Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C15/00—Cooling arrangements within the pressure vessel containing the core; Selection of specific coolants
  • G21C15/18—Emergency cooling arrangements; Removing shut-down heat
• • 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

Definitions

• the present invention relates to a nuclear reactor of the kind described in the claims.
• Critics of the nuclear power safety are questioning whether the above-mentioned measures are carried out in the right way and at the right time. This was, for example, not the case in the Three Mile Island accident.
• the object of the invention is to provide an emergency recir- culation system which permits a higher pressure drop over the core than what is permitted by the prior art as disclosed by the European patent application with publication number 157 321.
• the density difference between cold water and hot water is utilized to achieve pressure balance between a first density lock provided below the core and a second density lock provided above the core.
• the density difference between steam and cold water is utilized, which is considerably greater than the density difference between cold water and hot water, for achieving pressure balance between a first density lock provided below the core and a steam column and a column of cold water.
• Such an emergency recirculation system is achieved with the aid of the features described in the characterizing part of claim 1.
• Another object of the invention is to provide a passive cooling system which may be arranged in the nuclear reactor so as to enter into force when necessary. Such a passive cooling system is achieved with the aid of the features described in the characterizing part of claim 10.
• a nuclear reactor system according to the invention which is designed such that no actions have to be taken in an emergency situation, whereby the above- mentioned objections to the safety of the nuclear reactor are eliminated.
• the configuration of the system is such that each failure which is possible in reality leads to the reactor reaching a stable state of shutdown and ensured long-term cooling without any external actions being required.
• the core 1 is located at the bottom of a large reactor vessel 20, the lower part 30 of which may be made of prestressed concrete. Heat generated in the reactor is extracted, through existing circulation systems for cooling water, for useful purposes via heat exchangers, in the described example in the form of four steam generators 22a, 22b, two of these being shown in Figure 3. These steam generators 22a, 22b are arranged one in each circulation system and are preferably designed as steam generators in conventional pressurized-water reactors. From the steam generators 22a, 22b, the cooling water is transported back to the reactor by means of four main recirculation pumps 23, 24, which are arranged one in each respective recirculation system.
• Each pump 23, 24 delivers the water in its recirculation system to a connection piece in the upper part 25 of the reactor vessel.
• the cooling water flows down to the under side 27 of the core 1 through a number of channels 2a, arranged in an annular flow conductor 2, which also comprises channels 2b for upwardly-flowing water from the outlet 28 of the core.
• a cross section through the flow conductor is shown in Figure 2.
• the cooling water now heated, flows radially outwards through the outlets 28, which open out into the upwardly-extending channels 2b.
• the cooling water has reached the upper end of these upwardly-extending channels 2b, the flow is collected in an annular outlet header 4 before it is transported further to the steam generators 22a, 22b through four conduits 5.
• the inlets 6, 7 for water coming from the steam generators 22a, 22b are of two kinds. Half of the inlets 6 open out directly into a main space 3 provided in the upper part 25 of the vessel, whereas the other half of the inlets 7, where the water has a somewhat higher pressure, open out into an annular evaporator inlet header 8 provided inside the main space 3. From the evaporator inlet header 8, the flow passes as a driving flow to a number of injector pumps 9, arranged one in each of the downwardly-extending flow channels 2a in the flow conductor 2, whereby the water arriving at the main space 3 through the inlets 6 is pressurized. The pressu ⁇ rized mixture then flows on through the channels 2a to the underside 27 of the core.
• a partially tapered space 11 open at the top and the bottom, which is filled with pressure-maintaining steam except at the bottom thereof.
• Pressure-maintaining steam is supplied to the space via a conduit 10 from an external source such as an electric steam boiler.
• the space 11 is filled with reactor water which, at least in its surface layer 42, is saturated with pressure-maintaining steam.
• the pressure-maintaining steam also communicates openly via at least one condenser 15 with the water 29 in the upper part 25 of the reactor vessel which emanates from half of the steam generators 22a and which is separated from this water 29 by a relatively thin layer of water 26 saturated with pressure-maintaining steam.
• the satu- ration of this layer 26 is suitably achieved and maintained by arranging the conduit 10 for supply of pressure-maintaining steam immersed in the water 29. Because of the pressure drop across the core 1 and its inlet 27, the water level above the outlet 28 of the core is several metres lower than the water level for the water 26,29 in the upper part 25 of the reactor vessel. Both the water 26, 29 in the upper part of the reactor vessel and the water at the inlet 27 of the core communicate openly with a large volume of water with a high content of the neutron poison boric acid. The temperature of this pool water, which fills up the main part of the lower part 30 of the reactor vessel, is lower than 100°C. The pool water is divided into an inner volume 21 and an outer volume 12.
• the pool water is cooled with a cooling system, not shown in the figure.
• the mentioned direct hydraulic con ⁇ tact between hot reactor water and cold pool water occurs in packs of parallel vertical pipes, designated density locks 13, 14, the upper part of which contains hot reactor water whereas the lower part thereof contains cold pool water.
• the level of the interface is monitored with temperature measuring equip ⁇ ment.
• the main recirculation pumps 24 which are responsible for the driving flow of the injector pumps 9 are speed-controlled and controlled by a temperature meter in the lower density lock 14 such that the interface between hot reactor water and cold pool water under normal operating conditions is maintained at a predetermined level.
• This type of arrangement is previously known from the so-called PIUS concept and is described, inter alia, in ABB Journal No. 2, 1990. With these arrangements, pool water is prevented from penetrating into the core 1 during normal operation of the reactor.
• the designation 33 relates to a safety valve.
• a coolant preferably in the form of liquid ammonia
• a coolant is supplied to the secondary side of the condenser 15, whereby water flowing up through the space 11 from the core is cooled under evaporation of the coolant, the ammonia, in the condenser.
• water is condensed and is supplied to the water 26, 29 in the upper part 25 of the reactor vessel.
• the previously described forced circulation through the core 1 by means of the recirculation systems for cooling water ceases, and the core 1 is then cooled only by evaporation of pool water entering through the lower density lock 14.
• the condenser is supplied, as shown in Figure 3, with liquid coolant, ammonia, via the supply conduit 35 connected to a side outlet 19 in an intermediate vessel 17 which is supplied with a limited flow of coolant through a restrictor 37 from a storage tank 16.
• the evaporated coolant is conducted from the condenser 15 via a conduit 36 to an air cooler 34, which in Figure 3 is shown arranged in a cooling tower, where it is cooled and condensed through ambient air which is self- circulating by means of chimney effect.
• the liquid coolant is returned to the storage tank 16 via a conduit 43. This ensures a completely passive decay power cooling in the emergency circulation system.
• the liquid coolant is prevented from reaching the condenser 15 via the side outlet 19 in the inter- mediate vessel 17 by returning it to the storage tank by means of a mammoth pump effect in the conduit circuit 38, whereby the level of liquid coolant in the intermediate vessel 17 does not reach the side outlet 19.
• This restoring mammoth pump effect in the conduit circuit 38 is achieved by passing a minor part of the liquid coolant to a restrictor 39 and eva ⁇ porating it in an evaporator 18, whereupon steam is returned to the conduit circuit 38 and, by the mammoth pump effect, moves up the liquid coolant to a vessel 41 from where it runs back down into the storage tank 16.
• the evaporated part of the coolant is led to the air cooler 34, where it is cooled and condensed through ambient air which is self-circulating by means of the chimney effect.
• the liquid coolant is returned to the storage tank 16 via a conduit 43.
• the evaporation in the evaporator 18 is achieved by supplying hot cooling water from one of the main recirculation systems of the reactor to the primary side of the evaporator 18 by connecting it as a small evaporator circuit 40 in parallel with the reactor to one of the recir ⁇ culation systems of the reactor.
• the main recirculation pumps 23, 24 rapidly stop, and when the core is no longer fed with cooling water from the recirculation systems it takes its water from the inner pool water volume 21 through the lower density lock 14 without the water flow decreasing at the beginning.
• the incoming water at least partially fills up the previously steam-filled volume 11 above the core 1.
• the reactor is immediately shut off and cooled at the same time since the pool water is relatively cold. However, the water in the reactor is thereafter again heated by the decay power since the recirculation has ceased.
• the condenser 15 enters into operation as a result of ammonia no longer being returned to the storage tank 16 but supplied to the condenser 15, water steam emitted from the core is cooled and returned as cooled condensate available for decay power cooling of the core.
• the power discharged through the cooling in the condenser 15 exceeds the decay power of the reactor, the reactor is successively cooled down and finally reaches a stable state of passive long-term cooling. No external intervention is necessary to achieve the shutdown and decay power cooling described above.
• Loss of feedwater, heat sink In case of loss of feedwater, provided that no measures are taken, the steam generators 22a, 22b dry out, resulting in the temperature of the reactor water rising. Since the ' burnup compensation of the core 1 from the point of view of reacti ⁇ vity is based on the presence of gadolinium and/or any other burnable absorbers in the fuel, the boron content in the cooling water is always so low that the moderator temperature reactivity coefficient of the reactivity is always greatly negative and the power of the reactor decreases as a result of the heating. If no measures are taken, the primary system of the reactor, the recirculation systems for the cooling water to the core, will blow steam to the containment.
• the level in the primary system will drop such that the circu ⁇ lation in the outer circuits ceases, pool water thus penetra ⁇ ting into the core 1 through the lower density lock 14 and the reactor being shut off.
• the condenser is activated as pre- viously described in connection with loss of all electricity supply and the system is successively cooled and changes into a state of stable decay power cooling. No external intervention is required to achieve the shutdown and the decay power cooling described above.
• LOCA loss of primary cooling water in the event of a so-called LOCA will successively lower the level in the primary system in the same way as in the case of loss of feedwater, whereafter the passive system according to the invention will enter into operation in the same way as previously described, such that shutdown and a state of stable decay power cooling are attained without any external inter- vention.
• a large pipe rupture in the main recirculation systems a so-called large LOCA: Three different types of ruptures falling under this heading will be described below, namely: - rupture on a conduit 5, the hot leg, extending from the reactor,
• a rupture on the hot leg 5 results in fast penetration of pool water into the core 1 through the lower density lock 14, whereby the pressure and the temperature in the space 11 above the core 1 are reduced.
• the hot water 26, 29 at the top of the reactor will be evaporated as a consequence of the pressure reduction in the space 11, whereby at least part of the steam flows through the condenser 15 down to the space 11 above the core 1 and out through the location of the rupture.
• the condenser 15 is traversed in a direction opposite to that described in the previous cases and must, therefore, be designed therefor. Part of the evaporated water flows through the steam generator 22a, 22b in the rupture circuit.
• the core 1 is supplied with water from the external pool volume 12 through the restrictors 31 located at a suitable level between the inner 21 and outer 12 pool volumes in an amount sufficient for maintaining the temperature of the core 1 at an acceptable level.
• the condenser 15 is activated and assumes the cooling when the pressure in the reactor has dropped to atmospheric pressure, whereby shutdown and a state of stable decay power cooling are attained without any exter ⁇ nal intervention also in this case. Any residual gas in the steam is collected in the upper reactor space and is possibly released to the location of the rupture through a constantly open slender conduit.
• a rupture on the cold leg in conduits 6 delivering water to the upper part of the reactor results in the hot water being evaporated as a result of the pressure reduction and the steam formed flowing out through the location of the rupture, where ⁇ by at least part of the steam passes through the condenser 15 in the direction described in the previous examples relating to loss of electricity or loss of feedwater.
• pool water penetrates into the core 1 through the lower density lock 14 and the reactor is shut off.
• the condenser 15 is activated as previously described in connection with loss of all electricity supply and the system is successively cooled and changes into a state of stable decay power cooling. No external intervention is required for achieving the shutdown and the decay power cooling described above.
• a rupture on the cold leg in those conduits 7 which deliver driving flow to the outlet header 8 for driving flow to the injector pumps 9 may give rise to a brief flow reversal in the core 1, resulting in a temperature peak, before cold boron- containing pool water penetrates in through the lower density lock 14 and the reactor is shut off. This temperature peak is limited through a suitable design of the injector pumps 9.
• the condenser 15 is activated as previously described and the system is successively cooled and changes into a state of stable decay power cooling. No external intervention is required for achieving the shutdown and the decay power cooling described above.
• the decay power cooling according to the invention is, of course, carried out redundantly such that the condensers 15 with associated equipment may be knocked out by a leakage, an airplane crash etc., without losing this function.
• Figure 4 shows the final state with stable long-term cooling where all steam generated by the core 1 is condensed in the condenser 15 and returns to the reactor pool.
• a nuclear reactor plant according to the invention will normally be designed with a number of active auxiliary systems which in the normal case take the necessary measures as may be required by the situation, for example in the event of loss of feedwater, before it has proceeded as far as described in the examples above.
• the above qualitative description of a reactor system according to the invention in different emergency situations only aims at illustrating that the shutdown of the core and the decay power cooling in a reactor according to the invention are ensured without any form of external interven- tion, that is, in the event that none of the ordinary auxi ⁇ liary systems enters into operation.
• the reactor system according to the invention has been descri- bed above starting from a pressurized-water reactor with a core in the form of nuclear fuel elements arranged in water but is applicable to other light-water cooled devices for extracting fusion energy, which comprise a core arranged in water, such as a so-called spallator core which is partially supplied with neutrons by spallation of heavy atomic nuclei with the aid of high-energy protons from an accelerator.
• a condenser placed at the top of the reactor vessel enters into operation, also without taking any measures, by supplying coolant to the condenser when the normal cooling of the core is lost.
• This condenser cools and condenses water steam emitted from the core and makes the cooled condensate available for the long- term cooling of the core.
• Coolant which has evaporated in the condenser is condensed in an air cooler cooled by ambient air by means of convection as a result of the chimney effect, whereby the residual heat of the core is entirely passively transferred to the surroundings.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Structure Of Emergency Protection For Nuclear Reactors (AREA)

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Cited By (5)

Citations (1)

• 1994
  • 1994-04-22 SE SE9401398A patent/SE9401398L/sv not_active Application Discontinuation
• 1995
  • 1995-04-21 WO PCT/SE1995/000436 patent/WO1995029486A1/en active Application Filing

Patent Citations (1)

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