Abstract: During the hot functional test of one NPP, the neutron shielding material was heated and released from the reactor vessel shielding blocks. The structure and layout of the block were redesigned, and B4C was adopted as the neutron shielding material. This paper analyzes the improved design scheme in terms of the heat transfer, the radiation shielding and GSI191. The result  indicates that the improved design meet the requirements. During the supplemental hot function test, the temperature of neutron shielding block and module and the radiation dose in the containment were surveyed, and the effectiveness of the new design scheme is further verified.