Assuring the integrity of nuclear power plant reactor pressure vessels (RPV) is of upmost importance to the U.S. Nuclear Regulatory Commission since there is no backup or redundancy to this component. These vessels must maintain high toughness in order to assure integrity despite the fact the vessel toughness decreases with neutron irradiation from the running of the plant. Currently the toughness loss of the RPV is inferred from generic equations or the change in measured toughness of samples irradiated in the RPV. A nondestructive evaluation technique to monitor the toughness of the RPV would enhance integrity assessments of the vessel. Such an NDE technique must have the ability to measure the microstructural changes resulting from irradiation that effect the toughness of the RPV steel. Additionally the technique must be able to investigate the RPV through the thickness without removing the stainless steel weld cladding on the surface. Although the development of such an NDE technique may be difficult the U. S. NRC is supporting such research in hopes of developing more information concerning the toughness of U. S. RPVs.