Development of a Tangential Neutron Radiography System for Monitoring the Fatigue Cracks in Hydrogen Fuel Tanks

Purpose- To present an overview of the research and development carried out in a European funded framework 7 (FP7) project called SafeHPower, for the implementation of neutron radiography to inspect fatigue cracks in vehicle and storage hydrogen fuel tanks. Project background– Hydrogen (H2) is the most promising replacement fuel for road transport due to its abundance, efficiency, low carbon footprint and the absence of harmful emissions. For the mass market of hydrogen to take off, the safety issue surrounding the vehicle and storage hydrogen tanks needs to be addressed. The problem is the residual and additional stresses experienced by the tanks during the continuous cyclic loading between ambient and storage pressure which can result in the development of fatigue cracks. Steel tanks used as storage containers at service stations and depots and/or the composite tanks lined with steel are known to suffer from hydrogen embrittlement (HE). Another issue is the explosive nature of hydrogen (when it is present in the 18-59% range) where it is mixed with oxygen, which can lead to catastrophic consequences including loss of life. Monitoring systems that currently exist in the market impose visual examination tests, pressure tests and hydrostatic tests after the tank installation [1], [2]. Three inspection systems have been developed under this project to provide continuous monitoring solutions. Approach and scope- One of the inspection systems based on the neutron radiography (NR) technology that was developed in different phases with the application of varied strategies has been presented here. Monte Carlo (MCNP) simulation results to design and develop a bespoke collimator have been presented. A limitation of using an inertial electrostatic Deuterium-Tritium (D-T) pulsed neutron generator for fast neutron radiography has been discussed. Radiographs from the hydrogen tank samples obtained using thermal neutrons from a spallation neutron source at ISIS, Rutherford laboratory, UK have been presented. Furthermore, radiograph obtained using thermal neutrons from a portable D-T neutron generator has been presented. In conclusion, a proof in principle has been made to show that the defects in the hydrogen fuel tank can be detected using thermal neutron radiography.