Patent Number: 044477333
Section: description

SPECIFIC DESCRIPTION As can be seen from the drawing, the vessel is formed by a unitary one-piece body 1 of cast iron especially spherolytic cast iron, or cast steel and can serve to receive irradiated nuclear-reactor fuel elements. This container can have the construction of the containers of the above-identified applications and patents. The mouth of the container is stepped to form a recessed seat 3 in which a cast iron or cast steel plug-type absorbing or shielding cover 4 is received with elastomeric sealing rings 5 forming a multiple barrier collectively referred to hereinafter as the inner seal. A passage 1a running through the wall of the container can be closed by a plug formed by a screw 4a threaded into the cover and sealed relative thereto. The storage chamber 2 of the vessel is thus completely sealed against the exterior. Above the cover 4, a safety cover 6 is mounted in a seat 13 and is sealed as shown at 7 by a single 0-ring seal forming the outer seal of the invention. Between the inner seal 5 and the outer seal 7, the barrier compartment 8 is formed which can be filled with a control gas. The barrier compartment 8 communicates with a monitoring device represented diagrammatically at 9 as a gauge but including a threshold-responsive circuit which, upon detention of a pressure drop below a given threshold, can operate a gas analyser 14 which is capable of detecting species in the gas from compartment 8 and signaling whether these species include radioactive species from the chamber 2 of the vessel or species from the ambient atmosphere. A bore 10 serves to communicate between the compartment 8 and the device 9. When a further cover 11 is provided, an additional bore 10' may be formed in this cover and a hole drilled in a welded plate 10" to permit communication through this plate with the compartment 8 via a tube sealingly fitted through the holes. When, however, the cover 6 blocks the inner cover because of a failure of the inner seal 5, an intact plate 10" is welded in place and the compartment 8' becomes the new pressurized control compartment such that seal 7 becomes the inner seal and seal 12 the outer seal. The control gas in compartment 8 is at a pressure p.sub.1 which is significantly higher than the pressure p.sub.2 in the storage chamber 2 and than the atmospheric pressure p.sub.3. The pressure in chamber 2 (p.sub.2) is preferably 0.8 to 1.5 bar while the pressure p.sub.1 is about 6 bar. If the inner seal 5 fails, control gas flows in the direction of the arrow into the chamber 2 and the pressure in compartment 8 falls. This pressure drop is signaled by the monitoring device and can trigger an alarm to initiate repair proceedings. Preferably when the pressure drop falls below a predetermined threshold, the circuit 9 provides a continuous or periodic read-out of the pressure in compartment 8.