For BWR plants, shielding the inner bellows is particularly challenging. During refueling operation the concrete shield plugs above the reactor well are removed and replaced by water. This water filled gap becomes a source for both radiation and contamination.
NPO designed a specialized system to address the concerns with shielding this area. Some of the requirements were:
- Wedge tightly into the inner bellows gap
- Overlap shielding pieces to prevent streaming
- Create an FME barrier
- Withstand being stepped on
- Have handles for quick and efficient installation
- Be evaluated for leachables and resistance to corrosion in water
For the last requirement, NPO developed a new T-Flex® material, stainless steel. Stainless steel’s natural resistance to corrosion in water was a perfect fit was this project. The material was tested to MIL-STD-2041E for 1) leachable halides (bromide, chloride, fluoride) and nitrate, 2) leachable sulfur 3) heavy metals per ICP-AES and was determined to be acceptable for use.