Center reflector design
- Depth of key holes: currently 4 cm, probably more than we need. We want to make sure that the keys remain inserted into following blocks as the column buckles under DBEs. 1 cm for 25 cm thick blocks is probably enough. Also, instead of sharp breaks, use small fillets. Change the key hole shape accordingly.
- Thickness of the inner reflector blocks is currently 25 cm –> lobes are nearly square. Having this roughly square ratio works best for irradiation induced stresses.
- Control rod channels: move holes outward so that distances to edges of the lobes are ~ equal. Important for resulting shrinkage of the lobes from neutron irradiation.
- Coolant injection channels: change shape from circular to key shape to increase distance between channels. This will help to cope with tensile stress from pressure differential between the coolant channels and out of the reflector.
- For a more uniform neutron irradiation region geometry at surface of reflector, get the center of the curvature radius closer to the surface.
- Slot size: need to perform pressure loss calculations to determine the right size.
- Check if the changes in geometry have an impact on neutronics (bigger region of graphite absorber).
- Small coolant channels between core and control rod/coolant injection channels : have some that go to the control rod insertion channel and some that go to the coolant injection channel. These channels should be ~ 1 cm diameter. Number of rows of channels will be determined based on pressure drop.
- Injection channels: as we get higher than ~ 70 cm above bottom of the active core region, we don’t want to have too much flow coming through the center reflector à narrow down the size of the coolant injection channels (having a small circular region at the end of the slots will also help to reduce stress concentration at the end of the slots).
- Add instrumentation channels (8?) at the center of the inner reflector, with keys for alignment.
- Tie rods to carry tensile stress: possibly locate them at the outer corners of the lobes.
Lower region of the center reflector:
- Also reduce thickness of the keys to ~ 1 cm. Reduce radial thickness of the keys to ~ 2 cm. All these dimensions will be determined through buckling and FEM analyses. Key structure should not be symmetric (use odd number of keys).
Outer reflector design
- Block thickness can be double that of the inner reflector blocks (50 cm instead of 25 cm) because of lower neutron dose.
- Successive layers of blocks are staggered azimuthally so that when gaps open between blocks under thermal expansion (1% of the 6 m circumference, divided by 24 blocks = 2.5 mm) by-pass flow through the cracks is blocked.
- At the top, transition into metal for neutron shielding, where the DHX wells begin.