DE102012216480B3 - boiling water reactor - Google Patents

Abstract

The invention relates to a boiling water reactor (8) with a reactor pressure vessel (14) having a bottom wall (12) with a recess (10) through which a drive housing (10) of a control rod drive (6) is passed, wherein in the final assembled state, the drive housing ( 4) is welded to the bottom wall (12) or to a nozzle (80) connected to the bottom wall (12). In this context, a safety device (2) is to be specified by the housing (4) is kept in the demolition case by the bottom wall (12) of the reactor pressure vessel (14) with simple held assembly and good accessibility for maintenance, without additional voltage spikes and increased operational fatigue of the reactor pressure vessel (14). For this purpose, the invention provides that • below the welding point (16) a retaining device (2) for the drive housing (4) is formed in the event of failure of the weld (16) or a tear, the retaining ring enclosing the drive housing (4) (24) with a lower end face (40) and with an upper end face (44), • the lower end face (40) of the retaining ring (24) of an underneath annular step (30) of the recess (10) faces, • the upper end surface (44) of the retaining ring (24) facing an annular step (50) of the drive housing (4) faces, and • the retaining ring (24) is not in the power flow of the drive housing (4) in normal operation.

Description

The invention relates to a boiling water reactor with a reactor pressure vessel having a bottom wall with a recess through which a drive housing of a control rod drive is passed, wherein in the final assembly state the drive housing tube is welded to the bottom wall or with a bottom wall connected to the nozzle.

In a boiling water reactor, the control rods controlling the nuclear chain reaction are usually run from below through the bottom wall or bottom plate of the reactor pressure vessel. For this purpose, the bottom wall is provided with suitable bores or general recesses, through which in each case a drive housing tube or drive housing for the control rod drive is guided. The drive housing accordingly encloses the components required for holding or linear movement of the respective control rod into or out of the reactor core. On its outer periphery that is firmly seated in the final assembly in the recess and its opposite pressure-tight sealed drive housing with the bottom wall or welded to a connected to the bottom wall spigot.

In the event of breakage of the weld or other demolition, the control housing drive housing tube should be reliably held in the bottom wall of the reactor pressure vessel to prevent impingement of the control bars. At the same time a simple installation of the control rod drive should be ensured with good accessibility in case of maintenance. So far, in addition to external restraints with tie rods and compensating elements, which only partially meet the latter requirement, there is the idea of an internal retainer with bayonet lock, for example, in the German Patent No. 10 2011 008 202 AREVA NP GmbH is described. However, the solution generates voltage peaks at the cams of the bayonet, which can lead to material fatigue in the region of the reactor pressure vessel bottom in the event of temperature and pressure fluctuations.

The patent DE 199 47 103 C2 discloses in the figures and in the associated description a boiling water reactor with a drive housing arranged and fixed in the bottom wall of the reactor pressure vessel (US Pat. 7 ), which in addition a the drive housing enclosing retaining ring (outer shell 15 ), having a lower end surface, which is an annular step ( 35 ) facing the recess. In this case, according to paragraph [0044], a force flow is already provided when the weld connection is intact.

It is therefore an object of the present invention to provide a safety device by the housing of a boiling water reactor control rod drive is held in the demolition case by the bottom of the reactor pressure vessel with simple held assembly and good accessibility for maintenance, without affecting thermal expansion in both normal operation as possible even with an assumed meltdown - and without additional voltage peaks and increased operational material fatigue of the reactor pressure vessel.

The above object is achieved by the features of claim 1.

• • unterhalb der Schweißstelle eine Rückhaltevorrichtung für das Antriebsgehäuse im Falle eines Versagens der Schweißstelle oder eines Abrisses ausgebildet ist, die einen das Antriebsgehäuse umschließenden Rückhaltering mit einer unteren Stirnfläche und mit einer oberen Stirnfläche aufweist,
• • die untere Stirnfläche des Rückhalterings einer sie untergreifenden ringförmigen Stufe der Ausnehmung zugewandt ist,
• • die obere Stirnfläche des Rückhalterings einer sie übergreifenden ringförmigen Stufe des Antriebsgehäuse zugewandt ist, und
• • der Rückhaltering im Normalbetrieb, also bei Abwesenheit einer Versagenssituation und insbesondere bei intakter Schweißstelle/Schweißnaht und intaktem Antriebsgehäuse, nicht im Kraftfluss des Antriebsgehäuses liegt.

Accordingly, a boiling water reactor of the type mentioned is such that

• A retaining device for the drive housing is formed underneath the weld in the event of a weld failure or a break which has a retaining ring enclosing the drive housing and having a lower end face and an upper face,
• The lower end face of the retaining ring faces an annular stepped step of the recess,
• • the upper end face of the retaining ring faces an annular step of the drive housing that overlaps it, and
• • The retaining ring is not in the power flow of the drive housing in normal operation, ie in the absence of a failure situation and in particular with an intact weld / weld and intact drive housing.

The term "ring" here explicitly includes the case of a plurality of separate, circumferentially juxtaposed and separated by gaps or gaps between ring segments, so to speak of multiple circumferentially interrupted rings (see below).

This means that the retaining ring is not burdened by the weight of the drive housing in normal operation with an intact weld, or at least does not forward to the surrounding lower portion of the bottom wall, but that the load bearing and distribution over the weld in the uppermost area of the bottom wall or the connected with her, inwardly projecting into the reactor pressure vessel neck occurs. In this case, the retaining ring is expediently dimensioned such that it absorbs the forces transmitted to it by the lowering drive housing in case of breakage of the weld or in any other demolition case and passes over the stage of the recess in the bottom wall, ie only in Demolition case fulfills the load-bearing function assigned to it.

Advantageously, for this purpose, the lower end face or seat surface of the retaining ring is spaced by an axial gap from the step of the recess. Alternatively or additionally, the upper end surface or seat surface of the retaining ring is spaced by a gap from the stage of the drive housing tube. The gap is expediently large enough that it is maintained at expected thermal expansions in normal operation, but on the other hand small enough not to realize any significant acceleration distances for the demolition in the case of lowering reactor pressure vessel, and so to limit the impact forces to a manageable level.

Preferably, the recess in the bottom of the reactor pressure vessel is shaped and dimensioned such that on the one hand when mounting the drive housing tube can be inserted together with the retaining ring from below, and on the other hand, the drive housing tube in the final assembly position with little play in the recess.

Specifically, for this purpose, the retaining ring is in a first preferred variant in the circumferential direction of several, preferably four to eight similar, separate ring segments together, between the drive housing tube and the retaining ring from a plurality of separate ring segments, preferably two half rings, composite intermediate ring is arranged ,

In this way, at first the ring segments of the retaining ring placed around the drive housing tube during assembly and then the drive housing tube are pushed together with the loosely assembled retaining ring from below in the axial direction in the recess, the ring segments of the retaining ring initially not radially over the stage of Survive recess. This is effected only by the ring segments of the intermediate ring, which are then pushed from below in the axial direction between the drive housing tube and the ring segments of the retaining ring and spread them in a sense radially. As a result, the retaining ring finally radially engages over the step formed in the recess and is blocked by it in its axial movement downwards.

In this variant, it is expedient that the retaining ring and the intermediate ring protrude in the final assembly position, for example by means of molded projections down from the bottom wall, the ring segments of the intermediate ring by means of radial fixing screws and / or pins connected from the outside to the ring segments of the retaining ring and so against axial Shift are secured. Thus, the radial spreading of the retaining ring is securely maintained by the intermediate ring.

In a second advantageous variant of the retaining ring is in the final assembly directly to the drive housing tube, wherein the drive housing tube tapers below the retaining ring in at least the extent conically, in which the retaining ring projects radially beyond the step of the recess.

This means that in this variant also composed of a plurality of ring segments retaining ring is initially placed around the lower, tapered portion of the drive housing tube during assembly. Subsequently, the drive housing tube is inserted together with the retaining ring from below into the recess, and beyond the intended final assembly position of the drive housing tube out. Subsequently, the drive housing tube is lowered down to the final assembly position, while the retaining ring with a suitable, such as fork-like tool is held in its vertical position. As a result, slip the ring segments of the retaining ring over the conical / conical widening of the drive housing tube and are pressed radially outward, over the step of the recess in its spread end position. In this end position, the step of the recess blocks the movement of the retaining ring down.

In a sense, in the second variant of the intermediate ring of the first variant is firmly integrated into the drive housing tube.

It is particularly advantageous in all variants, when the step of the recess and the lower end face or seat of the retaining ring in mutually complementary manner with respect to the longitudinal direction of the drive housing are inclined, so as in the case of demolition, the at least partially laterally / radially directed introduction of the forces in the Optimize the bottom wall.

The advantages achieved by the invention are in particular that are secured by a built in the reactor pressure vessel bottom safety device with insert elements, the control rods of boiling water reactors in a simple and reliable manner against imposition of failure of the drive housing, without the risk present in other constructions of bias losses and without increased material fatigue of the reactor pressure vessel or the security device itself.

Several embodiments of the invention will be explained in more detail with reference to drawings. In it show in each simplified and schematic representation:

1 a first securing device for a drive housing of a control rod drive in longitudinal section,

2 the safety device according to 1 in an explosive, partly longitudinally cut and partly perspective view,

3 a second securing device for a drive housing of a control rod drive in longitudinal section,

4 a reactor pressure vessel of a boiling water reactor with a plurality of control rods, each associated with a drive housing having such a securing device, and

5 a section from 4 ,

Identical parts are provided with the same reference numerals in all figures.

The safety device, also referred to as a restraint device 2 according to 1 serves to secure a drive housing 4 a control rod drive 6 for a boiling water reactor 8th (see also 4 and 5 ). The drive housing 4 is through a recess 10 in the bottom wall 12 the reactor pressure vessel 14 led and in a only in 5 schematically indicated upper area at the weld 16 with the bottom wall 12 or with a nozzle connected to the bottom wall 80 welded.

The safety device 2 according to 1 includes a plurality of inner insert elements 18 made of steel, which in its entirety one the drive housing 4 form enclosing inner ring shell, which also serves as an intermediate ring 20 referred to as. The inner insert elements 18 make ring segments of the intermediate ring 20 In the exemplary embodiment, two half-rings or half-shells are present, which extend to the intermediate ring 20 complete.

The safety device 2 further comprises a plurality of outer insert elements 22 made of steel, which in their entirety form an outer ring shell enclosing the inner ring shell, which also serves as a retaining ring 24 referred to as. The outer insert elements 22 make ring segments of the retaining ring 24 In the embodiment, the retaining ring 24 from a total of six such ring segments (ie Sechstelringen) formed.

The intermediate ring 20 and the retaining ring 24 are in the final assembly position shown here in the annular space between the inner surface of the recess 10 in the bottom wall 12 and the drive housing 4 , The drive housing 4 and the recess 10 are each designed substantially tubular or cylindrical. Their axial direction points along the direction of the arrow 26 , and its radial direction points along the direction of the arrow 28 ,

The recess 10 has an inferior lower step 30 with a seat as well 32 designated lower boundary surface, seen in the axial direction, an upper stage 34 with an upper boundary surface opposite. Overall, one can also speak of the fact that the diameter of the otherwise cylindrical recess 10 in the bottom wall 12 in an axial section through a circumferential annular groove 36 is enlarged, in which case in the embodiment, the lower boundary surface and the upper boundary surface of the annular groove 36 Beveled relative to the horizontal. The lateral boundary surface or lateral surface extends vertically.

The retaining ring 24 forming outer insert elements 22 have at the upper head end on its outer side in each case a complementary to the annular groove 36 shaped, for positive engagement in the annular groove 36 provided projection 38 on. In particular, they have at the lower end of the projection 38 one of the seat 32 the ring groove 36 facing and here in the embodiment in the final assembly on her resting lower face 40 on. Finally, have the outer inserts 22 an upper end face 44 , which is horizontally oriented here in the embodiment and the outer edge according to the upper level 34 the recess 10 is beveled downwards.

The through the inner insert elements 18 formed intermediate ring 20 Overall, the contour of a simple cylinder shell.

The drive housing 4 has one of the upper end face 44 of the retaining ring 24 opposite, horizontally extending and through an axial gap 46 spaced from her contact surface 48 on, as a radial projection or as a step 50 of the drive housing 4 is designed and the drive housing 4 circulates annularly. In the below this stage 50 located lower section is the diameter of the drive housing 4 smaller than in the upper section above the step.

Here are the drive housing 4 and the recess 10 in the bottom wall 12 in terms of shape and diameter designed so that the drive housing 4 together with the Components of the safety device 2 from below into the recess 10 can be pushed to the final assembly position.

For the assembly, first the retaining ring 24 forming insert elements 22 around the drive housing 4 placed, and the drive housing 4 will then be in this pre-assembled state along the direction of the arrow 26 in the axial direction from below into the recess 10 pushed until the radial projections 38 and the ring groove 36 are about the same height.

Spreading the outer insert elements 22 , their respective outer projection 38 in the head area as already mentioned on the contour of the annular groove 36 is adjusted during assembly by inserting the inner Einlegelemente 18 of the intermediate ring 20 in the forming annular space between the drive housing 4 and retaining ring 24 causes. This ensures in the final assembly state, as in 1 shown, for a precisely matched and form-fitting arrangement of drive housing 4 , Intermediate ring 20 and retaining ring 24 in the recess 10 the bottom wall 12 ,

In doing so, as in 2 is visible, the enlarged as a result of Aufspreizens spaces between the outer insert elements 22 through oblong patches 52 , which are inserted from below into the spaces filled.

The inner insert elements 18 of the intermediate ring 20 Beyond that with the outer insert elements 22 of the retaining ring 24 over at least one each in the foot area below the bottom wall 12 arranged through an associated radial bore in the two insert elements 18 . 22 passed pen 60 connected, so that an axial displacement down and in particular a falling out of the inner insertion elements 18 is prevented from the arrangement. The pencils 60 are each about a guided outside the ring circumference along spring plate 62 with associated fixing screws 64 , which in radial orientation in associated holes in the outer insert elements 22 are screwed and have external screw heads, clamped in the manner of a snap closure (see also 2 ).

In the final assembly position, a firm connection of the drive housing 4 with the reactor pressure vessel 14 by welding in one here only in 5 schematically indicated upper area formed (circumferential weld / weld 16 ). In the head area of the retaining ring 24 is according to 1 a gap across the entire radial extent 46 between the upper end face 44 and the opposite contact surface 48 or level 50 of the drive housing 4 designed so that no upsetting force from the drive housing 4 on the retaining ring 24 is exercised, the retaining ring 24 So not in the power flow of the drive housing 4 lies. In other words, normally there is no force flow from the drive housing when the weld is intact 4 over the insert elements 18 . 22 to the lower seat 32 in the bottom wall 12 the reactor pressure vessel 14 instead of.

Alternatively, the retaining ring 24 with its upper face 44 on the drive housing 4 abut and at the bottom by a gap from the step 30 in the recess 10 be spaced. Also two columns, one above and the other below, are conceivable.

When loosening the welded joint, for example by tearing in the event of overstress, the drive housing would 4 without the security device 2 unhindered against the direction of the arrow 26 moving in the longitudinal direction and could unfavorable breakage from the bottom wall 12 the reactor pressure vessel 4 fall out. Due to the design of the retaining ring 24 In such a case, however, a blocking order is brought about: the drive housing 4 shifts only slightly down until the gap 46 is closed and the force acting in the axial direction of the drive housing 4 over the contact surface 48 to the upper end face 44 of the retaining ring 24 and from this over the lower end face 40 and the seat 32 to the bottom wall 12 is passed on.

Due to the oblique orientation of the facing bearing surfaces of the end face 40 and seat 32 also finds a partial deflection of the original opposite to the direction of the arrow 26 acting in the longitudinal direction force flow, so that also a radial force flow component along the direction of the arrow 28 emerges from the wall of the reactor pressure vessel 14 can be easily recorded.

In 3 is an alternative design of the safety device 2 shown, is dispensed with in a separate intermediate ring.

The drive housing shown here only to the right of the engraved symmetry axis 4 As seen in the longitudinal direction has three areas with different diameters, namely decreasing from top to bottom, on. The transition 57 between the lower portion and the middle portion is tapered. For mounting, there are the retaining ring 24 forming inlay elements 56 in the lower area with the smallest diameter and are shared with the drive housing 4 in the direction of the arrow 26 from below into the recess 10 the bottom wall 12 pushed (starting position in 3 shown in dashed lines). Upon reaching the intended installation height, the insert elements 56 fixed at this height by a tool attacking from below, while the drive housing 4 pushed back down a little bit. At the conical junction 57 to the middle portion with the larger diameter are the insert elements 56 radially outward into the associated annular groove 36 in the bottom wall 12 pressed and fixed in it, so that finally the in 3 formed with solid lines Montageendstellung formed.

Regarding shape and function of the retaining ring 24 applies mutatis mutandis to the first variant according to 1 and 2 Said. The gap 58 is located here in 3 below the retaining ring 24 between the lower end face 40 of the retaining ring 24 and the seat 32 the ring groove 36 in the bottom wall 12 could alternatively or additionally but also above the retaining ring 24 between the upper end face 44 of the retaining ring 24 and the opposite contact surface 48 of the drive housing 4 to be available.

According to 4 and 5 becomes the security device 2 used in a nuclear facility, namely preferably a boiling water reactor 8th holding a reactor pressure vessel 14 and at least one drive housing 4 for a control rod drive 6 includes. About the control rod drive 6 becomes the associated control rod 70 linear in the reactor core 72 in or out of it. Here is the drive housing 4 according to 5 through a bottom side, that is in the bottom wall 12 arranged recess 10 in the reactor pressure vessel 14 passed and therein at a weld 16 fixed. The weld 16 more precisely, it is located at the top of the bottom wall 12 the reactor pressure vessel 14 molded or attached neck 80 while the security device 2 as previously described in the lower part of the bottom wall 12 located.

LIST OF REFERENCE NUMBERS

2

Safety device / restraint

4

drive housing

6

CRDM

8th

boiling water reactor

10

recess

12

bottom wall

14

RPV

16

weld

18

inner insert element

20

intermediate ring

22

outer insert element

24

Retaining ring

26

Arrow / axial direction

28

Arrow / radial direction

30

lower level

32

seat

34

upper level

36

ring groove

38

head Start

40

lower end face

44

upper face

46

gap

48

contact area

50

step

52

filling

56

insertion element

57

crossing

58

gap

60

pen

62

spring plate

64

fixing screw

70

control rod

72

reactor core

80

Support

Claims (9)

Boiling water reactor ( 8th ) with a reactor pressure vessel ( 14 ), which has a bottom wall ( 12 ) with a recess ( 10 ), by which a drive housing ( 4 ) of a control rod drive ( 6 ) is guided, wherein in the final assembly state • the drive housing ( 4 ) with the bottom wall ( 12 ) or one with the bottom wall ( 12 ) connected nozzles ( 80 ), • below the weld ( 16 ) a restraint device ( 2 ) for the drive housing ( 4 ) in case of welding failure ( 16 ) or a tear-off which forms the drive housing ( 4 ) enclosing retaining ring ( 24 ) with a lower end face ( 40 ) and with an upper end face ( 44 ), the lower end face ( 40 ) of the retaining ring ( 24 ) of an annular step ( 30 ) of the recess ( 10 ), • the upper end face ( 44 ) of the retaining ring ( 24 ) of an annular step ( 50 ) of the drive housing ( 4 ), and • the retaining ring ( 24 ) in normal operation not in the power flow of the drive housing ( 4 ) lies. Boiling water reactor ( 8th ) according to claim 1, wherein the lower end surface ( 40 ) of the retaining ring ( 24 ) through a gap ( 58 ) from the stage ( 30 ) of the recess ( 10 ) is spaced. Boiling water reactor ( 8th ) according to claim 1 or 2, wherein the upper end face ( 44 ) of the retaining ring ( 24 ) through a gap ( 46 ) from the stage ( 50 ) of the drive housing ( 4 ) is spaced. Boiling water reactor ( 8th ) according to one of claims 1 to 3, wherein the recess ( 10 ) is shaped and dimensioned such that on the one hand during assembly, the drive housing ( 4 ) together with the retaining ring ( 24 ) can be inserted from below, and that on the other hand, the drive housing ( 4 ) in the final assembly position with little play in the recess ( 10 ) sits. Boiling water reactor ( 8th ) according to claim 4, wherein the retaining ring ( 24 ) seen in the circumferential direction of several, preferably four to eight, separate ring segments composed. Boiling water reactor ( 8th ) according to claim 5, wherein between the drive housing ( 4 ) and the retaining ring ( 24 ) one of a plurality of separate ring segments, preferably two half rings, composite intermediate ring ( 20 ) is arranged. Boiling water reactor ( 8th ) according to claim 6, wherein the retaining ring ( 24 ) and the intermediate ring ( 20 ) down from the bottom wall ( 12 protrude, and wherein the ring segments of the intermediate ring ( 20 ) by means of radial fixing screws ( 64 ) and / or pens ( 60 ) with the ring segments of the retaining ring ( 24 ) are connected and secured against axial displacement. Boiling water reactor ( 8th ) according to claim 5, wherein the retaining ring ( 24 ) directly on the drive housing ( 4 ) is applied, and wherein the drive housing ( 4 ) below the retaining ring ( 24 ) conically tapered to at least the extent in which the retaining ring ( 24 ) radially across the step ( 30 ) of the recess ( 10 ) survives. Boiling water reactor ( 8th ) according to any one of claims 1 to 8, wherein the step ( 30 ) of the recess ( 10 ) and the lower end face ( 40 ) of the retaining ring ( 24 ) are inclined in a complementary manner to each other with respect to the horizontal.

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