CA1195441A - Nuclear reactor fuel element having improved heat transfer - Google Patents
Nuclear reactor fuel element having improved heat transferInfo
- Publication number
- CA1195441A CA1195441A CA000421403A CA421403A CA1195441A CA 1195441 A CA1195441 A CA 1195441A CA 000421403 A CA000421403 A CA 000421403A CA 421403 A CA421403 A CA 421403A CA 1195441 A CA1195441 A CA 1195441A
- Authority
- CA
- Canada
- Prior art keywords
- fuel
- cladding
- molecular weight
- section
- gas
- 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.)
- Expired
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Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
- G21C3/02—Fuel elements
- G21C3/04—Constructional details
- G21C3/16—Details of the construction within the casing
- G21C3/17—Means for storage or immobilisation of gases in fuel elements
-
- 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
ABSTRACT OF THE DISCLOSURE
A nuclear reactor fuel element having improved heat transfer between fuel material and cladding is described.
The element consists of an outer cladding tube divided into an upper fuel section containing a central core of fission-able or mixed fissionable and fertile fuel material, slightly smaller in diameter than the inner surface of the cladding tube and a small lower accumulator section of the cladding tube being which is filled with a low molecular weight gas to transfer heat from fuel material to cladding during irradiation. A plurality of essentially vertical grooves in the fuel section extend downward and communicate with the accumulator section. The radial depth of the grooves is sufficient to provide a thermal gradient between the hot fuel surface and the relatively cooler cladding surface to allow thermal segregation to take place between the low molecular weight heat transfer gas and high molecular weight fission product gases produced by the fuel material during irradiation. The fission product gases migrate to the cooler cladding surface of the groove and descend by gravity into the accumulator section, while the low molecular weight remain in the fuel section, thus reducing diminution of the heat transfer properties of the low molecular weight gas. The accumulation may also contain gettering material to sorb certain high molecular weight gases to prevent their reentering the fuel section when the fuel element is cold.
A nuclear reactor fuel element having improved heat transfer between fuel material and cladding is described.
The element consists of an outer cladding tube divided into an upper fuel section containing a central core of fission-able or mixed fissionable and fertile fuel material, slightly smaller in diameter than the inner surface of the cladding tube and a small lower accumulator section of the cladding tube being which is filled with a low molecular weight gas to transfer heat from fuel material to cladding during irradiation. A plurality of essentially vertical grooves in the fuel section extend downward and communicate with the accumulator section. The radial depth of the grooves is sufficient to provide a thermal gradient between the hot fuel surface and the relatively cooler cladding surface to allow thermal segregation to take place between the low molecular weight heat transfer gas and high molecular weight fission product gases produced by the fuel material during irradiation. The fission product gases migrate to the cooler cladding surface of the groove and descend by gravity into the accumulator section, while the low molecular weight remain in the fuel section, thus reducing diminution of the heat transfer properties of the low molecular weight gas. The accumulation may also contain gettering material to sorb certain high molecular weight gases to prevent their reentering the fuel section when the fuel element is cold.
Description
~ 1 This invention relates to a nuclear reactor f uel element .
More ~p~ciEically, this inven~ion relates ~o a nuclear reactor fuel element having improved heat transfer capabilities between the fuel material and the cladding~
Mechanism~ which affect the radial heat ~ransfer process between the fuel material and the cladding can be considered to bP the actual fuels clad contact area, the gap separation between the f-lel and clad~ the thermal and physical properties : of the fuel and clad mating materials, the surace conditions of the fuel clad interface, radiation, and the inkerstitial fluid (i. e., the ga~).
Of these radial heat transfer mechanisms, the thermal conductivity of the gas pla~s an important roll in determining the gap conductance contribution to the total heat transfer.
Initially, the uel-cladding gap is filled with low molecular weight, high ~he~mal conductivity gas such as helium. Duri.ng bu~n up of the fuel, fission products are generated and a portion of these fission products (xenon and krypton) escape to the plenum region of the fuel element.
2D The resulting accumulation of these gases in the fuel. clad gap results in a lowering of the thermal conductance of the gap by virtue of the lower ~hermal conductivity of the gas mixture. The chemical state and concentration of the fi.ssion products (i.e~, element, oxide or complex compound) also influences the availability of oxygen within the fuel rod~
This in turn~ curtails the o~ygen potential of the fuel which is of first rank impor~ance in determining whether fuel can react chemically with the cladding, These reactions when they occur, result in corrosion of ~he metal and a consequent weakening of the cladding which is the primary barrier to the release of radioactivi~y. Thus any mechanisms which affect the local concentration and or distribution of gaseous species within the plenum is important.
Thermal diffusion is such a mechanism and it consists of a relative motion of the mass components of a gas mixture arising from temperature differences within the gas mixture as established by a temperature difference between two surfaces. Such a movement was experimentally confirmed by Chapman, 5~, and Dootson, F. WO, Phil~ ~6~ 33, 248 ~1917).
In 1938 Clusius, K.~ and Dickelr G., Naturvissenschaften, 26, 547 (1938) used this phenomenon to devise a continuous method of separating mixtures of gases and isotopes. A
more recent theoretical study indicated that a potentially substantial thermal segregation of gases could occur within a fuel rod under certain conditions. SO K~ Loyalka, V. K~
Chandola, L, B. Thomes, ~Clusius Dickel Effects in a Nuclear Fuel Rod" 9 ~ July 1979.
~ nuclear reactor fuel rcd desggn has been developed which takes advantage of, no~ only thermal diffusion~ but also convecti~e segregation to separate the poor thermal conducting high molecular we.ight fission ~ases from the more thermal conducting low molecular weight gases in order to improve heat transfer across the fuel-cladding gap.
As hereinbefore stated, thermal diffusion consists in a rela~ive mo~ion of ~he components of a gas mixture arising from temperature diferenes within the gas mixture as estab-lished by the temperature gradient be~ween two surfaces--in a fuel rod, between the outer surface of th~ fuel and ~he inner surface of the clad. Therefore, in a mixture initially 13 of uniform composition~ it leads to the development of a concentration gradient across ~he gapO Ordinary diffusion ~ends to eliminate the concentration gradien~ and steady-state condition is possi~le in which the separating effect of thermal difusion is balanced by the remixing effect of ordinary diffusion~ In a fuel rod, the axial, radial and circumferential temperature gradients seen by the gas in the gap all contribute ~o a partial separation of the ~omponen~s due to thermal diffusionD It ha~ also been found that gravitationally induced conYeCtion effects will further-more interact with the radial thermally induced concentrationdifferences and ultimately cause a migration o the heavier and li~hter ~aseous compon nts to the bottom and top of the rod, respectively~ The resulting axial concentration differences thus become far grea~er when both convec~ive and th~rmal diffusive effec~s operate together~ than if thermal diffusion acts alone.
The nuclear fuel element of the invention therefore consists of a tubular-shaped ou~er me~allic cladding having an inner surface and sealed ends, the interior of the g r~
-- 4 ~
clad~ing being divided into an upper, relatively long fuel section and a lower, relatively short yas accumulator section, the sections being in gaseous communication with each other.
A central core of actinide fuel ma~erial is disposed within the upper fuel section, the fuel ma~erial being slightly smaller in diameter than ~he inner surface of the cladding to form an annular space therebe~weenO A low molecular weight, high thermal conductivityr heat transfer gas is sealed within the cladding for conducting heat be~ween the 10 fuel material and the inner surace of of the cladding during irradiation of the Euel element. E~tending the length of the fuel section down ~o and in communication with the accumulator section is a~ least one, generally longitudinal groove formed in either the outer surface of fuel, the inner surface of the cladding, or partially in both~ The radial depth of the groove is sufficient to provide a zone of increased temperature difference between the hok outer surface of the uel and the relatively cooler inner surface of th~ cladding, to result in radial thermal 20 segregation between the low molecular weight heat transfer gas and the high molecular weigllt fission product gas, whereby the high molecular weight gases migrate to the relatively cooler cladding surface and flow by gravity down the groove to the accumulator~ In one embodiment;
the accumulator may contain material capable Gf reacting with, or gettering certai~ high molecular weight gas species as a mean~ of retaining the gas to preven~ diffusion into the the fuel section to dilute the heat transfer gas~
This can occur if the temperature gradient between fuel 5 _ and clad were reduced to zero as when the reactor is shut down.
It is therefore the object of the invention to provide a nuclear reactor fuel element having improved heat transfer across the fuel-cladding gap~ It is the o her object of the invention to provide a nuclear reactor fuel element which contains means or separating the low molecular weight heat transfer gas from high molecular weight i~sion product gases, in order to improve heat transfer across the fuel-cladding 10 gap.
Additional objects, advantages and novel features of the invention will be se~ forth in part in the description which follows ~ and in park will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the inventionO The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed ou~
in the appended cl aims .
Fig. 1 is a longitudiual sectional view of the fuel element of the invention~
Fig. 2 is a cross sectional view of the fuel element of Fig~ 1 along line 2~2 showing one embodiment o the o the invention.
Fig~ 3 is a cross-sectional view of the fuel element showing another embodiment of the inventionO
Fig. 4 is ~ cross-sec~ional view of the fuel el~men~
showing still another embodiment of the invention~
Reerring now to FigO 1, there is shown fuel element 10 consisting of an outer cladding tube 12, d:ivided into an upper, relatively long fuel chamber 14~ and a lower, rela-tively short accumulator chamber 16, the chambers being separated by an inwardly extending support ledge 18. Within chamber 14~ supported by ledge 18 is a central fuel core 20, having an outer surface 22 slightly smaller in diameter than the inner surface 24 of cladding ~ube 12, to provide a narrow annular space 26, th rebe~ween~ Evenly spaced about the diameter of surface 24t within the fuel section 14 are a plurality of longitudial grooves 28, which extend through section 14 downward to, and in communication with accumulator section 16. Each groove 28 has a cladding surface 30 and a fuel surface 32 which must be a suff.icien~ dis~ance apart to provide a temperature differential between the surfaces sufficient to result in thermal segrega~ion. Within section 15 i5 located a getter material 34 to sorb certain fission product gases and prevent them from re-entering fuel chamber 14 during periods when the fuel element i5 coolO
As ~hown în Fig 2 r grooves 28 are evenly spaced about 20 the circumference of inner surface 240 In Fig 3 the grooves are shown evenly spaced about outer surface 22 of fuel core 20~ while in Fig 4~ grooves ~ are spaced about both inner surface 24 and outer surface 22. In this embodimen~
it will be necessary to provide an arrangement to prevent rotation of the fuel relative to the clad in order that the grooves remain opposi te each other to insure that the temperature differential is providedO Other me~hods and configurations may be obvious to those skilled in the art, which will provide for local longitudinal zones o ~ 7 --increased temperature difference sufficient to cause r~dial thermal segregation4 The fuel element must contain at least one ~ preferably at least three evenly spaced grooves, to proYide adequa~e separation of gases. Preferably the grooves will extend from the top of ~he fuel section down to the lower accumulator section and may be straigh~ or ~hey may have a vertical spiral configuration.
The depth of the grooves, ~hat is ~he distance between the hot or fuel core surface, and the cooler or cladding surface, must be sufficient ~o provide a local radial tem-perature difference between fuel and cladding to result in a separation between the high moleculer weight fission product gases and the low molecular weight heat transfer gasr It has been found that a temperature difference of at least 60 C between the hot and cold walls is adequate to provide conditiorls for thermal di:~usion connective segregation of component gasPs. The exac~ channel depth ~ will depend upon the particular fuel material being used, the width of the annular space, thermal conductivity of the cladding material and other factors. In yeneral, the depth of the groove, that is the distance between the hot and cooler surfaces~ should be a~ least 0.005 cm (0.002 inches~ and no more than abou~ 0.254 cm (0~1 inches) ~o avoid the onset of convective gas effects from occuring in the ~roover The width of ~he channel may vary ~rom about OrO5 cm (0.02 inches) to about 1 cm (0.4 inches) depending on the interior circumference of ~he cladding and the number of groove s ~
Gettering material suitable for sorbing certain of the fission product gases specie.s such as Cesium 132 from 'che decay of Xenonl33 include zirconium metal chipso This material may be present in the accumulator section as discrete particles or it may be applied as a ~oating to the sec~ion wall. Alternatively~ ~he get~er material may be present in 'che as:~cumulator in ~he form of a vertical, open cylindrical-shaped porous sleeve which would support the fùel material in place of support ledge 18.
The following experiment, made to establish the feasi bility o the invention~ employs a single channel to minimize the accumulation of high molecular weigh~ fission gases within the fuel-clad gap in a nuclear fuel rod.
A simulated fuel rod apparatus was constructed which consisted of a single bore 228 cm long aluminum oxide rod within an aluminum cladding tube. Spacers were fixed to the A1203 "fuel" to maintain a nominal radial fuel-clad gap of h.063 cm. A metal heater wire was placed along the axis of the fuel boreO The fuel surface and centerline temperatures were monitored by -thermocouples placed approx-imately ~cm rom the bo~tom and top of the fuel stack~
Gas sampling ports were installed at the bottom and top plenum o the aluminum tube4 The exterior of the aluminum tube was water-cooled and malntained at a temperature of 20 to 25 C (inlet to outlet~ to establish a horizontal tem-peratllre gradient between the "ueli' and "clad" surfaces~
The results of two experiments are sv.mmarized in the Table below.
- 9 -~
(At.% Xe)Bal.He Gas Gas Gas Top C~L~ Bot. CoL~
Press. Comp~ Comp. Temp. Temp.
Comments (MPa) TOP BotO (K) (R) ~ -- . n _ _ _ _ _ 11.7~ Xe start gas*
80W/m power input Zero hours* 0.52 11~7 1107 320 317 96 hrs 0.31 10O1 26O8 318 325 52% Xe star$ gas 89 W/m power input Z~ro hours 0~35 5252 371 366 18 hrs 0,35 2596 344 563 48 hrs 0.24 2999 343 ~53 1 0 ~
Equilibration time- Approximately 70 hrs.
**Equilibration time: Approximately 8 hrs.
C.L. - Centerline fuel temperature readingO
The results show essentially 99~ Xe at ~he bottom of the rod for an initial starting gas mixture of 43% Heo52~Xe, after ~8 hours of operation.
Thus it can be seen ~ha~ the channels in the fuel element in combination with the placement of an accumulator at ~he bottom of a fuel rod serve to collect the higher molecular weight fission gas products (i.e~ Xe, Kr) created during uel burnup, allowing or a high helium gas concentration to remain at the highest power region ~i.e.~ near the center~ of the fuel rod. This increases the gap conductance in this region~ lowering the fuel centerline ~emperature.
This also maintains the oxygen poten~ial of the fuel by minimizing the buildup of fission products within the gap region, decreasing the extent of fuel/cladding chemical interaction.
More ~p~ciEically, this inven~ion relates ~o a nuclear reactor fuel element having improved heat transfer capabilities between the fuel material and the cladding~
Mechanism~ which affect the radial heat ~ransfer process between the fuel material and the cladding can be considered to bP the actual fuels clad contact area, the gap separation between the f-lel and clad~ the thermal and physical properties : of the fuel and clad mating materials, the surace conditions of the fuel clad interface, radiation, and the inkerstitial fluid (i. e., the ga~).
Of these radial heat transfer mechanisms, the thermal conductivity of the gas pla~s an important roll in determining the gap conductance contribution to the total heat transfer.
Initially, the uel-cladding gap is filled with low molecular weight, high ~he~mal conductivity gas such as helium. Duri.ng bu~n up of the fuel, fission products are generated and a portion of these fission products (xenon and krypton) escape to the plenum region of the fuel element.
2D The resulting accumulation of these gases in the fuel. clad gap results in a lowering of the thermal conductance of the gap by virtue of the lower ~hermal conductivity of the gas mixture. The chemical state and concentration of the fi.ssion products (i.e~, element, oxide or complex compound) also influences the availability of oxygen within the fuel rod~
This in turn~ curtails the o~ygen potential of the fuel which is of first rank impor~ance in determining whether fuel can react chemically with the cladding, These reactions when they occur, result in corrosion of ~he metal and a consequent weakening of the cladding which is the primary barrier to the release of radioactivi~y. Thus any mechanisms which affect the local concentration and or distribution of gaseous species within the plenum is important.
Thermal diffusion is such a mechanism and it consists of a relative motion of the mass components of a gas mixture arising from temperature differences within the gas mixture as established by a temperature difference between two surfaces. Such a movement was experimentally confirmed by Chapman, 5~, and Dootson, F. WO, Phil~ ~6~ 33, 248 ~1917).
In 1938 Clusius, K.~ and Dickelr G., Naturvissenschaften, 26, 547 (1938) used this phenomenon to devise a continuous method of separating mixtures of gases and isotopes. A
more recent theoretical study indicated that a potentially substantial thermal segregation of gases could occur within a fuel rod under certain conditions. SO K~ Loyalka, V. K~
Chandola, L, B. Thomes, ~Clusius Dickel Effects in a Nuclear Fuel Rod" 9 ~ July 1979.
~ nuclear reactor fuel rcd desggn has been developed which takes advantage of, no~ only thermal diffusion~ but also convecti~e segregation to separate the poor thermal conducting high molecular we.ight fission ~ases from the more thermal conducting low molecular weight gases in order to improve heat transfer across the fuel-cladding gap.
As hereinbefore stated, thermal diffusion consists in a rela~ive mo~ion of ~he components of a gas mixture arising from temperature diferenes within the gas mixture as estab-lished by the temperature gradient be~ween two surfaces--in a fuel rod, between the outer surface of th~ fuel and ~he inner surface of the clad. Therefore, in a mixture initially 13 of uniform composition~ it leads to the development of a concentration gradient across ~he gapO Ordinary diffusion ~ends to eliminate the concentration gradien~ and steady-state condition is possi~le in which the separating effect of thermal difusion is balanced by the remixing effect of ordinary diffusion~ In a fuel rod, the axial, radial and circumferential temperature gradients seen by the gas in the gap all contribute ~o a partial separation of the ~omponen~s due to thermal diffusionD It ha~ also been found that gravitationally induced conYeCtion effects will further-more interact with the radial thermally induced concentrationdifferences and ultimately cause a migration o the heavier and li~hter ~aseous compon nts to the bottom and top of the rod, respectively~ The resulting axial concentration differences thus become far grea~er when both convec~ive and th~rmal diffusive effec~s operate together~ than if thermal diffusion acts alone.
The nuclear fuel element of the invention therefore consists of a tubular-shaped ou~er me~allic cladding having an inner surface and sealed ends, the interior of the g r~
-- 4 ~
clad~ing being divided into an upper, relatively long fuel section and a lower, relatively short yas accumulator section, the sections being in gaseous communication with each other.
A central core of actinide fuel ma~erial is disposed within the upper fuel section, the fuel ma~erial being slightly smaller in diameter than ~he inner surface of the cladding to form an annular space therebe~weenO A low molecular weight, high thermal conductivityr heat transfer gas is sealed within the cladding for conducting heat be~ween the 10 fuel material and the inner surace of of the cladding during irradiation of the Euel element. E~tending the length of the fuel section down ~o and in communication with the accumulator section is a~ least one, generally longitudinal groove formed in either the outer surface of fuel, the inner surface of the cladding, or partially in both~ The radial depth of the groove is sufficient to provide a zone of increased temperature difference between the hok outer surface of the uel and the relatively cooler inner surface of th~ cladding, to result in radial thermal 20 segregation between the low molecular weight heat transfer gas and the high molecular weigllt fission product gas, whereby the high molecular weight gases migrate to the relatively cooler cladding surface and flow by gravity down the groove to the accumulator~ In one embodiment;
the accumulator may contain material capable Gf reacting with, or gettering certai~ high molecular weight gas species as a mean~ of retaining the gas to preven~ diffusion into the the fuel section to dilute the heat transfer gas~
This can occur if the temperature gradient between fuel 5 _ and clad were reduced to zero as when the reactor is shut down.
It is therefore the object of the invention to provide a nuclear reactor fuel element having improved heat transfer across the fuel-cladding gap~ It is the o her object of the invention to provide a nuclear reactor fuel element which contains means or separating the low molecular weight heat transfer gas from high molecular weight i~sion product gases, in order to improve heat transfer across the fuel-cladding 10 gap.
Additional objects, advantages and novel features of the invention will be se~ forth in part in the description which follows ~ and in park will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the inventionO The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed ou~
in the appended cl aims .
Fig. 1 is a longitudiual sectional view of the fuel element of the invention~
Fig. 2 is a cross sectional view of the fuel element of Fig~ 1 along line 2~2 showing one embodiment o the o the invention.
Fig~ 3 is a cross-sectional view of the fuel element showing another embodiment of the inventionO
Fig. 4 is ~ cross-sec~ional view of the fuel el~men~
showing still another embodiment of the invention~
Reerring now to FigO 1, there is shown fuel element 10 consisting of an outer cladding tube 12, d:ivided into an upper, relatively long fuel chamber 14~ and a lower, rela-tively short accumulator chamber 16, the chambers being separated by an inwardly extending support ledge 18. Within chamber 14~ supported by ledge 18 is a central fuel core 20, having an outer surface 22 slightly smaller in diameter than the inner surface 24 of cladding ~ube 12, to provide a narrow annular space 26, th rebe~ween~ Evenly spaced about the diameter of surface 24t within the fuel section 14 are a plurality of longitudial grooves 28, which extend through section 14 downward to, and in communication with accumulator section 16. Each groove 28 has a cladding surface 30 and a fuel surface 32 which must be a suff.icien~ dis~ance apart to provide a temperature differential between the surfaces sufficient to result in thermal segrega~ion. Within section 15 i5 located a getter material 34 to sorb certain fission product gases and prevent them from re-entering fuel chamber 14 during periods when the fuel element i5 coolO
As ~hown în Fig 2 r grooves 28 are evenly spaced about 20 the circumference of inner surface 240 In Fig 3 the grooves are shown evenly spaced about outer surface 22 of fuel core 20~ while in Fig 4~ grooves ~ are spaced about both inner surface 24 and outer surface 22. In this embodimen~
it will be necessary to provide an arrangement to prevent rotation of the fuel relative to the clad in order that the grooves remain opposi te each other to insure that the temperature differential is providedO Other me~hods and configurations may be obvious to those skilled in the art, which will provide for local longitudinal zones o ~ 7 --increased temperature difference sufficient to cause r~dial thermal segregation4 The fuel element must contain at least one ~ preferably at least three evenly spaced grooves, to proYide adequa~e separation of gases. Preferably the grooves will extend from the top of ~he fuel section down to the lower accumulator section and may be straigh~ or ~hey may have a vertical spiral configuration.
The depth of the grooves, ~hat is ~he distance between the hot or fuel core surface, and the cooler or cladding surface, must be sufficient ~o provide a local radial tem-perature difference between fuel and cladding to result in a separation between the high moleculer weight fission product gases and the low molecular weight heat transfer gasr It has been found that a temperature difference of at least 60 C between the hot and cold walls is adequate to provide conditiorls for thermal di:~usion connective segregation of component gasPs. The exac~ channel depth ~ will depend upon the particular fuel material being used, the width of the annular space, thermal conductivity of the cladding material and other factors. In yeneral, the depth of the groove, that is the distance between the hot and cooler surfaces~ should be a~ least 0.005 cm (0.002 inches~ and no more than abou~ 0.254 cm (0~1 inches) ~o avoid the onset of convective gas effects from occuring in the ~roover The width of ~he channel may vary ~rom about OrO5 cm (0.02 inches) to about 1 cm (0.4 inches) depending on the interior circumference of ~he cladding and the number of groove s ~
Gettering material suitable for sorbing certain of the fission product gases specie.s such as Cesium 132 from 'che decay of Xenonl33 include zirconium metal chipso This material may be present in the accumulator section as discrete particles or it may be applied as a ~oating to the sec~ion wall. Alternatively~ ~he get~er material may be present in 'che as:~cumulator in ~he form of a vertical, open cylindrical-shaped porous sleeve which would support the fùel material in place of support ledge 18.
The following experiment, made to establish the feasi bility o the invention~ employs a single channel to minimize the accumulation of high molecular weigh~ fission gases within the fuel-clad gap in a nuclear fuel rod.
A simulated fuel rod apparatus was constructed which consisted of a single bore 228 cm long aluminum oxide rod within an aluminum cladding tube. Spacers were fixed to the A1203 "fuel" to maintain a nominal radial fuel-clad gap of h.063 cm. A metal heater wire was placed along the axis of the fuel boreO The fuel surface and centerline temperatures were monitored by -thermocouples placed approx-imately ~cm rom the bo~tom and top of the fuel stack~
Gas sampling ports were installed at the bottom and top plenum o the aluminum tube4 The exterior of the aluminum tube was water-cooled and malntained at a temperature of 20 to 25 C (inlet to outlet~ to establish a horizontal tem-peratllre gradient between the "ueli' and "clad" surfaces~
The results of two experiments are sv.mmarized in the Table below.
- 9 -~
(At.% Xe)Bal.He Gas Gas Gas Top C~L~ Bot. CoL~
Press. Comp~ Comp. Temp. Temp.
Comments (MPa) TOP BotO (K) (R) ~ -- . n _ _ _ _ _ 11.7~ Xe start gas*
80W/m power input Zero hours* 0.52 11~7 1107 320 317 96 hrs 0.31 10O1 26O8 318 325 52% Xe star$ gas 89 W/m power input Z~ro hours 0~35 5252 371 366 18 hrs 0,35 2596 344 563 48 hrs 0.24 2999 343 ~53 1 0 ~
Equilibration time- Approximately 70 hrs.
**Equilibration time: Approximately 8 hrs.
C.L. - Centerline fuel temperature readingO
The results show essentially 99~ Xe at ~he bottom of the rod for an initial starting gas mixture of 43% Heo52~Xe, after ~8 hours of operation.
Thus it can be seen ~ha~ the channels in the fuel element in combination with the placement of an accumulator at ~he bottom of a fuel rod serve to collect the higher molecular weight fission gas products (i.e~ Xe, Kr) created during uel burnup, allowing or a high helium gas concentration to remain at the highest power region ~i.e.~ near the center~ of the fuel rod. This increases the gap conductance in this region~ lowering the fuel centerline ~emperature.
This also maintains the oxygen poten~ial of the fuel by minimizing the buildup of fission products within the gap region, decreasing the extent of fuel/cladding chemical interaction.
Claims (10)
1. In a nuclear reactor fuel element having a tubular-shaped outer metallic cladding having an inner surface and sealed upper and lower ends, a central cylindrical-shaped core of actinide fuel material having an outer surface disposed within the cladding tube to form a fuel section, the diameter of the outer surface being slightly less than the diameter of the inner surface of the cladding to provide a narrow annular space therebetween, and low molecular weight gas sealed within the cladding for improving heat transfer during irradiation between the hot outer surface of the fuel material and the relatively cooler inner surface of the cladding, whereby during irradiation of the fuel element, fissioning of the actinide fuel material produces high molecular weight fission product gases which mix with the low molecular weight gas and reduce the heat transfer capability of that gas, the improvement comprising, a small gas accumulator section within the cladding tube below the fuel section in communication with the fuel section, and at least one longitudinal groove means formed in either the outer surface of the fuel, the inner surface of the cladding or partially in both, said groove means extending the length of said fuel section to communicate with said gas accumulator section, said groove means communicating with said annular space to provide a local zone of increased temperature difference between the hot fuel surface and the relatively cooler cladding surface throughout the length of the fuel section, the temperature difference being sufficient to cause radial thermal segregation between the low molecular weight gas and the high molecular weight fission gas whereby the high molecular weight fission gas migrates to the cooler cladding surface by thermal diffusion and descends by gravity down the surface to the lower accumulator section, while the low molecular weight gas remains in the upper fuel section, thus separating the high molecular weight fission gases from the low molecular weight heat transfer gas, thereby maintaining the heat transfer capabilities of the heat transfer gas.
2. The fuel element of claim 1 wherein the fuel section of the fuel contains at least three evenly spaced longitudinal groove means.
3. The fuel element of claim 2 wherein the difference in temperature between the hot fuel surface and the relatively cooler cladding surface at the groove means is at least 60°C.
4. The fuel element of claim 3 wherein the distance, between the hot fuel surface and the cooler cladding at the groove means is at least 0.005 cm.
5. The fuel element of claim 4 wherein the distance between the hot fuel surface and cooler cladding surface at the groove means is from 0.005 cm to 0.25 cm.
6. The fuel element of claim 5 wherein the accumulator section contains a getter to react with certain high molecular weight fission gases to prevent them from re-entering the fuel chamber when the fuel element has cooled.
7. The fuel element of claim 6 where the getter is zirconium metal.
8. The fuel element of claim 7 wherein the groove means are located in the inner surface of the cladding.
9. The fuel element of claim 7 wherein the groove means are located in the outer surface of the fuel material.
10. The fuel element of claim 7 wherein the groove means are located partially in the inner surface of the cladding and partially in the outer surface of the fuel material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US35446582A | 1982-03-03 | 1982-03-03 | |
| US354,465 | 1982-03-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1195441A true CA1195441A (en) | 1985-10-15 |
Family
ID=23393439
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000421403A Expired CA1195441A (en) | 1982-03-03 | 1983-02-11 | Nuclear reactor fuel element having improved heat transfer |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS58166286A (en) |
| CA (1) | CA1195441A (en) |
| DE (1) | DE3307610A1 (en) |
| FR (1) | FR2522865A1 (en) |
| GB (1) | GB2116354B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2738387B1 (en) * | 1995-09-05 | 1997-09-26 | Commissariat Energie Atomique | ACTINID BURNER FUEL ELEMENT |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3274066A (en) * | 1965-10-05 | 1966-09-20 | Lloyd R Zumwalt | Unpurged fuel element |
| GB1292335A (en) * | 1969-04-23 | 1972-10-11 | Nuclear Power Group Ltd | Improvements in and relating to fuel elements for nuclear reactors |
| JPS51148193A (en) * | 1975-06-13 | 1976-12-20 | Toshiba Corp | A nuclear fuel element |
| JPS54152781A (en) * | 1978-05-24 | 1979-12-01 | Power Reactor & Nuclear Fuel Dev Corp | Nuclear fuel pellet |
| DE2823061A1 (en) * | 1978-05-26 | 1979-11-29 | Kraftwerk Union Ag | Pelletised fuel for water reactor - has fission product duct through pellet centres connected to grooves at periphery |
-
1983
- 1983-02-11 CA CA000421403A patent/CA1195441A/en not_active Expired
- 1983-02-15 GB GB08304111A patent/GB2116354B/en not_active Expired
- 1983-03-02 FR FR8303416A patent/FR2522865A1/en not_active Withdrawn
- 1983-03-03 DE DE19833307610 patent/DE3307610A1/en not_active Withdrawn
- 1983-03-03 JP JP58035222A patent/JPS58166286A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB2116354A (en) | 1983-09-21 |
| GB2116354B (en) | 1985-09-18 |
| FR2522865A1 (en) | 1983-09-09 |
| JPS58166286A (en) | 1983-10-01 |
| GB8304111D0 (en) | 1983-03-16 |
| DE3307610A1 (en) | 1983-09-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |