Patent Number: 047553472
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the construction of dry storage cells shown in FIG. 1 there is a preparation chamber 1 and an adjacent clean chamber 2 constituting a transfer corridor. Within the corridor there is track 3 which supports a train of transfer containers or buckets 4 each containing a canister 5 for receiving irradiated nuclear fuel. The preparation chamber has two posting facilities each comprising a tubular port member 6 extending from the preparation chamber into the clean chamber, the port member being normally closed by a removable closure plug 7 adjacent the preparation chamber. The other end of the port member 6 has opening 6a for embracing the body of a closed canister 5. The closure plug 7 carries a retractable retention means in the form of a grab 8, with a linear actuator 21, within the tubular port member for gripping and withdrawing the canister closure into the tubular port member. The grab has a hood 9 for sealably masking the outer surface of the canister closure designated 10. In one alternative construction the retention means is a vacuum operable gripping device and in a second a1ternative construction is a magnetically operated gripping device. In use the opening 6a of the tubular port member 6 seals about a canister 5 positioned immediately below and grab 8 with hood 9 is lowered within the tubular port member sealably to mask the canister closure 10. The grab is then engaged with the closure 10 and retracted to lift the closure clear of the canister. A grab (not shown) within the preparation chamber withdraws the closure plug 7 with a grab 8, hood 9 and a canister closure 10 into the preparation chamber the canister thereby forming an extension of the preparation chamber. Irradiated nuclear fuel, which may be in the form of a string of fuel elements, is then transferred into the canister whereupon the plug 7 with grab 8, hood 9 and canister closure 10 is restored to the tubular port member. The grab can then be extended to replace the closure 10 on the canister 5 whereupon the canister is retracted from the facility and removed for securing the closure by welding and checking for contamination of the external surfaces. In greater detail, the buckets 4 are carried in a bogie 11 and are sequentially positioned below a selected one of the facilities. As shown in FIG. 2 the plug 7 is secured to the port opening of the preparation chamber by clamps 12 and 13 and seals 14, 15, 16 are provided to ensure that contaminated surfaces of the port are not exposed to the clean chamber. The bucket situated below the facility is then raised by a jack 17 (FIG. 1) to engage the opening 6a with the canister carried in the bucket. A seal designated 18 is provided to seal the canister closure with the hood 9 and a seal designated 19 to seal the canister to the port member 6 following which the interspace bounded by the seals 16, 18 and 19 is vacuum tested by way of a connection 20 to check the efficiency of the seals. The seal 16 is then released and, as described hereinbefore, the grab 8 and linear actuator 21 remove the closure 10 from the canister whereupon the clamps 12 can be released and the assembly of plug 7, actuator 21, grab 8, hood 9 and closure 10 withdrawn into the preparation chamber. Irradiated fuel is then posted into the canister and the plug, actuator, grab, hood and closure assembly, replaced. After replacement the clamp 12 is re-engaged and the closure 10 is replaced on the canister by the actuator, seal 16 re-engaged and vacuum tested. The interspace is decontaminated by gas purges and seals 18, 19 released whereupon the bucket and canister is lowered into the transfer bogie and the canister subsequently transported to a closure welding facility. FIG. 3 illustrates an additional facility for handling defective canisters which may be required to be disposed of in the preparation chamber 1. Defective canisters are returned to the facility within a bucket 4 having a closure 22 fitted so that contamination is contained within the bucket. The procedure for with drawing the defective canister into the preparation chamber is generally similar to the foregoing procedure for withdrawing a canister closure into the fuel preparation chamber. The facility provides a second tubular port member 23 integral with the barrier wall between the preparation chamber 1 and the clean chamber 2 and extending co-axially into the clean chamber. The tubular port member 6 has an extension 24 and there are seals 25, 26, 27 similar to those designated 16, 18, 19 and a vacuum connection 28. The seals 18, 19, 26, 27 are of hollow section and are connectable to a vacuum source by selector valves (not shown). In their normal state the seals can embrace the canister 5 and container 4 in sealing manner but on connection to the vacuum source the seals are retracted into their housings to release the canister and container so that linear movement of the canister and container can take place out of contact with the seals. In an alternative construction the seals are arranged to sealingly embrace the canister and container when they are expanded by gas pressure and are retracted from contact at atmospheric pressure. In operation the posting port is sealed by seals 14, 15, 16 and 25 to ensure that contaminated surfaces of the port are not exposed to the clean chamber and the plug 7 is secured by clamps 12, 13. The bucket is raised by the jack 17 to engage the seals 26, 27 and vacuum tests made. The seal 25 is then released and the closure removal grab with its actuator 21 then withdraw the closure 22 into the first tubular port member 6 and after releasing the clamps 13 the assembly of tubular member 6, actuator 21, grab 8 and closure 22 can be lifted into the fuel preparation chamber. The canister 5 is then withdrawn into the preparation chamber from the bucket 4 and the assembly replaced in the outer sleeve 23. After replacement the clamp 13 is re-engaged and closure 22 is replaced on the bucket by the actuator 21. Seal 25 is re-engaged and vacuum tested. The interspace is decontaminated as previously described and the bucket subsequently transported for further decontamination.