US-12624698-B2 - Canned rotodynamic flow machine for a molten salt nuclear reactor and an active magnetic bearing for use in a flow machine for a molten salt nuclear reactor

US12624698B2US 12624698 B2US12624698 B2US 12624698B2US-12624698-B2

Abstract

A canned rotodynamic flow machine ( 1 ) configured for operating with a working fluid such as molten salt of a molten salt nuclear reactor. The stator windings are formed by one or more electrically conductive solid bars ( 12 ).

Inventors

ASLAK STUBSGAARD
Thomas Jam PEDERSEN
Thomas Steenberg

Assignees

COPENHAGEN ATOMICS A/S

Dates

Publication Date: 20260512
Application Date: 20240411
Priority Date: 20200731

Claims (15)

1 . A canned rotodynamic flow machine ( 1 ) configured for operating with a molten salt or a cover gas working fluid at temperatures above 500° C., said canned rotodynamic flow machine ( 1 ) comprising: an impeller ( 6 ) arranged in a volute ( 3 ), said volute ( 3 ) having an inlet ( 4 ) for said working fluid and an outlet ( 5 ) for said working fluid, an induction or reluctance motor or generator comprising: a stator ( 10 ), a rotor ( 8 ), a can ( 18 ) in the form of a containment shell which separates a working fluid area from a dry area containing the stator ( 10 ), with the rotor ( 8 ) arranged in the working fluid area, said rotor ( 8 ) being operably coupled to said impeller ( 6 ) by a shaft ( 7 ), said stator ( 10 ) comprising stator windings for inducing a magnetic field that penetrates the rotor ( 8 ), said stator windings being distributed in slots ( 11 ) arranged in said stator ( 10 ), wherein the part of the stator windings inside said slots ( 11 ) is formed by one or more electrically conductive solid stator bars ( 12 ), one or more active magnetic bearings supporting said shaft ( 7 ), wherein said one or more active magnetic bearings comprise: a bearing stator ( 110 , 210 ) and a bearing rotor ( 108 , 208 ), said bearing stator ( 110 , 210 ) comprising bearing stator windings for inducing a magnetic field that penetrates said bearing rotor ( 108 , 208 ), said bearing stator windings being distributed in one or more slots ( 111 , 211 ) arranged in said bearing stator ( 110 , 210 ), the part of the bearing stator windings inside said one or more slots ( 111 , 211 ) being formed by one or more electrically conductive solid bearing bars ( 112 , 212 ), said dry area containing the bearing stator ( 110 , 210 ), with the bearing rotor ( 108 , 208 ) arranged in the working fluid area.
2 . A canned rotodynamic flow machine ( 1 ) according to claim 1 , wherein said solid bearing bars ( 112 , 212 ) are positioned and held inside said slots ( 111 , 211 ) by one or more spacers ( 113 , 213 ) for electrically insulating said one or more solid bearing bars ( 112 , 212 ) from said stator ( 110 , 210 ) by spacing.
3 . A canned rotodynamic flow machine ( 1 ) according to claim 2 , wherein said spacers ( 113 , 213 ) are configured to space said solid bearing bars ( 112 , 212 ) from walls of said slot ( 111 , 211 ) and/or from other solid bearing bars ( 112 , 212 ) in the slot ( 111 , 211 ) concerned.
4 . A canned rotodynamic flow machine ( 1 ) according to claim 3 , wherein said spacers ( 113 , 213 ) support said solid bearing bars ( 112 , 212 ) locally and wherein said spacers ( 113 , 213 ) are provided at two or more axially spaced positions along the length of said solid bearing bars ( 112 , 212 ) in the slot ( 111 , 211 ) concerned.
5 . A canned rotodynamic flow machine ( 1 ) according to claim 1 , wherein said solid bearing bars ( 112 , 212 ) have a cross-sectional area of at least 5 mm 2 .
6 . A canned rotodynamic flow machine ( 1 ) according to claim 2 , wherein said solid bearing bars ( 112 , 212 ) are sufficiently rigid to maintain their shape under influence of magnetic forces generated when said motor or generator is operating, without coming in contact with the walls of the slot ( 111 , 211 ) in which they are received, and without coming in contact with other solid bearing bars ( 112 , 212 ) in the slot ( 111 , 211 ) in which they are received, with said solid bearing bars ( 112 , 212 ) being supported in said slot ( 111 , 211 ) by said spacers ( 113 , 213 ) only.
7 . A canned rotodynamic flow machine ( 1 ) according to claim 2 , wherein said solid bearing bars ( 112 , 212 ) are positioned inside said slots ( 111 , 211 ) by at least two spacers ( 113 , 213 ) that space the surface of said solid bearing bars ( 112 , 212 ) from the surface of said slots ( 111 , 211 ) and create a void between the surface of solid bearing bars ( 112 , 212 ) and the surface of said slots ( 111 , 211 ) for electrically insulating said one or more electrically conductive solid bearing bars ( 112 , 212 ) from said stator ( 110 , 210 ).
8 . An active magnetic bearing for use in a canned flow machine that operates with a working fluid, said active magnetic bearing being configured to operate in an environment having a temperature above 500° C., said active magnetic bearing comprising: a stator ( 110 , 210 ) and a rotor ( 108 , 208 ), said stator ( 110 , 210 ) comprising stator windings for inducing a magnetic field that penetrates said rotor ( 108 , 208 ), means ( 201 , 202 ) for detecting the position of said rotor ( 108 , 208 ) in communication with a controller configured for controlling a current supply to said stator windings, said stator windings being distributed in one or more slots ( 111 , 211 ) arranged in said stator ( 110 , 210 ), the part of the stator windings inside said one or more slots ( 111 , 211 ) being formed by one or more electrically conductive solid bearing bars ( 112 , 212 ), characterized by said solid bearing bars ( 112 , 212 ) being positioned inside said slots ( 111 , 211 ) by one or more spacers ( 113 , 213 ) for electrically insulating said one or more electrically conductive solid bearing bars ( 112 , 212 ) from said stator ( 110 , 210 ), a can ( 18 ), separating a working fluid area, from a dry area containing the stator ( 110 , 210 ), with the rotor ( 108 , 208 ) arranged in the working fluid area.
9 . An active magnetic bearing according to claim 8 , wherein said active magnetic bearing is a radial bearing and said slots ( 111 , 211 ) and said solid bearing bars ( 112 ) extend in said stator ( 110 ) along a straight line, or wherein said active magnetic bearing is an axial bearing and said slots ( 211 ) are circumferentially extending slots and said solid bearing bars ( 212 ) extend inside the circumferentially extending slots in said stator ( 210 ).
10 . An active magnetic bearing according to claim 8 , wherein said spacers ( 113 , 213 ) are configured to space said solid bearing bars ( 112 , 212 ) from walls of said slot ( 111 , 211 ) and/or from other solid bearing bars ( 112 , 212 ) in the slot ( 111 , 211 ) concerned.
11 . An active magnetic bearing according to claim 8 , wherein said spacers ( 113 , 213 ) support said solid bearing bars ( 112 , 212 ) locally and wherein said spacers ( 113 , 213 ) are provided at two or more axially spaced positions along the length of said solid bearing bars ( 112 , 212 ) in the slot ( 111 , 211 ) concerned.
12 . An active magnetic bearing according to claim 8 , wherein said solid bearing bars ( 112 , 212 ) have a cross-sectional area of at least 5 mm 2 .
13 . An active magnetic bearing according to claim 8 , wherein said solid bearing bars ( 112 , 212 ) are insulated only by being spaced from other elements of said active magnetic bearing by said spacers ( 113 , 213 ).
14 . An active magnetic bearing according to claim 8 , for use in a canned flow machine, said active magnetic bearing comprising the can ( 18 ), separating a working fluid area, from a dry area containing the stator ( 110 , 210 ), with the rotor ( 108 , 208 ) arranged in the working fluid area, said rotor ( 108 , 208 ) being contained in a containment shell ( 117 , 217 ) for protecting the rotor ( 108 , 208 ) from the working fluid.
15 . An active magnetic bearing according to claim 14 , wherein said active magnetic bearing has a clearance ( 20 ) between said rotor ( 108 , 208 ) and said stator ( 110 , 210 ), between said can ( 18 ) and said containment shell ( 117 , 217 ) and said active magnetic bearing is configured to be cooled by a flow of working fluid through said clearance ( 20 ).

Description

This application is a continuation of U.S. application Ser. No. 18/016,862, filed Jan. 18, 2023, pending, which is a national stage of International Application PCT/DK2021/050251, filed Jul. 29, 2021, which claims priority to Danish application PA202070505, filed Jul. 31, 2020 and Danish application PA202070506, filed Jul. 31, 2020. TECHNICAL FIELD The disclosure relates to a canned rotodynamic flow machine for operating with a working fluid such as molten salt, a cover gas, or other high temperature fluid of a molten salt nuclear reactor and to an active magnetic bearing for use flow machine for operating with a working fluid such as molten salt, a cover gas, or other high temperature fluid of a molten salt nuclear reactor. BACKGROUND A molten salt reactor (MSR) is a nuclear reactor where the nuclear reactor coolant and/or the nuclear fuel is a molten salt, typically a fluoride or chloride salt, with a melting point of around ˜500° C., operating at a temperature of around ˜600 to 700° C., and a boiling point of ˜1000° C. above the melting point. One of the many advantages of this type of reactor is that molten salts can be used as the heat transfer media at very high temperatures while still operating at or close to atmospheric pressure. Heat can be extracted from such reactors by pumping the molten salt in a loop between the ‘core’ and a heat exchanger with the reactor power being directly proportional to the temperature drop across the heat exchanger and the flow rate. Thus, high throughput, long-lasting, low maintenance, and reliable pumps are desired capable of pumping 700° C. molten salt. Due to the corrosive nature of molten fluoride and chloride salt, their operation requires an inert containment atmosphere, furthermore molten salt or molten salt vapors cannot be allowed to escape to the environment, putting strict requirements on molten salt reactor pumps to be completely leak tight. This poses a severe technical challenge, since the temperature, the aggressive nature of the molten salt combined with high radiation levels renders only very few suitable materials to work with. For example, permanent magnets cannot be used for the electric motor driving the pump, since these types of magnets start to irreversibly lose their magnetism well before reaching the above-mentioned operating temperature. Another example is dynamic seals, which are often applied in pumps, and are not available for the temperature range and aggressive environment that a pump for a molten salt reactor is subjected to and are generally much less reliable than static seals or welded joints. Molten salt reactors have been built and operated at Oak Ridge National Laboratory (ORNL) in the 1950s and 1960s with a research program lasting to the 1970s and other small programs around the world. ORNL investigated multiple pump designs, mainly ‘cantilever pumps’, where the pump and motor are connected by a long shaft to keep the motor at lower temperatures and radiation levels. ORNL operated a molten salt reactor, called the ‘Molten Salt Reactor Experiment’ for several years and the pump in this design was a cantilever pump type pump with oil lubricated bearings. This pump had several issues, among them that the oil leaked into the fuel salt. Other known molten salt pumps are used in concentrated solar power (CSP) systems also used molten salts as the heat transfer media, but the salts (nitrate salts) used are of a different kind than the ones used in commercial molten salt reactors (fluoride or chloride salts). Nitrate salts are less corrosive and unlike in a molten salt reactor fuel, the salt is not radioactive or hazardous. Thus, known nitrate salt pumps are cantilever pumps with a simple dynamic shaft seal. These are widely used and commercially available but have low requirement for leak tightness. One of the challenges associated with molten salt reactor pumps is that stator windings are typically constructed with insulated wires and there are no suitable insulation materials for the stator winding wires that can handle the above mentioned operating temperatures and conditions when dealing for example with molten salt of a nuclear molten salt reactor. Another challenge is that known electric motors and generators cannot operate at the high operating temperatures of molten salt reactors, thus, requiring the electric motor or generator unit and the connecting shaft to be cooled below the operating temperature of a medium of a typical molten salt reactor, which causes the salt vapor to deposit on cold surfaces within the dynamic seal, electric motor or generator, resulting in a shorter life-cycle of the equipment and increased risk of operating issues or release of radioactive material. Another challenge is that known bearings do not operate satisfactorily at the high operating temperatures of molten salt reactors, thus, requiring the electric motor or generator unit and the connecting shaft to be cooled below the operating temperature