Containment built-in refueling water tank

The present invention provides a containment built-in refueling water tank, which comprises a top plate, a bottom plate, an outer ring plate and an inner ring plate fixed between the top plate and the bottom plate, and a slag retention structure located between the outer ring plate and the inner ring plate, the inner ring plate is sleeved in the outer ring plate so as to divide a space enclosed by the bottom plate and the outer ring plate into an inner ring pool and an outer ring pool, and the inner ring pool is provided with a slag retention structure. A water inlet is formed in the position, corresponding to the outer ring tank, of the top plate, a water outlet is formed in the position, corresponding to the inner ring tank, of the bottom plate, a door opening allowing water in the outer ring tank to enter the inner ring tank is formed in the inner ring plate, and the disintegrating slag retention structure comprises two first filtering mechanisms arranged on the two sides of the water inlet respectively; t