Modular in-core flow filter for a nuclear reactor

A modular in-core flow filter is described for capturing potentially harmful debris during cold hydrostatic and hot functional testing of a nuclear reactor. Since testing is carried out before fuel assemblies are placed in the reactor, multiple filters, each being of the same size and configuration, are temporarily installed on the reactor lower core plate. Each filter includes a square metal base having a single axial opening which desirably covers four holes in the core plate. Fine mesh and coarse mesh screens are secured in the axial opening and the unit is removably attached to the core plate by brackets which extend through the metal base and engage the underside of the core plate but are actuated into position from the upper side of the core plate. When functional flow testing of the primary coolant system has been completed, the filters are removed