TANK INSPECTION NDE RESULTS FOR FISCAL YEAR 2007INCLUDING WASTE TANKS 35, 36, 37, 38 AND 15

Ultrasonic (UT) nondestructive examinations (NDE) were performed on waste storage tanks 35, 36, 37, 38 and 15 at the Savannah River Site as a part of the 'In-Service Inspection (ISI) Program for High Level Waste Tanks.' 1 The inspections were performed from the annular space of the waste storage tanks. The inspections included thickness mapping and crack detection scans on specified areas of the tanks covering all present and historic interface levels and selected welds with particular emphasis on the vapor space regions. Including the tanks in this report, all of the 27 Type III tanks at SRS have been inspected in accordance with the ISI plan. Of the four Type III tanks examined this year, all had areas of reportable thickness in either the Primary or Secondary tank. All of these areas on the primary tank are attributed to fabrication artifacts. None of the four Type III tanks examined this year showed evidence of service induced thinning on the primary wall. All four tanks had secondary wall and/or floor plates where the remaining thickness measured below the 10% wall loss criteria. Tank 15, a Type II, non-stress relieved, waste tank was also inspected this fiscal year as part of the ISI program. The same examination techniques were used on Tank 15 as on the Type III tanks. Tank 15 has been out of service due to leakage from stress corrosion cracking (SCC). Inspections were performed to validate known corrosion models and determine if crack growth occurred since the previous examination five years ago. Several cracks were found to have increased in length perpendicular to the weld seam. In the areas of the 27 Type III tanks inspected to date, ten tanks have reportable thickness in the primary wall and 17 have reportable thickness in the secondary tank walls or floor. All of the reportable thickness areas in the primary walls are from fabrication artifacts. Incipient pitting has been detected in five of the 27 Type III primary tanks. No cracking was detected in any of the areas examined in the Type III tanks