Nuclear reactor using controlled debris to mitigate ECCS strainer pressure head loss

An emergency core cooling system in a nuclear power plant for circulating cooling water during a time period beginning near the onset of a power plant loss of cooling accident (LOCA) producing debris including fibrous material and debris particles entrained in the cooling water during the LOCA, wherein the LOCA causes the temperature of the cooling water to increase from its temperature during normal power plant operation prior to the LOCA onset, the cooling system comprising:

• a strainer disposed in the emergency core cooling system at a location where it will be immersed in a reservoir of the cooling water during the LOCA, said strainer having a surface for retaining debris in the cooling water reservoir and perforations through the surface for permitting the cooling water to pass through the strainer;
• a pump disposed on a suction side of the strainer surface and operable during the LOCA to provide a pressure drop relative to a pressure side of the strainer surface opposite the suction side for causing the cooling water in the reservoir to flow toward the pressure side of the strainer surface, wherein the perforations are sized to inhibit passage of entrained fibrous material larger than the perforations and to allow passage of entrained debris particles smaller than the perforations;
• and
• a plurality of controlled-debris elements disposed in the emergency core cooling system for entrainment in the flow toward the strainer of cooling water in the reservoir during the LOCA, wherein:
• each element is constructed with a specific gravity vs. temperature profile so that the element has a specific gravity substantially the same as the cooling water when the cooling water reaches a predetermined increased temperature above its temperature during normal power plant operation after the LOCA onset for entraining the element in the flow of cooling water toward the strainer and depositing on the pressure side of the strainer surface a debris/element layer comprising a plurality of the elements and the debris;
• and
• the elements are configured to inhibit the deposit of fibrous material directly on the strainer suction surface and form open spaces between adjacent elements in the debris/element layer that allow passage of entrained debris particles through the debris/element layer and the strainer perforations to alleviate pressure head loss across the debris/element layer on the strainer during the LOCA.