02.05.2014 Views

Search - OECD Nuclear Energy Agency

Search - OECD Nuclear Energy Agency

Search - OECD Nuclear Energy Agency

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Figure 2. The natural convection impact on the unprotected beam jump from low power<br />

(start-up accident), assuming that the coolant flow enhancement system is unavailable:<br />

temperatures at the Demo Facility Average Assembly active fuel top.<br />

1673<br />

temperature (K)<br />

1473<br />

1273<br />

1073<br />

873<br />

673<br />

473<br />

Trends obtained by assuming<br />

constant the coolant flow rate:<br />

temperatures rise up to the clad<br />

melting level in about 40 s.<br />

Trends obtained by taking into account the natural convection mitigation<br />

0 10 20 30 40 50 60 70<br />

time (s)<br />

Clad melting temperature<br />

Fuel-pellet centre<br />

Fuel-pellet boundary<br />

Inner Clad<br />

Outlet Coolant<br />

Figure 3. Unprotected beam jump from low power (start-up accident) assuming that the coolant<br />

flow enhancement system is unavailable: trend of the Demo Facility coolant flow.<br />

100<br />

coolant flow (% of the nominal value)<br />

90<br />

80<br />

70<br />

60<br />

50<br />

40<br />

30<br />

20<br />

10<br />

coolant flow<br />

no natural convection<br />

0<br />

0 10 20 30 40 50 60 70<br />

time (s)<br />

3.3 The unprotected loss of flow<br />

The results presented above point out the natural convection capability to mitigate the<br />

consequences of a possible failure of the EADF active system of coolant flow enhancement. In the<br />

present section we further investigate this mitigation capability. In particular we assume the cooling<br />

system failure at nominal conditions without any beam power variation. Practically we preliminarily<br />

investigate the natural convection mitigation of an Unprotected Loss of Flow (ULOF) accident.<br />

517

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!