Method for preventing fretting damage to fuel rods, nuclear reactor fuel element, device for preventing fretting damage, and spacer in a fuel assembly of a nuclear reactor
원문보기
IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
G21C-003/336
출원번호
US-0612647
(2003-07-02)
우선권정보
DE-0003729 (2001-01-26)
발명자
/ 주소
Stabel-Weinheimer, J?rgen
Ren, Mingmin
출원인 / 주소
Framatome ANP GmbH
인용정보
피인용 횟수 :
13인용 특허 :
3
초록▼
Transverse vibrations of the pellet columns included in the fuel rods of fuel elements are limited by elastically mounting the fuel rod jacket tubes in the mesh of spacer grids. When the fuel rods are supported in this way, flexural vibrations of a higher order occur that lead to damage to the jacke
Transverse vibrations of the pellet columns included in the fuel rods of fuel elements are limited by elastically mounting the fuel rod jacket tubes in the mesh of spacer grids. When the fuel rods are supported in this way, flexural vibrations of a higher order occur that lead to damage to the jacket tubes caused by fretting. These vibrations are the less dampened the more rigid the fixture of the fuel rod is. These vibration conditions are more easily excited and more strongly dampened when the pellet columns are more mobile, thereby removing vibration energy from the fuel element and avoiding damage caused by fretting. The mobility of the columns can be increased by increasing the gap between the pellet and the jacket tube, or by using constructions in which a torque M?10 N mm on the fuel rod leads to a tilting angle φ?0.1°. For this purpose, the fuel rod can be retained in a mesh in such a manner that a distance d0?10 mm between the highest and the lowest point of contact of the fuel rod is maintained on the holding element of the mesh.
대표청구항▼
1. In a fuel element of a nuclear reactor cooled by a coolant flow of light water, a spacer assembly for a plurality of fuel rods, comprising:a spacer formed with mesh openings each for a fuel rod projecting therethrough and defining a given spacer plane; a plurality of holding elements disposed in
1. In a fuel element of a nuclear reactor cooled by a coolant flow of light water, a spacer assembly for a plurality of fuel rods, comprising:a spacer formed with mesh openings each for a fuel rod projecting therethrough and defining a given spacer plane; a plurality of holding elements disposed in each of said mesh openings and formed to laterally support said fuel rod and to limit and dampen a relative mobility of the fuel rod with respect to said spacer and for allowing the fuel rod to be set predominantly into tilting oscillations in the spacer plane by the coolant flow; and said holding elements exerting a maximum torque up to M (torque)=10 N·mm on a fuel rod at a tilting angle φ=0.1°, having an axis of rotation running perpendicular to the fuel rod in the spacer plane. 2. The spacer according to claim 1, wherein said holding elements in at least one of said mesh openings are formed with a plurality of elongate bearing surfaces for bearing against the fuel rod, said elongate bearing surfaces having a longitudinal extent of at least 1 mm, and wherein, in an unirradiated state of said spacer, a highest bearing point of the fuel rod in the respective said mesh opening lies at most 10 mm above a lowest bearing point of the fuel rod in said mesh opening.3. The spacer assembly according to claim 2, wherein the highest bearing point lies at most 5 mm above the lowest bearing point of the fuel rod in said mesh opening.4. The spacer assembly according to claim 2, wherein the highest bearing point lies at most 3 mm above the lowest bearing point of the fuel rod in said mesh opening.5. The spacer assembly according to claim 1, wherein said spacer is formed with inner mesh openings and said holding elements are disposed at least in said inner mesh openings.6. The spacer assembly according to claim 1, wherein said holding elements are disposed in all said mesh openings of said spacer.7. The spacer assembly according to claim 2, which further comprises, in each mesh opening including holding elements with said bearing surfaces, stops for limiting a lateral deviation of the fuel rod with respect to an at-rest position thereof to a range from 0.1 to 0.5 mm, said stops being formed in a plane above said bearing surfaces and a plane below said bearing surfaces.8. The spacer assembly according to claim 2, which further comprises, in each mesh opening including holding elements with said bearing surfaces, stops for limiting a lateral deviation of the fuel rod with respect to an at-rest position thereof to substantially at most 0.3 mm, said stops being formed in a plane above said bearing surfaces and a plane below said bearing surfaces.9. The spacer assembly according to claim 7, wherein a respective said stop is disposed above and below each said bearing surface.10. The spacer assembly according to claim 1, wherein said holding elements in at least one of said mesh openings are formed with a plurality of elongate bearing surfaces for bearing against the fuel rod, and the fuel rod is supported against said holding elements of said mesh opening at fewer than eight elongate bearing surfaces.11. The spacer assembly according to claim 2, wherein the fuel rod is supported against said holding elements of said mesh opening at fewer than eight elongate bearing surfaces.12. The spacer assembly according to claim 2, wherein said bearing surfaces are oriented parallel with respect to the fuel rod.13. The spacer assembly according to claim 2, wherein said bearing surfaces are distributed equidistantly over a periphery of the fuel rod.14. The spacer assembly according to claim 2, wherein said bearing surfaces are distributed in pairs and equidistantly over a periphery of the fuel rod.15. A fuel element for a nuclear reactor cooled by a flow of light water, which comprises: a foot, a head, and at least one spacer assembly according to claim 1 between said foot and said head.16. The fuel element according to claim 15, wherein said spacer assembly according to claim 1 is a bottom spacer of a plurality of spacers between said foot and said head.
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