Gas Transportation in Saturated Cementitious Materials
- PDF / 331,545 Bytes
- 8 Pages / 414.72 x 648 pts Page_size
- 77 Downloads / 229 Views
GAS TRANSPORTATION IN SATURATED CEMENTITIOUS MATERIALS K. IRIYA Civil Engineering Department, Obayashi Corp., Century Tower, 2-2-9 Hongo, Bunkyo-Ku, Tokyo-1 13, Japan. M. HIRONAGA, M. KAWANISHI Nuclear Fuel Cycle Dept., Central Research Institute of Electric Power Industry, Abiko Research Laboratory, Abiko-1646, Chiba Pref. 270-11, Japan. ABSTRACT: Radioactive waste repositories are constructed underground below ground water level. Main engineered barrier of the repository consists of structural walls, backfill mortar, and consolidated wastes. Cementitious materials are mainly adopted for the engineered barrier. Gas (hydrogen or methane) generation due to corrosion and microbial degradation is predicted, since the waste consists of metals like steel and organic material. It is important issue to define gas transport mechanism in cementitious materials in order to assess the gas release influence on the engineered barrier and pressure rise in the repository. Although cementitious materials have enough permeability to transport gas in dry condition, it is expected to be impermeable or so in saturated condition, in which repository is placed. In this paper, water and gas permeability both in dry and saturated conditions are investigated. The pressure in the vault, and gas transport mechanism is predicted. Certain threshold pressure exists, and it can be recognized that gas permeability is dependent on water saturation degree at 2 a pressure greater than the threshold pressure. Loading pressure of 0.7 MN / m is needed for the flow of gas in saturated concrete. Intrinsic gas permeability of 2 6.5 x 10-'9 m is obtained, which is very small value to keep the low pressure inside the vault. Consequently, it is predicted that gas cannot be transported through the intact concrete, however, it can be transported through defective zone which is developed during construction, and so on. 1. INTRODUCTION Radioactive waste is disposed off in the vault constructed in deep or shallow formation. The vault is constructed below the ground water level, and it should be assumed in water saturated condition immediately after closure in safety analysis. Many steel drums, in which waste including metals is consolidated, are disposed off in the vault. The pH value of about 13 is found in the vault, and oxygen is consumed due to aerobic corrosion. Anaerobic corrosion begins after consuming oxygen, and hydrogen gas is generated if no oxygen is supplied. Gas has to be transported through water saturated structural walls made of concrete. The pressure rises in the vault and causes certain damage to the walls if the gas is not passed through the concrete. In this paper, gas transport mechanism through water saturated concrete is investigated, and water transport path and pressure in the vault are predicted. After keeping all of the consolidated waste in stationary form in the vault, it is closed by cementitious backfill materials to be monolithic. 2. GAS PERMEABILITY TEST 2.1 Test Apparatus Gas permeability of concrete is generally assessed by one
Data Loading...
