Inner reflector design
- Update: instrumentation channels should go all the way through (top to bottom).
- In addition to tie rods in lobe corners, some of the channels will be instrumented with neutron flux measurement.
- Bottom of buoyant control rod channels must be a blind hole, so that pressure differential on the control rods will induce proper snubbing. Need to calculate required length of blind hole below perforated region of the control rod channel (will affect rod length, therefore stacking problem).
- Must be careful with stiffness of the channel to cope with pressure differential.
- Consider having some kind of porous structure at the bottom of the channels to ensure that the rods stop without damaging the structure itself if the channel walls are cracked and the pressure differential is not enough to stop the rod. Need a way to monitor if structures have been damaged.
- Have another inlet flow chanel in the thick bottom part of the reflector that merges into the control rod channels (more flow area, lower flow velocity). Refined flow areas and pressure differential calculations must be performed. Need to take into account entry losses at the bottom of the inflow channels.
- Add small channels (1 cm diameter) for flow outlet from the control rod channels. Adjust number and spacing of these channels based on desired flow distribution (based on pebble bed dynamics). Probably 2 columns of small channels per control rod channel.
- Tip of control rods: load with neutron poison? Amount of graphite? Need to make sure not to insert positive reactivity feedback (based on FHR core neutronics analysis)
- Plan for the Fall: work on COMSOL coupled stress and fluid analysis (Jae? Alex?)
- Taper entrance to the combustor (curvature radius should be 1/4 – 1/3 of line radius).
- Secondary hot duct to vent stack should be smaller (can take higher velocity).
- Annulus around combustor should be larger (1/4 of total area). Wall should be thin (at pressure equilibrium, takes highest temperature).
- Diamond structures (insulation) should be thinner to be flexible.
- Thickness of outer insulation will depend on heat losses and need to have outer wall temperature remain below regulatory limits (wall cannot be >50°C for workers protection). Based on fiberglass insulation thermal conductivity and natural convection heat transfer coefficient.
- Block with hot leg can be larger to accommodate size of hot leg (low dose rate).
- Hot duct liner should extend a bit down into the graphite reflector.
- Need to analyze thermal stress transient when flow reversal through DHX.
- Need to have small gap (1 cm?) between fixed and movable metal rings in upper core structure.
- Flow direction in defueling chute: probably want it to be downards so that upper core structures don’t get heated up, but will make defueling more complicated (pebbles cannot be entrained in flow outside of the core).
- Shell structure (above cold leg, below hot leg): get elevation transition closer to hot leg.
- Need to work on detailed design of reactor vessel/fire brick type of insulation/liner/concrete.