実規模原位置試験の連成挙動評価研究

Research on evaluation of coupled thermo-hydro-mechanical phenomena against full-scale in-situ experiment

千々松 正和*; 雨宮 清*; 山下 亮*

Chijimatsu, Masakazu*; Amemiya, Kiyoshi*; Yamashita, Ryo*

地層処分を確実に行なうためには、人工バリアの健全性を確保する必要がある。人工バリアの健全性において重要な要因の一つとなるのが緩衝材の施工技術であり、緩衝材が設計に基づいて施工されることが必要である。本研究では、緩衝材をブロックで施工した場合に考えられるブロック間や岩盤あるいはオーバーパックとの隙間の充填性に関する検討を実施することとし、隙間をベントナイトペレットで充填した際の充填性に関して検討を行う。検討対象は、ベントナイトペレット充填層の透水性および密度の経時変化、浸潤水が人工海水となった時の止水性等である。また、施工された緩衝材内には、処分後、廃棄体からの発熱、地下水の浸潤、周辺岩盤からの地圧や緩衝材の膨潤といった連成挙動が発現すると考えられる。これらの現象を理解、評価するためには、人工バリアを対象とした原位置での実規模試験の情報に基づき、適切なモデルを構築する必要がある。ここでは、スウェーデン・エスポ島で行なわれている実規模緩衝材を用いた実証試験(Prototype Repository Project)の連成解析評価を実施した。

In order to achieve the geological disposal of radioactive waste in safe, it is necessary to ensure the stability of the engineered barrier system (EBS). One of the most important factors for the stability of the EBS is the emplacement technology of the EBS. It is considered that the stability of the EBS is secured by the property emplacement based on the design requirement. In this research, the methods filling the gap between buffer and rock or buffer and over-pack were examined. Bentonite pellets were tested as the filling materials. To research the time-dependent phenomena of bentonite pellets after swelling, permeability tests were conducted with different period. Furthermore, to clarify the effect of test fluid, permeability test was conducted with synthetic seawater to compare the result with that of the test with distilled water. After emplacement of the engineered barrier system, it is expected that the near-field envilonment will be impacted by phenomena such as heat dissipation by conduction and other heat transfer mechanisms, infiltration of groundwater from the surrounding rock in to the engineered barrier system, stress imposed by the overburden pressure and generation of swelling pressure in the buffer due to water infiltration. In order to recognize and evaluate these coupled phenomena, it is necessary to make a confidence of the mathematical models and computer codes based on the information about the in-situ experiments regarding the engineered barrier system. In this research, technical investigations about the in-situ full-scale experiment (called Prototype Repository Project) in Aspo HRL facility by SKB of Sweden were performed.