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


2013-08-02 Design Meeting Notes

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.

Core design

  • 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.


(design meeting notes)

First Stage

first nozzle stage: should be an impulse stage. flow goes to sonic velocity, choke flow regime, pressure drop is significant. The blades are impulse blades, and pressure drop will be very low. The air will cool, across the nozzle.

gives you a way to control mass flow

the air that strikes the blades will be much cooler because of expansion to high velocity (20% temp drop)

How many rows of blades do we need, to get expansion ratio of about 4?

Second Stage

may be difficult to also get it in choked flow. so we have to choose between first or second stage being in chocked flow.

inlet manifold and nozzle must have about double the flow area, compared to those of the first stage

challenge: peak temperature is on the second stage, rather than the first stage. does this mean that impulse blades should be used here, rather than reactive blades?

Constant air mass flow

power varies by varying turbine inlet temperature. so when running at part load, these types of turbines will be inefficient.

Turbine casing width must stay below 3.5 m, to remain rail-transportable, excluding the external combustor, which connects via a flange

Combutor cooling flow:

420+1300 -> 670


torrous: you want to keep the velocity constant, so that you don’t have to accelerate and decelerate, and you get constant pressure

applies to inlet plenum upstream of each of the two turbine nozzles. also applies to the outlet plenum on the reactor vessel.

Cold Air Line

what is the design assumption on the diameter of the cold air pipe? also, need to transition to higher diameter, because we shift to insulated piping

need to rotate around so it comes off the bottom

Hot Air Line

add the extension

to mention:

  1. adding notes in wordpress
  2. design of torrous
  3. posting edrawing of latest design