scholarly journals A New Innovative Spherical Cermet Nuclear Fuel Element to Achieve an Ultra-Long Core Life for use in Grid-Appropriate LWRs

2007 ◽  
Author(s):  
David J Senor ◽  
Chad L Painter ◽  
Ken J Geelhood ◽  
David W Wootan ◽  
George H Meriwether ◽  
...  
Keyword(s):  
Fuel Element ◽  
Nuclear Fuel ◽  
Nuclear Fuel Element

Reliability in Microjoining Processes for Instrumented Nuclear Fuel Element Fabrication

2020 ◽  
Vol 1157 ◽  
pp. 31-37
Author(s):  
Călin Truţă ◽  
Adrian Amzoi ◽  
Dumitru Barbos
Keyword(s):  
Fuel Element ◽  
Nuclear Fuel ◽  
Structural Reliability ◽  
Added Value ◽  
Impedance Match ◽  
Normal Operation ◽  
Local Loss ◽  
Steel Coil ◽  
Nuclear Fuel Element ◽  
Prolonged Contact

The paper presents the assembling flux of thermocouple-instrumented nuclear fuel element for research reactor, from the point of view of the welding / brazing engineer, considering nuclear quality and safety requirements: fuel element structural reliability (no radioactive leaks through joints) and temperature signal reliability (thermocouple sheath integrity), this signal being an essential parameter for reactor normal operation and emergency shut-down. The paper is a real case study for an experimental instrumented element recently developed at INR-Pitesti describing technology choices as balance between fabrication complexity and risk of failure in joining processes, especially in later stages when added value increases. All joints (welded or brazed) fall into microjoining category, and it is shown how some special provisions may influence reliability. Focus is put on brazing thin-walled Inconel sheathed thermocouples, where erosion and local loss of ductility are known issues, leading to sheath rupture. Choosing as filler the less aggressive BNi-9 helped too little. A simple but efficient technique has been developed to address this matter adequate to narrow spaces inside a nuclear fuel element, where no room is available for solutions described in literature e.g. distal preplacing of filler. The solution prevents sheath from having prolonged contact with large volume of molten filler by using locally a miniature barrier (thin stainless-steel coil or sleeve) which only allows capillary wetting, being also a perfect real-time visual indicator of brazing progress and completion. As proved in the present paper, this method along with using filler formulation with lower Carbon content (without organic binder) enhances significantly, 8 times at least, resistance to bending fatigue. A particular vacuum brazing chamber design is employed: narrow quartz tube with external induction coil and top fitting letting outside the long thermocouples attached, reducing much the chamber volume and degassing. Careful impedance match is therefore required to overcome induction power loss due to the larger coil-to-workpiece gap. Additional joining problems are discussed e.g. inherent differential expansion of long parts during induction heating which afterwards may put tension upon braze during solidification and determine delayed cracking, this being avoided through wise order of operations. Another concern is the final precision weld between instrumentation segment having attached the hard-to-handle long thermocouples bunch and nuclear segment with the heavy Uranium pellets. The result of this research is successful assembling of first Romanian prototype with joints exhibiting He leak rate bellow 1E-09 std.cc/sec and overall reliability proved during reactor irradiation testing.

NUCLEAR FUEL ELEMENT CONCEPTS

1967 ◽  
Vol 79 (1) ◽  
pp. 59-68
Author(s):  
CHARLES O. SMITH
Keyword(s):  
Fuel Element ◽  
Nuclear Fuel ◽  
Nuclear Fuel Element

scholarly journals CHARACTERIZING HIGH-TEMPERATURE DEFORMATION OF INTERNALLY HEATED NUCLEAR FUEL ELEMENT SIMULATORS

2016 ◽  
Vol 5 (1) ◽  
pp. 67-84
Author(s):  
Alexander I. Belov ◽  
Randy W.L. Fong ◽  
Brian W. Leitch ◽  
Thambiayah Nitheanandan ◽  
Anthony Williams
Keyword(s):  
High Temperature ◽  
Fuel Element ◽  
Nuclear Fuel ◽  
Mechanical Response ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Mechanical Simulation ◽  
Loss Of Coolant Accident ◽  
Nuclear Fuel Element ◽  
Accident Conditions

The sag behaviour of a simulated nuclear fuel element during high-temperature transients has been investigated in an experiment utilizing an internal indirect heating method. The major motivation of the experiment was to improve understanding of the dominant mechanisms underlying the element thermo-mechanical response under loss-of-coolant accident conditions and to obtain accurate experimental data to support development of 3-D computational fuel element models. The experiment was conducted using an electrically heated CANDU fuel element simulator. Three consecutive thermal cycles with peak temperatures up to ≈1000 °C were applied to the element. The element sag deflections and sheath temperatures were measured. On heating up to 600 °C, only minor lateral deflections of the element were observed. Further heating to above 700 °C resulted in an element multi-rate creep and significant permanent bow. Post-test visual and X-ray examinations revealed a pronounced necking of the sheath at the pellet-to-pellet interface locations. A wall thickness reduction was detected in the necked region that is interpreted as a sheath longitudinal strain localization effect. The sheath cross-sectioning showed signs of a “hard” pellet–cladding interaction due to the applied cycles. A 3-D model of the experiment was generated using the ANSYS finite element code. As a fully coupled thermal mechanical simulation is computationally expensive, it was deemed sufficient to use the measured sheath temperatures as a boundary condition, and thus an uncoupled mechanical simulation only was conducted. The ANSYS simulation results match the experiment sag observations well up to the point at which the fuel element started cooling down.

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