GENES4/ANP2003, Sep. 15-19, 2003, Kyoto, JAPAN Paper 1233

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DEVELOPMENT OF INTERNAL CRD FOR NEXT GENERATION BWR

Tadashi NARABAYASHI, Tetsuzo YAMAMOTO, Michio SATO, Noriyasu KOBAYASHI, Tsuneji KAMEDA, Tadashi TOKUMASU, Shohei KAWANO and Tsuyoshi HAGIWARA

TOSHIBA Corporation 8 Shinsugita-cho, Isogo-ku, Yokohama 235-8523, Japan

Phone: +81-45-770-2324, Fax: +81-45-770-2483 e-mail: tadashi.narabayashi@toshiba.co.jp

Michitsugu MORI and Shuichi OHMORI R&D Center, Tokyo Electric Power Company

4-1 Egasaki-cho, Tsurumi-ku, Yokohama 230-8510, Japan Phone: +81-45-613-6701, Fax: +81-45-613-7899

e-mail: mori-mcy@rd.tepco.co.jp

Takayuki TERAI , Haruki MADARAME and Yuichiro MORIMOTO University of Tokyo

7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Phone: +81-3-, Fax:

e-mail: tera@q.t.u-tokyo.ac.jp

Keywords: next generation BWR, internal CRD, heatproof ceramics insulated coil, heat-resistant

motor, gravity driven scram, non-RIA, easy IVR

Abstract – In order to develop a competitive and higher performance Next Generation BWR compared with a fossil power plant, an internal CRD using a heatproof ceramics insulated coil is under development. In case of a 1700MWe next generation BWR, the internal CRDs are installed in a RPV whose size is equivalent to the 1356 MWe ABWR, and there will be no space required for CRDs and CRD exchange under RPV. These advantages realize a compact PCV and reduced volume of a reactor building. Moreover, the internal CRDs eliminate penetration via a bottom flange of RPV, and lower installation level of RPV in a drywell. This brings further advantages of elimination of RIA (Reactivity Induced Accidents) caused by CR withdrawing under pressure boundary broken, and easy IVR (In Vessel Retention) by vessel bottom cooling in case of severe accidents.

I. Introduction

The internal CRD consists of (1) a heat-resistant motor for normal adjustment of CR position, (2) heat-resistant solenoid drive latch mechanism for gravity driven scrum operation and (3) an electromagnetic power coupling for signal and power transmission from outside of RPV. These new devices need heat-resistant magnet coils used in high-

pressure and high temperature coolant in RPV. Therefore, the technical development for the internal CRD is performed focusing on the ceramics insulated coil approximately 600 deg C or more. The technical development items are as follows: 1) Development of heat-resistant motor and driving mechanism and latch magnet for gravity driven scram.

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2) Development of the ceramics insulated heat and radiation resistant coil. 3) Durability test of a ball bearing for the internal CRD in the high-pressure and high-temperature reactor coolant under BWR condition. 4) Evaluation of structural integrity and flow instability due to two-phase flow of core exit condition.

This program is conducted as one of the selected offers for the advertised technical developments of the Institute of Applied Energy founded by METI (Ministry of Economy, Trade and Industry) of Japan.

Fig. 1 The project cooperation teamwork

II. Plant Concepts The next generation BWR, the internal CRDs are

installed in a RPV whose size is equivalent to the 1356 MWe ABWR, as shown in Fig.2. Major components in the RPV are the double co-axial dryer, low pressure-drop separators, the internal CRD, the magnet coupling power connector, guide chimneys, core fuels installed in shroud-less core structure, and eight large RIPs with the tube core flow meter. The dimensions for major components are shown in Fig.3.

. Table 1 Major Specification

Fig.2 3D-CAD view of the next generation BWR Fig.3 The dimensions for major components

Current ABWR

Next generation BWR

Electrical output （MWe） 1356 1700 Thermal output （MWth） 3926 4922 Main steam flow（103kg/s） 2.11 2.64 RPV inner Diameter(m) 7.11 7.11 Type of core C-lattice C-lattice Number of fuel bundles 872 988 Number of CRDs 205 257 Number of separators 349 218 Dryer flow area (m2) 58 78 Rated core flow (104kg/s) 1.45 1.57 Number of ＲＩＰ 10 8

(1)Internal CRD MechanismDr. Narabayashi et.al,TOSHIBA- Electromagnetic System- Heat-Proof Morter- Electromagnetic Connector

(2) Ceramic insulated coilProf. Terai,

University of Tokyo- High-Temperature Test - Radiation Test

(3)Evaluation for BWR conditonDr. Mori & Mr. Ohmori, TEPCO

- Durability test of a ball-bearing- Nutron and Water Chemistry

(4) Flow & Structural integrityProf. Madarame,

University of Tokyo- Two-Phase Flow Instability- Two-Phase FIV

(1)Internal CRD MechanismDr. Narabayashi et.al,TOSHIBA- Electromagnetic System- Heat-Proof Morter- Electromagnetic Connector

(2) Ceramic insulated coilProf. Terai,

University of Tokyo- High-Temperature Test - Radiation Test

(3)Evaluation for BWR conditonDr. Mori & Mr. Ohmori, TEPCO

- Durability test of a ball-bearing- Nutron and Water Chemistry

(4) Flow & Structural integrityProf. Madarame,

University of Tokyo- Two-Phase Flow Instability- Two-Phase FIV

58 02

3,660

1,500

4,404

3,703

2,283

3,300

5,873

21,063

7 1 12

Double co-axial dryer

Internal CRD

Magnet-coupling power connector

RIP tube flow meter

Shroud-less core

CRD guide Chimney

Low pressure-drop separators

Eight large RIP

3

ABWR's RPV

Next-GenerationBWR's RPV

Suppression pool

Main steam line

10m

As shown in Fig. 4, there is a space of 10 meters under the RPV of the current ABWR. The height is needed to withdraw the CRD from the bottom of the RPV. The internal CRDs eliminate penetration via a bottom flange of RPV, and lower installation level of RPV in a drywell, as shown in Fig 5. These advantages realize a compact PCV and reduced volume of a reactor building.

Further advantages are elimination of RIA (Reactivity Induced Accidents) caused by CR withdrawing under pressure boundary broken, and easy IVR (In Vessel Retention) with a small volume of water for vessel bottom cooling in case of a severe accidents, as shown in Fig.6.

Fig. 4 Space under the RPV of the current ABWR

Fig 5. Lower installation level of RPV in a drywell

(a) Current ABWR (b) Next Generation BWR Fig.6 Simplification of bottom of the RPV

III. Power Devices for the Internal CRD

1. Magnet Coupling Power Connector

In order to realize the internal CRD system, electric power must be sent via pressure boundary and some kind of power connectors should be used for the annual maintenances of the CRDs and fuel shuffling in a core. Therefore, the magnet coupling power connector was developed. Fig.7 shows the principle of the magnet coupling power connector. There is a pressure boundary

Fig.7 A principle of the magnet coupling power connector

10m

HCU

IVR Cooler

IVR Cooler

TAF

TAF

NWL NWL

磁路2

φm(磁束)

二次コイル

二次電流

一次コイル

漏洩磁束

一次電流

磁路1

金属板(圧力バウンダリ)

空隙長

Iron core

Secondary coil

Pressure boundary

Primary coil

Gap

Magnet flux)

Iron core

Leakage flux

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(a) Secondary current is max. (b) Secondary current is 0

wall between two magnet coils. The magnet coupling power connector is a kind of transformer that can be divided into the primary and the secondary coils. The points to increase the transmission efficiency are provided to suppress the induction heating in the pressure boundary and to minimize the leakage flux.

Fig.8 shows the schematic concept of the magnet coupling power connector installed in the RPV. The magnet coupling power connector is a co-axial cylindrical structure of the primary outer coil and the secondary inner coil. When annual maintenance is performed, the internal CRDs and the secondary inner coils fixed with the CRD support plate are withdrawn upward.

Fig.8 The schematic concept of magnet coupling power connector installed in the RPV

Fig.9 Test section of a magnet coupling power connector

Table 2 Power loss fractions in the magnet coupling power connector

In order to evaluate the feasibility of the magnet

coupling power connector, a high-temperature mock-up test was conducted. Fig. 9 shows the test section of the magnet coupling power connector. The allowable maximum temperature of the heatproof ceramics insulated coils was 600 deg. C. The test section was installed in a high-temperature test vessel connected with the 7MPa pressure two-phase flow loop named NEXUS. Fig. 10 shows the power transfer efficiency curve for the primary voltage at 50Hz. Table 2 shows the power loss fractions in the magnet coupling power connector under the high-temperature condition of 286deg. C by FEM magnetic field analysis shown in Fig. 11. The power loss occurred mainly due to the Joule's loss by the coil's resistance

Fig. 10 The power transfer efficiency curve

Fig. 11 Results of magnetic-field analysis

Position Coil Can Sub. Total Primary 56.9% 22.1% 79.0%

Secondary 2.1% 18.9% 21.0% Total 59.0% 41.0% 100.0%

0

5

10

15

20

0 20 40 60 80 100 120 140 160

１次電圧V1(V)

電力伝送効率η(%)

10 deg. C

90 deg. C

283 deg. C

Primary coil voltage (V)

Powe

r tra

nsfe

r effi

cien

cy (%

)

Oneunit

Internal CRD

Power pipesnozzle

Powerpipe

Magnet-couplingpower connector

for signalfor power

PrimarySecondary

Oneunit

Internal CRD

Power pipesnozzle

Powerpipe

Magnet-couplingpower connector

for signalfor power

PrimarySecondary

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and induction-eddy current loss in the pressure can. Fig. 12 shows a FEM heat transfer analysis result of temperature distributions in the test section under the rated power transfer condition of 50W. The surface of the pressure cans was supposed to be 300 deg. C. The maximum temperature was approximately 360 deg. C, in the primary coil, and was low enough to the allowable maximum temperature of 600 deg. C. These measured data was used to improve the magnet coupling power connector, and we estimated the power transfer efficiency to be over 20%. Though the efficiency is not so high, the rated internal CRD's power is approximately only 50 W. Therefore, the primary power of the each CRD will be approximately 250W and the total power of 257 CRDs will be only 64kW. The power is very low compared with the CRD pump of the current ABWR.

Fig. 12 FEM heat transfer analysis result of temperature distributions (rated power conditions)

2. Internal CRD's Mechanism Fig. 13 shows the schematic drawing of the

internal CRD. The internal CRD consists of a latch mechanism and the rotation mechanism driven by the heatproof motor. The latch mechanism consists of a combination ball-nut and a holder sleeve lifted with a lift coil through a linear magnet coupling. The heatproof motor through a radial magnet coupling also drives the combination ball-nut.

Scram operation is attained by only turning power off the lift coil. Then, the holder sleeve is dropped and the combination ball-nut is divided into three pieces so that a ball screw shaft that lifts a control rod (CR) is dropped by the gravity force, as shown in Fig. 14 (a). When the lift coil power is turned on, the holder sleeve is lifted upward and the three divided combination ball-nut pieces are combined into one ball-nut. After this action, the heatproof motor drives the ball screw shaft and the CR is moved upward and downward smoothly. As shown in Fig. 15, a trial device of the latch mechanism was made. It was confirmed that the

device showed very smooth operation of latch and scram by using the dummy weight.

Fig. 13 Schematic drawing of the internal CRD

(a) Scram (b) Latch to lift CR Fig. 14 Latch mechanism of the internal CRD

'C300

310

320

330

340

360INFINITY

'C300

310

320

330

340

360INFINITY

Lift coil

Linearmagnetcoupling

Latch mechanism

Radialmagnetcoupling

Heatproofmotor

Planet gear

240mmOD

Lift coil

Linearmagnetcoupling

Latch mechanism

Radialmagnetcoupling

Heatproofmotor

Planet gear

240mmOD

Lift coil

Linearmagnetcoupling

Latch mechanism

Radialmagnetcoupling

Heatproofmotor

Planet gear

240mmOD

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(a) Latch test operation by using dummy weights

(b) The holder sleeve (c) Combination ball-nut Fig. 15 Trial device of the latch mechanism

3. Heatproof Motor

The specification of the heatproof motor is shown in Table 3. The type of the motor is synchronous using a samarium-cobalt magnet. The magnet is very strong and heat/radiation proof. The motor's power is three phases AC power of 50Hz. This frequency is suitable for supplying the AC power via the magnet coupling power connector. Three-dimensional magnetic-field analysis was conducted as shown in Fig.16. The maximum magnetic field was approximately 1.5T at the stator tee and rotor yoke. The value is low enough to suppress the motor loss. Especially, the magnetic field

of the stator yoke is approximately 1.0T. That contributes to the low-power loss and we conclude the motor is feasible.

Table 3 The specification of the heatproof motor

Fig. 16 Magnetic field analysis result for the heat proof motor

Fig. 17 Heatproof ceramics insulated stator coils

Number of poles 8

Torque (Nm) 7.0

Frequency (Hz) 50

Voltage (V) 180

Current (A) 1.60

Efficiency (%) 84.2

Iron loss (W) 57

Copper loss (W) 46.0

Coil resistance (Ohm) 6.0

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IV. Ceramics Insulated Heatproof Coil

1. Co-axial Structure of Coil Fig. 18 shows the co-axial structure of a ceramics

insulated heatproof coil. To prevent the oxidation of copper, the copper is covered with stainless steel cladding. The surface of the stainless steel clad is coated with inorganic polymer and ceramic insulator.

Fig. 18 Co-axial structure of a ceramics insulated heatproof coil

2. Ceramics Coil Durability Test We examined many of kinds of ceramic insulators,

such as Al2O3 or Al2O3-SiO2. Fig.19 shows some of the examples of ceramic fibers. Fig. 20 shows the heating test resuts after one hout at 1400 deg.C . Coarse-grain degradetion occered in the fibers. Fig. 21 shows the test result of the tensile-strength versus temperature. At approximately about 800 deg. C, the degradetion was very little. In order to select and improve the ceramics insulated coils, a high- tempearture chamber was installed at Prof. Terai's Lab. in the University of Tokyo, as shown in Fig.22. The chamber can heat coils with a ceramics bobbin up to 1000 deg. C.

(a) Al2O3 (b) Al2O3-SiO2 (c) Al2O3-B2O3-SiO2

Fig. 19 Examples of ceramics fibers

Fig. 20 Examples of ceramics fibers after heat test

Figures 23 and 24 show the mock-up of radiation hole of Yayoi reactor and a test capsule for radiation, respectively. The neutron flux doze is almost the same as the position of the internal CRD in an actual BWR's.

Fig. 21 Test data of tensile-strength vs. temperature

Fig.22 High-temperature chamber

Fig. 23 Mock-up of radiation hole Fig. 24 Capsule of Yayoi reactor for radiation

V. Evaluation of BWR Conditions 1. Neutron Flux at the Internal CRD

In order to estimate the neutron flux at the position of the internal CRD in an actual BWR, two-

Copper

StainlessSteel

InorganicPolymer

CeramicInsulator

Copper

StainlessSteel

InorganicPolymer

CeramicInsulator Temperature('C)

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two-dimensional neutron transport code DOT3.5 was used, as shown in Fig. 25. The analysis result showed each energy level of neutron as follows:

Fast Neutron Flux:106n/s/cm2 Middle Neutron Flux: 106n/s/cm2 Thermal Neutron Flux: 106n/s/cm2

The flux level was not so high, and the radiation test at the Yayoi reactor will be possible.

Fig. 25 Analysis result of neutron flux distribution in a BWR reactor, by using the 2D neutron transport analysis code DOT3.5

2. Durability Test of Ball Bearing In order to evaluate the robustness of the internal

CRD, a durability test apparatus is being made at the R&D center of TEPCO, as shown in Fig.26. The test specimens of the ball bearing and pin-roller were supplied by TOSHIBA. The test using high-pressure and high-temperature test will be started in the fiscal year of 2003.

Fig. 26 Ball bearing durability test apparatus

VI. Flow & Structural Integrity & LOCA Analysis 1. Two-Phase FIV Visualized Test

Around the internal CRD, two-phase flow from the core flows upward through the guide chimney. Therefore, two-phase flow instability and FIV (Fluid Induced Vibrations) should be evaluated. The visualized test apparatus for the two-phase FIV was installed at the Nuclear-Power Facility of the University of Tokyo, as shown in Fig.27 and the FIV test has been started promisingly.

Fig. 27 Two-phase FIV test facility and the

cooperation team key members

2. RPV Internal Structure Integrity

In order to evaluate the thermal stress and earthquake-resistant design, FEM analysis and aseismic analysis were conducted. Fig. 28 shows the RPV internal structures of the next-generation BWR, using the internal CRD. The points of the internal structure have the shroud-less structure supported by a rim-cylinder type core support plate, upper core grid and the CRD support grid. Fig. 29 shows the thermal stress analysis result by FEM. The thermal stress occurred by the difference of the thermal

Guide Chimney

Radius(m)

Internal CRD

Core

Shroud head

Separator

RPV Shield Concrete

9

expansion ratio between the carbon steel RPV and the stainless steel internals. The diameter of the rim-cylinder is 7.0m, and its height and thickness were changed as analysis parameters. The optimized height was 500 mm and thickness was 64.8 mm. The equivalent spring coefficient of the rim-cylinder was 107 kN/m.

Fig. 28 Drawing of RPV internal structures

Fig. 29 FEM deformation analysis result of a rim- cylinder to obtain an equivalent spring coefficient.

(a) Aseismic analysis model (b) Analysis result (1st mode, 4.8Hz)

Fig. 30 Aseismic design analysis

By using the weight and spring coefficients for each structure, aseismic analysis was conducted as shown in Fig. 30. As the analysis results, the internal structure resonance frequency is over 18 Hz; therefore, it is high enough to the fuel's 1st mode and the good aseismic performances were confirmed.

3. LOCA and Pressure Transient Analysis The internal structure of the next generation

BWR is much different from the current ABWR. Therefore, LOCA and the pressure transient analysis were conducted by using the TRAC code, as shown in Fig. 31. The model includes the RIP tube for shroud-less low elevation core structure and CR guide chimney. Fig. 32 shows the LOCA analysis results of water level in the RIP tube and outside of the short shroud. Though, the ECCS flow rate was the same as that of current ABWR of 1356 MWe, the results showed the full term flooding over the TAF (Top of active Fuel). Fig. 22 (b) showed the pressure transient

5.8m

3.7m

1.5m

4.4m

3.7m

2.3m

3.3m

5.8m

21m

7.1m

5.8m

3.7m

1.5m

4.4m

3.7m

2.3m

3.3m

5.8m

21m

7.1m

1

Core/Fuel

CR guidechimney

Shroud head

Separator

Dryer

Internal CRD

RPV

CRDsupport

grid

RPVsupport

skirt

Stabilizer

22

29

232425262728303132333435

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1918

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151413121110

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76543

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K2

grid

Uppercore

Coresupportplate K1

K3

K4

1

Core/Fuel

CR guidechimney

Shroud head

Separator

Dryer

Internal CRD

RPV

CRDsupport

grid

RPVsupport

skirt

Stabilizer

22

29

232425262728303132333435

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151413121110

98

76543

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Coresupportplate K1

K3

K4

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analysis when all the MSIVs were shut by some signals. The next-generation BWR's power is up-rated by 25% (1700MWe) compared with the current ABWR. The analysis was conducted under the condition of total SRV flow rate was the same as that of current ABWR of 1356 MWe, the pressure transient peak is only 2.5% higher than that of the current ABWR.

Fig. 31 LOCA and the transient analysis model for the TRAC code

(a) Water level during LOCA (b) Pressure transient after the MSIV closure

Fig. 32 TRAC analysis results

VII. Conclusions

The internal CRD using a heatproof ceramics insulated coil is under development. The internal

CRDs are installed in a RPV whose size is equivalent to the 1356 MWe ABWR, and there will be no space required for CRDs and CRD exchange under RPV.

These advantages realize a compact PCV and reduced volume of a reactor building. The internal CRDs will eliminate penetrations via a bottom flange of RPV, and will be able to lower installation level of RPV in a drywell. We conducted the following evaluations and the results showed the next- generation BWR is feasible and has merits of up rating compared with the current ABWR.

1) Plant concept to reduce the height of reactor

building 2) Internal CRD latch mechanism and heatproof

motor 3) The thermal stress and aseismic design analysis of

the shroud less RPV internal structure with the RIP tube.

4) LOCA and pressure transient analysis Acknowledgments

The development program of the internal CRD system with heatproof ceramics coils has been carried out based on this joint study, funded from IAE Japan as the national public research program.

The structural integrity & LOCA analysis were conducted as a joint study between TOSHIBA and TEPCO before this IAE Program.

The authors express their gratitude to Mr. Ryosuke Koike, Dr. Shoji Goto and Tsuyoshi Kobayashi of R&D Center, Tokyo Electric Power Company. The authors express many thanks to Mr. Mikihide Nakamaru, Mr. Kazuya Fukui, Dr. Eriko Yoneda, Mr. Noboru Saito, Mr. Yasuhiko Aida, Mr. Roichi Sugawara, Mr. Katsumasa Araoka and Mr. Toshinori Terashima of TOSHIBA Corp. References 1. Ishida et al., C41, Annual mtg. of AESJ (2000). 2. Kobayashi et. al., H12-H16, Annual mtg. of

AESJ (2000). 3. Koike et. al., G13-G16, autumn mtg. of AESJ

(2001).

RIP tube

CR Guide Chimney

RIP

RIP tube

LOCA

Feedwater

TAF

RIP tube & outside shroud

Next-Generation BWR1356MWe ABWR

Wat

er L

evel

(m)

Pres

sure

(Rat

ed %

)

Time (sec) Time (sec)