The Heavy-Section Steel Technology (HSST) Program at the Oak Ridge National Laboratory, under the sponsorship of the US Nuclear Regulatory Commission, is conducting analytical and experimental studies aimed at understanding the circumstances that would initiate the growth of an existing crack in a reactor pressure vessel and the conditions that would lead to arrest of a propagating crack. HSST wide-plate crack-arrest tests are being performed at the National Institute of Standards and Technology (NIST), Gaithersburg, Maryland, in a 27-MN-capacity testing machine. This report contains results for two tests that used A 533 grade B class 1 material. Each test used a 1 x 1 x 0.15 m thick single-edge notched plate (a/w = 0.2) that was subjected to a linear thermal gradient along the plane of crack propagation. The thermal gradient was applied to the specimen by cooling the notched edge and heating the other edge. By varying the crack-tip temperature and transverse temperature profile, the initiation load and depth of crack propagation were changed from test to test. During each test, strain and temperature measurements were obtained as functions of position and time. Load, crack-opening displacement, and acoustic-emission data were also obtained as functions of time. 24 refs., 91more » figs., 12 tabs.« less