1/5-scale experiment of a Mark I boiling-water reactor pressure-suppression system under hypothetical LOCA conditions Page: 3 of 26
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INTRODUCTION
Ie important aspect of the safety of boiling water reactor. (BWR) power
plnta is the structural integrity of the prwsoure-suppression system after
a hypothetical loss-of-coolant accident (LOCA). Normally, the integrity of
the system after a hypothetical LOCA is determined analytically with a con-
puter code, e.g. CONTEMPT-LT.1 Occesionally, experinents are conducted to
confirm that the containment systems are adequately designed, but not over- .
designed. At the request of the Water Reactor Safety Research Branch of the -
0. S. Nuclear Regulatory Comeiosio, we have recently completed a series of
air tested on a 1/5-scale tWR Mark I pressure oupresdion ayeeem that evaluate
vertical leads and the associated hydrodynasic phenomena in the pressure-
suppression system following a hypothetical LOCA.
The tWR Mark I pressure-.upreaeion system consisted of a drywell nurround-
Ing the nuclear reactor and an external toroidal wetvell. The drywall it
connected to the toroidal wetwell with eight vent pipns. The toroidal set-
well, approximately half-filled with water, provides a heat sink to condense
primary coolant released during a LOG. A LOCA is simulated by rupturing a
line and discharging primary coolant into the drywell. If a recirculation
line is hypothtically ruptured, about one-third of the cater inside the line
flashes to steam me it enter the low pressure region inside the drywall.
Air initially inside the drywell, follownd by stem, is channeled from the
drywell through vent pipes into a ringhsader (also a tone), and finally
through partially submerged dowcomere into the pool of water in the toroidal
weswell. A crass section of the flow path between the drywell and the toroi-
dal -Wtoell, as neil ws asecited hardware in the 1/5-scale experiment, are
chore in Figure 1.
- Bubbles ore formed as the gaos merge from the bottom of the dowucomer.
The .eatiated momentum interhnge produces rapidly istreuing pool pres-
sures, which in turn result in a downward load on the toroidal wetwell fol-
lowed by on upward lead. The peak of this hydrodynaically developed down-
load occurs at apprnximately the time the downcomers are cleared of water and
the bubbles esacrt to form. The peak upload occurs at approximately the time
the bubbles breas through the water surface into the air space existing in
the upper portion of the toroidal wetwell.
The peak download and peak upload occur within a fraction of a second
after the start of the hypothetical LOCA, baforo the stem reaches the tarosi-
dal wawll. That in, even though steam is discharged into the dywell during
a hypothetical LOCA, the associated hydrodynamic phenomena, and the associated
peak loads, result from the discharge of air into the toroidal wetwell. Only
after the peak loads occur does sem enter the toroidal wecell. And, became
the pek loads are associated with the discharge of air into the toroidal wet-
well, the fluid used to pressure the drywall in not a factor. Our experi-
mental program consists of two part.: air tests and stem testa. During the
sir-tese phase, we pressuriard the drywell with nitrogen (91) uo that we
simulated the drywall pressura-time history predicted with Reference 1. We
used KN because it was readily available and inexpensive. The project began
in April, 1976, and the 27 air tests were completed 'ay, 1977.
Steam tests in our 1j5-acale facie are planned for fiscal year 1978.
During this phase we will force saturated steam into the drywell to first
purge all air and the 1, 1ale through the water in the toroidal vtwell. The
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Pitts, J. H. & McCauley, E. W. 1/5-scale experiment of a Mark I boiling-water reactor pressure-suppression system under hypothetical LOCA conditions, article, July 8, 1977; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc1446339/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.