DE2051064A1 - Core for a combined fast converter breeder reactor - Google Patents

Description

BW 621 / CE 2939

2'J. 8. 70 ko / ko

Applicant's Combustion Egg ^ Uieering, Inc. Windsor, Connecticut, U.S.A.

Core for a combined fast Converter breeder reactor

The success of light or thermal reactors which use uranium as fuel is of great importance for the use of such power plants in the future. The uranium consumption of those already commissioned Power plants is no longer small in relation to the estimated uranium reserves. Therefore must be long-term Fuel supplies are secured if the generation of energy by nuclear power plants is further built up shall be.

Most promised for the production of nuclear energy are large fast breed reactors. Are sonic breeders Reactors that use plutonium as fuel and at the same time incubate plutonium from uranium 2 ^ 8 at a rate that is greater than that of plutonium » abrandes 1st. The doubling time «Ines such a reactor If the time required is a quantity of plutonium su breeding, dl Identical reactor is sufficient.

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Once in operation, batteries generate plutonium ai.n fipaltBtof ι * for further reactors, but one PIuton is unique! fs I ^{1 For} the initial fission material inventory in the breeding reactor, it is necessary until there are enough breeders that can survive. This source must be relatively large if a large network of breeders is to be put into operation quickly; shall be. Most of this plutonium will be produced by converter reactors that use 235 uranium fuel and convert 238 uranium to plutonium. Analyzes have shown that piutenium-producing converters ^{1 will} be needed many years after the introduction of fast breeders in order to satisfy the needs of the rapidly expanding capacity of fast breeders. The converter remains the main source of plutonium until 2000, even when fast breeders with a doubling time of 7.2 years until 1985 are available. However, if the breeders only have an average doubling time of 20 years, the converters slip the main plutonium source until 2040.

The total amount of uranium that is ultimately required for a converter = Breeder Reactor Netζ is required depends directly on the ratio of the tons of natural uranium oxide consumed per kg of fissile plutonium produced, which falls with a certain converter type. This ratio is for sohneil · converter much smaller, maybe only half • o large or less, than for Leiohtwaseer or thermal Converter. Therefore «· β was very cheap, similar converter Use together old breeders to reduce fuel consumption. This applies auoh, although fast Converters compared Hit these converters at the Generation of energy are economically limited. This is compensated by the increasing amount of plutonium, which per Unit of the electrical Auegangeleitung is produced. The aim is to bring the breeders more into the network and reduce uranium consumption.

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Fin we * ¹ more excellent J oint, which are considered at sohne5len reactors ιηυππ, the normal legally poeiHve reactivity ^ Koefflziert ftui is ürund bubbling in the coolant. In thermal reactors, e.g. B Light water reactors If the coolant forms bubbles, this results in a local reduction in the moderator concentration, which in turn results in a decrease in reactivity. Therefore this ⁶ JCVp from the thermal reactor is inherently stable. This does not apply to fast reactors, because the energy spectrum of the neutrons is harder, ie the mean energy of the neutrons is hWier when bubbles form in the coolant. The greater hardness of the spectrum is itself expressed in an increase in the mean number of neutrons which are produced in the fuel per absorbed skin electron. This effect together with the decreasing absorption of neutrons in the coolant result in a positive coefficient of reactivity due to the formation of bubbles. In addition, the coefficient of the coolant density would be negative, ie the reactivity would increase with decreasing coolant density. If this is caused by other factors such as B. the geometric arrangement of the nucleus, with which the growing neutron leakage, which accompanies the bubble formation, cannot be overcorapensated, the entire coefficient of activity remains positive and represents a safety risk. Even if the total coefficient of reactivity is kept as small as possible by geometrical arrangements that increase neutron leakage, the local reactivity coefficient in the center of the nucleus, where the neutron leakage itself is small, is still positive enough to be a hazard to build-.

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In order to avoid this safety risk, are reactor cores for fast breeders (US patent 3 287-224), which j η a central area uranium. 23Ji and Thorium 232, and in a central area plutonium and uranium 238 ent = and are surrounded by a blanket. However, these reactors have the serious disadvantage that thorium and Uranium 233 does not occur in nature on a large scale.

It is an object of the invention to specify a new reactor core that combines conversion and breeding in a fast reactor, uses natural uranium 235 as a fuel component and contributes to the safety risks due to a positive reactivity coefficient due to the formation of bubbles in the coolant a fast breeder avoids.

According to the invention, this is done by a central one Converter area, the fissile uranium 235 and the breeding Contains uranium 238, a middle breeder area following the converter area and fissile plutonium and 238 contains fertile uranium and an outer blanket that surrounds the converter and breeder areas and is fertile Contains uranium 238

The breeder area also surrounds the central converter area both in the horizontal and vertical direction and the blanket surrounds the converter and breeder areas also in the horizontal and vertical direction

The arrangement according to the invention has the following advantages. Because the neutron cross sections of uranium 235 and behave differently from plutonium with the neutron energy, it has been found that fast reactors loaded with uranium 235 (i.e. fast converters) have a considerably lower tendency

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too positive reactivity ^ coefficients due to the Bubble formation have as fast reactors that with Are equipped with plutonium (i.e. fast breeders). In addition, if part of the plutonium is a rapid Breeder is replaced by uranium 235, the tendency to one positive ReaktivLtäts coefficient decreases Uranium 235 preferably concentrated in the center of the reactor core «* where the tendency towards a positive reactive! ity <-> If coefficients can be mastered most difficultly, the dampening effect of uranium 235 is most widely distributed.

Another port step in reactor safety the use of uranium 235 instead of plutonium is the greater proportion of the braked neutrons that are produced in his Cleavage arise, and the speed of performance Attenuate changes to or and from reactivity changes. Again, the uranium 235 has the best effect when it is close is concentrated in the center of the reactor core, where a neutron has the greatest impact on the chain reaction.

The present invention thus relates to an arrangement of fissile and incubable material in the core of a nuclear reactor who reports the security risks due to the positive reactivity coefficients due to the formation of bubbles in fast breeders, which reduces the proportion of those effectively slowed down Neutrons increased without stupid brooding and the economic Significantly affect the characteristics of such fast breeders. In view of the fact that converter In connection with fast breeders for the Plutonium Ver supply must be used and in view of the fact that it is cheap to have fast converters

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turn, the invention suggests duns the Kon '/ er ο Lon and breeding combined into a single rapid reactor; will. That would be the coordination of the safety of the uranium 2jii> equipped converter with the high yield when breeding both Reactor types mean.

The invention will now be carried out with the aid of the accompanying drawings described. In the drawings show:

Figure Is part catfish in section the side view ui.uua Nuclear reactor;

Figures 2 and 2; sohematlsch vertical and horizontal

Cuts through the reactor core;

Figures 4, 5 and 6 s vertical sections through focal rods

for different areas of the reactor core.

In the case of similar reactors, the effects of the harsher Neutron spectrum and the increased neutron production due to the formation of bubbles in the coolant to generate a negative reactivity coefficients are compensated if simultaneously with the bubble formation of the neutron leakage from the fissile material is increased considerably. In the case of relatively small, fast breeders, the first is the neutron Leakage is relatively large and increases when bubbles form in the coolant so that an overall negative Coefficient of reactivity arises. However 1st; at large fast breeders the effect of neutron leakage less important is the increasing hardness of the spectrum and the increased neutron production give rise to an increase in reactivity. This problem is the most serious in the center of the reactor core, where the leakage loss is smallest 1st.

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According to the present invention, the central "part of the Core one? Coline. "U en reactor through an on converter area replaced, in dom uranium 235 is used instead of plutonium a3.s fissile material. The problem of reactivity!? - Kopff3 served Due to the formation of bubbles, it is 2/55 smaller for uranium as bej. Plutonium. The reasons for this are as follows? (3 .. the gap cross-section for plutonium increases with the neutron energy, on the other hand the fissure cross-section of uranium 235 falls in the energy range of interest. {? .. The decrease in the ratio of capture to cleavage processes with increasing Neutron energy is greater for plutonium than for uranium 235 in the one that comes into consideration for extremely fast reactors Energy liver 5oh. (3. The proportion of braked neutrons is with uranium 235 larger than with plutonium. It means that a certain increase in reactivity, e.g. due to the Bubble formation in the coolant results in a smaller or slower increase in the output of uranium 235 expresses

Figure 1 shows the fast converter breeder reactor 10 of the present invention. The reactor core 14, which consists of a number of individual fuel elements 16, is suspended within the reactor vessel 12. The reactor coolant, which is usually the case tendon] 3ο reactors liquid sodium passes through umr inlet 18 and flows downward in the annular space between the reactor vessel 12 and core wrap? 0th The coolant then flows upward through the reactor core 16 and exits the outlet 22.

Figures 2 and 3 show schematically the arrangement of the incubable and fissile material in the core 14 according to the present invention Invention. In the center of the kernel there is a Area 24, the converter area, the uranium 235 and uranium 238 contains The uranium 235 is the fission material and the uranium 238 the incubable material which is converted into plutonium during the operation of the reactor. The converter area

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24 is surrounded by the breeder area 26, the fissile Plutonium and fertile uranium 238 as with conventional ones Contains breeders. Although the breeder area in the illustration the converter «area in both axial and radial Direction, it is intended that the breeder area surrounds the converter area only in the radial direction and the parts of the breeder area that are above and below of the central converter area can be omitted. The exact details of the arrangement and relative sizes of converter 'and breeder areas depend heavily on the desired ratio of conversion to breeders, as well on the reactivity coefficient. The breeder area of the reactor is surrounded by the blanket, as is the case with conventional breeders contains spent uranium and fertile uranium 225. The blanket consists of the radial part 28 and the axial parts 30

Figures 4, 5 and 6 illustrate the different types of Brennetäben represent the construction of the In Figures 2 and shown reactor cores are used. The fuel rod 32 is used in the central part of the reactor core and contains a combination of breeding, fissile and spent material in such a way that the three separate Areas for blanket, conversion and incubation can be set up. Located in the upper and lower part of the fuel rod tablets 34, which consist of spent uranium. Even though only two such tablets have been shown, understands it turns out that the tablets vary in size and number can. Follow the blanket tablets 34 inside, Tablets 36, made from a mixture of plutonium and uranium 238 exist. These tablets 36 form the breeder area of the Reactor cores and lie above and below the converter area In the center of the fuel rod 32 tablets 38 are arranged, which contain a mixture of uranium 233 and uranium 238 and form the central converter area 24 of the reactor core.

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Figure 5 shows the fuel rod 40 "of the in the annular region between the central region and the converter Blanket 28 is used, this fuel rod 40 contains the tablets J54, the in the axial Blanket-BsreJ.ch Hegen 30 and the rest of Brennstaba contains the tablets 36, i.e. all of them extend from one axial blanket area to the other. The tabs 36 of the fuel rod 40 form the radial breeder area around the central converter area. The fuel rod 42 of FIG. 6 is used. ά \\ ν production of the radial blanket region 28. This rod includes the tablets £ 4, di.e it on its entire length with spent nuclear uranium filling.

Although the brUtbare and fissile material would be presented the brtltbaren MaterLaIs with two different types of fissile material into the converter and breeder areas \\\ i \ mixture, other arrangements within dee of the invention are possible. For example, the core Ln be different Tablotten with which the fuel rods are fitted in a suitable arrangement, the brUtbare and fissile material for each of these areas.

Appendix J Claims

2 sheets of drawings with
6 figures.

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Claims (3)

20h1064 ίο - 1.) Came for a combined quick conv; t't Reactor, characterized by a central na Kim / ert; ifi.v - Area, the fissile uranium 235 and breeding tower; ι j mm 2;) ö contains, a middle breeder area following the converter - B-M-Uloh, the fissile plutonium iaid bi-tH: - contains real uranium 238 and by a HuuMeruu Hiunket, that surrounds the converter and breeder Berelohe and roars «» Contains uranium 238. 2.) Core according to claim I, characterized in that the breeder area r; h both horizontal and vertical direction iun _t -; iM and the »Blanket the converter and breeder Deielohe ebunfalLs Ln horizontal and the vertical direction. 3.) Core naoh claim 2, consisting of a plurality of Burning rods characterized by a first set of Fuel rods In the central converter area, which is in your Center for the formation of the converter area uranium 2 ^ 5 and Uranium 2 ^ 8, in both ends forming part of the Blankets uranium 238 and between the ends and the middle also uranium 238 to form part of the breeder area contained, by a second, the first horizontally surrounding the first set of fuel rods, the one in the center to form another part of the ürllter-BoreIch Uranium 238 and also uranium 2J8 in both ends to form contained another part of the blanket and by a third, surrounding the second in the horizontal direction Set of fuel rods that contain uranium along their entire length and form another part of the blanket. BAD ORiGfNAL 109820/12 16 Blank page