A fuel system of an aircraft engine, comprising: a hydrogen fuel source; a hydrogen fuel circuit including a fuel conduit interface connecting a fuel conduit to a component of the fuel system; and a leak detection system operatively coupled to the hydrogen fuel circuit, the leak detection system including: a sweep flow source; a sweep line structure (107, 207, 121) having an inlet fluidly connected to the sweep flow source, the sweep line structure (107, 207, 121) having: an inner surface facing toward, extending around, and defining a cavity around the fuel conduit interface, and an outer surface opposite the inner surface, the cavity being fluidly sealed relative to the outer surface, a vent conduit (113, 213) that includes the cavity of the sweep line structure (107, 207, 121) and fluidly connects to atmosphere; a bypass line passing around the component to allow continuous sweep flow from the inlet to the vent portion (113, 213); a hydrogen sensor operatively connected to the vent conduit (113, 213) at a location upstream of an outlet of the vent conduit (113, 213) and downstream of the component, the hydrogen sensor operable to sense at that location one or both of: presence of hydrogen and concentration of hydrogen; and a controller (131, 154) configured to control the component as a function of signals received from the hydrogen sensors. a hydrogen fuel source; a hydrogen fuel circuit including a fuel conduit interface connecting a fuel conduit to a component of the fuel system; and a leak detection system operatively coupled to the hydrogen fuel circuit, the leak detection system including: a sweep flow source; a sweep line structure (107, 207, 121) having an inlet fluidly connected to the sweep flow source, the sweep line structure (107, 207, 121) having: an inner surface facing toward, extending around, and defining a cavity around the fuel conduit interface, and an outer surface opposite the inner surface, the cavity being fluidly sealed relative to the outer surface, a vent conduit (113, 213) that includes the cavity of the sweep line structure (107, 207, 121) and fluidly connects to atmosphere; a bypass line passing around the component to allow continuous sweep flow from the inlet to the vent portion (113, 213); a hydrogen sensor operatively connected to the vent conduit (113, 213) at a location upstream of an outlet of the vent conduit (113, 213) and downstream of the component, the hydrogen sensor operable to sense at that location one or both of: presence of hydrogen and concentration of hydrogen; and a controller (131, 154) configured to control the component as a function of signals received from the hydrogen sensors. a sweep flow source; a sweep line structure (107, 207, 121) having an inlet fluidly connected to the sweep flow source, the sweep line structure (107, 207, 121) having: an inner surface facing toward, extending around, and defining a cavity around the fuel conduit interface, and an outer surface opposite the inner surface, the cavity being fluidly sealed relative to the outer surface, a vent conduit (113, 213) that includes the cavity of the sweep line structure (107, 207, 121) and fluidly connects to atmosphere; a bypass line passing around the component to allow continuous sweep flow from the inlet to the vent portion (113, 213); a hydrogen sensor operatively connected to the vent conduit (113, 213) at a location upstream of an outlet of the vent conduit (113, 213) and downstream of the component, the hydrogen sensor operable to sense at that location one or both of: presence of hydrogen and concentration of hydrogen; and a controller (131, 154) configured to control the component as a function of signals received from the hydrogen sensors. an inner surface facing toward, extending around, and defining a cavity around the fuel conduit interface, and an outer surface opposite the inner surface, the cavity being fluidly sealed relative to the outer surface, a vent conduit (113, 213) that includes the cavity of the sweep line structure (107, 207, 121) and fluidly connects to atmosphere; a bypass line passing around the component to allow continuous sweep flow from the inlet to the vent portion (113, 213); a hydrogen sensor operatively connected to the vent conduit (113, 213) at a location upstream of an outlet of the vent conduit (113, 213) and downstream of the component, the hydrogen sensor operable to sense at that location one or both of: presence of hydrogen and concentration of hydrogen; and a controller (131, 154) configured to control the component as a function of signals received from the hydrogen sensors.