Raman and X-ray absorption spectroscopy studies of chromium–phosphorus interactions in high-bismuth high-level waste glasses

Abstract High-level waste (HLW) glasses containing bismuth, phosphorus, and chromium were investigated using Raman and X-ray absorption spectroscopy (XAS). The novel and practically important occurrence of foaming on cooling of these melts is associated with P and Cr from the HLW. In response, glasses were synthesized where Bi 2 O 3 and P 2 O 5 contents were varied independently. Relationships between P and Cr were found, where as P 2 O 5 -content increases, chromate Cr–O stretch Raman modes diminish intensity, while Cr XAS shows that Cr reduces, from 50% Cr 6+ + 50% Cr 3+ to nearly 20% Cr 6+ + 80% Cr 3+ , explaining the chromate mode behavior. In the most P 2 O 5 -rich glass, the chromate Cr–O distance increases by approximately 0.10 A, which may indicate bonding between CrO 4 and PO 4 tetrahedra, similar to that in chromo-phosphates. The presence of chromo-phosphate domains in HLW melts can be linked to oxygen generation as a source of the foaming.