STRUCTURAL MATERIAL FOR MOLTEN SALT REACTORS

Abstract

The present invention relates to a device adapted for producing energy by nuclear fission, the device comprising a core container of a core container material, which core container encloses an inner tubing of an inner tubing material, the inner tubing and/or the core container having an inlet and an outlet, the device further comprising a molten halide salt located in the core container or in the inner tubing, wherein the inner tubing comprises one or more sections consisting of single crystal corundum. The invention further relates to methods of controlling nuclear fission processes using the device and to the use of a corundum tube as a structural material in a nuclear fission device. The invention provides improved economy in molten salt nuclear fission processes.

Claims

1. A device adapted for producing energy by nuclear fission, the device comprising a core container of a core container material, which core container encloses an inner tubing of an inner tubing material, the inner tubing and/or the core container having an inlet and an outlet, the device further comprising a molten halide salt located in the core container or in the inner tubing, characterized in that the inner tubing comprises one or more sections consisting of single crystal corundum.

2. The device according to claim 1, wherein the device further comprises a moderator.

3. The device according to claim 2, wherein the molten halide salt is a fuel salt, and the halide is fluoride.

4. The device according to claim 1, wherein the material thickness of the inner tubing material is in the range of 1 mm to 10 mm.

5. The device according to claim 1, wherein the one or more sections of the inner tubing consisting of single crystal corundum constitute 70% to 100% of a total length of the inner tubing.

6. The device according to claim 1, wherein a volume of the inner tubing is in the range of 10% to 90% of a total volume of the core container.

7. The device according to claim 1, wherein the core container comprises a plurality of sections of the inner tubing spaced at a distance in the range of 0.5 cm to 10 cm.

8. The device according to claim 1, wherein the single crystal corundum is doped with a transition metal.

9. The device according to claim 1, wherein the inner tubing comprises metallic sections consisting of a metal selected from the list consisting of nickel based superalloys, Hastelloy N, and nickel.

10. The device according to claim 1, wherein two or more sections consisting of single crystal corundum are connected together by a butt joint or a lap joint mechanism, or wherein a section consisting of single crystal corundum and a metallic section are connected together by a butt joint or a lap joint mechanism.

11. The device according to claim 1, wherein the inner tubing is coated with nickel or with a Hastelloy.

12. The device according to claim 11, wherein the coating has a thickness in the range of 1 μm to 100 μm.

13. The device according to claim 2, wherein the moderator is a molten moderator salt comprising at least one metal hydroxide, at least one metal deuteroxide or a combination thereof, which molten moderator salt is located in the core container and the molten fuel salt is located in the inner tubing.

14. The device according to claim 13, wherein the inner tubing is made from single crystal corundum.

15. The device according to claim 13, wherein the moderator salt comprises water at a concentration to provide a pH2O in the range of 2.2 to 3.0.

16. The device according to claim 13, wherein the inner tubing does not have an inlet and an outlet.

17. The device according to claim 2, wherein the moderator is a molten moderator salt comprising at least one metal hydroxide, at least one metal deuteroxide or a combination thereof, which molten moderator salt is located in the inner tubing and the molten fuel salt is located in the core container.

18. The device according to claim 17, wherein the moderator salt comprises water at a concentration to provide a pH2O in the range of 2.2 to 3.0.

19. A method of controlling a nuclear fission process, the method comprising the steps of: providing a device according to claim 1, the core container of the device having the inlet and the outlet, introducing a molten fuel salt into the inner tubing, which molten fuel salt comprises halides of an alkali metal and a fissile element, introducing into the core container a molten coolant salt, providing a heat exchanger in fluid communication with the inlet and the outlet of the core container so as to define a heat exchange loop for removing heat from the coolant salt circulating in the heat exchange loop, circulating the coolant salt in the heat exchange loop so as to control the temperature of the fuel salt in the inner tubing.

20. The method of controlling a nuclear fission process according to claim 19, wherein the core container contains a blanket of a breeder material.

21. A method of controlling a nuclear fission process, the method comprising the steps of: providing a device according to claim 1, the inner tubing of the device having the inlet and the outlet, introducing a molten fuel salt into the inner tubing, which molten fuel salt comprises halides of an alkali metal and a fissile element, providing a heat exchanger in fluid communication with the inlet and the outlet of the inner tubing so as to define a heat exchange loop for removing heat from the molten fuel salt circulating in the heat exchange loop, circulating the molten fuel salt in the heat exchange loop so as to control the temperature of the fuel salt.

22. The method of controlling a nuclear fission process according to claim 19, wherein the halide is fluoride.

23. (canceled)

24. (canceled)

25. (canceled)

26. The method of controlling a nuclear fission process according to claim 21, wherein the halide is fluoride.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0065] In the following the invention will be explained in greater detail with the aid of an example and with reference to the schematic drawings, in which

[0066] FIG. 1 shows a photomicrograph of the serial number in a sample of corundum exposed to a molten fluoride salt;

[0067] FIG. 2 shows the enrichment vs. inner tubing thickness in a device of the invention and a MSR of the prior art;

[0068] FIG. 3 shows the conversion ratio vs. inner tubing thickness in a device of the invention and a MSR of the prior art;

[0069] FIG. 4 shows a side view of a device of the invention;

[0070] FIG. 5 shows the device of the invention connected to a heat exchanger;

[0071] FIG. 6 shows a top view of a device of the invention;

[0072] FIG. 7 shows a top view of detail of a device of the invention;

[0073] FIG. 8 shows a top view of detail of a prior art molten salt reactor.

[0074] As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION OF THE INVENTION

[0075] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0076] Fuel Salt Composition

[0077] The fuel salt (abbreviated FS) in general consists of a non-actinide carrier part (chosen for its thermodynamic properties), and an actinide component ensuring reactor criticality. The actinide component An.sub.i may further be split up in a fuel component and an added fertile component. The fuel salt vector F.sub.i is described by a pre-defined fuel vector which contains an initial plutonium component (typically Spent Nuclear Fuel (SNF) i.e. nuclear waste) along with additional components (some added after chemical reprocessing). The added (fertile) part is defined by the vector A.sub.i which is chosen from its role in the reactor burnup process and will typically consist of added thorium and uranium. The actinide composition is defined by the various fuel vectors and is captured by the following values of merit: [0078] F.sub.Pu the fuel plutonium (cation mole) fraction; [0079] Δ.sub.Th the fuel thorium (cation mole) fraction of the added fertile vector; [0080] F.sub.A the added (fertile) (cation mole) fraction.

[0081] Here the two first fractions refer to the cation mole fractions of the fuel vector and the added fertile vector, respectively. The fuel salt is defined by the various fuel vectors, a carrier salt vector CS.sub.i, along with the following values of merit for the fuel salt: [0082] FS.sub.Pu the fuel salt plutonium (cation mole) fraction; [0083] FS.sub.Th the fuel salt thorium (cation mole) fraction; [0084] FS.sub.CS the carrier salt (cation mole) fraction.

[0085] Here “fraction” refers to the cation mole fraction of the combined fuel salt. With these definitions, the fuel salt vector can be written: (FS).sub.i=FS.sub.CS CS.sub.i+(1−FS.sub.CS) An.sub.i. The actinide vector is split up according to: An.sub.i=(1−F.sub.A) F.sub.i+F.sub.AA.sub.i. Here F.sub.Pu of F.sub.i consists of plutonium isotopes and Δ.sub.Th of A.sub.i consists of thorium. We note that the following relations exist between the salt parameters:

FS.sub.Pu=(1−FS.sub.CS)(1−F.sub.A)F.sub.Pu; FS.sub.Th=(1−FS.sub.CS)F.sub.A.Math.A.sub.Th

[0086] An exemplary fuel salt contains the following fuel salt vectors: CS.sub.i ═NaF; A.sub.i=ThF.sub.4. This fuel is summarised in Table 3.

TABLE-US-00003 TABLE 3 A preferred fuel salt composition Fraction cmol % Motivation FS.sub.CS 78 Eutectic point F.sub.Pu 80 Chemical reprocessing f.sup.238U   97.5 Chemical reprocessing A.sub.Th 100  Waste burning F.sub.A ≈90  Optimization study f.sup.238Pu   0.5 Industry waste standard f.sup.239Pu 69 Industry waste standard f.sup.240Pu 25 Industry waste standard f.sup.241Pu  2 Industry waste standard f.sup.242Pu  1 Industry waste standard f.sup.241Am   2.5 Industry waste standard S.sub.Pu ≈2 — S.sub.Th ≈20  —

Preferred Device of the Invention

[0087] A preferred device 100 of the invention is illustrated in FIG. 4, where it is depicted from the side. Specifically, FIG. 4 shows the device 100, which has a core container 20, which core container 20 encloses an inner tubing 10 with a molten fuel salt 1. The core container 20 has a total volume, and the total volume of the core container minus the inner tubing 10 represents the internal volume 2. The internal volume 2 may contain a molten moderator salt, a molten coolant salt, a graphite moderator or a noble gas. The inner tubing has one or more, e.g. two as depicted in FIG. 4, inlets 6 in fluid communication with an inlet manifold 61, which in turn is in fluid communication with the inner tubing 10. The inner tubing 10 communicates with an outlet manifold 62, which collects the flow, in this case of molten fuel salt 1 in a single outlet 7. The direction of the flow is indicated with the symbol “>”. The device 100 may be connected to a heat exchanger 4 for eventually converting heat generated from the fission reaction into electricity as illustrated schematically as a “black box” model in FIG. 5. The inlets 6 and the outlet 7 are in fluid communication with an inlet 41 and an outlet 42, respectively, of a heat exchanger 4 to provide a heat exchange loop 40. The details of the heat exchanger 4 are not shown in FIG. 5. The core container material is a nickel based alloy, specifically a Hastealloy. The inner tubing 10 comprises sections of tubes of corundum and sections of tubes made from a nickel based alloy. Any straight section of the inner tubing 10 may be a corundum tube and in the embodiment shown, the sections with angles are made from tubes of Hastelloy. The tubes of the different sections are lap joined together.

[0088] The device 100 may further comprise an additional safety feature 8 comprising an overflow system in addition to the commonly used salt plug system of the prior art. This safety system prevents meltdowns, hinders accidents from human operator error, automatically shuts down in case of out of scope operation conditions, and may flush the fuel inventory to a passively cooled and sub-critical dump tank below the core vessel in case of a loss of operation power.

[0089] The reactor size is determined from two conditions; circulation time and negative temperature feedback for both fuel and moderator. In practice the operating power density can be adjusted through physical feedback mechanisms in the reactor core. In particular, the negative temperature feedback of both the fuel salt and the moderator means that the power density can be controlled by adjusting the external energy in-flow. Since core circulation may carry delayed neutrons away from the chain reaction, the mass flow rate through the reactor core should be held constant for optimal reactor control and safety reasons. Rather than changing the internal core flow, it is more desirable to control the power production by varying the mass flow through the external heat exchanger 4. In order to attain maximal reactor control, the mass flow rate through the device 100 should be chosen so that the change in the reactor reactivity as compared to no circulation is as small as practically possible. In this way, in case of pump failure scenario, the concentration of decaying precursors in the reactor core will only be minimally larger than at normal operation.

[0090] FIG. 6 shows a top view of a section of the device 100 shown in FIG. 4. Thus, the inner tubing 10 is distributed in a hexagonal pattern in the core container, which has a cylindrical cross-section with an external cladding 5. The external cladding may also be referred to as a blanket or shielding. A hexagonal pattern is superimposed on the cross-section of the device 100, but this pattern is not intended to represent any specific material.

[0091] FIG. 7 and FIG. 8 illustrate and compare the packing of the inner tubing 10 of a preferred device of the invention (FIG. 7) and a MSR (FIG. 8) where graphite 3 is used as a moderator. The superimposed hexagonal patterns show how a metal hydroxide/deuteroxide moderator allows a much denser packing of the inner tubing 10 than available in the graphite moderated MSR thus providing a much smaller form factor F.

EXAMPLE

Example 1

[0092] In order to test the stability of corundum in an appropriate molten salt, a sample of corundum was added to a molten FLiNaK salt (4.4 g LiF, 1.8 g NaF and 8.9 g KF) at 600° C. and kept in the molten FLiNaK salt for 25 hours. Prior to exposure to the molten salt the dry mass of the sample was recorded. The sample was removed from the molten salt, washed with water and dried in an oven and cooled to ambient temperature until a constant weight was obtained. The comparison of the mass of the sample before and after treatment showed a weight gain of 0.001 g (corresponding to 0.082% w/w or 0.3 mg/cm.sup.3) was observed. Thus, no degradation of the corundum sample was observed.

[0093] The corundum sample (in the form of a cylindrical slab of 12.1 mm diameter and 3 mm thickness) had a serial number engraved into the side of the sample, and after 25 hours in the molten FLiNaK that serial number was still clearly visible as is evident in FIG. 1.

Example 2

[0094] Model calculations for a device of the invention were made and compared to a device of the prior art based on Hastelloy N. The results are shown in FIG. 2 and FIG. 3. Specifically, the enrichment and the conversion ratios were calculated as functions of the inner tubing thicknesses for fuel salts of the composition 50.5% NaF 21.5% KF 28.0% UF.sub.4 at criticality, where the structural material is Hastelloy N (prior art, left panels) and corundum (invention, right panels). The calculations show that both enrichment and conversion ratios are improved for the device of the invention, and furthermore in the device of the invention there is very limited effect of increasing the inner tubing thickness, which is in contrast to the prior art device where there is a pronounced negative effect of increasing the inner tubing thickness.