Unit 1 Plant power was stable at 90% following a plant startup. The Auxiliary Operator (AO) performed a pre-job brief with shift management before adding hydrogen to the main generator. While performing the addition, the AO attempted to verify open a half-inch hydrogen addition valve. The AO was unable to move the valve by hand and mistakenly assumed the valve was stuck on its closed seat. The valve is a normally open valve and the procedure step was to verify the valve was, in fact, open. The AO obtained a pipe wrench to assist in freeing the valve off of its "closed" seat. Using the pipe wrench, the valve handwheel was turned in the open direction. The AO attempted to open the valve by hand again. Unable to move the valve by hand, the pipe wrench was used to further open view more