NITROGEN IN A STEAM-GENERATOR OF A PWR UNDER SBLOCA CONDITIONS - EXPERIMENTAL INVESTIGATIONS IN THE PKL TEST FACILITY AND COMPARISON WITH ANALYTICAL STUDIES
B. Schoen et P. Weber, NITROGEN IN A STEAM-GENERATOR OF A PWR UNDER SBLOCA CONDITIONS - EXPERIMENTAL INVESTIGATIONS IN THE PKL TEST FACILITY AND COMPARISON WITH ANALYTICAL STUDIES, Experimental thermal and fluid science, 15(3), 1997, pp. 238-252
Since 1976, extensive investigations of the thermal hydraulic behavior
of a pressurized water reactor (PWR) during various accident scenario
s have been carried out by Siemens/KWU at the integral test facility P
KL, which simulates a typical four-loop 1300 MWe PWR of KWU design. On
e major topic of the current investigations includes tests under small
break loss of coolant accident (SBLOCA) conditions, postulating addit
ional system failures. During plant cool down in the course of SBLOCAs
, besides other measures, the subsystems of the emergency core cooling
system are initiated. Below a primary pressure of 26 bar, the accumul
ators (ACCs) automatically inject water into the primary system. With
the postulation of additional system failures in the presented PKL exp
eriment, nitrogen (N-2) can enter the primary system at a primary pres
sure > 10 bar before the ACCs are shut off. Under these very hypotheti
cal SBLOCA conditions, nitrogen can accumulate in the steam generator
U-tubes, whereby the heat removal mechanism changes from natural circu
lation to reflux-condenser mode. This phenomenon is analyzed in detail
; interesting two-phase flow patterns were observed with heat removal
under water-steam countercurrent flow with nitrogen present. This PKL
experiment shows that a sudden stagnation of natural circulation in al
l loops caused by nitrogen at considerably reduced inventory does not
impede heat removal from the core; it results in the very effective re
flux-condenser mode. The system stabilizes itself at a specific pressu
re and temperature level, and consequently the removal of the core pow
er is ensured for a given period, until further measures are initiated
. (C) Elsevier Science Inc., 1997.