Sodium leakage

Where-high purity MU is provided for higher pressure WT boiler plant FW, some form of continuous analyzers for measuring treated water pH and conductivity are almost always installed, as are sodium (Na) ion-selective electrodes for detection of sodium leakage. Automatic online silica analyzers also may be installed, but they measure only reactive (ionizable) silica (Si02), not colloidal or total silica, so caution is required where unforeseen silica leakage may present a problem. 

Where MU is intended for power boiler FW, particularly strict limits are imposed on sodium leakage (breakthrough) and silica leakage to prevent FW contamination and subsequent downstream caustic gouging corrosion, caustic cracking corrosion, or silica deposition. 

Twin-bed DI plants in good operating condition typically produce a slightly alkaline treated water with a sodium leakage level of perhaps 1 to 3 ppm, a silica leakage of 0.05 to 1.0 ppm, and a resistivity of typically 0.1 to 0.5 megaohm per cm (Mfl/cm). 

Select a deionization system to treat 250 gal/min (56.8 m3/h) of water at 60°F (289 K) that has the following dissolved components (concentrations in parts per million as CaCC>3 equivalent) calcium, 75 sodium, 50 magnesium, 25 chloride, 30 sulfate, 80 bicarbonate, 40 and silica, 10 (as Si02). Maximum tolerable sodium leakage is 2 ppm silica leakage is to be under 0.05 ppm. Service-cycle length must be at least 12 h. The system is to use sodium hydroxide (available at 120°F) and sulfuric acid for regeneration. 

Other monovalent cations of low selectivity for the resin such as potassium ion (K ) and ammonium ion (NH4 ) would show similar leakage characteristics. For UK waters a typical average sodium leakage would be about lmg(Na)r, increasing with increasing sodium fraction of the total cations. 

In contrast, conduction velocity is slow in muscle fibers at the SA and AV nodes. Unlike the majority of cardiac muscle cells, these pacemaker cells have an unstable resting potential ( — 60 mV) due to a cell membrane alteration that allows sodium ions to leak into the cell without a concurrent potassium ion efflux. This sodium leakage reduces the membrane potential allowing even more sodium ions to move into the cell. In addition to the inward sodium movement, there is also an inward calcium flow which causes the pacemaker cells to have a more positive resting potential. Finally, the cell produces an action potential at 40 mV. This phenomenon is called spontane-... 

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 ... 

Evidence of fretting on a further 13 tubes adjacent to the baffle was found, all close to the seams between the six plates forming the baffle. It was concluded that sodium leakage through the seams, shown in Figure 2.3, caused flow-induced vibration of the tubes resulting in contact with the duct and giving rise to wear and the eventual failure of tube 6. 

To reduce the amount of sodium leakage and damage by spilt sodium, the drain... 

These countermeasures will enhance the safety and reliability of the plant with regard to sodium leakage incidents. 

This paper summarizes the sodium leak incident, the cause of thermocouple well tube failure, and the improvement and countermeasure programs against sodium leakage incidents. 

DETECTION AND SUPPRESSION FOR SODIUM LEAKAGE 3 WELLS PER LOOP... 

A comprehensive review wasperformed concerning sodium leakage. The review concentrated on the following three points ... 

These were chosen in order to investigate if systems and com ponents with regard to the sodium leakage could be improved or not. 

The design of the sterns and components was also reexamined considering the experience and knowledge accumulated at other fast reactors, research and development results and new findings. As a result of the review, some additional aspects were appeared. Some existing systems and components related to sodium leakage were found to require modification, and it was recommend that new systems and components should be introduced. Typical systems and components are ... 

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. 

Main Sodium Leakage Monitoring Display Panel... 

T0 reduce the quantity of sodium leakage, the drain system was found to require two improvements. One is the addition of a new drain line pipe at the inlet of the secondary pump. The other is the replacement of all drain lines by pipes of larger diameter. In the existing system, each drain line has two drain valves in series to prevent accidental draining by single valve action error. In future so as to assure the draining, each drain line will have double drain valves in parallel. After these improvements, the drain time will be shortened from approximately 50 minutes to 20 minutes. It is estimated that it takes 40 minutes from the occurrence of sodium leakage to finish the drain for the secondary circuit. The modified drain system is shown in Fig.9. 

The comprehensive safety review was completed in March 1998. It has been demonstrated that the following improvements are effective against the sodium leakage incidents and enhance the safety and reliability of the plant. 

Integrated sodium leakage monitoring system will be introduced. 

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