Breeder reactor using metallic spent nuclear fuel from light water reactor

Abstract

To provide a reactor capable of securing long-term energy from accumulated spent nuclear fuels from a light water reactor.SOLUTION: Power is generated using a reactor having a low power density and a void reactivity coefficient of zero. The inherent safety can be enhanced as much as possible by reducing the output scale. Even if a coolant is lost, cooling can be achieved using air or nitrogen. Metallic spent nuclear fuel (10), obtained by metallizing oxide-based spent nuclear fuel from a light water reactor, is used.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to the burning of spent nuclear fuel in light water reactors. [Background technology]

[0002] It seems that development of nuclear reactors that use enriched uranium with thermal neutrons from a moderator and helium is progressing, claiming that it is highly safe. However, there is no mention of how to handle spent nuclear fuel. It seems that they are trying to further increase the accumulated amount of spent nuclear fuel. Even if reprocessing of spent nuclear fuel is limited to light water reactors, it will not solve the problem of final disposal sites. DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0003] There is an enormous accumulation of spent nuclear fuel from light water reactors. The main composition of spent nuclear fuel from light water reactors is a plutonium enrichment of about 1 wt%, and an enrichment of uranium 235 of about 0.5 wt%. It has not been reprocessed because it has not been specifically decided when and into which reactor it will be loaded. Furthermore, there is no solid technology for reprocessing spent nuclear fuel from light water reactors, which is an oxide. There appears to be experience with reprocessing metallic nuclear fuel from a military perspective. There have been advances in dry reprocessing in recent years, and it appears possible to convert oxides into metals. Figure 1 shows the burnup behavior related to the main components when metallic uranium 238 is burned without neutron leakage, estimated based on the fact that the minimum critical mass without a reflector for metallic uranium 238 is about 100 kg (22.8 kg for U235, 5.6 kg for Pu239). Figure 2 shows the burnup behavior related to the infinite multiplication factor based on Figure 1. Looking at Figures 1 and 2, if metalized light water reactor spent nuclear fuel is collected in large quantities, neutron leakage will be reduced, and it will likely reach criticality and be able to be burned. Light water reactor spent nuclear fuel contains about 1 wt% plutonium enrichment and about 0.5 wt% uranium 235 enrichment, so criticality is probably possible. The enrichment level of weapons-grade plutonium is set at 90 wt% or more from the viewpoint of transportation. From the viewpoint of fizzling, the enrichment level of weapons-grade plutonium is required to be 90 wt% or more in order to reduce the amount of plutonium-240. In Figure 1, there is almost no Pu240 ratio. Therefore, fizzle does not need to be considered. There is no need to exceed the criticality significantly in a short time. There is no need to greatly increase the Pu239 enrichment. As the burnup increases, the accumulation of fission products becomes significant and neutrons are absorbed unnecessarily, so the infinite multiplication factor should decrease, but in Figures 1 and 2, the accumulation of fission products has been ignored. Xenon and samarium will be a problem with slow neutrons, but will not be a problem with fast neutrons. Fast neutron absorption by the platinum group metals and hafnium will be a problem. The values ​​in both figures are rough calculation results, but can be verified by calculations using the nuclear calculation code SRAC. Assuming that Pu239 is 100% as in Figure 2, Pu239 decreases as burnup progresses, but Pu240, 241, and 242 increase, and kinf (group 1 without neutron moderation. Fission products are not considered) shows almost no change due to burnup. kinf remains large. [Means for solving the problem]

[0004] Method 1 is a light water reactor spent nuclear fuel metallized breeder reactor. The light water spent nuclear fuel metallization breeding reactor comprises a nuclear fuel container (100), a neutron moderating low-temperature coolant (220) flowing inside the nuclear fuel container (100), and a number of controlled reflectors (110) laid on the top surface of the nuclear fuel container (100), all contained in a radiation shielding container (200). The neutron moderating coolant (220) is a heavy noble gas or a liquid of a low melting point heavy metal. The nuclear fuel container (100) is made up of a number of flat sealed containers (1200) arranged in a lattice pattern. The flat sealed container (1200) contains metallic light water reactor spent nuclear fuel (10) made by metallizing oxide light water reactor spent nuclear fuel in a stainless steel sealed container (1000). A sealed cylinder (1100) is placed on top of the sealed container (1000) to allow the liquefaction and expansion of the metallic light water reactor spent nuclear fuel (10). A bottom neutron reflector (221) is fixed to the bottom surface of the sealed container (1000), and a side neutron reflector (222) is fixed to the outer side surface of the sealed container (1000) disposed on the outer periphery.

[0005] Heavy rare gases are rare gases other than helium. They include xenon, argon, krypton, and xenon. They have a lower neutron moderation effect than helium (Patent Document 1). Low melting point heavy metals are metals with a low melting point and large mass. Examples include gallium, tin, lead, and bismuth. They have a very low neutron moderation effect. It will be placed inside the dome of a dome stadium. Safety will be enhanced by volume rather than sturdiness. Rare gases hardly become radioactive, so there is no problem even if they leak into the outside world. The radioactive lifetime of the released fission products is relatively short. If they are constantly filtered and released into the environment, large amounts of fission products will not be released into the environment in the event of an accident. [Patent Document 1] Patent application 2023-131719

[0006] Method 2 is a limited light water reactor spent nuclear fuel metallized breeder reactor. The dimensions of the metallic light water reactor spent nuclear fuel (10) of the first embodiment are 17 cm in length and width, and 17 cm or less in thickness. Since it is not exposed, neutron leakage is suppressed, and therefore the critical state can be ensured. Effect of the Invention

[0007] In principle, the reactor of the present invention accumulates less Pu240. Pu240 is difficult to produce if there is little Pu239. Even if it is produced, Pu240 undergoes nuclear fission. Even when it becomes spent nuclear fuel, it can be handled without worrying about fizzling. There is no need for a final disposal site, and it is possible to reduce the amount of spent nuclear fuel from light water reactors while making effective use of it. can. The large amounts of U238 contained in spent nuclear fuel from light water reactors can be converted into a metal and effectively disposed of. Metallic light water reactor spent nuclear fuel (10) is made by reprocessing spent oxide light water reactor nuclear fuel and turning it into metal. Even if heavy elements such as iron group and platinum group metals are contained in the metallic light water reactor spent nuclear fuel, this does not pose any significant obstacle to criticality or combustion. In reprocessing, the emphasis is on removing light metals. There is no need for a final disposal site. More and more local governments are applying to be selected as interim storage sites. This will put a stop to the expansion of depopulated areas. BEST MODE FOR CARRYING OUT THEINVENTION

[0008] We have been able to provide a nuclear reactor that can burn spent nuclear fuel from light water reactors. Disposal of spent nuclear fuel is expected to become possible. Example 1

[0009] Example 1 is a light water reactor spent nuclear fuel metallized breeder reactor. Figure 3 is an external view of a light water reactor spent nuclear fuel metallized breeder reactor. The nuclear fuel container (100) is made up of a number of flat sealed containers (1200) arranged in a lattice pattern. The flat sealed container (1200) contains metallic light water reactor spent nuclear fuel (10) made by metallizing oxide light water reactor spent nuclear fuel in a stainless steel sealed container (1000). A bottom neutron reflector (221) is fixed to the bottom surface of the sealed container (1000), and a side neutron reflector (222) is fixed to the outer side surface of the sealed container (1000) disposed on the outer periphery. A neutron-moderating low-temperature coolant (220), such as a heavy noble gas or a liquid heavy metal with a low melting point, flows through the nuclear fuel vessel (100). A number of control reflectors (110) are laid on the upper surface of a nuclear fuel container (100). The nuclear fuel container (100) and the control reflector (110) are housed in a radiation shielding container (200). Neutrons leaking in the planar direction of the metallic light water reactor spent nuclear fuel (10) can travel between the metallic light water reactor spent nuclear fuel (10) contained in adjacent sealed containers (1000), so there is effectively no neutron leakage in the planar direction. A sealed cylinder (1100) with an open bottom and closed top is placed on top of the sealed container (1000). It stores the expanded amount of metal light water reactor spent nuclear fuel (10) that melts. A coolant insertion pipe is connected to the nuclear fuel container (100) so that a neutron moderating low coolant (220) flows into the nuclear fuel container (100).

[0010] The neutron moderating low-temperature coolant (220) flowing on the top surface of the flat sealed vessel (1200) and the bottom surface of the bottom neutron reflector (221) receives heat from the metal light water reactor spent nuclear fuel (10). The coolant that has received heat and become high temperature passes through a coolant discharge pipe connected to the nuclear fuel container (100), the radiation shielding container (200), and reaches the power generating device installed outside. After completing its work in the power generating device and becoming cold, the coolant passes through a radiation shielding container (200) and enters the nuclear fuel container (100) through a coolant insertion tube. The controlled reflector (110) is made of a coil of electrically insulated wire wound multiple times, with a movable neutron reflector iron core passing through it. If it is likely to go beyond criticality, the movable neutron reflector iron core is pulled out along the surface of the nuclear fuel container (100), and neutrons leaking from the metallic light water reactor spent nuclear fuel (10) are absorbed by the radiation shielding container (200). If subcriticality is imminent, a movable neutron reflector iron core is inserted along the surface of the nuclear fuel container (100), and neutrons leaking from the metallic light water reactor spent nuclear fuel (10) are reflected by the movable neutron reflector iron core and returned to the metallic light water reactor spent nuclear fuel (10), thereby maintaining criticality. The top of the nuclear fuel container (100) is removable.

[0011] In case of emergency, borax or sodium pentaborate solution is sprinkled on the nuclear fuel container (100) to absorb leaking neutrons. It can also be cooled with outside air. It can also be cooled with nitrogen gas or carbon dioxide gas. The sodium pentaborate solution absorbs leaking neutrons. If the roof of the radiation shielding container (200) is made of boron-doped stainless steel, it will absorb leaked neutrons. The sides of the radiation shielding container (200) will be made of boron-doped concrete to absorb leaked neutrons (it will be made fragile and an aqueous solution of sodium pentaborate will be injected in an emergency). The bottom of the radiation shielding container (200) will be made of boron-doped concrete with rebar embedded in it to absorb leaked neutrons. The earthquake resistance of the flat sealed container (1200) is improved if it is supported by a seismic isolation platform.

[0012] The controlled reflector (110) may be constructed of multiple coils of electrically insulated wire wound around a movable neutron absorbing iron core. If it is likely to go beyond criticality, a movable neutron absorbing material-added iron core is inserted along the surface of the nuclear fuel container (100) so that the movable neutron absorbing material-added iron core strongly absorbs neutrons leaking from the metallic light water reactor spent nuclear fuel (10). If it looks like the reactor is about to become subcritical, the movable neutron absorbing material-added iron core is pulled out along the surface of the nuclear fuel container (100), and the small number of neutrons that have leaked from the metal light water reactor spent nuclear fuel (10) (the small number because the reactor is subcritical) are allowed to leak out as they are and absorbed by the radiation shielding container (200), maintaining the reactor's subcriticality. In addition, criticality is maintained by inserting and removing neutron absorbing plates vertically into the gaps between adjacent flat sealed containers (1200).

[0013] Example 2 is a limited light water reactor spent metallized fuel breeder reactor. The metallic light water reactor spent nuclear fuel (10) in the first embodiment has dimensions of 17 cm in length and width, and a thickness of 17 cm or less. If the thickness is 17cm, it is critical, if it is less than 17cm, it is subcritical. Because it has a reflector, even a thickness of 15cm can be critical. It is desirable that the thickness of the metallic light water reactor spent nuclear fuel (10) be about 10 cm, and that the controlled reflector (110) cover the upper surface of the metallic light water reactor spent nuclear fuel (10) to make it critical. [Industrial Applicability]

[0014] With the nuclear reactor of this invention, it is possible to secure long-term energy from accumulated spent nuclear fuel from light water reactors. It can withstand long-term defensive battles. Furthermore, if applied to land mines or naval mines, it can provide robust defense. Since the proportion of Pu240 is low, it does not implode, but simply put two subcritical blocks into a solid tube and combine them with explosives to explode. Since light water reactor spent nuclear fuel is an oxide, all that is needed is to remove the oxygen and turn it into a metal. However, since the question is whether the United States will allow it, we will handle it in small quantities and implement it when the time comes. With this technology, Japan's light water reactors can be sold to foreign countries without incurring Japan's unlimited liability for damages. At first glance, small gas reactors and high-temperature gas reactors appear to have no problems, but it seems like they are pretending not to notice. It is believed that there are no problems with gas reactors because the Wigner effect has been resolved and that the problem has been solved by replacing British structural materials with Japanese materials in Japan. The construction of HTGRs has been fraught with twists and turns, so were there no problems with operating hours or availability? To investigate these issues, experimental and conceptual reactors are being built jointly by Japan and the UK (the UK's latest aircraft carrier is prone to problems. Designed in the UK, manufactured in Japan? Manufacturing responsibility in Japan), and Japanese trading companies are investing in US ventures with courage and bravery. As we have seen with the Olympics and the World Expo, we are being forced to make additional investments. In the past, when several companies tried to jointly provide North Korea with a light water reactor, GE refused. Nuclear reactors are a matter of technical competition, and when several companies work together, you never know what will happen. Japan adopted Sweden's internal pump BWR to create the ABWR. Germany has been researching coal-fired gas-fired reactors for many years. It would not be surprising if at least one small Japanese trading company were to investigate Sweden or Germany's technology. Because the reactor of the present invention is simple, it is expected that the reactor of the present invention can be designed, inspected, repaired, and maintained in a manner similar to that of a private automobile inspection center. [Brief description of the drawings]

[0015] [Figure 1] Combustion behavior of metallic uranium-238 in relation to its main components when burned. [Diagram 2] Combustion behavior related to infinite multiplication factor based on Fig. 1. [Diagram 3] FIG. 1 is an external view of a light water reactor spent nuclear fuel metallized breeder reactor according to the present invention. [Explanation of symbols]

[0016] 10 is metal light water reactor spent nuclear fuel. 100 is a nuclear fuel container. 110 is a control reflector. 200 is a radiation shielding container. 220 is a low-temperature neutron moderating material. 221 is the bottom neutron reflector. 222 is the side neutron reflector. 1000 is a sealed container. 1100 is a sealed cylinder. 1200 is a flat sealed container.

Claims

1. The light water spent nuclear fuel metallization breeding reactor comprises a nuclear fuel container (100), a neutron moderating low coolant (220) flowing inside the nuclear fuel container (100), and a number of controlled reflectors (110) laid on the upper surface of the nuclear fuel container (100), all of which are housed in a radiation shielding container (200); The neutron moderating coolant (220) is a heavy rare gas or a liquid of a low melting point heavy metal; The nuclear fuel container (100) is made up of a number of flat sealed containers (1200) arranged in a lattice pattern. The flat sealed container (1200) contains a metal light water reactor spent nuclear fuel (10) made by metallizing oxide light water reactor spent nuclear fuel in a stainless steel sealed container (1000), A sealed cylinder (1100) is placed on top of the sealed container (1000) to allow the liquefaction and expansion of the metal light water reactor spent nuclear fuel (10); A light water reactor spent nuclear fuel metallized breeder reactor, characterized in that a bottom neutron reflector (221) is fixed to the bottom surface of the sealed vessel (1000), and a side neutron reflector (222) is fixed to the outer side surface of the sealed vessel (1000) arranged on the outer periphery.

2. The dimensions of the metal light water reactor spent nuclear fuel (10) of claim 1 are 17 cm in length and width, and 17 cm or less in thickness.

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