Research-scale melter test report

Abstract

The Melter PerformanceAssessment (MPA) activity in the Pacific Northwest Laboratory's (PNL)(a) Hanford WasteVitrificationPlant (HWVP) Technology Development (PHTD) effort is intendedto determinethe impactof noble metals on the operationallife of the referenceHWVP melter. As a partof this activity, a parametricmelter test was completed using a Research-Scale Melter (RSM). The RSM is a small, approximately1/100-scale melter, 6-in.-diameter, thatallows rapidchanging of process conditions and subsequentre-establiehmentof a steady-statecondition. The test matrix contained nine differentsegments thatvaried the melter operatingparameters(glass and plenumtemperatures)and feed properties(oxide concentration,redox potential, and noble metal concentrations)so that the effects of these parameterson noble metal agglomerationon the melter floor could be evaluated. The RSM operatedfor 48 days and consumed 1,300 L of feed, equatingto 153 tankturnovers.The runproduced531 kg of glass, During the latterportionof the run, the resistance between the electrodes decreased. Upon destructiveexaminationof the melter, a layer of noble metals was found on the bottom. This was surprisingbecausethe glass residencetime in the RSM is only 10% of the HWVP plant melter. The noble metals layer impacted the melter significantly. Approximately1/3 of one paddle electrode was melted or corrode_l off. The cause is assumed to be localized heating from short circuitingof the electrode to the noble metallayer. The metal layer also removed approximately 1/2 in. of the refractoryon the bottom of the melter. The mechanismfor this damage is not presently known. Samples taken from the bottomof the RSM contained a 2 to 4-ramlayer of precipitated noble metals. ScanningElectron Microscopy/EnergyDispersive X-Ray (SEM/EDX) analyses of the layer found that it consisted of metallic particles(10 to 20/_m) of a Ru/Rh alloy surroundedby two separate, continuous phases. One of these continuous phases was an alloy of metallic Pd/Ag/Te with a small amount of Ru metal. The other continuousphase was pureRuO2. It is assumedthat the layer was made up of RuO2 needles and alloys of Pd/Rh/Ag/Te until the last segment of the run which was rununder reducingconditions (Fe+2/_Fe-0.25). This reductionof the RuO2 has significance with respect to HWVP operation. At Fe+2/_Fe = 0.19 palladium alloy spheres were formed. At Fe+2/_Fe = 0.25 there were no visible RuO2 crystals. All of the RuO2 at this point was apparently reducedto metal. This was not expectedto occur so close to the plant redox operatinglimit. The upperredox operating limit for the plant is Fe+2/_Fe-0.23. Under these conditions, the floes of RuO2 could reduceto metallic ruthenium and alloy with rhodium.This would increasethe rate of noble metals sedimentation and thus shorten the life of the melter. (a) PNL is operatedfor the U.S. Departmentof Energy by Battelle Memorial Instituteunder ContractDE-AC06-76RLO 1830. iii Mass balance calculations indicate that approximately 5 % of the noble metals present in the feed precipitate...

Vitrification of noble metals containing NCAW simulant with an engineering scale melter (ESM): Campaign report

“…This predicted trend is consistent with observations made in the RSM experiments (Cooper, Elliott, et al 1993) from a limited amount of temperature probing of the melter during operation. No temperature probing was done in the ESM.…”

“…The electric conductivity used in pre-test simulations was determined from a correlation3 based on the target glass. The correlation, identified in the present work as ESWpre, is the same correlation used in RSM pre-test simulations (Cooper, et al 1993). The correlation is given as:…”

Hanford tank waste simulants specification and their applicability for the retrieval, pretreatment, and vitrification processes

“…Thus, the waste disposal problem was diminished. The addition of the rest of the components, including the solubkdslightly soluble components, noble metals, and minor components (Cooper et al 1993) is similar to the laboratory scale procedure. The sirnukmt preparation was carried out with one large mixing tank.…”

Letter Report on the Issue of Noble Metals in the DWPF Melter

“…In Research Scale Melter (RSM) studies at PNNL, the results suggested that there was a significant nonlinear increase in the amount of noble metal compounds deposited on the melter floor. With a 2-fold increase in the nominal noble metal content of the NCAW melter feed simulant there was a corresponding 9-fold increase in the fraction settling to the RSM floor (Cooper et al, 1994).…”

“…The LEWC has a noble metal content that is very similar to that of the SRS HM and the Hanford NCAW. (Cooper, et al, 1994) and sponsored testing in the Engineering Scale Melter (ESM) at the Institute für Nuklear Entsorgungstechnik at Kernforshungzentrum Karlsruhe (INE/KfK) in Karlsruhe, Germany (Grunewald et al, 1993a(Grunewald et al, , 1993b. SRTC ran several small-scale melter tests before operating the Integrated DWPF Melter System (IDMS) from 1988 -1995.…”