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Fast burst reactors in the u.s.a.

01 Jan 1965-
TL;DR: In order to increase the fission yield per burst, efforts have been directed toward the development of cores which maintain dimensional stability when subjected to more extreme temperature cycles than may be tolerated in normal uranium metal.
Abstract: In order to increase the fission yield per burst, efforts have been directed toward the development of cores which maintain dimensional stability when subjected to more extreme temperature cycles than may be tolerated in normal uranium metal There also have been attempts to eliminate inertial difficulties related to the quenching delay associated with the finite time for translating fission energy into surface or volume expansion This delay leads to an effective broadening of the bursts at a given yield The second series of burst reactors as referred to here are those which employ an alloy of uranium, specifically 10 weight percent molybdenum (U-10 w/o Mo), in which extensive metallurgical tests have indicated relatively small crystal growth and excellent phase stability during or following repeated large temperature cycles (~500°C) Research Reactor) at Oak Ridge National Laboratory, Molly-G or FBR (Fast Burst Reactor) at White Sands Missile Range, and Super Kukla at Lawrence Radiation Laboratory; three additional models similar to HPRR and Molly-G are in the final planning stages, one at Sandia Corporation, one at Aberdeen Proving Grounds, and one at LASL None of these reactors has produced more than a total of ~300 bursts to be compared with many thousands formore » a typical reactor of the first series Accordingly, such devices may be considered in a relatively early stage of development« less

Summary (3 min read)

1. INTRODUCTION

  • Historically, the development of fast prompt-burst reactors was an outgrowth of a program to determine the behavior of supercritical systems, particularly, to confirm the effectiveness of thermal expansion in quenching reactivity.
  • The experimental behavior of the early simple versions has been used accordingly as a basis for normalizing fast-reactor-dynamics calculations .r 11 While such operation comes closer than usual to damaging conditions, careful attention to operational control has resulted in the generation of many thousands of prompt bursts on the first series of fast-burst reactors without serious incident.
  • Near-fission-spectrum neutron bursts from these reactors have been employed in 1) basic fission studies, e.g., the extensive measurements of delayed neutron and delayed gamma parameters 121, 2) radiation dosimetry, 3) calibration of radiation alarms for criticality.

DISCLAIMER

  • Portions of this document may be illegible in electronic image products.
  • Images are produced from the best available original document.
  • By fuel integrity as a result of severe shocks associated with the rapid temperature increases.
  • Pure uranium metal, particularly as cast, is subject to surface roughening, anisotropic crystal growth, and creation of internal voids.
  • Mechanical shock to structural members is also a limiting factor in most of the early burst machines.

A

  • In order to increase the fission yield per burst, efforts have been directed toward the development of cores which maintain dimensional stability when subjected to more extreme temperature cycles than may be tolerated in normal uranium metal.
  • There also have been attempts to eliminate inertial difficulties related to the quenching delay associated with the finite time for translating fission energy into surface or volume expansion.
  • The second series of burst reactors as referred to here are those which employ an alloy of uranium, specifically 10 weight percent molybdenum (U-10 w/o Mo), in which extensive metallurgical tests have indicated relatively small crystal growth and excellent phase stability during or following repeated large temperature cycles (-, 500°C).
  • Research Reactor) at Oak Ridge National Laboratory, Molly-G or FBR (Fast Burst Reactor) at White Sands Missile Range, and Super Kukla at Lawrence Radiation Laboratory; three additional models similar to HPRR and Molly-G are in the final planning stages, one at Sandia Corporation, one at Aberdeen Proving Grounds, and one at LASL.

3. REACTOR DESIGNS AND DESCRIPTIONS

  • Table I lists startup dates for the burst reactors considered here together with some pertinent characteristics.
  • The first three are not in operation currently, but are included for historical interest.
  • Lady Godiva and Kukla Scientific Laboratory, was basically spherical in shape -6.8 in.
  • Diameter with two horizontal parting planes to permit disassembly into three roughly equal sections for large shutdown effectiveness.

SPR I

  • This core was nickel-flashed as was the original, and additionally was overplated with cadmium to reduce neutron coupling with the variety of objects to be irradiated externally.
  • Bperience with such reactors has demonstrated some burst lengthening as a result of neutron back scattering from massive samples placed nearby even if there is cadmium shielding.
  • The reactor stand is supported on a hydraulically-operated elevator which lowers it into a pit after operation.
  • A 12-inch-thick lead radiation shield slides over the pit to permit personnel entry into the building soon after a burst has been produced.
  • 2As defined in 131, the inertial effect arises from the delay required for a pressure wave to travel from the interior of a fuel piece to a surface where the major reactivity quenching takes place.

I n earlier d e s i g n s ,

  • In preliminary operations of HPRR, burst yields in excess of lo1' fissions were readily obtained with some minor shock damage observed and corrected, and it is safe to say that the maximum yield is shock-limited.
  • The maximum observed temperature increases Of -5OO0C may be considered an upper limit for routine operation because of the onset of U-Mo phase transformation beyond Reactor portability is achieved in the RPRR system by suspend-0 -500OC.
  • The HPRR reactor generates "tailless" bursts or prompt power pulses which are not followed by the plateau mentioned previously.
  • In the case of HPRR, a shock wave causes separation of the plate from the safety block latching magnet, and a compressed spring ejects the safety block to yield an effective scram in -225 usec.

To satisfy require-

  • The height is variable and nominally 37 in.
  • Tungsten disc attached to the sample container.
  • For continuous control, a gang of 6 shim rods operated individually or in combination enter the core from above and employ double-ballscrew actuators.
  • Reactor shutdown is accamplished by dropping the lower core half which is also hydraulically actuated.
  • The maximum temperature increase observed in preliminary opera-18 No inertial shock effects have been experi-.

5. REACTOR SAFETY

  • Because of low repetition rates, time-averaged operating power levels for fast burst reactors are generally less than a kilowatt.
  • This means that the radioactive fission fragment inventory is small and its dispersal as a result of an explosive accident generally would not be a matter of public-safety concern.
  • Questions of more legitimate concern are those associated with possible low-level disruptive damage which may accompany the stepwise assembly necessary.

Q .

  • From direct radiation is provided by remote operation from a distant or well-shielded control room.
  • That possibility is normally considered to define the maximum credible accident that serves as a basis for judging the need for containment or conf inement .
  • The problem of predicting energy release under ramp conditions has been considered by G. E. Hansen f121 who shows that the probability that the neutron population remains below a specified level at a particular reactivity depends primarily upon the time fluctuation in establishment of a persistent neutron chain and secondarily on the time fluctuation in growth of a chain.
  • The upper curve is representative of burst rod reactivity insertion without external source for many of the small burst reactors.
  • The spontaneous fission source strength, So, in Godiva I1 is c\, 100 n/sec but is often increased to 300 n/sec by multiplication after safety block insertion and before burst rod insertion, while the natural source for Molly-G and HPRR is about P twice that of Godiva 11.

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Content maybe subject to copyright    Report

.-
-
-.
SM
62/53
FAST
BURST
REACTORS IN THE U.S.A.
,L%.rA
I
4"
-==JTT*-
Thomas F. Wimett, Staff Member, University 'of-"'California,
LOS
Alamos Scientific Laboratory, Los Alamos, New Mexico
1.
INTRODUCTION
Historically, the development of fast prompt-burst reactors
was an outgrowth
of
a
program to determine the behavior of super-
critical systems, particularly, to confirm the effectiveness of
thermal expansion in quenching reactivity. The experimental be-
havior of
the early simple versions has been used accordingly
as
a
basis for normalizing fast-reactor-dynamics calculations
.r
11 While
such operation comes closer than usual to damaging conditions,
careful attention to operational control has resulted in the gen-
eration of many thousands of prompt bursts on the first series
of
fast-burst reactors without serious incident.
1
Reactors of the first series are fabricated from highly
en-
riched
(-
93.5%
U-235)
cast uranium metal and include Lady Godiva
and Godiva
I1
at
Los Alamos Scientific Laboratory, Kukla and Fran
at Lawrence Radiation Laboratory, and
SPR
I
at Sandia Corporation.
Near-fission-spectrum neutron bursts from these reactors have been
employed in
1)
basic fission studies, e.g., the extensive measure-
ments
of
delayed neutron and delayed gamma parameters
121,
2)
radia-
tion dosimetry,
3)
calibration of radiation alarms for criticality
*'-J
I
'Two oversized bursts were experienced on Lady Godiva (which was
not specifically designed as a burst reactor) as a result of errors
in operational control. Damage suffered included bending of core
supports, breaking
of
assembly bolts, and deformation of central
fuel plates in the second and most extreme excursion.
F
A
.
*a

DISCLAIMER
This report was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor any agency Thereof, nor any of their employees,
makes any warranty, express or implied, or assumes any legal
liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial product,
process, or service by trade name, trademark, manufacturer, or
otherwise does not necessarily constitute or imply its endorsement,
recommendation, or favoring by the United States Government or any
agency thereof. The views and opinions of authors expressed herein
do not necessarily state or reflect those of the United States
Government or any agency thereof.

DISCLAIMER
Portions of this document may be illegible in
electronic image products. Images are produced
from the best available original document.

accidents,
4)
radiobiology, and
5)
interaction
of
radiation with
matter such as germanium crystals
[3,41,
semiconductors, and
biological systems.
by fuel integrity as a result of severe shocks associated with the
rapid temperature increases. Pure uranium metal, particularly as
cast,
is
subject to surface roughening, anisotropic crystal growth,
and creation of internal voids. Such effects.were observed and
were presumably caused by burst thermal cycling and irradiation and
occurred for temperature rises (from ambient)
-
200°C
--
far below
the melting temperature. Mechanical shock to structural members
is also a limiting factor in most of the early burst machines.
(Fran is an exception as will be discussed later.)
Maximum burst yields in the first series generally are limited
?A
'4
A
In order to increase the fission yield per burst, efforts have
been directed toward the development of cores which maintain dimen-
sional stability when subjected to more extreme temperature cycles
than may be tolerated in normal uranium metal.
There also have
been attempts to eliminate inertial difficulties related to the
quenching delay associated with the finite time for translating
fission energy into surface or volume expansion.
This
delay leads
to an effective broadening of the bursts at a given yield. The
second series
of
burst reactors as referred to here are those which
employ an alloy of uranium, specifically 10 weight percent molyb-
denum (U-10 w/o
Mo),
in which extensive metallurgical tests have
indicated relatively small crystal growth and excellent phase
stability during or following repeated large temperature cycles
(-,
500°C).
Research Reactor) at Oak Ridge National Laboratory, Molly-G or FBR
(Fast Burst Reactor) at White Sands Missile Range, and Super Kukla
at Lawrence Radiation Laboratory; three additional models similar
to
HPRR
and Molly-G are in the final planning stages, one at Sandia
Corporation, one at Aberdeen Proving Grounds, and one at LASL. None
of these reactors has produced more than a total of
~\r
300
bursts
to
be compared with many thousands for a typical reactor
of
the first
series. Accordingly, such devices may be considered in a relatively
early stage of development.
Included in this reactor series are HPRR (Health Physics
2. PROCEDURE FOR BURST GENERATION
All reactor systems discussed here, except where noted, employ
-2-

the same basic procedure for prompt burst production, namely: 1)
establishment of the delayed critical control rod positions by
low
power operation with the burst rod withdrawn;
2)
retraction of the
safety block to permit decay of delayed neutron precursors born
during the steady-state operation;
3)
reinsertion of the safety
block followed shortly by the rapid insertion of the burst rod
(worth
*
1$ excess reactivity) to boost the reactivity to the pre-
(scram) of safety block and rods triggered by detection of power
level in the burst.
If
an external neutron source
is
used during
the steady-state operation, it is generally withdrawn to a less
effective position during the burst mode in order to minimize
"preinitiation", or the generation
of
a burst before maximum excess
reactivity is attained by the burst rod.
-.
E
determined super-prompt-critical value;
4)
automatic withdrawal
8.
3.
REACTOR
DESIGNS
AND
DESCRIPTIONS
Table
I
lists
startup dates for the burst reactors considered
here together with some pertinent characteristics. The first three
are not in operation currently, but are included for historical
interest.
Lady Godiva and Kukla
Scientific Laboratory, was basically spherical in shape
-
6.8
in.
diameter with two horizontal parting planes to permit disassembly
into three roughly equal sections for large shutdown effectiveness.
Kukla
[61,
shown in
Fig.
1, was designed and constructed
by
Lawrence
Radiation Laboratory and is similar to Lady Godiva, except that
it
is
mechanically supported from underneath rather than by hangers
as in the original, and, in addition, employs a cylindrical section
(safety block)
-
7
kg uranium to be withdrawn for shutdown. Both
use motor-driven screw actuators for uranium control rods and
pneumatic cylinders for high-speed actuation of the safety blocks
and burst rods. The exposed uranium surfaces of Kukla are nickel-
flashed and overplated with 10
-
15 mils of cadmium to eliminate
corrosion and to reduce neutron room-return effects, while the sur-
face of Godiva is bare. Total fuel mass is
-
53
kg
in each reactor.
The detailed burst behavior of Kukla
is
assumed to be identical to
that
of
Godiva, which is discussed in the literature.[31
Lady Godiva
[3,51,
designed and constructed by
Los
Alamos
-3-

Citations
More filters
01 Jan 2017
TL;DR: Bevins et al. as mentioned in this paper used a metaheuristic-based optimization algorithm, Gnowee, to solve ETA optimization problems with mixed-integer and combinatorial design vectors and high-cost, noisy, discontinuous, black box objective function evaluations.
Abstract: Author(s): Bevins, James | Advisor(s): Salybaugh, Rachel N | Abstract: At its core, research represents an attempt to break from the "this is the way we have always done it" paradigm. This idea is evidenced from the start in this research effort by the problem formulation to develop a new way to generate synthetic debris that mimics the samples that would be collected for forensics purposes following a nuclear weapon attack on the U.S. or its allies. The philosophy is also demonstrated by the design methodology used to solve the synthetic debris problem, using methods not commonly applied to nuclear engineering problems. Through this research, the bounds of what is deemed possible in neutron spectral shaping are moved ever so slightly.A capability for the production of synthetic debris and fission products was developed for the National Ignition Facility (NIF). Synthetic debris has historically been made in a limited fashion using sample doping techniques since the cessation of nuclear weapons testing, but a more robust alternative approach using neutron spectral shaping was proposed and developed by the University of California-Berkeley and Lawrence Livermore National Laboratory (LLNL). Using NIF as a starting source spectrum, the energy tuning assembly (ETA) developed in this work can irradiate samples with a combined thermonuclear and prompt fission neutron spectrum (TN+PFNS). When used with fissile foils, this irradiation will produce a synthetic fission product distribution that is realistic across all mass chains.To design the ETA, traditional parametric point design approaches were discarded in favor of formal optimization techniques. Finding a lack of suitable algorithms in the literature, a metaheuristic-based optimization algorithm, Gnowee, was developed for rapid convergence to nearly globally optimum solutions for complex, constrained engineering problems with mixed-integer and combinatorial design vectors and high-cost, noisy, discontinuous, black box objective function evaluations. Comparisons between Gnowee and several well-established metaheuristic algorithms are made for a set of continuous, mixed-integer, and combinatorial benchmarks. These results demonstrated Gnoweee to have superior flexibility and convergence characteristics over a wide range of design spaces. The Gnowee algorithm was implemented in Coeus, a new piece of software, to perform optimization of design problems requiring radiation transport for the evaluation of their objective functions. Currently, Coeus solves ETA optimization problems using hybrid radiation transport (ADVANTG and MCNP) to assess design permutations developed by Gnowee. Future enhancements of Coeus will look to expand the geometries and objective functions considered to those beyond ETA design.Coeus was used to generate an ETA design for the TN+PFNS application on NIF. The design achieved a reasonable match with the objective TN+PFNS and associated fission product distributions within the size and weight constraints imposed by the NIF facility. The ETA design was built by American Elements, and initial validation tests were conducted at the Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. These experiments used foil activation and pulse height spectroscopy to measure the ETA-modified spectrum. Additionally, pulse height spectroscopy measurements were taken as the ETA was built-up component-by-component to measure the impact of nuclear data on the ability to model the ETA performance. Some initial analysis of these results is included here.Finally, an integral validation experiment on NIF was proposed using the Coeus generated ETA design. A scoping study conducted by LLNL determined the proposed experiment and ETA design are within NIF facility limitations and current radio-chemistry capabilities. The study found that the proposed ETA experiment was "low risk," has "no show stoppers," and has a "reasonable cost." All that is needed is a sponsor to close the last funding gap and bring the experiment to fruition. This research broke with the current sample doping approach and applied neutron spectral shaping to design an ETA that can create realistic synthetic fission and activation products and improve technical nuclear forensics outcomes. However, the ETA presented in this research represents more than a stand alone point design with a limited scope and application. It is proof of a concept and the product of a unique capability that has a wide range of potential applications.This research demonstrates that the concept of neutron spectral shaping can be used to engineer complex neutron spectra within the confines of physics. There are many possible applications that could benefit from the ability to generate custom energy neutron spectra that fall outside of current sources and methods. The ETA is the product of a general-purpose optimization algorithm, Gnowee, and design framework, Coeus, which enables the use of Gnowee for complex nuclear design problems. Through Gnowee and Coeus, new ETA neutronics designs can be generated in days, not months or years, with a drastic reduction in the research effort required to do so. Most importantly, the new designs could be for applications completely disconnected from the current research and do not have to even be ETA designs at all. The capability of Gnowee and Coeus have the potential to greatly improve the design process in many fields of nuclear engineering.

17 citations


Cites methods from "Fast burst reactors in the u.s.a."

  • ...2: Neutron sources used to simulate the prompt NW neutron environment in comparison with a representative TN+PFNS [86, 87, 100, 104, 148, 160, 166, 169, 189, 202, 207, 225, 229]....

    [...]

  • ...The Qualification Alternatives to the Sandia Pulsed Reactor (QASPR) program was started in 2005 due to the impending closure of SPR10, a FBR that was a close approximation of spectral and temporal characteristics of the NW fission source term [182, 225]....

    [...]

  • ...2 Neutron sources used to simulate the prompt NW neutron environment in comparison with a representative TN+PFNS [86, 87, 100, 104, 148, 160, 166, 169, 189, 202, 207, 225, 229]....

    [...]

Dissertation
01 Jan 2014
TL;DR: In this paper, the single and two-phase heat transfer in high aspect ratio mini-channels has not been well-characterized, especially in regard to the onset of nucleate boiling.
Abstract: Heat transfer in high aspect ratio mini-channels has important applications for materials test reactors using plate-type fuel. These fuel plates typically possess coolant channels with hydraulic diameters on the order of 4 mm or less. The single and two-phase heat transfer in such channels has not been well-characterized, especially in regard to the onset of nucleate boiling. While surface effects are known to dramatically influence the incipience of boiling, they have not been widely considered under forced convection. Since the limiting safety system setting for the MITR is the onset of nucleate boiling, there is considerable interest in better characterizing the phenomenon in such channels. This study presents a first-of-a-kind, two-phase flow facility designed to measure the singlephase heat transfer coefficient and onset of nucleate boiling in a high aspect ratio mini-channel over a wide range of flow conditions while also permitting high speed visualization of the entire surface. The single-phase heat transfer coefficient is measured for mass fluxes ranging from 750 kg/m2-sec up to 6000 kg/m2-sec and for subcoolings ranging from 20 °C to 70 °C. The onset of nucleate boiling superheat and heat flux are measured for mass fluxes ranging from 750 kg/m2sec to 3000 kg/m2-sec and for subcoolings ranging from 10 °C to 45 °C. Measurements are supported with high speed videography to visualize bubble incipience when conditions permit. The influence of surface wettability on the incipience point is also investigated by performing tests on a surface oxidized at high temperature in air. Using a boundary layer analysis along with experimental data obtained in the study, a semianalytical correlation is developed to predict the single-phase heat transfer coefficient in high aspect ratio rectangular channels. The correlation accounts for effects from secondary flows and heating asymmetry, and is suitable for both the transition and fully turbulent flow regimes. The new correlation predicts the Nusselt number with a mean absolute error of 4.9% in the range of 2.2

17 citations


Cites methods from "Fast burst reactors in the u.s.a."

  • ...U-10Mo alloy fuel was employed because it could undergo repeated rapid temperature cycles of 500 °C with relatively small crystal growth and excellent phase stability [33]....

    [...]

01 Jan 2017

5 citations


Cites background or methods from "Fast burst reactors in the u.s.a."

  • ...The reactor operates by the rapid insertion of excess reactivity that places the system into a super prompt critical state and produces a short (~25-700 micro-seconds) burst (or pulse1) of neutrons (1016-1018) [1, 2]....

    [...]

  • ...5 critical operation in 1951, but did not achieve burst operation until 1953 [12, 2]....

    [...]

  • ...In the years following the burst operation of Godiva, many FBRs were manufactured using lessons learned from the previous designs [2]....

    [...]

  • ...U-Mo bolts were also fabricated for use, which made the system more homogeneous [2]....

    [...]

  • ...Negative temperature-reactivity feedback, or thermal expansion, quenches the reactor and returns it to a sub-critical state [1, 2]....

    [...]

01 Jan 2016
TL;DR: In this paper, the transmission spectra of multimode ytterbium-doped optical fibers (YDFs) were measured during each irradiation and the spectral shapes and attenuation were compared at similar doses.
Abstract: Multimode ytterbium-doped optical fibers (YDFs) are increasingly utilized in military applications involving fiber lasers and amplifiers. YDFs were irradiated with three different radiation sources (neutron, gamma, and mixed gamma/neutron) in order to determine the independent effects that gamma and neutron radiation have on the fibers. The transmission spectra of the fibers were measured during each irradiation and the spectral shapes and attenuation were compared at similar doses. Comparisons of the spectra showed that gamma radiation results in increased attenuation over the 550-975 nm wavelengths. Fast neutrons were found to contribute to increased attenuation near 500 nm. Neutron radiation also caused up to twice the amount of radiation induced absorption that gamma radiation did over all wavelengths in the spectrum measured from 500-1100 nm at the same dose. The spectrum from 980-1100 nm was the same shape between the fast neutron and gamma-only irradiations. This indicates that a Co source could potentially be used to approximate the effects on the operating range of YDFs resulting from fast neutrons. A recovery prediction model was also applied and evaluated against actual recovery data. It was found to be unreliable as an accurate predictor of the initial (∼15 minutes) recovery of YDFs exposed to a dose rate of 65 krad(Si)/hr neutron and 9 Mrad(Si)/hr gamma. By adjusting one parameter in the model to account for the initial faster rate of recovery, the model was able to closely approximate the recovery of the fibers after longer irradiations out to longer recovery periods.

4 citations


Cites background from "Fast burst reactors in the u.s.a."

  • ...The U-235 core is 6-8 inches in diameter and 7(5) 8 inches high with a total mass of 81 kg [21]....

    [...]

01 Jan 2017
Abstract: The goal of this research was to develop and characterize a deterministic model of a fast burst reactor (FBR) using a discrete ordinates neutral particle transport code, PENTRAN. The White Sands Missile Range FBR design was chosen for this research because of its strategic importance to the DoD. Specifically, it produces a very short duration, high energy neutron flux which is representative of the neutron flux output created by a nuclear weapon. One, two, and three dimensional PENTRAN models of the FBR were developed and neutron transport based eigenvalue calculations were performed. These eigenvalue calculations were conducted using two different sets of nuclear cross-section data: the Bugle-96 47-energy group library (intended for a thermal reactor design), and a collapsed 10-group version of the Bugle-96 library which captured the fast neutron energy groups and a single thermal group. The PENTRAN neutron transport calculation results were compared to an analogous MCNP Monte Carlo model using continuous energy neutron cross sections. The least computationally expensive PENTRAN neutron flux calculations, which also compares favorably with the MCNP calculations, was a 24 direction S4 Pn-Tn based quadrature with a first order Legendre Polynomial (P1) expansion of the scattering term and the 10 energy group neutron crosssection library. Future work is required to refine the model because the modeled configuration results in a supercritical system when such a configuration should produce a subcritical system.

3 citations


Cites background or methods from "Fast burst reactors in the u.s.a."

  • ...[4] The reactor located at WSMR is called the Molly-G design....

    [...]

  • ...Alamos National Laboratory (LANL) [4]....

    [...]

  • ...The configuration modeled resulted in a supercritical system despite the fact the configuration should have resulted in a subcritical system [4]....

    [...]

  • ...[4] These components include: the fuel assembly, safety block, support plate, Inconel bolts, and stainless-steel core....

    [...]

  • ...This is short for molybdenum-alloy Godiva, which is a reference to the Godiva II reactor created by Los Alamos National Laboratory (LANL) [4]....

    [...]

References
More filters
01 Jan 2017
TL;DR: Bevins et al. as mentioned in this paper used a metaheuristic-based optimization algorithm, Gnowee, to solve ETA optimization problems with mixed-integer and combinatorial design vectors and high-cost, noisy, discontinuous, black box objective function evaluations.
Abstract: Author(s): Bevins, James | Advisor(s): Salybaugh, Rachel N | Abstract: At its core, research represents an attempt to break from the "this is the way we have always done it" paradigm. This idea is evidenced from the start in this research effort by the problem formulation to develop a new way to generate synthetic debris that mimics the samples that would be collected for forensics purposes following a nuclear weapon attack on the U.S. or its allies. The philosophy is also demonstrated by the design methodology used to solve the synthetic debris problem, using methods not commonly applied to nuclear engineering problems. Through this research, the bounds of what is deemed possible in neutron spectral shaping are moved ever so slightly.A capability for the production of synthetic debris and fission products was developed for the National Ignition Facility (NIF). Synthetic debris has historically been made in a limited fashion using sample doping techniques since the cessation of nuclear weapons testing, but a more robust alternative approach using neutron spectral shaping was proposed and developed by the University of California-Berkeley and Lawrence Livermore National Laboratory (LLNL). Using NIF as a starting source spectrum, the energy tuning assembly (ETA) developed in this work can irradiate samples with a combined thermonuclear and prompt fission neutron spectrum (TN+PFNS). When used with fissile foils, this irradiation will produce a synthetic fission product distribution that is realistic across all mass chains.To design the ETA, traditional parametric point design approaches were discarded in favor of formal optimization techniques. Finding a lack of suitable algorithms in the literature, a metaheuristic-based optimization algorithm, Gnowee, was developed for rapid convergence to nearly globally optimum solutions for complex, constrained engineering problems with mixed-integer and combinatorial design vectors and high-cost, noisy, discontinuous, black box objective function evaluations. Comparisons between Gnowee and several well-established metaheuristic algorithms are made for a set of continuous, mixed-integer, and combinatorial benchmarks. These results demonstrated Gnoweee to have superior flexibility and convergence characteristics over a wide range of design spaces. The Gnowee algorithm was implemented in Coeus, a new piece of software, to perform optimization of design problems requiring radiation transport for the evaluation of their objective functions. Currently, Coeus solves ETA optimization problems using hybrid radiation transport (ADVANTG and MCNP) to assess design permutations developed by Gnowee. Future enhancements of Coeus will look to expand the geometries and objective functions considered to those beyond ETA design.Coeus was used to generate an ETA design for the TN+PFNS application on NIF. The design achieved a reasonable match with the objective TN+PFNS and associated fission product distributions within the size and weight constraints imposed by the NIF facility. The ETA design was built by American Elements, and initial validation tests were conducted at the Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. These experiments used foil activation and pulse height spectroscopy to measure the ETA-modified spectrum. Additionally, pulse height spectroscopy measurements were taken as the ETA was built-up component-by-component to measure the impact of nuclear data on the ability to model the ETA performance. Some initial analysis of these results is included here.Finally, an integral validation experiment on NIF was proposed using the Coeus generated ETA design. A scoping study conducted by LLNL determined the proposed experiment and ETA design are within NIF facility limitations and current radio-chemistry capabilities. The study found that the proposed ETA experiment was "low risk," has "no show stoppers," and has a "reasonable cost." All that is needed is a sponsor to close the last funding gap and bring the experiment to fruition. This research broke with the current sample doping approach and applied neutron spectral shaping to design an ETA that can create realistic synthetic fission and activation products and improve technical nuclear forensics outcomes. However, the ETA presented in this research represents more than a stand alone point design with a limited scope and application. It is proof of a concept and the product of a unique capability that has a wide range of potential applications.This research demonstrates that the concept of neutron spectral shaping can be used to engineer complex neutron spectra within the confines of physics. There are many possible applications that could benefit from the ability to generate custom energy neutron spectra that fall outside of current sources and methods. The ETA is the product of a general-purpose optimization algorithm, Gnowee, and design framework, Coeus, which enables the use of Gnowee for complex nuclear design problems. Through Gnowee and Coeus, new ETA neutronics designs can be generated in days, not months or years, with a drastic reduction in the research effort required to do so. Most importantly, the new designs could be for applications completely disconnected from the current research and do not have to even be ETA designs at all. The capability of Gnowee and Coeus have the potential to greatly improve the design process in many fields of nuclear engineering.

17 citations

Dissertation
01 Jan 2014
TL;DR: In this paper, the single and two-phase heat transfer in high aspect ratio mini-channels has not been well-characterized, especially in regard to the onset of nucleate boiling.
Abstract: Heat transfer in high aspect ratio mini-channels has important applications for materials test reactors using plate-type fuel. These fuel plates typically possess coolant channels with hydraulic diameters on the order of 4 mm or less. The single and two-phase heat transfer in such channels has not been well-characterized, especially in regard to the onset of nucleate boiling. While surface effects are known to dramatically influence the incipience of boiling, they have not been widely considered under forced convection. Since the limiting safety system setting for the MITR is the onset of nucleate boiling, there is considerable interest in better characterizing the phenomenon in such channels. This study presents a first-of-a-kind, two-phase flow facility designed to measure the singlephase heat transfer coefficient and onset of nucleate boiling in a high aspect ratio mini-channel over a wide range of flow conditions while also permitting high speed visualization of the entire surface. The single-phase heat transfer coefficient is measured for mass fluxes ranging from 750 kg/m2-sec up to 6000 kg/m2-sec and for subcoolings ranging from 20 °C to 70 °C. The onset of nucleate boiling superheat and heat flux are measured for mass fluxes ranging from 750 kg/m2sec to 3000 kg/m2-sec and for subcoolings ranging from 10 °C to 45 °C. Measurements are supported with high speed videography to visualize bubble incipience when conditions permit. The influence of surface wettability on the incipience point is also investigated by performing tests on a surface oxidized at high temperature in air. Using a boundary layer analysis along with experimental data obtained in the study, a semianalytical correlation is developed to predict the single-phase heat transfer coefficient in high aspect ratio rectangular channels. The correlation accounts for effects from secondary flows and heating asymmetry, and is suitable for both the transition and fully turbulent flow regimes. The new correlation predicts the Nusselt number with a mean absolute error of 4.9% in the range of 2.2

17 citations

01 Jan 2016
TL;DR: In this paper, the transmission spectra of multimode ytterbium-doped optical fibers (YDFs) were measured during each irradiation and the spectral shapes and attenuation were compared at similar doses.
Abstract: Multimode ytterbium-doped optical fibers (YDFs) are increasingly utilized in military applications involving fiber lasers and amplifiers. YDFs were irradiated with three different radiation sources (neutron, gamma, and mixed gamma/neutron) in order to determine the independent effects that gamma and neutron radiation have on the fibers. The transmission spectra of the fibers were measured during each irradiation and the spectral shapes and attenuation were compared at similar doses. Comparisons of the spectra showed that gamma radiation results in increased attenuation over the 550-975 nm wavelengths. Fast neutrons were found to contribute to increased attenuation near 500 nm. Neutron radiation also caused up to twice the amount of radiation induced absorption that gamma radiation did over all wavelengths in the spectrum measured from 500-1100 nm at the same dose. The spectrum from 980-1100 nm was the same shape between the fast neutron and gamma-only irradiations. This indicates that a Co source could potentially be used to approximate the effects on the operating range of YDFs resulting from fast neutrons. A recovery prediction model was also applied and evaluated against actual recovery data. It was found to be unreliable as an accurate predictor of the initial (∼15 minutes) recovery of YDFs exposed to a dose rate of 65 krad(Si)/hr neutron and 9 Mrad(Si)/hr gamma. By adjusting one parameter in the model to account for the initial faster rate of recovery, the model was able to closely approximate the recovery of the fibers after longer irradiations out to longer recovery periods.

4 citations

01 Jan 2017
Abstract: The goal of this research was to develop and characterize a deterministic model of a fast burst reactor (FBR) using a discrete ordinates neutral particle transport code, PENTRAN. The White Sands Missile Range FBR design was chosen for this research because of its strategic importance to the DoD. Specifically, it produces a very short duration, high energy neutron flux which is representative of the neutron flux output created by a nuclear weapon. One, two, and three dimensional PENTRAN models of the FBR were developed and neutron transport based eigenvalue calculations were performed. These eigenvalue calculations were conducted using two different sets of nuclear cross-section data: the Bugle-96 47-energy group library (intended for a thermal reactor design), and a collapsed 10-group version of the Bugle-96 library which captured the fast neutron energy groups and a single thermal group. The PENTRAN neutron transport calculation results were compared to an analogous MCNP Monte Carlo model using continuous energy neutron cross sections. The least computationally expensive PENTRAN neutron flux calculations, which also compares favorably with the MCNP calculations, was a 24 direction S4 Pn-Tn based quadrature with a first order Legendre Polynomial (P1) expansion of the scattering term and the 10 energy group neutron crosssection library. Future work is required to refine the model because the modeled configuration results in a supercritical system when such a configuration should produce a subcritical system.

3 citations