Core Barrel Shielding
Tuesday, April 11th, 2017
In 2013 NPO designed and built a custom Core Barrel Shield for Palisades Nuclear Plant in Covert, MI. The shielding was implemented in Palisades’ 23rd refueling outage and was a great success. The story of the project’s success spread in May 2015 when the Palisades plant was recognized during the Nuclear Energy Institute’s best industry practice awards for the innovative shielding package to reduce radiation exposure through a more cost effective, safer method for core support barrel inspections.
For inspection purposes, every 10 years the core support barrel (CSB) must be removed from the reactor vessel and placed on its storage stand on the reactor cavity floor. Once removed from the vessel, the CSB extends approximately 42 inches out of the water. Shielding must be placed over the 42 inches that extend from the water due to the very high radiation levels emanating from it.
Previous methods of shielding the CSB were difficult to install and not very successful in shielding the top of the CSB. These methods resulted in a lot of exposure during installation as well as elevated dose for workers in other areas of the containment building.
NPO was called into action in April of 2013 to start conceptualizing a design for an effective shielding package that could meet the stringent and challenging requirements of such a large project inside the nuclear power plant containment building. By May of 2013 we received the purchase order for our design and the engineering and project management teams began turning the wheels for design and production.
The complete package included a 3 piece circular walkway with integrated shielding, removable hand rails that doubled as a track for the inspection robot, an assembly stand, (336) lead blankets with special grommets and (5) custom storage containers. The 34,000 lb unit had to be small enough to fit through an equipment hatch and, once inside, easily assembled and placed atop the core barrel with a crane. NPO also provided a structural analysis and assisted in the load testing on-site.
The project yielded a 10% reduction in general area dose rates and an 80% reduction in the proximity of the core barrel. In addition to reducing radiation exposure, the new package resulted in a time savings for assembly and installation and minimized usage of laydown space inside containment. With the shielding package assembled and installed as one structure, productivity and efficiency also increased.
NPO employed every facet of the company to complete this project in a short timeframe. Multilevel collaboration between the customer, sales, engineering, quality, production and our vendors was a key component to the overall success.
Thanks to everyone whose contributions made this project such a success!