CA1140275A - Plenum separator system for pool-type nuclear reactors - Google Patents
Plenum separator system for pool-type nuclear reactorsInfo
- Publication number
- CA1140275A CA1140275A CA000333949A CA333949A CA1140275A CA 1140275 A CA1140275 A CA 1140275A CA 000333949 A CA000333949 A CA 000333949A CA 333949 A CA333949 A CA 333949A CA 1140275 A CA1140275 A CA 1140275A
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- CA
- Canada
- Prior art keywords
- plenum
- coolant
- vessel
- core
- hot
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Abstract
18 48,109 ABSTRACT OF THE DISCLOSURE
A plenum separator system for separating the hot plenum from the cold plenum and from the reactor vessel wall in a pool-type nuclear reactor. One or more inter-mediate plena containing substantially stagnant and ther-mally stratified coolant provide axial separation of the hot and cold plena. A dual pass forced bypass flow through annuli at the upper portion of the reactor vessel wall, in conjunction with the intermediate plenum and an annular gas space adjacent the reactor vessel wall, provide radial separation of the hot plenum and the vessel wall.
A plenum separator system for separating the hot plenum from the cold plenum and from the reactor vessel wall in a pool-type nuclear reactor. One or more inter-mediate plena containing substantially stagnant and ther-mally stratified coolant provide axial separation of the hot and cold plena. A dual pass forced bypass flow through annuli at the upper portion of the reactor vessel wall, in conjunction with the intermediate plenum and an annular gas space adjacent the reactor vessel wall, provide radial separation of the hot plenum and the vessel wall.
Description
:
`:
1 48,10 PLENUM SEPARATO~ SYSIEM FOR
POOL-TYPE NUCLEAR REACTORS
_ACKGROUND OF rHE INVENTION
- Field of the Invention:
~i~.
This invention relates to pool-type nuclear reactors and more particularly provides an arrangement for substantially separating the hot and cold coolant plena in a pool-type liquid metal cooled fast breeder reactor.
-Description of the Prior Art-;' _.
;In a pool-type nuclear reactor a large reactor vessel contains the major components, such as the reactor core, coolant pumps and main heat exchangers, within a pool of liquid coolant such as sodium. Generally, the coolant is pumped from a cold plenum into and through the core, and discharged into a hot plenum. From the hot plenum the coolant flows through the heat exchangers, transferring heat energy to another coolant, typically for the ultimate purpose of electric power generation, and is discharged back to the cold plenum.
A major component of such reactors has been a structure, known alternatively as a plenum separator, reactor jacket, inner tank, primary tank, insulated internal tank or internal thermal liner, which separates the hot -h~ ~if~
`` ~ Z i ~
;; 2 48,109 coolant in the hot plenum from the reactor vessel wall so ; as to alleviate thermal transients and stresses. This component also serves to somewhat separate the hot and cold plena in some configurations. In typical e~isting pool . reactor des-igns the plenum separator is a cylindrical shell which is arranged to place low temperature sodium coolant ' in an annular region in contact with the reactor vessel wall. In most arrangements, the free or upper surface of this cold coolant changes in elevation during reactor operation, and particularly at start-up and shutdown, by up to eight feet as a result of the pressure differentials between the plenums necessary to circulate the coolant through the primary heat exchangers. Such cycling is undesirable as it results in substantial thermal transients on the vessel wall and the plenum separator. An arrange-ment which alleviates the elevation change is that of the Soviet BN-600 plant which pumps coolant from the cold pool upwardly through an annulus adjacent the vessel wall and into the top of the hot plenum. While this arrangement alleviates the elevational fluctuations, it requires a forced pumping and the coolant passing through the annulus is not available for core cooling, presenting an overall loss of efficiency. Additional thermal stress concerns are also raised in the BN-600 and other pool reactor arrange-ments as the lower support structure, which typically supports the weight of the core components, is directly exposed on its top surface to the hot coolant and on its bottom surface to the cold coolant. This temperature dif-ferential can range up to approximately 300F. Such arrange-ments also typically require ]arge amounts of under-sodium ~1402';~
3 48,109 insulation in the region of the plenum separator, the long-term operational characteristics of which are not totally certain.
Accordingly, it is desirable to provide a plenum separator arrangement which al]eviates the above and other thermal transient and stress concerns while providing acceptable reactor system efficiency.
SUMMARY OF THE INVENTION
This invention provides a plenum separator system for pool-type nuclear reactors which substantially lessens undesirable thermal effects on major components. A primary - feature of the invention is the addition of one or more intermediate plena, containing substantially stagnant and stratified coolant, which separate the hot and cold plena and particularly the hot plena from critical reactor com-ponents. This plenum separator system also includes a plurality of components which together form a dual pass flow path annular region spaced from the reactor vessel wall by an annular gas space. The bypass flow through the flow path is relatively small and is drawn from the main coolant pumps and discharged to an intermediate plenum.
The intermediate plenum, which for purposes of description is hereinafter referred to as an inner inter-mediate plenum and an outer intermediate plenum, segregates the hot coolant, such as liquid sodium, from the cold sodium coolant, in both axial and radial directions. The inner intermediate plenum is an annulus which surrounds the core, which core is radially contained within a cylindrical core barrel. The plenum extends radially between the core barrel and the lower portion of a cylindrical neutron ~1402`~5 ; 4 '~, log shield, the primary function of which is ~o al],eviate '. activation of the secondary coolant -flowing through the ,' primary heat exchangers. The inner intermediate plenum ; extends axially substantially the helght of the core barrel~
bounded on the bottom by the lower support structure and on the top by an inner horizontal baffle which is an annular plate spanning the distance between the core barrel and the neutron shield. Below and radially about a portion of the lower support structure is the cold plenum, and above the inner horizontal baffle is the hot plenum. The inner intermediate plenum will rise in temperature during reactor start-up and achieve a substantially stagnant and stratified thermal profile at normal operating conditions. A relative-ly small amount of coolant will be discharged from the inner intermediate plenum through the area of attachment of the simply supported inner horizontal baffle, as a result ' of thermal expansion of the coolant during start-up. A
reverse effect occurs during reactor cool-down. Otherwise, the inner intermediate plenwn is substantially quiescent.
The outer intermediate plenum is also an annular region which contains vertical passages for containing the : primary heat exchangers and cylindrical standpipes about the primary pumps. It extends radially generally between the upper portion of the neutron shield and a bypass flow annulus adjacent the reactor vessel wall. It extends axially between a bottom plate of the lower support struc-ture and an outer horizontal baffle. Below the lower support structure is the cold plenum from which the primary pump suction draws coolant, and above the outer horizontal baffle is the hot sodium plenum. The relatively small rate ~ 40~X~ ~
. 5 ~,109 of bypass flow is discharged into ~:he outer intermediate - plenum, and a corresponding flow is discharged as leakage ,, passed the juncture of the primary heat exchangers with the bottom plate of the lower support structure and small flow areas about the outer horizontal baffle. The bypass flow need be of relatively small magnitude as a result of an annular gas space adjacent the upper portion of the reactor vessel wall. During normal operation the outer intermedi-ate plenum also remains substantially stagnant and strati-fied.
The bypass fluid for cooling the central portionof the reactor vessel wall, above the cold plenum, is drawn from the pumps into a distribution channel and discharged upwardly between the reactor vessel wall and a flow baffle defining the outer periphery of the outer intermediate plenum. The flow baffle is a bottom supported, substantial-ly cylindrical shell with a conical transition between a lower and an upper segment. The flow baffle is accordingly free to expand upwardly with changes in its thermal profile.
Also bottom supported is a plenum ~eparator plate compris-ing two concentric cylindrical shells joined at their tops by a transition which is spaced above and straddles the top of the flow baffle. The outer shell is a structural sup-port for the inner shell and also functions as a shield for the upper portion of the reactor vessel wall. The inner shell is a thinner membrane which is insulated preferably on the face closest to the reactor vessel. The bypass sodium accordingly passes upwardly between the reactor vessel wall and the flow baffle, and then enters the annu-lus formed between the upper segment o-f the flow baffle and 114Q~ ;~5 ; 6 48,109 the outer shel.l of the plenum separator plate. It contin-ues to flow upwardly and over the -top of the flow baffle, reversing direction and flowing downwardly in an annulus between the i.nner side of the flow baffle and the insula-tion on the plenum separator plate inner shell. This coolant is then discharged into the outer intermediate plenum, containing the primary heat exchangers, so that heat absorbed by the bypass flow is transferred through the shells of, and into, the heat exchangers.
It is thus apparent that the vessel wall is main-tained acceptably cool since its lower portion is adjacent the cold plenum, i.ts central portion is adjacent the bypass flow which is adjacent the outer intermediate plenum, and its upper portion is adjacent an annular gas space in di.rect communication with the cover gas above the level of the coolant in the hot plenum. The gas space is, however, insulated from the hot plenum liquid coolant by the dual bypass flow, and the large thermal gradient from the hot plenum is taken across the insulation plates affixed to the plenum support plate inner shell. This structure also functions as a cool.ant aerosol condenser to control. the condensation of coolant vapor and maintain the annular gas space substantially free of liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
_ _ . . ..
: The advantages, nature and additional features of the invention will become more apparent from -the following description, taken in connection with the accompanying drawings, i.n which:
Figures lA and lB together are an elevational cross section of a pool-type nuclear reactor in accordance ~o~
7 48,l09 with the invention; and ~ igure 2 is an enlarged view of a portion of the reactor of Figures lA and lB.
DESCRIPTION OF THE PREFERRED EMBO~IMENTS
Referring now to the Figures, there is shown a portion of a pool-type nuclear reactor plant utilizing a liquid coolant, such as a liquid metal, for example, sodium, incorporating a plenum separator system. It is to be understood that the reactor shown is substantial]y cylindri-cal and that the view shown in Figures lA and lB represents a cross section along two radii. The components shown in-clude, radially from exterior to interior, a concrete shield and support 10, vessel thermal insulation 12, a guard tank 14, a reactor vessel 16, a primary heat exchanger 18 and coolant pump 20, a neutron shield 22, a core barrel 24, and fuel assemblies 26 making up a core 28. Typically there are a plurality of primary pumps 20 and hea-t exchang-ers 18, such as four pumps 20 and six heat exchangers 18, although only one of each is shown. The core 28 includes a ` 20 -egion of both fertile and fissile fuel surrounded by an additional region of fertile fuel, and is contained radial-ly by the core barrel 24. The core 28 is supported upon a lower support structure 34 which includes a core support structure 36, an extension plate 54, and a bottom plate 52.
Above the core is an upper internals structure, shown merely by the envelope 40, which includes a plurality of components for aiding communication between the exterior of the reactor and the core 28 and for guiding such compon-ents as reciprocatin~ly insertable control rods. The typical level of sodium coolant during normal operation is ,:
8 48,109 shown by the line 42. Above 1:he level 42 is a cover gas space 44, typically containing an inert gas such as argon, and above the cover gas is a plurality of rotatable plugs 48 supported by a reactor roof structure 46.
The primary pump 20 draws suction from a cold pool or plenum 50 of sodium, which is bounded by the bottom portion of the reactor vessel 16, the bottom plate 52, extension plate 54, and the core support structure 36. The main coolant flow path is from the cold plenum 50 upwardly to the pump impeller section 56, and downwardly into and through conduit 58. The coolant discharged from the plur-ality of conduits 58 (one shown) mixes in an annular region 60 within the core support structure 36, and passes upward-ly through the core 28, absorbing heat energy. The coolant enters the core at a temperature in the range of 670F and is discharged at a temperature in the range of 950F. The flow through the core is on the order of one hundred million pounds of sodium per hour at an average velocity of approxi-mately twenty-five feet per second. It therefore exits into the hot sodium pool. or plenum 62, discussed herein-after, with a great deal of turbulence. From the hot plenum 62, the sodium enters the primary heat exchangers 18 (one shown) through a plurality of inlets 64 and flows downwardly, transferring heat to a secondary coolant, such as sodium, flowing, for example, in a downcomer 66, to the bottom of the heat exchanger 18, and then upwardly through the shell side of the heat exchanger. The primary sodium coolant then exits the heat exchangers 18 through outlets 68, returning to the cold plenum 50, thus completing the main circuit~ Additlonal and considerably smaller flow 1~4~2~7S
9 ~8,109 rate flow paths include coolant distributed through the core support structure 36 to and through the neutron shield 22 (shown by arrow 70), pump seal leakage flow distributed : to the hot plenum 62 (shown hy arrow 72), and controlled bypass flow for cooling the reactor vessel discussed in detail hereinafter. The flow through the neutron shield is approximately 100,000 pounds per hour, and pump seal leakage represents approximately 10,000 pounds per hour from all four pumps 20.
10In accordance with the invention the hot plenum 62 is a turbulent flow area, bounded below by the core fuel assemblies 26, an inner horizontal baffle 74, and an outer horizontal baff].e 76. It is bounded radially at i.ts lower portion by the neutron shield 22, and at its upper portion by an inner shell 78 of a plenum separator plate 80. The top of the hot plenum is bounded by the cover gas space 44.
The plenum separator system separates the hot plenum 62 from the cold plenum 50 and also from the reactor vessel wall. It includes the plenum separator plate 80 and an inner intermediate plenum 82 and an outer intermediate plenum 84. The inner intermediate plenum is bounded axial-ly by the core support structure 36 and the inner hori.zon-tal baffle 74, and is bounded radially by the core barrel 24 and the neutron shield 22.
The inner horizontal baffle 74 is an annular plate which is preferably affixed along its outer periphery and simply supported at the core barrel along its inner periphery. By defining the annular shaped inner intermedi-ate plenum 82, the baffle 74 restric-ts the turbulent cur-rents of the hot plenum so that thermal stratification of ;r~
~ 0 48,109the sodium below the baffle 74 deve]ops, preventing the 950~ hot sodium from contacting the 670F core support structure 36. There is substantially no pressure differen-tial across the inner horizontal baffle 74 so that the inner intermediate plenum is substantially quiescent except during reactor start-up or shutdown when, due to thermal expansion or contraction of the sodium within the plenum 82, a corresponding amount o-E sodium leaves or enters the plenum through small flow paths at the inner periphery of the inner horizontal baffle 74.
The outer horizontal baffle 76 is also an annular plate, preferably simply supported at at least one peri-phery. Pressure vents 85 are preferab~y incorporated in the baffle 76, and can also be incorporated in the inner horizontal baffle 74, to assure that pressure is equalized on each side of the baffle, thus reducing leakage flows and mechanical loading. The baffle 76 contains cylindrical apertures 86 and 88 which respectively surround primary pump standpipes 90 and the primary heat exchangers 18.
There is preferably no flow passed these junctures into the outer intermediate plenum and expandable seals such as metallic bellows can be utilized to seal about the apertures.
Together, the outer 84 and inner 82 intermediate plenum axially separate the hot 62 and cold 50 plena. Insulation 93 is preferably provided about the pump standpipes 90, above and below the outer horizontal baffle 76 to protect the high pressure chamber of the pump. The outer horizon-tal baffle 76 should be positioned as high as possible within the reactor system so as to increase the volume of 3n the outer intermediate plenum 84 and decrease the volume of 3~it~0~5 11 48,109 the hot p]enum 62. This orientation provides a more etfi-cient reactor and heat transfer since the hot plenum becomes more turbulent for a given sodium flow rate and provides a more direct flow path between the core 28 and the primary heat exchangers 18.
The plenum separator system also includes a vertically oriented f].ow baffle 94 (Figure 2) which is bottom supported and thus free to expand axially. It is preferably affixed to the bottom plate 52 or the top plate of a bypass flow distribution channe] 96. The flow baffle 94 includes a lower segment 98 and upper segment 100, both of which are cylindrical and concentrically spaced from ~he reactor vessel wall. The segments 98~ 100 are ~joined by a . conical transition p].ate 102. A sodium shield 104, compris-ing the outer portion of the plenum separator plate 80, parallels the transition and the upper segment 100 of the baffle 94. The separator plate 80 is also bottom supported - and includes a transition 106 between the sodium shield 104 and the inner shell 78, the transition 106 extending above the flow ~baffle 94. Thermal insulation 108, such as Technigaz, commercially available from Glitsch Gryogenics, is preferabl.y affixed to the outer side of the inner shell : 78. Such insulation can also be affixed to the inner side of the shell 78. It can be seen that the large radial thermal gradient from the hot plenum is taken across the insulation. This configuration forms a series of annuli inc].uding an annulus 110 between the flow baffle lower segment 98 and the reactor vessel wall, a~d annulus 112 between the flow baffl.e upper segment 100 and the sodium shield 104, and an annulus 114 between the flow baffle ~02s~
12 ~8,109 upper segrnent 100 and the separator inner shell 78 and insulation 108~
During normal reactor operation bypass flow is discharged from each of the primary pumps 20, controlled by : a flow control orifiee 116, through conduit: 118 to the anllular bypass flow distribution channel 96. It then flows upwardly through annulus 110 and annulus 112, is reversed in direction, and flows downwardly through annulus 114 to be discharged into the outer intermediate plenu~ 84.
10The transition 102 configuration lowers the velocity of the bypass flow as it merges with coolant in the outer intermediate plenum 84, thereby not substantially disrupting the desirable coolant stratifieation. The tran-sition configuration also adds stiffness to the flow baffle 94 and plenum support plate 80 whieh are large diameter, thin walled shells. The overall bypass eonfiguration also inereases ~he flow velocity near the reactor vessel wall, assuring sufficient vessel wall cooling. The configuration additionally defines a gas space annulus 120 in communica-tion with the cover gas space ~4, which, in conjunction with the bypass flow and insulation, thermally shields the upper portion of the vessel wall and facilitates utiliza-jtion of a so-called "cold roof" structure. Condensation of codium vapor within the gas space annulus 120 is alleviated by the top section of the transi-tion 106 acting as an aerosol condenser which chills sodium aerosol from the hot plenum 62, cools it by heat exchange with the bypass flow, : and allows the sodium to drip back into the hot plenum 62.
It can be seen therefore that the plenum separator system also segregates the hot plenum 62 from the reactor vessel 13 48,109 16 wall. in a radial direction.
Although the bypass cooling represents a small portion of the total reactor coolant flow, approximately one percent, it will be noted that the loss of heat from the cold plenum 62 to the bypass flow is to a large degree recovered by transfer from the outer intermediate plenum 84 through the primary heat exchanger shell into the coolant flowing through the heat exchanger 18. The coolant within the outer intermediate plenum 84 remains substantially .10 thermally stratified and quiescent as a quantity of coolant corresponding to that entering the plenum 84 is continuously discharged as leakage across the intermediate plenum 84-cold plenum 50 boundary, shown by the arrows 124, and as a small -~discharge about the outer horizontal baffle 76. The major portion of this discharge will be as leakage 124, since the pressure differential across the outer horizontal baffle 76 is negligible during most operating conditions while the pressure differential into the cold plenum is approximately :three psi, and taken across the lower support structure.
It will be noted that if there is an excess of leakage flow as compared to the bypass flow, sodium will move from the hot pool into the intermediate pool at the interface of the horizontal baffle and the primary heat exchangers. It will a'so be noted that these displacements of so~ium into the outer intermediate plenum 84 are at locations where the receiving plenum sodium temperature is substantially equal to the temperature of the displaced sodium, and that the velocities are small, thus minimizing thermal differential concerns.
A pressure relief valve 126 or external flow path il~O2 ~
14 ~8,109 can also be utilized at the top of the plenum separator plate 80 to vent any gas which is trapped in the upper portion of the annulus such as d~ring initial fill of the system. ~owever, once the annular bypass flow paths are filled with sodium, the paths should remain as a solid flow system. It will therefore be noted that even when the primary pumps 20 are completely shut down, a siphon flow will exist in the annular flow paths, but the direction of flow may reverse. The sodium will receive heat from the hot plenum and rise within the annulus 114. The sodium in annulus 112 will reject heat to the vessel and flow down-wardly. However, under pony motor flow the coolant bypass flow path is solid and flow will contin~e to circulate in its normal direction to maintain the reactor vessel wall at acceptably cool temperatures.
It will now be apparent to those ski]led in the art that the disclosed plenum separator system arrangement provides substantial operational and fabrication advantages for pool-type nuclear reactors as compared to the prior art. The system provides good reactor vessel wall cooling, allowing utilization of a cold roof structure. It allevi-ates thermal cycling and stresses imposed upon components which in the prior art have directly separated the hot and cold plena, and provides both axial and radial separation of the hot plenum from the reactor vessel as well as from the cold plenum. Thermal transients due to sodium surface elevation variation are eliminated.
The components utiliæecl are relatively simple to fabricate, install and analyze, utilizing basic geometric shapes. The components are arranged and supported to l~ S
48,lO9 easily accommodate differential thermal expansiorl, such as the bottom supported components adjacent the reactor vessel wall. These factors result in a high reliability design which shoulcd require little maintenance thr~ghout the operating life of the reactor plant.
Additionally, the effect upon reactor efficiency as a result of the bypass coolant flow is slight since the volumetric flow rate required is low and a substantial portion of the heat transferred is recovered by the primary ln heat exchangers. Reactor efficiency is further enhanced since the utilization and orientation of an intermediate plenum allows a substantial reduction in the volume of the hot plenum.
Further, the pressure differential between the hot and cold plena is more distributed than in previous arrangements, t:o a large degree being taken over the inter-;mediate plenum as well as the lower support structure.
Where the pressure differentials do result in flow across components, the temperatures are close and the flow rates ~ 20 small, alleviating detrimental stresses. The overall ;;configuration also alleviates the need for exotic materials and methods of constructic)n.
It will be apparent that many modifications andadditions are possible without departing from the scope of the teaching.
-
`:
1 48,10 PLENUM SEPARATO~ SYSIEM FOR
POOL-TYPE NUCLEAR REACTORS
_ACKGROUND OF rHE INVENTION
- Field of the Invention:
~i~.
This invention relates to pool-type nuclear reactors and more particularly provides an arrangement for substantially separating the hot and cold coolant plena in a pool-type liquid metal cooled fast breeder reactor.
-Description of the Prior Art-;' _.
;In a pool-type nuclear reactor a large reactor vessel contains the major components, such as the reactor core, coolant pumps and main heat exchangers, within a pool of liquid coolant such as sodium. Generally, the coolant is pumped from a cold plenum into and through the core, and discharged into a hot plenum. From the hot plenum the coolant flows through the heat exchangers, transferring heat energy to another coolant, typically for the ultimate purpose of electric power generation, and is discharged back to the cold plenum.
A major component of such reactors has been a structure, known alternatively as a plenum separator, reactor jacket, inner tank, primary tank, insulated internal tank or internal thermal liner, which separates the hot -h~ ~if~
`` ~ Z i ~
;; 2 48,109 coolant in the hot plenum from the reactor vessel wall so ; as to alleviate thermal transients and stresses. This component also serves to somewhat separate the hot and cold plena in some configurations. In typical e~isting pool . reactor des-igns the plenum separator is a cylindrical shell which is arranged to place low temperature sodium coolant ' in an annular region in contact with the reactor vessel wall. In most arrangements, the free or upper surface of this cold coolant changes in elevation during reactor operation, and particularly at start-up and shutdown, by up to eight feet as a result of the pressure differentials between the plenums necessary to circulate the coolant through the primary heat exchangers. Such cycling is undesirable as it results in substantial thermal transients on the vessel wall and the plenum separator. An arrange-ment which alleviates the elevation change is that of the Soviet BN-600 plant which pumps coolant from the cold pool upwardly through an annulus adjacent the vessel wall and into the top of the hot plenum. While this arrangement alleviates the elevational fluctuations, it requires a forced pumping and the coolant passing through the annulus is not available for core cooling, presenting an overall loss of efficiency. Additional thermal stress concerns are also raised in the BN-600 and other pool reactor arrange-ments as the lower support structure, which typically supports the weight of the core components, is directly exposed on its top surface to the hot coolant and on its bottom surface to the cold coolant. This temperature dif-ferential can range up to approximately 300F. Such arrange-ments also typically require ]arge amounts of under-sodium ~1402';~
3 48,109 insulation in the region of the plenum separator, the long-term operational characteristics of which are not totally certain.
Accordingly, it is desirable to provide a plenum separator arrangement which al]eviates the above and other thermal transient and stress concerns while providing acceptable reactor system efficiency.
SUMMARY OF THE INVENTION
This invention provides a plenum separator system for pool-type nuclear reactors which substantially lessens undesirable thermal effects on major components. A primary - feature of the invention is the addition of one or more intermediate plena, containing substantially stagnant and stratified coolant, which separate the hot and cold plena and particularly the hot plena from critical reactor com-ponents. This plenum separator system also includes a plurality of components which together form a dual pass flow path annular region spaced from the reactor vessel wall by an annular gas space. The bypass flow through the flow path is relatively small and is drawn from the main coolant pumps and discharged to an intermediate plenum.
The intermediate plenum, which for purposes of description is hereinafter referred to as an inner inter-mediate plenum and an outer intermediate plenum, segregates the hot coolant, such as liquid sodium, from the cold sodium coolant, in both axial and radial directions. The inner intermediate plenum is an annulus which surrounds the core, which core is radially contained within a cylindrical core barrel. The plenum extends radially between the core barrel and the lower portion of a cylindrical neutron ~1402`~5 ; 4 '~, log shield, the primary function of which is ~o al],eviate '. activation of the secondary coolant -flowing through the ,' primary heat exchangers. The inner intermediate plenum ; extends axially substantially the helght of the core barrel~
bounded on the bottom by the lower support structure and on the top by an inner horizontal baffle which is an annular plate spanning the distance between the core barrel and the neutron shield. Below and radially about a portion of the lower support structure is the cold plenum, and above the inner horizontal baffle is the hot plenum. The inner intermediate plenum will rise in temperature during reactor start-up and achieve a substantially stagnant and stratified thermal profile at normal operating conditions. A relative-ly small amount of coolant will be discharged from the inner intermediate plenum through the area of attachment of the simply supported inner horizontal baffle, as a result ' of thermal expansion of the coolant during start-up. A
reverse effect occurs during reactor cool-down. Otherwise, the inner intermediate plenwn is substantially quiescent.
The outer intermediate plenum is also an annular region which contains vertical passages for containing the : primary heat exchangers and cylindrical standpipes about the primary pumps. It extends radially generally between the upper portion of the neutron shield and a bypass flow annulus adjacent the reactor vessel wall. It extends axially between a bottom plate of the lower support struc-ture and an outer horizontal baffle. Below the lower support structure is the cold plenum from which the primary pump suction draws coolant, and above the outer horizontal baffle is the hot sodium plenum. The relatively small rate ~ 40~X~ ~
. 5 ~,109 of bypass flow is discharged into ~:he outer intermediate - plenum, and a corresponding flow is discharged as leakage ,, passed the juncture of the primary heat exchangers with the bottom plate of the lower support structure and small flow areas about the outer horizontal baffle. The bypass flow need be of relatively small magnitude as a result of an annular gas space adjacent the upper portion of the reactor vessel wall. During normal operation the outer intermedi-ate plenum also remains substantially stagnant and strati-fied.
The bypass fluid for cooling the central portionof the reactor vessel wall, above the cold plenum, is drawn from the pumps into a distribution channel and discharged upwardly between the reactor vessel wall and a flow baffle defining the outer periphery of the outer intermediate plenum. The flow baffle is a bottom supported, substantial-ly cylindrical shell with a conical transition between a lower and an upper segment. The flow baffle is accordingly free to expand upwardly with changes in its thermal profile.
Also bottom supported is a plenum ~eparator plate compris-ing two concentric cylindrical shells joined at their tops by a transition which is spaced above and straddles the top of the flow baffle. The outer shell is a structural sup-port for the inner shell and also functions as a shield for the upper portion of the reactor vessel wall. The inner shell is a thinner membrane which is insulated preferably on the face closest to the reactor vessel. The bypass sodium accordingly passes upwardly between the reactor vessel wall and the flow baffle, and then enters the annu-lus formed between the upper segment o-f the flow baffle and 114Q~ ;~5 ; 6 48,109 the outer shel.l of the plenum separator plate. It contin-ues to flow upwardly and over the -top of the flow baffle, reversing direction and flowing downwardly in an annulus between the i.nner side of the flow baffle and the insula-tion on the plenum separator plate inner shell. This coolant is then discharged into the outer intermediate plenum, containing the primary heat exchangers, so that heat absorbed by the bypass flow is transferred through the shells of, and into, the heat exchangers.
It is thus apparent that the vessel wall is main-tained acceptably cool since its lower portion is adjacent the cold plenum, i.ts central portion is adjacent the bypass flow which is adjacent the outer intermediate plenum, and its upper portion is adjacent an annular gas space in di.rect communication with the cover gas above the level of the coolant in the hot plenum. The gas space is, however, insulated from the hot plenum liquid coolant by the dual bypass flow, and the large thermal gradient from the hot plenum is taken across the insulation plates affixed to the plenum support plate inner shell. This structure also functions as a cool.ant aerosol condenser to control. the condensation of coolant vapor and maintain the annular gas space substantially free of liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
_ _ . . ..
: The advantages, nature and additional features of the invention will become more apparent from -the following description, taken in connection with the accompanying drawings, i.n which:
Figures lA and lB together are an elevational cross section of a pool-type nuclear reactor in accordance ~o~
7 48,l09 with the invention; and ~ igure 2 is an enlarged view of a portion of the reactor of Figures lA and lB.
DESCRIPTION OF THE PREFERRED EMBO~IMENTS
Referring now to the Figures, there is shown a portion of a pool-type nuclear reactor plant utilizing a liquid coolant, such as a liquid metal, for example, sodium, incorporating a plenum separator system. It is to be understood that the reactor shown is substantial]y cylindri-cal and that the view shown in Figures lA and lB represents a cross section along two radii. The components shown in-clude, radially from exterior to interior, a concrete shield and support 10, vessel thermal insulation 12, a guard tank 14, a reactor vessel 16, a primary heat exchanger 18 and coolant pump 20, a neutron shield 22, a core barrel 24, and fuel assemblies 26 making up a core 28. Typically there are a plurality of primary pumps 20 and hea-t exchang-ers 18, such as four pumps 20 and six heat exchangers 18, although only one of each is shown. The core 28 includes a ` 20 -egion of both fertile and fissile fuel surrounded by an additional region of fertile fuel, and is contained radial-ly by the core barrel 24. The core 28 is supported upon a lower support structure 34 which includes a core support structure 36, an extension plate 54, and a bottom plate 52.
Above the core is an upper internals structure, shown merely by the envelope 40, which includes a plurality of components for aiding communication between the exterior of the reactor and the core 28 and for guiding such compon-ents as reciprocatin~ly insertable control rods. The typical level of sodium coolant during normal operation is ,:
8 48,109 shown by the line 42. Above 1:he level 42 is a cover gas space 44, typically containing an inert gas such as argon, and above the cover gas is a plurality of rotatable plugs 48 supported by a reactor roof structure 46.
The primary pump 20 draws suction from a cold pool or plenum 50 of sodium, which is bounded by the bottom portion of the reactor vessel 16, the bottom plate 52, extension plate 54, and the core support structure 36. The main coolant flow path is from the cold plenum 50 upwardly to the pump impeller section 56, and downwardly into and through conduit 58. The coolant discharged from the plur-ality of conduits 58 (one shown) mixes in an annular region 60 within the core support structure 36, and passes upward-ly through the core 28, absorbing heat energy. The coolant enters the core at a temperature in the range of 670F and is discharged at a temperature in the range of 950F. The flow through the core is on the order of one hundred million pounds of sodium per hour at an average velocity of approxi-mately twenty-five feet per second. It therefore exits into the hot sodium pool. or plenum 62, discussed herein-after, with a great deal of turbulence. From the hot plenum 62, the sodium enters the primary heat exchangers 18 (one shown) through a plurality of inlets 64 and flows downwardly, transferring heat to a secondary coolant, such as sodium, flowing, for example, in a downcomer 66, to the bottom of the heat exchanger 18, and then upwardly through the shell side of the heat exchanger. The primary sodium coolant then exits the heat exchangers 18 through outlets 68, returning to the cold plenum 50, thus completing the main circuit~ Additlonal and considerably smaller flow 1~4~2~7S
9 ~8,109 rate flow paths include coolant distributed through the core support structure 36 to and through the neutron shield 22 (shown by arrow 70), pump seal leakage flow distributed : to the hot plenum 62 (shown hy arrow 72), and controlled bypass flow for cooling the reactor vessel discussed in detail hereinafter. The flow through the neutron shield is approximately 100,000 pounds per hour, and pump seal leakage represents approximately 10,000 pounds per hour from all four pumps 20.
10In accordance with the invention the hot plenum 62 is a turbulent flow area, bounded below by the core fuel assemblies 26, an inner horizontal baffle 74, and an outer horizontal baff].e 76. It is bounded radially at i.ts lower portion by the neutron shield 22, and at its upper portion by an inner shell 78 of a plenum separator plate 80. The top of the hot plenum is bounded by the cover gas space 44.
The plenum separator system separates the hot plenum 62 from the cold plenum 50 and also from the reactor vessel wall. It includes the plenum separator plate 80 and an inner intermediate plenum 82 and an outer intermediate plenum 84. The inner intermediate plenum is bounded axial-ly by the core support structure 36 and the inner hori.zon-tal baffle 74, and is bounded radially by the core barrel 24 and the neutron shield 22.
The inner horizontal baffle 74 is an annular plate which is preferably affixed along its outer periphery and simply supported at the core barrel along its inner periphery. By defining the annular shaped inner intermedi-ate plenum 82, the baffle 74 restric-ts the turbulent cur-rents of the hot plenum so that thermal stratification of ;r~
~ 0 48,109the sodium below the baffle 74 deve]ops, preventing the 950~ hot sodium from contacting the 670F core support structure 36. There is substantially no pressure differen-tial across the inner horizontal baffle 74 so that the inner intermediate plenum is substantially quiescent except during reactor start-up or shutdown when, due to thermal expansion or contraction of the sodium within the plenum 82, a corresponding amount o-E sodium leaves or enters the plenum through small flow paths at the inner periphery of the inner horizontal baffle 74.
The outer horizontal baffle 76 is also an annular plate, preferably simply supported at at least one peri-phery. Pressure vents 85 are preferab~y incorporated in the baffle 76, and can also be incorporated in the inner horizontal baffle 74, to assure that pressure is equalized on each side of the baffle, thus reducing leakage flows and mechanical loading. The baffle 76 contains cylindrical apertures 86 and 88 which respectively surround primary pump standpipes 90 and the primary heat exchangers 18.
There is preferably no flow passed these junctures into the outer intermediate plenum and expandable seals such as metallic bellows can be utilized to seal about the apertures.
Together, the outer 84 and inner 82 intermediate plenum axially separate the hot 62 and cold 50 plena. Insulation 93 is preferably provided about the pump standpipes 90, above and below the outer horizontal baffle 76 to protect the high pressure chamber of the pump. The outer horizon-tal baffle 76 should be positioned as high as possible within the reactor system so as to increase the volume of 3n the outer intermediate plenum 84 and decrease the volume of 3~it~0~5 11 48,109 the hot p]enum 62. This orientation provides a more etfi-cient reactor and heat transfer since the hot plenum becomes more turbulent for a given sodium flow rate and provides a more direct flow path between the core 28 and the primary heat exchangers 18.
The plenum separator system also includes a vertically oriented f].ow baffle 94 (Figure 2) which is bottom supported and thus free to expand axially. It is preferably affixed to the bottom plate 52 or the top plate of a bypass flow distribution channe] 96. The flow baffle 94 includes a lower segment 98 and upper segment 100, both of which are cylindrical and concentrically spaced from ~he reactor vessel wall. The segments 98~ 100 are ~joined by a . conical transition p].ate 102. A sodium shield 104, compris-ing the outer portion of the plenum separator plate 80, parallels the transition and the upper segment 100 of the baffle 94. The separator plate 80 is also bottom supported - and includes a transition 106 between the sodium shield 104 and the inner shell 78, the transition 106 extending above the flow ~baffle 94. Thermal insulation 108, such as Technigaz, commercially available from Glitsch Gryogenics, is preferabl.y affixed to the outer side of the inner shell : 78. Such insulation can also be affixed to the inner side of the shell 78. It can be seen that the large radial thermal gradient from the hot plenum is taken across the insulation. This configuration forms a series of annuli inc].uding an annulus 110 between the flow baffle lower segment 98 and the reactor vessel wall, a~d annulus 112 between the flow baffl.e upper segment 100 and the sodium shield 104, and an annulus 114 between the flow baffle ~02s~
12 ~8,109 upper segrnent 100 and the separator inner shell 78 and insulation 108~
During normal reactor operation bypass flow is discharged from each of the primary pumps 20, controlled by : a flow control orifiee 116, through conduit: 118 to the anllular bypass flow distribution channel 96. It then flows upwardly through annulus 110 and annulus 112, is reversed in direction, and flows downwardly through annulus 114 to be discharged into the outer intermediate plenu~ 84.
10The transition 102 configuration lowers the velocity of the bypass flow as it merges with coolant in the outer intermediate plenum 84, thereby not substantially disrupting the desirable coolant stratifieation. The tran-sition configuration also adds stiffness to the flow baffle 94 and plenum support plate 80 whieh are large diameter, thin walled shells. The overall bypass eonfiguration also inereases ~he flow velocity near the reactor vessel wall, assuring sufficient vessel wall cooling. The configuration additionally defines a gas space annulus 120 in communica-tion with the cover gas space ~4, which, in conjunction with the bypass flow and insulation, thermally shields the upper portion of the vessel wall and facilitates utiliza-jtion of a so-called "cold roof" structure. Condensation of codium vapor within the gas space annulus 120 is alleviated by the top section of the transi-tion 106 acting as an aerosol condenser which chills sodium aerosol from the hot plenum 62, cools it by heat exchange with the bypass flow, : and allows the sodium to drip back into the hot plenum 62.
It can be seen therefore that the plenum separator system also segregates the hot plenum 62 from the reactor vessel 13 48,109 16 wall. in a radial direction.
Although the bypass cooling represents a small portion of the total reactor coolant flow, approximately one percent, it will be noted that the loss of heat from the cold plenum 62 to the bypass flow is to a large degree recovered by transfer from the outer intermediate plenum 84 through the primary heat exchanger shell into the coolant flowing through the heat exchanger 18. The coolant within the outer intermediate plenum 84 remains substantially .10 thermally stratified and quiescent as a quantity of coolant corresponding to that entering the plenum 84 is continuously discharged as leakage across the intermediate plenum 84-cold plenum 50 boundary, shown by the arrows 124, and as a small -~discharge about the outer horizontal baffle 76. The major portion of this discharge will be as leakage 124, since the pressure differential across the outer horizontal baffle 76 is negligible during most operating conditions while the pressure differential into the cold plenum is approximately :three psi, and taken across the lower support structure.
It will be noted that if there is an excess of leakage flow as compared to the bypass flow, sodium will move from the hot pool into the intermediate pool at the interface of the horizontal baffle and the primary heat exchangers. It will a'so be noted that these displacements of so~ium into the outer intermediate plenum 84 are at locations where the receiving plenum sodium temperature is substantially equal to the temperature of the displaced sodium, and that the velocities are small, thus minimizing thermal differential concerns.
A pressure relief valve 126 or external flow path il~O2 ~
14 ~8,109 can also be utilized at the top of the plenum separator plate 80 to vent any gas which is trapped in the upper portion of the annulus such as d~ring initial fill of the system. ~owever, once the annular bypass flow paths are filled with sodium, the paths should remain as a solid flow system. It will therefore be noted that even when the primary pumps 20 are completely shut down, a siphon flow will exist in the annular flow paths, but the direction of flow may reverse. The sodium will receive heat from the hot plenum and rise within the annulus 114. The sodium in annulus 112 will reject heat to the vessel and flow down-wardly. However, under pony motor flow the coolant bypass flow path is solid and flow will contin~e to circulate in its normal direction to maintain the reactor vessel wall at acceptably cool temperatures.
It will now be apparent to those ski]led in the art that the disclosed plenum separator system arrangement provides substantial operational and fabrication advantages for pool-type nuclear reactors as compared to the prior art. The system provides good reactor vessel wall cooling, allowing utilization of a cold roof structure. It allevi-ates thermal cycling and stresses imposed upon components which in the prior art have directly separated the hot and cold plena, and provides both axial and radial separation of the hot plenum from the reactor vessel as well as from the cold plenum. Thermal transients due to sodium surface elevation variation are eliminated.
The components utiliæecl are relatively simple to fabricate, install and analyze, utilizing basic geometric shapes. The components are arranged and supported to l~ S
48,lO9 easily accommodate differential thermal expansiorl, such as the bottom supported components adjacent the reactor vessel wall. These factors result in a high reliability design which shoulcd require little maintenance thr~ghout the operating life of the reactor plant.
Additionally, the effect upon reactor efficiency as a result of the bypass coolant flow is slight since the volumetric flow rate required is low and a substantial portion of the heat transferred is recovered by the primary ln heat exchangers. Reactor efficiency is further enhanced since the utilization and orientation of an intermediate plenum allows a substantial reduction in the volume of the hot plenum.
Further, the pressure differential between the hot and cold plena is more distributed than in previous arrangements, t:o a large degree being taken over the inter-;mediate plenum as well as the lower support structure.
Where the pressure differentials do result in flow across components, the temperatures are close and the flow rates ~ 20 small, alleviating detrimental stresses. The overall ;;configuration also alleviates the need for exotic materials and methods of constructic)n.
It will be apparent that many modifications andadditions are possible without departing from the scope of the teaching.
-
Claims (5)
1. A pool-type nuclear reactor having a coolant liquid comprising:
a core supported on a lower support structure;
a pump;
a cold plenum from which said pump directs coolant to said core;
a hot plenum into which coolant exiting said core is directed; and a core barrel radially surrounding said core;
an annular shaped inner intermediate plenum adjacent to and radially surrounding said core barrel, bounded below by said lower support structure and bounded on top by an inner horizontal baffle;
an annular shaped neutron shield adjacent to and radially surrounding said inner intermediate plenum;
an annular shaped outer intermediate plenum adjacent to and surrounding at least the upper portion of said neutron shield, bounded by said lower support structure and bounded on top by an outer horizontal baffle;
said inner and outer intermediate plena contain-ing substantially stagnant and thermally stratified coolant and completely segregating liquid in said hot plenum from liquid in said cold plenum.
a core supported on a lower support structure;
a pump;
a cold plenum from which said pump directs coolant to said core;
a hot plenum into which coolant exiting said core is directed; and a core barrel radially surrounding said core;
an annular shaped inner intermediate plenum adjacent to and radially surrounding said core barrel, bounded below by said lower support structure and bounded on top by an inner horizontal baffle;
an annular shaped neutron shield adjacent to and radially surrounding said inner intermediate plenum;
an annular shaped outer intermediate plenum adjacent to and surrounding at least the upper portion of said neutron shield, bounded by said lower support structure and bounded on top by an outer horizontal baffle;
said inner and outer intermediate plena contain-ing substantially stagnant and thermally stratified coolant and completely segregating liquid in said hot plenum from liquid in said cold plenum.
2. The reactor of claim 1 wherein a preselected amount of coolant is directed from said pump to said outer 17 48,109 intermediate plenum and an amount of coolant corresponding to the preselected coolant discharged into said outer intermediate plenum is discharged from said outer plenum into said cold plenum.
3. The reactor of claim 2 further comprising a heat exchanger disposed within said vessel, coolant from said hot plenum being passed through said heat exchanger in thermal interchange with a secondary colder fluid and being discharged into said cold plenum during normal reac-tor operation being.
4. The reactor of claim 1 wherein said core, pump, plena and volume are disposed within a substantially cylindrical vessel and said reactor further comprises structure for directing a preselected flow of coolant from said pump upwardly along a portion of said vessel above said lower plenum and then into structure forming a solid flow dual pass annulus, said structure being disposed between said hot plenum and said vessel, said preselected flow being discharged into said segregating volume, said reactor further including a roof atop said vessel, the level of coolant in said hot plenum being spaced from said roof so as to form a cover gas space between said level and roof, said dual pass annulus being radially spaced from an upper portion of said vessel so as to form 2 gas space annulus between said structure forming said dual pass annulus and said vessel, said structure including a shield affixed to said vessel which extends upwardly above the level of coolant in said hot plenum, said gas space annulus being in direct fluid communication with said cover gas space and segregated from all of said liquid coolant 18 48,109 within said vessel by said shield and said cover gas space, whereby said vessel is cooled at a lower level by said cold plenum, at an intermediate level by said pre-selected flow of coolant along said vessel, and at an upper portion by said gas space annulus.
5. A pool-type nuclear reactor having a liquid coolant., comprising:
a vessel, a pump disposed within said vessel;
a core, a core barrel radially surrounding said core;
a lower support structure affixed to said vessel and supporting said core within said vessel;
a cold plenum from which said pump draws coolant and directs coolant to said core, said cold plenum being bounded by said lower support structure and vessel, coolant in said cold plenum being adjacent the lower side of said lower support structure;
a hot plenum into which coolant exiting said core is discharged;
an inner intermediate plenum disposed axially between said hot plenum and the upper side of said lower support structure, and disposed radially adjacent and about said core barrel, said inner intermediate plenum being separated from said hot plenum by an annular shaped inner horizontal baffle simply supported at one edge, said inter-mediate plenum containing a volume of substantially stagnant and thermally stratified coolant, said inner intermediate plenum receiving and discharging coolant solely through expansion and contraction of said contained coolant; and 19 48,109 an annular shaped neutron shield adjacent to and radially surrounding said inner intermediate plenum.
a vessel, a pump disposed within said vessel;
a core, a core barrel radially surrounding said core;
a lower support structure affixed to said vessel and supporting said core within said vessel;
a cold plenum from which said pump draws coolant and directs coolant to said core, said cold plenum being bounded by said lower support structure and vessel, coolant in said cold plenum being adjacent the lower side of said lower support structure;
a hot plenum into which coolant exiting said core is discharged;
an inner intermediate plenum disposed axially between said hot plenum and the upper side of said lower support structure, and disposed radially adjacent and about said core barrel, said inner intermediate plenum being separated from said hot plenum by an annular shaped inner horizontal baffle simply supported at one edge, said inter-mediate plenum containing a volume of substantially stagnant and thermally stratified coolant, said inner intermediate plenum receiving and discharging coolant solely through expansion and contraction of said contained coolant; and 19 48,109 an annular shaped neutron shield adjacent to and radially surrounding said inner intermediate plenum.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US93862878A | 1978-08-31 | 1978-08-31 | |
| US938,628 | 1978-08-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1140275A true CA1140275A (en) | 1983-01-25 |
Family
ID=25471701
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000333949A Expired CA1140275A (en) | 1978-08-31 | 1979-08-14 | Plenum separator system for pool-type nuclear reactors |
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| Country | Link |
|---|---|
| CA (1) | CA1140275A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4664876A (en) * | 1983-03-16 | 1987-05-12 | Central Research Institute Of Electric Power | Fast breeder reactor |
-
1979
- 1979-08-14 CA CA000333949A patent/CA1140275A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4664876A (en) * | 1983-03-16 | 1987-05-12 | Central Research Institute Of Electric Power | Fast breeder reactor |
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