2013-08-28 Design Meeting Notes

Design Report

  • Need to have a design report done in time to generate a summary for ICAPP (final papers due January 2014).
    • Need to have a draft design report for December.
    • Also need to have a draft white paper for the January workshop by December.
    • Regis Matzie (and Jim Rushton?) to review preliminary design. October 7-8 (preferred). Need to send draft design report in advance (mid-september) and have plant layout figured out.
    • Outcome of the meeting: 1/ take action for Mark-1 design, or 2/ implement changes for Mark-2 design.

Plant Layout

  • Low pressure air duct diameter might have to bump up to 2 m to stay at reasonable circulating power (high pressure air duct is ~ 1.5 m).
  • Most compact configuration could be ~11.5 m from center of RV to center of CTAHs. Resulting thermal expansion could be up to 12 cm.
  • Shutdown conditions:
    • All plant is stopped and put in hot standby
    • One CTAH is drained, the other is used for normal shutdown cooling
    • Elevation of crane above grade must accommodate pulling out the longest object from below grade (probably RV).

2013-08-29 - Plant layout top and side view

CTAH Design

  • CTAH head and bottom: ASME standard dished head (flanged and dished)
  • CAD model should start with external vessel of the CTAH

2013-08-29 - CTAH


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)

Flibe Inventory

Flibe inventory will be calculated based on volumes of the FHR sub-systems and components containing the primary salt. A list of these sub-systems and components is provided here. Some volumes can be directly computed from the current FHR CAD model. When geometry/volumes are unknown, the sub-system or component has been italicized and sources for future calculations are provided where possible.


  • Active core region
  • Defueling chute

Reactor internals

  • Coolant injection channels
  • Control rod channels
  • Inner reflector bypass paths (estimate from graphite blocks geometry, thermal expansion and resulting gap size)
  • Pebble injection lines
  • Free space below pebble bed (will depend on pebble injection method as well as divider plate geometry)
  • Outer reflector bypass paths (estimate from graphite blocks geometry, thermal expansion and resulting gap size)

Cold leg

  • 2 x CTAH to drain tank (need to locate drain tank)
  • 2 x stand pipe (need to estimate level swell based on flow velocity and properly size the stand pipes)
  • 2 x drain tank to reactor cavity wall (need to locate drain tank)
  • 2 x reactor cavity wall to reactor vessel wall
  • 2 x reactor vessel to downcomer coolant distribution system
  • downcomer

Hot leg

  • Hot salt collector ring
  • Hot salt extraction (collector ring to reactor vessel wall)
  • Hot salt extraction (reactor vessel wall to reactor cavity wall)
  • Hot salt extraction (reactor cavity wall to hot salt well) (need to locate hot salt well)
  • Hot salt well (need to estimate volume; based on level swell, what else?)
  • 2 x hot salt well to CTAH (need to know relative locations of hot salt well and CTAHs)

CTAH (need to estimate CTAH tube bundle total volume)

DHX (primary side)

  • Hot leg to DHX (need to figure out pathway)
  • DHX (shell side) (need to adapt numbers from MSBR heat exchangers; look at Cristhian’s RELAP model; implement heat transfer coefficient multiplicator based on twisted tube HX performance)
  • Check valve
  • Valve to downcomer (need to figure out pathway; this will be a bypass path under normal operation)

DRACS loop

  • DHX (tube side) (need to adapt numbers from MSBR heat exchangers; look at Cristhian’s RELAP model; implement heat transfer coefficient multiplicator based on twisted tube HX performance)
  • NDHX (tube side) (need to adapt numbers from European Breeder Reactor and other metal-cooled reactors designs; look at Cristhian’s RELAP model)
  • DRACS piping (total inventory will be based on required elevation difference between the DHX and NDHX centerline and pipe size to drive natural circulation; performance will be based on a 2/3 rule and 2% nominal power extraction [or should this be 6%?], hence 1% nominal power [or 3%?] per DHX; need to determine design average and delta T between hot and cold leg of the DRACS loop, based on DHX LMTD)

Fuel handling system

  • Defueling mechanism
  • Storage space (use wet canisters? room filled with flibe? should we use some multiplication factor of the core salt inventory? Mike is working on this)