FI131111B1 - Capsule for a group of control rod assemblies in a nuclear reactor, a control system for a nuclear reactor, a fuel and control system for a nuclear reactor, a nuclear reactor and method of using the nuclear reactor - Google Patents

Abstract

According to a first aspect of the present disclosure, there is provided a housing (180) with a casing (174), which defines an inner volume for receiving a plurality of control rod assemblies (140). An inlet (178) is formed into the casing (174) for connecting the inner volume into a flowing connection with a cavity (176) inside the casing wall. A pump (200) is provided to the cavity (176) for motivating fluid from the inner volume of the casing (174) through the inlet (178) and out of the housing (180) via the cavity (176).

Description

A HOUSING FOR A PLURALITY OF CONTROL ROD ASSEMBLIES OF A NUCLEAR

REACTOR, A CONTROL SYSTEM FOR A NUCLEAR REACTOR, A FUEL AND

CONTROL SYSTEM FOR A NUCLEAR REACTOR, A NUCLEAR REACTOR, AND A

METHOD OF OPERATING THE NUCLEAR REACTOR

FIELD

The present disclosure relates to nuclear reactors.

BACKGROUND

Nuclear fission reactors generate heat via a process of neutron chain reaction. The operating state of the reactor is adjusted by changing the neutron absorption rate in the reactor core. In — general terms, this is referred to as reactivity control. One of the established methods for reactivity control is to use movable control rods containing neutron absorbing material, such as cadmium or boron. Inserting the control rods deeper into the reactor core increases, and withdrawing the rods reduces neutron absorption.

The conventional technical solution for control rod systems is to place the rod drive mechanisms (i.e. the electric motors that move the rods up and down) outside the reactor pressure vessel. In pressurized water reactors (PWRs) the rod drives are attached on the top lid of the vessel.

Control rods of boiling water reactors (BWRs) are operated from below, with the drive shafts penetrating the vessel bottom. + In some reactor concepts the control rod drive mechanisms are placed inside the pressure vessel.

N

S 20 One of the advantages of using in-vessel rod drives is that the possibility of fast control rod

O ejection transients is eliminated by design, due to the lack of pressure differential over the drive

O mechanism. = a While such nuclear reactors may be operated very efficiently once the nuclear reaction has

S started, the range of control offered by conventional control rod mechanisms may be unideal 2 25 for conditions, in which the reactor is operated in reduced output, which restricts natural

N circulation of the primary coolant.

Indeed, there is a need to further improve the breadth of adjustability of nuclear reactors with in-vessel control rod mechanisms for operation in reduced output.

SUMMARY

The invention is defined by the features of the independent claims.

According to a first aspect of the present disclosure, there is provided a housing with a casing, which defines an inner volume for receiving a plurality of control rod assemblies. The casing has an inlet for accessing a cavity inside the casing wall. A pump is provided to the cavity for motivating fluid received through the inlet and out of the housing via the cavity.

According to a second aspect of the present disclosure, there is provided a control system for a nuclear reactor. The control system features such a housing and contained at least partially therein a plurality of control modules each including a rod assembly integrated to a drive assembly with a frame.

According to a third aspect of the present disclosure, there is provided a fuel and control system for a nuclear reactor. The fuel and control system features a plurality of fuel units incorporated to a respective plurality of control modules.

According to a fourth aspect of the present disclosure, there is provided a nuclear reactor, which features a pressure vessel containing a reactor core and such a fuel and control system operatively associated with the reactor core.

According to a fifth aspect of the present disclosure, there is provided a method of operating such a nuclear reactor. The method involves selectively operating the nuclear reactor in a non- assisted natural circulation mode, in which primary coolant flows through a passive fluid circulation path. The method also involves selectively operating the nuclear reactor in an assisted circulation mode, in which at least portion of the primary coolant flows through the i

S cavity motivated by the pump.

O . .

O One or more embodiments of the first aspect may include one or several features from the © K. .

O following itemized list:

I . . . . . . a 25 — the inner volume of the casing is configured to receive, at least in part, a plurality of & control modules;

K

O — each control module comprises a control rod assembly and a drive assembly, which is

N

I configured to drive the corresponding control rod assembly; — the pump is submerged into the cavity; — the inlet is formed to the surface of the casing that defines the inner volume;

— the inlet is formed to an outer surface of the casing; — the casing comprises a mounting surface, to which the cavity terminates; — the housing comprises a connector grid plate; — the connector grid plate is mounted directly or indirectly on the mounting surface; — the connector grid plate comprises a plurality of connectors for a plurality of drive assemblies; — the connector grid plate comprises a first main electrical connector counterpart for consolidating electrical connections of the plurality of connectors; — the housing comprises a second main electrical connector counterpart on the casing; — the second main electrical connector counterpart is configured to form an electrical connection with first main electrical connector counterpart; — the housing comprises a support grid plate; — the support grid plate is attached to the mounting surface; — the support grid plate is configured to provide mechanical support for the plurality of drive assemblies; — the support grid plate and the connector grid plate are stacked with each other; — the support grid plate and the connector grid plate comprise an opening for exposing the cavity; — the pump comprises an axle; — the pump comprises a motor provided at one end of the axle; — the pump comprises an impeller on the axle; — the pump comprises a power connector; — the power connector is provided to the second end of the axle;

N — the connector grid plate comprises a pump connector, & 25 — the pump connector is configured to connect to the power connector of the pump; © — the housing comprises a collective electric wiring loom;

I — the collective electric wiring loom extends from the casing;

W — the collective electric wiring loom consolidates a plurality of electrical connections from = the connector grid plate;

N 30 — the housing comprises a plurality of such cavities and respective pumps provided in the

N casing around the inner volume; — the cavity comprises or cavities each comprise an ejector nozzle.

— the drive assembly of each control module is electrically connected to the connector grid plate; — the drive assembly is secured to the housing by the support grid plate;. — each frame comprises a first frame attachment counterpart, which is configured to provide a first attachment between the respective drive assembly and the respective frame; — each frame comprises a frame lower section, which is configured to provide a second attachment between the respective frame and the respective fuel unit so that the fuel and control module is configured to move as one unit; — each frame comprises a frame upper section and a frame lower section; — the frame comprises a frame height, which spans between the frame upper section and the frame lower section; — the frame height is equal to or greater than the height of the fuel unit; — the frame height is configured to allow the control rod assembly to travel a distance required for throttling a nuclear core; — the fuel and control system comprises an instrumentation and an instrumentation guide for housing a plurality of instrumentation wiring for the instrumentation; — the instrumentation guide is incorporated into the frame, which comprises an instrumentation electrical connector; — the connector grid plate comprises a respective plurality of instrumentation electrical connector counterparts connected to the plurality of instrumentation electrical connectors of the respective plurality of frames; — the pressure vessel comprises a lead-through for the collective electrical wiring loom;

S — the nuclear reactor comprises a riser barrel inside the pressure vessel; a 25 — the riser barrel contains the reactor core and the fuel and control system; = — theriser barrel defines a passive fluid circulation path = — the passive fluid circulation path passes through a riser above the reactor core; 2 — the passive fluid circulation path passes through an upper plenum above the riser;

S — the passive fluid circulation path passes through a downcomer formed between the 2 30 pressure vessel wall and riser and reactor core;

N — the passive fluid circulation path passes through a lower plenum below the reactor core; — the passive fluid circulation path passes through the reactor core; — the inlet is formed to an outer surface of the casing;

— the cavity communicates with the downcomer through the inlet; — the riser barrel comprises an opening aligned with the inlet for permitting passage of primary fluid from the downcomer into the cavity of the casing; — the housing is placed inside the riser barrel; 5 — the pump is or the pumps are located above the reactor core; — the pressure vessel is contained inside a containment vessel, — method involves performing a start-up procedure of the nuclear core in assisted circulation mode.

Considerable benefits are gained with the aid of the novel proposition. By incorporating a pump — (or pumps) in the casing of the housing for in-vessel control rods, an optional assisted circulation of primary coolant may be achieved without disturbing natural flow of the primary coolant.

According to one embodiment, electrical connections for the pump(s) are incorporated to a collective electrical wiring loom, which is used for powering control rod drive mechanisms.

Accordingly, the pump(s) may be conveniently connected to a main control system of the nuclear power plant during assembly of the control module with a minimized number of lead- through openings on the pressure vessel wall.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following certain exemplary embodiments are described in greater detail with reference to the accompanying drawings, in which: < FIGURE 1A illustrates a cross-sectional view of a nuclear reactor in accordance with at least

S some embodiments operating under natural flow conditions with pumps omitted

O for the sake of simplicity;

S FIGURE 1B illustrates a cross-sectional view of a nuclear reactor in accordance with at least

E 25 some embodiments operating under assisted flow conditions;

O . = FIGURE 1C illustrates a cross-sectional view of a nuclear reactor in accordance with an

N alternative embodiment operating under assisted flow conditions;

N

FIGURE 2 illustrates a perspective view of the fuel and control module in accordance with at least some embodiments;

FIGURE 3 illustrates a perspective view of an exploded view of the fuel and control module of FIGURE 2;

FIGURE 4 illustrates a perspective view and a top view of a drive assembly;

FIGURE 5 illustrates a perspective view and a top view of a frame:

FIGURE 6 illustrates a perspective view and a section view of a control rod assembly;

FIGURE 7A illustrates a perspective explosion view of a housing;

FIGURE 7B illustrates a top view of the connector grid plate of FIGURE 7A;

FIGURE 8 illustrates a partially exploded perspective view of three fuel and control modules, and

FIGURE 9 illustrates a perspective partial explosion view of the casing and pump of the housing of FIGURE 7A.

EMBODIMENTS

“Fuel unit” is known as a fuel assembly in the field of nuclear engineering. “Electrical connector” refers to an electrical connection, for example electrical leads or wires which may — connect to a socket or other leads of another component. “Electrical connector counterpart” refers to a socket or another electrical connection, for example an electrical connection meant to connect the ends of electrical leads. “Attachment” without the connotation of “electrical” may refer to a physical attachment between surfaces or components and may refer to mating surfaces between surfaces or components. i

N . . . .

S 20 In the present context expressions "primary fluid" and "primary coolant" can be used

O interchangeably.

S

I In the present context, the expression ”pump” refers to a device or arrangement for motivating ox . . . . . a a fluid. A pump may be a mechanical device or according to another embodiment a pneumatic © . .

Q or an electromagnetic motivator.

LO

O .

N 25 Inthe present context, the expression “ambient volume” refers to a space not within the casing

N wall. The inner volume defined by the casing qualifies as an ambient volume as does the space surrounding the casing.

FIGURE 1A illustrates a nuclear reactor 170 in accordance with at least some embodiments.

The nuclear reactor 170 comprises a reactor core 172 encased in a pressure vessel 171, which in turn comprises a lid 173. The reactor core 172 is located at a lower section of the pressure vessel 171. The pressure vessel 171 defines an inner volume of the nuclear reactor 170. The — reactor core 172 is located inside the pressure vessel 171.

A fuel and control system is located inside the pressure vessel 171. The function of the fuel and control system is to provide the fuel for operating the reactor core 172 as well as a mechanism for controlling the nuclear reaction. Accordingly, the fuel and control system includes a control system, which controls several fuel units 150. To achieve that the control system includes — several control modules that each feature a control rod assembly 140 and a drive assembly 110 that drives the corresponding control rod assembly 140. Each control rod assembly 140 is associated with a respective fuel unit 150. The drive assembly 110, the control rod assembly 140, and the fuel unit 150 is integrated into a fuel and control module 100 by a frame 130, the details of which will become apparent here after. The number of fuel and control module 100 — varies between different reactor types but the exemplary embodiment shown in the FIGURES features 37 fuel and control modules 100.

According to this illustrated embodiment the fuel and control system is located inside the pressure vessel 171. While in operation, the fuel units 150 of the fuel and control system are located in the lower section of the pressure vessel 171, in which the fuel units 150 are gathered together to make up the reactor core 172.

The nuclear reactor 170 is shown in FIGURE IA in a simplified manner, omitting, for example, pumps. The exemplary nuclear reactor 170 is a district heating reactor but the principles 3 disclosed herein are applicable to other reactor types as well. The nuclear reactor 170 features

N a double-vessel configuration with the pressure vessel 171 contained within a containment

S 25 — vessel 210, which is closed by a lid 211. It is, however, to be noted, that the embodiments herein

S discloses are egually applicable to a single-vessel configuration. An annular inner wall is

E provided within the pressure vessel 171 to create a riser barrel 179. The riser barrel 179 may © extend from the housing 180 towards the upper plenum 191. Alternatively the riser barrel 179 5 may envelop the housing 180 and even the reactor core 172. The purpose of the riser barrel 179

O 30 is to define a fluid circulation path for the primary fluid or coolant contained in the pressure vessel 171. The riser barrel 179 forms a riser 190 on top of the reactor core 172. The riser 190 is the inner volume defined by the riser barrel 179. The space defined between the riser 190,

i.e. the top level of the riser barrel 179, and a split seam between the pressure vessel body and lid 173, is an upper plenum. The space between the split seam and the lid 173 is a pressurizer.

An annular space is formed between the riser barrel 179 and the pressure vessel 171 as a downcomer 194. A heat exchanger 193 is provided between the upper plenum 191 and the downcomer 194. The downcomer 194 communicates with a lower plenum 195, which is formed between a bottom mesh of the reactor core 172 and the bottom of the pressure vessel 171.

FIGURE 1A sketches nuclear reactor 170 under normal operation, in which primary fluid flows along a passive fluid circulation path. In a passive natural circulation mode primary coolant flows through the fluid circulation path by means of convection without assistance. The passive — fluid circulation path begins at the reactor core 172, at which the primary fluid is heated, raises up through the riser 190, diverts down to the heat exchanger 193 at the upper plenum 191, continues down the downcomer 194, and back to the reactor core 172 through the lower plenum 195. The control system, which will be described in greater detail here after, will have a sufficient control range to control the operation of the nuclear reactor 170 under passive natural circulation mode, in which full or great output causes the primary fluid flow fast by means of convection.

FIGURE 2 and FIGURE 3 illustrate the fuel and control module 100. The fuel and control module 100 has the drive assembly 110, as mentioned before, a frame 130, a control rod assembly 140, and the fuel unit 150.

FIGURE 4 illustrates the drive assembly. According to the illustrated embodiment, the drive assembly 110 has a drive motor frame 112 and a drive motor 111 located inside the drive motor frame 112. The drive motor frame 112 surrounds the drive motor 111 to hold the drive motor

S 111 in place and provides drive motor frame 112 attachments to other components. The drive

O motor frame 112 isrigidly attached to a drive flange 120. The drive motor frame 112 and the 2 25 — drive flange 120 may be attached by welding or the drive motor frame 112 and drive flange 120 z may be cast as a single component or may be assembled with bolts or other fasteners. The drive > flange 120 enables an attachment between the drive assembly 110 and the frame 130. The drive

S flange 120 has a first frame attachment 116 that provides the attachment, which is a temporary

N attachment. The drive flange 120 has a drive motor 111 electrical connector 114 and an

N 30 instrumentation opening 115. The electrical connector 114 may be an inductive connector.

According to the illustrated embodiment FIGURE 4, the drive assembly 110 has a linear translator 117 coaxially attached to the drive assembly. The drive assembly 110 has a linear translator opening 113 located coaxially with the drive motor. The linear translator opening 113 extends through the drive motor 111 where the linear translator 117 translates through. The linear translator opening 113 extends through the drive motor 111 so that the drive motor 111 is wrapped around the outer surface of the linear translator 117. The linear translator 117 has a shaft opening 118, which extends from at a first linear translator end to a second linear translator end. At the second linear translator end, there is an electromagnet 119 in which the shaft opening 118 extends through.

FIGURE 5 illustrates the frame 130. According to the illustrated embodiment the frame 130 has a profile 131, a frame upper section 134 and a frame lower section 136. The frame 130 has a frame height, which is the distance between the frame upper section 134 and the frame lower section 136. The frame 130 has an instrumentation guide 132, which may be in the form of a hollow tube, rod or a cover. The instrumentation guide 132 acts as a guide for the instrumentation electrical wires, or wiring, and holds them in place. According to at least some embodiments, instrumentation guide 132 is permanently attached to the frame 130 or is incorporated into the frame 130, and the instrumentation guide 132 may be manufactured as part of the frame 130. The instrumentation guide 132 also serves the purpose to not disrupt the movement of other components such as the control rod assembly 140. For example, if the instrumentation electrical wires were loose they could tangle with a plurality of control rods 144 and cause an unsafe malfunction in the control rod assembly 140, such as preventing the control rods 144 from travelling downwards. At a first instrumentation guide end there is an instrumentation electrical connector 133, which is attached to the instrumentation electrical

S wires. The instrumentation guide 132 continues through the frame lower section 136. At a

N 25 — second instrumentation guide end there is an instrumentation for taking measurements. The

S second instrumentation guide end and the instrumentation may be located in the fuel unit 150. = The instrumentation guide end may be split to accommodate for the attachments between

E components, such as the fuel unit 150 and the frame 130. The instrumentation guide 132 may

O branch into different branches to provide passage for electrical wiring to other sensors, such as 5 30 a temperature sensor in other locations in the fuel and control module 100. For example, a

O temperature sensor may be located near the frame 130. At the frame lower section 136 there are a plurality of control rod openings 137 and there may be a mesh 138.

According to the illustrated embodiment FIGURE 5, at the frame upper section 134 there is a first frame attachment counterpart 135 that attaches, temporarily, to the first frame attachment 116 of the drive assembly. According to the illustrated embodiment, the first frame attachment counterpart 135 is the form of a pin and the first frame attachment 116 is in the form of a hole which guides the first frame attachment counterpart 135 into the first frame attachment 116.

This manner of attaching provides a temporary attachment that hold the drive assembly 110 and the frame 130 in place when the reactor is in operation.

As is shown in FIGURE 3, the frame 130 is a distinct component from the fuel unit 150. The frame lower section 136 is used to attach the frame 130 to the fuel unit 150. More specifically, the frame 130 sits atop the fuel unit 150. The fuel unit 150 preferably contains a top crate best shown in FIGURE 3 for attachment to the frame lower section 136.

FIGURE 6 illustrates the control rod assembly 140. The control rod assembly 140 has a shaft 141 at a first control rod assembly end, a plate 142 and a plurality of control rods 144 at a second control rod assembly end. The control rods 144 are rigidly attached to the shaft 141 by — a plurality of supports 143. The plate 142, which is made of a material known to attach to electromagnets, for example, a ferromagnetic material, attaches at least temporarily to the electromagnet 119 of the drive assembly. Thus, the attachment between the plate 142 and the electromagnet 119 provide an attachment between the control rod assembly 140 and the drive assembly. In at least some embodiments, at least a portion of the shaft 141 is coaxially located inside the shaft opening 118 of the drive assembly. The length of the shaft 141 is approximately the same length as the range of movement, i.e. the height of the fuel unit 150. The control rods 144 are arranged so that they are guided through the control rod openings 137 of the frame 130. 3 FIGURE 3 illustrates a view of the fuel unit 150. According to at least some embodiments, the

N control rods 144 interact with the fuel unit 150 and are placed inside the fuel unit 150. The

S 25 — control rods 144 may be placed inside the fuel unit 150 where most of a length of the control

S rods 144 are inside the fuel unit 150. The length of the control rods 144 may be the same or

E slightly less as the height of the fuel unit 150. The length of the control rods 144 is long enough © to be able to cover the entirety of an active height of the fuel unit 150. As shown in FIGURE 2, 5 a fuel unit upper section is attached to the frame lower section 136. This attachment is secured

O 30 to allow the fuel unit 150 to be moved with the frame 130.

FIGURE 7A and FIGURE 7B illustrate a view of a housing 180 for containing the control system. Another comparable housing may surround the reactor core 172 as a radial reflector or the housing 180 may be extended to surround the reactor core 172. The housing 180 has a peripheral casing 174. The outer shape of the casing 174 is designed to fit within the riser barrel 179. The inner shape of the casing 174 is shaped to accept the fuel and control units as volumetrically efficiently as possible.

As already mentioned, the control system is designed to have a sufficient control range to control the operation of the nuclear reactor 170 under passive natural circulation mode, in which full or great output causes the primary fluid flow fast. In restricted output situations, such as start up, however, the nuclear reactor 170 may be run in an assisted circulation mode, in which primary coolant flows motivated by one or more than one pump 200. The purpose of the assisted circulation mode is to induce flow to the pressure vessel 171 to accelerate start up or to ensure efficient operation under partial load.

FIGURE 1B shows two pumps 200 incorporated into the housing 180 for providing assisted circulation. The number of pumps 200 may be varied between one and more than one, e.g. between two and eight, more particularly two, three, or four. The pumps 200 are used to draw — primary fluid into a cavity 176 formed into the casing 174 of the housing 180 through an inlet 178 on the inner surface of the casing 174. The inner surface defines the inner volume of the housing 180 that is used to contain control modules. Depending on the position of the control rods, i.e. elevated or lowered, the portion of control rods being contained in the housing 180 varies accordingly.

FIGURE 1C shows an alternative placement of the inlet. According to the alternative embodiment the inlet 178 is located on the outer surface of the casing 174. The outer surface is the surface opposing the inner surface that defines the inner volume of the housing. The inlet 3 178 communicates with the downcomer 194 either directly or, if the riser barrel 179 envelops

N the housing 174, through an opening formed to the riser barrel 179. Such a placement of the

S 25 inlet 178 has the additional benefit of drawing in primary fluid in relatively cool temperature

S compared to the embodiment shown in FIGURE 1B, in which the incoming primary coolant

E has been heated by the nuclear core 172. As a result, the primary fluid may be pumped in a © relatively cool temperature, which is more effective and which is less prone to cavitation. 3 Additionally, the relatively cool primary fluid cools the motor 201 of the pump 200.

N 30 The cavity 176 has an outlet 177, which communicates with the riser 190 for exhausting primary fluid motivated by the pump 200. According to one embodiment, the outlet 177 is devised as an ejector nozzle. The outlet 177 is preferably designed to create a relatively intense side stream of primary fluid, which attracts the main stream flowing along the passive fluid circulation path to flow faster than without the assistance of the pump 200. It is foreseeable that the side stream passing through the cavity 176 has a lesser flux than that of the main stream following the passive fluid circulation path.

FIGURE 9 illustrates the relationship between the pump 200 and the casing 174 in a partial exploded view of the housing 180. FIGURE 9 shows an isolated sector of the casing 174. The inner surface of the casing 174, which defines an inner volume for containing the control modules, is shaped to follow the pattern, in which the control modules are held. In the illustrated example the control modules are held in a grid configuration. The outer surface of the casing 174 is curved to comply to the shape of the pressure vessel 171. These shapes may be varied according to the application.

A cavity 176 is formed within the casing 174, i.e. inside the casing wall. The cavity 176 serves two functions. Firstly, the cavity 176 provides a space for the pump 200. Secondly, the cavity 176 provides a deviation or a side stream to the passive fluid circulation path. In the assisted circulation mode, at least some of the primary fluid flows through the cavity 176 motivated by the pump 200. The inlet 178 is provided to the inner surface of the casing 174 thus bringing the cavity 176 into a flowing connection with the inner volume of the housing 180 (FIGURE 1B).

Alternatively the inlet 178 is provided to the outer surface of the casing 174 and to the riser barrel 179 thus bringing the cavity 176 in a flowing connection with the downcomer 194 (FIGURE 1C). Fluid may therefore flow from the lower plenum 195 through the nuclear core 172 or from the downcomer 194 into the inner volume of the casing 174 and to the riser 190 through the cavity 176. 3 At the top of the casing 174 there is a mounting surface 175, which receives plates that will be

N discussed here after in greater detail. The cavity 176 opens to the mounting surface 175, where

S 25 from the assisted flow will exit. As can be seen from FIGURE 1B, the cavity 176 is shaped to

S receive the pump 200 in an embedded manner such that the pump 200 may be completely

E contained in the cavity 176. © = The pump 200 features a motor 201 at a bottom end, an axle 202 extending between the first

N bottom end and a second top end, and an impeller 203 formed on the axle 202. The impeller

N 30 203 The axle 202 may be exposed between the impeller 203 and motor 201 at the inlet 178 so that impeller would no be exposed through the inlet 178. The cavity 176 may also be deep enough below the inlet 178 for accepting the motor 201.

A power connector 205 is provided at the top end of the pump 200 for powering the motor 201.

The power connector 205 is carried by a support structure that sits on top of the second or top end of the axle 202. A lead 204 connects the power connector 205 to the motor 201. The lead 204 is cleared from the impeller 203 to enable rotation, which gives the pump 200 a non-circular cross-sectional shape. This is reflected in the equally non-cylindrical shape of the cavity 176.

The lead 204 may form part of the support structure, which may include a bearing for the axle 202. The power connector 205 may be a galvanic or inductive connector or any type generally used in the field. Preferably, the power connector 205 is a relatively shallow connector requiring little dexterity to couple. With such a connector arrangement, the pump 200 may be a simple component that is installed into the cavity and then connected to the main control system of the power plant with a convenient connector plate. This is very beneficial in practical installations, which are done in a radiating underwater environment, potentially with a robotized arm.

Returning to FIGURE 7A, which shows the casing 174 and the associated support grid plate 181 and connector grid plate 182. Both grid plates are provided with cavity openings 189 aligned with the cavities 176 for permitting exit flow of the primary fluid.

During operation, a support grid plate 181 may be located on top of the upper surface 175 and above the reactor core 172. The support grid plate 181 has support grid plate openings, which are located above each fuel and control module 100. The support grid plate 181 provides structural support for other components, therefore the nuclear reactor 170 may have another arrangement known per se to support the fuel and control modules 100. According to the illustrated embodiment, a connector grid plate 182 is placed on top of the support grid plate 181. According to another embodiment, the connector grid plate 182 is located below the + support grid plate 181. The connector grid plate 182 is a component with a body that is at least

S partially solid and at least partially hollow. The connector grid plate 182 has a plurality of wires

O 25 for distributing electric power and electric connections to a plurality of fuel and control modules

O 100, where the wires may be located within the hollow portions of the connector grid plate 182.

I According to at least some embodiments, the plurality of wires of the connector grid plate 182 a © run along and inside the body of the connector grid plate 182. The connector grid plate 182 has = a plurality of connector grid plate openings 188 where each opening 188 is located above a fuel

N 30 and control module 100. The support grid plate openings may be the same or similar size than

N the connector grid plate openings 188. The connector grid plate 182 has a plurality of drive motor and instrumentation electrical connector counterparts 187, in which each connector grid plate opening 188 has one drive motor and instrumentation electrical connector counterpart

187. Each drive motor and instrumentation electrical connector counterpart 187 is configured to connect to the drive motor electrical connector 114 and the instrumentation electrical connector 133 of each fuel and control module 100. According to at least some embodiments, the drive motor and instrumentation electrical connector counterpart 187 has one socket or appropriate counterpart for each of the drive motor electrical connector 114 and the instrumentation electrical connector 133. In other words, the drive motor and instrumentation electrical connector counterpart 187 may have two sockets or appropriate counterparts.

According to at least some embodiments, at least a portion of the fuel and control module 100 is located under the grid plates 181, 182. A portion of the drive assembly 110 and the control rod assembly 140 may be located above the grid plates 181, 182, however the connector grid plate opening 188 and the support grid plate opening are openings where the entire structure of each of the drive assembly, the frame 130, the fuel unit 150, and the control rod assembly 140, cannot go through due to the size of these openings. According to at least some embodiments, the width of the grid plate opening 188 is smaller than the width of the frame 130 and the width — of the drive flange 120.

The connector grid plate 182 has a first main electrical connector counterpart 184, which connects to a main electrical connector counterpart 185. The nuclear reactor 170 may have a connector block 186 where, according to the illustrated embodiment FIGURE 7A, the main electrical connector counterpart 185 is located on. The main electrical connector counterpart 185 may be an inductive connector. The nuclear reactor 170 has a collective electric wiring loom 183 which are connected to a power source on a first electric cable end and to the connector block 186 at a second electric cable end. A portion of the collective electric wiring + loom 183 are the cables used to transmit data from the instrumentation.

S

N The following paragraphs describe the usage of components of the fuel and control module 100.

S

O 25 The nuclear reactor 170 as illustrated in FIGURE 1 has the pressure vessel 171 in which the z fuel and control module 100 has a drive assembly 110 located inside the pressure vessel 171.

W This means that the drive assembly 110 is operated in a fluid contained in the pressure vessel = 171. The fluid acts as the coolant for the reactor core. & < During operation, the drive motor and instrumentation electrical connector counterpart 187 is connected to the drive motor electrical connector 114 and the instrumentation electrical connector 133. While these connectors are connected, the first main electrical connector counterpart 184 and the main electrical connector counterpart 185 are connected and therefore power and electrical connections are being supplied by the collective electric wiring loom 183 to the drive motor 111 and the instrumentation via the main connector and the drive motor electrical connector 114. As a result, the connector grid plate 182, when installed, provides an electrical connection to the drive motor 111 and the electromagnet 119, provides transmission of data and other signals to and from the instrumentation, and provides electric current to power the instrumentation. The connector grid plate 182 has a body that is at least partially solid.

According to at least some embodiments, when the connector grid plate 182 is installed, each of the drive motor and instrumentation electrical connector counterparts 187 connects to the corresponding drive motor electrical connector 114 and the instrumentation electrical connector 133 of each fuel and control module 100. This manner of connecting allows the electrical connections to be made all at once (due to the at least partially solid body of the connector grid plate 182), rather than having to connect the electrical connection individually. As a result, a function of the connector grid plate 182 is to make electric connections time-efficient. The — connector grid plate 182 acts as a bridge between the collective electric wiring loom 183 and the drive motor electrical connector 114 with the instrumentation electrical connector 133.

Therefore, the installment and detachment of the connector grid plate 182 determines whether the electrical connections provided to the drive motor 111 and the instrumentation are connected or not. When the connector grid plate 182 is installed and providing power and electric connections, the connector grid plate 182 is in a connected state. The same holds true to the pump 200.

The connector grid plate 182 also allows signals of data to transmit from the instrumentation to a receiving device for receiving data which is located outside of the nuclear reactor 170. <

S The collective electric wiring loom 183 may be connected directly to the main electrical

O 25 connector counterpart 185 so that when the main electrical connector counterpart 185 is in

O connection with the first main electrical connector counterpart 184, the collective electric

I wiring loom 183 provide electric power to the connector grid plate 182 from the power source. a © When the coolant is a liquid, the electric connectors and electric connector counter parts are 3 “wet-mated”, meaning that the connection can be established while submerged in the coolant. &

When the grid plates 181, 182 are attached to the nuclear reactor 170 and are therefore electrically connected and in operation, the grid plates 181, 182 prevent the drive assembly, the frame 130, and the fuel unit 150 from being transported. In other words, the grid plates 181,

182 and the fuel and control module 100 are arranged where the fuel and control module 100 cannot be removed from the pressure vessel 171 unless the grid plates 181, 182 are removed first. Therefore the grid plates 181, 182 hold the drive assembly 110, the frame 130, and the fuel unit 150 in place. The drive assembly 110 may cause the control rod assembly 140 to be at — least partially withdrawn from the fuel unit 150, however the grid plates 181, 182 hold the drive assembly 110 in place, and the control rod assembly 140 is unable to travel through the drive assembly 110 due to the electromagnet 119 and supports 143 not fitting through the linear translator opening 113. Further, the control rod assembly 140 can move the distance of the active height within the fuel unit 150. — When the fuel units 150 are ready to be replaced, the refueling operation commences.

A reloading machine can make contact with the frame 130 in order to remove the fuel and control module 100 out of the reactor core 172. The removal of the fuel and control module 100 out of the reactor core 172 is called a first transportation state. In other words, when the reloading machine is lifting the frame 130, the following components are being lifted also: the — drive assembly, the control rod assembly 140 and the fuel unit 150. Therefore the drive assembly, the frame 130, the control rod assembly 140 and the fuel unit 150 move as one single unit during the first transportation state. This is accomplished by the attachment the frame 130 makes between the drive assembly 110 and the fuel unit 150.

As mentioned previously, the frame 130 has a frame height. The frame 130 creates a space which is open or preferably at least partially enclosed. The frame height is a certain length to allow the control rod assembly 140 to travel at least partially within the space of the frame 130 while the fuel and control module 100 is in operation in the pressure vessel 171. The frame 3 height therefore affects the range of movement of the control rod assembly 140 and the control

N rods 144. The movement of the control rod assembly 140 and the control rods 144 while in

S 25 — operation is for changing the neutron absorption rate in the reactor core 172. This movement

S may be referred to as control movement.

I

: The fuel unit 150 has a plurality of control rod guide tubes for the control rods 144 to travel = into, and where the control rods 144 can travel at least most of the height of the fuel unit 150.

N Located at the bottom of each control rod guide tube, When the fuel unit 150 is transported, the

N 30 control rods 144 and the control rod assembly 140 is transported with the fuel unit 150. The active height of the fuel unit 150 may determine the frame height since the control movement range within the fuel unit 150 may be the same or substantially the same as the control movement range within the space of the frame 130. The attachments within the fuel and control module 100 during the first transportation state, the frame 130 is attached to both the drive assembly 110 and the fuel unit 150. Further, the control rod assembly 140 is in connection with the fuel unit 150 when the control rods 144 are in the lowered state. As a result, when the frame 130 is transported, the transporting of the frame 130 causes the drive assembly, the fuel unit 150, and the control rod assembly 140 to be transported also. The structural integrity of the frame 130 or the profile 131 enables the fuel and control module 100 to transport as a one unit.

FIGURE 8 illustrates the drive assembly 110 and the control rod assembly 140 being separated from the fuel unit 150 and fuel assembly.

It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting. — Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

Asused herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique

S member. Thus, no individual member of such list should be construed as a de facto

O eguivalent of any other member of the same list solely based on their presentation in a © 25 common group without indications to the contrary. In addition, various embodiments and z examples of the present invention may be referred to herein along with alternatives for the

W various components thereof. It is understood that such embodiments, examples, and = alternatives are not to be construed as de facto eguivalents of one another, but are to be

N considered as separate and autonomous representations of the present invention.

N

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without — the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in — depending claims are mutually freely combinable unless otherwise explicitly stated.

Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality. i

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REFERENCE SIGNS LIST

FEATURE FEATURE drive assembly lid (of pressure vessel) shaft opening support grid plate 121 | reloading machine opening 184 | first main electrical connector counterpart

N 130 | frame 185 | second main electrical connector

N counterpart

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<Q < = a 132 | instrumentation guide 187 | drive motor and instrumentation

S electrical connector counterpart 3

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Claims (26)

CLAIMS:

1. A housing (180) for a plurality of control rod assemblies (140) of a nuclear reactor (170), the housing (180) comprising a casing (174), which defines an inner volume for receiving the plurality of control rod assemblies (140), characterized by: — at least one cavity (176) formed into the casing (174), — an inlet (178) formed into the casing (174) for permitting fluid flow from an ambient volume into the at least one cavity (176), and by — a pump (200) provided to the at least one cavity (176) for motivating fluid from the ambient volume of the casing (174) through the inlet (178) and out of the casing (174) via the at least one cavity (176).

2. The housing (180) according to claim 1, wherein the pump (200) is submerged into the at least one cavity (176).

3. The housing (180) according to claim 1 or 2, wherein the inlet (178) is formed to the surface of the casing (174) that defines the inner volume.

4. The housing (180) according to claim 1 or 2, wherein the inlet (178) is formed to an outer surface of the casing (174).

5. The housing (180) according to any one of the preceding claims, wherein: — the casing (174) comprises a mounting surface (175), to which the at least one cavity (176) terminates, — the housing (180) comprises a connector grid plate (182), which is mounted N directly or indirectly on the mounting surface (175), the connector grid plate N (182) including a plurality of connectors (187) for a plurality of drive assemblies = (110) as well as a first main electrical connector counterpart (184) for = consolidating electrical connections of the plurality of connectors (187), and o 25 wherein S — the housing (180) comprises a second main electrical connector counterpart (185) 3 on the casing (174), the second main electrical connector counterpart (185) being N configured to form an electrical connection with first main electrical connector counterpart (184).

6. The housing (180) according to claim 5, wherein: — the housing (180) comprises a support grid plate (181), which is attached to the mounting surface (175) and configured to provide mechanical support for the plurality of drive assemblies (110), and wherein — the support grid plate (181) and the connector grid plate (182) are stacked and comprise an opening (189) for exposing the at least one cavity (176).

7. The housing (180) according to claim 4 or 5, wherein: — the pump (200) comprises a power connector (205) and wherein — the connector grid plate (182) comprises a pump connector, which is configured to connect to the power connector (205) of the pump (200).

8. The housing (180) according to any one of the preceding claims, wherein the housing (180) comprises a collective electric wiring loom (183) extending from the casing (174) and consolidating a plurality of electrical connections from the connector grid plate (182).

9. The housing (180) according to any one of the preceding claims, wherein the casing (174) comprises a plurality of such cavities (176) and respective pumps (200) provided in the casing (174) around the inner volume.

10. The housing (180) according to any one of the preceding claims, wherein the cavity comprises or cavities (176) each comprise an ejector nozzle (177).

11. A control system for a nuclear reactor (170), the control system comprising: + — ahousing (180) according to any one of the preceding claims, and S — aplurality of control modules contained at least partially in the inner volume of O the casing (174), each of which control modules comprising: 2 o acontrolrod assembly (140), = 25 o a drive assembly (110), and W o a frame (130), which couples the drive assembly (110) to the control rod = assembly (140), wherein frame (130) provides a space for control S movement of the control rod assembly (140).

12. The control system according to claim 11, wherein the drive assembly (110) of each control module is electrically connected to the connector grid plate (182).

13. The control system according to claim 11 or 12, wherein the drive assembly (110) is secured to the housing (180) by the support grid plate (181).

14. A fuel and control system for a nuclear reactor (170) comprising: — a control system according to any one of the preceding claims 11 to 13, and — afuelunit (150) integrated into each control module by a respective frame (130), which is attached on top of the respective fuel unit (150) and aligns the control rods of the respective control rod assembly (140) with respective control rod guides of the fuel unit (150).

15. The fuel and control system according to claim 14, wherein: — each frame (130) comprises a first frame attachment counterpart (135), which is configured to provide a first attachment between the respective drive assembly (110) and the respective frame (130), and wherein — each frame (130) comprises a frame lower section (136), which is configured to provide a second attachment between the respective frame (130) and the respective fuel unit (150) so that the fuel and control module (100) is configured to move as one unit.

16. The fuel and control system according to claim 14 or 15, wherein each frame (130) comprises a frame upper section (134) and a frame lower section (136) wherein: — the frame (130) comprises a frame height which spans between the frame upper section (134) and the frame lower section (136), — the frame height is equal to or greater than the height of the fuel unit (150), and wherein

N e. S — the frame height is configured to allow the control rod assembly (140) to travel O a distance reguired for throttling a nuclear core (172). 9 > 25

17. The fuel and control system according to any one of the preceding claims 14 to 16, E wherein: S — the fuel and control system further comprises an instrumentation and an 2 instrumentation guide (132) for housing a plurality of instrumentation wiring for i the instrumentation, — the instrumentation guide (132) is incorporated into the frame (130), which comprises an instrumentation electrical connector (133), and wherein

— the connector grid plate (182) comprises a respective plurality of instrumentation electrical connector counterparts connected to the plurality of instrumentation electrical connectors (133) of the respective plurality of frames (130).

18. A nuclear reactor (170) comprising: — a pressure vessel (171) — areactor core (172) contained inside the pressure vessel (171), and — a fuel and control system according to any one of the preceding claims 14 to 17 contained in the pressure vessel (171), wherein the housing (180) is provided on top of and operatively associated with the reactor core (172).

19. The nuclear reactor (170) according to claim 18, wherein the pressure vessel (171) comprises a lead-through for the collective electrical wiring loom (183).

20. The nuclear reactor (170) according to claim 18 or 19, wherein the nuclear reactor (170) comprises a riser barrel (179) inside the pressure vessel (171), which riser barrel (179) defines a passive fluid circulation path through: — ariser (190) above the reactor core (172), — an upper plenum (191) above the riser (190), — a heat exchanger (193) below the upper plenum (191), — a downcomer (194) below the heat exchanger (193) formed between the pressure vessel wall and the riser barrel (179) and reactor core (172), and — a lower plenum (195) below the downcomer (194) and the reactor core (172).

21. The nuclear reactor (170) according to claim 20, wherein: N — theinlet(178)is formed to an outer surface of the casing (174) and wherein 3 — the at least one cavity (176) communicates with the downcomer (194) through 2 the inlet (178). E 25 22. The nuclear reactor (170) according to claim 20, wherein: © — the inlet (178) is formed to an outer surface of the casing (174), 5 — theriser barrel (179) envelops the reactor core (172) and the fuel and control O system, and wherein

— the riser barrel (179) comprises an opening aligned with the inlet (178) for permitting passage of primary fluid from the downcomer (194) into the at least one cavity (176) of the casing (174).

23. The nuclear reactor (170) according to claim 20 or 22, wherein the housing (180) is placed inside the riser barrel (179).

24. The nuclear reactor (170) according to any one of the preceding claims 18 to 23, wherein the pump(s) (200) is/are located above the reactor core (172).

25. A method of operating the nuclear reactor (170) according to any one of the preceding claims 18 to 24, the method comprising: — selectively operating the nuclear reactor (170) in a passive natural circulation mode, in which primary coolant flows through a passive fluid circulation path by means of convection without assistance from the pump(s) (200), and — selectively operating the nuclear reactor (170) in an assisted circulation mode, in which at least portion of the primary coolant flows through the at least one cavity (176) motivated by the pump(s) (200).

26. The method according to claim 25, the method comprising performing a start-up procedure of the nuclear core (172) in assisted circulation mode. <t A Oo N © <Q O oO I = © oO PP LO 0) A O N