EP0281680B1 - Verfahren zur Reinigung einer Zusammenstellung von abgebrannten Brennelementen - Google Patents

Verfahren zur Reinigung einer Zusammenstellung von abgebrannten Brennelementen Download PDF

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Publication number
EP0281680B1
EP0281680B1 EP19870118413 EP87118413A EP0281680B1 EP 0281680 B1 EP0281680 B1 EP 0281680B1 EP 19870118413 EP19870118413 EP 19870118413 EP 87118413 A EP87118413 A EP 87118413A EP 0281680 B1 EP0281680 B1 EP 0281680B1
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EP
European Patent Office
Prior art keywords
alkali metal
chamber
fuel assembly
temperature
fuel
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
Application number
EP19870118413
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English (en)
French (fr)
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EP0281680A1 (de
Inventor
Dong K. Chung
Charles Earl Jones, Jr.
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Boeing North American Inc
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Rockwell International Corp
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Filing date
Publication date
Application filed by Rockwell International Corp filed Critical Rockwell International Corp
Publication of EP0281680A1 publication Critical patent/EP0281680A1/de
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Expired legal-status Critical Current

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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof

Definitions

  • the present invention broadly relates to a method of cleaning a spent fuel assembly which has been removed from service in a nuclear reactor. It particularly relates to a method of cleaning such a spent fuel assembly contaminated with a radioactive alkali metal and in which the fuel assembly comprises a spent fissile material selected from the group consisting of oxides and carbides of uranium and/or plutonium or a metallic uranium/plutonium alloy.
  • the typical breeder reactor utilizes an alkali metal as a coolant.
  • a primary coolant is circulated via a pump through a core of fuel assemblies and then through a heat exchanger from which thermal energy is extracted by indirect heat exchange with a secondary coolant.
  • the primary coolant picks up a certain amount of radioactivity in passing through the core. All components in contact with this primary coolant also become contaminated with the radioactive constituents. Thus, any component in contact with such coolant after removal from service must be cleaned, not only to remove the highly reactive coolant but also the radioactive contaminants.
  • One method utilized for cleaning such components is to wash them with an organic solvent such as alcohol or wash them with water.
  • the disadvantage of these methods is that they produce a large volume of liquid, low-level radioactive waste with its attendant storage and disposal problems.
  • Another technique utilized is to heat the contaminated parts to a sufficient temperature to volatilize the alkali metal and the radioactive constituents.
  • a fuel assembly removed from a breeder reactor presents a particularly unique problem.
  • the cladding of some of the individual fuel pins comprising the fuel assembly could have been cracked or ruptured such that some of the alkali metal will be within the cladding of the individual pins.
  • the spent fuel assembly after removal from service, will continue to generate some heat generally referred to as decay heat.
  • the individual pins could generate sufficient heat to rupture the cladding of those pins which were still intact with the release of more radioactive material.
  • the use of external heating would be equally inapplicable. Obviously there is a need for a procedure uniquely adapted to the cleaning of a spent fuel assembly which has been in contact with an alkali metal coolant.
  • FR-A-2.394.871 discloses one such procedure, wherein the fuel assembly is placed in a sealed chamber.
  • the alkali metal is volatilized in a process, wherein the chamber is repeatedly cooled by a cooling gas and briefly evacuated by connecting the chamber with a large evacuated vessel.
  • the volatilized alkali metal is thereby transferred to the large vessel, where it condenses and can be removed.
  • the present invention provides a method of decontaminating a fuel assembly contaminated with a radioactive alkali metal.
  • a fuel assembly comprises a plurality of elongated metal pins or tubes containing a spent fissile material.
  • the present invention is particularly suitable for fuel assemblies containing a fissile material selected from the group consisting of carbides and oxides of uranium and/or plutonium and which are going to be reprocessed.
  • the method comprises a plurality of sequential steps. First, the fuel assembly is placed in a sealed chamber. A heated inert gas is passed through the chamber to heat the fuel assembly to a temperature sufficient to cause evaporation of the alkali metal but not so high as to affect the structural integrity of the individual metal pins.
  • the chamber is evacuated to a pressure of about less than 6,7 N/m2 (0.05 mm of mercury) and preferably less than 0,67 N/m2 (0.005 mm of mercury) and maintained at that pressure until the temperature of the fuel assembly increases to a level which could affect the structural integrity of the metal pin, typically about 540°C (1000°F).
  • a cool, inert gas is introduced through the chamber and the fuel assemblies to reduce the temperature of the fuel assembly back to a safe level, typically about 430°C (800°F).
  • the vacuum and cooling steps are repeated as often as required to insure removal of substantially all of the radioactive alkali metal.
  • the decontaminated fuel assemblies may then be removed from the chamber and are suitable for shipment to a chemical reprocessing center.
  • the inert gas utilized is argon and the gases removed from the sealed chamber are passed in indirect heat exchange relationship with a coolant for the condensation and removal of any vaporized alkali metal contained therein.
  • the coolant will be one which is inert with respect to the alkali metal, for example, alcohol or other organic liquids.
  • the gas removed from the chamber when it is being evacuated is also passed through a cryogenic trap to insure substantially complete removal of any remaining radioactive alkali metal from the gas.
  • the alkali metal will be either sodium or a mixture of sodium and potassium.
  • the method of the present invention is particularly applicable for use in a fuel storage building which is maintained in an inert atmosphere and generally is located adjacent the reactor from which the fuel assemblies are removed.
  • the inert gas within the facility may be used for the heating and cooling, and after treatment for removal of sodium or other alkali metal, may be introduced into an existing gas cleaning facility which is provided within such storage buildings.
  • the sole figure is a schematic of an arrangement of apparatus for use in the practice of the present invention.
  • the present invention provides a method of decontaminating fuel assemblies which is uniquely suited for fuel assemblies removed from a breeder reactor.
  • a coolant typically sodium potassium or a mixture thereof
  • the reactor core comprises an array of fuel assemblies provided with passageways for the circulation of the coolant therethrough.
  • Each fuel assembly is in turn comprised of a plurality of fuel pins.
  • the fuel pin typically is an elongated, stainless steel cylinder or tube which is sealed at each end and contains, throughout a substantial portion of its length, fuel pellets.
  • the outer metal portion of the pin generally is referred to as the cladding.
  • the fuel pellet is formed from an oxide or carbide of uranium and/or plutonium, some of the uranium may be converted to plutonium during service as a result of exposure to the fast neutrons.
  • breeder reactor facilities include an adjacent fuel storage building which is maintained under an inert atmosphere, typically argon gas. New fuel assemblies for loading in the reactor as well as spent fuel assemblies removed from the reactor, are temporarily stored in such a facility. It is an advantage of the present invention that it is particularly suited for use in such an environment.
  • the apparatus includes a sealed chamber 12 for containing a spent fuel assembly 14.
  • Fuel assembly 14 rests on a baffle member 16 and extends therethrough.
  • Baffle member 16 engages the outer periphery of fuel assembly 14 to insure that those gases entering an upper portion 18 of chamber 12 must flow through fuel assembly 14 and into a lower portion 20 of chamber 12.
  • Lower portion 20 of chamber 12 is provided with a recirculation outlet conduit 24 which is in fluid communication with a blower 26 which discharges into a recirculation inlet conduit 28 which is located above baffle member 16.
  • conduit 28 also is provided with an electrical heater 30.
  • Blower 26 is driven by a motor 32 which is interconnected to blower 26 via a magnetic coupling 34. Typically there also will be provided some means for preventing the transfer of heat from blower 26 back to magnetic coupling 34. As depicted, this would be accomplished by a cooling jacket 36 provided with an inlet and outlet for the flow of a cooling fluid therethrough.
  • Chamber 12 also includes a conduit 38 and valve 40 for the introduction of an inert gas into chamber 12 in upper portion 18. Any inert gas may be used, typically the inert gas will be argon, particularly when the method of the present invention is practiced within a fuel storage cell which is maintained under an inert atmosphere of argon.
  • An upper end of chamber 12 is provided with a discharge conduit 42 for conducting gas exiting upper portion 18 of chamber 12 to a condenser 44.
  • Condenser 44 includes means for passing a coolant through an internal cooling coil 46 to condense any sodium vapors contained in the gas passing therethrough. Generally the coolant will be an organic fluid which is inert with respect to the alkali metal to prevent any reaction in the event of a leak.
  • Condenser 44 further includes a sump portion 48 for the collection of condensed alkali metal coolant.
  • a conduit 50 provides fluid communication between condenser 48 and a cryogenic trap 52 and also a bypass conduit 54.
  • cryogenic trap 52 Downstream of cryogenic trap 52 are two vacuum pumps 56 and 58. Pumps 56 and 58 are in fluid communication with cryogenic trap 52 via conduits and valves 60,61 and 62. Pump 58 is also provided with a discharge conduit 64.
  • a fuel assembly 14 is placed within chamber 12 which is then sealed.
  • An inert gas typically argon, is introduced into chamber 12 through conduit 38 and valve 40.
  • spent fuel assembly 14 will have an initial temperature of about 400°F (204°C).
  • Power is supplied to motor 32 which drives blower 26 via magnetic coupling 34 to cause circulation of the argon from lower portion 20 of chamber 12 through conduit 24 and back to upper portion 18 of chamber 12 via conduit 28. Power also is supplied to electric heater 30 until the temperature of the fuel assembly is increased to about 430°C (800°F).
  • vacuum pump 58 will be a dry, reciprocating vacuum pump which is operated for a sufficient time to decrease the chamber pressure from atmospheric to approximately 1330 N/m2 (10 mm of mercury), during which time blower 26 is maintained in operation.
  • secondary vacuum pump 56 typically an oil-sealed rotary pump
  • Valves 60 and 62 are opened and 61 closed.
  • the chamber pressure is then further decreased from 1330 N/m2 (10 mm of mercury) to at least 6,7 N/m2 (.05 mm of mercury).
  • the secondary vacuum pump 56 is operated until the pressure within chamber 12 is reduced to 0,67 N/m3 (0.005 mm of mercury) or less. During this time, blower 26 is inoperative.
  • the gas and entrained sodium vapor is withdrawn via conduit 42 and cooled in condenser 44. Any residual sodium vapor leaving through conduit 50 is removed in cryogenic trap 52.
  • the condensed sodium may be recovered at a later point in time. Typically, this would be accomplished in condenser 44, for example, by increasing the coolant temperature to melt the sodium and then draining it from sump 48.
  • the fuel assembly temperature will continue to increase as a result of the decay heat. When the temperature reaches the maximum safe temperature for the cladding of the individual fuel pins, generally about 540°C (1000°F), the vacuum treatment is stopped.
  • Valves 60, 61 and 62 are closed and pumps 56 and 58 turned off.
  • Valve 40 is open and chamber 12 is filled with argon gas to one atmosphere via conduit 38. After chamber 12 is filled with gas, valve 40 is closed and valve 55 opened. Power is supplied to motor 32 to drive blower 26 and the majority of the argon gas is circulated through valve 55 and conduit 54 in a reverse direction through condenser 44 and back to chamber 12 via conduit 42. The cause of the reverse circulation is the backpressure created by the presence of heater 30 in conduit 28.
  • a valve could be provided in conduit 28 downstream of heater 30 to ensure that all of the gas circulated through conduit 54.
  • the gas is circulated through chamber 12 and fuel assembly 14 until the temperature of the fuel assembly is reduced back to a desired level, typically below 430°C (800°F).
  • the vacuum treatment and cooling are repeated as required to insure substantially complete removal of the radioactive alkali metal contaminant.
  • the number of cycles required is readily determinable through experimentation. It will be appreciated that various other valves and instrumentation such as pressure sensors, temperature sensors, also would normally be incorporated as well as additional redundant gas cleaning techniques. However, those matters are well within the skill of those versed in the art.

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  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Food Science & Technology (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Cleaning By Liquid Or Steam (AREA)
  • Cleaning In General (AREA)

Claims (9)

  1. Verfahren zum Dekontaminieren einer Anordnung (14) von Brennstoffelementen, die mit einem radioaktiven Alkalimetall kontaminiert sind, wobei jede Brennstoffelementanordnung eine Mehrzahl von Metallstiften aufweist, die verbrauchtes spaltbares Material enthalten, mit folgenden Schritten:
    (a) Anordnen der Brennstoffelementanordnung (14) in einer abgedichteten Kammer (12),
    (b) Umwälzerhitzen unter Durchführung eines erhitzten, inerten Gases durch die Kammer, um die Brennstoffelementanordnung auf eine Temperatur aufzuheizen, die ausreichend für eine Verflüchtigung des Alkalimetalls, aber nicht ausreichend zur Beschädigung der Metallstifte ist,
    (c) Evakuieren der Kammer mittels Pumpe auf einen Druck von weniger als 6,7 N/m² (0,05 mm Hg) zur weiteren Förderung der Verflüchtigung des Alkalimetalls und Halten der Kammer bei diesem Druck, bis die Zerfallshitze des spaltbaren Materials einen Temperaturanstieg der Brennstoffelementanordnung auf einen Pegel bewirkt, der nachteilig für die Unversehrtheit der Metallstifte wäre,
    (d) Umwälz-Kühlen der Brennstoffelementanordnung durch Hindurchführen eines kühlen inerten Gases durch die Kammer, um die Temperatur der Brennstoffelementanordnung auf einen gewünschten Pegel zu verringern,
    (e) Wiederholen der Evakuierungs- und Kühlschritte in erforderlichem Ausmaß, um die Entfernung von im wesentlichen allem radioaktivem Alkalimetalls sicherzustellen, und
    (f) Herausnehmen der dekontaminierten Brennstoffelementanordnungen (14) aus der Kammer (12).
  2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das spaltbare Material aus der Karbide und Oxyde enthaltenden Gruppe gewählt ist, daß die Umwälzerhitzung gemäß Schritt (b) mit auf eine Temperatur von 430°C (800°F) aufgeheiztem Argon durchgeführt wird, daß die Umwälz-Kühlung im Schritt (d) mit Argon bewirkt und bei einer Temperatur von 540°C (1.000°F) begonnen und bei einer Temperatur von 430°C (800°F) beendet wird, wobei die Schritte (c) und (d) in erforderlicher Anzahl wiederholt werden, um die Entfernung von im wesentlichen allem radioaktivem Alkalimetall sicherzustellen.
  3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß Gas, das aus der abgedichteten Kammer (12) in den Schritten (c) und (d) ausgetreten ist, in indirekter wärmeaustauschbeziehung mit einem Kühlmittel für die Kondensation und Entfernung von jeglichem verdampftem Alkalimetall aus ihm geführt wird.
  4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß das beim Schritt (c) austretende Gas ferner durch eine Tiefsttemperaturfalle (52) geleitet wird, um eine im wesentlichen vollständige Entfernung jeglichen verbleibenden radioaktiven Alkalimetalls aus dem Gas sicherzustellen.
  5. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die abgedichtete Kammer (12) in einem Brennstoffelement-Lagergebäude angeordnet ist, das in einer inerten Atmosphäre gehalten ist.
  6. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das Alkalimetall Natrium ist.
  7. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das Alkalimetall eine Mischung aus Natrium und Kalium ist.
  8. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Kammer (12) im Schritt (c) auf einen Druck von weniger als ungefähr 0,67 N/m² (0,005 mm Quecksilber) evakuiert wird.
  9. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die von Verunreinigungen befreiten Brennstoffelementanordnungen (14) für die Wiedergewinnung von spaltbarem Material von diesen verarbeitet werden.
EP19870118413 1987-03-09 1987-12-11 Verfahren zur Reinigung einer Zusammenstellung von abgebrannten Brennelementen Expired EP0281680B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US2332187A 1987-03-09 1987-03-09
US23321 1987-03-09

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EP0281680A1 EP0281680A1 (de) 1988-09-14
EP0281680B1 true EP0281680B1 (de) 1992-03-11

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JP (1) JPS63235900A (de)
DE (1) DE3777392D1 (de)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH09178895A (ja) * 1996-04-09 1997-07-11 Kawasaki Heavy Ind Ltd 高速炉炉心構成要素のナトリウム除去処理設備
FR2803083B1 (fr) * 1999-12-24 2002-05-10 Framatome Sa Procede et dispositif de nettoyage d'un assemblage de combustible d'un reacteur nucleaire
DE102006042501B4 (de) * 2006-09-07 2010-11-25 Eisenmann Anlagenbau Gmbh & Co. Kg Verfahren und Anlage zum Trocknen von Gegenständen
FR2933227B1 (fr) * 2008-06-25 2010-07-30 Commissariat Energie Atomique Procede de traitement d'une structure contenant du sodium et une matiere radioactive

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DE2727360C2 (de) * 1977-06-16 1986-02-27 INTERATOM GmbH, 5060 Bergisch Gladbach Verfahren und Vorrichtung zur Abdestillation von Flüssigmetall von Reaktorkernelementen
JPS63186195A (ja) * 1987-01-27 1988-08-01 三菱原子力工業株式会社 使用済炉心構成要素洗浄装置

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DE3777392D1 (de) 1992-04-16
EP0281680A1 (de) 1988-09-14
JPS63235900A (ja) 1988-09-30

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