Finding workers to be supervisors even though their tasks and responsibilities were governed "to a great extent" by federal guidelines and company policies
Denying enforcement of Board's order where Board held that employees' exercise of judgment related only to their "own responsibilities, [was] based on their experience and technical expertise, [and did] not evidence any control over personnel"
Rejecting evidence that assignments were made pursuant to routine and pre-determined classifications because evidence showed that supervisors "weighed the relative urgency of immediate and unforeseen problems and directed Plant Operators to undertake necessary tasks"