Thomas J. Rowland
DOE-WV

Gregory P. Rudy
DOE-SR

John D. Wagoner
DOE-RL

The United States Department of Energy (DOE) has had great success with its program to vitrify high-level radioactive waste (HLW). The continued safe operation of two facilities making radioactive waste glass at the Savannah River Plant (Defense Waste Processing Facility, DWPF) and the West Valley Demonstration Project (WVDP) bode well for the vitrification program now in place at Hanford.

In early 1996, DWPF became the first plant in the U. S. to vitrify HLW. After decades of planning and laboratory and pilot scale testing, the facility is now producing a canister of glass per day and is operating safely and efficiently. At the time of this writing, DWPF is over half way through the first sludge batch.

In June 1996, the WVDP became the second U. S. vitrification facility to come on line. Again, the years of planning and testing have paid off handsomely. Expected production rates have been attained (about three canisters per week) and plant availability has been operating at about a 77% rate. Successful completion Phase I of the project is on schedule for mid-1998.

The vitrification program at the Hanford site is being managed differently from the DWPF and WVDP. At Hanford, the Secretary decided to Privatize the pretreatment and immobilization of the High Level Waste contained in the 177 tanks. The privatization initiative was divided into two Phases, Phase I which is a small production facility designed to vitrify 40MT of Immobilized Low Activity Waste per day and 1MT of Immobilized High Level Waste per day. In September 1996, two $27 million contracts were awarded to BNFL, Inc. and Lockheed Martin Advanced Environmental Systems to develop their technical, financial, regulatory, construction, operational, and deactivation approach to provide DOE immobilization services. DOE will decide in late Spring 1998 whether one, none or both have demonstrated an ability to perform the contract as currently defined. If successful, the contractor(s) will begin the second part of their contract this Summer which will include detailed design, permitting, and attaining financial closure leading to construction in FY2000. Phase II will be considered in the early part of the 21st century to provide full production facilities capable of vitrifying over 100MT of Immobilized Low Activity Waste per day and 6MT of Immobilized High Level Waste per day. This vitrification initiative is building on the lessons learned from other initiatives in the complex and around the world.

With the successful operation of two vitrification facilities and the successful implementation of the vitrification process for Hanford HLW, the DOE has much to boast about for 1997.

Savannah River Site (SRS) high level waste (HLW) is stored in 51 tanks as alkaline liquid, sludge, salt cake, and supernate. The current inventory of 33 million gallons (126,500 m³) with 502 million curies of radioactivity is stored in underground single- and double- shelled carbon-steel tanks built between 1954 and 1981. The preparation of some HLW for vitrification has begun with HLW sludge-washing in extended sludge processing (ESP). Characterization data for SRS HLW are based on sampling and process knowledge.

The DOE has accepted the Westinghouse Savannah River Company (WSRC) recommendation to suspend efforts to restart the In-Tank Precipitation (ITP) facility for treatment of high-level waste salt. The department is proceeding immediately with a study of this process and alternative approaches for separating salt wastes. Included in the study will be an independent review and validation of the Department's path forward and any new processes for the waste. During the study, other waste will continue to be treated at DWPF. Westinghouse's recommendation was based on the failure of chemical tests to resolve concerns about benzene generated by the in-tank precipitation process. This process is intended to separate high-level radioactive waste from the low-level radioactive salt wastes contained in a large portion of the 34 million gallons of high-level waste stored at the Savannah River Site. Benzene is an operational safety concern because it is a flammable chemical. The ITP problems with benzene control have been evaluated for more than 10 years. Until February 1998, WSRC believed that solutions to the problem could be resolved by further analysis and process changes (including chemical and operational changes).

Sludge that is removed from waste tanks is washed in the ESP facility to reduce the concentration of soluble salt in the sludge before it is fed to the DWPF. Sludge processing includes four processing steps: 1) aluminum dissolution (required for H-Area HLW) using sodium hydroxide and elevated tank temperature, 2) washing with inhibited water to remove dissolved solids, 3) gravity settling, and 4) decanting the salt solution to the Tank Farm for evaporation. Before washing, H-Area HLW sludge is mixed with sodium hydroxide to dissolve aluminum. When all washing (which could take as many as 5 cycles) is complete, the sludge is consolidated into one tank to be fed to the DWPF. Processing begins again using a third tank for co-processing with the empty tank from the prior batch. Four slurry pumps in each processing tank supply the agitation for washing. Wash water that results from this process will either be transferred to an evaporator system or stored for reuse to dissolve saltcake, depending on the salt concentration.

The objective of the DWPF S-Area Vitrification process (Figure 1) is to take the liquid high-level radioactive waste and permanently immobilize it as a glass solid. The vitrification operations include chemically treating two unique waste streams, mixing them with ground borosilicate glass and then heating the mixture in a joule-heated melter to 1150 degrees Centigrade. The molten mixture is then poured into ten foot tall by two foot diameter stainless steel canisters and allowed to harden. The outer surface of each canister is then decontaminated to Department of Transportation standards, welded closed and temporarily stored onsite for eventual transport to a permanent federal geological repository. The DWPF requires several recurrent projects to maintain operations: additional Glass Waste Storage Buildings, Saltstone Vaults, Melters, and Failed Equipment Storage Vaults (used to store failed melters and other large equipment).

As of the fall of 1997, more than one million pounds of glass have been poured into more than 251 canisters. The production rate through the FY04 is anticipated to be 200 canisters per year, increasing to 250 canisters per year in the outyears. It is expected to take 20 to 25 years to turn the entire site inventory of high-level waste into glass.

The major process innovation in 1997 had to do with the filling of the canisters. Because of air movements through the melter, the pour stream would waver as it traveled down the discharge chamber occasionally clogging the opening to the canister. This effect resulted in considerable downtime unblocking the discharge chamber. A special insert has been installed that provides a clean, well-defined knife edge that allows the glass stream to remain in the center of the chamber opening, away from the walls. The insert is replaceable so that a new edge can be supplied when the old one wears away.

Further process improvements such as these to waste preparation will be needed to exceed the 200 canister per year level. Funding for DWPF attainment improvements has been identified in the outyears. It is assumed that operating experience will improve waste processing performance, such that the program end date can be achieved by the end of 2022.

Radioactive vitrification processing came on line at the WVDP in June 1996. The previous decade had been spent testing a full-scale glass melter, building the new plant, and refining the process that would immobilize the 600,000 gallons of high-level waste in the one waste tank at the site. The experience obtained and careful planning of all aspects of the process have yielded excellent results so far. An outline of the process is shown in Figure 2.

During the first year-and-a-half of radioactive processing, glass production rates in excess of 35 kilograms per hour have typically been achieved. As of December 1997, more than 350,000 kilograms of glass containing more than seven million curies of cesium-137 and strontium-90 have been processed. Glass production system availability has surpassed 75%, due in part to design modifications and changes in operational and maintenance strategies developed from operational experience.

Some of the innovations responsible for the high system availability are a direct result of lessons learned in the non-radioactive testing and the early stages of radioactive production. Batch makeup cycle time has been reduced since the start of radioactive operations. Due to the consistency of the waste, slurry acceptance engineers now generate chemical premix recipes well in advance of the final (post waste analysis) recipe. Independent verification of recipe calculations have virtually eliminated the need for corrective (and time consuming) chemical shims. The turnaround times for chemical analyses in support of feed batch preparation have experienced dramatic improvement relative to initial estimates. Early analytical cell mockup training and the experience gained by the lab technicians has reduced the time required for the various feed batch analyses by more than 50% thereby saving 66 hours on the total batch cycle time. This is significant in that if this were not the case, batch preparation would be the limiting factor in the vitrification process. As a result, the melter can be fed continuously.

Shortly following the start of radioactive operation, a significant restriction in the melter off-gas piping (prior to the SBS) developed. The restriction was suspected to be caused by the collection of dried melter feed adhering to the inside surface of the centimeter diameter piping. Remote radiation surveys showed the buildup to be occurring at an acute (45 degree) elbow just a few feet from the melter. Design modifications incorporated to mitigate the blockage included the following:

• A water flush line was installed into the melter air injection line. Water is periodically introduced into the off-gas stream to steam clean the piping.
• A flow-restricting orifice was installed in the air line supplying motive force air for the melter ADS pump. Reduction in the airflow rate reduced the atomization of the melter feed as it was pulsed into the melter plenum. This made it less likely for the feed material to be swept into the off-gas piping.

The first set of silicon-carbide discharge heater elements exceeded their expected life by approximately three months (12 months vs 9 months). Changes in operational strategies for the heaters and providing automatic backup power minimizes heater cycling and prolongs heater life. This modification is significant in that remote heater replacement requires idling the melter for two to three weeks.

Maintaining a steady pour stream and clear discharge port is essential to continued glass production. During startup testing with nonradioactive glass, the WVDP melter experienced chronic blockages in the glass pour stream. The blockages were the result of a failed barrier between the melt chamber and the discharge chamber, allowing glass migration and subsequent buildup at the bottom of the discharge chamber. The melter was repaired and placed back into service. Just prior to radioactive operations, excessive production and an accumulation of very thin glass fibers (angel hair) led to blockages in the glass pour stream. Prior to radioactive operations, the glass buildup was removed and a flow-reducing orifice was installed to reduce the airflow from the discharge chamber to the main melt chamber. Limiting the airflow through the discharge chamber seemed to successfully reduce angel hair production to an acceptable level. Angel hair formation, however, has not been nor will it ever be completely eliminated. Periodic accumulation of angel hair in the melter discharge port has been successfully overcome by rebalancing the discharge heater loads to maximize the temperature around the discharge port and melt the accumulated glass from the chamber.

Most of the down-time associated with the WVDP vitrification campaign can be attributed to failure and repair of remotely operated equipment. Repair and replacement of the melter feed jumper resulted in nearly a two month outage. However, considerable preplanned vitrification maintenance was rescheduled and accomplished during the unscheduled downtime. In addition, the WVDP was successful in their first attempt to perform hands-on maintenance to a vitrification cell remote component, following remote decontamination in the vitrification cell. The melter feed jumper was decontaminated to allow hands-on repair of its remotely operated piping connectors.

The vitrification process systems have been performing as designed since initiating radioactive operations. Exhaustive functional and integrated testing using waste simulant combined with adherence to design requirements has limited the unscheduled downtime within the WVDP vitrification process. Strong problem solving skills and efficient use of unscheduled process downtime for scheduled maintenance has contributed greatly to the high system availability at the WVDP and the project is on schedule to complete the first phase of vitrification in mid-1998.

A new method of contracting work at DOE sites is being tested for the Hanford vitrification system. The contractor will assume safety and financial responsibility, while the DOE assures the overall safety of the program and pays only upon delivery of the product. It is anticipated that cleanup will be accomplished more effectively and that the DOE, and the stakeholders, will save money in the long term.

Two contractors, BNFL, Inc. and Lockheed Martin Advanced Environmental Systems (LMAES) have been selected for Phase I, Part A of the Tank Waste Remediation System (TWRS) Privatization Initiative. During this part of Phase I, the contractors spent the last 16 months, September 1996 to January 1998, developing specific deliverables for DOE to review which could lead to an authorization to proceed with the construction and operation of waste treatment facilities during Part B. Authorization to proceed could be determined as early as late Spring 1998.

A new organization within the Richland Operations Office has been created to provide safety regulatory oversight for the TWRS contractors. The new organization is known as the Office of Radiological, Nuclear and Process Safety Regulation for TWRS Privatization Contractors, or Regulatory Unit (RU). The Regulatory Unit's mission is to ensure public, worker, and environmental safety in the privatization effort. It represents a first step in separating DOE's operational responsibilities from safety oversight responsibilities.

The RU will conduct the regulatory process in an open fashion. To maximize information available to the public, all pertinent regulatory information will be made available for public review. The RU will provide the public with multiple opportunities to observe, review, and comment on the entire process.

A policy of openness is intended to ensure that public participation is an integral and effective part of DOE activities and that decisions are made with the benefit and consideration of important public perspectives. This policy provides a mechanism for bringing a broad range of diverse viewpoints and values early into the decision-making process. This early involvement will enable DOE to make more informed decisions, improve quality through collaborative efforts, build mutual understanding and trust between DOE and the public it serves.

Excellent progress is being made around the DOE complex in the vitrification of high-level radioactive waste. The efficient and safe operation of the two vitrification plants at Savannah River and West Valley coupled with the innovative contracting method being introduced at Hanford demonstrate to our stakeholder the clear dedication and technical expertise required to close the circle on the environmental legacy of our nation's nuclear complex.

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