DE1218077B - Nuclear reactor whose steam-forming moderator circulates in natural circulation - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

G 21 c

German KL: 21g-21/20

Number: 1218 077

File number: U 6618 VIII c / 21 g

Filing date: November 4, 1959

Opening day: June 2, 1966

The invention relates to a nuclear reactor whose steam-generating moderator circulates in natural circulation and the core of which has channels through which the moderator flows and which extend in the direction of the moderator flow expand.

Boiling water reactors, especially those with natural circulation, are subject to restrictions imposed by the problems of heat dissipation are related. Steam plugs form in boiling water reactors, which arise from the confluence of individual bubbles with a high proportion of voids and vapor pockets form, which practically fill the entire cross-section of the natural circulation coolant channels. When the mean density of the two-phase mixture (liquid and vapor) decreases, the mean one increases Speed accordingly, leading to greatly increased frictional pressure gradients in the vicinity of the Duct outlet leads.

It has also been found that the vapor plugs that form near the duct outlet briefly sheathing the heating surfaces and ultimately destruction of the fuel elements due to overheating cause. There is a temporary increase in temperature of the heating surface, its size depends on the heat flow and the duration of the jacket. If this temperature rise is sufficient is strong, the result is an unstable condition that leads to overheating. It is therefore essential that so long as much as possible the formation of large masses of vapor is prevented, which completely fill the channel.

The invention has the object to provide a nuclear reactor in which the by the Formation of vapor plugs near the duct outlet caused friction pressure drop as much as possible is low and in which the caused by the formation of hollow pockets in the vicinity of the channel outlet Fuel overheating is significantly reduced.

A nuclear reactor with a steam-generating moderator has already become known, in which this means favorable operating conditions are achieved that the channels in which the moderator from below flows above, expand in the direction of the moderator flow, so that the mixture of lower density a relatively large flow cross-section is presented in the vicinity of the channel outlet.

In the known arrangement, in a reactor vessel with a rectangular plan, adjacent, parallel rows of fuel elements are arranged, with each row between them each wedge-like moderator elements are located, which in cross section have the shape of an upright Have triangles, so that the fuel elements

Nuclear reactor, its steam-generating moderator
circulates in natural circulation

Applicant:

United States Atomic Energy Commission,

Germantown, Md. (V. St. A.)

Representative:

Dr.-Ing. W. Abitz, patent attorney,

Munich 27, Pienzenauer Str. 28

Named as inventor:
Seymour George Bankoff,
Pasadena, Calif. (V. St. A.)

Claimed priority:
V. St. ν. America November 4th 1958
(771931)

each opposite a suitable wall and the between the fuel elements and Moderator share channels formed for the passage of the coolant-moderator mixture upwards expand.

The present invention provides an arrangement in which the use of fixed moderator sections is not required and in which an expansion of the coolant channels with better utilization of the available space, which is partly due to the omission bulky elements, such as the moderator wedges mentioned, which, due to their wide base area have considerable space requirements, is achieved.

The nuclear reactor of the type mentioned is characterized in that these channels through Walls whose surfaces are concentric to the cylindrical outer wall of the core form, the vertices of which are common to all concentric walls at a point Axis cherish, and formed by arranged between these walls fuel plates which are arranged one behind the other and aligned in radial planes.

As a result of the expansion of the coolant channels through which the moderator flows, the middle one remains

507 577/339

3 4

Velocity of the fluid from the lower wall of a coolant channel with its middle to the upper end of the channel includes a relatively uniform axis, can be calculated. According to a further, so that the large increase in friction formation of the invention is the angle β with the losses in the vicinity of the channel outlet is avoided maximum value of the ratio of the friction. In a reactor with natural circulation, 5 means for a mixture of liquid and steam on this, that the circulation speed is significantly greater increasing pressure drop Δ P (ο) in a channel than that of a straight channel of the usual type straight, parallel walls to the friction caused by the same length. for a mixture of liquid and vapor on-The invention further establishes a relation to the represented pressure drop Δ P (β) in an expanding joint, through which the angle ß, which each io the channel in the following relation:

Δ P (P) (2-Oj ₁

ΔΡ (β) i \ " _{,, η} , Ji ₁ -". . m -, - 3

19th

(l + 2j.tg / S) cos / SJI ¹ Λ-α + Λ-tgjS)
ο

D ₀ is the hydraulic diameter, where L is the For a better understanding of the invention this

Represents the total length of the channel and D _{0 shows} the hydraulic diameter of the channel which follows in connection with the drawings and which is described in more detail by the reference 20, namely shows
ratio of the cross-sectional area of the channel to four times. 1 is a view in vertical section of a

net scope is defined, where K _{1 is} the cavity boiling water reactor according to the invention,

proportion, J ₁ the ratio - £ - for the total length. F ^ig ·? ί «^ Jscher representation a top

D ₀ ° is after the section line 2-2 of F1 g. 1,

of the canal and j the ratio - £ - «r a mean ²⁵ . ^F ^ - 3 a view in vertical section emes

A> the fuel elements for the m F1 g. 1 and 2 represent

Length of the channel is. placed reactor, the section after the line 3-3

The wetted perimeter and cross-sectional area of FIG. 4 is performed,

are around the bottom of the channel around F i g. 4 is a view in section along the line 4-4

measured. If the ratio as a function of the 30 of FIG. 3,

Angle β for a reactor with a given F i g. 5 is a view in vertical section of a

O _{1 is} plotted, the corresponding angle β of the second type of fuel element for use is the one at which the ratio is a maximum in the one shown in FIG. 1 and 2 shown reactor,
achieved. For the best possible results in achieving F i g. 6 is a view in horizontal section of the

the optimum angle β of the extension becomes 35 in FIG. 3 shown fuel element according to the cross-sectional geometry of the channel in the calculation line 6-6 of FIG. 3,

gen at the vertical center kr of the channel constant _Λ ^F j &. ^{6a ei} ^ ^e fragmentary view in horizontal section

2 by the second type of fuel element after the

held. This has the consequence that the cross-sectional line 6a-6a of FIG. 5,

geometry of the lower end of the channel with every 40 F i g. 7 shows a view from below according to the value of β assigned to line 7-7, and this results in FIG. 3,

changing values of J ₁ for use in FIG. 8 is a partial view in section through one of the

Representation of the diagram of the function. For each control element of the in F i g. 1 and 2, however, there is a certain value of J ₁ , tors along line 8-8 of FIG. 9,
so that there are no major problems with the calculations 45 F i g. 9 is a sectional view of the control element after the function. In the context of the invention of the line 9-9 of FIG. 8th,

was used in the calculations of several reactor configurations. 10 is a view in horizontal section

Gurations found that the function has a maximum according to the line 10-10 of FIG. 8th,
value at very small angles, usually in the range F i g. 11 is a graph showing the

below 1 °. 50 Relationship between the ratio of the two-phase

In the case of a reactor with widening channels, the friction pressure drop in a straight channel for the two-phase pressure drop is smaller for the same weight ratio in the vicinity of the channel outlet. flow in an equivalent, expanding accordingly the heat flow in a channel and the expansion angle shows in degrees,
widening canal is less than in the case of a straight one. In this way modified reactor core, which also has the characteristics, the critical position on the channel for the burnout of the invention.

relocated downwards from the channel outlet, so that the reactor shown is a water-cooled,

an approximation to the ideal state takes place in the case of a water-moderated reactor, in which inherent stability which the critical position along the length of the channel 60 as a result of the increased neutron loss and the is distributed. It is also to be warmed that in the case of a reac- increased neutron resonance absorption in the U-238 at tor with a straight channel, a power drain to the formation of bubbles is achieved. The reactor 70 a circulation loss due to the expulsion of electricity in a cavity 72 in a concrete structure74 arranged means from both ends of the coolant channels, with a thermal insulation 76 between can lead. With widening channels, 65 would represent reactor 70 and the walls of cavity 72 the expulsion of the fluid is primarily provided.

from the diverging end of the same at lower. The reactor 70 is more disadvantageous with a pressure vessel 82 Effect on the circulation. see that has a cylindrical shape and is perpendicular

5 6

is arranged within the cavity 12. Each pressure vessel 82 is slidably disposed in a support channel 117 with a flange 83 around its net that extends through the support 114. Provided around the upper end, which rests on a shoulder 84 formed by the removable fuel elements 116 ent concrete structure 74. hold by thermal neutrons fissile Ma-At the upper end of the cavity 72 is a removable 5 for maintaining the neutron-chainable cover 85 with the help of two ring bodies 86 and consist of two types 118 and 119. and 87 attached, which are attached with an annular A neutron chain reaction cannot be initiated and maintained with the uranium formed in the upper end of the cavity 72, which is in the recess 88 in locking engagement. The isotope content found within a processing ring 89 serves to isolate the interior of the water body (H ₂ O). For this reason, the reactor 70 and the cavity 72 are surrounded by the fuel elements 118 that contain fissile material, the outside air. that of uranium with the iso-

The pressure vessel 82 encloses a container 91, while the fuel elements are contained

and a liner 92 of corrosion-resistant 119 fissile material attached to the U-235

Steel is heavily enriched on its inner surface to a corrosion of the 15 isotope, as well as uranium with the in

Steel container 91 to prevent. The inner diameter of nature's found isotope content,

of the corrosion-resistant steel lining 92 from FIG. 1 and 2 it follows that the core 95

is about 228.6 cm. The pressure vessel 82 rests on approximately the shape of an inverted perpendicular

a cylindrical container support 93 which has a truncated cone at the foot. This form is the result of the

of the container 91 is attached and on the concrete 20 special design of the fuel elements, in

construction 74 rests. The foot of the container 91 which the coolant channels provided therein

has the shape of a spherical portion 94 that coincides with in the direction of passing through it

95 designated reactor core within the pressure flow are divergent conical, as below

vessel 82 supports. described. For the use of fuel

The height of the pressure vessel 82 between the 25 elements of equal length for the whole core

Flange 83 and the spherical section 94 is approximately the surface 114a of the core holder 114 im

503 cm, measured along the axis of the pressure vessel 82. essentially in the form of a segment of a sphere and

The pressure vessel 82 is designed for pressures up to 56.2 kg / cm ² concentric to the area which is through the

and is formed at the top of the fuel elements 116 at a pressure of 42.2 kg / cm ²

operated. 30 turns. The support channels 117 are with their axes

The cavity 72 surrounding the pressure vessel 82 is arranged perpendicular to the surface 114a around the combustion hat also a cylindrical shape about 304.8 cm. To keep fabric elements in their conical arrangement. As can be seen, the thermal insulating layer 76 on the outer surface is the underside 114έ of the core holder Pressure vessel is attached, the loss of tion 114 is also essentially in the form of a Thermal energy formed from the interior of the pressure vessel 35 spherical section, which leads to the top 114a out to a minimum. The heat isolate is concentric.

tion 76 consists in the illustrated embodiment in FIG. 2 represents the dashed line labeled 95a

made of asbestos and has a thickness of about 30.5 cm. Outline the cross-section of the core 95 at its

Between the heat insulation 76 and the surfaces of the lower end. The labeled 95b full deflection

of the cavity 72, an air gap 96 is provided, the 40 continuous contour line in the right half of FIG. 2

the pressure vessel 82 also from the concrete structure represents the cross section of the core at its in FIG. 1

tion 74 thermally insulated. with 100 designated vertical center, while

The entire cavity 72 with an auxiliary container is the full outline 95c on the left

105 lined from steel, so that from the print page of the F i g. 2 shows the cross section at the upper end of the

Vessel 82 represents leaking liquid in the auxiliary container 45 core.

105 is held. Further, cavity 72 is as shown in FIG. 3 to 5 show both types a number of coolant tubes 107 in the auxiliary of fuel elements 118 and 119 at their one container 105 adjacent concrete structure 74 at the end of built-in shafts 120 that are removable give, through which a liquid coolant, in the case of the inside of the channels 117 in the holder 114 is presented Construction water, to drain the 50 are arranged. The shafts 120 are with central channels Heat flows into the concrete structure 74, which is exposed to the outside of the shafts penetrates to prevent destruction of the concrete. 120 through three openings 122 at one end of the

The cover 85 is made of concrete 108 and is connected by shafts 120. The openings 122 surrounded by a steel container 108a. Furthermore, the have the shape of sections of a circle which go through Lid 85 can be formed with an annular shoulder 109 from ribs 123, which also serve to formed, the fuel elements 116 within the holder for receiving the locking elements 86 and 87 is used, and on its underside with a 114 when loading in the required way auskugelig formed cavity 110 provided, which to prepare.

The elements 118 have two side plates 124 vessel 82 forms as described below. Through 60 on opposite sides of the shafts 120 and on Lids 85 extend by means of steam seals, which form a rectangular outlet 113, a plurality of control rod drive pre-fittings 126 extend as shown in FIG. 6 sets 111 for the control rods 112. posed. The side plates 124 are each with four

The reactor core 95 rests on a cylindrical indentations 127, the indentations being a core holder 114, which is provided with uprights 115 on opposite plates 65 opposite one another, which are attached to the bottom 94 of the pressure vessel 82. There are four between the side plates 124 are. The core 95 is made up of a plurality of plates 128, the thickness of which is approximately equal to that of the Removable fuel elements 116 are formed, one of which is depressions, arranged and in each other

7 8

opposite recesses 127 anchored. The uranium-zirconium alloy in the form of two plates 141 recesses 127 are carved out in the side plates 124 with a length of 81.3 cm and a thickness of that the spaces or channels 128a 1.29 mm, which are separated from each other by a zirconium between adjacent plates 128 are separated in the direction of piece 142 that diverge conically at the top with a thickness of 6.985 mm, as in FIG. 3 shown. The 5 and a length of 81.3 cm and in F i g. 6 a dar-side plates 124 are made in their width in adaptation. The alloy contains 5% uranium and 95 ° / ₀ of the tapered arrangement of plates 128 also zirconium, wherein the uranium ankegelig on the U-235 isotope. From Fig. 4, it follows that the plates is gereichert 128 so that it 93.5 ° / ₀ of the uranium are tapered in its width so that the channels forms, 128a alloy. Each of the parts 140a and 140c has a length of approximately 20.3 cm in its width in the upward direction, while the part 140 is yawing. The conical channels 128a are correspondingly about 81.3 cm in length. The entire body is intended for the teachings given above. 140 is with a jacket 134 made of zircon with a

The elements 118 have side plates 124 clad with a thickness of 0.508 mm. Each plate 138 has

Zircon are made with a thickness of about 3.18 mm, a thickness of about 9.5 mm and a width of about

and a length of 132 cm, the distance of 15 95.3 mm at the vertical center 100, and the sides

Side plates 124 at the vertical center 100 of the widen at an angle of ¹ ^ ⁰ with the

Core is 92 mm. Each of the side panels 124 is the centerline of the panel.

weitert at an angle of about ¹ → ⁰ of the channels 117 of the core support 114 are ansenkrechten axis of the fuel element 118. The ordered such that the elements 116 abut against each other, plates 128 have a thickness of about 9.5 mm and 20 so that the uranium-containing plates 128 and 138 are approximately a distance of about 15.9 mm from each other at the same distance from each other and in the essentially vertical center 100 of the core. Each disk 128 is borrowed as in FIG. 2, are arranged that at an angle of approximately ^χ / ₄ ° with respect to which they form approximately an inverted vertical cone center line of the adjacent channels 128a, as mentioned above,
orderly. Each of the plates 128 has a length of 25. The fuel elements 116 are arranged in rows at -121.9 mm and a width of 95.3 mm at the vertical, with the side plates 124 adjacent to the right center 100 of the core and expanding in them Rows abut one another and a total of sixteen widths at an angle of about ¹ Z ₄ ⁰ with the vertical rows are provided. From Fig. 2 shows that, on the right-hand center line of the plate in adaptation to the view from below, the first conical arrangement of the side plates 124, designated 143a. Each of the 30 rows contains two fuel elements 118, the second plate 128 consists of a body 129 and a row 143b five fuel elements 118, the third coating 130. The coating 130 has a thickness of row 143c eight fuel elements 118, the fourth 0.508 mm and consists of zirconium. The body 129 row 143a "seven fuel elements 118 and two consists of 93 ¹ I ₂ ⁰ I ₀ uranium with the elements 119 arranged in the middle of the row in nature, the isotope content found, 5% zirconium and IVa ⁰ zo niobium. 3S next row 143e nine elements 118 and three

The core holder 114 consists of corrosion ^ elements 119, the three elements 119 through

resistant steel and has a thickness of about 51 cm. Elements 118 separate and between four elements

The shafts 120 of the two fuel elements 118 118 at one end and three elements 118 at the

and 119 have annular parts 131 arranged in the other ends of the row. The next

Channels 117 fit the bracket and rectangular 40 row 143 / contains eight elements 118 and four egg-

Parts 132 on the side plates 124. The diameter elements 119, the four elements 119 by EIe-

the annular parts 131 is slightly smaller than ments 118 are separated from each other and between

the diameter of the channels 117 in the core support three elements118 at one end of the row 143 /

114 and is approximately 88.9 mm. The rectangular and two elements at the other end of row 143 /

Parts 132 expand in adaptation to the arrangement 45. The next row contains 143g

widening of the side panels 124. The upper exit seven elements 118 and five elements 119, with the

Extension 126 is hollow and rectangular in shape; five elements 119 are arranged between elements 118

the dimensions being the top of the side panels and two members 118 at one end

124 are adapted. In each exit lug 126 there is row 143g and one element on the other

a plurality of openings 133 are provided while 50 is located at the end of the row. The next series

the rectangular end is open and an exit 143A contains nine elements 118 and five elements

opening 134 forms. The outlet extension 126 consists of 119, with the five elements 119 between elements

Corrosion-resistant steel and has a length of 118 are arranged and two elements 118 are attached

about 10.2 cm. ■ located at one end of the row 143 / z while

The fuel elements 119 have the same 55 three elements 118 at the other end of the row 143h

Shafts 120 and outlet lugs 126 and the side are arranged. The information given above

parts 124 as the corresponding parts of the fuel relate to the lower half of the core 95 (ge

elements 118 on. The end pieces have the same look in FIG. 2), the upper hook of the core is 95,

widening width as well as depressions 127 to, as can be seen from FIG. 2 results, designed in a similar way.

Recording of plates 138. Between the plates 138 60 The reactor is also equipped with twelve neutron absorbing

there are tapered channels 138a, which provide regulating members 112 upwards. The regulators

diverge, where the extension ^{angles are about 1} I ^ H2 with extension rods 144 of the standard

from the center line of the canal. Drive device 111 connected, which is through

Each of the plates 138 has a body 140 which extends from steam seals 113 in the reactor lid 85,

three parts 140a, 140b and 140c. The part 140a 65 The control members 112 are slidable in tubular shape

as well as the part 140c consist of 93 ¹ I ₂ ⁰ I ₀ natural housings 147 mounted (Fig. 8, 9 and 10), which

Uranium, 5 ° / ₀ zirconium and I ¹ I ₂ ⁰ I ₀ niobium in the form of a in the core 95 of the reactor in more detail below

rectangular plate. The portion 1405 is spaced from one another in a described manner

9 10

will. The tubular housings 147 also have the next following row 143 / on the right. The following angular shape and are provided with holes 149 . However, row 143g contains four control elements, the housings 147 being made of zirconium and having both outer walls with three fuel elements 116 with a thickness of about 6.3 mm. The intermediate rods between them and the ends of the row 143g extension rods 144 are also made of zirconium and are arranged and each of the other two rules have a diameter of about 12.7 mm. The members 112 by a fuel element 118 and a control member 112 themselves are in the form of plates of fuel element 119 separated from one another. The 150, the thickness of which is 6.3 mm and the one with a next row 143A, again does not contain a control element coating 151 made of stainless steel from a 112. The above description applies to the lower thickness of 0.5080 mm. The control elements io half of the core 95, the upper half is similar to 112, have a length of about 0.91 m and a width can be seen from FIG. 2 results.

of 88.9mm at the vertical center 100 of the real- In Fig. 11 is a graphical representation

torkerns 95. The regulating members as well as the tubular type in which the function for the ratio R '

Housings 147 expand in width by ^X / ₄ ^O in the two-phase frictional pressure drop in an equal

Adaptation to the expansion of the surrounding 15-valued straight channel to the two-phase pressure drop

Fuel elements 116. The control rod drive device- at the same weight flow rate in

lines 111 can be of a type known per se, an expanding channel for the preceding one

in which the position of the control rods 112 is shown the reactor described in detail. As can be seen

can be controlled, but a rapid onset is the maximum of the function at an angle β

the control rods in an operationally reliable manner in the event of a 20 between 15 to 20 minutes, after which it falls off quickly

Enable excursion of nuclear reactivity. and at an angle of about 30 minutes below the

As can be seen from FIG. 2, also from below. Value one drops. The physical interpretation

see, the first row 143a contains the fuel for this rapid decline is that when the

Fabric elements 116 no regulating elements 112. The same widening angle increases, the throttling effect on

applies to the second row 1436 and the third row 143c. 25 channel inlet the reduction of the friction loss

The fourth row 143d , however, contains two ■ rule- near the duct outlet more than makes up for,

members 112, which from the ends of the row 14So "one in the following list are some of the

Three fuel elements 116 are spaced apart. The main design features of the foregoing

The next following row 143e does not contain any control elements, given the reactor described:

Longitudinal pressure vessel 228.5 cm in diameter - 502.8 cm in height

Pressure in the pressure vessel. “42.2 kg / cm ²

Moderator H ₂ O

Volume ratio of H ₂ O: U 2.5: 1

Core diameter 137.1 cm at the vertical center 100

Core height 121.9 cm

Maximum temperature of the fuel element surface 268.4 ° C

Maximum core fuel element temperature 321.6 ° C

Reactor power 20,000 kW

Generator power 5,000 kW

Efficiency 25 ° / ₀

Core volume 18001 in total

Average power density 11 kW / 1 of the core -

18 kW / 1 of the coolant

Maximum power density 24 kW / 1 of the core -

39.5 kW / 1 of the coolant

Saturated steam flow 7.619 lcg / sec.

Feed water supply 454 l / min.

Condensate return temperature 43.3 ° C

Average vapor bubble content in the exiting coolant 20%

Height proportion when boiling 65%

Medium vapor bubble content of the core 6,5 ° / ₀

Maximum heat flow 407 040 kcal / m ² h

Internal circulation ratio, d. H. the ratio of the water mass flow for the steam mass flow in the reactor .. 140: 1

Fuel elements 118 plates approximately 9.53 mm thick

93.5 ° / ₀ natural uranium + 5 ° / ₀ Zr + 1 V / o Nb 0.0508 mm zirconium coating, height 121.9 cm,

15.88 mm water channel with an extension of V4 ⁰

Fuel Elements 119 Natural uranium ends with a length

20.32 cm

Claims (1)

11 12 30 aggregates in the central zone of the reactor Enriched zone 81.28 cm long Zr-U-235 alloy plates
Zirconium coating - 0.25 mm
Body - 2.03mm, 5% U-235,
95% Zr water channel 15.88 mm Critical mass - operation plus burn-up of the enriched
Fuel 10 kg - U-235 and 5.443 t natural uranium Power distribution Enriched uranium output 25% / ₀ Natural uranium output 75% / ₀ Safety and regulation 12 boron steel control rods in the core. Burn-off by adding U-235 fuel.
Transitional state by inserting the
Neutron trap rule rod Ak in the vapor bubbles (operation) 0.5% Ak of temperature 2.1% Ak with 20% vapor bubbles 4.9% hot or 0.7% cold Ak with 50% vapor bubbles 8.5% hot or 6.3% cold A expansion of uranium as a result of a power excursion,
which drives out water and the resonance absorption
the melting of the fuel increased 0.17% k Effect of removing a control rod 1% k Effect of adding a fortified fuel ■
Bar 0.4% k on average or 1.0% maximum Mean lifetime of prompt neutrons 5 · 10 "" ° seconds Radial flow, that is, the ratio of the maximum flow
thermal neutrons to the mean flux thermal
Neutrons in a horizontal plane 2.2 Axial flow, d. H. the ratio of the maximum flow thermal Neutrons to the mean thermal neutron flux along the central axis of the reactor 1.43 Neutron flux (mean) 10 ¹³ n / cm ² / sec. Fig. 12 shows another embodiment of the claims:
Kerns according to the 1st nuclear reactor given by the invention, its steam-generating fashion teachings. The core 400 has an outer jacket 402 circulating naturally and the core of which has in the form of a vertical circular cone 4 ° channels through which the moderator flows bluntly. Inside the outer jacket 402 there is a series of spacers which expand in the direction of the moderator flow, characterized by jackets 404 in the form of straight circular channels in that these channels are formed by walls whose upper truncated cones and with the outer jacket are cylindrical Outer wall of the core form a common tip and a common axis 45 concentric circular truncated conical surfaces, dehav. Fuel elements 406 are located between each apex on a point of the axis jacket 402 common to all of the spacers 404 and between the outer concentric walls and the outermost spacer 404 , and are arranged by fuel plates arranged between these walls, each plate being formed by the core axis that extends radially outward. Each plate expands 50 arranged one behind the other in radial planes and necessarily in its width, as in FIG. 12 are aligned. shows. Furthermore, the plates must have an increasing 2. Nuclear reactor according to claim 1, characterized ge-thickness, which indicates with increasing distance from that the angle ß, which each wall of the core center increases, to channels 408 of a right-a Kühhnittelkanals with its central axis monagonal Cross-section between adjacent fuel 55 closes by maintaining the maximum value of the ratio of fuel plates 406 . Taking into account the pressure drop AP (0) occurring due to friction for a mixture of liquid sifting through the teachings given by the invention and steam, other designs can of course also be provided for the reactor core in a channel with straight, parallel walls. to that by friction for a mixture of The invention is not limited to the pressure drop shown and occurring in liquid and vapor Embodiments described limited, but defined AP (β) in an expanding channel that can be different within its framework, this relationship being by means of the following experience changes. Formula can be calculated: Δ PiP) (2 - «Μ AP (S) Λ 19 ο ' ^{2 (1} - ^Äl) J [(l + 2 ₇ .tg /?) CosH ί ¹ Λ-α + Λ-tgÄ
0 where L is the total length of the channel and D _{0 is} the hydraulic diameter of the channel, which is defined by the ratio of the cross-sectional area of the channel to four times the wetted circumference, where Oc _{1 is} the void fraction, y _{x is} the ratio - = - for the total length of the channel and y the ratio
Channel is. for a medium length of the Documents considered: German Auslegeschrift No. 1027 338; Belgian Patent No. 555 025; British Patent No. 793,919. For this purpose 2 sheets of drawings 507577/339 5.66 ® Bundesdruckerei Berlin