Simulation of SBWR startup transient and stability Page: 7 of 20
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4B models is given in Ref.  and that of its input descriptions is provided in Ref. . Here we
point out the following important models required for a credible simulation of the SBWR startup
(1) Accurate low-pressure properties from 0.03 bar to 40 bar.
(2) A heat slab model for stored energy in structure materials.
(3) A flow-dependent loss coefficient model.
(4) A Reactor Water Cleanup and Shutdown Cooling System (RWCU/SDC) model for
level control during the SBWR startup.
(5) A control rod drive (CRD) flow model.
(6) A turbine bypass control model at pressures higher than 19 bar.
These models have been implemented in the RAMONA-4B code.
It should be mentioned that the heat transfer models for boiling and condensation at low pressures
are not well established at present in the literature. Furthermore, the accuracy of these models at low
pressures has not been validated for RAMONA-4B. Since the accuracy of these models may have
a direct impact on the predicted phase change, thermal and flow characteristics, the results presented
here should be considered qualitatively only.
2.2.2 Calculation Model for the Startup Transient
A simulation of startup conditions for the SBWR has been performed at BNL using the RAMONA-
4B code. Since information on the spatial and temporal movements of the control rods are not
available from the GE report, a time-dependent power ramp profile as proposed by GE has been
imposed as a boundary condition and a thermal-hydraulic only calculation performed with a
simplified core model. The simplified core model is necessitated by the need to run the startup
transient over a long period of time (5-6 hours) in order to show the important characteristics of the
early part of the startup transient. The simplified core model consists of four parallel coolant
channels including the bypass channel. The chimney, steam dome, downcomer, and the lower
plenum were also included. Table II presents the geometric parameters and nodalization scheme of
the RAMONA-4B input deck.
RAMONA-4B Input Deck for the Startup Transient
Component D.comer 1 D.comer2 Lower P1.1 Lower P1.2 Core Riser Dome
No. of Nodes 9 3 2 3 18 6 1
Height (m) 10.58 4.78 2.14 2.05 2.74 10.58 6.95
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Cheng, H.S.; Khan, H.J. & Rohatgi, U.S. Simulation of SBWR startup transient and stability, article, June 1, 1998; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc702243/m1/7/: accessed March 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.