Organic tank safety project: Effect of water partial pressure on the equilibrium water contents of waste samples from Hanford Tank 241-BY-108

Water content plays a crucial role in the strategy developed by Webb et al. to prevent propagating or sustainable chemical reactions in the organic-bearing wastes stored in the 20 Organic Tank Watch List tanks at the US Department of Energy`s Hanford Site. Because of water`s importance in ensuring that the organic-bearing wastes continue to be stored safely, Duke Engineering and Services Hanford commissioned the Pacific Northwest National Laboratory (PNNL) to investigate the effect of water partial pressure (P{sub H2O}) on the water content of organic-bearing or representative wastes. Of the various interrelated controlling factors affecting the water content in wastes, P{sub H2O} is the most susceptible to being controlled by the and Hanford Site`s environmental conditions and, if necessary, could be managed to maintain the water content at an acceptable level or could be used to adjust the water content back to an acceptable level. Of the various waste types resulting from weapons production and waste-management operations at the Hanford Site, Webb et al. determined that saltcake wastes are the most likely to require active management to maintain the wastes in a Conditionally Safe condition. A Conditionally Safe waste is one that satisfies the waste classification criteria based on water content alone or a combination of water content and either total organic carbon (TOC) content or waste energetics. To provide information on the behavior of saltcake wastes, two waste samples taken from Tank 241-BY-108 (BY-108) were selected for study, even though BY-108 is not on the Organic Tanks Watch List because of their ready availability and their similarity to some of the organic-bearing saltcakes

Methyl iodide sorption by reduced silver mordenite

At the Pacific Northwest Laboratory (PNL), we performed two sets of experiments to determine the effects of pertinent operational parameters and gas compositions on organic radioiodine (in particular methyl iodide (CH/sub 3/I)) capture by silver mordenite (AgZ). In the first set of experiments, we studied the effects of (1) hydrogen pretreatment of AgZ, (2) change in particle size of AgZ, and (3) the presence of water in the gas phase. In the second set of experiments we evaluated on a semi-quantitative basis the effects of nitric oxide (NO), nitrogen dioxide (NO/sub 2/), superficial face velocity, and temperature on CH/sub 3/I capture by reduced (hydrogen pretreated) silver mordenite (Ag/sup 0/Z). These studies have shown that AgZ, especially Ag/sup 0/Z, is an effective trap for CH/sub 3/I. However, its effectiveness varies with changes in operational parameters and is affected by other gases found in the process off gas of a nuclear reprocessing plant. Optimum trappig efficiency was achieved with Ag/sup 0/Z rather than AgZ, 20-40 mesh Ag/sup 0/Z rather than 0.16 cm extrudate, moisture in the gas stream, higher temperatures up to 200/sup 0/C, absence of NO, and lower superficial face velocities down to 3.75 m/min. Additionally, CH/sub 3/I can be converted to elemental iodine (I/sub 2/) in the presence of NO or NO/sub 2/ by controlling the operational parameters. Since I/sub 2/ is easier to trap than organic iodides, this should improve trapping efficiency,

Ferrocyanide Safety Project: Comparison of actual and simulated ferrocyanide waste properties

In the 1950s, additional high-level radioactive waste storage capacity was needed to accommodate the wastes that would result from the production of recovery of additional nuclear defense materials. To provide this additional waste storage capacity, the Hanford Site operating contractor developed a process to decontaminate aqueous wastes by precipitating radiocesium as an alkali nickel ferrocyanide; this process allowed disposal of the aqueous waste. The radiocesium scavenging process as developed was used to decontaminate (1) first-cycle bismuth phosphate (BiPO{sub 4}) wastes, (2) acidic wastes resulting from uranium recovery operations, and (3) the supernate from neutralized uranium recovery wastes. The radiocesium scavenging process was often coupled with other scavenging processes to remove radiostrontium and radiocobalt. Because all defense materials recovery processes used nitric acid solutions, all of the wastes contained nitrate, which is a strong oxidizer. The variety of wastes treated, and the occasional coupling of radiostrontium and radiocobalt scavenging processes with the radiocesium scavenging process, resulted in ferrocyanide-bearing wastes having many different compositions. In this report, we compare selected physical, chemical, and radiochemical properties measured for Tanks C-109 and C-112 wastes and selected physical and chemical properties of simulated ferrocyanide wastes to assess the representativeness of stimulants prepared by WHC

Application of the risk-based strategy to the Hanford tank waste organic-nitrate safety issue

This report describes the results from application of the Risk-Based Decision Management Approach for Justifying Characterization of Hanford Tank Waste to the organic-nitrate safety issue in Hanford single-shell tanks (SSTs). Existing chemical and physical models were used, taking advantage of the most current (mid-1997) sampling and analysis data. The purpose of this study is to make specific recommendations for planning characterization to help ensure the safety of each SST as it relates to the organic-nitrate safety issue. An additional objective is to demonstrate the viability of the Risk-Based Strategy for addressing Hanford tank waste safety issues

Statement of work for Los Alamos National Laboratory on ferrocyanide studies

During management of the Hanford Single-Shell Waste Tanks (SST), the site operator precipitated cesium from the supernate as nickel cesium ferrocyanide to allow disposal of the supernate as low-level waste. This freed valuable tank storage space for receipt of additional radioactive waste generated by Hanford defense operations. Concern has arisen that the ferrocyanide could react explosively with nitrate, another waste component, and/or its radiolysis product nitrite. The current Hanford Principal Contractor, Westinghouse Hanford Company (WHC), has requested that the Pacific Northwest Laboratory (PNL) evaluate the potential for explosive ferrocyanide reactions on a worst case basis. The worst case is believed, at this time, to be a mixture of nickel cesium ferrocyanide and a mixture of nitrate and nitrite without any dilution by inert waste constituents. PNL will perform energetic and small-scale explosion tests. The large-scale explosion tests (s) will be performed by Los Alamos National Laboratory (LANL

The reactivity of cesium nickel ferrocyanide towards nitrate and nitrite salts

Beginning in late 1988, the Pacific Northwest Laboratory (PNL) began an experimental program at the request of Westinghouse Hanford Company (WHC) to investigate the effects of temperature on the oxidation reaction between synthetic nickel cesium ferrocyanide (FeCN) and nitrates and nitrites representative of materials present in some of the Hanford single-shell tanks (SSTs). After completing a preliminary series of experiments in 1988, the program was expanded to include five tasks to evaluate the effect of selected compositional and operational parameters on the reaction and explosion temperatures of FeCN and nitrate and/or nitrite mixtures. 10 refs., 4 figs., 6 tabs

Interim report cyanide safety studies

Over the past few years several proposals have been prepared to investigate the potential hazard of ferrocyanide-nitrate reactions that may occur in some Hanford waste tanks. In 1988 Westinghouse Hanford Company (WHC) decided to perform some of the suggested experimental work. Based on the proposal submitted in July, 1988, it was agreed to do a portion of the work during FY 1988. This report summarizes the results of that work, provides a preliminary analysis of the results, and includes recommendations for further study. The work completed consists of a brief literature search, preparation and analysis of several cesium nickel ferrocyanide, Cs{sub 2}NiFe(CN){sub 6}, oxdiation studies using Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG), and small scale explosion tests

Status of radioiodine control for nuclear fuel reprocessing plants

This report summarizes the status of radioiodine control in a nuclear fuel reprocessing plant with respect to capture, fixation, and disposal. Where possible, we refer the reader to a number of survey documents which have been published in the last four years. We provide updates where necessary. Also discussed are factors which must be considered in developing criteria for iodine control. For capture from gas streams, silver mordenite and a silver nitrate impregnated silica (AC-6120) are considered state-of-the-art and are recommended. Three aqueous scrubbing processes have been demonstrated: Caustic scrubbing is simple but probably will not give an adequate iodine retention by itself. Mercurex (mercuric nitrate-nitric acid scrubbing) has a number of disadvantages including the use of toxic mercury. Iodox (hyperazeotropic nitric acid scrubbing) is effective but employs a very corrosive and hazardous material. Other technologies have been tested but require extensive development. The waste forms recommended for long-term storage or disposal are silver iodide, the iodates of barium, strontium, or calcium, and silver loaded sorbents, all fixed in cement. Copper iodide in bitumen (asphalt) is a possibility but requires testing. The selection of a specific form will be influenced by the capture process used

Recycle of iodine-loaded silver mordenite by hydrogen reduction

In 1977 and 1978, workers at Idaho National Engineering Laboratory (INEL) developed and tested a process for the regeneration and reuse of silver mordenite, AgZ, used to trap iodine from the dissolver off-gas stream of a nuclear fuel reprocessing plant. We were requested by the Airborne Waste Management Program Office of the Department of Energy to perform a confirmatory recycle study using repeated loadings at about 150/sup 0/C with elemental iodine, each followed by a drying step at 300/sup 0/C, then by iodine removal using elemental hydrogen at 500/sup 0/C. The results of our study show that AgZ can be recycled. There was considerable difficulty in stripping the iodine at 500/sup 0/C.; however, this step went reasonably well at 550/sup 0/C or slightly higher, with no apparent loss in the iodine-loading capacity of the AgZ. Large releases of elemental iodine occurred during the drying stage and the early part of the stripping stage. Lead zeolite, which was employed in the original design to trap the HI produced, is ineffective in removal of I/sub 2/. The process needs modification to handle the iodine. Severe corrosion of the stainless steel components of the system resulted from the HI-I/sub 2/-H/sub 2/O mixture. Monel or other halogen-resistant materials need to be examined for this application. Because of difficulty with the stripping stage and with corrosion, the experiments were terminated after 12 cycles. Thus, the maximum lifetime (cycles) of recycle AgZ has not been determined. Mechanistic studies of iodine retention by silver zeolites and of the behavior of silver atoms on the reduction stage would be of assistance in optimizing silver mordenite recycle

Evaluation of silver mordenite for radioiodine retention at the PUREX Process Facility Modification

To determine the bed-loading capacities and the effluent iodine concentrations at normal, off-normal, and standby conditions, PNL performed a series of statistically designed parametric tests using a bed of AgZ 12 cm long x 1 cm diameter. In addition, tests were performed to determine the effect of bed length, the effect of a second bed, the effect of extended standby conditions, and the efficiency of hydrogen-reduced AgZ (Ag/sup 0/Z). Results of these experiments are presented in this report