WO2019025315A1

WO2019025315A1 - Device and method for flow measurement in the reactor core of a boiling-water reactore

Info

Publication number: WO2019025315A1
Application number: PCT/EP2018/070455
Authority: WO
Inventors: Egon KÖNIGSTEIN; Wolfgang Schuch
Original assignee: Framatome Gmbh
Priority date: 2017-08-03
Filing date: 2018-07-27
Publication date: 2019-02-07
Also published as: DE102017117626A1; DE102017117626B4

Abstract

The object of the invention is to specify a device with which the inflow regions of the fuel elements (6) in the reactor pressure vessel (2) of a boiling-water reactor (4) can be quantified with regard to their hydraulic flow resistance. This object is achieved, according to the invention, by a measuring device (32) for flow measurement in the reactor core (8) of a boiling-water reactor (4) having a flow channel (44), in which a metering orifice (50) is arranged, and wherein measuring lines (52, 56) branch off from the flow channel (44), by means of which lines a pressure difference a established at the metering orifice during continuous flow can be measured, and wherein the flow channel (44) is arranged in a housing (34) which substantially has the external shape and the external dimensions of a fuel element (6) used in the boiling-water reactor (4), so that the measuring device (32) can be introduced into the reactor core (8) and removed again instead of a fuel element (6).

Description

description

Apparatus and method for flow measurement in the reactor core of a boiling water reactor

The invention relates to a device and a method for flow measurement in the reactor core of a boiling water reactor.

In the reactor pressure vessel (RDB) of a boiling water reactor (SWR), the coolant is sucked by the internal coolant pump from the annulus between the RPV wall and the core shell and then flows from below to the fuel assemblies. The coolant is accelerated by the pumps and has an inhomogeneous velocity distribution with distinct peaks. Until it enters the fuel elements, it undergoes a deflection by 180 ° and several cross-sectional widenings and -Zerengungen. The entrance apertures to the fuel elements are located directly at the level of the lower core grid (UKG), resulting in different Zug geometries due to the UKG webs and the different orientation of the entrance panels. These different inflow geometries also result in different hydraulic flow resistances. However, these differences in the inflow to the BWR fuel elements are not yet quantifiable and therefore not taken into account in the interpretation.

The present invention is intended to shed some light on this and make these position-specific differences quantifiable. Knowing and quantifying the hydraulic penalties of certain fuel assembly positions in the reactor core can both use margins and increase safety margins. In addition, neutron-physical mission planning will gain in accuracy.

The object of the invention is therefore to provide a device and an associated operating method with which the inflow regions to the fuel elements in Reactor pressure vessel of a boiling water reactor can be quantified in terms of their hydraulic flow resistance. The device should be easy to manufacture and handle while allowing reliable measurements.

With regard to the device, the stated object is achieved by a device for flow measurement in the reactor core of a boiling water reactor having the features of claim 1. The associated operating method is specified in claim 10.

Advantageous embodiments are the subject of the dependent claims and the following description.

The inventive device for flow measurement in the reactor core, in short measuring device, can be described by the following features:

• The measuring device has the outer dimensions of a BWR fuel assembly and can also be handled like a fuel assembly. That is, it can be transported by the fuel assembly loading machine and placed in any free position in the reactor core.

• By means of the fuel assembly loading machine, the measuring device z. B. during a planned interruption of the reactor operation (Outage), such as when fuel change, set to a free position in the reactor core.

• In the interior of the measuring device, after the coolant inlet and an inlet section, a metering orifice with associated measuring lines for detecting the pressure difference applied to the metering orifice is arranged. After an outlet section behind the metering orifice, an internal circulation pump is advantageously arranged. The inflow and outflow of orifice and pump is preferably formed by a cylindrical tube.

• This allows the determination of the integral single-phase flow resistance from the bottom of the reactor pressure vessel until it enters the fuel assembly of the core position to be measured. For this purpose, the internal, advantageously speed-controlled circulating pump is started and passes through a given speed bandwidth, wherein the present in normal reactor operation coolant throughput is simulated by the fuel assembly.

• In this process, the coolant sucked in by the pump flows through the orifice plate, with which the position-specific throughput can be determined exactly. For each position, data such as pump speed and pressure difference are recorded via the orifice plate.

• Differences between the different feed geometries of the different positions in the reactor core can be quantified from these data sets using a simple calculation algorithm.

In other words, in order to determine the flow resistance of a specific feed geometry, the pump is started in the measuring device and advantageously undergoes a speed variation, the intake mass flow being varied by the measuring device and generating a measurable pressure difference at the metering orifice. By means of the calibrated standard diaphragm, the mass flow is determined exactly and can be assigned to the respective speed of the pump. A simple calculation algorithm can be used to determine the integral flow resistance for this feed geometry. With the knowledge of this experimentally determined flow resistance, the neutron physical core design as well as the transient calculations can be carried out more precisely, opening up economic and safety margins.

An embodiment of the invention will be explained in more detail with reference to the accompanying drawings. It shows in a simplified and schematic representation:

FIG. 1 a longitudinal section through a reactor pressure vessel of a boiling water reactor with a reactor core arranged therein,

FIG. 2 shows an enlarged detail of FIG. 1 with a device for

Flow measurement in the reactor core, FIG. 3 is a top plan view of the flow measurement device of FIG. 2, and

FIG. 4 is a bottom plan view of the reactor core according to arrow IV in FIG

FIG. Figure 1 illustrates the different fuel injections at the lower core grid of the reactor core.

The same or equivalent parts are provided in all figures with the same reference numerals.

FIG. 1 shows a longitudinal section through a conventionally constructed reactor pressure vessel 2 of a boiling water reactor 4. Within the reactor pressure vessel 2, a plurality of nuclear fuel-containing fuel elements 6 forms a reactor core 8 during reactor operation. During reactor operation, the reactor core 8 is flowed through by a reactor coolant or briefly coolant, in a light water reactor essentially water, which is heated by the decay heat emitted by the fuel assemblies 6 and thereby boiled. After flowing through a steam dryer 10 arranged above the reactor core 8, the saturated steam leaves the reactor pressure vessel 2 at the top end and is fed via a connected line system to a steam turbine, in which it relaxes to perform work. After subsequent condensation in a condenser, the liquefied reactor coolant is returned through the conduit system back to the reactor pressure vessel 2, thereby closing the refrigeration cycle. The transport of the reactor coolant is effected in accordance with the forced circulation principle by associated coolant pumps, which are usually located within the reactor pressure vessel 2.

The elongate fuel elements 6 are supported upright during reactor operation between an upper core grid 12 and a lower core grid 14. The lower core grid 14 encloses as shown in FIG. 2 by means of suitable recesses, a plurality of control rod guide tubes 16, in which neutron-absorbing control rods 18 for controlling the nuclear reaction longitudinally slidably guided. The upwardly projecting from the lower core grid 14 heads 20 of the control rod guide tubes 16 form seats for the fuel assemblies 6. The respective fuel element 6 has at the lower end, for example, a conically tapered tip, which is inserted during the loading of the reactor core 8 in a self-centering manner from above into the associated seat and then rests on the annular border. One speaks therefore also of a conical seat. At the upper core lattice 12, recesses are made in alignment with the seat on the lower core lattice 14, which recesses are matched to the outer contour of the fuel elements 6, which is typically square in cross section, and fix them laterally in the vertically aligned operating position. The entirety of upper and lower core lattices 12, 14 is also referred to simply as core lattice.

In this way, a plurality of lattice-like distributed positions in the reactor core 8 is realized in plan view from above or from below, which are loaded according to the current loading plan with a fuel assembly 6. The loading and unloading of the reactor core 8 with fuel elements 6 takes place during a revision process with the aid of a fuel element loading machine installed in the reactor building. It is a crane-like construction, which engages the respective fuel assembly 6 at the upper end and lowers when loading from above through the respective recess in the upper core lattice 12 into the seat on the lower core lattice 14 or lifts when unloading in the reverse direction.

On the outer circumference of the reactor core 8 is surrounded by a substantially cylindrical core shell 22, that between the core shell 22 and the container wall of the reactor pressure vessel 2, an annular space 24 remains. Through this annular space 24, the liquid reactor coolant introduced into the reactor pressure vessel 2 flows first from top to bottom, changes its direction below the lower core grid 14 near the bottom of the reactor pressure vessel 2, and enters the control rod guide tube heads 16 through laterally peripheral openings or entrance apertures 26 one, finally, from bottom to top through the fuel elements 6 or through the corresponding voids (gaps) through in the core grid from the reactor core 8.

In summary, in the reactor pressure vessel 2 of a boiling water reactor 4, the reactor coolant is drawn by the internal coolant pumps from the annulus 24 between the wall of the reactor pressure vessel 2 and the core shell 22 and then flows from below to the fuel elements 6. The coolant is accelerated by the pumps and has an inhomogeneous velocity distribution with distinct peaks. Until it enters the fuel assemblies 6, it undergoes a deflection by 180 ° and several cross-sectional widenings and -Zerengungen. The entrance apertures 26 to the fuel elements 6 are located approximately at the level of the lower core grid 14, whereby due to the guide webs 28 on the lower core grid 14 and the different orientation of the entrance apertures 26 and the core instrumentation measuring lances 30, different inflow or inflow geometries are created. This is shown in FIG. 4 illustrates a bottom plan view of lower core grid 14 and overlying components in the direction of arrow IV in FIG. 1 includes.

The above-characterized, present in a boiling water reactor plant different hydraulic Zuströmgeometrien in the reactor core 8 are not yet quantified because they are not measurable on site and are therefore not taken into account in the core and fuel assembly. For the flow path from the bottom of the reactor pressure vessel 2 to the entry into the respective fuel element 6, several different Zuströmgeometrien can be named, each representing an integrated bandwidth of a single-phase total resistance. This flow resistance can be characterized in the language of fluid mechanics, for example by the pressure loss coefficient, also called zeta value. In order to be able to quantify these differences in the previously immeasurable different hydraulic inflows to the respective fuel element 6 on site and thus to improve the design methods, according to the present invention, a portable device for flow measurement in the reactor core 8 is provided, which will be described in more detail below becomes. The in FIG. 2 illustrated device for flow measurement in the reactor core 8, short measuring device 32, has external dimensions which substantially correspond to those of a fuel assembly 6. That is, the measuring device 32 can be handled as a fuel assembly 6 with the present in the reactor building fuel assembly loading machine and - instead of a fuel assembly 6 - set to a free position in the core grid and remove again. The measuring device 32 can therefore also be referred to as a dummy fuel element.

The measuring device 32 has for this purpose a housing 34 with the outer shape and dimension of a fuel assembly 6, typically in the form of a square box of the bottom advantageously ends with a centering cone 36 and above with a support member for the fuel assembly loading machine. For example, the total length (height) of the measuring device 32 may have a value of 4 m, with a maximum width (edge length in the cross section according to FIG. In the operating position, the measuring device 32 is seated with its weight at the bottom in a self-sealing conical seat 38 on a head 20 of a Steuerstabführungsrohres 16 above the lower core grid 14, quite analogous to a fuel assembly 6. At the upper end of the measuring device 32 in an associated precisely fitting recess of the upper core grid 12 held such that a lateral fixation takes place, but if necessary, it can be pulled upwards, also quite analogous to a fuel element. 6

Inside the box-shaped housing 34 is a cylindrical tube 42 which is arranged concentrically to the longitudinal axis 40 and which encloses a flow channel 44 for the reactor coolant. The diameter of the flow channel 44 is for example 8 cm. At the lower front end, namely in the region of the centering cone 36, the flow channel 44 has a preferably circular or annular inlet opening 46, and at the upper end end there is a corresponding outlet opening 48. If the measuring device 32 is in the operating position in the core grid is therefore during the circulation of the reactor coolant caused by a pump (see below) Flow channel 44 flows inside the measuring device 32 in the longitudinal direction from bottom to top of the reactor coolant.

To perform the desired measurements, a metering orifice 50, in particular a ring orifice, is inserted or formed in the flow channel 44, which significantly reduces the diameter of the flow channel 44 at this point to a well-defined, known value, for example 4 cm. The installation position of the metering orifice 50 is preferably located in the lower third of the flow channel 44. The metering orifice 50 is preferably located in a plane perpendicular to the longitudinal axis 40.

Just below the metering orifice 50, for example 1 cm below it, a first measuring line 52 is connected to the circumference of the flow channel 44. This means that the measuring line 52 communicates with the flow channel 44 via an opening recessed into the wall of the flow channel 44. The opening and the measuring line 52 have a relatively small diameter of, for example, 0.6 cm. The measuring line 52 is led out in the - compared to the flow channel 44 sealed - intermediate space 54 between the tube 42 and the housing 34 upwards out of the measuring device 32 and connected via a not visible here line section end to a pressure gauge, which are located outside of the reactor core 8 can. In an alternative variant, the pressure measuring device or the transducer can also be located within the measuring device 32. The measuring line 52 thus allows a tap and via the connected pressure gauge, a measurement of the pressure in the flow channel 44 immediately before (upstream) of the metering orifice 50 with only minimal influence of the flow in the flow channel 44th

In an analogous manner, a second measuring line 56 is connected to the circumference of the flow channel 44 above the metering orifice 50, for example 1 cm above it. The measuring line 56 thus communicates in terms of flow via an opening or passage, which is let into the wall of the flow channel 44, with the flow channel 44. The opening and the measuring line 56 have a relative moderately diameter of, for example, 0.6 cm. Also, the measuring line 56 is guided in the - compared to the flow channel 44 sealed - gap 54 between the tube 42 and the housing 34 upwards and connected via a not visible here line section end to a pressure gauge. This may be the pressure measuring device already mentioned in connection with the first measuring line 52 or a separate pressure measuring device. The measuring line 56 thus allows a tap and via the connected pressure measuring device, a measurement of the pressure in the flow channel 44 immediately behind (downstream) of the metering orifice 50 with only minimal influence of the flow in the flow channel 44.

By the upstream of the metering orifice 50 adjusting dynamic pressure, the pressure is higher there than on the downstream side. From the measured pressures upstream and downstream of the metering orifice 50, the differential pressure can be determined by subtracting the measured values. Alternatively, the first and the second measuring line 52, 54 may be connected to a (differential) pressure gauge, which directly determines the differential pressure or the pressure difference.

Furthermore, a circulating pump or short pump 58 is arranged in the flow channel 44 for actively influencing and promoting the flow of the reactor coolant. The pump 58 is preferably located above (downstream) the metering orifice 50 and is advantageously designed as an axial pump. In FIG. 2 are designed as axial pump motor, electrically driven motor 60 and the axial impeller 62 of the pump 58 can be seen. The motor 60 is surrounded by a flow around on all sides, streamlined fairing with low flow resistance. The connected to the motor 60 cables 64 and electrical lines for power supply and speed measurement of the motor 60 are guided via a sealed passage in the wall of the tube 42 in the gap 54 between the tube 42 and housing 34 and a not visible here line section an associated control and evaluation unit connected. The control and evaluation unit includes means for measuring and setting the current engine speed according to a predetermined measurement program. The control and evaluation unit advantageously also contains an evaluation routine for the measured differential pressure at the metering orifice 50. This evaluation routine can be coupled to a routine for evaluating and adjusting the engine speed. The control and evaluation unit is arranged in the variant shown here outside the housing 34 of the measuring device 32, so that the measuring device 32 is a measuring probe with integrated sensor (pressure sensor) and actuators (pump) but with outsourced control and evaluation unit. The control and evaluation unit can be located outside of the reactor pressure vessel 2 in a control room, for example.

In an alternative variant, the control and evaluation unit can also be integrated into the measuring device 32. In this variant, the device is overall expediently designed for an autonomous mode of operation with automatic execution of a previously programmed measurement sequence, without operator intervention during the actual measurement in the reactor core 8.

An advantageous sequence of a measuring program can be described as follows:

After lifting out a fuel element 6 sitting on a core position to be measured, the measuring device 32 is inserted there with the fuel assembly loading machine. Alternatively, the measuring device 32 can also be placed directly on an existing space.

• For flow rate measurement, pump 58 is started and runs to a specified basic speed.

The speed of the internal pump 58 is now increased successively up to a predetermined maximum speed. Alternatively, any speed variation can be traversed as a function of time.

The reactor coolant is drawn in from below by the pump 58 and flows through the measuring device 32. When flowing through, the reactor coolant generates a pressure difference across the metering orifice 50, which is measured, in accordance with the mass flow resulting at the respective speed of the pump 58.

• The speed and the measured pressure difference are recorded continuously and are therefore assigned to this core position.

• The pump 58 is switched off and the measurement is finished.

• Subsequently, the measuring device 32 is lifted out of the reactor core 8 again and, if desired, again a fuel assembly 6 is used.

• This process can be repeated until all different core positions have been measured.

The introduction of the measuring device 32 in the desired position in the reactor core 8 takes place during an interruption of the normal reactor operation, the so-called revision or Outage, with open reactor pressure vessel 2. The measurement is advantageously carried out during the Outage. Through the pump 58 integrated in the measuring device 32, a flow through the measuring device 32 and the upstream inflow region 66 is achieved without the coolant pumps of the reactor system having to run. The total expected time required for the measurement is significantly shorter than the duration of a normal outage. In this respect, an impairment of the Outage processes is not expected. The measuring device 32 needs except the power supply for the circulating pump located inside and for the pressure difference measuring cell no tools.

In principle, a variant of the measuring device 32 is possible, which makes measurements during normal reactor operation. In this variant, if necessary, the pump 58 in the flow channel 44 can be dispensed with, since the circulation of the reactor coolant is then accomplished by the coolant pumps of the reactor. With regard to the pressure difference measuring cell, in this variant an encapsulation which protects against radiation and heat is advantageous.

With the aid of the measuring device, the existing hydraulic differences in the feed geometry from the bottom of the reactor pressure vessel to the combustion Element-entry measured experimentally and quantified, for example, in the form of a zeta value. From this point on, the insights gained can make the calculations for the core interpretation more precise.

LIST OF REFERENCE NUMBERS

2 reactor pressure vessels 64 cables

4 boiling water reactor 66 inflow region

6 fuel element

8 reactor core

10 steam dryer

12 upper core grid

14 lower core grid

16 control rod guide tube

20 head

22 core coat

24 annulus

26 entrance panel

28 guide bar

30 core instrumentation

measuring probe

32 measuring device

34 housing

36 centering cones

38 conical seat

40 longitudinal axis

42 pipe

44 flow channel

46 inlet

48 outlet opening

50 orifice plate

52 measuring line

54 gap

56 measuring line

58 pump

60 engine

62 axial impeller

Claims

claims

1 . Measuring device (32) for flow measurement in the reactor core (8) of a boiling water reactor (4) with a flow channel (44) in which a metering orifice (50) is arranged, and wherein measuring lines (52, 56) branch off from the flow channel (44), by means of which a pressure difference which adjusts itself on the orifice plate (50) can be detected, and wherein the flow channel (44) is arranged in a housing (34), which essentially corresponds to the outer shape and the outer dimensions of one in the boiling water reactor (4 ) has, so that the measuring device (32) instead of a fuel assembly (6) in the reactor core (8) can be introduced and removed again.

2 measuring device (32) according to claim 1, which is such that it is manageable by an un modified fuel assembly loading machine.

3. Measuring device (32) according to claim 2, wherein in the flow channel (44) a pump (58) is arranged for the transport of reactor coolant.

4. Measuring device (32) according to claim 3, wherein the pump (58) is designed as an axial pump.

5. Measuring device (32) according to claim 3 or 4, wherein the pump (58), viewed in the flow direction of the reactor coolant, is arranged behind the metering orifice (50).

6. Measuring device (32) according to one of claims 3 to 5, wherein the pump (58) is driven by a variable speed electric motor.

7. Measuring device (32) according to one of the preceding claims, wherein the flow channel (44) by a cylindrical tube (42) within the housing (34) is limited.

8. measuring device (32) according to claim 6, wherein the measuring lines (52, 56) in an intermediate space (54) between the tube (42) and the housing (34) out of the measuring device (32) out.

9. Measuring device (32) according to one of the preceding claims, wherein the housing (34) occupies a self-sealing conical seat (38) on a head (20) of a control rod guide tube (16).

10. A method for determining the flow resistance in the inflow region (66) of a fuel assembly (6) in a boiling water reactor (4), wherein a measuring device (32) according to any one of claims 1 to 9 instead of a fuel assembly (6) in the reactor core (8). is used and is measured at the orifice (50) in flow with reactor coolant adjusting differential pressure.

1 1. The method of claim 10 wherein the measurement is during an interruption of normal reactor operation with the reactor pressure vessel (2) open, and wherein the reactor coolant is conveyed through the flow passage (44) through a pump (58) disposed in the flow passage (44).

12. The method of claim 1 1, wherein the rotational speed of the pump (58) is varied during the measurement and the differential pressure at the orifice (50) is measured in dependence on the rotational speed.