Abstract: One or more boost pumps for a liquid hydrogen fuel system are disposed within the fuel tank and fully flooded. An electrical connector of each boost pump is sealed from the fuel tank and accessible from an exterior of the fuel tank while the boost pump is installed. Each boost pump can be independently replaced using a toolbox. Each boost pump is purged of fuel before being replaced by introducing a gas at a center region of the boost pump. The toolbox and new boost pump are purged prior to removal of the old boost pump. Each boost pump can be formed from modular components.