BWR Nuclear Fuel Assembly Short Model, 300mm rods, 7X7 Array with 3X3 Water Channel

"Build-A-Bundle" Nuclear Fuel Assembly Activity for outreach projects with high-school (STEM) students.
Students press their own pellets and fill one rod. The rest of the bundle is printed and pre-assembled ahead of the lesson.
Accommodations are made for an optional electrical system to light the water channel when the rods are placed in their correct positions. This is the part that is a work in progress.

*Update 1-10-2018, added decimated versions of lower tie plate and water channel to lower triangle count and file size. Added an array of 169 pellets for easier print bed layout.
*Update 1-12-2018, added solid pellet and solid pellet array. (Pellets with no inner hole. Same outer dimensions).
*Update 3-6-2018, replaced Spacer.stl with version that has holes for active flow, like the LTP and UTP.

3D Printed Parts with eSUN PLA Pro (https://www.amazon.com/dp/B01EKEMB7Q)
Lower_Tie_Plate.stl - Qty: 1, Supports: Touching Buildplate, Layers: 0.1mm, Infill: 50%, Wall Thickne