The SWR 1000 (about 3000 MW^) from SIEMENS is equipped with emergency condensers. With the assumptions

same flow resistances as in the SWR 1000

200 tubes with the same material and geometries as used in NOKO

temperature in the Reactor Pressure Vessel about 100 C temperature of the outside pool 30°C

a total power of about 12 MW could be transferred.

This corresponds to a decay heat at about two days after scram.

A change in flow resistances, number of tubes and pool temperature would change the amount of energy transferred but not the mode of heat transfer.

For long periods it has to be considered that the water pool has to be cooled.

Another possibility would be to bring the Reactor Pressure Vessel to a pressure below 1 MPa and allow boiling of the water pool. Then energy would be removed from the water pool via the building condensers to a pool outside the containment.

2. CONCLUSIONS

A test with the NOKO facility has confirmed that the Emergency Condensers as proposed for the SWR 1000 from SIEMENS can transfer decay heat produced in the core region to an outside water pool. The capacity, however, is not high enough to cope with the total amount of decay heat immediately after scram. However, after some time — depending on the actual design — this heat transfer mode is effective.

[1] IAEA-TECDOC-936, Terms for Describing New, Advanced Nuclear Power Plants.

[2] IAEA-TECDOC-626 : Safety Related Terms For Advanced Nuclear Plants.

[3] PROPOSED SCALING LAWS FOR SINGLE-PHASE NATURAL CIRCULATION

Consider a simple nonuniform diameter natural circulation loop as shown in Fig. 1 with a horizontal heat source at the bottom and a horizontal heat sink at the top. The heat sink is maintained by providing cooling water to the secondary side of the cooler at a specified inlet temperature of Ts. In this analysis, the secondary side temperature is assumed to remain constant. The heat flux at the heat source is maintained constant. Assuming the loop to be filled with an incompressible fluid of constant properties except density (Boussinesq approximation where density is assumed to vary as p=pr[1-P(T-Tr)]) with negligible heat losses, axial conduction and viscous heating effects, the governing differential equations can be written as