Faster-than-real-time simulation of nuclear reactor accidents: the TRAC-NPA code Page: 3 of 11
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1. lNTROliUt TION
The Transient Reactor Am I vs is Code i TRACI is an advanced best-est imatc
systems code | nr aralvz. ing light-water rtiit ti'r ( LWR ) accidents. It is being
develoDcd at the Los Aiamos National Laboratory ur.de r the s por.si.r sli i p of the
kcaclor Safety Research Division of the US Nuclear Regulatory Commission (NRC).
TRAC' is used around the world for reactor safety applications.
A preliminary TRAC version was completed i r. December 1976. The first
publicly released version was TRAC-Pl (Ref. 2). completed 1 r. December 1977.
Latti versions, primarily TRAC-PI J2 and TRAC-Pfl . have been released to over 60
organ i 7a t ions. The last code in the TRAC' series. TRAC-PI1/MODI (Ref. 3). was
ready to be released i r. July ! *■> 8 .A. An extension of TRAC-PH /MODI . TRAC'-NPA. was
designed especially lor real-time simulation. fRAC-NPA is dosciihed i r. Sec. IV.
The TRAC code originally was design’d primarily for the analysis of large-
break lcss-of-coolant acciderts (LC X' A s > i u pressurized water reactors (PWRs).
However, lollowin’ the Three-Mile Island (TM1) accident, the necessity for
analysis of longer term small-break transients became very apparent. The seir.i-
implicit numerical method used in TRAC-Pl.)? and earlier TRAC versions is adequate
for shorter term large-break transients but is extremely i r.e f I' i c i e nt lor slower
transients: that is. the time-siep sizes resulting Iron the ma t e l i a I ( ourar.t
.'.luhilitv lime of the sen: i - i nip 1 i c i t method are much smallei than reasonable
error control requires. An obvious cure lor this problem is the use ol a lullv
implicit numerical method: liowevei. this alternative is not attractive because
it requires substantial charges in the TRAC code and multiplies the cost per
cell per step of the ll •J-dvr.ar.i c s solution hy a factor of six. The stabilily-
enhiirc l r.g twe'-slep l SI TS' method1 was created t o improve the running time of the
exist i r. g TRAC code with minimal impact or. the code structure and results. The
SITS method, described i r. Sec. II. eliminates the material Co u rant stability
limit by adding :i stabilivei step to the basic scni-imp Iic i t equations. This
method increases or.lv the computation cost per step hy 20 to
I lie SITS mi t he'd was i nip 1 cine r. t ed for the one-d imens i or. a 1 hydrodynamic
compone nts ol I RAC PI 1 and TRAC-PI’l/MOI'l and lias resulted in faster running
times for systems that ale modeled using only the one-d i me n s i or,a I components,
lor example, the Semi sc a 1 e Mod • .< sma I I - break test was rur. "TO times faster using
TRAC-PI 1 as compared to IR\( -PI)?. \ one-d i mens i >>na I simulation ol a TMI-type
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Woodruff, S.B. Faster-than-real-time simulation of nuclear reactor accidents: the TRAC-NPA code, article, April 1, 1985; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1085692/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.