Secondary sodium circuits

A circumferencial crack was detected by beaded wires on a moulded 321 steel tee junction in the Phenix secondary sodium circuit after 90,000h of operation. The crack was located in the heat-affected zone of the weld between the tee and the adjacent piping. It was shown that the crack occurred because of high stresses induced by an important misalignment. 

The incidence of cracking in the steel of various secondary sodium circuit components,... 

Three minor incidents of Na/NaK leak in the secondary sodium circuit and three minor incidents of water leak from the water / steam subheaders of SG are described here. 

FIG. 5 Drain system and Storage system of secondary sodium circuit. 

The addition of a safety control rod to the reactor. The partitioning of the secondary sodium circuits in the Steam Generator building to improve protection against sodium fires ... 

The reactor is cooled by 3 secondary sodium circuits each of them having one SG of modular concept. Each SG is composed of the economizer-evaporator, the superheaters and the resuperheaters stages each of them is composed of 12 modules. Forty-seven modules from 2 SG s superheater and resuperheater have to be repaired. A superheater module has the S shape and is composed of a 27 m long-( ) 200 mm shell, containing 7 water vapour tubes (Fig. 1). The sodium flows around the tubes. The tubes are maintained by regularly spaced grids. 

Some characteristics of the main secondary sodium circuits ... 

Three welds from a length of secondary sodium circuit (superheater) pipework that had operated at about 550°C and three samples containing known defects in the Superheater 3 vessel shell (all of these being in Type 321 steel welded with Type 347 consumable) were removed for metallurgical examination. This was primarily to study delayed reheat (relaxation) cracking. No cracking attributable... 

A secondary pipework transition weld between Type 321 steel pipework from the superheater and a 2 V4CrlMo nozzle at the inlet of the evaporator on secondary sodium circuit 1 was examined metallurgically, including use of transmission electron microscopy. This weld had operated at 490 C. No evidence was found of any mechanism that was likely to have led to failure of this type of weld during longer term operation. 

Secondary sodium circuit are employed to separate the steam plant from the core. It means that because of the low activity of the secondary sodium that the dose to operators is very low. The steam generators and decay heat removal circuits are arranged in pairs on a simple r al layout. 

These examinations have been restricted to the secondary sodium circuit, since the funding available precluded the study of primary circuit components such as the Above Core Structure or Intermediate Heat Exchangers. The secondary circuit studies are in three parts ... 

Decay heat removal loops. The normal route for the removal of decay heat in a fast reactor is via the secondary sodium circuits and the steam plant. Should this route not be available, decay heat in PFR could be rejected by one or more of three thermal syphon loops, each filled with eutectic sodium/potassium alloy. Each loop extracted heat through an immersed coil, intercq>ting some of the primary sodium as it flowed from the core towards an intermediate heat exchanger, and delivered the heat by natural convection to the outside atmosphere through a sodium-potassium/air heat exchanger built into the wall of the secondary containment building. 

Figure 6.14 shows the various components of the protective system for an SGU and secondary sodium circuit. Isolation and dumping would be initiated by operation of the rupture discs or by receipt of signals in excess of pre-determined limits fi-om the leak-detection instrumentation shown in Figure 6.13. 

There is a capability to isolate each primary loop from the reactor using two gate valves on the suction and pressure pipelines of the circuit. On the pressure pipeline of each loop downstream of the PSP a flap-type check valve is provided eliminating coolant backflow in the event of a PSP trip in one loop when the other PSPs are operative. The secondary sodium circuits comprise EHX heat transfer tubes, pipelines, secondary sodium pumps and steam generators. Due to utilization of the reactor energy for fresh water production the steam-water system has some specific features. Steam from the SG is supplied to turbines of two types a condensing turbine (K-100-45) and a back-pressure turbine (K-50-45). Exhaust steam flows from the back-pressure turbine and from intermediate bleeds of K-100-45 turbine are supplied to the water desalination facilities. At a heat output of 750 MW the reactor produces ... 

Of the six liquid metal cooled SMRs, three are sodium cooled fast reactors (KALIMER, BMN-170 and MDP), and 3 are lead-bismuth cooled fast reactors (RBEC-M, PEACER-300/550, and Medium Scale Lead-bismuth Cooled Reactor). All designs implement indirect thermodynamic cycles. All sodium cooled SMRs incorporate intermediate heat transport systems (secondary sodium circuits to transport heat to a steam turbine circuit and to prevent the possibility of a contact of water with the primary sodium). All lead-bismuth cooled SMRs have no intermediate heat transport system. All designs use steam turbine power circuit. 

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