Cook’s turbine cleanup2 August 2018
The Cook nuclear plant in Michigan, USA, opted to transport 700,000kg of turbine parts for decontamination in Oak Ridge, Tennessee. UniTech explains why.
WHEN THE DONALD C. COOK nuclear plant in Bridgeman, Michigan, replaced its turbines and corresponding outer casings — which were close to 91m in length — disposing of the obsolete turbines demanded a unique but crucial decontamination process.
The plant, owned by American Electric Power and operated by Indiana Michigan Power (an AEP subsidiary), partnered with UniTech Services Group to develop a strategic turbine disposition plan that would limit the utility’s onsite liability, and allow decontamination and recycling to take place offsite.
The major hurdle was determining a feasible method of transporting 687,192kg of turbine components to UniTech’s Oak Ridge service centre, eliminating the typical utility planning required before onsite turbine decontamination can commence. A utility choosing to decontaminate onsite would face a significant financial investment to train contractors and buy equipment.
UniTech project manager Jeff Wilson commented: “Most nuclear plants just don’t have the manpower to complete this work onsite, or don’t have the will to take on that substantial liability.”
“We were able to employ a receiving and processing method that solved those cost and liability issues,” he confirmed. “This method should prove viable for other large-scale projects in the future.”
DC Cook’s large turbine components were too heavy for long-distance trucking. UniTech’s Oak Ridge Service Centre instead worked with DC Cook and Barnhart Crane & Rigging to ship large pieces by barge.
UniTech, Barnhart’s Oak Ridge Division, the US Department of Energy’s Oak Ridge office and the Community Reuse Organisation of East Tennessee worked together to refurbish a barge access area near the Oak Ridge Service Centre, in the East Tennessee Technology Park. The access area had been defunct for several decades.
Barnhart shipped the turbine components via the Mississippi, Ohio and Tennessee navigable river systems. Turbine components were welded to the barge for continuous stability throughout travel. The barge departed from St. Joseph, Michigan on 10 September, 2017 and arrived at the Oak Ridge barge area in the early morning hours on 27 September after 17.5 days in transit.
Receiving & processing
Barnhart crews spent two days draining the barge water, breaking welds and setting up cranes for land transportation. It took two full days to unload and stage all six turbine casings from the barge and prepare for trucking to Oak Ridge. The barge was free released, and departed on 1 October. Over the next two days, upper turbine casings were moved 5km to UniTech’s facility at a cautious pace of 1.6km/hr, not including the movement of powerlines. Upper casings were received, decontaminated and cut for recycling in a 72-hour timespan, completed by 2:30 a.m. on 5 October.
Processing of lower casings began on 10 October and finished on 15 December.
UniTech processed six casings.
Each tool and metal decontamination project has unique monitoring process needs. For the DC Cook turbines, UniTech used both standard and specialised monitoring processes. Traditional hand frisking methods pose human error risks, including: inconsistent detector-to-item distance; difficulty with obtaining full item coverage; maintaining a consistent scan speed; determining alarm limit; and determining alarm limit in a fluctuating background. In recent years, UniTech has engineered new hand frisking methods that minimise human error. As part of improved monitoring methodology, UniTech employs a series of new detector configurations and new detector shapes to ensure optimum monitoring of heavy and odd-shaped items. UniTech uses a variety of custom monitoring equipment, including internal surface monitors, so that sound monitoring results can be gathered for each and every piece of material.
UniTech’s decontamination methods for tool and metal decontamination projects include:
- High-pressure washing with surfactants;
- Low pressure steam & chemical pre-soak;
- CO2 dry ice;
- Aluminium oxide;
- Walnut shells;
- HEPA-controlled and precise manual decontamination; and
- Proprietary ChemClean process.
A gamma spectroscopy process was used to verify decontamination of inaccessible areas and as a basis of validation for free release survey documentation.
Within 48 days, 687,192kg of turbine components were processed and invoiced for services. None of the material was disposed as low-level radioactive waste (LLRW). Most (659,977kg, or 97%) was recycled during final disposition and 20,412kg (3%) was free released to a Tennessee-approved low-level Class 1 landfill.
“While processing of turbine components is the same as other metals, disposition is a little bit different because everything has to be resized,” explained JoAnn Dauberger, technical sales & customer service manager at UniTech’s Oak Ridge Service Centre. Recycled components were cut to fit in a flatbed trailer and large components were cut to fit inside a landfill disposal container.
“Segmentation was very important to this project in particular, with nearly all materials being prepped for recycling,” she noted.
Completing the project offsite amounted to $2.2 million in savings for the utility, based on industry rates for the contractors, training and handling needed for onsite decontamination, as well as comparison of direct radioactive waste versus landfill disposal.
Offsite disposition proved to be the most cost-effective method for DC Cook, minimising the utility’s responsibility for the materials and optimising the amount of materials that could be recycled.
“Strong relationships with vendors for moving heavy equipment, key staff members with thirty-plus years each of decontamination experience and a facility capable of doing a job of this scope and size [UniTech’s Oak Ridge Service Centre] were really the difference makers on this project,” said Wilson.
Delivering the promise
Wilson said barge shipment is a viable option for other decontamination and decommissioning projects. It would enable offsite decontamination and disposition of other sizeable nuclear plant equipment, including reactor heads and steam generators. Offsite decontamination of large equipment also incentivises utilities to choose recycling as a cost-effective and sustainable method of disposition.
The DC Cook project and a Candu 6 reactor tooling decontamination project – completed concurrently – meant UniTech completed two unique decontamination projects in December 2017, totalling 1860t of materials.
The US nuclear industry strategy, ‘Delivering the Nuclear Promise,’ aims to implement the most significant savings opportunities in the most efficient manner possible. Whether decommissioning or upgrading power generation capacity, it is vital to find cost-effective methods of equipment disposition, preferably in methods that lead to recycling and reuse of materials.
The decontamination and recycling of obsolete DC Cook turbine components is an example of strategic industry collaboration in action, and UniTech says it hopes to collaborate with US utilities on similar projects in the foreseeable future.
“Choosing a method in which LLRW disposal is eliminated significantly reduces cost for utilities. It’s really a win-win situation,” said Dauberger.