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

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7. COMPUTER PREDICTION OF THERMAL-HYDRAULIC
PARAMETERS FOR NORMAL RECOVERY
7.1 Introduction
The purpose of this chapter is to present the results of BWR-LACP
calculations (see Sect. 4) of system behavior for two different portions
of the Station Blackout:
1. Normal Recovery: DC power from the unit battery remains available
during this period; therefore RCIC and HPCI injection flows are assumed
available throughout, and
2. Loss of 250 vdc Batteries: The batteries are assumed to fail after
four hours, causing failure of RCIC and HPCI injection, ultimately leading
to uncovering of the core about eight hours after the blackout.
The normal recovery portion of the Station Blackout is discussed in
detail in Sects. 3 and 6. Operator actions assumed here are consistent
with those sections. Results were calculated to five hours* for normal
recovery in order to provide some overlap with the MARCH code severe ac
cident calculations (see Sects. 9 and 10), which assume that the boil-off
begins after four hours from a fully pressurized condition. The Loss of
250 vdc Batteries results are given in this section in order to provide an
estimate of system behavior possible after loss of dc power if the plant
is depressurized during the normal recovery period.
7.2 Conclusions
Major conclusions drawn from the calculated results are given below,
succeeded by a detailed discussion of code input assumptions and transient
results.
7.2.1 Normal Recovery — Conclusions
If power were recovered within five hours of the inception of the
Station Blackout, a normal recovery would be possible. System parameters
are within acceptable ranges after five hours:
1. The 250 vdc batteries, by assumption, last the full five hours.
2. Reactor vessel level is within the normal control range, about 5.08 m
(200 in.) above the top of active fuel.
3. Reactor vessel pressure is being controlled at about 0.69 MPa (100
psia).
4. About 354 m3 (93,500 gal.) of water have been pumped from the Con
densate Storage Tanks, which had an assured capacity of 511 m3
(135,000 gal.) before the blackout.
5. Suppression pool temperature is about 82°C (180°F), but this should
not be a problem for the T-quencher type of SRV discharge header pip
ing.
6. Containment pressures are elevated to about 0.17 MPa (25 psia), well
below the 0.53 MPa (76.5 psia) design pressure.
*These results are extended to seven hours in Appendix G.