2013-09-20 Design Meeting Notes


  • DHX sits at bottom of metal lid
  • Arrangement on plate for modularity
  • Large radius elbows for DRACS loop to allow for flexible inspection instruments to be inserted
  • DHX to TCHX centerlines will be ~6m, which is a distortion compared to scaling from CIET (would be ~8.5m)
  • Each DHX should remove 2% of nominal power. 2/3 failure logic.

Hot well

  • Level difference between two hot leg penetrations in hot well creates a seal loop. 0.5m of head can be accommodated if isolation valve fails.
  • Look at calculation for hot well height required above penetrations for thermal expansion (600°C to maximum accident condition temperature) + level swell from pump operation.

Reactor cavity cover – refueling deck hatches

  • Need to have a center circular hatch to pull out center reflector
  • Hatch for reactor vessel
  • Hatches for 3 DRACS (see picture)
  • Seal for DRACS hatch could be integrated in frame design of DRACS
  • Because of high number of penetrations in cover, may need to have it be steel
  • Missile shield above has fewer penetrations and could be concrete

2013-09-20 Cavity Covers

Level swell

  • Design objective: 2.0 m of head from cold leg to hot leg (level swell in cold leg standpipe)
  • May need full 2.0 m available inside reactor vessel to accommodate full level swell (therefore need to increase vessel height to 13 m), although probably lower because the level swell in the control rod insertion channels doesn’t take head losses from cold leg and downcomer
  • If reactor vessel’s height increases by 1 m, control rod drive must be even longer (top must remain uncovered) (see picture)

2013-09-20 Vertical Stacking


2013-09-20 Vertical Stacking 2


2013-08-19 Design Meeting Notes

Isolation Valves

  • Free surface on hot well makes it physically impossible to pressurize the hot leg (hence the containment). Same with free surface on stand pipes on the cold leg.
  • Need isolation valves for containment and CTAHs. For hot well, use gate valve to seal entrance from hot leg (see picture).
  • In hot well, for each primary pump, have a plug for inlet to isolate the pump. This way, one loop can be operational while the other is offline.
  • Other option: 2 hot wells, with 2 hot leg valves, and dam between the 2 wells to prevent communication between the 2 if needed (with additional requirement that elevation change in the wells across all operating conditions shouldn’t be too high). In that case, have 2 parallel hot legs coming out of the vessel all the way to each well. This way, one can perform maintenance on one well while keeping the other full for decay heat removal.
  • Also option to have one hot leg coming to a hot well with 2 compartments, 2 seats, 2 gate valves (see picture).
  • On cold leg, stand pipe might look like “cold well” with cold trap filter. Filter must be at higher elevation than drain tank. Isolation valve can be another gate valve (like hot well isolation valve). Design cold well to overflow into hot well.
  • Surface area in hot well must be large to reduce level swell. Not that critical everywhere else in the system (including cold leg stand pipe). In cold leg stand pipe, add neutrally buoyant volume displacer (graphite?) to reduce salt inventory (see picture). This will have a thin diaphragm for water hammer (if explosion in CTAH).

Decay Heat Removal

  • MSBR had a DRACS for the drain tank, using flibe (so that if there was a leak, they wouldn’t contaminate primary salt)
  • For FHR, use DRACS loop with salt, transfer heat to water, then to air stack. No need for huge air stack since some decay heat will just heat up and boil water.
  • See picture: if following CIET scaling, NDHX would end up being in the space between top of reactor cavity and control rod drive missile shield.
  • Need to isolate water from NDHX to limit parasitic heat removal.
  • Water would be on tube side of NDHX.
  • The water will be at 100°C (heat removal through boiling). This way, not too low temperature (avoid freezing) and not too high temperature (worse heat transfer). Air cooled condenser will condense water back (at 100°C). Any steam that doesn’t condense will be exhausted not to generate extra pressure in the system.

2013-08-09 Design Meeting Notes


  • New Items
    • Cavity cap penetrations
    • Hot salt well sizing
    • Pebble HIS volume
  • Old Items
    • Full pull length
    • Level swell

Level swell

  • Reactor vessel should extend at least 2 m above hot leg level to accommodate level swelling.

Cavity cap

  • Top cap of reactor cavity should be at least 1m thick (biological shield). Should be lined with 1/2m thick insulation. Outside of the insulation must be actively cooled (see picture).
  • There should be ports in the top dome for shutdown and control rods, instrumentation and inspection lines, DRACS loops, defueling machines. Start with ports for the electrical heater as proof of concept for more ports and plugs with insulation (see picture).

Cavity Top w/ Plug and Cavity Wall Lining

Hot well

  • Assume total salt inventory is ~4 times core inventory: 25 m3
  • Expansion of the salt from 600 to 700°C is ~3%: 0.75 m3
  • Assuming a 3 m2 hot well surface (approximately 2 m diameter circular, or equivalent oval), need ~0.3 m high tank to accommodate level swell. Probably more for safety purposes if we go to higher temepratures under some transients.


  • Relocate them closer to reactor: lines from hot well to CTAHs would come back at an angle from hot well (helps to accommodate for thermal expansion, see picture).

Hot Well - CTAH Piping (must accommodate thermal expansion)