Water rod in fuel assembly

In a water rod, there is a portion covered only with steams in the upper portion thereof, and the temperature of the structural components covered only with the steams is elevated to high temperature. Then, the downcoming pipe for coolants is brought into an intimate contact with the inner wall of a uprising tube by a pressing pipe. Even if the structural components in the water rod are covered with steams, the heat of the high temperature structural components is removed by thermal conduction by way of the inner wall of the uprising pipe, to suppress the temperature elevation. Then, lowering of tensile strength, hydrogen embrittlement, corrosion, etc. are prevented, to ensure the reliability and integrity of the water rod. Since the pressing pipe is pressurized from the inner side for pressing the downcoming pipe, or coolants downcoming flow channel is formed by a non-contact space of the inner pipe, the structure described above can be attained without welding. Accordingly, spectral operation can be conducted safely. (N.H.)