Efficiency of subset simulation in the design of lined rock caverns for storage of hydrogen gas

Abstract

Efforts to substitute the use of fossil fuels in industry by hydrogen gas requires the storage of large volumes of gas with a reliable pressure vessel design. The Hydrogen Breakthrough Ironmaking Technology (HYBRIT) initiative aims to make the whole steel making process in Sweden fossil-free with the storage of industrial scale quantities of hydrogen in underground Lined Rock Cavers (LRCs). The LRC concept is a relatively new design methodology that can be further developed with respect to safety and economic efficiency and reliability-based design methods provide one option to comply with codes and regulations. High reliability is required for the storage of hydrogen gas and the computational time becomes unpractical for the evaluation of a complex system such as the LRC. In this paper, the efficiency of Subset Simulation (SuS) regarding accuracy, precision and required number of samples is studied for the calculation of probability of failure against fatigue of the steel lining. It can be observed that by increasing the number of samples per level and increasing the conditional probability of failure the precision increases as well as the total number of samples. The accuracy of the SuS is checked with respect to Monte Carlo simulation (MCS) showing good agreement and with greater precision for fewer number of samples. A case study is performed for the geologic conditions of Sweden showing that the considered failure mode is unlikely for high stresses and good rock mass quality.