AU2002300581B2 - Automatic Cooling of Irradiation Samples at a Research Reactor - Google Patents

Description

AUG. 2002 19:42 SPRUSON FERGUSON NO. 6182 P. 4 S&F Ref: 585750

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Framatome ANP GmbH Freyeslebenstr, 11 D-91058 Erlangen Germany Hans-Joachim Roegler Spruson Ferguson St Martins Tower,Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Automatic Cooling of Irradiation Samples at a Research Reactor The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c [R:\LIB115525O.dac:sn AUG. 2002 19:42 SPRUSON FERGUSON NO.6182 P. Nuclear Reactor, Particularly Research Reactor or Experimental Reactor Techmical Field The invention relates to a nuclear reactor with a reactor core which is arranged in a flow channel for a coolant enclosed by a reflector tank, wherein a plurality of sample chambers s are integrated in the reflector tank.

Background of the Invention Such a nuclear reactor can be designated particularly for use as a research reactor or experimental reactor, By contrast to the so-called power reactor, which is designed basically for continuous generation of comparatively large amounts of electrical energy in io continuous operation, such a research reactor or experimental reactor will serve for performing other tasks such as, for example, irradiation experiments, production of radioisotopes and other experimental applications. The research reactor or experimental reactor is usually designed for a substantially lower nominal power in comparison with a power reactor and, accordingly, has smaller overall dimensions. In addition, it is operated is at comparatively lower pressures and temperatures.

The research reactor or experimental reactor usually comprises a so-called reactor core in which fissionable material is held and, if necessary, subjected to a controlled chain reaction by fission. As a consequence of the incidental consumption of part of the fissionable material, energy is liberated, on the one hand, and dissipated by appropriate cooling. On the other band, apart from further fission products, during fission there are generated neutrons which are used either for maintaining the chain reaction in the reactor core or for irradiation experiments in an area outside the reactor core proper.

Generating a sufficient neutron flux density is required for maintaining the chain reaction in the reactor core. In view of the comparatively small tinee-dimensional size of the reactor core of a research reactor or experimental reactor in comparison with a power reactor, the loss of neutrons through the outer boundary of the reactor core must be considered to a comparatively larger extent when the neutron balance is computed. The loss of neutrons in the boundary zone of the reactor core is significant particularly in the case of a reactor core of comparatively small extension so that in the case of reactor cores of such small extension, usually their embedding in so-called reflector material is provided. For this purpose, the reactor core, which, for the purpose of cooling, is often arranged in a flow channel for a coolant, is placed within the reflector tank enclosing the flow channel, with the reflector tank filled with a so-called reflector material. The reflector material serves to reflect part of the neutrons emitted from the reactor core into as the outside region and to return ten into the reactor core space proper. For this purpose, 2 materials with an appropriate cross section for neutron reflection are usually selected as reflector materials, with heavy water (D 2 0) having particularly suitable properties.

In a research reactor or experimental rector, usually a number of sample chambers are arranged around the reactor core for producing radioisotopes for research applications or for generating other nuclear reactions, as well as for carrying out other irradiation experiments with neutrons leaving the reactor core. Each of these sample chambers can be loaded with one or more irradiation samples which can be exposed to irradiation by neutrons leaving the reactor core under predetermined experimental conditions. In order to ensure at the sample position a sufficiently high neutron flux density which is not excessively attenuated by the shielding effect of the reflector :material, the sample chambers are usually integrated in the reactor core or at a suitable position in the reflector tank.

Heat is usually liberated by the nuclear processes which usually occur as a consequence of the sample irradiation in the sample chambers. Therefore, cooling of the samples in the sample chambers is required for safety reasons, on the one hand, and for the intended maintaining of the experimental conditions or test conditions, on the other hand. For this purpose the sample chamber, or each sample chamber, is usually inserted in a flow channel and adapted to be supplied with coolant via the same. The coolant channel associated with the respective sample chamber is usually run in forced operation, wherein appropriate pumps or pump stations are provided for maintaining the flow through the coolant channel. This concept for cooling the samples in the sample chambers is comparatively expensive and prone to breakdown. Alternative cooling by simple natural convection, which is also practised, is insufficient in may cases.

Object of the Invention The problem underlying the invention is therefore to disclose a nuclear reactor of the above-specified type in which reliable and secure cooling of the samples in the sample chambers is ensured at particularly low cost.

Summary of the Invention According to an aspect of the invention, there is provided a nuclear reactor with a reactor core arranged in a flow channel for a coolant enclosed by a reflector tank, wherein a plurality of sample chambers is integrated in the reflector tank, each of which is adapted to be supplied with coolant via an associated branch channel, wherein the branch channel, or each of the branch channels, communicates at the entry with an inflow region and at the exit with an outflow region of the flow channel.

[R:\LIBXX]4694.doc:njc 2a According to the invention, this problem is solved in that each of the sample chambers is adapted to be supplied with coolant via an associated branch channel, wherein the branch channel, or each branch channel, communicates at the entry with an inflow region and at the exit with an outflow region of the flow channel enclosing the reactor core.

The invention is based on the consideration, that secure and reliable cooling of the samples in the sample chambers can be obtained with simple means in all operational state of the reactor by configuring the cooling of the sample chambers in the form of a [R:\LIBXX]4694.doc:njc passive system, with greatest possible ommission of active components. Such a passive system can be realised by coupling the sample chambers on the side of the coolant to the flow system which is anyhow provided for cooling the reactor core. Accordingly, for adjusting or maintaining the flow of coolant through the sample chambers, the s pressure differential present in the cooling circuit above the reactor core is used. In order to make use of this pressure differential in the form of a pumping action on the respective sample chamber, the sample chamber is on the side of the coolant connected in parallel to the reactor core in the form of a bypass or a detouring. The invention uses, inter alia, the finding that, by virtue of such a connection, an adequate supply of coolant to the sample chambers is ensured in all operational states of the nuclear reactor: only of the reactor core is in operation and, hence, forced contact with coolant must always be ensured, will the samples be irradiated in the sample chambers, and this, in turn, results in the genereation of heat in the sample chambers and, hence, need for cooling. In this case, the sample chambers are supplied with coolant in parallel to the reactor core. If, on the other hand, the reactor is not working, need for cooling may arise, for example, as a consequence of heat due to delayed decays. There convective cooling of the reactor core without active contact with the coolant develops, and its pressure drop above the core is available for providing for cooling of the samples generating a comparatively small amount of heat in the sample chambers. However, if the reactor core can remain completely without cooling, no need for cooling of the samples in the sample chambers arises because of the lack of irradiation.

A nuclear reactor of this design is particularly suitable for use as a research reactor or experimental reactor.

In order to ensure a suffiently high neutron flux density in the region of the reactor core proper and of the sample chambers containing the sample material, the reflector tank is conveniently filled with a reflector material. The reflector material can be any material which by virtue of its cross section for neutrons, ensures slowing down of the neutrons leaving the reactor core and sufficient reflection back into the same. In particular, graphite, beryllium or light water (1120) can be provided as the reflector material; but heavy water (D20), particularly in liquid form, is preferred as the reflector material.

By connecting the branch channels associated with the sample chambers on the side of the coolant in parallel with the flow channel associated with the reactor core, the coolant flow is divided over the totality of these channels. The ratio of branching or dividing is determined basically by the dimensions or the geometrical relations of the various channels, particularly the channel cross sections. In order to ensure sufficient and AUG. 2002 19:43 SPRUSON FERGUSON NO.6182 P. 7 4 adequate cooling of a sample in a sample chamber in all instances, the dimensions, particularly the flow resistance of the branch channel associated with the respective sample chamber, is advantageously adapted in relation to the flow channel and to the pumping power of an associated coolant pump to the greatest coolant requirement to be s expected in the respective sample chamber.

In an other or alternative embodiment, an adjustable throttle element is associated with the branch channel or with each branch channel. Supplying coolant to the respective sample in dependence upon its need or load via the throttle element is possible, and the cooling power made available can be used as an additional degree of freedom, when lo tests or experiments are made. The throttle element can be permanently inserted or can be exchangeable.

In order to facilitate in a particularly simple way the loading of the respective sample chamber with the samples to be studied, on the one hand, and to obtain a particularly flexible adaptation of the dimensions of the respective branch channel in relation to the flow channel, the branch channel, or each branch channel, is made of two parts in a particularly advantageous configuration. With a first part, the branch channel encompasses the sample chamber proper which in its dimensions matches the dimensions to be expected for the sample to be accommodated. This part, which includes the sample chamber proper, can be pot-shaped with a comparatively large overall cross section, with the bottom of the pot serving for accommodating the sample and with the pot's edge joined with the upper lid of the reflector tank, leaving a filling opening. On the side of the coolant this first part of the branch channel is followed by a second part which has a cooling line with a cross section reduced in comparison with the respective sample chamber. The first part ensures secure, load-bearing accommodation of the sample; the dimensions in regard to the flow characteristics are obtained, via the flow resistance, by suitable selection of the cross section of the coolant line provided in the second part.

In an other advantageous embodiment, the coolant line, or each coolant line, is curved.

Thermal and mechanical stress are eliminated in a coolant line with such a curvature, and such a curved coolant line mechanically decouples the samples proper from the ensuing pipe section. Also thermal stress is particularly reliably avoided as the curved coolant line allows compensation of thermal expansion without detrimental effects on other components.

The advantages obtained with the invention reside particularly on the fact that the branch channels, which on the side of the coolant are parallel with the flow channel associated with the reactor core, effect dependable loading of the sample chambers in the form of a AUG. 2002 19:43 SPRUSON FERGUSON NO.6182 P. 8 passive system. Flow through the sample chambers is ensured by the pressure differential which is maintained over the reactor core. H1igh mechanical and thermal load bearing capacity is ensured with this concept by using the coolant lines following the sample chamber on the side of the coolant. The two-part configuration of the branch channels by combining the pot-shaped sample chamber with the subsequent, comparatively thin coolant line allows secure accommodation of the samples with little space required in the reflector tank so that a comparatively large volume is still available for accepting the reflector.

Brief Description of the Drawing An embodiment of the invention is described in detail by way of a drawing. The figure shows a vertical section of part of a nuclear reactor.

Detailed Description of the Preferred Embodiment The nuclear reactor I of the figure is designed as a researech reactor or experimental reactor. It comprises a reactor core 2 in which fissionable material is contained as nucleare fuel. A controlled chain reaction with generation of free neutrons and release of energy is maintained in the reactor core. Owing to its design as a researech reactor or experimental reactor, the nuclear reactor I is built for a comparatively low nominal thermal output of 1 100 MW. In these cases, the reactor core 2 has a comparatively small three-dimensional extension in relation to this nominal power, In order to limit significant neutron losses through the surface of the reactor core 2, the reactor core 2 is surrounded by a reflector tank 4. The reflector tank 4 is filled with heavy water (020) as the reflector material which effects at least partial reflection of neutrons emitted from the reactor core 2 back into the same.

'Me reactor core 2 is adapted to be cooled for safe and controllable operation. To this end, it is arranged within a flow channel 6 for coolant, with the flow channel passing centrally through the reflector tank 4. In the embodiment, the flow channel 6 has circular cross section; but other cross sections such as, for example, square or rectangular cross section, can be provided.

The reflector tank 4, which on top is closed with a lid flange 8, rests with its tank bottom 10 on a support flange 12. The support flange 12, in turn, is supported via a support frame 14 on the bottom 16 of a water tank 18 which completely encloses the reflector tank 4. The water tank 18 is filled with light water (1120).

The nuclear reactor 1 serves, inter alia, for carrying out tests or experiments or nuclear reactions by irradiating samples with neutrons. To this end, a number of sample chambers 20, 22, 24, which can be filled with samples 26, 28, 30, are associated with the AUG. 2002 19:44 SPRUSON FERGUSON NO.6182 P. 9 6 reactor core 2. The samples 26, 28, 30 can be so-called targets or capsules or igots or other irradiation samples. The sample chambers 20, 22, 24 are arranged in a region in which a neutron flux density sufficient for carrying out irradiation is present. For this purpose, the sample chambers 20, 22, 24 are integrated at appropriate positions in the reflector tank 4.

When the samples 26, 28, 30 are irradiated with neutrons from the reactor core 2, experiment-specific activation, conversion, spallation or decay processes can be excited or triggered in the samples 26, 28, 30. Such an irradiation implies the release of heat from the respective sample 26, 28, 30. For safety reasons, but also for the sake of reliably o0 maintaining the set experimental conditions, the sample chambers 20, 22, 24 are designed to be capable of being cooled for dissipation of the heat released upon irradiation of the samples 26, 28, 30. An intrinsically passive system, without active components and therefore without components which need be monitored and are also prone to failure, is provided for the cooling of the sample chambers 20, 22, 24. Each of the sample chambers 20, 22, 24 has an associated branch channel 32, 34, 34 thirough which the respective sample chamber 20, 22, 24 can be supplied with coolant.

For a substantially passive cooling concept, each of the branch channels 32, 34, 36 is at its entrance connected with an inflow region 38 and at the exit with an outflow region 40 of the flow channel 6 associated with the reactor core 2. The inflow region 38 and the outflow region 40 result from the direction of flow of the coolant; in the case of reversing this direction of flow, they change theft function. Each branch channel 32, 34, 36 at its entrance communicates with the inflow region 38 and at its exit with the outflow region of die flow channel 6. By virtue of this configuration, the pressure differential, which in the flow channel 6 is provided and maintained for sufficient cooling of the reactor core 2, is used beyond the reactor core 2 also for maintaining flow through the sample chambers 20, 22, 24. Thus, other active components for maintaining such a flow are not required.

Other embodiments are provided for the form of the branch channels 32, 34, 36 in the embodiment according to the figure for firther explanation. Of course, all or several of the branch channels 32, 34, 36 can be formed in a unique configuration according to a single concept.

The branch channel 34 comprises a pipe 42 which basically runs with its full length through the reflector tank 4 and forms in its interior the sample chamber 22. By contrast, the branch channels 32, 36 are designed substantially as two-part components. To this end, the branch channel 32 and the branch channel 36 each comprise a pipe section 44 AUG. 2002 19:44 SPRUSON FERGUSON NO-6182 P. 7 and 46, respectively, as a first part which in its interior forms the respective sample chamber 20, 24. The pipe sections 44, 46, as well as the full-length pipe 42, have their inner cross section adapted to the dimensions of the respective sample 26, 28, 30 for easy loading of the same and are joined with their upper edge with the lid flange 8. The pipe sections 44, 46 are pot-shaped and limited by a lower bottom plate 48 and respectively, on which the respective sample 26 or 30 rests. The pipe sections 44, 46 are attached to the lid flange 8 in the form of a suspended arrangement.

The flow channels 32, 36 are completed in the form of a second part by a coolant line 52 and, respectively 54, following the respective sample chamber 20, 24 on the side of the coolant. The cross section of the coolant lines 52, 54 is reduced in comparison with the respective sample chamber so that the flow cross section of the respective branch channel 32, 36 is given basically by the cross section of the coolant line 52, 54, respectively. Bly suitable selection of the cross section of' the coolant line 52, 54, the respective branch channel 32, 36 in regard to its dimensions can be particularly advantageously adapted to the prevailing coolant requirements. The dimensions of all the branch channels 32, 34, 36 are adapted to greatest coolant requirements to be expected for the samples 26, 28, 30 in a particular design.

Pie coolant lines 52, 54 are curved. Coolant line 52 is designed basically for a vertical inflow and outflow of the coolant but has in its centre region a curvature in the form of an undulation. By contrast, coolant line 54 is designed for vertical inflow and horizontal outflow of the coolant and accordingly curved. The curved form of the cool ant lines 52, 54 ensure thermal and mechanical decoupling of the respectiver sample chamber 20, 24 from the bottom of the reflector tank 4. Mechanical movement or thermal expansion of the components therefore do not cause mechanical or thermal twisting so that the nuclear reactor 1 can be operated in a particularly stable manner.

On the exit side (or on the entry side, in the case of flow reversal), the branch channels 32, 34, 36 discharge into a channel system 56 which is formed between the tank bottom and the support flange 12 and, on the side of the coolant, connected to the outflow region 40 of the flow channel 6. The channel system 56 can comprise a plurality of individual, groove-like, radial channels and/or a circular or segment-shaped intermediate space.

An adjustable throttle element 60, 62, 64, respectively, is assigned to each branch channel 32, 34. The coolant flow through the respective branch channel 32, 34, 36 can be adjusted with the throttle element 60, 62, 64 and, in particular, can be adapted to the individual cooling requirements of the respective sample 26, 28, AUG. 2002 19:44 SPRUSON FERGUSON NO. 6182 P, 11 8 List of reference numbers 1 2 4 6 8 10 12 14 16 18 20, 22,24 26, 28, 30 32, 34, 36 38 42 44, 46 48, 50 52, 54 56 60, 62, 64 nuclear reactor reactor core reflector tank flow channel lid flange tank bottom support flange support frame bottom water tank sample chambers samples branch channel inflow region outflow region pipe pipe sections lower bottom plate coolant line channel system throttle element

Claims (8)

1. A nuclear reactor with a reactor core arranged in a flow channel for a coolant enclosed by a reflector tank, wherein a plurality of sample chambers is integrated in the reflector tank, each of which is adapted to be supplied with coolant via an associated branch channel, wherein the branch channel, or each of the branch channels, communicates at the entry with an inflow region and at the exit with an outflow region of the flow channel.

2. The nuclear reactor according to claim 1, which is designed as a research reactor or experimental reactor.

3. The nuclear reactor according to claim 1 or 2, the reflector tank of which is filled with a reflector material, particularly with heavy water (D 2 0).

4. The nuclear reactor according to any one o f claims 1 to 3, wherein the size of the branch channel or of each of the branch channels is at the exit adapted in relation to the flow channel and the pumping rate of an associated coolant pump to the greatest coolant requirement to be expected for the respective associated sample.

The nuclear reactor according to any one of claims 1 to 4, wherein an adjustable throttle element is assigned to the flow channel or to each of the flow channels.

6. The nuclear reactor according to any one of claims 1 to 5, in which the branch channel or each of the branch channels comprises a coolant line adjacent to the respective sample chamber on the side of the coolant and having a cross section reduced in comparison with the respective sample chamber.

7. The nuclear reactor according to claim 6 in which the coolant line or each coolant line is curved.

8. A nuclear reactor substantially as hereinbefore described with reference to the accompanying drawing. Dated 22 January, 2004 Framatome ANP GmbH Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON [R:\LIBXX]4694.doc:njc