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 airlock doors open upward and are fitted with counter weights for ease of operation. The airlock doors st the sodium pool end of each airlock are insulated to protect the elastomeric gas seals.from exposure to hightemperatures. Air is evacuated to the outside. Argon is evacuated to the sodium pool space. 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 bottom of each airlock has a dolly track that guides two independent dollies. At the sodium pool end of this track there is a stop to prevent dollies falling into the sodium pool.

The dolly closest to the sodium pool is herein referred to as dolly #1. The dolly further from the sodium pool is herein referred to as dolly #2.

INSERTION OF FUEL BUNDLES:
Initially the inner door of the airlock is closed.

Fuel bundles are delivered to a FNR location in 12 m long horizontal gas tight shielded transport containers mounted on flat deck trucks. Within each such container a fuel bundle rests on two to three rail guided dollies. The fuel bundle transport container has a rear door that opens upwards. The outer door of the airlock also opens upwards.

The flat deck truck backs up to approximatey align the transport container with the air lock. Then jacks supporting the transport container are used to achieve precise transport container to air lock alignment.

Then the rear door of the transport container and the outer door of the air lock are both openned. Then the fuel bundle together with its dollies is slid into the airlock.

Then the outer door of the airlockis closed. Then the airlock is evacuated by pumping the contained air to the outside. Then argon is addmitted to that air lock.

When the argon pressure in the airlock equals the argon pressure over the sodium pool the inner airlockdoor is openned.

The fuel bundle is pushed inwards until dolly #1 hits its pool side stop.

The gantry crane main rail is rotated to line up with the airlock axis.

The gantry crane hooks on to the fuel bundle and lifts and drags. The fuel bundle swings upright.

The gantry crane moves the fuel bundle to its desired location.

The gantry crane rotates the fuel bundle to its desiredorientaion.

The gantry crane lowers this fuel bundle to the desred position.
 

Later the gantry crane attached the fuel bundle indicator tube.

REMOVAL OF FUEL BUNDLES:
Initially the airlock outer door is closed and the airlock dollies are located over the pool deck.

The indicator tube is removed.

Fuel bundle corner clips are removed.

with suitable regard as to uel bundle removal order the selected fuel bundle is lifted straightup.

The fuel bundle is held in place to allow sodium to drip dry.

The fuel bundle is moved until it is directly over dolly#2 while the dollies are against the pool end stop.

The fuel bundle is lowered onto dolly #2.

The antry crane dolly moves slightly toward the pool centre while slackening the support arrangement. This action causes dolly #2 to slide outwards taking the bottom of the fuel bundle with it.

Pull the fuel bundle fully into the airlock.

Close the inner air ock oor.

Pump the argon out of the air lock.

Open the outer air lock door.

lide the used fuel bundle. into the transportation container.

Close the outer airlock door. Close the transportation container door.
 

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 intermediate heat exchange bundle top discharge fitting is a 16 inch X 16 inch X 16 inch tee which retains a recessed lifting point that can accommodate 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 about its long axis for insertion into an equipment transfer airlock.

BELOW AND ABOVE THE AIRLOCKS
The concrete shear walls associated with the airlocks provide vertical passageways for accessing various levels in the FNR. Below the airlocks these access locations include:
Baseplate Level;
Dump Tank Level;
Heat exchange gallery Level
Service space below NaK pipes.

The inside height of the equipment transfer airlock is set by Intermediate Heat Exchange bundle dimensions:
Cold feed pipe Top curve = 16 inch
Cold feed pipe diameter = 16 inch
Cold feed pipe inside curve diameter = 32 inch cold feed pipe radius = 8 inch
Cold feed pipe flange radius = 16 inch
Manifold projection beyond cold feed pipe flange = 8 inch
Total = 96 inch, dolly height additional

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 track.

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.