Steam-water circuit monitoring

In addition to external conditioning processes and the need to provide internal chemical treatments to some or all steam-water circuits within the steam cycle, the scope of boiler water treatment includes, as mentioned earlier, the provision of suitable technical resources sufficient to control the steam-water chemistry within defined limits appropriate for the boiler plant under consideration. Because these steam-water control limits tend to narrow considerably with increase in boiler pressures (and heat-flux densities), suitable monitoring and control procedures may require implementing actions with knife-edge precision. 

Oil systems have been avoided wherever possible to minimise the risk of oil fires.. The quick actuating valves on the water steam side and sodium side are pneumatic driven. Cooling is by nitrogen for primary cold trap and by air for secondary cold trap. For austenitic stainless steel piping, leak before break concept is used where leak monitoring provision exists. To minimise sodium fires, all the sodium pipes within the reactor containment building are double walled. The dump valves are duplicated in sodium circuits to enhance reliability of dumping, in case of a sodium leak. 

The satisfactory performance of the general requalification programme of the plant throughout the year permitted collecting a maximum of data on the operation of the reactor, the monitoring systems, and the equipment of the water-steam circuits while the power level (90 % NP) reached at the end of the year permitted the performance of three specific tests. 

Fission product noble gases entering the water-steam circuit in the event of a tube leak are completely volatilized and transported with the steam to the main condenser where they are extracted and released via the off-gas stack. This release is monitored by a continuously operating detector device located in the condenser off-gas line. Non-volatile fission and activation products which are transported over the leak to the water-steam circuit remain completely in the water phase of the steam generator by the action of the blowdown purification system their activity concentration is kept at a level which is controlled by the injection rate on the one hand and by the purification rate on the other. Because of the very low vapor pressures of these elements and their chemical compounds (dissolved ions or insoluble oxides/hydroxides), their transport to the steam under the prevailing conditions (270 °C, 7 MPa) is only possible by droplet entrainment. This means that partitioning between liquid and steam phases is proportional to the steam moisture content, which is usually well below 0.1%. 

For sterilization the jacket is heated by steam. Valves 4-6, 8, and 10 are closed and the pump 7 is off. Valve 11 is opened to drain the jacket. After a short period, valve 11 is closed and valve 12 is opened. Valve 1 is opened to let steam into the jacket. The condensate drains through the steam trap 13. The temperature and pressure of the circuit are monitored at TICl and PIl. Cooling is carried out by closing valves 12 and 1 valves 8 and 4 are opened. Cooling water enters the circuit at valve 4, Aows up the jacket and out to the cooling water return line (Fig. 21). All operations are generally automated for consistent and error-free condol. 

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