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42 Irradiation assisted stress corrosion cracking system. present within materials. This system possesses two positron sources a Na-22 and Ge-68 which allows for the detection of defects at the near surface of materials or further in the bulk. The positrons from the source enter the material and annihilate with electrons. This annihilation results in two gamma rays 511 keV that are generated and subsequently measured with high purity gamma ray spectrometers as shown in the figure below. This system has been designed to conduct two dimensional scanning or point measurements of specimens. The specimen size that can be accommodated ranges from millimeters in length and width up to 75 mm by 150 mm. Irradiation assisted stress corrosion cracking IASCC system The IASCC test system is installed in two hot cells. The first test cell houses two autoclaves outfitted with Instron servohydraulic actuators and capable of simulating boiling water reactor BWR normal and hydrogen water chemistries as well as pressurized water reac- tor PWR environments using a closed loop recirculating chemistry control system and an autoclave to enclose test specimens within the environment. The servohydraulic actua- tors and associated specimen testing hardware locat- ed inside the autoclaves are designed to handle up to a 100 KN applied force allowing fracture toughness testing of full-sized 1TCT compact tension speci- mens in addition to the irradiation assisted stress corrosion cracking test capability. Crack growth is monitored using a reversing current DC potential drop DCPD system. The cell is shielded to allow up to a 45000 Rhr gamma contact source to be handled for extended periods. The IASCC test cell has a companion utility cell with equivalent shield- ing. The utility cell is outfitted with a tool port for introduction of necessary hardware and serves as the transit point for irradiated specimens as it is also outfitted with a cask ring underneath the cell designed to mate with a modified GE-100 cask. It is also outfitted with a small JEOL JCM-5000 bench- top SEM to allow fractography of tested specimens.