Note: Descriptions are shown in the official language in which they were submitted.
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Tunable Fusion Blanket for Load Following and Tritium Production
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
100011 The United States Government has rights in this invention pursuant to
Contract
No. DE-AC52-07NA27344 between the U.S. Department of Energy and Lawrence
Livermore National Security, LLC, for the operation of Lawrence Liveimore
National
Laboratory.
CROSS-REFERENCE TO RELATED APPLICATION
[0002] This United States Patent Application is related to and claims priority
from
commonly assigned earlier filed United States Provisional Patent Application
entitled
"Tunable Fusion Blanket Offering the Ability to Produce Extra Tritium and Load
Follow,"
filed January 28, 2011, as U.S. Application No. 61/437,508, and Patent
Cooperation Treaty
Application entitled "Inertial Confinement Fusion Chamber," filed November 8,
2011, as
PCT Serial No. US2011/059814. Each of these applications is incorporated by
reference
herein.
BACKGROUND OF THE INVENTION
100031 This invention relates to the production of electrical power using
fusion reactions.
In particular, the invention relates to a fusion chamber for an inertial
confinement fusion
power plant in which continuous real-time adjustment of fusion power and
tritium production
rates are enabled.
100041 The National Ignition Facility (NIF), the world's largest and most
energetic laser
system, is now operational at Lawrence Livermore National Laboratory (LLNL) in
Livermore, California. One goal of operation of the NIF is to demonstrate
fusion ignition for
the first time in the laboratory. Initial experiments are calculated to
produce yields of the
order of 20 MJ from an ignited, self propagating fusion burn wave. The
capability of the
facility is such that yields of up to 150-200 MJ could ultimately be obtained.
The NIF is
designed as a research instrument, one in which single "shots" on deuterium-
tritium
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containing targets are performed for research. A description of the NIF can be
found in
Moses et al, Fusion Science and Technology, Volume 60, pp 11-16 (2011) and
references
therein.
[0005] There is a rapidly growing need for power, and especially for clean
power. At
LLNL a project known as Laser Inertial-confinement Fusion Energy, (often
referred to herein
as "LIFE") is working toward introduction of fusion based electric power
plants into the U.S.
economy before 2030, and in a pre-commercial plant format before that. LIFE
technology
offers a pathway for the expansion of carbon-free power around the world. It
will provide
clean carbon-free energy in a safe and sustainable manner without risk of
nuclear
proliferation.
[0006] One challenge with respect to LIFE, just as with any technology for
generating
electrical power to be distributed to large numbers of consumers, is the
requirement for
differing amounts of power to be provided at different times, e.g. at
different times of day,
month and year. Consumers expect to have highly reliable electric power,
necessitating that
power plants produce more power, for example, for air conditioning, during
warmer months
or days, than at other times of the year. The result is that utilities
providing that electrical
power must be able to increase and decrease the amount of electric power
produced by their
facilities. Thus, among the challenges with respect to fusion power, is
providing mechanisms
by which a reliable long-lived fusion chamber can be provided in which the
fusion reactions
occur, yet which can provide greater or lesser amounts of heat at different
times for
generation of electric power.
[0007] In the technology described herein, a fusion power plant is provided
with a fusion
chamber into which capsules containing deuterium and tritium fuel are
introduced multiple
times per second. As the individual fuel capsules contained within hohlraums
("targets")
reach the center of the chamber, banks of lasers fire on the targets, heating
and compressing
the fuel to create a fusion reaction. Heat from the fusion reaction is
captured by coolant
circulating around the chamber. This heat is then used to generate
electricity. A desired
aspect of plant operation is production of tritium to replace that burned in
previous targets.
[0008] Our approach to the architecture of the fusion chamber utilizes a
segmented tubular
design for the first wall, as described in more detail in the commonly
assigned patent
application "Inertial Confinement Fusion Chamber" referenced above. That
design provides
a fusion chamber with efficient thermal coupling, low mechanical stress, and a
high strength
to weight ratio. The modular approach of the fusion chamber also decouples it
from the
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optical system, allowing rapid removal and replacement of the blanket and
first wall modules
with only a need to make and break plumbing connections, not reconfigure
accurate optical
pathways. The fusion chamber is cooled with liquid lithium coolant circulating
through
individual segments of the fusion chamber.
[0009] This invention offers the operator of a fusion power plant the added
flexibility of
adjusting the tritium breeding ratio and thermal power by means of filling or
emptying
regions within the fusion blanket. These adjustments allow for fusion plant
load-following,
enabling the fusion blanket to be tuned to deliver different amounts of
thermal power and
corresponding electric power to the grid in real-time, and to also control the
amount of tritium
production.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Figure 1 illustrates the fusion chamber and its segmented design;
[0011] Figure 2 is a perspective view of one-half of one segment of the fusion
chamber;
[0012] Figure 3 is a cross-sectional view of one segment of the fusion chamber
shown in
Figure 2; and
[0013] Figure 4 is another cross-sectional view of a segment of the fusion
chamber shown
in Figure 2 illustrating additional compartments used to provide control over
output power
and tritium breeding.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Figure 1 is a diagram illustrating the overall design of a fusion
chamber 20 as may
be used for implementation of our invention. This chamber 20 will be situated
within a
fusion power plant such as described in our co-pending United States patent
application
entitled "Inertial Confinement Fusion Power Plant Which Decouples Life-Limited
Components From Plant Availability," filed November 8, 2011, as serial number
PCT/US2011/059820, the contents of which are herein incorporated by reference.
[0015] As shown in Figure 1, the chamber consists of multiple identical
sections 100. Each
section 100 can be factory built and shipped to the power plant site using
conventional
transportation equipment. Within an on-site maintenance facility, described in
our co-
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pending application referenced immediately above, the modular chamber sections
are
mounted within a common support frame. The fully assembled chamber and frame
are then
transported for installation within a vacuum vessel surrounding the chamber.
Installation of
the chamber requires only the connection of cooling inlet pipes and outlet
pipes to each
quarter-section of the chamber, which is independently plumbed.
[0016] Figure 2 is a perspective view of a one-half segment 100 of the fusion
chamber 10.
As illustrated, the segment has a first wall which consists of parallel
arranged tubes 110
which cover the underlying structure, and through which lithium coolant is
circulated. The
beam port openings 120 in the segment are also illustrated. Lithium is sent
first to a plenum
that feeds coolant to one-quarter of the full chamber. Coolant is first routed
to the first wall
tubes, where it experiences the highest heat flux. Upon exiting from the first
wall tubes, the
lithium is circulated into the blanket entry port 130. Coolant existing the
blanket does so
through port 140. The four one-quarter sections of the full chamber are
independently
plumbed.
[0017] To enable the laser beams to reach chamber center forty-eight openings
120 totaling
about 5% solid-angle are provided. At the beam ports, the first wall pipes are
routed radially
outward and then they wrap around on the back side of the blanket. Additional
openings are
provided at the top and bottom of the chamber for interfaces with the target
injection system
and the debris clearing / vacuum pumping / target catching systems,
respectively.
[0018] Figure 3 is cross section through the mid-point of an ordinary segment
100, that is a
segment which does not include the features of this invention. Depending upon
the extent to
which adjustment of power production and tritium breeding are desired, only
some segments
of the fusion chamber may include the features of this invention. On the other
hand, greater
flexibility can be achieved by including the features of this invention in all
segments of the
chamber, one such segment being illustrated in Figure 4 below.
[0019] In Figure 3 the first wall tubing 110 is illustrated, along with the
underlying
structure 150. Liquid lithium coolant enters the tubing 110 through a plenum
160 which is
coupled to all of the tubes of the segment 100. A similar plenum (not shown)
on the other
side of the segment collects the liquid lithium after it has passed through
the tubing 110.
Once lithium exits the first wall tubing 110, it may be recirculated into the
underlying
structure 150 for additional heating of the coolant. In an alternate
implementation all of the
lithium is recirculated, which results in the need for only one cooling loop
for segment 100.
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If desired, the first wall tubing 110 and the underlying structure 150 can be
independently
plumbed to satisfy different cooling requirements and/or enable the use of
alternate coolants.
[0020] Cooling of the underlying structure 150 is designed such that the
coldest coolant is
delivered to the structural materials. This is accomplished through use of
"skin cooling" with
the coolant entering the blanket at the top and flowing down at high speed
through smaller
cooling channels. The coolant turns around when it reaches the bottom of the
blanket and
then flows up through the bulk region 170 at much lower speed. The low
temperature and
high speed in the skin region provides the most effective cooling. The blanket
coolant is
introduced through port 130 and extracted from a similar port 140.
100211 As described in more detail in the patent applications referenced
herein, coolant
entering the first wall tubes at 470 C will leave the first wall and enter the
underlying
structure (blanket) at approximately 510 C. The coolant reaches approximately
550 C at the
bottom of the blanket. With bare steel, the coolant heats up at the top of the
blanket to an
outlet temperature of 575 C. Higher temperatures can be achieved through use
of
nonstructural insulating panels. For example, tungsten is compatible with
liquid lithium to
more than 1300 C. Our design used bare steel and provides lithium at an exit
temperature of
575 C. By appropriate selection of materials, however, a future fusion chamber
design
would allow even higher temperatures.
[0022] The fusion chamber is designed according to the ASME piping code.
Specifically,
the chamber is designed to one-third of a given material's ultimate tensile
strength, two-thirds
of its yield strength, two-thirds of its creep rupture strength and a 0.01%
creep rate per 1000
hours. Temperature-dependent properties are used in such evaluations.
[0023] Our invention provides a fusion chamber that offers the operator of the
power plant
the flexibility of adjusting the tritium breeding ratio and the thermal power
by filling or
draining regions within the fusion blanket. These real-time adjustments may be
required
when it is desired to produce additional tritium, for example, to overcome
shortages resulting
from lower-than-expected production, or higher-than-expected losses, or to
produce tritium to
fuel new fusion facilities. These adjustments allow for the fusion power plant
to load follow,
enabling it to be tuned to deliver different amounts of thermal power, and
corresponding
electrical power, to the grid in real time.
[0024] The real-time adjustment of the tritium breeding ratio and the themial
output power
is accomplished by filling compartments, e.g. compartment 170, in the fusion
blanket with tin
or other materials that have the desired neutron interaction properties. The
material can be
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inserted and removed to the desired level to increase or decrease the thermal
power output
and increase or decrease the corresponding tritium breeding ratio. The
materials used can be
stagnant, flowing liquid, or movable solids. If desired, additional neutron
producing
materials such as beryllium or beryllium titanium (Bei2Ti) can further improve
performance.
By enabling the fusion blanket to capture neutrons and energy released from
the fusion
reaction, the collected energy may be converted to tritium for new fusion fuel
production and
to thennal power in the form of flowing high temperature coolant.
[0025] Figure 4 illustrates one implementation of the compartments 200. The
compartments 200 are formed from high temperature refractory metal alloys to
allow
maximum theimal power production while maintaining high strength in the
structural
components. These alloys include tungsten and vanadium, as well as other
materials. The
compartments can be selectively filled and emptied with high temperature
resistant materials
such as tin or gadolinium,
[0026] In previous inertial fusion energy engines, thermal power was proposed
to be
reduced by reducing fusion target output, reducing the repetition rate of the
fusion source, or
dumping excess thermal power using cooling towers. Each of these approaches
negatively
impact the economics of the power plant. In contrast, our approach enables
adjustment of
theimal power and tritium production without negatively impacting the
economics of the
power plant.
[0027] In the illustrated embodiment of Figure 4, tin is employed within the
tungsten
chambers 200. The tin is stagnant, but it can be pumped into position or
drained (or
otherwise inserted and removed) to change the fusion engine from "power mode"
with the tin
present, to "tritium breeding mode" with the tin removed. Our analysis of the
tritium
breeding ratio and the gain of the bulk material are shown in the table below.
With an all
liquid lithium cooled blanket, that is, with all segments of the fusion
chamber being as
illustrated in Figure 3, the tritium breeding ratio and gain are shown in the
first row. With
tungsten compartments containing tin (and emptied of tin), the tritium
breeding ratio and gain
are shown in the second and third rows of the table. Finally with tungsten
compartments
loaded and drained with a Be12Ti/Sn blanket, the results are shown in the last
two rows of the
table.
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Design Tritium Breeding Ratio Gain
All Lithium Blanket 1.48 1.12
Loaded Tin Blanket 1.15 1.21
Drained Tin Blanket 1.33 1.14
Loaded Be12Ti/Sn Blanket 1.02 1.32
Drained Be12Ti/Sn Blanket 1.18 1.27
[0028] In contrast to prior approaches, our invention allows real-time
adjustment. The
fusion thermal power produced and tritium production rate can be constantly
tracked and
traded off with operating conditions as needed to product excess tritium for
new plant startup
or to reduce power production of the plant during low demand periods.
[0029] The foregoing has been a description of a preferred embodiment of the
invention. It
will be appreciated that variations may be made in the manner by which the
materials are
added to or removed from the fusion blanket to enable control of the thermal
power output
and the tritium breeding ratio. Accordingly, the scope of the invention as
defined by the
appended claims.
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