Sodium purification

Sodium purification methods are generally identical to those for lithium (see 7.2.2.1.3), but the relative efficiencies of the methods diflfer ... 

During all the reactor sodium purification phase thermal hydraulic monitoring of the reactor took place in... 

As a protective measure, the auxiliary reactor sodium purification circuit of the storage drum was re-filled in order to maintain the exceptional reactor sodium purification available through the two circuit cold traps... 

Shutdown for sodium purification was used to make a thorough analysis of the direct and indirect causes of the events and to take corresponding measures re-examination of the plant maintenance and operating procedures, potential review of expertise available and needed around the operator... 

Primary Sodium and Irradiated Fuel Storage Drum Sodium Purification Systems... 

The cold trap 30J1-1A installed in the primary sodium purification is not filled with sodium and is stored under standby conditions while the cold trap SOU-IF is temporally removed out of service after a sodium leak event occurred on October , 1993. 

The most serious leak occured in the primary sodium purification system pipeline on October 7, 1993. The volume of the spilled sodium was about 1000 litres but owing to sufficiently effective performanceof the leak suppression system the release of radioactivity outside the plantwas only 10 Ci. The increased exposure of the plant and public did not occur. 

Primary sodium purification system Electric heaters, radioactive aerosol monitoring Insufficient selfcompensation of pipelines 1000 kg... 

In order to make measurements of caesium-137 activity, special device containing graphite pellet was installed in the loop connected in parallel to the primary sodium purification system. Just after the event of January 21, 1987, some decrease of the system indications was observed. Further, indications of the system came back to the previous level, however, some feature in caesium behaviour was noticed. While in the period preceding described events the decrease of the system indications in case of the reactor shutdown and sodium temperature reduction down to 250°C was 30-40%, later this decrease became as large as 10-12 times. After full power of the reactor had been reached, sodium temperature being as high as 530-540T, indications of caesium activity measurement system returned to the rated level. 

At the present time, sodium purification technique with the use of cold traps based on decreasing solubility of the major part of impurities in sodium with temperature decrease has found the most wide practical application [5.3, 5.4]. In the cold trap sodium is cooled within the settling tank and the section upstream the filter. This results in reduction of oxygen and hydrogen concentrations respectively to 1 and 0.05 ppm. Cold trap is capable of retaining impurities in amount up to -30% of its volume [5.5]. 

Two types of FP traps have been installed in JOYO. One is a cesium trap installed in the primary coolant sodium purification system to capture cesium released from failed fuels. An open pore, foam-like glassy carbon that consists of thin struts of Reticulated Vitreous Carbon (RVC) is used as a material for collecting cesium. The capacity of this trap is designed to be 7.4E+12 Bq. The other trap is a Cover Gas Clean-up System (CGCS) to collect and store the noble fission gas released from failed fuels. Although it is planned that only one failed fuel pin will be in the core at any time, the CGCS is designed to handle the releases of up to twelve failed fuel pins. 

The system for sodium purification in the cold filter-traps is intended for purification of primary circuit sodium from oxides, hydrates, carbonates and other impurities. The sodium purification system comprises five cold filter-traps with connection to charge and discharge pipelines Purification system is connected to loops No 2 and 3 of primary circuit. The sodium purification scheme can be seen in Fig. 7. 

Sodium flows out of the pressure head leg of DU500 main (second or third loop) to the pressure header of primary circuit sodium purification system and then flows to operable cold filter-trap. Here sodium is purified from soluble impurities owing to its cooling to the impurity setting-out and trapping temperature. After purification sodium is returned to (second or third loop) to the pump suction pipeline. 

One of the most important tasks is to assure reliable operation of the primary systems and components with simultaneous decrease of personnel dose rates. Now highly effective stationary system for sodium purification from caesium (SSOT) is provided on the reactor facility. 

In 1981, a contract with ANSALDO/NIRA (Italy) was signed to design and construct three sodium loops and auxiliary systems. Due to insufficient Ending the loops were never constructed. In 1996 funding has been finally provided for assembling the first loop (named SS-10), which is to be used as a test bed for experiments related to sodium purification and transferring. The loop will be constructed in EEN and completion is expected by mid-97. 

The sodium purification system, made up of narrow pipes, could not be totally drained. It was completely cut up into small sections which were washed in a special cell in the hot building connected to RAPSODIE buildings. 

The sodium purification units are also in the tank. The cold traps, plugging indicators, and pumps would be inserted through shield plugs just like the pumps and heat exchangers. Figure 8 shows an arrangement around the central reactor vessel. 

Primary Sodium Purification System (Cold Trap)... 

Foust, O.J. (1979) Sodium-NaK Engineering Handbook. Vol 5. Sodium Purification, Materials, Heaters, Coolers, and Radiators Gordon Breach, New York. 

X -leak in the bellow of the sodium purification system valve ... 

The primary sodium purification system consists of an in-vessel EM pump and an exvessel cold trap, heat exchangers and plugging meter, arranged in a shielded concrete cell with steel liner and inert gas. The pipework outside the purification cell has double walls. In the case of sodium leakage the purification ceil atmosphere (argon with sodium aerosols) is relieved into the buffer vessels of the reactor cover gas system. 

Each secondary sodium purification loop is associated with one m n secondary loop and one direct reactor cooling loop. All associated loops are arranged in the same Steam Generator Building compartment and are supplied from the same electrical division. Each of the six parallel and independent purification loops consists of a cold trap with recuperative heat exchanger, a plugging meter unit, an EM pump and the pipework with valves. 

Two nitrogen-cooled cold-traps for primary sodium purification are incorporated in the reactor vessel (Fig. 9.22). Sodium is fed to the filtertrap by an electromagnetic pump from the "cold" plenum of the reactor. It is possible to replace the filter-traps. 

Primary sodium purification Purification of the primary sodium is accomplished by two cold traps located outside the main vessel. Organic cooling with a NaK jacket is provided. 

Auxiliary systems The auxiliary systems of CEFR-25 include the sodium purification systems and the primary and secondary argon cover gas systems. The primary sodium purification system is composed of an electro-magnetic pump, two cold traps (one as standby), an economizer, and plugging meter, filter, storage tank and valves, is located in a shielded cell. 

The system is connected to the primary circuit by pipes and can be isolated by two stop valves. With this system the primary sodium can be kept below following impurity concentrations oxygen 10 ppm, hydrogen 0.5 ppm and carbon 20 ppm. The primary cover gas system serves as an isolation between the atmosphere and the sodium, and as a buffer for the reactor vessel, reactor roof and mechanism seals. The system is composed of a vapour trap, filters, decay tank, cesium trap, and compressor. The sodium purification and argon cover gas systems for the secondary sodium are similar to those for the primary sodium, but there is no cesium trap in the purification system or decay tank in the cover gas system. 

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