Nuclear coolant pump seal and methods of sealing

A method of sealing a pump, the method comprising:

• directing pressurized fluid through a first section of a staging flow path towards a first seal;
• increasing angular velocity of the pressurized fluid as it traverses said staging flow path by motion of a rotor assembly of said pump, wherein said increasing said angular velocity comprises directing said pressurized fluid over at least one accelerating surface of said rotor assembly;
• directing the pressurized fluid through a second section of said staging flow path towards a second seal, wherein each of the first and second seal have a stator seal member and a rotor seal member, said rotor seal member comprise a first and second expansion control ring around said rotor seal member, said first expansion control ring configured to expand out of contact with said rotor seal member at a lower temperature than said second expansion control ring,
• restricting thermal expansion of at least one of said first and second seal below a threshold temperature;
• tightening at least one of said first and second seal in response to elevated fluid temperature above said threshold temperature.

A seal assembly for a pump, comprising:

• a gland housing for mounting to a pump casing;
• a staging flow path within the gland housing defining first and second seal chambers;
• a rotor assembly pumping a coolant fluid through said gland housing, the rotor assembly having at least one acceleration surface, wherein fluid passing through the staging flow path is accelerated by said at least one acceleration surface;
• and
• first and second seal stages within said first and second seal chambers, each having a stator seal member and a rotor seal member, said stator seal member and rotor seal member are configured to engage one another to form a seal at a sealing interface defined between said stator seal member and said rotor seal member;
• an inlet passage for feeding the coolant fluid into said staging flow path and past said at least one acceleration surface,
• wherein said sealing members are configured to thermally expand and wherein said sealing members are configured to restrict expansion of said rotor seal member below a threshold temperature,
• wherein said rotor seal member comprise a first and second expansion control ring around said rotor seal member, said first expansion control ring configured to expand out of contact with said rotor seal member at a lower temperature than said second expansion control ring.