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Proceedings ArticleDOI

A fusion chamber design with a liquid first wall and divertor

11 Nov 2003-pp 288-295

AbstractThe APEX study is investigating the use of free flowing liquid surfaces to form the inner surface of the chamber around a fusion plasma. We present a design for the chamber of a 3840 MW fusion reactor based on the configuration for the chamber and magnets from ARIES-RS but with a fast flowing molten salt of mixed Be, Li and Na fluorides for the first wall and divertor and molten salt blanket with a ferritic steel structure. Our design analysis includes strong radiation from the core and edge plasma, (liquid) MHD effects on the weakly conducting molten salt, a recycling first wall stream that enables a high efficiency thermal conversion, and evaluations of breeding, neutronics, tritium recovery and safety.

Topics: Divertor (63%), Molten salt (59%), Fusion power (53%), Blanket (50%)

Summary (2 min read)

Introduction

  • In their designs, modeling of the plasma edge defines the heat loads, and thermal-hydraulic analyses show that the heat removal is adequate.
  • In FY2002 the authors began their design with the molten salt, Flinabe, described later.

II. CHAMBER CONFIGURATION

  • In their design, strong radiation from the core plus strong radiation from the divertor region is used to reduce the peak heat load in the divertor and balance the power loads of the divertor and first wall.
  • The recent plasma transport modeling by Rognlien and Rensink, finds a stable operating window for a highly radiating edge plasma including steady state modeling solutions in which about 95% of the power coming into the scrape-off layer is radiated near the X-point for alpha powers in the range of 300-360 MW.
  • This work is described briefly in their companion paper[1] and elsewhere[2,31].
  • The plots are maps of flourine radiation in the lower portion of the chamber cross section with strong impurity line-radiation concentrated near the X-point and below.

III. FLOW PATHS AND HEAT TRANSFER

  • Fig. 3 shows the flow streams and bulk temperatures.
  • The approach is based on the standard “K-_” model used widely in engineering applications to characterize turbulent flow, and was modified by Smolentsev and others to include the effects of MHD on the turbulence, particularly in the region of fluid near the free surface.
  • Near the bottom of the chamber, these first wall streams become the inboard and outboard divertor flow2.
  • The rise in surface temperature for the divertor stream is about 135ºC; this, added to the bulk temperature of 420ºC leaving the first wall gives a peak of about 555ºC.
  • The Flinabe flow enters each side channel of the blanket at 422°C and 0.18 m/s, flows to the front and then enters the multiplier region at 483°C and flows at 0.013 m/s into the interior space most of which is an open volume.

IV. ENERGY CONVERSION AND MATERIALS

  • For good power conversion efficiency, the authors need a large operating temperature window.
  • The power balance in their design is based on (a) the distribution of the alpha and auxiliary power plus (b) the management of coolant flow that includes a recirculating stream for the first wall, shown in Figure 3.
  • The authors have little data on the physical properties of Flinabe; they believe these are similar to Flibe, but with a lower melting temperature and the same BeF2 concentration at the same temperature.
  • This lower melting point extends the window of operating temperature enough that a workable design appears possible.
  • The primary structural material for the blanket, and auxiliary structures, is an advanced ferritic steel.

V. MECHANICAL DESIGN

  • The authors believe the designs can be made robust in terms of the mechanical and EM forces that such a structure must withstand.
  • The authors have had neither time nor resources to develop engineering details that would show mechanical response of the structure to various types of off normal events and transient loading that are associated with a detailed engineering design and safety analysis.

VI. NEUTRONICS

  • The lower Li concentration requires a comparatively more of the neutron multiplier beryllium to improve the tritium breeding ratio (TBR).
  • Ref. [2] summarizes an initial assessment of tritium breeding and a final assessment, the latter corresponded to the design described here with the blanket having an advanced ferritic steel structure with a 60-mm-thick Be bed of 57% packing density.
  • In the space here the authors can present only a brief summary of the work on tritium breeding and neutronics.
  • The minimum shield thicknesses, based on endof-life neutron fluences, are ~56 cm in the inboard side and ~26 cm in the outboard side3.
  • The total 24Na activity is much lower than the total structure activity and is expected not to be a major concern when Flinabe is used in fusion systems.

VII. TRITIUM PROCESSING

  • Using this solubility along with the rates of tritium production and flow and temperature of Flinabe, Author Sze calculates that the tritium partial pressure over the Flinabe to be about 40 Pa at the exit of the reactor.
  • Gas purging is the easiest method for recovering tritium from Flinabe, and a vacuum disengager process is proposed for this purpose.
  • A key step in the process is using a vacuum system to pump tritium from the molten salt coolant.
  • Whether secondary systems for tritium recovery are affordable has not yet been evaluated.

VIII. SAFETY

  • Safety assessments[50,53] were performed for their blanket design, but here the authors have space here only for the conclusions.
  • Given the rate of releases from the APEX liquid wall blanket design, the facility must be isolated within an additional two weeks to remain below the 10 mSv limit.
  • The authors are strongly supported by the APEX and ALPS Teams and through significant commitment by the Dept. of Energy’s US Fusion Energy Science Program they have utilized expertise in plasma edge modeling, advanced mechanical and systems design, and heat transfer.

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UCRL-PROC-200898
A Fusion Chamber Design with a
Liquid First Wall and Divertor
R.E. Nygren, D.K. Sze, B.E. Nelson, P.J. Fogarty, C.
Eberle, T.D. Rognlien, M.E. Rensink, S. Smolentsev,
M.Z. Youssef, M.E. Sawan, B.J. Merrill, R. Majeski
November 12, 2003
20th Symposium on fusion Engineering
San Diego, CA, United States
October 14, 2003 through October 17, 2003

Disclaimer
This document was prepared as an account of work sponsored by an agency of the United States
Government. Neither the United States Government nor the University of California 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 the University of California. The views and opinions of authors expressed herein
do not necessarily state or reflect those of the United States Government or the University of California,
and shall not be used for advertising or product endorsement purposes.

1
Abstract: The APEX study is investigating the use of free
flowing liquid surfaces to form the inner surface of the
chamber around a fusion plasma. We present a design for
the chamber of a 3840MW fusion reactor based on the
configuration for the chamber and magnets from ARIES-
RS but with a fast flowing molten salt of mixed Be, Li and
Na fluorides for the first wall and divertor and molten salt
blanket with a ferritic steel structure. Our design analysis
includes strong radiation from the core and edge plasma,
(liquid) MHD effects on the weakly conducting molten salt,
a recycling first wall stream that enables a high efficiency
thermal conversion, and evaluations of breeding,
neutronics, tritium recovery and safety.
.
I. INTRODUCTION
This paper briefly summarizes a design for the chamber
of a magnetic fusion reactor with flowing liquid walls
facing the plasma. While removing surface heat, the
continuously-renewed liquid surface is unaffected by the
radiation damage and thermal stresses that limit the
performance of solid chamber walls. A companion paper
summarizes the divertor design[1] and a longer paper[2]
provides more detail and includes extensive references
and discussions of R&D issues. The design effort, part
of the Advanced Power Extraction (APEX) study[3],
utilizes work on plasma interactions with liquid surfaces
performed in the Advanced Limiter-Divertor Plasma
Facing Systems (ALPS) study[4]. The ideas for fusion
reactors with liquid metals and even liquids with free
surfaces are not all new[5-23], but new ideas have been
developed in APEX and the depth of the underlying
science and engineering exceeds previous work.
Chamber technology serves two of three fundamental
functions of fusion energy systems. The first is confining
the plasma itself. The second and third are (1) breeding
of sufficient tritium to fuel a self-sustained reactor, and
(2) practical, reliable, safe, economical power extraction.
Economics pushes fusion toward high power density and
high-temperature coolants; these set requirements for
.
*Sandia is a multi-program laboratory operated by Sandia
Corporation, a Lockheed Martin Company, for the United States
Department of Energy under Contract DE-AC04-94AL85000.
tritium breeding and heat removal.[3] Three principal
features of the fusion chamber are the (1) first wall and
divertor, (2) the blanket, and (3) the shield (Fig. 1). We
also include supporting systems such as those for tritium
processing and heat exchange. We have adapted the
basic magnetic configuration from an existing design
study for a 2170 MW D/T fusion power plant called
ARIES-RS[24,25] with 16 toroidal field coils, a major
radius of 5.5 m and aspect ratio of 4, and incorporated a
liquid surface first wall and divertor and a liquid blanket.
We have explored mechanical designs for several
concepts and each has included detailed CAD renderings
and several innovative features.[2] In 1999-2000, we
studied a design with the molten salt Flibe as the
working liquid, and, in 2000-2001, designs with Li and
with Sn-Li. Excessive surface temperature (vaporization
of F) limited the Flibe design, and poor thermal
efficiency due to the relatively low temperature for
evaporation of Li limited the Li design.[26] In 2001 we
began designs with a Sn first wall and Pb-Li blanket.
The analysis of plasma surface interactions gave a fairly
good operating temperature range with the surface
temperature limit of Sn being 810-840°C for the FW and
1630°C (1480°C for Ga) for the divertor. Simple
correlations for the MHD forces and the assumption of
an insulating wall showed that ~20mm-thick flow
streams launched at 10 m/s would flow down and adhere
to concave substrate. The difficulty of modeling the
magneto-hydrodynamic (MHD) effects that dominate
the fluid flow precluded more detailed analyses, and this
area is being actively investigated through both
modeling and experimental work in APEX.[27]
We refer readers to another paper[2] for descriptions of
many innovative features. For example, in utilizing a
Sn-Li mixture, the lower activity of the Li in the mixture
and lower evaporation rate raised the allowable surface
temperature of the first wall from 380°C for Li to 590°C
for 0.8Sn-0.2Li[28,29], and segregation of Li to the
surface (driven by a reduction in the surface tension)
was also identified as an issue and possible benefit.[30]
A Fusion Chamber Design with a Liquid First Wall and Divertor
R.E. Nygren, D.K. Sze
a
, B.E. Nelson
b
, P.J. Fogarty
b
, C. Eberle
b
,T.D. Rognlien
c
, M.E. Rensink
c
,
S. Smolentsev
d
, M.Z. Youssef
d
, M. E. Sawan
e
, B.J. Merrill
f
and R. Majeski
g
Sandia National Laboratories
*
, PO Box 5800, Albuquerque, NM 87185
a
University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0417
b
Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831
c
Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550-9234
d
University of California, Los Angeles, MAE Dept. Box 951597, Los Angeles, CA 90095-1597
e
University of Wisconsin, Madison; Madison, WI 53706
f
Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415
g
Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543-0451
UCRL-PROC-200898

2
Inboard
Blanket
Module
3/Sector
Shield
Module
Outboard
Blanket
Module
5/Sector
Heating &
Current Drive
Modules
blanket back wall
nozzle
module
outboard
first wall
flow
in-
board
first
wall
flow
divertor
module
deflector
shield liner & drain
Figure 1. (left). Chamber components: blanket and shield modules (top), first wall and
divertor flow paths and modules (bottom).
Figure 2. (above) UEDGE “maps” of fluorine radiation. See text.
Figure 3. (below) Flow streams and bulk Flinabe temperatures (right) and cross-section of
outboard blanket module (left).

3
Other examples include modifiying the flow substrate to
improve flow around penetrations, flexible SiC bags that
contained the liquid blanket, and "self shielding" nozzles
invented by authors Nelson and Fogarty.
In our designs, modeling of the plasma edge defines the
heat loads, and thermal-hydraulic analyses show that the
heat removal is adequate. Evaluation of thermal
transport shows an operating point with reasonable
thermal efficiency and neutronic analyses show adequate
tritium breeding. Evaluations of safety indicate
manageable approaches to the issues. Since our focus is
on chamber technology, we do not develop descriptions
of the magnets, balance of plant, reactor hall, etc.
In FY2002 we began our design with the molten salt,
Flinabe, described later. It has similarities to Flibe but a
lower melting point. We began with some skepticism
since molten salts have poor thermal conductivity and
good thermal conductivity would seem to be an a priori
requirement for any first wall and divertor material. In
this regard, our APEX/ARIES design with Flinabe is a
startling and pleasing result.
II. CHAMBER CONFIGURATION
In our adaptation of ARIES-RS, we increased the power
density by specifying a fusion power of 3840 MW to
define the heat loads for the first wall and divertor, so
that a total power of 909 MW (767 MW alpha power,
142 MW auxiliary power) will be transmitted as surface
heat loads to the first wall and divertor (Table 1).
TABLE I
POWER BALANCE PARAMETERS FOR APEX CHAMBER SYSTEM
First wall area
434
m
2
Average neutron wall loading
7.08
MW/m
2
Average surface heat flux
1.76
MW/m
2
Fusion power
3840
MW
Alpha power
767
MW
Auxiliary power to plasma
142
MW
Power to the first wall
765
MW
FW nuclear heating
400
MW
Total power removed by FW
1165
MW
Power to the divertor
144
MW
FW surface heat flux, average
1.76
MW/m
2
FW surface heat flux, maximum
3.5
MW/m
2
Neutron power
3073
MW
Neutron wall loading, average
7
MW/m
2
Neutron wall loading, maximum
10
MW/m
2
Blanket energy multiplication
1.06
Blanket thermal power
3257
MW
Total thermal power
4024
MW
Total power (thermal + aux.)
4166
MW
In high power density devices, a large fraction of the
alpha power must be converted into radiation to make
the heat load on the divertor manageable. While large
radiative cooling can mitigates the peak heat loads, it
also tends to decrease the thermal isolation and stability
of the core plasma. In our design, strong radiation from
the core plus strong radiation from the divertor region is
used to reduce the peak heat load in the divertor and
balance the power loads of the divertor and first wall.
The power to the first wall of 765 MW is 84% of the
total particle power of 909 MW while the balance of
power to the divertor (144 MW) is only 16%.
The recent plasma transport modeling by Rognlien and
Rensink, finds a stable operating window for a highly
radiating edge plasma including steady state modeling
solutions in which about 95% of the power coming into
the scrape-off layer is radiated near the X-point for alpha
powers in the range of 300-360 MW. This work is
described briefly in our companion paper[1] and
elsewhere[2,31]. Figure 2 shows a sample result for a
series of solutions at progressively higher values of P
c
,
power convected from the plasma core into the edge
plasma. The plots are maps of flourine radiation in the
lower portion of the chamber cross section with strong
impurity line-radiation concentrated near the X-point
and below. The set of four cases shows a progression
from a case that is not stable (MARFE), through two
cases (300 and 400 MW) with stable operation, to the
440 MW case that is unstable and “burns through” onto
the target. The 300 MW case had a peak heat flux
(particle + radiation) at the divertor plate of only ~8
MW/m
2
and a peak heat flux to the first wall of ~2
MW/m
2
for a density at the edge of the core
of ~1.5x10
20
m
-3
, H (D/T) throughput of ~3.1x10
23
particles/s with
divertor plates orthogonal to magnetic flux surfaces and
H pumped at private flux surface for stability. The
Fluorine density at core boundary varies poloidally over
the range 3.7-7.3x10
17
m
-3
(0.24% - 0.49% of hydrogen;
1% is the limit based on core radiation loss). This work
supports the conclusion that it is reasonable to
investigate designs based upon relatively modest peak
heat fluxes (8-10 MW/m
2
) in the divertor.
III. FLOW PATHS AND HEAT TRANSFER
Fig. 3 shows the flow streams and bulk temperatures.
The inboard and outboard first wall streams flow from a
set of nozzles at the top of the chamber that inject the
Flinabe onto the front surfaces of the blanket modules.
One set of nozzles feeds the inner first wall, another set
feeds the outer first wall. The overlapping streams from
the “self-shielding” nozzles prevent any line-of-sight
from the plasma directly to a nozzle.[2]
The thickness of the first wall flow at midplane is 23
mm and the flow speed is 10 m/s. The first wall flow
length is ~6.5 m. The Flinabe starts at 402°C and rises
to 420°C at the bottom of the first wall. The penetration
of the surface heat and nuclear heating contribute about
equally to the rise in bulk temperature of ~18ºC. The
surface temperature, which reaches 509°C at the bottom
of the first wall, was calculated by Smolentsev using a

Citations
More filters

25 May 2000
Abstract: The use of liquid walls for fusion reactors could help solve problems associated with material erosion from high plasma heat-loads and neutronic activation of structures. A key issue analyzed here is the influx of impurity ions to the core plasma from the vapor of liquid side-walls. Numerical 2D transport simulations are performed for a slab geometry which approximates the edge region of a reactor-size tokamak. Both lithium vapor (from Li or SnLi walls) and fluorine vapor (from Flibe walls) are considered for hydrogen edge-plasmas in the high- and low-recycling regimes. It is found that the minimum influx is from lithium with a low-recycling hydrogen plasma, and the maximum influx occurs for fluorine with a high-recycling hydrogen plasma.

40 citations


Journal ArticleDOI
Abstract: As candidate blanket concepts for a U.S. advanced reactor power plant design, with consideration of the time frame for ITER development, we assessed first wall and blanket design concepts based on the use of reduced activation ferritic steel as structural material and liquid breeder as the coolant and tritium breeder. The liquid breeder choice includes the conventional molten salt Li 2 BeF 4 and the low melting point molten salts such as LiBeF 3 and LiNaBeF 4 (FLiNaBe). Both self-cooled and dual coolant molten salt options were evaluated. We have also included the dual coolant lead-eutectic Pb-17Li design in our assessment. We take advantage of the molten salt low electrical and thermal conductivity to minimize impacts from the MHD effect and the heat losses from the breeder to the actively cooled steel structure. For the Pb-17Li breeder we employ flow channel inserts of SiC f /SiC composite with low electrical and thermal conductivity to perform respective insulation functions. We performed preliminary assessments of these design options in the areas of neutronics, thermal-hydraulics, safety, and power conversion system. Status of the R&D items of selected high performance blanket concepts is reported. Results from this study will form the technical basis for the formulation of the U.S. ITER test module program and corresponding test plan.

28 citations


Cites background from "A fusion chamber design with a liqu..."

  • ...380oC) and the MS FLiNaBe [3], which has a measured melting point of 305 to 320oC [4]....

    [...]


Journal ArticleDOI
Abstract: Three-dimensional analysis has been made using the MCNP Monte Carlo code and ENDF/B-VI nuclear data. The nuclear characteristics of a fusion-fission hybrid reactor such as tritium breeding ratio, energy multiplication factor, fissile fuel breeding, first wall radiation damage, and heat deposition have been investigated in a liquid first wall, blanket, and shield for the various mixture compositions of molten salt and heavy metals for blanket layer thicknesses of 20, 30, 40, and 50 cm. The neutron flux load at the first wall is assumed to be 10 MW/ m 2 . The flowing molten salt wall is composed of flibe (Li 2 BeF 4 ) as the main constituent with increased mole fractions of heavy metals, 2 to 10% ThF 4 and UF 4 . In terms of all parameters, the mixtures with UF 4 show better performance than the mixtures with ThF 4 . The atomic displacement and the helium, tritium production rates remain well below the presumable limits for all mixture compositions of molten salt and heavy metals and thicknesses of the blanket.

22 citations


01 Sep 2003
Abstract: The US Enabling Technology Program in fusion is investigating the use of free flowing liquid surfaces facing the plasma. We have been studying the issues in integrating a liquid surface divertor into a configuration based upon an advanced tokamak, specifically the ARIES-RS configuration. The simplest form of such a divertor is to extend the flow of the liquid first wall into the divertor and thereby avoid introducing additional fluid streams. In this case, one can modify the flow above the divertor to enhance thermal mixing. For divertors with flowing liquid metals (or other electrically conductive fluids) MHD (magneto-hydrodynamics) effects are a major concern and can produce forces that redirect flow and suppress turbulence. An evaluation of Flibe (a molten salt) as a working fluid was done to assess a case in which the MHD forces could be largely neglected. Initial studies indicate that, for a tokamak with high power density, an integrated Flibe first wall and divertor does not seem workable. We have continued work with molten salts and replaced Flibe with Flinabe, a mixture of lithium, sodium and beryllium fluorides, that has some potential because of its lower melting temperature. Sn and Sn-Li have also been considered, and themore » initial evaluations on heat removal with minimal plasma contamination show promise, although the complicated 3D MHD flows cannot yet be fully modeled. Particle pumping in these design concepts is accomplished by conventional means (ports and pumps). However, trapping of hydrogen in these flowing liquids seems plausible and novel concepts for entrapping helium are also being studied.« less

3 citations


Dissertation
01 Jan 2014

1 citations


Cites background from "A fusion chamber design with a liqu..."

  • ...Bu sebeple soğutucu olarak lityum dışındaki alternatif olabilecek malzemelerin trityum üretimi ve kimyasal özellikleri incelenmiştir [7,29-31, 33-39, 44-51]....

    [...]

  • ...APEX hibrit reaktöründe soğutucu olarak Flibe (Li2BeF4), Flinabe eriyik tuzları ile Li20Sn80, Li, Li17Pb83 sıvı metalleri tercih edilmiştir [7,12, 22-33, 42-51]....

    [...]

  • ...Flinabe ile nötronlar azaldığı için daha az sayıda nötron, lityum ile trityum üretimi için reaksiyona gireceğinden Flinabe’nin trityum üretimi Li20Sn80 sıvı metalinden daha düşüktür [7,12, 26-35, 42-52]....

    [...]

  • ...Flibe, düşük aktivasyon ve düşük elektriksel iletkenliğine sahip olması ile soğutucu olarak tercih edilir [7,12, 22-33, 42-51]....

    [...]


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