Study On The Corrosion Behavior Of Nuclear Waste Container In Deep Geological Disposal Environment

The huge amount of nuclear waste generated inevitably during the period of nuclear usage has been a tough problem which aroused great attention. Considering the threat from its leakage if unreasonable disposal method is adopted, the urgent affairs are disposal method assessment and safety evaluation after a comprehensive discussion. The most acceptable and welcomed method is “deep geological disposal” including an artificial barrier and natural barrier which constitute the “multi-barrier system”. The artificial barrier involves the solidified nuclear waste, compacter and buffer backfilled materials and the natural barrier generally is the local rock. When underground water permeates to the surface of nuclear waste container through the buffer backfilled materials and the heat releases from the nuclear disintegration in the disposal period, an aggressive corrosion-oriented environment is generated. In the meanwhile, the trapped oxygen in the disposal will be consumed gradually during the initial years and hydrogen evolution will become the dominate reaction afterwards, contributing to the possible hydrogen brittlement of the waste container because of the hydrogen desorption and permeation. As the first protective parclose to ensure well sealing of the waste, nuclear waste container needs to be studied on the corrosion behavior in the long term disposal period.This paper studied the corrosion behavior of Q235 steel, TA2 and TA8-1 which were preselected as the container materials in simulated deep geological disposal environment of Beishan area to be served as the preselected high-level nuclear waste disposal area in our country. Electrochemistry technology was adopted in both underground water and highly compated bentonite environments. The results show that higher temperatures facilitate the performance of corrosion products compared with lower temperatures. The corrosion rate in highly compacted bentonite environment proves to be smaller than that of underground water environment especially for titanium and titanium alloy which present a much smaller corrosion rate in saturated compacted bentonite than that of lower water contents. However, the corrosion rate shows an obvious increase when it comes to the higher water content apart from saturated condition compared with the other water contents due to the boundary generated from saturated and unsaturated compacted bentonite. The decrease of water content in compacted bentonite limits the hydration of ions and the number decrease of conductive ions leads to a higher bentonite resistance, becoming the limitation step of corrosion in low water content. The decline of corrosive potential for all three materials keeps coherence with the water content decrease in general. What’s more, oxygen diffusion becomes the main corrosion controlling step for high water content benonite.The maximum of corrosion rate is predicted to exist in the temperature rapid increase stage when the bentonite water content rises abruptly or just after the bentonite saturation stage. Because of the temperature declining and long term deoxidation disposal environment, the corrosion rate holds a low extent.