This report summarizes the result of studies concerning the range of
applicability of two subchannel codes for a variety of thermal-hydraulic
analyses. The subchannel codes used include COBRA IIIC/MIT and the
newly developed code, COBRA IV-I which is considered the benchmark
code for the purpose of this report. Hence, through the comparisons
of the two codes, the applicability of COBRA IIIC/MIT is assessed
with respect to COBRA IV-I.
A variety of LWR thermal-hydraulic analyses are examined. Results
of both codes for steady-state and transient analyses are compared.
The types of analysis include BWR bundle-wide analysis, a simulated rod
ejection and loss of flow transients for a PWR. The system parameters
were changed drastically to reach extreme coolant conditions, thereby
establishing upper limits.
In addition to these cases, both codes are compared to experimental
data including measured coolant exit temperatures in a core, interbundle
mixing for inlet flow upset cases and two-subchannel flow blockage
The comparisons showed that, overall, COBRA IIIC/MIT predicts most
thermal-hydraulic parameters quite satisfactorily. However, the clad
temperature predictions differ from those calculated by COBRA IV-I and
appear to be in error. These incorrect predictions are caused by the
discontinuity in the heat transfer coefficient at the start of boiling.
A review is made of the computer codes developed in the
U.S. for thermal-hydraulic analysis of nuclear reactors. The
intention of this review is to compare these codes on the
basis of their numerical method and physical models with
particular attention to the two-phase flow and heat transfer
characteristics. A chronology of the most documented codes
such as COBRA and RELAP is given. The features of the recent
codes as RETRAN, TRAC and THERMIT are also reviewed. The
range of application as well as limitations of the various
codes are discussed.; Sponsored by Boston Edison Company and others under MIT Energy Laboratory Electric Utility Program.
Several different models and correlations were developed
and incorporated in the sodium version of THERMIT, a thermal-
hydraulics code written at MIT for the purpose of analyzing
transients under LMFBR conditions. This includes: a mechanism
for the inclusion of radial heat conduction in the sodium coolant
as well as radial heat loss to the structure surrounding the test
section. The fuel rod conduction scheme was modified to allow
for more flexibility in modelling the gas plenum regions and
fuel restructuring. The formulas for mass and momentum exchange
between the liquid and vapor phases were improved. The single
phase and two phase friction factors were replaced by correlations
more appropriate to LMFBR assembly geometry.
The models incorporated in THERMIT were tested by running
the code to simulate the results of the THORS Bundle 6A experiments
performed at Oak Ridge National Laboratory. The results demonstrate
the increased accuracy provided by the inclusion of these effects.; "Sponsored by U.S Department of Energy, General Electric Co. and Hanford Engineering Development Laboratory."
A two dimensional numerical model for the simulation of sodium boiling
transient was developed using the two fluid set of conservation equations.
A semiimplicit numerical differencing scheme capable of handling the problems
associated with the ill-posedness implied by the complex characteristic roots
of the two fluid problems was used, which took advantage of the dumping effect
of the exchange terms.
Of particular interest in the development of the model was the identi-
fication of the numerical problems caused by the strong disparity between the
axial and radial dimensions of fuel assemblies. A solution to this problem
was found which uses the particular geometry of fuel assemblies to accelerate
the convergence of the iterative technique used in the model.
The most important feature of the model was its ability to simulate severe
conditions of sodium boiling, in particular flow reversal, which was shown in
the tests performed with the model.
Three sodium boiling experiments were simulated with the model, with good
agreement between the experimental results and the model predictions.; "Sponsored by U.S Department of Energy, General Electric Co. and Hanford Engineering Development Laboratory."
The practice of Demand-Side Management (DSM) has evolved over the past three decades in response to lessons learned from implementation in different global settings, and also in response to the changing needs of restructured power markets. The most notable change that is occurring today is the inclusion of programs that emphasize price responsiveness in the DSM portfolio. Traditionally, DSM programs were confined to energy efficiency and conservation programs with reliability-driven load management programs being used occasionally to manage emergency situations. Electric prices were taken as a given when designing such programs, hampering the eventual success of all such efforts. This Primer has been written to introduce the new concepts of price-responsive DSM that are currently being investigated in a variety of different market settings. It highlights different criteria and taxonomies for classification and evaluation of DSM programs and recommends programs that will likely provide a better fit with the objectives, expected needs and outcomes of DSM initiatives in developing and transition countries. As defined in this primer, such initiatives include both load shifting programs (that either clip peak loads or shift energy used in the peak period to off-peak periods) and efficiency programs (that reduce the total amount of energy). The purpose of the primer is to provide successful examples of price-responsive DSM programs from the developed world and by discussing their workings...
A simple fuel cycle cost model has been formulated, tested satisfactorily (within better than 3% for a wide range of cases)
using a more elaborate computer program, and applied to evaluate a variety of PWR fuel cyclesand fuel management options, with an
emphasis on issues pertinent to the NASAP/INFCE efforts. The uranium and thorium cycles were examined, lattice fuel-to-moderator and burnup were varied, and once-through and recycle modes were
examined. It was found that increasing core burnup was economically advantageous, particularly if busbar or total system cost is considered in lieu of fuel cycle cost only, for both once-through and recycle modes, so long as the number of staggered core batches is increased concurrently. When optimized under comparable ground rules, the once-through fuel cycle is competitive with the recycle option; differences are well within the rather large (+ 20%) one sigma uncertainty estimated for the overall fuel cycle costs by propagating uncertainties in input data. Optimization on mills/kwhre
and ore usage, tones/GWe,yr, are generally, but not universally, compatible criteria.
To the extent evaluated, the thorium fuel cycle was not found to be economically competitive. Cost-optimum thorium lattices were found to be drier than for current PWRs...
This study deals with the development of a computer pro-
gram for steady-state and transient BWR subchannel analysis.
The conservation equations for the subchannels are obtained
by area-averaging of the two-fluid model conservation equa-
tions and reducing them to the drift-flux model formulation.
The conservation equations are solved by a marching type
technique which limits the code to analysis of operational
transients only. The transfer of mass, momentum and energy
between adjacent subchannels is split into diversion cross-
flow and turbulent mixing components. The transfer of mass
by turbulent mixing is assumed to occur in a volume-for-
volume scheme reflecting experimental observations. The
phenomenon of lateral vapor drift and mixing enhancement with
flow regime are included in the mixing model of the program.
The following experiments are used for the purpose of the
assessment of the code under steady-state conditions:
1) GE Nine-Rod tests with radially uniform and nonuniform
2) Studsvik Nine-rod tests with strong radial power tilt
3) Ispra Sixteen-rod tests with radially uniform heating
Comparison of calculated results with these data shows
that the program is capable of predicting the correct trends
in exit mass velocity and quality distributions.; Originally presented as the author's thesis...
A code has been developed for the comprehensive analysis
of a fault tree.' The code designated UNRAC (UNReliability
Analysis Code) calculates the following characteristics of an
Tnput fauTt tree:
a) minimal cut sets,
b) top event unavailability as point estimate and/or
in time dependent form,
c) quantitative importance of each component
d) error bound on the top event unavailability
UNRAC can analyze fault trees, with any kind of gates (EOR,
NAND, NOR, AND, OR), up to a maximum of 250 components and/or
For generating minimal cut sets the method of bit manipu-
lation is employed. In order to calculate each component's
time dependent unavailability, a general and consistent set of
mathematical models is developed and the repair time density
function is allowed to be represented by constant, exponen-
tial, 2nd order erlangian and log-normal distributions. A
normally operating component is represented by a three-state
model in order to be able to incorporate probabilities for
revealed faults, non-revealed faults and false failures in
For importance analysis, a routine is developed that will
rearrange the fault tree to evaluate the importance of each
component to system failure...
The WOSUB-codes are spin-offs and extensions of the
MATTEO-code . The series of three reports describe WOSUB-I
and WOSUB-II in their respective status as of July 31, 1977.
This report is the first in a series of three, the
second of which contains the user's manual  and the third
 summarizes the assessment and comparison with experimental
data and various other subchannel codes.
The present report introduces the drift-flux and vapor
diffusion models employed by the code, discusses the solution
method and reviews the constitutive equations presently built
into the code. Wherever applicable, possible exteriors of the
models are indicated especially with due regard of the findings
presented in .
Overall, the review of the model and the package of
constitutive equations demonstrate that WOSUB-I and II
constitute true alternatives for BWR bundle and PWR test bundle
calculations as compared to the commonly applied COBRA-IIIC,
and COBRA-IIIC/MIT codes which were primarily designed for PWR
subchannel and core calculations, respectively. In fact, the
incorporation of the drift flux and the vapor diffusion pro-
cesses into a subchannel code has to be cdnsidered.a major step
towards a more basic understanding and a well balanced engineer-
ing approach without the extra burden of a true two-fluid two-
Recommendations for improvements in the various areas
are indicated and should serve as guidelines for future develop-
ment of this code which in light of the encouraging results pre-
sented in  seems to be highly warranted.
The WOSUB-code is still in the stage of evolutionary
development. In this context...
The WOSUB-codes are spin-offs and extensions of the MATTEO-
code [ 2 ]. The series of reports describe WOSUB-I
and WOSUB-II in their respective status as of July 31, 1977.
This report is the second of a series of three reports
describing the WOSUB code. It gives a detailed description of
the input data, flow charts, and output, and contains the list-
ings of WOSUB-I and WOSUB-II. For the purpose of future ex-
tensions parameters, common blocks and variables used in the
code are listed in full detail.
WOSUB-I and WOSUB-II are subchannel computer codes for the
steady-state and transient analysis of the thermal-hydraulic
characteristics of Boiling Water Reactor (BWR) fuel rod bundles.
Both codes are also applicable'to analyze PR bundles, especially
when these are ducted--a situation which most often arises in
The main difference between WOSUB-I and WOSUB-II is that
the former is designed to analyze small bundles, whereas the
latter is capable to handle symmetric sections of today's large-
sized BWR bundles. In addition, WOSUB-II does not contain all
of the additions made in WOSUB-I yet, because it is deemed
appropriate to introduce these into the smaller code first,
before they are implemented into the bigger one.
Both codes are still in the stage of evolutionary develop-
This project describes the electricity demand and energy consumption
management system and its application to Southern Peru smelter. It is composed
of an hourly demand-forecasting module and of a simulation component for a
plant electrical system. The first module was done using dynamic neural
networks with backpropagation training algorithm; it is used to predict the
electric power demanded every hour, with an error percentage below of 1%. This
information allows efficient management of energy peak demands before this
happen, distributing the raise of electric load to other hours or improving
those equipments that increase the demand. The simulation module is based in
advanced estimation techniques, such as: parametric estimation, neural network
modeling, statistic regression and previously developed models, which simulates
the electric behavior of the smelter plant. These modules facilitate
electricity demand and consumption proper planning, because they allow knowing
the behavior of the hourly demand and the consumption patterns of the plant,
including the bill components, but also energy deficiencies and opportunities
for improvement, based on analysis of information about equipments, processes
and production plans, as well as maintenance programs. Finally the results of
its application in Southern Peru smelter are presented.
There is growing interest in lowering the energy consumption of computation.
Energy transparency is a concept that makes a program's energy consumption
visible from software to hardware through the different system layers. Such
transparency can enable energy optimizations at each layer and between layers,
and help both programmers and operating systems make energy aware decisions.
The common methodology of extracting the energy consumption of a program is
through direct measurement of the target hardware. This usually involves
specialized equipment and knowledge most programmers do not have. In this
paper, we examine how existing methods for static resource analysis and energy
modeling can be utilized to perform Energy Consumption Static Analysis (ECSA)
for deeply embedded programs. To investigate this, we have developed ECSA
techniques that work at the instruction set level and at a higher level, the
LLVM IR, through a novel mapping technique. We apply our ECSA to a
comprehensive set of mainly industrial benchmarks, including single-threaded
and also multi-threaded embedded programs from two commonly used concurrency
patterns, task farms and pipelines. We compare our ECSA results to hardware
measurements and predictions obtained based on simulation traces. We discuss a
number of application scenarios for which ECSA results can provide energy
transparency and conclude with a set of new research questions for future work.; Comment: 29 pages...
In this report we present a network-level multi-core energy model and a
software development process workflow that allows software developers to
estimate the energy consumption of multi-core embedded programs. This work
focuses on a high performance, cache-less and timing predictable embedded
processor architecture, XS1. Prior modelling work is improved to increase
accuracy, then extended to be parametric with respect to voltage and frequency
scaling (VFS) and then integrated into a larger scale model of a network of
interconnected cores. The modelling is supported by enhancements to an open
source instruction set simulator to provide the first network timing aware
simulations of the target architecture. Simulation based modelling techniques
are combined with methods of results presentation to demonstrate how such work
can be integrated into a software developer's workflow, enabling the developer
to make informed, energy aware coding decisions. A set of single-,
multi-threaded and multi-core benchmarks are used to exercise and evaluate the
models and provide use case examples for how results can be presented and
interpreted. The models all yield accuracy within an average +/-5 % error
Energy models can be constructed by characterizing the energy consumed by
executing each instruction in a processor's instruction set. This can be used
to determine how much energy is required to execute a sequence of assembly
instructions, without the need to instrument or measure hardware.
However, statically analyzing low-level program structures is hard, and the
gap between the high-level program structure and the low-level energy models
needs to be bridged. We have developed techniques for performing a static
analysis on the intermediate compiler representations of a program.
Specifically, we target LLVM IR, a representation used by modern compilers,
including Clang. Using these techniques we can automatically infer an estimate
of the energy consumed when running a function under different platforms, using
One of the challenges in doing so is that of determining an energy cost of
executing LLVM IR program segments, for which we have developed two different
approaches. When this information is used in conjunction with our analysis, we
are able to infer energy formulae that characterize the energy consumption for
a particular program. This approach can be applied to any languages targeting
the LLVM toolchain...
The static estimation of the energy consumed by program executions is an
important challenge, which has applications in program optimization and
verification, and is instrumental in energy-aware software development. Our
objective is to estimate such energy consumption in the form of functions on
the input data sizes of programs. We have developed a tool for experimentation
with static analysis which infers such energy functions at two levels, the
instruction set architecture (ISA) and the intermediate code (LLVM IR) levels,
and reflects it upwards to the higher source code level. This required the
development of a translation from LLVM IR to an intermediate representation and
its integration with existing components, a translation from ISA to the same
representation, a resource analyzer, an ISA-level energy model, and a mapping
from this model to LLVM IR. The approach has been applied to programs written
in the XC language running on XCore architectures, but is general enough to be
applied to other languages. Experimental results show that our LLVM IR level
analysis is reasonably accurate (less than 6.4% average error vs. hardware
measurements) and more powerful than analysis at the ISA level. This paper
provides insights into the trade-off of precision versus analyzability at these
levels.; Comment: 22 pages...
Dynamic voltage and frequency scaling proves to be an efficient way of
reducing energy consumption of servers. Energy savings are typically achieved
by setting a well-chosen frequency during some program phases. However,
determining suitable program phases and their associated optimal frequencies is
a complex problem. Moreover, hardware is constrained by non negligible
frequency transition latencies. Thus, various heuristics were proposed to
determine and apply frequencies, but evaluating their efficiency remains an
issue. In this paper, we translate the energy minimization problem into a mixed
integer program that specifically models most current hardware limitations. The
problem solution then estimates the minimal energy consumption and the
associated frequency schedule. The paper provides two different formulations
and a discussion on the feasibility of each of them on realistic applications.