Patent Number: 
Section: claims

1. A concrete cask comprising:a metal canister accommodating spent fuel;a concrete container body for accommodating the canister inside the container body;a cooling passage provided between an external peripheral surface of the canister and an internal peripheral surface of the container body, and allowing air for cooling the external peripheral surface of the canister to pass; anda top space provided between a top surface of the canister, and inside of a lid of the container body, whereina baffle plate for suppressing introduction of air rising through the cooling passage to the top space is provided,wherein the baffle plate is mounted on a top external peripheral surface of the canister, and has such a shape that an external periphery around a top end of the canister expands towards a top. 2. The concrete cask according to claim 1, whereina cover plate for covering a lid welded part provided at the top surface of the canister. 3. A concrete cask comprising:a metal canister accommodating spent fuel;a concrete container body for accommodating the canister inside the container body;a cooling passage provided between an external peripheral surface of the canister and an internal peripheral surface of the container body, and allowing air for cooling the external peripheral surface of the canister to pass; anda top space provided between a top surface of the canister, and inside of a lid of the container body, whereina baffle plate for suppressing of air arising through the cooling passage to the top space is provided,wherein a mounting bracket for mounting the baffle plate on the canister is provided, and the baffle plate is mounted on a top end part of the canister or near the top end part of the canister by the mounting bracket. 4. The concrete cask according to claim 3, whereina coefficient of thermal expansion of the mounting bracket is smaller than a coefficient of thermal expansion of a metal material forming the canister.