Options for Improvement to Protect Yourself and Others
By Lawrence Jassin
Since 2004, Nuclear Power Outfitters (NPO) LLC, Lisle, Illinois, has been conducting expert ALARA assessments at various U.S. nuclear plants, providing a detailed road map to achieve lower collective radiation exposure. The idea actually started earlier when NPO and its strategic partner Vallen participated in formal ALARA discussions with both the STAR and Utilities Service Alliance organizations. Best practices were shared amongst the participating utilities. NPO’s focus is on the effective use of shielding and contamination control products.
ALARA practices encompass a broad range of tools, including, but not limited to:
• Source term reduction;
• Mock-up training;
• Communication; and
An expert ALARA assessment at a commercial nuclear plant requires NPO personnel to be on the site for three to five days, usually during an outage. Typically, the first day or two are spent receiving the required training to become an escorted nuclear worker with access to high radiation areas. Once access is granted, an independent review of all plant shielding packages is conducted, typically requiring three to five hours. Plant shielding packages contain information regarding:
• Scaffolding set up;
• Lead blanket quantities; and
• Installation instructions, including timing and dose estimates with and without shielding.
An assessment is made to determine the challenges associated with each shielding package, options to make the shielding more effective by techniques such as moving it closer to the source, and impact on activities expected to occur in the vicinity of the shielding. In some instances, the possibility to upgrade the shielding to permanent shielding is considered. Once the assessor has a good handle on the status quo, a meeting is held with key health physics and radiation protections personnel.
It has been noticed that most shielding is installed during the second shift of an outage day. “Improvements to ALARA shielding programs are becoming more challenging, as outages become shorter,” says Earl Jacobson, founder of NPO. Taking part in the shift transition meetings is an important component of an assessment. Discussions are held to solicit information on the results of the shielding. By obtaining information directly from both shifts and from the health physics technicians who conducted the surveys and were involved in the shielding installation, the assessor is able to gain the proper perspective on what matters most and where improvements can be made. A full walk-down takes place during the second shift and photos and measurements are taken at this time.
OPTIONS FOR IMPROVEMENT
With the information on the plant’s practices understood, input from the key personnel registered, and a firsthand view of many of the packages or hot spots witnessed, the assessor can begin to establish a set of options for improvement. Improvements typically fall into the following three categories:
1. Transition of temporary shielding packages to permanent;
2. Improvements in deployment time for installing shielding; and
3. Changes to the positioning of the shielding to effectively place more shielding mass in the path of the source term.
Regarding the transition to permanent shielding, there have been indications that the NRC is becoming more vigilant in enforcing that temporary shielding is temporary, or in service for less than 90 days. Many plants have rather simplistic arrays of lead blankets located in or around hot spots on valves, pumps, pipes and vessels. In some cases raw lead is exposed around piping. An important meeting that takes place during an assessment is with the person in engineering who reviews shielding packages. An understanding about the requirements that engineering has for shielding must be understood early in the process. This includes weight limitations for hanging shielding on pipes or grating, considerations for making shielding permanent, temperature considerations and 10 CFR 50.59 regarding configuration control.
A recent project at Indian Point NPP in New York involved the replacement of water shield drums which needed to be set up for each outage to shield the regenerative heat exchanger. As the image at the top of the previous page shows, the heat exchanger is located near a personnel ladder. The new track system, involving 12 16-inch wide, 10-foot tall, 1-inch thick lead-encased panels providing a 10th value thickness at 1 MeV gamma, was permanently installed during the Spring 2010 outage. Set-up time for the new shield system was greatly reduced as compared to the water shield installation time, thus lowering dose.
While the track system is a permanent installation, the shielding was moved via overhead track into a storage compartment during power operations. This storage feature reduced the engineering time to approve this project by simplifying the seismic calculations. While not part of the original scope, the engineering department at Indian Point may consider a review to allow these shields to remain in use during power operation at a later time. This would eliminate set-up time while making the full system permanent.
Another area of improvement gaining popularity in the industry is the introduction of adjustable serpentine rack systems. These new designs are beginning to take the place of scaffolding. Provided in three-foot sections, the new serpentine rack system is used to hang lead blankets from 6 feet to 8 feet high, and can be set up by the radiation protection department, as opposed to “carpenters” at a plant, which can lead to conflicts with scheduling outage work. The new serpentine racks have an open structure on the bottom for straddling floor interferences and a detachable upper section for working around piping. The net result in many instances is a work space that is less obstructed than with typical scaffolding set ups.
One of the most important options now offered to ALARA management is the multitude of materials now being used for shielding. The use of metals, such as tungsten and iron blended with silicone, allows for custom-molded shields that put more mass in the path of the radiation and allow for easier installation. As compared to potentially ill-fitting lead blankets near pipes and valves, less overall weight is necessary. Tungsten metal, with a density of 19.3 g/mL, provides high mass in the path, but its cost is significantly higher per kilogram than iron (ρ=7.9 g/mL) and lead (ρ=11.3 g/mL).
As tungsten prices escalate with other commodities, compromises in overall thickness can be considered by blending iron with the tungsten, or choosing an iron-only silicone design. The demands of each shielding application are factored into selecting the best material or combination of materials for the project. Projects which can accommodate thicker shielding or general area shielding will tend towards the iron silicon shielding, blankets, lead or water over tungsten, based on lower cost per pound.
Shielding effectiveness or attenuation of a particular radiation source is predominately a result of the mass of shielding placed in the path, regardless of material in the typical power plant setting where gamma energies from Cs-137 at 0.661 MeV to Co-60 averaging 1.25 MeV represent a key consideration. Whether you are using lead wool blankets, tungsten metal or in silicone, water or steel, the weight properly placed in the path of the radiation will be the key determiner of attenuation and protection for the workers. The higher temperature rating of metal/silicone shields (400⁰ F), when compared to traditional PVC lead blankets, is another issue that must be considered.
Effective options with tungsten silicone products include ribbon and pipe shield formats. With the ribbons, typically 2-4 inches wide, 1/8-inch or 1/4-inch thick and 8 feet long, a customized shield can be created without the expense of a custom mold. The ribbons are extremely flexible, have a lower profile than blankets, or even iron/silicone, and can conform to many surfaces.
Disposal of tungsten and iron silicone products can be less costly than lead, although the actual cost for low level mixed radwaste disposal is currently in the range of $500 per cubic-foot. For large area shielding, use of lead blankets, solid lead or water shields may be the best alternative. Coupled with innovative rack, track and lattice systems, even the old lead blanket can still be a cost-effective choice.
The detailed reports from an assessment may contain 20-30 suggested changes, complete with photographs and design concepts. A reference guide is also included which illustrates dozens of ALARA shielding solutions from other plants. Utilities should refer to these reports each year and implement the ideas in order to improve their standing amongst their peers and the protection of their workers. As larger utilities re-establish fleet ALARA program managers, working with these independent expert assessments allows the utility to get an appreciation for the priority, opportunity for improvement and the engineered shielding solution proposed, all in one place.
Together with its new parent company, Eichrom Technologies, NPO is leveraging not only its own experience working with utilities and government installations, but Eichrom’s as well. Eichrom, founded in 1990 as a result of technical transfer of chemical separation technology from Argonne National Laboratory, operates under the ISO 9001:2008 quality system registration.
Since the acquisition of NPO in 2008, NPO’s manufacturing capacity has been expanded, a new radiochemistry laboratory has been built and the combined company is expanding its product line to offer an even greater array of solutions to its common customers worldwide. This increase in manufacturing capacity allowed NPO to recently send shielding products to Europe and North America while still handling emergency shipments to Japan.
About the Author:
Lawrence Jassin is currently serving as director of sales and marketing at Eichrom Technologies LLC in Lisle, Illinois. Eichrom is a specialty chemical and shielding manufacturer with worldwide sales. Mr. Jassin joined Eichrom in 1993 after working for Illinois Water Treatment, now part of US Filter and Pall Corporation. A graduate of the University of Wisconsin-Madison with a BS in Chemical Engineering, he has focused his career on separations involving ion exchange, filtration and extraction chromatography. In 2008, Mr. Jassin became responsible for the shielding and contamination control product line of Nuclear Power Outfitters after their acquisition. Earl Jacobson, Founder of NPO, has contributed greatly to Mr. Jassin’s appreciation and understanding of how to develop successful engineered ALARA solutions. For more information, visit www.eichrom.com and www.alarasolutions.com.