ML20058L216

Emus Diverse Sys for Reactor Water Level Measurement in Bwrs

ML20058L216
Person / Time
Site:	05200001
Issue date:	10/31/1993
From:	SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER
To:
Shared Package
ML20058L206	List: ML20058L204 ML20058L209 ML20058L216 ML20058L229
References
NUDOCS 9312160189
Download: ML20058L216 (12)

Text

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Karlstnin, October 1993 i

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E M U S

-A Diverse System for Reactor Wa t e r Level \

M e a s:u r e m e n t l in B o ilin g W a t e r -R e 'a c t o r s ^

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Siemens AG Power Generation Group (KWU)

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, Trbla of cont nts i

1 Introduction  :

2 Reactor Water Level Measurement using EMUS 2.1 Measuring Principle j 2.2 Operation of EMUS Sensors 2.3 EMUS Signals during Power Operation 3 Components of EMUS ReactorWater Level Measurement System 3.1 EMUS Sensors i

3.2 Transmitter and Receiver Electronics 3.3 Evaluation Electronics  !

4 References i

5 Technical Data i i

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( EMUS : E_lektro-Magnetic generated Ultra found )

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1 ReactorWater Lev:1 M=ur ment i

Reactor water level measurement in the reactor pressure vessel (RPV) is important for safe reactor operation. Owing to this safety function the reactor water level l measurement system is generally provided with redundancy. In the event of an accident the signals from the reactor water level measurement system are used by the reactor protection system to initiate accident control measures. Reactor water level ,

measurement is also used as a basis for the initiation of important measures by l l

limitation systems as well as closed-loop and open-loop control systems. The method used for this measurement function is generally based on differential pressure l measurement. Siemens is now offering the EMUS system for reactor water level .

measurement to supplement existing differential pressure measurement systems. This j system uses ultrasonic waves produced electromagnetically (EMUS: i l

Electromagnetically-produced Ultrasound), therefore providing diversity for this safety-related task. .

EMUS makes it possible for power plant operators to equip existing BWR plants and I new plants with a diverse system for reactor water level measurement. The use of a ,

diverse system improves accident control through diverse event initiation (probabilistics) and allows compliance with licensing authority requirements for i

diversity in reactor water level measurement.

l Backfitting RPVs with EMUS is a simple matter requiring no changes to existing structures. A permanent magnet in the EMUS sensors ensures reliable fixture to the RPV wall. The flexible cable connections between the EMUS sensors and the transmitter / receiver electronics can simply be routed through existing spare l penetrations. The electronic equipment cabinets required for the measurements can be l set up at an easily-accessible location outside the containment.

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2 R:rct::rWit;r Lovst Visecur:m2nt u:Ing EMUS 2.1 Measuring PrincirJe used by EMUS l' i

j Measurements using the EMUS system are based on the use of ultrasound which i exhibits differing transmission and reflection at the interface between two substances

depending ca their acoustic impedance. The difference between a steet/ water interface j or steel / gas mixture interface is particularly suitable for measurement. Under normal

, conditions (temperature of 20 *C) it represents approximately 9% of the total energy.

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Reactor water level measurement uses sensors which generate and receive l electromagnetic u_ltrasound. Generating and receiving the ultrasound is based on the

physical uniformity of Lorentzforce in conjunction with a magnetic field with a 2

superposed high-frequency electric current.

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i Figure 1: Generating of Ultrasound through Electromagnedc Excitation h The Fraunhofer institute for Nondestructive Testing in Saarbruecken has developed EMUS sensors which make use of an incident transverse wmva. The magnetic field is lJ perpendicular to the steel surface and the high-frequenci; current perpendicular to the

magnetic field. The current coil is of a flat design. j In order to detect a steam / water mixture the portion of the wave reflected at the RPV ,

I wall inside surface is received by a second sensor and evaluated (Figure 2).

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, Transmission of th3 sound en:rgy into th) wat:r reduces th) cmplitud:s of tha l

' ultrasonic sign:1 and this s:rv:s to d:tect tha pres:nce of wat:r. If no wat:r is pres nt 4 inside the RPV at the measuring point, the reflection amplitude is not attenuated thus j indicating a steam mixture.

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Generating and Receiving Signal using Transverse Waves 2.2 Operation of EMUS Sensors Figure 3 is a schematic showing of the arrangement of the EMUS sensors at one

' elevation on the RPV. The three sensors for one elevation are fixed horizontally to the outside RPV wall. The sensors are held in place partly by the permanent magnets in the sensors and also by additional holding magnets.

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Figure 3: Arrangement of Sensors on Reactor Pressure Vessel As the ultrasound enters the RPV wall at an angle of 40*, separate transmitting and receiving sensors are required. In the above schematic the transmitter is on the left.

Two receiving sensors 1 and 2 are installed for each measuring elevation.

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i The ultranund emitt::d from ths EMUS transmitt::r penstrat::s th3 RPV wall cnd hits ths -

inner surface of ths RPV wall, upon which ths ultrasound energy is split:

- Part of the energy is reflected at the inner surface of the RPV wall and retums to the outside surface .

- Part of the energy is transmitted into the water, if water is present ,

i Receiving sensor 1 can then be placed at an appropriate position to receive the signal reflected from the RPV wall inner surface. The reflected ultrasound is then converted to -

an electric signal at receiving sensor 1, as well as being iuther reflected at the RPV wall outer and inner surfaces. In each case a portion of the erergy is transmitted into the water at the RPV wall inner surface in the event that water is_ present. The portion of the energy transmitted into the water is approximately 9% of the energy reaching the interface under normal conditions, i.e. at a temperature of 20 *C. This process is repeated each time the ultrasound reaches the interface between the RPV wall inner-surface and the water. In the event that no water is present at the interface, none of the '

ultrasound energy is transmitted, instead the' energy is completely reflected.

Where water is present the ultrasound is transmitted at an angle of approximately 10' l into the water. After passing through the water the energy is reflected at an RPV internal (reflector), again passes through the water and reenters the RPV wall through  ;

wave conversion. After passing through the RPV wall the ultrasound reaches the first .

EMUS receiving sensor and is converted into an electric si0 nal.

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2.3 EMUS Signals during Power Opsrction j '

As described in 2.2 above, different signals are received depending on the RPV water l

level. These signals are evaluated in the evaluation electronics and result in the

following typical amplitude histories

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- Elevation 1 14 5 m - Elevation 2 14.6 m

- Elevation 4 14.9 m j j

- E4evation 3 14 8 m l

l Figure 4: Backwall Echoes at Reactor Full Power l

i A relatively smooth signal history with smaller amplitudes can be observed at those l i

j elevations below the water level. The elevations above the reactor water level' exhibit erratic signal histories over the measuring period. The fluctuation in amplitudes is the l result of streams of water running down the inner RPV wall which cause short-duration  !

intermittent transmission of the ultrasound energy.

These varying amplitude histories are converted into YES/NO statements for signal generation.

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In order to illustrate the functional capability of this diverge system for reactor water level measurement, Figure 5 shows the time history for differential pressuro I

measu'rement (delta P) in comparison with level measuremer.t using the EMUS system  !

1 in a test at 60% reactor power Both systems indicate the samo levels.

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Figure 5

Level Measurement by DlWerential Pressure Method and using EMUS

! 3 Components of EMUS Reactor Water Level Measurement System EMUS comprises the EMUS sensors, transmitting / receiving electronics and evaluation electronics. The components are shown in the following figure.

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Figure 6: Diagram of EMUS Reactor Water Level Measurement System i

I installation of the sensor units is extremely easy as a permanent magnet in the sensors i fixes them firmly to the RPV wall.

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i 3.1 EMUS Senxrs i

l I As trie maximum temperature prevailing on the outer wall of the RPV is around 300 *C, I the EMUS sensors must be designed for continuous use at this temperature over a ,

j period of several years. The static magnetic field required for generation of the l

) ultrasound is produced by a permanent magnet.

l j Each EMUS transmitting or receiving sensor basically comprises a housing, a j cylindrical permanent magnet of the size of a fist, a carrier for the high-frequency coil, a j high-frequency coil as well as a cover in which the coil carrier is embedded.

j Figure 7 shows an EMUS sensor with its approximately 15 m-long connecting cable i qualified for use in the reactor area.

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3.2 Transmitting and Receiving Electronics j The tr'ansmitter and. receiver electronics are set' up outside the containment.L Cable lengths between the sensor equipment and the transmitter and receiver electronics can ,

be up to 65 m, allowing maintenance on transmitter and receiver electronics during reactor power operation. The electronics are-installed in an electronic equipment cabinet and comprise the following plug-in modules:

transmitter '

amplifier, receiver fan j power supply unit.  ;

The transmitter and receiver electronics are r, elf-monitoring. ]

3.3 Evaluation Electronics The evaluation electronics can be set up in an electronic equipmentLeompartment, for? j i

example, close to the main control room. They comprise: ,

a computer module (processor) . .;

- workstation with keyboard oscillograph. ,

The evaluation electronics are self-monitoring. Connections are provided for.leveli l indication, alarm and fault annunciations in the main control room.- j s

t 4 References i

1990 KRB 11, Unit C BWR .1308 MW.  : SIEMENS/KWU-- 1 KRB 11, Unit B BWR 1308 MW SIEMENS/KWU -  ;

1991 in close cooperation with the Customer KGB of Gundremmingen Nuclear Power Station (KRB ll) in Germany, an EMUS reactor water level measurement system with 4 different -

measuring elevations was installed in Units B and C including evaluation' electronics,. ,

main control room indication and linkup to the main control room computer. The reactor - l water level measurement system was taken over by the customer in 1992 following j confirmation of compliance with measuring requirements. ]

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5 Technical Data i

Measuring principle Transmission of ultrasound energy into water .

Type of ultrasound waves used Transverse waves with vertical polarization and 40' beam angle upon introduction into ,

vessel wall Generating and receiving Through electromagnetic ultrasound' trans-  :

ultrasound ducers ,

i Measuring points Each equipped with one transmitting and two receiving sensors ,

Yes/no statement per' measuring point via'  :

Evaluation of water level backwall echo trend Confirmation of indication Via reflector echo evaluation from vessel and-consideration of conditions in vesse ,

System response time in Approx.10 secs . ,

j event of level changes l

Application During all reactor operating phases (cold, hot l

! and intermediate conditions) ,

Vessel diameter > 2000 mm ,

Vessel wall thickness > 50 mm [

l Vessel material Outside ferritic steel, inside cladding < 10 mm (where provided) i Distance between < 150 mm (where provided) ~  !

reflector /vesselinner wall l l

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vessel outer _ ' wall, : with- horizontal j Sensor arrangement On -

alignment and held by_ permanent magnets l

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Arrcngim:nt of Either horizont:1 cround the circumference of  :

rin:su, ring equipment the v:ssel.with .the possibility of providing' .i' redundancy for - 'e I. vel indication at ' .one' elevation, or vortical above one another with a i- level statement at various elevations.

Ambient temperatures Sensors < 300 *C ~

Transmitter / receiver / < - 30 *C ~

control electronics (SEKE)- ..

Evaluation electronics (AWE) < '.30*C-2 ,

Air humidity < 80 % -

Cable lengths Sensors / SEKE < 65 m '

SEKE/ AWE < 300 m;  ;

Measurement electronics - Computer-controlled, self-monitoring ,

Output of results Parallel interface-. to ' main -- control room - -

computer.for alarm and fault indication  !

- Main control room level indication - ,

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