PURPOSE: To provide an attached heat removal means of a passive containment vessel cooling system type, allowing backfitting to an existing nuclear reactor system.

CONSTITUTION: An attached heat removal system includes a structure 50 erected outside a reactor containment vessel 12 at a position adjacent thereto, and a heat exchanger 62 is provided in a cooling water pool 60 in the upper divided chamber 52 of the structure 50. A water pool 63 is provided in the lower divided chamber 56 of the structure 50. Also. the heat exchanger 62 is communicated to a dry well space 20 via an inlet pipeline 66 and an outlet pipeline 68. A heated fluid present in the containment vessel 12, therefore, flows to the heat exchanger 62. thereby being cooled. Thereafter. the condensate portion of the fluid is returned from the heat exchanger 62 to the dry well space 20. On the other hand, the non-condensing gas portion of the fluid is introduced into the water pool 63 in the lower divided chamber 56.