SUBJECT: M.S. Thesis Presentation
BY: John Payne
TIME: Thursday, March 28, 2013, 11:00 a.m.
PLACE: Love Building, 109
TITLE: Feasibility Study of a Controllable Mechanical Seal for Reactor Coolant Pumps
COMMITTEE: Dr. Richard Salant, Chair (ME)
Dr. Jeffrey Streator (ME)
Dr. Scott Bair (ME)


In a nuclear power plant, a critical system for both safety and performance is the reactor cooling system, which utilizes one or more large centrifugal pumps. Most reactor coolant pumps contain a multi-stage mechanical face seal system for fluid containment. The main advantage of mechanical seals is their self-adjusting properties. These seals are tuned so that they automatically adjust to varying fluid conditions to provide adequate leakage control. However, over time, wear, chemical deposition, or changing operating conditions can alter the face gap, which is the critical geometry between the sealing faces of a seal. An altered face gap can lead to too much or not enough fluid leakage, which must be maintained within a certain range to provide lubrication and cooling to the seal faces without excessive coolant volume loss.

This document will examine possible causes of undesirable leakage rates in a commonly-used reactor coolant pump assembly. Next, a method of increasing the ability of a mechanical seal to adapt to a wider range of conditions will be proposed. This method involves modifying an existing seal face to include a method of active control. This active control focuses on deliberately deforming one face of the mechanical sealing face pair. This deformation alters the face gap in order to moderate and correct undesirable leakage rates. Two methods of actuation, hydraulic pressure and piezoelectric deformation, will be proposed.

Finally, a model of the controllable seal faces will be introduced. This model includes a method of numerically solving the Reynolds equation to determine the fluid mechanics in the lubrication problem in the seal face and coupling the solution with a deformation analysis in a finite element model of a seal face. The model includes a study of the effects of induced deformation in the seal via both hydraulic and piezoelectric actuation and the ability of this deformation to control the leakage rate.