Station blackout at Browns Ferry Unit One - Oak Ridge National ...

20
the steam dryers to the steam dome. The natural circulation rate is de
pendent on a number of variables including: water level in the downcomer
annulus, water-steam level above the core, core steaming rate, and density
of the water-steam mixture in and above the core. One phenomenon that
makes the calculation more difficult is that when water level gets low
enough the recirculation of water from the steam separators ceases and
water flows from the downcomer annulus only as required to counter-balance
water lost by boil-off from the core.
The equation used to calculate core inlet flow is:
where
KfWci2 = Pdc*Ldc - Ptp * Ltp
Kf = empirically determined friction coefficient
wci = core inlet tiow
Pdc = downcomer water density
Ldc = downcomer water level (ref. to zero at bottom of active
fuel)
Jt = elevation-averaged density of water-steam mixture in and
above core
LtD = level of steam-water mixture above bottom of active fuel.
The value of the friction coefficient, Kf, was calculated from the
natural circulation curve on Fig. 3.7-1 of the BFNP FSAR by forcing agree
ment with the predictions of this equation at the 30% thermal power point.
This procedure resulted in a reasonably good approximation of the flow at
other points, as shown on Fig. 4.1. _
The rate of recirculation of water back to the downcomer annulus is
calculated as a function of the water-steam mixture level in the steam
separators:
where
wrecir = * f