A chemical admixture that improves the durability of concrete by adding it to the concrete when manufacturing nuclear power plants. It is a non-shrinkable grout material which plays a role of extending the service life by complementing the problem caused by unevenly supported support by applying injection to a part where the support ratio of the precision machine and the turbine lower base is important. High density non-shrink grout material used to fill openings of nuclear power plants. It is made of refractory mortar which protects the steel and concrete in case of fire and prevents the collapse of the structure and prevents deformation of the steel frame.