US3613643A

US3613643A - Combined once-through and natural circulation vapor generator

Info

Publication number: US3613643A
Application number: US851769A
Authority: US
Inventors: Robert O Barratt
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1969-07-18
Filing date: 1969-07-18
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: FR2055294A5; JPS5118561B1; ES381909A1

Abstract

A sodium-heated vapor generator used in connection with a sodium-cooled fast breeder reactor is provided with means for supplying feedwater to the vapor generator in the event of feed pump failure, low-load operation, or reactor shutdown. Accordingly, a check valve will complete a natural circulation circuit to provide the necessary feedwater until water can be supplied from a suitable emergency supply.

Description

United States Patent lnventor Robert O. Barratt Parsippany, NJ.

Appl. No. 851,769

Filed July 18, 1969 Patented Oct. 19, 197 l Assignee Foster Wheeler Corporation Livingston, NJ.

COMBINED ONCE-THROUGH AND NATURAL CIRCULATION VAPOR GENERATOR 3 Claims, 2 Drawing Figs.

US. Cl 122/34, 122/406 Int. Cl F22b 1/06 Field of Search 122/32, 34, 406, 407

T0 STEAM USER Relerences Cited UNITED STATES PATENTS 3,473,519 10/1969 Hansen 122/32 3,177,659 4/1965 Berman 122/32 X 2,704,534 3/1955 Dalin et al. 122/407 Primary Examiner-Kenneth W. Sprague Attorneys-John E. Wilson, John Maier, Ill and Marvin A.

Naigur ABSTRACT: A sodium-heated vapor generator used in connection with a sodium-cooled fast breeder reactor is provided with means for supplying feedwater to the vapor generator in the event of feed pump failure, low-load operation, or reactor shutdown. Accordingly, a check valve will complete a natural circulation circuit to provide the necessary feedwater until water can be supplied from a suitable emergency supply.

STEAM GENERATOR 7 STEAM GENERATOR PATENTEDUBT 19 SH 28 3 NUCLEAR 3o NUCLEAR REACTOR souRcE FIG] STEAM GENERATOR vlcx ' laz INVIIN'I'UR.

ROBERT O. BAR T COMBINED ONCE-THROUGH AND NATURAL CIRCULATION VAPOR GENERATOR BACKGROUND OF THE INVENTION Although vapor-generating systems of the once-through type have been widely used, there are generally a number of drawbacks when once-through systems are used in connection with nuclear applications. Accordingly, when a sodium-heated once-through vapor generator is used with a sodium-cooled fast breeder reactor, it represents the final source of cooling for the reactor, and this source of cooling must always be available even if the main supply of feedwater is discontinued due to failure of the feed pump or shutdown of the reactor. Thus, when the feed pump fails there must be an alternate system to continue the heat transfer circuit from the nuclear reactor. This is also necessary when the reactor is shutdown, since heat is generated for a lead period which amounts to low-load operation of the vapor generator. When a oncethrough system is used it is not possible to operate without external control means, and if such control means are not available the ability of the system to transfer heat is lost.

In accordance with the present invention, start up, shutdown, and low-load operation of a once-through vapor generator may be accomplished by providing a natural circulation circuit for the recirculation of a portion of the working fluid from the drum storage to the vapor generator, thereby providing a reliable source of cooling during periods when outside sources of control are lost. Thus, a principle object of the present invention is to provide a sodium-heated oncethrough vapor generator with an auxiliary natural circulation circuit so that a source of cooling will always be available even if the main supply of feedwater becomes discontinued.

SUMMARY OF THE INVENTION In accordance with an illustrative embodiment demonstrating features and advantages of the present invention there is provided a once-through vapor generator capable of operation under variable load conditions and achieving indirect heat exchange between liquid sodium and feedwater. The vapor generator includes means defining a main flow path having vapor-generating tubes and means for maintaining the vapor-generating tubes in contact with the liquid sodium. There is also provided means for supplying feedwater to the main flow path such that a two-phase mixture of steam and water is passed through the main flow path, and vapor separation means in flow communication with the main flow path for receiving the two-phase mixture and separating the steam from the water. Regulating valve means are operatively connected between the means for supplying feedwater and the main flow path and responsive to the feedwater flow in the main flow path such that the regulating valve means will move from an open position to a closed position in accordance with a decrease in the flow of the feedwater. A check valve circuit means is operatively connected in flow communication between the vapor separation means and the pressure-reducing valve means such that the water from the vapor separation means is passed to the vapor-generating tubes whereby natural circulation flow is established in the main flow path.

BRIEF DESCRIPTION OF THE DRAWINGS The above brief description, as well as further objects, features, and advantages of the present invention will be more fully appreciated by reference to the following detailed description of a presently preferred but nonetheless illustrative embodiment in accordance with the present invention, when taken in connection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic illustration of a combined nuclear reactor and once-through vapor generator system; and

FIG. 2 is an enlarged sectional view showing in details the once-through and natural circulation circuitry in accordance with the present invention.

2 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and more particularly to FIG. '1, hot liquid sodium is delivered to a vapor generator I0,'of the once-through type, through a sodium inlet line 12, and the liquid sodium, which has undergone heat transfer, emerges from the lower portion 16 of vapor'gener'ator l0 througha sodium outlet line 18. The liquid sodium in line 18 is passed by feed pump 22 to a nuclear source 24 which includes an intermediate heat exchanger 26 and nuclear reactor 28. The hot liquid sodium is circulated through line 30 into indirect heat exchange with coils 34 of the intermediate heat exchanger 26 and line 36 and pump 38 are provided forreturning the liquid sodium to the nuclear'rea'ctor 28.

As best shown in FIG. 2, the vapor'generator I0 is provided with a separator drum 40 for switch over to natural circulation operation. The working fluid, tobe henceforth referred to as feedwater, is forced by pump means at the feedwater heaters which are not illustrated through a line 42, to a junction designated 46 where -a portion of the feedwater is carried along a line 48 to a regulator valve 50. A line 52 from valve 50 is connected at a junction 53 to a line 54 which in turn is connected to vapor generator 10. The regulator valve 50 serves as a means for matching the feedwater flow with the steam output demand of vaporgenerator l0. Vapor generator 10,- as illustrated in FIG. 2, may be comprised of a'parallel multiple tube serpentine configuration such as described and claimed in copending application Ser. No. 743,679, entitled Sodium Heated Steam Generator", and filed on July 10, I968.

The vapor generator 10 includes a pressure vessel 56 in which there is provided a main flow path comprising an inlet header 58, downcomer 60, serpentinetubes 66 and an outlet header 68. Upon entering the header 58 from line 54, the feedwater flows through downcomer 60 into the serpentine tubes 66 and isbrought into indirect heat exchange with the hot liquid sodium. A two-phase mixture of steam and water flows upwardly in serpentine tubes 66 and emerges as superheated steam in the outlet header 68.

The separator drum 40 is connected by line in flow communication with outlet header 68 for receiving the superheated steam. The bottom end of separator drum 40 is connected by a line 70 to a conical nozzle deflector 72. The steam in line 70 is conveyed into nozzle deflector 72, the upper portion of which is 'provided with a group of mechanical separators 73 that are well known in the art. A series of dryers 74 are positioned above the mechanical separators 73, such that the steam passes through the dryers 74 prior to passingthrough outlet 75 to a superheater and steam user not shown in the drawings. The water from mechanical separators 73 and dryers 74 flows downwardly in the separator drum 40 to form a water reservoir 76 below deflector nozzle 72. Additional water is supplied to the reservoir 76 through line 78 which is provided with a feedwater valve 80. The normal water level required in separator 40 is indicated on a gauge 84, and this level is maintained by mechanical or electrical systems well known in the art which are connected to valve 80, as schematically shown by line 86. An outlet overflow valve 88 is connected to the bottom of separator 40 through which excess water is directed, thereby preventing overflowing through deflector nozzle 72. The feedwater valve is connected to an auxiliary supply of feedwater by means of line 89, pump 90 and valve 91.

To establish natural circulation flow in the vapor generator 10, a nonreturn check valve 92 is connected through line 94 between thebottom of separator 40 and junction 53. At fullload operation, with once-through flow in vapor generator 10, the regulator valve 50 will be in a fully open position. During low-load operation of vapor generator 10, the regulator valve 50 will be in a partially open position in direct response to the low feedwater flow rate in line 48, and this will result in a relatively low pressure in line 52. This low-pressure condition will cause check valve 92 to open due to the hydrostatic head developed above valve 92 by the water reservoir 76.

The hydrostatic head of reservoir 76 in cooperation with the mechanical separation shroud from the mechanical separators 73 which act as a girth baffle, will induce natural circulation in vapor generator 10. In this manner, the water from reservoir 76 will flow downwardly through line 94, check valve 92 and line 54, which will serve as a downcomer to complete the natural circulation flow loop during low-load operation. When natural circulation flow has been fully established, the regulator valve 50 can be moved to a fully closed position and the vapor generator will temporarily utilize the feedwater from the reservoir 76 until a suitable additional source can be obtained. The additional feedwater can be obtained from the once-through supply line 42 or from the auxiliary supply of line 89.

From the foregoing it can be appreciated that the vapor generator 10 achieves continuous operation at full-load to low-load operating conditions. Accordingly, when it is necessary to close down the nuclear reactor 28 and heat transfer occurs for a lead period which cannot support once-through operation in vapor generator 10, it is possible to switch over to natural circulation flow and maintain a continuous vaporgenerating sequence. The ability to change over to natural circulation at low-load operation is a safety feature which is desirable for nuclear systems combined with once-through heat transfer circuitry, since continuous flow attendant with cooling will be assured even though a failure occurred which would eliminate the once-through flow.

A latitude of modification, change and substitution is intended in the foregoing disclosure and is some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

What is claimed is:

l. A once-through vapor generator capable of operation under variable load conditions and achieving indirect heat exchange between liquid sodium and feedwater comprising means defining a main flow path including vapor-generating tubes,

means for maintaining said vapor generator tubes in contact with said liquid sodium,

means for supplying feedwater to said main flow path such that a two-phase mixture of steam and water is passed through said main flow path,

vapor separation means in flow communication with said main flow path for receiving said two-phase mixture and separating the steam from the water,

regulating valve means operatively connected between said means for supplying feedwater and said main flow path and responsive to the feedwater flow in said main flow path such that said regulating valve means will move from an open position to a closed position in accordance with a decrease in flow of said feedwater, and

check valve circuit means operatively connected in flow communication between said vapor separation means and said regulating valve means such that said water from said vapor separation means is passed to said vapor-generating tubes whereby natural circulation flow is established in said main flow path.

2. A once-through vapor generator capable of operation under variable load conditions and achieving indirect heat exchange between liquid sodium heated by a nuclear reactor and feedwater comprising means defining a main flow path including vapor-generating tubes,

means for maintaining said vapor generator tubes in contact with said liquid sodium;

vapor separation means positioned above and in flow communication with said main flow path for receiving said two-phase mixture and separating the steam from the water to form a hydrostatic head above said mam flow path,

regulating valve means operatively connected between said means for supplying feedwater and said main flow path responsive to the feedwater flow in said main flow path such that said regulating valve means will move from an open position to a closed position in response to a decrease in flow of said feedwater, and

check valve circuit means operatively connected in flow communication between said vapor separation means and said regulating valve means such that said hydrostatic head will cause said water from said vapor separation means to pass to said vapor-generating tubes whereby natural circulationflow is established in said main flow path.

3. A once-through vapor generator capable of operation under variable load conditions and achieving indirect heat exchange between liquid sodium heated by a nuclear reactor and feedwater comprising means defining a main flow path including vapor-generating tubes,

means for supplying feedwater to said main flow path such that a two'phase mixture of steam and water is passed through said main flow path,

a separator drum positioned above and in flow communication with said main flow path for receiving said two-phase mixture and for mechanically separating the steam from the water to form a shroud of water in said separator drum, and a hydrostatic head above said main flow path,

regulating valve means connected between said means for supplying feedwater and said main flow path responsive to the feedwater flow in said main flow path such that said regulating valve means will move from an open position to a closed position in direct proportion to and in response to a decrease in flow of said feedwater, and

check valve circuit means operatively connected in flow communication between said vapor separation means and said regulating valve means such that said hydrostatic head in cooperation with said shroud of water will induce natural circulation flow in said main flow path.

Claims

1. A once-through vapor generator capable of operation under variable load conditions and achieving indirect heat exchange between liquid sodium and feedwater comprising means defining a main flow path including vapor-generating tubes, means for maintaining said vapor generator tubes in contact with said liquid sodium, means for supplying feedwater to said main flow path such that a two-phase mixture of steam and water is passed through said main flow path, vapor separation means in flow communication with said main flow path for receiving said two-phase mixture and separating the steam from the water, regulating valve means operatively connected between said means for supplying feedwater and said main flow path and responsive to the feedwater flow in said main flow path such that said regulating valve means will move from an open position to a closed position in accordance with a decrease in flow of said feedwater, and check valve circuit means operatively connected in flow communication between saiD vapor separation means and said regulating valve means such that said water from said vapor separation means is passed to said vapor-generating tubes whereby natural circulation flow is established in said main flow path.

2. A once-through vapor generator capable of operation under variable load conditions and achieving indirect heat exchange between liquid sodium heated by a nuclear reactor and feedwater comprising means defining a main flow path including vapor-generating tubes, means for maintaining said vapor generator tubes in contact with said liquid sodium; means for supplying feedwater to said main flow path such that a two-phase mixture of steam and water is passed through said main flow path, vapor separation means positioned above and in flow communication with said main flow path for receiving said two-phase mixture and separating the steam from the water to form a hydrostatic head above said main flow path, regulating valve means operatively connected between said means for supplying feedwater and said main flow path responsive to the feedwater flow in said main flow path such that said regulating valve means will move from an open position to a closed position in response to a decrease in flow of said feedwater, and check valve circuit means operatively connected in flow communication between said vapor separation means and said regulating valve means such that said hydrostatic head will cause said water from said vapor separation means to pass to said vapor-generating tubes whereby natural circulation flow is established in said main flow path.

3. A once-through vapor generator capable of operation under variable load conditions and achieving indirect heat exchange between liquid sodium heated by a nuclear reactor and feedwater comprising means defining a main flow path including vapor-generating tubes, means for maintaining said vapor generator tubes in contact with said liquid sodium, means for supplying feedwater to said main flow path such that a two-phase mixture of steam and water is passed through said main flow path, a separator drum positioned above and in flow communication with said main flow path for receiving said two-phase mixture and for mechanically separating the steam from the water to form a shroud of water in said separator drum, and a hydrostatic head above said main flow path, regulating valve means connected between said means for supplying feedwater and said main flow path responsive to the feedwater flow in said main flow path such that said regulating valve means will move from an open position to a closed position in direct proportion to and in response to a decrease in flow of said feedwater, and check valve circuit means operatively connected in flow communication between said vapor separation means and said regulating valve means such that said hydrostatic head in cooperation with said shroud of water will induce natural circulation flow in said main flow path.