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 and people.

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 rollers to permit easy sliding in and out of heavy loads.

The maximum overall length of each airlock is 12 m, as set by the building architecture (1 m + 8 m + 1 m + 1 m + 1 m). This overall length includes the thicknesses of the airlock doors and the thermal insulation and cooling for the hot sodium pool side face of the inner airlock door.

The maximum outside width of airlocks is limited to 2 m by adjacent NaK pipes and pipe flanges.

The inner airlock doors must open upwards to avoid collision with adjacent NaK pipes and the horizontally positioned pool deck level tipping trays.

The inside volume of fuel bundle 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 8 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 intermediate heat exchange bundle 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 have 1 m diameter protective cages around the tubes to protect the exposed tubes during crane and roller manipulation.

Intermediate heat exchange bundle airlocks also enable entrance and exit of suitably suited workers.

Each intermediate heat exchange bundle transfer airlock has minimum internal dimensions of: 10.5 m long X 1.5 m wide X 2.9 m high.

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

Inside the sodium pool space and aligned with the airlocks are tipping equipment trays that extend over the sodium pool. When horizontal a tipping tray is at pool deck level. When vertical the tray is 2 m inside the sodium pool wall. The tray hinge is 1 m above the sodium pool surface. The axis of the tray hinge is parallel to the sodium pool wall. The hinge is supported by a frame attached to the inside of the pool wall.

The purpose of a tipping tray is to rotate new horizontally inserted equipment to the vertical position and and to rotate used vertical axis equipment to the horizontal position for horizontal extraction.

The inside airlock doors open onto tipping trays that are up to 2 m wide. These trays are about the same length as the fuel bundles and the intermediate heat exchange bundles.

When horizontal a tipping tray is at the sodium pool deck level. When vertical the tray is 2 m inside the sodium pool wall.

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 tipping trays have equipment clips to prevent long axis eqquipment accidentally fallingoff the tray when it is in its vertical position.

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

The intermediate heat echange bundles must be positioned in the airlock with the cold feed pipe 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 subsequent fastening in place..

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

An important secondary benefit of the tipping trays is to reduce 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 outwards. With the trays horizontal the equipment is pushed onto the trays. Then the gantry crane is attached and the tray is rotated to its vertical position. Then the fuel bundle or intermediate heat exchange bundle is in the 0.8 m wide 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.
 

This web page last updated May 19, 2025