XYLENE POWER LTD.

FNR AIR LOCKS

By Charles Rhodes, P.Eng., Ph.D.

Each FNR has four airlocks. Two airlocks are intended for transferring fuel bundles. The other two airlocks are intended for transferring intermediate heat exchange bundles, open steel lattice components, replacement NaK pipe sections and people. The internal length of the air locks is 11.03 m.

To prevent air entry into the sodium pool space and to prevent loss of argon from the sodium pool space, when both airlock doors are closed an airlock is pumped down to a vacuum .

The inner and outer airlock doors should be interlocked so that both doors of the same airlock can never be open at the same time.

The outer airlock doors open outward and the inner airlock doors open inward into the sodium pool space. This arrangement ensures good airlock door seal when an airlock is evacuated. Air is evacuated to the outside. Argon is evacuated to the inside. If the equipment in the airlock is being inserted, the airlock is refilled with argon. If the equipment in the airlock is being extracted, the airlock is refilled with air.

The bottom of each airlock is at the sodium pool deck level to match flat deck truck requirements.

The inside bottom of each airlock is fitted with a dolly or rollers to permit easy sliding in and out of heavy loads.
 

EQUIPMENT AIRLOCK DIMENSIONS

The overall height of the intermediate heat exchange bundle assembly is:
32 inch + 10 inch + 6 m + 10 inch + 1 m + 0.7 m + 1.0 m + 8 inch + 16 inch + 3 inch
= 79 inch + 8.7 m
= 10.70 m

This dimension sets the minimum inside length of an equipment transfer airlock.

Note that the top discharge fitting is a 16 inch X 16 inch X 16 inch tee which retains a recessed lifting point that can accommodte two hooks. Note that this lifting point is displaced from the vertical pipe axis to ensure that when the gantry lifts an Intermediate Heat Exchange Bundle the gantry places it in the correct orientation for insertion into an equipment transfer airlock.

The radial width of the intermediate heat exchange bundle assembly is:
72 inch + blanking plate thickness + (329.7 inch - 313.7 inch) = 88 inch + blanking plate
= 2.286 m

This dimension sets the minimum inside height of the equipment airlock assuming that the airlock top and bottom are flat. In reality the equipment airlock inside height must be higher to allow a bottom equipment dolly.

The equipment airlock inside width must accommodate the 42 inch wide outer curve of the intermediate heat exchange bundle manifolds.

The overall airlock length allowance is 14 m of which 2 m are devoted to a aerogel insulation plug. That leaves about 1 m of airlock length for the two airlock doors.

The inner airlock doors must open upwards to avoid collision with adjacent NaK pipes and the horizontal pool deck.

The inside volume of equipment transfer airlocks is minimized to minimize evacuation time and argon losses during each fuel bundle transfer.

Each fuel bundle transfer airlock has internal dimensions of about 11 m long X 0.3 m wide X 0.3 m high.

The outer side of each fuel bundle transfer airlock is designed to mate with a truck mounted shielded fuel bundle transporation container.

The volume of equipment transfer airlocks is much larger than for a fuel bundle transfer airlock to accommodate intermediate heat exchange bundle assemblies or suitably suited personnel.

Intermediate heat exchange bundles may need protective cages around the tubes to protect the exposed tubes during manipulation.

The airlock doors are temperature protected to prevent thermal damage to their door seals.

Inside the sodium pool space and aligned with the airlocks are equipment roller trays and guides.

The purpose of a roller tray is to assist in rotation of horizontally inserted equipment to the vertical position and return of equipment to the horizontal position for horizontal extraction.

The inside airlock doors open onto tipping trays that are up to 3 m wide.

The tray length beyond its hinge is limited to about 6 m so that the tray and its load will not collide with cooling fuel bundles. It might be necessary to remove a few cooling fuel bundles to attain this objective.

The equipment trays have rollers and end pivot bars to allow easy equipment sliding when the tray is in its horizontal position.Note that the fuel bundle trays are cycled much more frequently than the equipment tipping trays.

The intermediate heat exhange bundles must be positioned in the airlock with the cold NaK feed pipe and flanges on top.

An intermediate heat exchange bundle must be rotated 90 degrees about its long axis to permit bundle movement through the guard band around the sodium pool and rotated 90 degrees again before fastening in place.

To create sufficient space for operation of the intermediate heat exchanger tray a few fuel bundles may have to be temporarily relocated.

An important benefit of the equipment trays is to minimize the required ceiling height which reduces the wall height around the sodium pool and also reduces the required argon bladder capacity.

The outer airlock doors must be sufficiently robust to withstand an opening tornado induced gauge pressure of at least 0.02 MPa).

Both fuel bundles and intermediate heat exchange bundles are horizontally loaded with their tops pointing inwards. The equipment is pushed onto the trays. Then the gantry crane is attached and the load is dragged to the pool edge where it rotates to its vertical position. Then the fuel bundle or intermediate heat exchange bundle is in the guard band outside the fuel assembly where it can be moved around the reactor. The procedure is reversed for extraction of fuel bundles or intermediate heat exchange bundles. They are laid onto the trays with their lifting points close to the air locks.
 

This web page last updated September 7, 2026.