GB1574458A

GB1574458A - Nuclear fuel reprocessing apparatus

Info

Publication number: GB1574458A
Application number: GB29023/77A
Authority: GB
Original assignee: IHI Corp
Current assignee: IHI Corp
Priority date: 1976-07-12
Filing date: 1977-07-11
Publication date: 1980-09-10
Also published as: DE2731248C3; DE2731248A1; FR2358728B1; FR2358728A1; DE2731248B2

Description

(54) NUCLEAR FUEL REPROCESSING APPARATUS (71) We, ISHIKAWAJIMA HARIMA JUKOGYO KABUSHIKI KAISHA, a Company organised under the laws of Japan, of No. 2-1, 2-Chome, Otemachi, Chiyoda-ku, Tokyo-to Japan, do hereby declare this invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to nuclear fuel reprocessing apparatus, and in this specification the term "nuclear fuel" includes fuels which have been irradiated and which have not been irradiated, and also fuels whether or not they are associated with protective sheaths.

It is an object of the present invention to provide nuclear fuel reprocessing apparatus which is safe against leakage of radio-active material into the atmosphere, and which requires a minimum of maintenance involving having access to the interior of the apparatus.

According to the present invention, nuclear fuel reprocessing apparatus comprises an enclosed furnace having gas entry and exhaust ports, and nuclear fuel feed and discharge openings, and a generally horizontal grid mounted within the furnace to be capable of vibration.

Preferably the grid is suspended within the enclosed furnace being connected to a diaphragm wall or other component which can be deflected, and which is coupled to a vibrator so that the grid can be vibrated within the furnace without having to have a drive shaft extending through the wall of the furnace, and that vibration can help to reprocess the fuel and break it up so that it can leave by the discharge opening for direct connection in a sealed container.

The fact that the furnace is enclosed means that there are no spaces between relatively slidable surfaces in communication with the interior and the exterior of the furnace which require seals which can leak and which require maintenance from time to time.

The invention may be carried into practice in various ways and two embodiments will now be described by way of example in relation to an example of prior art with reference to the accompanying drawings; in which Figure 1 is a diagram of a previously proposed nuclear fuel reprocessing apparatus, Figure 2 is a cross section through a reprocessing apparatus in accordance with the invention; and Figure 3 is a further embodiment of the present invention including two pieces of apparatus, one for oxidising nucler fuel, and one for reducing the reprocessed fuel so oxidised.

The apparatus of Figure 1 has a rotary drum a with a number of inclined fins b driven by a rotary shaft d supported by bearings f and driven by a low-speed motor and gearing g from outside the furnace. The drum a is enclosed within a furnace shell c which is itself covered by a thermally insulating layer I in which are embedded heating and/or cooling coils (not shown).

Gland seals e are incorporated at the shaft bearings to prevent or reduce leakage of gas from inside the furnace to the surrounding atmosphere.

Air or oxygen is introduced into the furnace through an inlet port h and leaves at an outlet port i for oxidizing nuclear fuel fed into the furnace through an inlet opening j leading into the rotary drum a. The action of the rotary inclined fins b breaks up the fuel into fine particles, and agitates it so that it comes readily into contact with the oxygen introduced at h, and oxidation is achieved in the reprocessed particles which leave the furnace through the discharge opening k at one end of the drum a. The gas leaves at i.

It is very difficult to provide a gland seal at e which is completely proof against leakage, and that is a great disadvantage where any leakage of radio-active gas into the atmosphere can be very dangerous. In any case gland seals have to be renewed from time to time and that is a dangerous operation for the maintenance staff.

In manly nuclear fuel reprocessing operations, a rather similar reduction furnace is also used in which a reducing gas is fed in at h and the same difficulties arise.

Accordingly the furnace shown in Figure 2 has been devised, and that consists of a generally cylindrical or rectangular horizontally disposed furnace f of totally enclosed construction with integral end walls 11 which are formed with thin local necks so that they are capable of being vibrated. The shell of the boiler is covered with a heat insulating layer 3 embodying heating and cooling coils 1 and 2 for controlling the temperature within the furnace. There are cooling fins 15 at each end of the shell.

A nuclear fuel feed opening 4 leads into the furnace from above, as do oxygen and gas entry and exhaust ports 5 and 6. There are two discharge openings leading downwards from the lower half of the furnace, namely a first discharge opening 7 for fine particles of reprocessed nuclear fuel. And a second discharge opening 8 of larger cross sectional area for the discharge of larger particles of fuel and sheaths from the fuel. A vacuum pump (not shown) is used to withdraw the gas from the exhaust port 6.

A separating plate or grid 9 with a large number of small holes 16 for the small reprocessed fuel particles is disposed generally horizontally within the furnace shell, being inclined slightly downwards from the inlet end to the discharge end. The grid effectively divides the interior of the shell into an upper part for the fuel to be reprocessed, and a lower part for the reprocessed part which has passed through the openings in the grid. There is a larger opening 17 at the down stream end of the grid through which larger particles can drop into the discharge opening 8.

The grid is joined at opposite ends to the centres of the diaphragm end walls 11, and is also suspended by wires or other hangers 10 from within the furnace so that when a mechanical vibrator 12 coupled to one of the diaphragm end walls 11 is in operation, the grid is vibrated generally in its plane, and that vibration tends to break up the particles of fuel, and stir them for intimate contact with the oxygen introduced at 5, and to assist in causing the reprocessed fine particles to pass through the holes 16 onto a downwardly directed chute 13 to be led to the discharge opening 7. The amplitude and frequency of the vibrations can be selected to suit the particular application, and can indeed be variable in any operation.

There are thermally insulating partitions 14 extending generally vertically, and axially spaced apart towards the ends of the furnace shell to protect the diaphragm end walls 11 and to prevent excessive loss of heat through them. The grid 9 extends through openings in the partitions 14.

In operation the furnace is heated so that its interior is at a temperature between 450"C and 750"C due to the heating coils, the decay heat of the nuclear fuel, and the heat produced as a result of oxidation.

When the nuclear fuel to be reprocessed contains plutonium, the oxidation proceeds as follows:

and typically

but when no plutonium is contained, the oxidation proceeds as follow:

and typically 3UO2+O2U3O,, During oxidation the fuel is pulverised and volatile fission products are withdrawn through the exhaust port 6 by a vacuum pump. The fine fuel particles are collected at 7, and any larger particles and pieces of sheath are collected at 8, which is at the downstream end of the downwardly inclined grid 9.

The embodiment of Figure 3 differs from the embodiment just described, principally in that there is a second similar reduction furnace b in addition to the oxidation furnace a which is as described above. This allows a fuel processing cycle to be achieved.

The discharge opening 7 from the furnace a leads to a transfer device 18 from which the fuel particles are fed into the reduction furnace b. The transfer device 18 incorporates means for preventing the gases from the respective furnaces from mixing.

The larger discharge opening 8 from the furnace a leads to a sealed container 19 for the collection of the larger particles.

The reduction furnace b is generally similar to the furnace a having a shell F' with a fuel inlet opening 20 leading from the device 18, a reducing gas entry port 22, and an exhaust port 23, the exterior wall of the furnace shell being covered with a heat insulating layer 24 containing heating coils 25.

The grid 27 is suspended in a similar manner from hangers 21 from the diaphragm end walls 31, and there is a single discharge opening 28 from the downstream end of the grid, and that leads to a discharge pipe 29 below the furnace.

There are axially spaced vertical insulating partitions 30, and an external vibrator 32 very similar to the corresponding components in the furnace a.

The fuel to be fed to the furnace a at 4 comes from a charging chamber 34 supplied from a hopper 33 for controlling the amount of a batch of fuel to be processed. The discharge pipe 29 from the furnace b leads to a control device 26 which separates larger particles from the smaller particles, and directs the acceptable fine particles through a duct 36 to a sealed receptacle 37. The coarser particles separated at 26 are recycled at 35 to the charging device 34.

Both the furnaces have inspection windows 38 and 39 so that an operator can see what is going on inside.

In operation both furnaces operate substantially as described. In the reducing gas atmosphere in the reducing furnace b, the temperature is above 700"C.

When the nuclear fuel to be processed contains plutonium, the reduction proceeds as follows:

and typically U3O8+PuO2+2H23UO2+PuO2+2H2O but when the nuclear fuel to be processed contains no plutonium, the reaction proceeds as follows UO2+x+H2UO2+H2O and typically

In both furnaces the reprocessing apparatus is assisted by the vibration of the plates, and in the reduction furnace b, the reduction gaseous products including steam are exhausted from the exhaust port 23 by a vacuum pump.

The furnace b does not show cooling coils 2 similar to those of the furnace a but they can be incorporated if desired.

In a modification the second furnace could act as an additional oxidation furnace for larger particles of fuel which have not been sufficiently oxidised in the first oxidising furnace a.

It will be appreciated that in both embodiments of the invention the furnaces do not include relatively rotating or sliding parts which require to be sealed against the escape of contaminated gases, and also that there are not rotating and other bearings which have to be periodically inspected and maintained.

Oxidation and reducing operations are assisted by vibration of the grid, and the chemical reactions proceed very efficiently.

The frequency and amplitude of vibration can be varied and adjusted to suit particular requirements. The vibration not only helps the chemical reactions, but also helps to transport the nuclear fuel along the furnace towards the discharge openings, and the speed of transfer of the fuel can be chosen by appropriate choice of the amplitude and frequency of vibration.

The windows enable the operations to be monitored visually.

WHAT WE CLAIM IS: 1. Nuclear fuel reprocessing apparatus comprising an enclosed furnace having gas entry and exhaust ports, and nuclear fuel feed and discharge openings, and a generally horizontal grid mounted within the furnace to be capable of vibration.

2. Apparatus as claimed in Claim 1 including means for vibrating the grid.

3. Apparatus as claimed in either of the preceding claims in which the furnace has a diaphragm wall to which the grid is connected, the diaphragm wall being arranged to be vibrated.

4. Apparatus as claimed in any of the preceding claims in which there are no relatively sliding surfaces the region between which communicates with the interior and the exterior of the furnace.

5. Apparatus as claimed in any of the preceding claims including a vacuum pump for exhausting gas from the port.

6. Apparatus as claimed in any of the preceding claims in which the grid is in the form of a plate with a large number of small holes for particles of reprocessed nuclear fuel, and at least one larger further hole for larger particles of fuel or fuel sheaths.

7. Apparatus as claimed in Claim 6 in which the grid is inclined downwards in the direction of the larger diameter hole.

8. Apparatus as claimed in any of the preceding claims in which the nuclear fuel feed opening is above the discharge opening and the grid is positioned between them so that nuclear fuel after reprocessing can pass to the discharge opening after passing through the grid.

9. Apparatus as claimed in Claim 8 including an inclined guide plate extending from below the grid to the fuel discharge opening.

10. Apparatus as claimed in any of the preceding claims including means for separating fuel from the discharge opening

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The grid 27 is suspended in a similar manner from hangers 21 from the diaphragm end walls 31, and there is a single discharge opening 28 from the downstream end of the grid, and that leads to a discharge pipe 29 below the furnace. There are axially spaced vertical insulating partitions 30, and an external vibrator 32 very similar to the corresponding components in the furnace a. The fuel to be fed to the furnace a at 4 comes from a charging chamber 34 supplied from a hopper 33 for controlling the amount of a batch of fuel to be processed. The discharge pipe 29 from the furnace b leads to a control device 26 which separates larger particles from the smaller particles, and directs the acceptable fine particles through a duct 36 to a sealed receptacle 37. The coarser particles separated at 26 are recycled at 35 to the charging device 34. Both the furnaces have inspection windows 38 and 39 so that an operator can see what is going on inside. In operation both furnaces operate substantially as described. In the reducing gas atmosphere in the reducing furnace b, the temperature is above 700"C. When the nuclear fuel to be processed contains plutonium, the reduction proceeds as follows: and typically U3O8+PuO2+2H23UO2+PuO2+2H2O but when the nuclear fuel to be processed contains no plutonium, the reaction proceeds as follows UO2+x+H2UO2+H2O and typically In both furnaces the reprocessing apparatus is assisted by the vibration of the plates, and in the reduction furnace b, the reduction gaseous products including steam are exhausted from the exhaust port 23 by a vacuum pump. The furnace b does not show cooling coils 2 similar to those of the furnace a but they can be incorporated if desired. In a modification the second furnace could act as an additional oxidation furnace for larger particles of fuel which have not been sufficiently oxidised in the first oxidising furnace a. It will be appreciated that in both embodiments of the invention the furnaces do not include relatively rotating or sliding parts which require to be sealed against the escape of contaminated gases, and also that there are not rotating and other bearings which have to be periodically inspected and maintained. Oxidation and reducing operations are assisted by vibration of the grid, and the chemical reactions proceed very efficiently. The frequency and amplitude of vibration can be varied and adjusted to suit particular requirements. The vibration not only helps the chemical reactions, but also helps to transport the nuclear fuel along the furnace towards the discharge openings, and the speed of transfer of the fuel can be chosen by appropriate choice of the amplitude and frequency of vibration. The windows enable the operations to be monitored visually. WHAT WE CLAIM IS:

1. Nuclear fuel reprocessing apparatus comprising an enclosed furnace having gas entry and exhaust ports, and nuclear fuel feed and discharge openings, and a generally horizontal grid mounted within the furnace to be capable of vibration.

2. Apparatus as claimed in Claim 1 including means for vibrating the grid.

into larger particles and smaller particles, and means arranged to recirculate the larger particles to be passed through the apparatus again.

11. Apparatus as claimed in any of the preceding claims including a heat insulating layer around the furnace in which are embedded heating coils and/or cooling coils.

12. Nuclear fuel reprocessing apparatus constructed and arranged substantially as herein specifically described with reference to Figure 2 of the accompanying drawings.

13. Nuclear fuel reprocessing apparatus as claimed in any of the preceding claims in which the discharge opening leads to the fuel feed opening of a second nuclear fuel reprocessing apparatus, one apparatus being supplied with air or oxygen at the gas entry for oxidizing fuel to be reprocessed, and the other apparatus being supplied with a reducing gas at the gas entry port reducing the reprocessed fuel from the first apparatus.

14. Nuclear fuel reprocessing apparatus constructed and arranged substantially as herein specifically described with reference to Figure 3 of the accompanying drawings.