress ratio of 3 with several disposal inclination angles.Under free fall,the maximum tensile stress in canister is determined by falling height and inclination angle.Upon rock fall without rock splitting,the maximum tensile stress in canister is determined by rock weight and contact type between rock and canister.Inclusion of rock splitting in model calculation can produce stress much lower than by traditional continuum method.The tip of the rock will crack first once the rock is hitting the canister,leaving the canister safe in the first place,which is different from that in continuum analysis.This implies the energy dissipation between rock blocks due to fracturing of rock during rock impact is not negligible.As the cohesion and residual friction angle between rock blocks increase,the stress induced in canister also increases,while the tension makes limited contribution to elevated stress.Another interesting finding is that as the rock block volume ratio gets smaller,the stress induced by impacting rock decreases first but then keeps to a constant value once certain threshold is reached.This suggests by reaching certain rock block volume ratio may be enough to reproduce dynamic impact-induced cracking,instead of decreasing rock block size constantly.Although local failure is expected under dynamic impact,a soft buffer layer with certain thickness outside the canister can guarantee static and dynamic stability of SiC canister together with appropriate emplacement.
Yanan ZHAO , Yihang ZHAO , Zhongming JIANG , Hongmin ZHAO . Preliminary Study on Static and Dynamic Stability of Canister for High-level Radioactive Nuclear Waste Disposal Based on Discrete Element Method[J]. Gold Science and Technology, 2023 , 31(4) : 592 -604 . DOI: 10.11872/j.issn.1005-2518.2023.04.010
http://www.goldsci.ac.cn/article/2023/1005-2518/1005-2518-2023-31-4-592.shtml
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