Patent Number: 051788241
Section: description

Referring now to FIG. 1, a collection apparatus 10 is shown for collection of particulates from a grinding apparatus 12. The collection apparatus 10 comprises a vessel 14 having declivitous sides 15 descending to an outlet 16 connected to one side of a top valve 17. A tubular upright collection chamber 18 is connected at its upper end to the other side of the top valve 17, and is closable at its lower end by a lower valve 22. An ultrasonic sensor 24 is positioned just below the top valve 17 to monitor particulate level at that position in the chamber 18, and a compressed air inlet 25 into the chamber 18 locates between the sensor 24 and the top valve 17. An overflow 26 extends near the top of the vessel 14, and a recirculation circuit 28 including a pump 30 is connected between the declivitous sides 15 to a position above the grinding apparatus 12. The grinding apparatus 12 comprises parallel grinding wheels 34, 35 respectively located above a trough 36 which has a bottom outlet 38 extending so as to discharge into the vessel 14. In operation, nuclear fuel pellets 40 (eg uranium oxide) are fed between and along the grinding wheels 34, 35 to provide a required diameter of pellet 40. The recirculation circuit 28 discharges water over the grinding wheels 34, 35 and the water together with particulates 42 (eg 1 to 4 .mu.m) drop into the trough 36 and from there through the outlet 38 into the vessel 14. With the top valve 17 open and the lower valve 22 closed, the particulates 42 fall and settle in the chamber 18, whilst the water is recirculated by the recirculation circuit 28, any water flowing through the overflow 26 being collected and subsequently returned to the vessel 14. The particulates 42 gradually collect as a sludge 44 in the chamber 18 until they reach a level where they are detected by the sensor 24. The top valve 17 is then closed, the lower valve 22 opened, and compressed air introduced for a short period through the inlet 25 to eject the sludge 44 from the bottom of the chamber 18. The lower valve 22 is then closed, and the top valve 17 opened, to repeat the collection cycle in the chamber 18. Referring now to the modification shown in FIG. 2, the collection apparatus 50 shown is in many respects identical to the collection apparatus 12 of FIG. 1, except that in place of the recirculation circuit 28 of FIG. 1, a filter circuit 52 is used. The filter circuit 52 comprises an outlet pipe 54 from the vessel 14 connected to a pump 56 arranged to discharge to a conventional cross-flow filter 58. A clean water filtrate outlet 60 from the filter 58 is arranged to discharge between the grinding wheels 34, 35, whilst a through-flow outlet 62 from the filter 58 is returned into the vessel 14 above the outlet pipe 54. As an option, a flush-down pipe 66 (shown in broken line) may be connected between the through-flow outlet 62 and the side of the trough 36 to assist in flushing the particulates 42 from the trough 36 into the vessel 14. In order to inhibit rapid blocking of the filter 58 from the particulate 42, an initial feed of particulate U.sub.3 O.sub.8 may be introduced at 68 to form a permeable coating 70 (see FIG. 3) at the ingress side of filter element 72 of the filter 58. For example, particulate U.sub.3 .sub.8 having a size distribution of between 45 and 90 .mu.m at a loading of about 229 gm in 30 liters of water mixed with U.sub.3 O.sub.8 having a size distribution of 1&lt;45 .mu.m at a loading of about 50 gm in 30 liters of water has been found suitable to provide an effective coating. An example of a suitable cross-flow filter 58 may be obtained from: Fairy Microfiltrex Limited PA1 Fareham Industrial Park PA1 Fareham PA1 Hampshire PA1 P016 8XO PA1 United Kingdom PA1 Bestobell Mobrey PA1 190-196 Bath Road PA1 Slough PA1 Berkshire PA1 SL1 4DN PA1 United Kingdom An example of a suitable sensor 24 to sense a sludge interface may be obtained from: It will be appreciated that the sensor may form part of a circuit for automatically operating the top valve 17, the lower valve 22, and the air inlet 25 in response to signals from the sensor. With some particulates and with frequent discharge of the sludge 44, the use of the air inlet 25 might be dispensed with. Although the invention has been described in relation to the manufacture of nuclear oxide fuels, the invention has applications with alternative nuclear fuels, and for non-nuclear materials. It will be understood that although obturating means in the form of valve means (eg ball valve means) have been described in relation to FIGS. 1 and 2, alternative suitable obturating means may be used preferably to provide a relatively clear axial path for the discharge of the sludge 44 therethrough.