C-2-1

Development of the In-service Inspection and Repair Technologies toward the Commercialization of Fast Breeder Reactor

Takuya YAMASHITA (Japan Atomic Energy Agency)

Abstract
Since the FBR plants in commercial stage is designed 60 years reactor life which is twice of the prototype FBR "Monju", maintenance technologies considering aging and damage for a long term using at high temperature are needed. Development of the in-service inspection and the repair technologies needed for maintenance of the commercial used FBR is discussed after reviewing the features of the FBR plants, and experience of ISI and repair of the experimental FBR “Joyo" and the "Monju".

Keywords
Fast Breeder Reactor, Joyo, Monju, In-service Inspection, Maintenance

C-2-2

FEM Analyses of Creep in Welded Modified 9Cr Steel Considering Microstructures in Weld and HAZ

Yuji NAKASONE (Tokyo University of Science) and Takuo SUZUKI (Tokyo Metropolitan College of Industrial Technology)

Abstract
Modified 9Cr-Mo steel is a candidate structural steel for demonstration fast breeder reactors (FBR’s). Due to low thermal activation, the steel can maintain steady-state deformation during long-term creep. The creep strength of its weldment is lower than that of the base metal. Because of different creep strain rate in the solidified weld metal and heat-affected zone (HAZ), creep deformation in HAZ can be lowered but maximum principal stress augmented in fine-grained HAZ to cause detrimental Type IV cracks in this zone.

In this study, FEM analyses were made on long-term creep of over 60 years in double U groove welded Modified 9Cr-Mo steel with typical microstructures in the welded region of the steel taken into consideration. The typical welded region of the steel consists of solidified weld, coarse grain HAZ, fine grain HAZ, interfacial HAZ and base metal. These microstructures were modeled as polycrystal structures having slip systems approximated by rectilinearly anisotropic deformation properties.

Keywords
9Cr-Mo Steel, Type IV Creep Crack, FEM Creep Analysis, Microstructure, Norton’s Law

C-2-3

R & D on Irradiation Damage Management Technology for FBR Structural Materials

Shigeru TAKAYA, Yuji NAGAE, Eiichi WAKAI and Kazumi AOTO (Japan Atomic Energy Agency)

Abstract
Proper management of neutron irradiation damage on structural materials is important to ensure the health of long-life fast breeder reactor (FBR) plants. Therefore, the effective index for irradiation damage or the combination of those should be developed. In this study, the effects of dose, helium, and the ratio of helium to dose on tensile and creep properties of FBR grade type 316 stainless steel were investigated in the assumed irradiation damage range of FBR structural materials, that is, up to about 1 displacement per atom for dose and up to about 30 appm for helium. As result, it was shown that dose is the most promising. In addition, a nondestructive evaluation method of dose using a vibrating sample magnetometer is also introduced.

Keywords
Dose, Helium, The ratio of helium to dose, Tensile, Creep, Nondestructive evaluation

C-2-4

Maintenance activities for sodium leak detection system in Monju

Keitaro MUTO (Japan Atomic Energy Agency)

Abstract
Monju is sodium cooled Fast Breeder Reactor. Monju resumed operations on May 5th, 2010 after an intermission for about 14 years following a sodium leak accident. During the shut-down period, sodium system was operated and there were some troubles of sodium leak detectors. To improve leak detectors performance and reliability, detectors modification and improved maintenance activities were applied. For example, a contact type sodium leak detector (CLD) in the secondary sodium system was modified to increase to ion-migration resistance and periodical insulation measurement was added to the maintenance activities. Based on the maintenance and operation experience and the technology development will be reflected to the improvement of the performance and reliability of sodium leak detectors.

Keywords
Fast Breeder Reactor, Monju, Sodium Leak Detector, Maintenance Activities

C-2-5

Effect of Nitrogen Content on Creep Rupture Properties of 9Cr-1Mo-V-Nb Steel with Simulated HAZ Heating

Yoshiatsu SAWARAGI (SUMITOMO METAL TECHNOLOGY,INC.) and Aturo ISEDA (Sumitomo Metal Industries, Ltd.)

Abstract
The creep rupture properties of 9Cr-1Mo-V-Nb steel welded joints changed with chemical compositions. In this study, the simulated HAZ heating below or over Ac1 temperature of 830°C　was conducted in order to investigate microstructural changes of welded joints of the steel. The results are summarized as follows.

(1) hardness and creep rupture strength of 9Cr-1Mo-V-Nb steel heated at 850°C decreased significantly after post-weld heating at 740°C for 5h. it was confirmed that recovery and softening of martensitic structure were accelerated by partially austenite (γ)-transformed heating just over A_c1 temperature.

(2) Finely dispersed Vanadium Nitride (VN), which increased in amount by addition of nitrogen, was ovserved for simulated HAZ specimen heated at 850°C. The precipitation of VN were confirmed to retard recovery and resulted to improve creep rupture strength of welded joint effectively.

Keywords
heat resistant steel, 9Cr steel, creep rupture strength, hardness, simulated HAZ, recovery, softening, nitrogen

C-2-6

Evaluation of Defect and Damage for Structural Materials of Energy Device by Using Electromagnetic Techniques

Takayuki SUZUKI (National Institute of Advanced Industrial Science and Technology), Takumi KUROTA (University of Tsukuba), Akira SASAMOTO, Yoshihiro NISHIMURA (National Institute of Advanced Industrial Science and Technology) and Tokuo TERAMOTO (University of Tsukuba)

Abstract
Evaluation of defect and damage for structural materials of energy device was performed by using electromagnetic techniques. For degradation of thermal aging magnetic characterization of weld specimens of HCM12A was performed. Comparing the specimen aged at 550°C for 2000 hours with that aged at 500°C for 600 hours, it was found that the changes in magnetic flux densities was clearly observed near the weld metal and heat affected zone for the specimen aged at 550°C for 2000 hours. Then the degree of degradation for weld specimen could be evaluated by the changes of magnetic flux densities. For degradation of defect and crack changes in leakage magnetic flux densities around surface defect of SS400 were measured by fluxgate sensor. And by using inverse analysis of Tikhonov regularization, magnetic charge distribution of defect was calculated from the measured leakage magnetic flux densities and the defect size was successfully reconstructed.

Keywords
Energy Device, Thermal Aging, Defect, Magnetic Flux Leakage, Inverse Analysis, Fluxgate Sensor, Tikhonov Regularization

C-2-7

Non-destructive Material Evaluation by Measuring Magnetic properties by Magnetic Sensors

Yuichiro KAI, Yuji TSUCHIDA and Masato ENOKIZONO (Oita University)

Abstract
This paper presents a non-destructive evaluation method to evaluate hardness and hardening depth of carbon steels by measuring magnetic properties. Magnetic properties of carbon steel samples under different hardening temperature condition are examined by using the FSES method. The results show that the magnetic properties of the hardened carbon steels differ from each other depending on the hardening temperature. It can be said that the FSES method is useful to evaluate the hardening depth and the hardness.

Keywords
Magnetic property, Carbon Steel, Hardening, Material evaluation, Magnetic sensor, Non-destructive Evaluation

C-2-8

Development of a Sodium Leak Detector based on Atomic Spectroscopy using a Laser Diode

Satoshi OGURA, Kenichi WATANABE, Atsushi YAMAZAKI, Akira URITANI (Nagoya University) and Chikara ITO (Japan Atomic Energy Agency )

Abstract
We proposed a novel sodium leak detection technique based on laser spectroscopy to improve the reliability of sodium leak monitoring. In this technique, sodium atoms are excited into a first excitation level by atmospheric plasma before laser spectroscopy. The detection limit concentration was preliminarily evaluated to be comparative to the sodium aerosol detector. We confirmed that the maximum of 3p level population can be achieved at a proper plasma burning condition.

Keywords
Sodium cooled fast reactor, Sodium leak detector, Laser spectroscopy, Laser diode, Atmospheric plasma

C-2-9

Neutron Dosimetry for Fast Reactor Surveillance

Chikara ITO, Shigetaka MAEDA (Nagoya University, Japan Atomic Energy Agency), Takafumi AOYAMA (Japan Atomic Energy Agency) and Tetsuo IGUCHI (Nagoya University)

Abstract
Neutron dosimetry techniques have been developed for fast reactor surveillance in long-term irradiation as the range of 10⁰ -10¹ years. The high accurate and precise measurement of ⁹³Nb(n,n')^93mNb reaction rate was established for fast reactor dosimetry. The effect of gamma-ray self-absorption was decreased by dissolution and evaporation to dryness of niobium dosimeter in the established method. It was confirmed that the ⁹³Nb(n,n')^93mNb reaction rate could be measured with an uncertainty within 3 % by this method. A helium accumulation fluence monitor (HAFM) has been developed for precise and reliable neutron dosimetry. It has been found that the HAFM measurement system can measure neutron fluence with an uncertainty of 7 %. by using the enriched boron (¹⁰B enrichment in 93 %) and beryllium. A high sensitive gas measurement system was developed using the laser resonance mass spectrometry (RIMS) method for Failed fuel detection and location technique in fast reactors. The RIMS can be also applicable for neutron fluence evaluation by measuring the change of xenon isotopic ratio.

Keywords
neutron dosimetry, fast reactor surveillance, niobium dosimeter, helium accumulation fluence monitor (HAFM), laser resonance mass spectrometry (RIMS)

C-2-10

Maintenance experience of Experimental Fast Reactor Joyo (1)
The outline of maintenance activities in Joyo

Kozo SUMINO, Tetsuhiko KOBAYASHI, Kazunori ISOZAKI and Akihiro YOSHIDA (Japan Atomic Energy Agency)

Abstract
In the experimental fast reactor Joyo, maintenance work was conducted based on the classification of safety importance over thirty years. Through the experience, it was confirmed that particular effort was not necessary for the maintenance of sodium cooling systems by controlling the coolant purity properly. Additionally, as a result of the technical review on aging for whole plant, significant aging phenomenon that is particular with sodium cooled fast reactor was not observed.

Keywords
Joyo, Fast Reactor, Liquid Sodium Coolant, Maintenance

C-2-11

Maintenance experience of Experimental Fast Reactor Joyo (2)
The maintenance experience on the electromagnetic pumps in Joyo sodium cooling system

Masayoshi SUTO, Takashi SUGAYA and Kozo SUMINO (Japan Atomic Energy Agency)

Abstract
Maintenance for five electromagnetic pumps in sodium cooling system of Joyo has been conducted successfully considering their operational and environmental conditions. As a result of the periodical surveillance over thirty years, it was confirmed that the pumps could be maintained their integrity during the planned service period of Joyo. Additionally, based on the experiences, the long term maintenance program for electromagnetic pumps was decided.

Keywords
Joyo, Sodium Cooling System, Electromagnetic Pump, FLIP, Maintenance

C-2-12

Maintenance experience of Experimental Fast Reactor Joyo (3) The countermeasure for wear of the crankshaft bearing of the diesel generator

Isao FUNAKI, Shigeharu TOBITA, Akinori NAGAI and Kazunari NISHINO (Japan Atomic Energy Agency)

Abstract
In Joyo, maintenance program for the emergency diesel generators was revised, because it was confirmed that the wear on the crankshaft bearing was caused by the accumulation of carbon particles through the repetition of short term operation over thirty years.

Keywords
Wear, Crankshaft Bearing, Emergency Diesel Generator, Maintenance