Steam shrinking your waste1 February 1998
Steam Reforming (SR) is a relatively new waste processing technique that can destroy most types of organic hazardous materials and reduce the volume of radiologically contaminated waste. Experience to date, including from the Trojan nuclear plant, convinces GTS Duratek, which holds the patents for the process, that SR will become a major player in the radioactive waste processing market over the next two decades. And as a non-incineration thermal technique, it will be particularly appealing to regulators and environmentalists.
Steam Reforming is expected to be used primarily for processing organic liquids and/or solid waste streams. SR operations have already been performed on a wide variety of radioactive waste and GTS Duratek expects that its use at nuclear power plants will increase dramatically over the next few years.
The process generally reduces the non-radiological hazards of waste streams through evaporation and decomposition of organic materials with non-volatile radio-nuclides, metals, glass and mineral-like materials being concentrated into a residue that looks very similar to incinerator ash.
To date, GTS Duratek, SEG (acquired by GTS Duratek in April 1997) and Synthetica Technologies (the original developer and patent originator of the technology), have commercially deployed three different types of SR systems, both mobile and fixed-base, at three different locations. The latest was in 1997 at the Trojan nuclear plant.
EPA LICENSING ADVANTAGES
While SR systems produce a final waste form that looks very similar to incinerator ash, they are not incinerators and so are not subject to the stringent EPA licensing requirements and restrictions currently applied to incinerators. In fact, SR systems employ a reducing environment (low oxygen) to process waste, which is the opposite of the oxidation environment (high oxygen) employed by an incinerator. The reducing environment of an SR system minimises, or completely eliminates, the production of Particles of Incomplete Combustion (PICs), like dioxins and furans, which are commonly generated in incinerators. As SR does not generate PICs, it has been classified as an “environmentally friendly technology” by environmental groups like Greenpeace, Sierra Club and Citizens for a Better Environment. The US Department of Energy has also selected SR as a “Process of Choice” for the processing of its radioactive and mixed waste streams.
Steam Reforming can process all types of organic materials, including radioactive wastes from commercial nuclear power plants, and other hazardous wastes, mixed wastes, biological and chemical agents and explosive materials. Wastes processed have been in all physical forms – solids, liquids, sludges and gases – and include paper, wood, resins, sludges, oily wastes, animals, aqueous liquids, biological materials, plastic, cloth, charcoal, oil, EDTA, filters, decon solutions, sponge jet blast media etc.
The three nuclear facilities where commercial SR systems were deployed – the Palo Verde nuclear station, Oak Ridge nuclear facility and the Trojan nuclear station – cover a large range of these wastes:
Palo Verde nuclear station
The initial commercial application of SR was in 1994 at the Palo Verde station. A mobile SR system was deployed, under a sub-contract to B&W Nuclear Technologies, to process approximately 350 000 gal of EDTA steam generator cleaning solutions. The SR system was sized to ensure that the solutions stored in tanks would be removed in time for the next scheduled steam generator cleaning project. Prior to deploying the system at the site, it was successfully put through full-scale Proof-of-Principal testing using surrogate EDTA solutions.
When the SR system was placed into operation at Palo Verde, the system throughput was found to be significantly below that obtained during the tests. This was due to the clogging of the waste discharge port. The problem was determined to be caused by foaming agents which had been added to the EDTA solutions stored at Palo Verde but which were not added to the surrogate EDTA solutions. A foam quenching process was developed and applied to eliminate the clogging problem.
Despite this problem, the SR system demonstrated that it could efficiently process EDTA solutions and render them non-hazardous and achieve an effective volume reduction of about 30:1.
The largest commercial application of the SR technology implemented to date was done at Oak Ridge where it installed a fixed-base SR system in its Central Volume Reduction Facility (CVRF) in 1995 for the purpose of processing radiologically contaminated Dry Active Wastes (DAW) being generated by hospitals, universities, research facilities and pharmaceutical companies.
SR was selected for the processing of these wastes in 1994 in anticipation that most small generators of low level radioactive wastes (LLRW) were no longer going to have access to a disposal site following the closure of the Barnwell LLRW Disposal Site to most generators. Prior to this time, most of these wastes were being incinerated by SEG and then shipped directly to Barnwell. However, with the added requirement that processed wastes had to be returned to the generator for storage, until such time as a new disposal site opened, incineration of these small generator wastes in SEG’s large incinerators was no longer practical. Cross contamination of utility wastes with the radionuclides present in small-generator wastes was the primary concern. Likewise, small generators did not want mixed fission products showing up in their processed wastes which also had to be returned for storage. Consequently, the use of an SR system was deemed to be a practical solution to these problems as it provided similar volume reductions as incineration and allowed for efficient segregation of wastes during all phases of processing. By mid 1995, SEG had completed installation and start-up of its fixed base SR system.
Shortly after start-up of the SR system, the Barnwell facility reopened to all LLRW generators, except for the North Carolina generators, and thereby eliminated the need for the SR system to process small-generator waste. However, SEG decided to go ahead with this work since continued operation of Barnwell was uncertain.
In 1996 SEG processed over 80 000 pounds of small-generator waste which included DAW of all types and many items, including frozen animals. In every case, the SR effectively processed every type of waste tested and provided superior volume reduction of 10 to 50:1, depending upon the amount of non-organic material contained in the waste.
SEG determined during the first year of commercial operation that its SR system provided volume reductions similar to that obtained from incinerators. However, by the end of 1996, it became clear that Barnwell would remain open and as the cost of the much smaller SR was much more than the much larger incinerators, SEG decided to stop using the SR for small-generator waste. The SR system is currently used to perform full-scale SR treatability and Proof-of-Principal tests for commercial and government customers.
Trojan nuclear plant – 1997
The most recent GTS Duratek application of SR processing involved the processing of fuel pool filters and Greater Than Class C (GTCC) materials at the Trojan nuclear plant. The filters contained fuel fragments/pellets and lead shot which prevented them from being disposed at any existing commercial LLRW disposal site. The GTCC materials were organic or contaminated with organic debris which prevented them from being stored in dry fuel storage casks at the site’s Independent Spent Fuel Storage Installation (ISFSI) as the customer could not effectively remove the organic material and demonstrate compliance with NRC requirements for dry storage and disposal.
GTS Duratek segregated, and then characterised and processed these materials in the Trojan spent fuel pool using its SR technology. This was done in a manner which effectively removed all organic material and water permitting the materials to be packaged in compliance with NRC regulatory requirements for dry storage and disposal and transportation. This was the first time any GTCC organic materials and filter material had ever been processed and packaged for storage in a dry fuel storage cask in compliance with NRC regulations for removal of organic (potential hydrogen generating) materials. This was also the first time anyone has been able to effectively demonstrate compliance with the NRC’s stringent hydrogen gas generating limits of <0.592 moles (<5 vol% H2) in the storage container over the anticipated storage life of the material.
Since this material exhibited relatively high dose rates, GTS Duratek designed and built a number of shielded special waste handling systems to permit safe segregation, processing and packaging of the filters and GTCC materials in the fuel pool area of the plant. Special design Steam Reforming process canisters (process cans), transfer bell and a new Can Feed Evaporator were designed and built to facilitate safe and efficient material handling, processing and packaging. The entire SR system was configured and modularised so it could be easily set up within the limited spaces available in the Trojan spent fuel pool area.
A number of special tools and components were also designed and built by GTS Duratek to facilitate safe waste sorting and segregation operations. These components included: Process Capsule Storage Rack; Debris Transfer Can Rack; Waste Sorting Table; Can Removal Station; Can Loading Station; and long handled tools.
All processing equipment, procedures and support systems including the SR system and Can Feed Evaporator were tested in an integrated POP test at the Hanford Reactor WNP-1 using a full range of surrogate wastes before being transferred to Trojan and set up in the bottom of the New Fuel Storage Pit. All special design waste handling components and tools were placed into the Trojan Transfer Canal.
The process capsule is sized to fit within the cells of Trojan’s Sierra Nuclear dry fuel storage casks. Waste handling and processing is shown in the Trojan debris removal/steam reforming project process flow diagram.
This mobile SR system is believed to be the only system currently available which can perform the following tasks:
• Effectively remove organic contaminants and water from GTCC materials and fuel-bearing debris/components/filters that are to be stored in dry storage casks.
• Destroy organic GTCC materials and volume reduce them for storing in dry storage casks.
• Demonstrate compliance with NRC requirements for removal of organics and water (potential hydrogen generating material) from materials requiring dry storage, disposal and transport.
• Render organic filter material into inorganic material, volume reduce this material and package the material for long-term dry storage, transport and disposal.
• Pre-process, volume reduce and package materials which can be returned to spent fuel storage pools to await availability of on-site dry storage.
Furthermore, SR systems can be used to volume reduce and package high activity filters that can be disposed as LLRW. Such filters are shredded and rendered into a highly volume reduced residue (100:1 VR is common). The volume reduced residue and metal fragments are collected in a common process can for LLRW disposal or dry storage, should the resultant volume reduced residue exceed class C waste.