Abstract: A method of measuring hydrogen leakage from a generator core into generator coolant water flowing through the generator stator windings comprising the steps of: providing a core hydrogen gas environment within the generator; flowing coolant water in a flowpath through the generator stator windings and a conduit to a coolant water reservoir; flowing air at a rate of less than 0.15 into the conduit and the coolant water after the coolant water exits the stator windings; measuring the quantity of air flowing into the conduit and into the coolant water; venting gas through a vent line from a contained vapor space over the coolant water within the coolant water reservoir; and measuring the hydrogen content of the gas vented from the reservoir; whereby hydrogen leakage from the generator core environment through the stator windings into the generator coolant water can be determined in amounts down to about 0.2 CFD.