Hanford single-shell tanks 241-t-203 and 241-t-204 validation of level decrease evaluation - 15343
Hanford single-shell tanks (SSTs) 241-T-203 (T-203) and 242-T-204 (T-204) were two tanks that showed decreasing waste surface level trends. All factors that could impact each tank's level change rate were evaluated with the conclusion being the level decreases could be explained by evaporation. The evaporation estimates contained several assumptions, so a test was performed to determine if the estimates could be supported by data. The breather filter valves on these two tanks were closed for one year in order to shut off the primary means of tank air exchange to the atmosphere. The results for tank T-203 showed the net level change for the year was zero which supported the evaporation rate estimate (and provided further information that the tank was not leaking). The data for tank T-204 were very erratic and prevented conclusive results, but the waste level showed a significant reduction in level decrease rate and supported the tank evaporation rate estimate. (authors)