NUCLEAR POWER PLANTS, SOLUTIONS-CENTRALES NUCLEARES, SOLUCIONES

NUCLEAR POWER PLANTS, SOLUTIONS-CENTRALES NUCLEARES, SOLUCIONES

Si para el 2050, la demanda de electricidad, habrá crecido un 160%, no me vengan con cuentos de Caperucita.

Tenemos de evitar que siga creciendo “El calentamiento global” (que no “el cambio climático”, ya que este concepto es otra estupidez, pues el clima cambia constantemente) y para ello debemos eliminar las emisiones CO₂ principal responsable de ese calentamiento, por el efecto invernadero y las de distintos óxidos y anhídridos de Nitrógeno (N₂), en general N_xO_Y y óxidos de Azufre (S₈) como el SO₂ y el SO₃ (tan perjudiciales para la vida vegetal y animal).

Con las renovables de todas clases, debido a su falta de constancia de producción (irregular producción) y a su coste de instalación y mantenimiento, no solucionaremos ni el 35% de las necesidades energéticas del próximo futuro (dentro de 20 años), ni en cantidad de producción, ni en coste. (y ni el pueblo, ecologista él, ni la industria), quieren pagar más que ahora (que la electricidad ya es cara).

Esto nos lleva a buscar nuevas fuentes de producción de electricidad, de manera que, si eliminamos las plantas de generación que utilizan combustibles fósiles y las renovables, no pueden constituir más que una parte de la generación de electricidad, irremediablemente, tenemos que volver a recurrir a la generación de energía eléctrica, utilizando, entre otras alternativas, la energía eléctrica generada en las plantas nucleares.

Pero hay un miedo, justificado a la utilización de esta tecnología y además, se magnifican con suma ignorancia, por parte de periodistas y políticos, los riesgos que conllevan, las plantas nucleares.

Es cierto que las plantas existentes, diseñadas hace unos 30 o 40 años, no eran tan seguras como las que ahora pueden construirse.

El público traga todo y los medios, difunden un mensaje apocalíptico, que tenía un cierto sentido hace 30 años. Las plantas nucleares, tenían defectos de diseño, que no tuvieron en cuenta los posibles accidentes que han sucedido, ni sus causas, ni sus consecuencias.

Pero hoy, con los nuevos diseños, basados en las nuevas tecnologías y en la experiencia de más de 40 años, en plantas de nueva construcción, ni se pueden producir los accidentes que sucedieron, ni los residuos representa el mismo problema que entonces, ni la proliferación de armas nucleares, puede progresar de forma peligrosa. Todo el proceso está mucho más controlado y aún puede controlarse mejor.

Con los nuevos diseños, los nuevos sistemas y protocolos de control y la minimización de la generación de residuos y en muchos casos la reutilización, por reintroducción en el circuito de producción de los mismos, el peligro de accidentes como los de Three Miles Island, Chernobil o Fukushima, queda reducido a su mínima expresión y en caso de repetirse el accidente, las consecuencias quedan reducidas a cero (salvo en el estricto espacio ocupado por la planta accidentada, siempre que el diseño sea parecido al que mostramos aquí).

Presento como ejemplo este diseño (cuyo costo inicial de implantación, se amortiza con una extensión de la vida de la planta, establecida desde el principio de funcionamiento).

AL FINAL HAY 18 PAGINAS DE MEMORIA DESCRIPTIVA EN INGLES

AT THE END THERE ARE 18 PAGES OF DESCRIPTIVE MEMORY  ENGLISH, 

Como puede verse, es patentable.
As you can see, it's patentable.

Además, con este diseño de base, es bastante fácil explicar el alto grado de seguridad aumentada, por lo que, utilizándolo, aumenta exponencialmente, la capacidad de negociación con todos los actores sociales (ciudadanía, políticos e inversores), para obtener su aprobación, para la construcción de este tipo de centrales.

If by 2050, the demand for electricity will have grown by 160%, don't give me tales of Little Red Riding Hood.

We must prevent "Global warming" (not "climate change" from continuing to grow, as this concept is another stupidity, as the climate is constantly changing) and for this, we must eliminate the main CO₂ emissions responsible for such warming, because of the greenhouse effect and those of various oxides and anhydrides of Nitrogen (N₂), in general, N_xO_Y and sulphur oxides (S₈) such as SO₂ and SO₃ (so harmful to plant and animal life).

With renewables of all kinds, due to their lack of production consistency (irregular production) and their cost of installation and maintenance, we will not solve either 35% of the energy needs of the next future (within 20 years) nor in quantity of production, not even in cost. (and neither the people, environmentalist him, nor the industry), want to pay more than now (that electricity is already expensive).

This leads us to look for new sources of electricity production, so that if we eliminate power plants that use fossil fuels and renewable fuels, they can only constitute a part of electricity generation, inevitably, we need to resort again to electricity generation, using, among other alternatives, the electricity generated in nuclear plants.

But there is a fear, justified in the use of this technology, and in addition, they are magnified with great ignorance, by journalists and politicians, the risks involved, nuclear plants.

It is true that the existing plants, designed about 30 or 40 years ago, were not as safe as those that can now be built.

The public swallows everything and the media, spreading an apocalyptic message, which had a certain meaning 30 years ago. Nuclear plants had design flaws, which did not take into account the possible accidents that have occurred, nor their causes, nor their consequences.

But today, with new designs, based on new technologies and the experience of more than 40 years, in newly built plants, neither accidents can occur, nor waste represents the same problem as then, nor the proliferation of nuclear weapons, can progress dangerously. The whole process is much more controlled and can still be better controlled.

With new designs, new control systems and protocols and minimisation of waste generation and in many cases reuse, by the reintroduction into the production circuit thereof, the danger of accidents such as those of Three Miles Island, Chernobyl or Fukushima, is reduced to its minimum expression and in case of repeat the accident, the consequences are reduced to zero (except in the strict space occupied by the rugged plant, provided that the design is similar to the one shown here).

I present as an example of this design (whose initial cost of implementation, is amortized with an extension of the life of the plant, established from the beginning of operation). 

In addition, with this basic design, it is quite easy to explain the high degree of increased security, so, using it, it increases exponentially, the ability to negotiate with all social actors (citizenship, politicians and investors), to obtain their approval to build such power plants.

DESCRIPTION

EP 2 814 038 B1     2

Description

The object of the Invention

[0001] The present invention relates to an underground nuclear power plant comprising a safety system, in which a fuse element and a gravity elevator stand out. [0002] Particularly, in the nuclear power plant and safety system with fuse element and gravity elevator, the buildings of the power plant subjected to contamination are buried below sea level and under borated water basins, and the plant has a safety system free of electrical and electronic components to act in the event of possible accidents comprising, among others, means for flooding the buildings of the power plant with thermal fuses and gravity elevators for operator evacuation in the event of an emergency.

[0003] The present invention will, therefore, be of interest for the atomic energy industry sector.

Description of the State of the Art

[0004] It is well known that the main safety problem in nuclear power plants consists of the lack of cooling of the reactor at a given time, the reactor temperature rais-ing and its fuel reacting uncontrollably.

[0005] In the event of an accident due to a lack of cooling, the nuclear fuel that is in the reactor can melt, forming what is referred to as corium. Corium is a magma result-ing from the elements of the core melting and is essentially formed by a mixture of nuclear fuel, the covering of the fuel elements (zirconium alloy or the like) and the various components of the care with which it comes into contact (rods, tubes, supports, clamps, etc.)

[0006] This is one of the most serious accidents that can occur, where it is necessary to cool the reactor to prevent the proliferation of the reaction of the fissionable ma­terial and the possible release thereof from the containment barriers, usually the reactor vessel and the containment building.

[0007] Furthermore, in this process since the fuel rods, control rods and other elements of the vessel melt together, gases are produced that can lead to explosions. [0008] To contain situations of this type, it is necessary to cool with borated water which dilutes the gases generated in the process in addition to blowing off the heat produced.

[0009] One of the problems encountered is that the cooling water sometimes does not reach its location either due to a malfunction of the injection pumps for said fluid or due to a lack of power supply for operating them. [0010] A possible solution would, therefore, be to design power plants were the cooling fluid enters without the need for pumps, so the water tanks must be located at a higher level than the buildings to be cooled.

[0011] The present improved nuclear power plant structure provided with a fuse element cooling device entails a step forward as it satisfactorily solves the afore-

mentioned safety problems in conventional nuclear power plants.

[0012] Documents US 3 712 851 A and XP009138062 disclose examples of power plants of the state of the art.

5

Description of the Invention

[0013] The nuclear power plant object of the present invention that is described below is formed by an original

10     power plant structure, buried at a certain depth, such that it can be cooled in the event of an accident by means of a cooling water tank for emergency situations, preferably containing seawater, located on the surface above the power plant, the cooling water thus being able to circulate

15       due to gravity without the need for pumping. After digging an open pit in the terrain intended for receiving the power plant, the nuclear power plant is built with the correspond-ing construction criteria and building a concrete compartment for housing it, including earthquake-resistance criteria

20     t, and it is subsequently buried using part of the soil that was dislodged while digging using access ramps. This arrangement means that once the service life of the power plant has expired, it is not necessary to dismantle the power plant as occurs with current surface-installed

25 nuclear power plants.

[0014] The nuclear power plant with a safety system is primarily based on a particular arrangement of the elements forming the nuclear power plant in combination with different safety elements, largely minimizing electric

30     and electronic components, the most relevant safety element being the arrangement and use of passive thermal fuse elements, which allow giving way to the automatic entrance of water into the reactor core when the reactor temperature reaches a predetermined a set-point temperature

35.

[0015] The nuclear power-plant consists of a specific and particular arrangement of the different components or elements of a nuclear plant buried at a site close to the sea as an inexhaustible water source for the purpose

40     of improving safety and likewise including different components or devices to increase the safety of the power plant. Specifically, the nuclear power plant object of the invention comprises three buried basic installations, namely: a reactor containment building located underground, a

45     turbine or power generation building also located under-ground, and at least one waste and/or nuclear fuel ware-house. On the surface, it also has a power plant control building as well as transformers and connection with the high voltage line.

50     [0016] By means of the arrangement of the buildings according to the present invention, the different buildings are separated from one another, allowing the isolation thereof when needed, flooding the containment building and the waste or nuclear fuel warehouses and/or burying

55 said buildings. Specifically, the underground buildings can be buried independently preferably by using pyro-technic rings located at each entrance and/or exit of each building when an emergency situation occurs. With this

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the arrangement, personnel can control the most dangerous buildings of the power plant in an isolated manner, and in the event of an accident that forces burying or flooding the compromised buildings, the personnel remains far from the radiation. As mentioned, the power plant has at least one nuclear waste and/or nuclear fuel warehouse that remains buried and in communication with the reac­tor of the installation permanently, therefore the fuel does not have to be transferred out of the power plant. Once said the warehouse has been filled, it is flooded and/or buried forever, being isolated from the remaining components of the power plant. The number of nuclear warehouses will be the number necessary for storing the waste that may be generated during the power plant service life. One or some warehouses intended for storing virgin nu­clear fuel can also be arranged among these warehouses or buildings.

[0017] At least one borated water basin is arranged between the coast and the sea, above the part of the power plant that is buried, in contact with the sea, allowing the cooling and/or flooding of the different components of the power plant in the event of an emergency.

[0018] Additionally, and as mentioned, the safety system of the power plant has a fuse element for the nuclear power plant, and more particularly for the reactor of a nuclear power-plant consists of arranging thermal fuses to flood the reactor in the event of high temperature. One fuse can be arranged in the reactor vessel to flood it and another one can be arranged in the core vessel to flood it when a predetermined or set-point temperature for each fuse is reached, and a third fuse can even be arranged to flood the concrete containment building. The safety fuse does not incorporate any electric or electronic mechanism, being completely passive and autonomous such that once the set-point temperature is reached, it melts completely and suddenly (eutectic alloy), allowing the borated water stored in a basin or tank located above the reactor to enter due to gravity (with a passive pressure compensation system so that the column of borated cool-ing water is not rejected through the flooding pipes). The flooding system is formed by covers or hatches that melt at a specific temperature, causing them to open when a set-point or predetermined temperature is reached in the event of an accident.

[0019] Other safety systems are also envisaged in the installation such as an evacuation system for operators who are underground in the event of an emergency formed by at least one gravity elevator, pumping system for drying after flooding one of the buildings and once the accident is controlled; a pipe cleaning system assuring the pipe flow rate; passive valves actuated either by means of floats or loaded springs at a specific pressure; among others.

[0020] Therefore, the object of the invention is a nu­clear power plant according to claims 1 to 14.

[0021] Technology today allows building nuclear power plants with virtually nil probability of a serious accident that may have a repercussion on the habitat and on the

health of those living around it. To that end, the present invention takes the following criteria into account:

-      locating the power plant close to the sea, and

5       -     locating reactors underground (attempting to avoid
seismic areas), although even in seismic areas, the design proposed in the present invention is valid if it is designed taking earthquake-resistance criteria in-to account.

10

[0022] The present invention is particularly conceived for fourth-generation reactors of not more than 500 MW, limiting the fuel mass in the reactor such that in the event of a core fusion, it is easier to put out the fuel mass of a reactor with such power.

15     

[0023] Furthermore, to reduce the probability of faults, the design of the control equipment is simplified such that the electronics are limited to armour-clad radiation, temperature, seismic wave controls, etc., and the number of

20 said the equipment is reduced, thereby reducing the probability of failures thereof.

[0024] As mentioned, the coolant fluid is kept at a specific constant level by means of valve and float opening systems which take the cooling water from main borated

25     water basins. These main basins are built one level lower than sea level and above the buried buildings, in turn having a water feed system using floats that open gate valves to allow the entrance of seawater and of a concentrated boron solution. Said borated solution is stored

30       in secondary basins that pour this solution into the main basins also through gate valves with a float. A continuous, inexhaustible supply of borated water, which is the basic coolant of the power plant is thus assured for the reactor. [0025] The amount of boron is maintained in these secondary

35  concentrated boron solution basins by means of directly pouring the solution into the basins. Since they are below sea level, it is not possible for the content of the basins to spill into the sea. Also, and to assure that the foregoing does not occur, both the main and secondary 

40 basins incorporate covers or plates floating on the water contained therein, said plates being anchored to the bottom of the basins to prevent the water from evaporation and to minimize the mixing of seawater and other elements. Said basins can additionally comprise fixed

45 structures covering their entire surface.

[0026] Said basins are responsible for providing cooling water to the different buildings and components of the underground power plant, and mainly to the reactor. The main basins containing borated water also receive

50 at the bottom thereof the exhaust or blow-off pipes for the gases that may be generated in the different containers or buildings, such as the core, the core vessel, the concrete building, waste and nuclear fuel storage buildings, in the event of an accident. The exhaust or blow-

55     off-gases thus condense when they reach the basin, be-ing diluted therein. Said ducts or pipes start from high pressure and temperature safety valves installed in the walls of the concrete reactor containment building, in the

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the reactor vessel and in the core vessel.

[0027] The power plant ob]ect of the present invention is designed so that in the event of an accident in the reactor, the basic safety devices are activated without requiring human action and largely minimizing the participation of electronic and electric components. To that the end, it comprises a cooling fuse device as the main safety element which, in the event of an accident or malfunction as a result of which the reactor reaches a high predetermined temperature, hatches or covers comprised in the cooling fuse or thermal fuse will melt, such that when said hatches melt, the reactor is communicated with cool-ing ducts or pipes that enable introducing borated cooling water into the reactor from the main basins.

[0028] These hatches or covers comprised inside the fuse device are made from a eutectic alloy that melts when a specific temperature is reached, allowing the passage of the borated water contained in the cooling ducts or pipes to the reactor containment building, to the reactor vessel and/or to the core vessel, thereby allowing the cooling and dilution of the gases that may have been generated with the melting of the fuel rods or other elements in the reactor.

[0029] The eutectic alloy is one which, in the liquid state, reaches a solidification temperature referred to as a eutectic temperature when slowly cooled, where the liquid → alpha solid solution + beta solid solution reaction, called the eutectic reaction, takes place. The fuse devices can be located in the wall itself of the reactor containment building, in the wall of the reactor vessel and/or in the wall of the core the vessel, such that the alloy is capable of maintaining in its solid-state the required mechanical characteristics of the walls in which it is located, but when exceeding a specific temperature it converts to its liquid state, melting and allowing borated cooling water to flow into the different compartments of the reactor.

[0030] The aforementioned high pressure and temperature safety valves installed in the containment building, in the reactor vessel and in the core vessel, has the function of blowing off the high-pressure surges that can occur shortly after the borated water starts to enter the containment building, the reactor vessel and the core vessel. The number of water inlet pipes and blow-off pipes must be enough to blow off the gas that is generated and at the same time allow sufficient cooling water, such that as water enters and depending on the temperature, such water evaporates, exiting through the blow-off pipes, allowing the entrance of more cooling water. The number of pipes will be the number necessary for assuring the entrance of cooling water in an attempt to obtain safety redundancy.

[0031] In the event that the temperature of the core rises above a set-point or predetermined safety value, the different safety fuses will start to act such that the fuse located in the core vessel will act first, enabling it to be flooded, then the one located in the reactor vessel will act and finally, the one located in the containment building will act until the core is cooled.

[0032] Once the nuclear accident or emergency situation that led to flooding the different parts of the power plant is controlled, the plant can be recovered by means of extracting the cooling water by means of a pumping

5       station provided for that purpose and carrying the contaminated borated water to the borated water basin through the gas exhaust pipes of the reactor (containment, reactor vessel and core vessel).

[0033] As mentioned, the different buildings of the pow-

10     er plant ob]ect of the invention are buried and connected by a network of horizontal and vertical tunnels that work like a communication path for the operators in normal operating conditions of the power plant and as an escape route after a possible nuclear accident. Said horizontal

15 tunnels have at different points, mainly at the accesses thereto, steel doors and lead plates that are operated manually and preferably with the aid of counterweights which allow isolating the intermediate areas of the vertical communication escape and safety tunnels in the event

20     of an accident.

[0034] The power plant comprises elevators in said vertical tunnels to access the underground buildings and tunnels, these elevators being able to be of two types, some being electrically operated so that in normal 
operating conditions the operators can go up and down, and others being gravity elevators, without any

25   need for electricity, which only allows going up and is used exclusively in the event of an emergency to escape from inside the power plant. The gravity elevators particularly, which are

30 equivalent to emergency elevators that do not require electricity for their exclusive climbing operation is preferably installed parallel to the elevator for normal use in the vertical escape tunnels and are designed to operate without a motor and without electricity, since they work

35     due to passive elevation using the force of gravity. These elevators can also be used in other installations and situations in which the escape requires going up.

[0035] The gravity elevator, which is the fourth ob]ect of the present invention, has all the typical constructive 

40       elements of any elevator, including all the safety elements, but does not include a motor and therefore has no electric or electronic components, and it is an elevator that can only be used once for a single climb. The elevator car is anchored to the ground from where the emergency climb

45     must take place by means of a restraint cable which can be cut from inside said the car in order to use the elevator in the event of an emergency. In the top part, the elevator car is secured to the main cable at the opposite end of which, after looping around the main sheave, there is located the main counterweight

50  which, when the restraint cable is cut, will cause passive elevation of the car with its occupants inside due to gravity.

[0036] The existence of a cutting element, preferably an explosive type cutting element is contemplated for

55 cutting said restraint cable, the existence of manual shears suitably sized so that they can be used by a person of the average constitution for cutting the cable manually further being contemplated. Therefore, if upon activating

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the explosive cable cutting element, which is preferably a dual charge element, the pyrotechnic element fails both times the cable could be cut manually by means of the mentioned shears. Furthermore, all the cavities and actuators necessary for being able to operate the cable cutter from inside as well as for being able to manually cut the cable is placed in the elevator car.

[0037] The tension or weight exerted by the main counterweight is slightly greater, by approximately 20%, then the empty weight of the car plus the weight corresponding to the main cable, such that if one or two people enter the car and cut the restraint cable thereof, they will begin to climb up to the surface by the tractive force exerted by gravity as a result of the excess weight of the main counterweight, which maintains a virtually constant climbing tension.

[0038] Additionally, the emergency elevator of the invention also contemplates the existence of a system of secondary counterweights. Therefore, if the number of people entering the elevator car to climb up and escape to the surface means that the tension of the main counterweight is not enough to cause the car to climb, secondary cables which are each attached to a secondary counterweight and to a ground anchor will be anchored to it. Once the necessary secondary cables are an-chored, the ground anchors of said secondary cables are cut such that the weight of each secondary counterweight transmits the corresponding complementary climbing tension. This occurs until the climb begins.

[0039] In any case, once the car starts to lift up, the climbing speed must be controlled by means of additional safety and climbing control systems provided for that purpose, which, for the sake of safety, will preferably be installed in duplicate. Said systems can comprise:

-     A brake lever, which is suitably sized so that a person of the average constitution can push it with enough force applied to friction blocks which in turn touch a friction track installed along the upward path to thus control the climbing speed.

-      A speedometer to control the climbing speed.

-     A system of gear wheels meshing, from inside, with a rack installed along the path, all of this sized so that a person of the average constitution can make the elevator climb by transmitting manual force to it. The elevator car will always be out of balance for the climb due to the weight imbalance.

-     A system of inertia dampers installed at the end of the path (top and bottom) to slow the elevator down such that the inertia withstood by the passengers does not cause vascular damage or damage of any other type.

-     The secondary pulling cable anchor systems use du­al pyrotechnic systems or a lever system sized for a person of the average constitution, which close clamps around the cable, having a non-slip system, coated internally with corundum powder, for example.

-      Mini-oxygen cylinders and masks.

[0040] Finally, it should be mentioned that all the steel cables are greased, but furthermore, the restraint cables of the secondary counterweights are sheathed in steel tubes to prevent dangerous jerks and snagging that

5       would occur when climbing without tension and once they have been cut.

[0041] In turn, in the present invention it must be taken into account that the safety tunnels for external connections and services are preferably vertical, as is the implementation of the different sets of 

10     pipes, which are always arranged vertically.

[0042] Likewise, all the entrances and exits are protected by pyrotechnic rings to be able to seal off the power plant in the event of an unrecoverable failure thereof.

15     [0043] Finally, the power-plant has a transmission line for the generated electric power coming out of the high-low voltage alternators located in an underground build­ing and taking it to the high voltage transformers located in the exterior for transmitting the power to the transmission
20 and the distribution network. This line mainly has a su­perconductor cable to reduce losses in connection be-tween the alternator and high voltage transformers located on the surface.

25     Description of the Drawings

[0044] Attached to the present specification is a set of drawings which, by way of non-limiting example, represent a preferred embodiment susceptible to any variation

30  in detail that does not entail a fundamental alteration of the essential features of the invention.

Figure 1 depicts a schematic plan view of the main buildings buried in a nuclear power plant according

35              to the present invention.

Figure 2 depicts a schematic side view of the main

components of the nuclear power plant.

Figure 3 depicts a schematic side view of the reactor

vessel and of the reactor core as well as a detail of

40              the thermal fuses and related components.

Figure 4 shows a schematic side view of the reactor

containment building and a detail of the fuses and

related components.

Figure 5 depicts a schematic elevational view of the

45    emergency elevator, the main parts and elements it comprises, as well as the configuration and arrangement thereof, being shown therein.

Figure 6 depicts a schematic elevational view of the car with some of the additional climbing speed control systems.

50.     Preferred Embodiment of the Invention

[0045] A detailed description of a preferred embodiment
-55  of a nuclear power plant and of a safety system with a fuse element objects of the present invention will be given below.

[0046] Figure 1 shows the main buildings and rooms,

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which will be buried, of the power plant for example in a plan view during the construction of the power plant, in which an open pit has been dug using access ramps 40 to the burying levels and the main buildings, namely, the containment building 6, the generation building 7, the different waste and nuclear fuel buildings or warehouses 9, as well as the tunnels 11 horizontally connecting the different buildings with one another, and the vertical tunnels 10 connecting said horizontal tunnels 11 with the surface, have subsequently been built.

[0047] As can be seen in Figure 2, which depicts an already built power plant, all the components of the power plant except the transformer and power plant control building 5, is buried, particularly the containment build­ing 6, with the reactor and the core, the generation build­ing 7, and the fuel element and waste buildings or ware-houses 9. The control and electrical transformer building 5 located on the surface is electrically connected with the components of the power generation building (7) for transmitting the generated electric power.

[0048] The buried components are located below the level of a main cooling water tank or basin 8 which is connected with an inexhaustible water source such as the sea 16 and located at a sufficient design depth, according to the features of the reactor 1 and the sizing of the design power thereof, the active nuclear part being underground, and only the connection and transmission infrastructure 5 for connecting and transmitting the energy produced to the power grid as well as auxiliary components being located on the surface.

[0049] To place the power-plant below sea level 16, the terrain where the underground power plant is going to be located is excavated, and after building the plant on said terrain according to suitable construction criteria, such as the construction of a concrete compartment, and taking into consideration earthquake-resistance criteria, part of the excavated soil is used to bury the power plant, such that said plant is buried and below the level of the main cooling water tank, i.e., below the sea 16, as well as the main basin 8.

[0050] The containment building 6 internally comprises the reactor vessel 2 inside which the core vessel with the reactor core 1 is located. The core 1 is the reactor itself and is formed by fissionable fuel, and it is where a nuclear accident can take place if the temperature thereof gets out of control, being able to melt and forming what is referred to as corium or magma resulting from the elements of the core 1 melting, consisting of nuclear fuel, the covering of the fuel elements and the remaining components of the core with which it comes into contact. The core vessel 1 is a pressure vessel built from carbon steel with a thickness between 20 and 25 cm and with other internal steel coverings and it is the first barrier against the exit of the corium. The reactor vessel 2 is the second safety container of the core 1 of the reactor and is built from special steel with a thickness of not less than 20 cm. The containment building 6 is the final barrier for contain-ing corium in the event of an accident and is built from

high-strength concrete with a thickness of at least 150 cm with an inner lead covering. This building is connected with the power production building 7 and with nuclear fuel and waste warehouses 9.

5 [0051] The different underground rooms or buildings are communicated with one another by means of hori­zontal tunnels 11 and with the outside by means of ver­tical tunnels 10, allowing the transit of operators between the different buildings and with the outside. The horizontal

10 tunnels 11 further, comprise preferably manually operated safety hatches 12 which allow isolating the differ-ent rooms from one another in the event of an emergency for the main purpose of being able to flood the different rooms with the cooling water from the main water tank

15       or basin 8. The vertical tunnels 11 are arranged in different places in the power plant to facilitate the operator exit in the event of an emergency. Said vertical tunnels 11 preferably comprise electric elevators for use during the normal operation of the power plant, and gravity elevators

20     100 not requiring electric power and only allowing climb-ing for operator evacuation in the event of an emergency. [0052] In relation to the gravity elevators 100, which can only be used for a single climb and are preferably arranged parallel to the ordinary operating elevators, Fig-

25 ures 4 and 5 show a diagram of one of the said elevators. The elevator 100 in question conventionally comprises a car 120 secured at the top by a main cable 130 looped around a main sheave 140 and incorporates at its opposite end a main counterweight 150, with the particularity

30     that said car 120 is anchored to the ground by means of a restraint cable 160, the weight of said main counter-weight 150 being slightly greater by approximately 20% than the empty weight of the car 120 plus the weight of the main cable 130, such that if one or two people enter

35     the car and cut the restraint cable, the car climbs as the counterweight falls due to gravity.

[0053] The elevator has an explosive cutting element for cutting said restraint cable 160 consisting of a dual charge detonating device, as well as a manual cutting

40 element preferably consisting of shears (not depicted). The car 120 further has actuators (not depicted) to operate said cutting elements for cutting the restraint cable 160 from the inside, as well as cavities for accessing them and other additional climb control systems that may

45 be incorporated, as will be explained below.

[0054] Additionally, the elevator 100 has a system of secondary counterweights 170 to allow increasing the car capacity. Each of said secondary counterweights 170 is secured to a secondary cable 180 which, looping

50 around a secondary sheave 190, is fixed at one of its ends to a ground anchor 110, whereas at the other end it has means for being fixed to a fastener 111 provided for that purpose in the car 120.

[0055] The elevator 100 can have a greater or lesser

55 number of said counterweights and secondary cables and their corresponding ground anchors and fastenings in the car according to the needs in each case. Although Figure 4 depicts several secondary counterweights 170,

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only one of them has been depicted in its complete form with its ground anchor 110.

[0056] Furthermore, as systems of safety and as systems for controlling the climbing speed the elevator can have:

-     A brake lever 112 acting on friction blocks 113 which in turn travel on a track 114 installed along the up-ward path.

-      A speedometer.

-     Gear wheels 115 meshings with a rack 116 installed along the path.

-      Inertia dampers 117 installed at the end of the path.

[0057] Furthermore it also has dual explosive cutting elements or a manual lever system (not depicted) for cutting the anchors of the secondary cables 180.

[0058] It is important to stress that the end of said secondary cables 180 securing them to the ground anchor 110 are sheathed in steel tubes 118 as a protection system to prevent jerks when climbing without tension. The car 120 also has mini-oxygen cylinders and masks (not depicted).

[0059] Continuing with the description of the power plant, the cooling water tank 8 is the main basin containing borated water and it is connected with the sea 16 as inexhaustible water and cooling source, and it is in turn connected with at least one secondary basin 82 where a borated solution is stored. Said basins are located below sea level 16 and above the buried buildings, being connected with the sea and with one another by means of floats which open gate valves that allow feeding water and maintaining the level thereof. The main basin 8 or an underground appendage 81 thereof is connected with the different buildings by means of cooling pipes 13 which carry the borated water from said basin 8 due to gravity, without the need for pumps. Likewise, the outlets of the pipes used for steam exhaust 14, 15 in the event of an accident which comes from the different buildings, mainly the containment building 1, end at the bottom of said basin 8 such that the contaminated steam condenses as it comes into contact with the water of the basin 8.

[0060] The main basin 8 and secondary basin 82 com-prise covers or plates 83 floating on the water contained therein, said plates 83 being anchored to the bottom of the basins 8, 82. Said plates 83 will preferably be built by means of a stainless steel grid covered with a polymer foam that is thick enough for the plates to float on the water, and that is resistant to solar radiation to prevent evaporation of the water and resistant to etching caused by the seawater. The mentioned plates or covers 83 are anchored to the bottom of the basins 8, 82 by means of cables 84 with high tensile strength resistant to seawater and with a length equal to the maximum height of the walls of each basin 8, 82. Said material can be steel or a polymer. These floating plates 83 minimize the mixture of seawater and of other elements with the borated water of the basins 8, 82. The basins could also incorporate

fixed structures covering their surface (not shown). [0061] The cooling pipes 13 connect with the containment building 6 through fuse elements 3 which are incorporated in the walls of the containment building 6, of the

5          reactor vessel 2 and of the core vessel 1. It can evidently be located in only one of the walls of one of the elements. Each fuse element 3 comprises a hatch 32 that opens automatically in the event of nuclear reactor overheating which is formed by an eutectic alloy material 32 having

10     features similar to the walls separating the different elements of the reactor from one another, the core vessel 1, the reactor vessel 2 and the containment building 6, but which are susceptible to melting in overheating conditions and communicate each of the elements 1, 2, 6,

15 with at least one cooling pipe 13, preferably more than one pipe, in an attempt to obtain safety redundancy, which in turn, connects with the main basin 8.

[0062] The reactor has a double steel vessel and is provided with at least two fuses 3.1, 3.2, one in each of

20     the inner vessel or core vessel 1 and outer vessel or the reactor vessel 2, respectively, connected with independent borated water ducts 13.1, 13.2, each one being able to circulate the borated water between each inner and outer vessel. As described above, the reactor is enclosed

25     in a containment building 6 also preferably provided with a third fuse 3.3 connected to a third pipe 13.3 to allow the entrance of cooling borated water.

[0063] As mentioned, the fuse 3 is ceramic or metal a hermetic sealing calculated for being melted when a 
specific temperature is reached and is integrated into the walls of the vessels 1, 2 or of the containment-

30      building 6. It is particularly integrated into said walls by means of a solid anchor either by welding or by screws, forming part of the wall as it has the same features as the said wall, namely,

35 the same mechanical strength as any other part of the wall, or of the core vessel 1 or the reactor vessel 2, or of the containment building 6.

[0064] The fuses 3 melt suddenly at a predetermined temperature to make way for the borated water that floods

40 and cools the inside of any of the vessels 1, 2 or the containment building 6. The fuses 3 comprise a cover made from a eutectic material 32 and designed for being melt when a predetermined or set-point temperature is reached, followed by an insulating material 33 and an

45       insulating cover 34. The melting point of the eutectic ma­terial will range between 2000 and 2500°C and once the melting temperature is reached, it will melt all of a sudden. [0065] Arranged after said eutectic cover 32 there is an insulating plug 33, after which there is located an in-

50     insulating cover 34. These two elements serve to prevent the heat of the eutectic cover 32 during the ordinary operation of the power plant from being transmitted to the borated water contained in pipe 13 which is connected with the thermal fuse 3, this heating being able to

55 cause a dangerous pressure increase in the pipe 13. [0066] In the event of the core 1 overheating and once the melting temperature of the eutectic material is reached, which will be less than the melting temperature

7

13                                 EP 2 814 038 B1                               14

of the core 1, the eutectic cover 32 melts suddenly, causing the hydrostatic pressure of the water column of the cooling pipe 13 connected to the borated water basin 8 to push the insulating cover 34 on the thermal insulating plug 33, making them enter the core 1 and opening up the access path of the borated water into the building 6 or vessel 1, 2 to cool the reactor.

[0067] The fuse 3 preferably has in its lower part a specific housing for housing a low pressure valve 31, connected with low-pressure pipes 15 which open up once the first boil-off gases are produced when the borated water comes into contact with the hot elements of the inside of the vessels 1, 2 or of the building 6. Since the eutectic alloy of the cover 32 melts suddenly due to the effect of the hydrostatic pressure of the water column, at first the water enters the vessels 1, 2 or building 6 be-cause the mentioned low-pressure relief valves 31 instantaneously prevent the water column from being pushed upwards or towards basin 8.

[0068] The reactor is also provided with high pressure and temperature safety valves 4 connected with high-pressure pipe 14 for blowing off the high pressure surg­es that may occur with the entrance of borated water into the core 1 and into the core vessel 2.

[0069] On the other hand, the power plant has a pumping station for recovering the plant by means of extracting the cooling water into the borated water basin through the reactor gas outlet or exhaust pipes (core and core vessel).

[0070] The cooling system using borated water ex-tends not only to the reactor 1, 2 and its containment building 6 but to other buildings such as the power generation building 7 containing the turbines and alternators or the fuel storage building 9 or any other room with radioactive material that must be flooded and cooled in the event of an accident.

[0071] On the other hand, the power plant and all its entrances and exits are surrounded by pyrotechnic rings for blasting the plant in the event of an emergency and permanently sealing it off.

[0072] Finally, the shape, materials and dimensions may be variable and generally, insofar as it is accessory and secondary, provided that it does not alter, change or modify the essential nature of the improvements herein described.

Claims

1. A nuclear power plant comprising at least

- a containment building (6) inside which a nu­clear reactor (1, 2) is located,

- a power generation building (7) inside which the turbines and other electricity-generating components are located, and

- a nuclear material building or warehouse (9) for storing nuclear waste or nuclear fuel,

all the aforementioned buildings being buried and, except the power generation building, connected by means of cooling pipes (13) with at least one cooling water tank (8) located above

5                       them and communicating with the sea (16) and
below sea level (16), such that the waterfalls due to gravity in the case of needing to cool or flood said buildings (6, 7, 9) and

further comprising

10                     - pipes used for steam exhaust (14) coming from
at least the containment building (6) and ending at the bottom of the water tank (8), and - means of valve and float systems for keeping the tank (8) at a constant water level.

15

2.      The power-plant according to claim 1, characterized in that, the reactor containment building (6) internally has a reactor vessel (2) inside which there is arranged a core vessel (1) which houses the core (1),

20              at least one of the walls of at least the containment building (6) or of the vessels (1, 2) comprising a fuse element (3) connected with a cooling pipe (13).

3.      The power-plant according to claim 1 or 2, characterized in that it comprises

25               pipes (15) for the exit of steam connecting the inside of the vessels (1, 2) through a fuse element (3) with the cooling water tank (8) and pipes (14) for the exit of steam connect-ing through security valves (4) the inside of the vessels-

30          (1, 2) with the cooling tank (8).

4.      The power-plant according to claim 1, characterized in that the tank (8) contains borated water.

35     5. The power plant according to claim 1, characterized

in that, it comprises control and electrical trans-former building (5) located on the surface and electrically connected with the components of the power generation building (7) for transmitting said generated electric power. -

40              

6.      The power-plant according to claim 1, characterized in that, the buried buildings are communicated with one another by means of horizontal underground

45              tunnels (11) having manually operated hatches (12) to isolate the different buildings from one another.

7.      The power-plant according to claims 6, characterized in that, it comprises vertical tunnels (10) for

50              communicating the surface with the buried buildings or with the horizontal tunnels (11).

8.      The power-plant according to claim 7, characterized in that said vertical tunnels (11) comprise gravity

55              elevators (100) and electric elevators.

9.      The power plant, according to claim 1, characterized in that the containment building (6) internally

8

15                                 EP 2 814 038 B1                               16

has a reactor vessel (2) inside which there is in turn arranged a core vessel (1) which houses the core (1), at least one of the walls of at least the containment building (6) or of the vessels (1, 2) comprises a fuse element (3) incorporated in the wall and connected to one end of a cooling pipe (13) connected at its opposite end to a cooling water tank (8), and comprises pipes for the exit of steam (15) connecting the inside of the containment building (6) and/or the inside of the vessels (1, 2) through the fuse (3) with the cooling water tank (8).

10.   The power-plant according to claim 9, characterized in that the water tank (8) is located above the containment building.

11.   The power-plant according to claim 9, characterized in that, the water tank (8) is at least one main basin (8) of borated water connected with the sea (16) and with at least one secondary basin (82) for storing a borated solution, both basins (8, 82) being below sea level.

12.   The power-plant according to claim 9, characterized in that, the fuse element (3) comprises a cover or hatch (32) located therein and is made from eutectic alloy material, said cover (32) being in contact with the inside of the building (6) or vessel (1,2), and then an insulating material (33, 34) is arranged in contact with the water of the cooling pipe (13), such that said insulating material (33, 34) prevents the heating of the water in the pipe when the eutectic alloy has still not melted due to overheating inside the building (6) or vessel (1, 2).

13.   The power-plant according to claim 9, characterized in that, it further comprises a fuse (3) in a wall of the containment building (6), in a wall of the reactor vessel (2) and in a wall of the core vessel (1).

14.   The power-plant, according to claim 1 and 9, characterized in that it comprises a fuse (3) being placed in at least one of the walls of at least the containment building (6) or of the vessels (1, 2), the fuse (3) com-prising:

- hermetic sealing with a eutectic alloy cover (32) with one end that corresponds with the inside of the walls, followed at the opposite end by an insulating plug (33) followed by an insulating cover (34), to be connected through this end to a pipe (13) containing cooling water, and - a specific housing for housing a low pressure valve (31) to be connected with a pipe for the exit of steam (15), that opens when the first boil-off gases are generated as the water comes into contact with the hot elements inside the vessels (1, 2) or the building (6