Patent Number: 
Section: claims

1. A neutron shield comprising:a plurality of containers each of which contains a powdered neutron absorbing material and which are stacked with one another in a vertical direction;a cladding tube which houses the containers and which is arranged outside a nuclear reactor core;an upper chamber which is provided at an upper portion of an interior of the cladding tube and into which gas leaked outward from the containers and caused by a neutron absorbing reaction of the powdered neutron absorbing material configured to absorb neutrons leaking from the nuclear reactor core is guided; anda support mechanism disposed in the upper chamber and configured to support the respective containers by pressing an uppermost container in the stacked containers in the stacking direction so as to permit deformation caused by thermal expansion or swelling,wherein a clearance is formed between the containers and the cladding tube in a state in which the containers are housed in the cladding tube. 2. The neutron shield according to claim 1, wherein each of the containers contains the powdered neutron absorbing material while keeping a space left in an upper portion of an inside of the container in the stacked state thereof. 3. The neutron shield according to claim 1, wherein the container includes a shroud tube filled with the powdered neutron absorbing material, a cover plate for closing an upper opening of the shroud tube, and a bottom plate for closing a lower opening of the shroud tube so as not to tightly close a neutron absorbing material filling region.