The purpose of this report is to provide the results of the first annual self-assessment to confirm readiness to replace the mixer pump (pump No.1) in Tank 241-SY-101, should the mixer pump fail or need to be replaced for some other reason.

Several compounds were evaluated in a number of optical configurations in order to test the optical response of these compounds to changes in humidity. Reichardt`s betaine (Reichardt`s dye, ET-30 dye, 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridinio)phenolate), a solvatochromic molecule, and several vapochromic compounds were tested, and each responded to a wide range of humidity by exhibiting shifts in visible absorption. All compounds in the study suffered from some degree of hysteresis upon humidity cycling. It is unclear as to the mechanism for this hysteresis, but future work will attempt to either model or remove the hysteresis effects. In the case of the vapochromic compounds, the hysteresis may be due to structural changes in the crystal lattice of the solid state compound. A prototype sensor configuration was also developed involving an attenuated total reflectance probe. The future of the project will deal with elucidating the hysteresis mechanisms for each compound, evaluating several other vapochromic compounds, and testing different immobilization schemes for the compounds under study. In addition, several other optical technologies will be investigated for application in optical humidity sensing.