Patent Application
20170365367
This application claims priority to KR Patent Application No. 10-2016-0077351 filed on Jun. 21, 2016. The disclosure of that prior filed application is incorporated herein by reference.
The present invention provides a dry interim storage container for spent nuclear fuel.
The spent nuclear fuel generated in light water reactors and heavy water reactors is stored in interim storage before permanent disposal. The spent nuclear fuel produces high radiation and heat due to the decay of the instable or radioactive fission products over the time. The spent nuclear fuel discharged from the reactor of the nuclear power plant after the irradiation is stored in a water bath for cooling decay heat and neutron shield in the site of the nuclear power plant for a certain period. The spent nuclear fuel, which has been stored for a while and whose radiation level and temperature have dropped below a certain level, is drawn out and stored dry in a concrete or metal storage container.
In the case of temporary storage in the site of the nuclear power plant, the spent nuclear fuel is stored for about 30-50 years. When the spent nuclear fuel is stored in the interim storage, it may be kept for up to 100-300 years or longer, before final disposal. The interim storage container for spent nuclear fuel may be also transported to the other place, if needed, while maintaining the integrity of both the container and the spent nuclear fuels inside the container. Therefore, it is important to secure the long term soundness of the spent nuclear fuel to be stored, and it is necessary to efficiently transfer the heat of the spent nuclear fuel, which is generated by decay heat, to the outside.
As an example of the prior art for casks to store the spent nuclear fuel, Korean Patent No. 10-0727092 describes a technique to provide a waste container containing silver or silver compound for the spent nuclear fuel. According to the art above, when the container containing the spent nuclear fuel is damaged, the container is effective in reducing the amount of radioactive iodine discharged therefrom.
However, in the prior art, the inert gas helium (He) is charged into the storage container as a coolant during dry storage, wherein the He pressure is regulated as approximately 4 bar for cooling the spent nuclear fuel during storage. When an inert gas is filled in container, extra management cost is required to prevent leakage and to maintain the pressurized condition with monitoring. In addition, in that case, the coolant used there is a gas having low thermal conductivity so that it is not a very efficient coolant for the spent nuclear fuel to get a sufficient degree of cooling, suggesting that it is difficult to secure the long term soundness of the spent nuclear fuel.
To overcome the disadvantages of the prior art, the present inventors studied and developed an interim storage container for the spent nuclear fuel, which is filled with metal particles with high thermal conductivity as much as the spent nuclear fuel and the outer wall of the storage room are contacted with them, in order to eliminate the decay heat generated from the spent nuclear fuel efficiently, leading to the completion of the present invention.
(Patent Reference 1) Korean Patent No. 10-0727092
It is an object of the present invention to provide a storage container for spent nuclear fuel that effectively delivers the decay heat of spent nuclear fuel out of the container and satisfies low maintenance costs and long term soundness.
To achieve the above object, the present invention provides an interim storage container for spent nuclear fuel which is filled with metal particles in the storage room for the storage of spent nuclear fuel.
The present invention provides an interim storage container for spent nuclear fuel comprising:
a cylindrical body;
an inner container having multiple storage rooms for spent nuclear fuel that is located in the inside of the main body;
a cylindrical outer shell equipped in the outside of the main body;
a neutron shielder to block the neutrons located in between the main body and the outer shell; and
a lid connected to the top of the main body, and
containing metal particles in the storage room for spent nuclear fuel.
Further, the present invention provides a method for cooling the spent nuclear fuel during the period of interim storage comprising the following steps:
preparing an interim storage container for spent nuclear fuel composed of a cylindrical body; an inner container having multiple storage rooms for spent nuclear fuel that is located in the inside of the main body; a cylindrical outer shell equipped in the outside of the main body; a neutron shielder to block the neutrons located in between the main body and the outer shell; and a lid connected to the top of the main body (step 1); and
filling the empty sections in the storage room with metal particles before, during or after loading the spent nuclear fuel in the storage room of the container prepared in step 1 (step 2).
The dry storage container for spent nuclear fuel of the present invention is filled with particles when the spent nuclear fuel is stored, so that the cooling efficiency is higher than the conventional method using gas coolant at high pressure. The accident scenario of overheating of the spent fuel due to leakage of high pressure gas coolant from the conventional dry storage container can be inherently eliminated by filling the particles inside the container. Before disposal of the spent nuclear fuel, particles filling the dry storage container can be recovered and re-used for other dry storage containers. Particles inside the container can also function as both the radiation shield and the buffer against impact during transportation of the dry storage container.
The application of the preferred embodiments of the present invention is best understood with reference to the accompanying drawings, wherein:
Hereinafter, the present invention is described in detail.
The present invention provides an interim storage container for spent nuclear fuel which is filled with metal particles in the storage room for the storage of spent nuclear fuel.
Hereinafter, the interim storage container for spent nuclear fuel of the present invention is described in more detail.
The interim storage container for spent nuclear fuel of the present invention is characteristically filled with metal particles in the storage room where the spent nuclear fuel or the spent nuclear fuel aggregate is stored.
The dry storage container for spent nuclear fuel generally used as the interim storage for spent nuclear fuel can be composed of an inner container having multiple storage rooms where the spent nuclear fuel is stored and an outer container covering the inner container. In this invention, the storage rooms where the spent nuclear fuel is stored are filled with metal particles.
The metal particles herein are filled in the empty space of the storage rooms where the spent nuclear fuel is stored, and in particular the metal particles are preferably filled in contact with the outer side of the spent nuclear fuel.
In the interim storage container for spent nuclear fuel of the present invention, the metal particle can be one or more metals selected from the group consisting of boron (B), carbon (C), magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), gold (Au), silver (Ag), platinum (Pt), and the alloys thereof, and more preferably the metal particle is selected from the group consisting of copper (Cu), zinc (Zn), aluminum (Al), magnesium (Mg), molybdenum (Mo), silicon (Si), carbon (C), zirconium (Zr), and the alloys thereof.
The particle size of the metal particle is preferably 0.1 mm-10 mm, more preferably 0.5 mm-5 mm, and most preferably 1 mm-3 mm. If the particle size of the metal particle is less than 0.1 mm, there is a problem that the economic efficiency is low due to the additional cost for particle processing. If the particle size exceeds 10 mm. the cooling efficiency is reduced due to the coarse particles.
For more efficient cooling, the storage room can be filled with particles with even particle size (substantially the same size particles), but more preferably filled with particles with different particle sizes. Particularly, metal particles with the particle size of 0.1 mm-1 mm are mixed together with those particles with the particle size of 1 mm-10 mm. In that case, more efficient cooling can be achieved by locating the metal particles having smaller particle size in between the metal particles having bigger particle size.
The metal particle in this invention can for example be spherical or polyhedral. To accomplish more efficient cooling by decreasing the fraction of empty spaces that can reduce the thermal conductivity in the course of filling the metal particles, it is preferred for the metal particle to be in the form of sphere or polyhedron. Considering the economic efficiency accomplished by reducing the weight of the particle, the metal particle can be in the form of solid or hollow. The size and the hollow structure of the filling metal particles are determined by evaluating the temperature distribution and heat transfer characteristics of the storage container for spent nuclear fuel.
Further, the thermal conductivity of the metal particle is preferably at least 1.0 W/cm·K, more preferably 1.0 W/cm·K-10.0 W/cm·K, and most preferably 1.2 W/cm·K-4.2 W/cm·K. The thermal conductivity has to be considered to efficiently cool the decay heat generated from the spent nuclear fuel filled in the empty space of the storage room for spent nuclear fuel. If the thermal conductivity of the metal particle is less than 1.0 W/cm·K, the decay heat generated from the spent nuclear fuel cannot be cooled down efficiently.
In addition, considering the long term storage of the spent nuclear fuel at a high temperature, the thermal stability of the metal particle filling in has to be considered.
For example, the melting point is one factor to be considered. The melting point of the metal particle in this invention is preferably at least 500° C., and more preferably 500° C.-4000° C. Also, the metal particle is expected not to be changed in its phase at a temperature under the melting point. When the metal particle having a single phase without phase transformation at a temperature under the melting point is used, it can provides uniform cooling performance without physical property changes according to the long term storage.
Further, the neutron absorption rate of the metal particle is preferably 1×104 neutron/cm-2 neutron/cm, and more preferably 2×104 neutron/cm-1 neutron/cm. Considering the characteristics of the spent nuclear fuel emitting neutrons and radiation, the degree of radio-activation of the metal particle is also an important factor to be considered. If the radio-activation caused by the emitted neutrons is excessive, the metal particles to be filled are treated as separate radioactive waste, which increases the amount of waste. However, when it is necessary to prevent the nuclear criticality of the spent nuclear fuel, it is possible to add an element that absorbs neutrons such as boron (B) to the metal particle material.
In addition, when the metal particle material absorbs neutrons, the atomic mass increases and could become unstable, and decay with radiation emission. To reduce the possibility of radioactivation, it is preferable that the atomic mass of stable isotopes of metal particle element is 0˜3 higher than that of the reference isotope (an isotope having the highest existence ratio) of the element having a high presence ratio. Then, the element of the metal particles can be still stable even after absorbing neutrons.
The present invention also provides an interim storage container for spent nuclear fuel comprising:
a cylindrical body;
an inner container having multiple storage rooms for spent nuclear fuel that is located in the inside of the main body;
a cylindrical outer shell equipped in the outside of the main body;
a neutron shielder to block the neutrons located in between the main body and the outer shell; and
a lid connected to the top of the main body, and containing metal particles in the storage room for spent nuclear fuel.
Hereinafter, the interim storage container for spent nuclear fuel of the present invention is described in more detail.
The interim storage container for spent nuclear fuel of the present invention comprises a cylindrical body; an inner container having multiple storage rooms for spent nuclear fuel that is located in the inside of the main body; a cylindrical outer shell equipped in the outside of the main body; a neutron shielder to block the neutrons located in between the main body and the outer shell; and a lid connected to the top of the main body; and characteristically includes the metal particles filled in the storage room for the spent nuclear fuel.
The metal particles herein are filled in the empty space of the storage rooms where the spent nuclear fuel is stored, and in particular the metal particles are preferably filled in contact with the outer side of the spent nuclear fuel.
In the interim storage container for spent nuclear fuel of the present invention, the main body is cylindrical, which plays a role of supporting the interim storage container for spent nuclear fuel and to secure the loading space.
In addition, the lid herein is connected to the top of the main body to seal the spent nuclear fuel.
In the interim storage container for spent nuclear fuel of the invention, the outer shell is equipped on the outer side of the main body, which is cylindrical. The neutron shielder is located in between the main body and the outer shell in order to block the neutrons.
In the interim storage container for spent nuclear fuel of the invention, the inner container is located in the inside of the main body, wherein multiple storage rooms are formed to store the spent nuclear fuel.
The spent nuclear fuel can be discharged from light water reactors or heavy water reactors, and the spent nuclear fuel may be present as an aggregate.
The storage room for spent nuclear fuel is filled with metal particles, by which excellent cooling performance is exhibited through the filled metal particles.
Particularly, the metal particle is one or more metals selected from the group consisting of boron (B), carbon (C), magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), gold (Au), silver (Ag), platinum (Pt), and the alloys thereof, and more preferably the metal particle is selected from the group consisting of copper (Cu), zinc (Zn), aluminum (Al), magnesium (Mg), molybdenum (Mo), silicon (Si), carbon (C), zirconium (Zr), and the alloys thereof.
The particle size of the metal particle is preferably 0.1 mm˜10 mm, more preferably 0.5 mm˜5 mm, and most preferably 1 mm˜3 mm. If the particle size of the metal particle is less than 0.1 mm, there is a problem that the economical efficiency is low due to the additional cost for particle processing. If the particle size exceeds 10 mm, the cooling efficiency is reduced due to the coarse particles.
For more efficient cooling, the storage room can be filled with particles with even particle size, but more preferably filled with particles with different particle sizes. Particularly, metal particles with the particle size of 0.1 mm˜1 mm are mixed together with those particles with the particle size of 1 mm˜10 mm. In that case, more efficient cooling can be achieved by locating the metal particles having smaller particle size inbetween the metal particles having bigger particle size.
The metal particle in this invention can be spherical or polyhedral. To accomplish more efficient cooling by decreasing the fraction of empty spaces that can reduce the thermal conductivity in the course of filling the metal particles, it is preferred for the metal particle to be in the form of sphere or polyhedron. Considering economical efficiency accomplished by reducing the weight of the particle, the metal particle can be in the form of solid or hollow.
Further, the thermal conductivity of the metal particle is preferably at least 1.0 W/cm·K, more preferably 1.0 W/cm·K˜10.0 W/cm·K, and most preferably 1.2 W/cm·K˜4.2 W/cm˜K. The thermal conductivity has to be considered to efficiently cool the decay heat generated from the spent nuclear fuel filled in the empty space of the storage room for spent nuclear fuel. If the thermal conductivity of the metal particle is less than 1.0 W/cm·K, the decay heat generated from the spent nuclear fuel cannot be cooled down efficiently.
In addition, considering the long term storage of the spent nuclear fuel at a high temperature, the thermal stability of the metal particle filling in has to be considered.
For example, the melting point is one factor to be considered. The melting point of the metal particle in this invention is preferably at least 500° C., and more preferably 500° C.˜4000° C. Also, the metal particle is expected not to be changed in its phase at a temperature under the melting point. When the metal particle having a single phase without phase transformation at a temperature under the melting point is used, it can provides uniform cooling performance without physical property changes according to the long term storage.
Further, the neutron absorption rate of the metal particle is preferably 104 neutron/cm˜2 neutron/cm, and more preferably 2×104 neutron/cm˜1 neutron/cm. Considering the characteristics of the spent nuclear fuel emitting neutrons and radiation, the degree of radio-activation of the metal particle is also an important factor to be considered. If the radio-activation caused by the emitted neutrons is excessive, the metal particles to be filled are treated as separate radioactive waste, which increases the amount of waste. However, when it is necessary to prevent the nuclear criticality of the spent nuclear fuel, it is possible to add an element that absorbs neutrons such as boron (B) to the metal particle material.
In addition, when the metal material absorbs neutrons, the atomic mass increases and could become unstable, and decay with radiation emission. To reduce the possibility of radio-activation, it is preferable that the atomic mass of stable isotopes of metal particle element is 0-3 higher (up to 3 times higher) than that of the reference isotope (an isotope having a highest existence ratio). Then the element of the metal particles can be still stable even after absorbing neutrons.
Before storing the spent nuclear fuel in the interim storage container, the process of eliminating the remaining moisture from the spent nuclear fuel is necessary. At this time, if the moisture is removed after filling the metal particles as designed in this invention, it is possible to prevent the temperature of the spent fuel from rising excessively during the moisture removal process in the conventional inert or vacuum atmosphere.
Further, the present invention provides a method for cooling the spent nuclear fuel during the period of interim storage comprising the following steps:
preparing an interim storage container for spent nuclear fuel composed of a cylindrical body; an inner container having multiple storage rooms for spent nuclear fuel that is located in the inside of the main body; a cylindrical outer shell equipped in the outside of the main body; a neutron shielder to block the neutrons located in between the main body and the outer shell; and a lid connected to the top of the main body (step 1); and
filling the empty sections in the storage room with metal particles after loading the spent nuclear fuel in the storage room of the container prepared in step 1 (step 2).
Hereinafter, the method for cooling the spent nuclear fuel during the period of interim storage is described in more detail step by step.
First, in the method for cooling the spent nuclear fuel during the period of interim storage, step 1 is to prepare an interim storage container for spent nuclear fuel composed of a cylindrical body; an inner container having multiple storage rooms for spent nuclear fuel that is located in the inside of the main body; a cylindrical outer shell equipped in the outside of the main body; a neutron shielder to block the neutrons located in between the main body and the outer shell; and a lid connected to the top of the main body.
The interim storage container for spent nuclear fuel of the invention is as described above, so the description is omitted herein.
Next, in the method for cooling the spent nuclear fuel during the period of interim storage, step 2 is to fill the empty space of the storage room for spent nuclear fuel prepared in step 1 with metal particles.
According to the method for cooling the spent nuclear fuel of the invention, the heat generated from the spent nuclear fuel stored therein is directly delivered to the main body of the interim storage container by those metal particles and therefore the cooling efficiency is higher and the maintenance cost is lower than the conventional method using gas at high pressure.
Particularly, the metal particles herein are the combined metal particle mixture composed of the metal particles having the particle size of 0.1 mm-1 mm and the metal particles having the particle size of 1 mm-10 mm.
Practical and presently preferred embodiments of the present invention are illustrative as shown in the following Examples.
However, it will be appreciated that those skilled in the art, on consideration of this disclosure, may make modifications and improvements within the spirit and scope of the present invention.
The characteristics of the metal particle applicable to the interim storage container for spent nuclear fuel of the invention were analyzed as follows.
For the selection of the metal particles, the first thing to consider is that the metal particle has to have a high thermal conductivity. Secondly, the metal particle has to have a high melting point. Thirdly, the metal particle has to have a low neutron absorptiveness. However, when it is necessary to prevent the nuclear criticality of the spent nuclear fuel, it is possible to add an element that absorbs neutrons such as boron (B) to the metal material.
(1) Analysis of Thermal Conductivity and Melting Point of Metal Particles
The thermal conductivity and melting point of boron (B), carbon (C), magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), gold (Au), silver (Ag), and platinum (Pt) were analyzed. The results are shown in
As shown in
As shown in
(2) Analysis of Neutron Absorptiveness of Metal Particles
The neutron absorptiveness of boron (B), carbon (C), magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), gold (Au), silver (Ag), and platinum (Pt) was analyzed. The results are shown in
Considering that the spent nuclear fuel has the characteristics of emitting neutrons and radiation, the radio-activation degree of the particle material is also an important factor to consider. If the radio-activation caused by neutron irradiation is excessive, the used metal particles are treated as separate radioactive waste, which increases the amount of waste.
As shown in
(3) Analysis of Element Component Ratio and Radiation Behavior According to Atomic Mass of Metal Particles
The atomic masses of the isotopes and their radio-activation by neutron irradiation such as boron (B), carbon (C), magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), gold (Au), silver (Ag), and platinum (Pt) were analyzed. The results are shown in
The element dependent activation is also an important factor to consider along with the neutron absorptiveness. In general, if an element absorbs a neutron, the atomic mass of the element increases, making the element unstable, later decaying with radiation emission. To reduce the possibility of radio-activation, the atomic mass of a stable isotope for each element is preferably higher than the atomic mass of a reference element (with the highest existence ratio).
As shown in
The following experiment was performed to prove the effect of the present invention.
A dry storage container, which is a stainless steel structure imitating the nuclear fuel aggregate, was constructed as shown in
The dry storage container was placed in a 400° C. heating furnace to perform thermal equilibrium. The dry storage container was taken out and filled with copper particles, followed by cooling in the air in Example 1. In Example 2, the dry storage container was filled with copper particles first, and then placed in a 400° C. heating furnace, followed by thermal equilibrium. Then, the dry storage container was taken out and cooled down in the air.
In a Comparative Example, the dry storage container was placed in a 400° C. heating furnace without being filled with copper particles, followed by thermal equilibrium. Then, the dry storage container was cooled down in the air.
The cooling curve of the outer surface of the stainless steel rod according to each of the Examples and the Comparative Example is shown in
In the case of Example 1, it was observed that the cooling performance over the time was improved as compared with the case of cooling without copper particles.
The time required for cooling from 400° C. to 100° C. took 3649 seconds in the case of Example 1, 2475 seconds in the case of Example 2 and 4127 seconds in the case of Comparative Example. Therefore, it was confirmed that the cooling efficiency was improved by at most 40% as compared with the Comparative Example.
Those skilled in the art will appreciate that the conceptions and specific embodiments disclosed in the foregoing description may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. Those skilled in the art will also appreciate that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended Claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0077351 | Jun 2016 | KR | national |
