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Journal Articles

Development of prototype reactor maintenance, 1; Application to piping system of sodium-cooled reactor prototype

Kotake, Shoji*; Chikazawa, Yoshitaka; Takaya, Shigeru; Otaka, Masahiko; Kubo, Shigenobu; Arai, Masanobu; Kunogi, Kosuke; Ito, Takaya*; Yamaguchi, Akira*

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 6 Pages, 2017/04

A maintenance management required to prototype nuclear power reactors is proposed. Monitoring and control of sodium impurity and thermal transient are extremely important for sodium boundary maintenance for sodium-cooled fast reactors. At the fast stage of the prototype reactor Monju operation, degradation mechanism on the piping should be demonstrated based on operation experiences. Therefore inspection on a representative position for crack indication and pipe thickness is proposed. Due to less experience of SFR plants, early detection of boundary failure is considered. For a matured operation stage, when degradation mechanism is well demonstrated based on inspection data, inspection cycle could be extended. And for commercial reactors, maintenance without inspection will be established based on accumulated operation experiences including those of the prototype reactor Monju.

Journal Articles

Development of prototype reactor maintenance, 2; Application to piping support of sodium-cooled reactor prototype

Arai, Masanobu; Kunogi, Kosuke; Aizawa, Kosuke; Chikazawa, Yoshitaka; Takaya, Shigeru; Kubo, Shigenobu; Kotake, Shoji*; Ito, Takaya*; Yamaguchi, Akira*

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 6 Pages, 2017/04

Applications for maintenance program on piping support of prototype fast breeder reactor Monju are studied. Based on degradation mechanism, snubbers in Monju primary cooling system showed lifetime more than the plant lifetime of 30 years by experiments conservatively. For the first step during construction, visual inspection on accessible all supports could be available. In that visual inspection, mounting conditions and damages of all accessible supports could be monitored. One of major features of the Monju primary piping system is large thermal expansion due to large temperature difference between maintenance and operation conditions. Thanks to that large thermal expansion, integrity of the piping support could be monitored by measuring piping displacement. When technologies of piping displacement monitoring are matured in Monju, visual inspection on piping support could be shifted to piping displacement monitoring. At that stage, the visual inspection could be limited only on representative supports.

JAEA Reports

Thermal stratification tests in Monju upper plenum, 1; Temperature distributions under normal and scram conditions with 40% power operation

Doi, Yoshihiro; Muramatsu, Toshiharu; Kunogi, Kosuke

PNC-TN9410 96-117, 60 Pages, 1996/05

PNC-TN9410-96-117.pdf:1.94MB

Thermal stratification phenomena are observed in an upper plenum of liquid metal fast breeder reactors (LMFBRs) under reactor scram conditions, which give rise to thermal stress on structural components. Therefore it is important to evaluate chracteristics of phenomena in the design of the internal structure in an LMFBR plenum. To evaluate the thermal stratification characteristics of the prototype fast breeder reactor, MONJU, axial temperature distributions were measured with a thermocouple tree installed into the upper plenum for normal and scram conditions with 40% power operation. The axial temperature distribution for the normal operation showed thermal stratification phenomena that temperatures were about 410$$^{circ}$$C under the level of the fuel subassembly top, about 480$$^{circ}$$C around the level of the flow holes and about 490$$^{circ}$$C above the level of the upper flow holes. Temperature fluctuations were observed at the levels of the lower flow and upper flow holes. RMS (Route Means Square) of functuation at the lower and upper flow holes were 1.6 $$^{circ}$$C and 1.5$$^{circ}$$C, respectively. Based on the temperature histories of the upper plenum during scram conditions, temperature decreasing rate, temperature gradient and rising rate of stratification interface were evaluated. The temperature decreasing rates were about 5.0 $$^{circ}$$C/sec at the core outlet, 2.0 $$^{circ}$$C/sec around the level of flow holes and from 0.3 to 0.4$$^{circ}$$C/sec at the top of the inner barrel. The temperature gradients were about 160 $$^{circ}$$C/m, 90$$^{circ}$$C/m, 45$$^{circ}$$C/m and 170 $$^{circ}$$C/m at the time of 120 sec, 180 sec, 600 sec and 4800 sec from the reactor scram, respectively. The rising rate of stratification interface is about 1.0 m/h for the period from 120 sec to 600 sec with the onset of reactor scram. On the other hand, the rising rate is about 0.6 m/h after 600 sec from the scram. The rising rate at the top of the inner barrel is 0.2 m/h ...

Oral presentation

The Results obtained from the 20 years of "Monju" plant data, 5; Effect of natural convection prevention plate in primary sodium pump

Morioka, Tatsuya; Sawazaki, Hiromasa; Uchida, Takenobu; Sato, Takeshi; Nakamura, Yoshihide; Shiotani, Hiroki; Kunogi, Kosuke

no journal, , 

Thermal natural convection occurred in Ar gas region between the inner and outer casing of the sodium pump in the past, which induces asymmetric circumferential temperature distribution on the casings. This thermal effect causes the contact of the pump shaft with the lower hydrostatic bearing, which places the bearing at risk for damage. This phenomenon strongly appears in long size pumps of sodium fast reactors. To prevent this risk for Monju primary sodium pump, convection prevention plates are installed between the inner and outer casing of the pump. Monju plant data indicates the plates decrease the circumferential temperature difference, and then no contact arose between the pump shaft and the bearing.

Oral presentation

The Results obtained from the 20 years of "Monju" plant data, 10-2; Effect of natural convection prevention plate in primary sodium pump

Morioka, Tatsuya; Hashidate, Ryuta; Sawazaki, Hiromasa; Kunogi, Kosuke

no journal, , 

Thermal natural convection occurred in Ar gas region between the inner and outer casing of the sodium pump in the past, which induces asymmetric circumferential temperature distribution on the casings. This thermal effect causes the contact of the pump shaft with the lower hydrostatic bearing, which places the bearing at risk for damage. To prevent this risk for Monju primary sodium pump, convection prevention plates are installed between the inner and outer casing of the pump. The soundness which in 2017 spring meeting, Monju plant data indicates the plates decrease the circumferential temperature difference, and then no contact arose between the pump shaft and the bearing. The circumferential temperature difference of the layer lower part is big compared with the layer upper part and the central part. We confirmed that difference in temperature among the measurement points of the lower gas layer was affected by the sodium vortex prevention plates.

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