초록 ▼

A fuel assembly has part length and full length fuel rods, and a pair of large-diameter water rods which occupy an area which can accommodate 7 fuel rods. Natural uranium regions are provided in the upper and lower end portions of the effective fuel zone of the fuel assembly. An intermediate region

A fuel assembly has part length and full length fuel rods, and a pair of large-diameter water rods which occupy an area which can accommodate 7 fuel rods. Natural uranium regions are provided in the upper and lower end portions of the effective fuel zone of the fuel assembly. An intermediate region between these upper and lower natural uranium regions provides an enriched uranium region which has three axial sections: an upper section, a middle section and a lower section. The middle section has the highest average enrichment, the lower section has the medium average enrichment and the upper section has the smallest average enrichment. The difference in the average enrichment between the middle section and the lower section is smaller than that between the middle section and the upper section. The upper section has a lower concentration of burnable poison than other sections of the enriched uranium region. According to this arrangement, a greater burn-up degree of the fuel assembly can be achieved with minimal increment of the average enrichment, while preserving sufficiently large safety margin such as the thermal margin of the reactor and the reactor cold shut down margin.

대표청구항 ▼

A fresh fuel assembly for loading in a nuclear reactor, charged with uranium and no plutonium and having a plurality of fuel rods and at least one water rod surrounded by said fuel rods, said fuel assembly comprising: a fuel-charged zone including axially upper and lower end regions charged with nat

A fresh fuel assembly for loading in a nuclear reactor, charged with uranium and no plutonium and having a plurality of fuel rods and at least one water rod surrounded by said fuel rods, said fuel assembly comprising: a fuel-charged zone including axially upper and lower end regions charged with natural uranium and an enriched uranium region between said upper and lower end regions, said enriched uranium region having three sections of an upper section, a middle section and a lower section of different levels of enrichment; said middle section having an average enrichment of a level higher than an average enrichment level of said upper and lower sections; a difference in the average enrichment level between said middle section and said lower section being smaller than a difference in the average enrichment level between said middle section and said upper section; wherein the fuel assembly comprises said fuel rods arranged in nine columns and nine rows; wherein a pair of water rods are disposed adjacent to each other in a central portion of the cross-section of said fuel assembly so as to occupy an area substantially equal to an area to be occupied by seven fuel rods; wherein a part of said plurality of fuel rods comprises burnable-poison-containing fuel rods containing uranium and a burnable poison and the rest of said plurality of fuel rods comprises uranium fuel rods containing uranium and no burnable poison; wherein a part of said uranium fuel rods have axially upper and lower end regions charged with natural uranium, and an enriched uranium region between said upper and lower end regions, said enriched uranium region having three sections of an upper section, a middle section and a lower section of different levels of enrichment, said middle section having an enrichment of a level higher than an enrichment level of said upper and lower sections, a difference in enrichment level between said middle section and said lower section being smaller than a difference in enrichment level between said middle section and said upper section; and wherein a burnable poison content per unit axial length in the upper section of each burnable-poison-containing fuel rod is smaller than a burnable poison content per unit axial length in other sections of said enriched uranium region of the burnable-poison-containing fuel rod.