(477a) Impact of Impurities and Degradation Products during Chemical Processing of High Level Waste in the Defense Waste Processing Facility

SRNL-STI-2017-00221

Impact of Impurities and
Degradation Products During Chemical Processing of High Level Waste in the
Defense Waste Processing Facility

Dan P. Lambert, Wesley H.
Woodham, Matthew S. Williams, J. David Newell, Jack Zamecnik, Savannah River
National Laboratory, Aiken, SC, USA

Abstract

Testing was completed to
develop a chemical processing flowsheet for the Defense Waste Processing
Facility (DWPF), designed to vitrify and stabilize high level radioactive
waste.  DWPF processing uses a reducing acid (formic acid) and an oxidizing
acid (nitric acid) to rheologically thin the slurry and complete the necessary
acid base and reduction reactions (primarily mercury and manganese).  Formic
acid reduces mercuric oxide to elemental mercury, allowing the mercury to be
removed during the boiling phase of processing through steam stripping.  In
runs with active catalysts, formic acid can decompose to hydrogen and nitrate
can be reduced to ammonia, both flammable gases, due to rhodium and ruthenium catalysis. 
Replacement of formic acid with glycolic acid eliminates the generation of rhodium-
and ruthenium-catalyzed hydrogen and ammonia. In addition, mercury reduction is
still effective with glycolic acid. Hydrogen, ammonia and mercury are discussed
in the body of the report.

However, other flammable degradation products from
the antifoam and from impurities in the glycolic acid combine to add additional
flammable gases. Studies were completed to understand the impact of impurities
and reaction products in the glycolic acid (formic acid, formaldehyde,
methoxyacetic acid, and methanol) and the degradation products in the antifoam
(propanal, hexamethyldisiloxane, and trimethylsilanol).