Korea (KO) has developed and participated in the Test Blanket Module (TBM) program in the ITER, in which Ferritic Martensitic (FM) steel was used as the structural material for the TBM first wall (FW). To develop the fabrication method for the TBM FW and verify its integrity, a half-scale sub-module mock-up was fabricated and integrity test has been prepared; A dimension of it is a 444 mm height, 260 mm width, and 435 mm depth. A mock-up was assembled by HIPping of the previous fabricated components between the welded front and back plates, and then machining these plates to form the completed sub-module FW. To investigate the deformation of the cooling channels after the fabrication of the mock-up, neutron radiography was carried using neutron radiography facility. Pressure and He leak tests were successfully performed without any leak and failure. The flow rates in each channel were measured with the conventional ultrasonic sensor but it shows non-uniform flow distribution at each channel differently from the estimation by ANSYS-CFX. HHF test conditions were evaluated through the ANSYS-CFX analysis considering the above measured flow rates in each channel and it shows non-uniform temperature distribution of the FW mock-up. We will re-assemble or fabricate the manifold and perform the flow test before HHF test in the near future.