Monju

Fig. 11. Reactor core of MONJU, the Japanese fast-breeder reactor. Courtesy of Power Reactor and Nuclear Fuel Development Corp.

MONJU fast-breeder reactor, 17 588 Monkeypox, 3 136 Monkshood, 2 103... 

France has the largest implementation of breeder reactors with its 250-MW Phenix reactor and 1200-MW Super-Phenix. The Phenix went into operation in 1973 and the Super-Phenix in 1984. Japan has its 300-MW Monju reactor which was put into service in 1994. While India has the 500-MW PFBR and 13.2-MW FBTR. These reactors produce about 20% more fuel than they consume. Optimum breeding allows about 75% of the energy in natural uranium to be used compared to 1% in a conventional light water reactor. 

Large amounts of sodium waste arise from fast neutron reactors (Phenix and Superphenix in France, Dounreay in the UK, Monju in Japan), which are cooled by large amounts of liquid sodium, which is contaminated by 137Cs during its functioning. We shall see that it is possible to remove radioactive cesium after conversion of liquid sodium to sodium hydroxide. 

Development Corp. Monju FBR (Tsuruga, Fukui) 280 LMFBR... 

A secondary sodium leak and fire at the Monju (Japan) plant in December 1995, caused by a temperature sensor well broken by vibration, caused a long operational delay and required plant modifications. The total mass of non-radioactive sodium which leaked was 640 42kg due to delay in sodium draining from the loop. There were no adverse effects for operating personnel or the surrounding environment. 

To prevent a recurrence of the Monju secondary sodium leakage incident comprehensive design review activities were started for the purpose of checking the safety and reliability of the plant. As a result, several aspects requiring improvement were identified and improvements and countermeasures were studied. The main improvements and countermeasures are as follows ... 

The event at the Monju plant caused a serious interruption to reactor operation. For this reason there will be undoubtedly important efforts to reduce the incidence of sodium leaks and to improve the protection against the consequences of fires. 

The comprehensive operational experience with LMFRs BN-350, Phenix, PFR, BN-600, Superphenix and Monju has shown that, if plant components have been designed and manufactured without errors and representative specimens or models have been tested prior to installation, reliable operation can be ensured during the whole operational life. 

A. MIYAKAWA, H. MAEDA, Y. KANI, K. ITO Monju Construction Office,... 

Monju is Japan s prototype fast breeder reactor 280 MWe(714MWt), fueled with mixed oxides of plutonium and uranium, cooled tty liquid sodium. Construction was started in 1985 nd initial criticality was attained in April 1994... 

TABLE 1. PRINCIPLE DESIGN AND PERFORMANCE DATA OF MONJU... 

After a plant trip test, Monju restarted operation on 6th December 1995. On 8th December, power was being raised for the next plant trip tests, part of 40% electric power tests. The thermal power had reached 43% when an alarm sounded at 19 47 dueto an off-scale sodium temperature at the outlet of IHX in the secondary circuit loop C. Afire alarm (smoke detector) sounded at the same time. A sodium leak alarm in the secondary circuit followed. The plant conditions of Monju at that time are shown in Fig. 1. The presence of smoke was confirmed when the door of the piping room was opened. The plant operators decided to begin normal shutdown operations becausethey judged it was a small sodium leak had occurred. Reactor power-down operations began at 20 00. 

It was possible to detect the sodium leakage because Monju already had sodium leak detectors and fire detectors in the secondary circuit. However it was found that these were insufficient for the operators to grasp accurately the conditions in the room at an early stage. To help the operators confirm sodium leakage more quickly and easily, the detectors will be increased in number and diversified method and an integral leakage monitoring system will be installed. 

The fire sensors are able to detect sodium leakage by two different methods. One is smoke (aerosol) detection and the other is by temperature increase in the room where a sodium fire occurs. Monju already used the former method and this type of sensor will be increased to detect the sodium leakage more quickly and more certainly. The latter method type fire sensors MU be introduced for greater diversity in the detection of the sodium fires. Visual information was found to be useful for operators to know the condition of the room, and so, TV cameras will be installed in the secondary circuit. 

Suzuki, T. et al., 1996, Monju Secondary Heat Transport System Sodium Leak , Proceeding of 1 0 Pacific Basin Nuclear Conference, Kobe, Japan. 

Miyakawa, A. Monju Construction Office, Japan Nuclear Cycle Development Institute, 1-banchi, 2-chome, Shiraki, Tsuruga-shi, Fukui-ken, Japan... 

In Japan, fast reactor development program symbolises national nuclear fuel recycling program, as it is stated in the national long-term plan [2.3]. The experimental fast reactor Joyo has shown excellent performance for more than 20 years. The prototype reactor Monju (280 MW(e)) was stopped temporarily due to the leak in the non-radioactive secondary circuit in 1995. The design of demonstration fast reactor (DFBR-600 MW(e)) is in progress [2.4, 2.5]. 

Exchange detailed technical information on fast reactor operation and/or decommissioning experience with DFR, PFR (UK) KNK-II (Germany) Rapsodie, Phenix, Superphenix (France) BR-10, BOR-60, BN-600 (Russian Federation) BN-350 (Kazakhstan) SEFOR, EBR-II, Fermi, FFTF (USA) FTBR (India) JOYO, MONJU (Japan) ... 

JNC considers it extremely important to reflect the lessons learnt from previous experience in the fast reactor field to the operation and maintenance of Monju and the design of future reactors. 

The post analysis results from a plant wide dynamics code MIMIR-N2 are in excellent agreement with the experimental data as shown in Fig. 12. Various key parameters are clarified to improve the calculation accuracy through the study. In the short-term analysis, the evaluation of thermo-hydraulic behavior in the core is largely affected by the inter-assembly heat transfer effect, the pump flow coast characteristics and coolant flow distribution. For the long-term analysis, it is important to assess precisely the buoyant head effect in the IHX, the heat exchange effects in the lower plenum of the IHX and others. The experimental result is also applied to the assessment of natural convection characteristics in the MONJU reactor. 

A sodium leak accident occurred in the MONJU secondary cooling loop in December 1995. At that time, the 11 annual inspection was being performed at JOYO and an inspection of sodium piping and components was immediately carried out to confirm their integrity and to verify that there were no sodium leaks. After the MONJU accident, an investigation was completed by the Safety Authority and findings on the cause of the sodium leaks and ways to mitigate their effects were published. 

In the same time, the international cooperation was strong enough to also enlarge the French specialist view and let them embrace all the variety of design and technical options (principally DFR and PFR British Plants BOR60, BN350 and BN600 Soviet Plants, Joyo and Monju Japanese Reactors). 

There was the key staff, who are now nearing retirement or have already retired, in the Monju design process. Interviews them about their experience are being made. The computerized system, based on this knowledge, is in two parts ... 

There would be mutual benefits for both JNC and its partners in constructing the extranet and ISAN system. Obviously JNC would benefit from the vast experience of fast reactor operation amassed by our partners. But the success of Monju is also important for the future of fast reactor development outside Japan, and the communication would give our partners access to and operational reactor and new experience. 

Figure 3 shows JNC s international contacts and agreements as viewed from Monju. JNC have multilateral agreements or international organizations that provide a forum for cooperation on fast reactors. There are bilateral agreements in the some fields fast reactors, advanced technology and so on. 

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