A comparison of radioactive waste from first generation fusion reactors and fast fission reactors with actinide recycling

TL;DR: In this paper, the authors compared the long-term activation of actinides in a commercial and an experimental fast fission Reactor with a commercial fusion Reactor and showed that the latter is less hazardous than the former.

Abstract: Limitations of the fission fuel resources will presumably mandate the replacement of thermal fission reactors by fast fission reactors that operate on a self-sufficient closed fuel cycle. This replacement might take place within the next one hundred years, so the direct competitors of fusion reactors will be fission reactors of the latter rather than the former type. Also, fast fission reactors, in contrast to thermal fission reactors, have the potential for transmuting long-lived actinides into short-lived fission products. The associated reduction of the long-term activation of radioactive waste due to actinides makes the comparison of radioactive waste from fast fission reactors to that from fusion reactors more rewarding than the comparison of radioactive waste from thermal fission reactors to that from fusion reactors. Radioactive waste from an experimental and a commercial fast fission reactor and an experimental and a commercial fusion reactor has been characterized. The fast fission reactors chosen for this study were the Experimental Breeder Reactor 2 and the Integral Fast Reactor. The fusion reactors chosen for this study were the International Thermonuclear Experimental Reactor and a Reduced Activation Ferrite Helium Tokamak. The comparison of radioactive waste parameters shows that radioactive waste from the experimental fast fission reactormore » may be less hazardous than that from the experimental fusion reactor. Inclusion of the actinides would reverse this conclusion only in the long-term. Radioactive waste from the commercial fusion reactor may always be less hazardous than that from the commercial fast fission reactor, irrespective of the inclusion or exclusion of the actinides. The fusion waste would even be far less hazardous, if advanced structural materials, like silicon carbide or vanadium alloy, were employed.« less

Summary

2.1 Introduction

• Radioactive waste parameters can either be specific or absolute.
• Specific ones axe generally used to establish classifications or standards and absolute ones give a hint to the total haaaxd associated with radioactive waste.
• Specific radioactive waste parameters will always relate to the volume of radioactive waste -having dimensions "per m^"; absolute radioactive waste parameters are derived through multiplication of the specific radioactive waste parameters by the volume of radioactive waste.
• Specific radioactive waste parameters are independent of a particular waste form, or a particular waste form volume, as long as no significant dilution of radionuclides in radioactive waste takes place during radioactive waste handling.
• Absolute radioactive waste parameters lineaxly depend on a particular waste form volume.

2.4 Whole Body 7-Dose Rate

• Whole body 7-dose rates axe determined for point radioactivity sources, assuming that all relevant radionuclides in radioactive waste eire lumped together in one spatial point.
• Self-shielding due to the actual shape of radioactive waste thus is not accounted for.

BHFRW

• And BHFRW as calculated axe multiplied by e.g. a factor of IO""* or less, equivalent to the above outlined dilution effect.
• Institutional control of access to a shallow (and deep) repository can be assumed to be effective for about lOOy after begin of storage, during which period inadvertent intrusion can be virtually excluded [49] .

2.7 Radioactive Waste Classification

• In addition, Reference [8] specifies another class of radioactive waste, termed D. This additional class is essentially the same as class C, with the exception, that the waste form of radioactive waste is considered to be purely metallic.
• The RWC index for this class is determined by Equations 2.39 and 2.40.

2.8 Intruder Dose Rate

• The whole body dose rate to an inadvertent intruder depends on the time at which the inadvertent intrusion occurs.
• This time usually is measured after institutional control ceases to exist.
• If the beginning of storage takes place within by after discharge of radioactive waste from the nuclear reactor, then the inadvertent intrusion could occur no more than roughly lOOi/ later.
• This relatively early inadvertent intrusion yields conservative intruder dose rates, in contrast to a later inadvertent intrusion.
• Intruder dose rates aire relatively meaningless for times during institutional control, but nevertheless give an approximation of the radiation level above the shallow repository for those times.

2.8.1 Construction Scenario

• The auxiliary barrier factors used in this study are given in Table 2 .4.
• The auxiliary barrier factor fwn24 °f *^^ waste form barrier factor determines how long radioactive waste has been in contact with water.

Factor

• The auxiliary barrier factor /u;n23 o^ the waste form barrier factor determines to which extent radioactive waste will be segmented according to its chemical properties.
• The auxiliary barrier factors used in this study are given in Table 2 .6.
• Homogenization of components substantially lessens the need for computer memory and disk storage space and for computer CP L'^time, because not every material of a component has to be accounted for separately, especially, if those materials consist of similar elements.
• Section 1.2 shows that radioactive waste from fast fission and fusion reactors contains different nuclides, so that nuclide data libraries for fast fission calculations usually do not feature the complete set of nuclides necessary for fusion calculations, and vice versa.
• Both methods can best be illustrated by describing the integration of the different computer codes employed.

3.3.1 VMIBOB Code

• The actual material and component shape is too complicated to be considered exactly.
• But it appears reasonable to malce the above approximations, because retracting and protruding parts of an actual material or component can throughout average themselves out and thus the actual volume can be close to the approximated volume.
• The principle of averaging out might hold true also for the assumption of pure cylindrical geometry, although the more exact treatment would require to consider the reactor as a non-perfect torus with D shaped cross section.

3.3.2 ONEDANT Neutron Transportation Code

• An ASCII nuclide neutron cross section library comes along with the code package.
• The input file to ONEDANT must specify the radial build of the components at the reactor midplane, the volume fraction of each material in a component (calculated by VMIBOB) and the concentration of each element in a material (in [^J^^^]).
• Also, the radial build of the components at the reactor midplane must be split up into fine and coarse grid points to allow discretization.
• The neutron flux decay constant p,c can be derived from the radii R^ and Pco and the neutron flux at those radii by solving a linear system of two equations resulting from Equation 3.9.

3.4 OPCPOST &: RECPOST Codes

• Radioactivity, whole body 7-dose rate, decay power and BHP of all components at the above times on the one hand and RWC indices and intruder dose rates of all components at the above times on the other hand are calculated and written to sepaxate ASCII output files.
• In addition radioactive waste parameters of all nuclides of the components can be written to corresponding separate ASCII output files.

3.5.1 FcLst Fission Reactors

• OPCPOST then calculates the radioactive waste parameters of the components at the above times.
• Data transfer axnong all three computers is effected by the NETTY utility.

4.1 Introduction

• Only the radioactive waiste handling for fast fission reactors shall be outlined here, because no detailed information is avEiilable on radioactive waste handling for fusion reactors.
• Furthermore, only the chemical aspects of radioactive waste handling for fast fission reactors shall be concentrated on, because chemistry is the key issue.

Parallel to the development of reactor and fuel cycle facility at ANL, Rockwell International (RI) and General Electric (GE) provided in 1988

• With their reactor studies Sodium Advanced Fast Reactor (SAFR) [24] and Power Reactor Inherently Safe Module [42] own reactor designs for the IFR concept.
• Reactors and fuel cycle facilities according to the IFR concept will feature breeding and reprocessing.
• The reprocessing employed for IFR is significantly different from the one used for EBR-II, as stated in Section 4.4.
• EBR-II win be equipped with an IFR core in 1990 and the HFEF/South will be renamed back into FCF, then featuring the equipment necessaxy for IFR reprocessing.
• In fact, EBR-II has already been used in 1986 to demonstrate the safety properties of the IFR concept [45] .

Dc

• The inboard section in addition has an ohmic heating coil, which is referred to in this study as the poloidal coil.
• Note, that in contrast to the components of a fast fission reactor, each component typically consists of more than one material.
• Two components not considered in this study axe the divertor and the limiter, which have a minute volume in compaxison to the rest of the components.
• The second objective of ITER is to demonstrate that the fusion reaction can be employed to generate net energy.

Stage

• The technology phase provides a duration of about ten years without a number of plasma shots specified.
• For this study, it is assumed that the maximum achievable performance of ITER with a steady state plasma is a total of 0.5y operation per year at 1.0^^^.
• Furthermore this study assumes that this will be the case only for the last two years of the IQy technology phase.
• Assuming a linear increase of the performance by a total of O.ly every two The protective layer consists of carbon fiber tiles for the inboard section.

Those may be cooled by conduction or radiation. A sprayed layer of tung-

• The outboard section most likely has no protective layer [21] .
• The breeder blanket of the inboaxd section consists of a sandwich of one layer of breeder material between two layers of multiplier material.
• The breeder blajikets have not been designed to produce the tritium necessary for a self-suflUcient closed fuel cycle, but will operate as realistically as possible under power reactor conditions.
• The volume derived for the toroidal coils by a cylindrical approximation therefore was multiplied by 0.86 for the inboard section and 0.21 for the outboard section.
• Since work on ITER was continued after completion of this study.

4.4.1 EBR-II and IPR Pyroprocesses

• In Sections 4.4.3 and 4.4.4, a somewhat simplyfied and idealized description of the EBR-II and IFR pyroprocesses is presented.
• 44] that can not be regarded in the frame of this study, the essential technique of EBR-II and IFR pyroprocessing is explained in some detail.
• Also, it is suitable to first review some of the chemistry that forms the basis of the pyroprocesses.

4.4.2 Basic Chemistry

• Free energies of formation for the chlorine oxidation products of some of the elements of the chemical classification groups axe provided in Table 4 .12.
• A similar table cam be composed, e.g. for oxygen oxidation products, with the order only slightly changed.

4.4.3.2.1 Skull Oxidation

• Step Oxidation of the skuU in an argonoxygen atmosphere at 750°C will oxidize the actinide, metal and noble metal atoms that were mechanically retained in the dross to actinide, general and noble metal oxides.
• This powder then is submitted to the skull reclamation step [44] .

4.4.3.2.2 Skull Reclamation

• The powder is suspended in a liquid halide, where the noble metal oxides axe reduced to noble metal atoms by adding Zn, which has a higher oxidation potential than noble metals.
• Liquid halide can be considered an electrolyte.
• Noble metal oxides therefore dissociate in liquid halides and may recombine with electrons to metal atoms.
• Actinide metal oxides axe subsequently reduced to actinide metal atoms by adding MgZn alloy, which has a higher oxidation potential than Zn.
• The actinide metal atoms then will precipitate zmd can mechanically be sepaxated from the remainder of the halide.

4.4.4.1.2 Separation

• Hence by chosing two diffierent cathode metals, the goal of precipitating driver emd breeder fuel can be achieved in one step, i.e. the lower oxidation potential cathode metal precipitates all actinides and provides the driver fuel, the higher oxidation potential cathode metal precipitates uranium slightly better than the other actinides and hence provides the breeder fuel.
• Chosing uranium as the higher oxidation potential cathode allows the entire cathode with adhering uranium precipitation to be treated as an entity in the following recovering process.
• As to the lower oxidation potential cathode, liquid cadmium again lends itself, as well as for the anode [5] .

5.1.2 Cycle, Life-tixne &; Decommissioning Radioactive Waste

• Another importjint concept is the radioactive waste present in the reactor at the time of decommissioning.
• Decommissioning is assumed to take place lOy after reactor shut down or end of life-time, which is equivalent in this study to lOy after discharge of the components from the reactor.
• Definitions of cycle, life-time and decommissioning radioactive waste in this study axe displayed in Table 5 .2 for the different reactors.
• The radioactive waste parameters are not normalized to the power output, but axe evaluated and presented for the reactors cis btult.
• Therefore, the different power output should always be kept in mind when looking at the comparison.

5.3 Radioactivity

• For these reaisons, a description of the temporal behavior shall be forgone for the remaining radioactive waste parameters.
• Rather, particularities shall be noted and the behavior with respect to possible standards for those radioactive waste parameters in order to fulfill certain requirements shall be illustrated.

5.5 Decay Power

• Consequently a much higher specific and absolute decay power results for fuel thein for the remainder of the components.
• That also means that fuel is especially "hot" for the first couple of days after discharge.
• Both specific and absolute decay power come down to the decay power of the first wall at less than ly after discharge.
• The graph for fuel starts to feJl off at Id after discharge already, displaying the fact that the short-lived radionuclides decay soon.

5.7 Radioactive Waste Classification

• In that case it would not matter for classification purposes and the graphs.
• The above uncertainty about the Nb isotopes ^^Nb and ®^'"iV6, respectively, was reported to Argonne National Laboratory, but no final clarifica-tion of this uncertainty was obtained [14] .

5.8.1 Construction Scenario

• The course of the intruder dose rate under the construction scenario over time after discharge is shown in Figures 5. 20.
• Of all high level radioactive waste components only the first wall of ITER significantly exceeds the standard of 5.7 10~^^ for unrestricted areas set by 10CFR20.
• Back wall and breeder blanket of ITER and first wall of RAFHT as well as fuel of EBR-II and IFR approach this standard from the lower side or just touch it.
• In particular it should be noted that, except for the first wall of ITER, no component at any time after institutional control ceases to exist will lead to an intruder dose rate greater than the 10CFR20 standard.

5.8.2 Agriculture Scenario

• All components classified as high level radioactive waste exhibit an intruder dose rate greater than the 10CFR20 standard.
• As a discrepancy to their classification, also clad eind duct of IFR and steel shield of ITER exceed this standard.
• This is acceptable in the case of clad and duct, since they classify for class C radioactive waste with a RWCc classification index of only slightly less than 1 and hence exist in the "grey zone".

Full text

DOE/ET/51013—292
DE91 016969
PFC/RR-91-9
A COMPARISON of RADIOACTIVE WASTE
from FIRST GENERATION FUSION REACTORS
and FAST FISSION REACTORS with
ACTINIDE RECYCLING*
M. Koch and M.S. Kazimi
April 1991
Plasma Fusion Center
and
Department of Nuclear Engineering
Massachusetts Institute of Technology
Cambridge, MA 02139 U.S.A.
*This work was partially supported by EG&G Idaho, Inc.
and the U.S. Department of Energy under DOE Contract
No.
DE-AC02-78ET-51013 and DE-FG02-91ER-54110
Reproduction, translation, publication, use and
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in whole or in part, by or for the United States government
is permitted
if
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A Comparison of Radioactive Waste
from First Generation Fusion Reactors
and Fast Fission Reactors with
Actinide Recycling
by
M. Koch and M.S Kazimi
Abstract
Limitations of the fission fuel resources will presvtmably mandate the replace-
ment of thermal fission reactors by fast fission reactors that operate on a
self-
sufficient closed fuel cycle. This replacement might take place within the next
one hvmdred years, so the direct competitors of fusion reactors will be fission
reactors of the latter rather than the former type. Also, fast fission reactors,
in contrast to thermal fission reactors, have the potential for transmuting long-
lived actinides into short-Uved fission products. The associated reduction of the
long-term activation of radioactive waste due to actinides makes the comparison
of radioactive waste from feist fission reactors to that from fusion reactors more
rewarding than the comparison of radioactive waste from thermal fission reactors
to that from fusion reactors.
Radioactive waste from an experimental and a commercieil fast fission reactor
and an experimental and a commercial fusion reactor heis been characterized. The
fast fission reactors chosen for this study were the Experimental Breeder Reactor
II (EBR-II) and the Integral Fast Reactor {IFR). The fusion reactors chosen for
this study were the International Thermonuclear Experimental Reactor (ITER)
Eind a Reduced Activation Ferrite Helium Tokamak (RAFHT).
The four reactors considered operate on an idealized self-sufficient closed
fuel cycle, i.e. actinides and tritiimi are regarded as fuel emd recycled back
to the reactor. In the caise of the two fast fission reactors, actinide recycUng
is possible without detrimental effects to the neutronics, because at the very
high average neutron energies in these reactors, not only plutonitun, but also
most other actinides become fissionable, i.e. constitute fuel rather than poison.
Reedisticeilly, the radioactive waste from the two faist fission reactors will contain
some actinides and that from the two fusion reactors will contain some tritiiun.
However, since actual separation efficiencies are expected to be in the 99.9%
range, the radioactive waste wiU contain less than 0.1% of the actinides or the
tritivun. In contrast, thermal fission reactors do not operate on a self-svifficient
closed fuel cycle and hence their radioactive waste contains up to 100% of the
actinides.
The fast fission and the fusion reactors have been approximated as a set of
homogenized reactor components of simple cylindrical and/or hexagonal geom-
etry. Reactor components as radioactive waste were characterized by several
2

pareuneters. These parEimeters describe the volume and activation of radioactive
waste and are pertinent to US regulatory standards.
Build-up and decay of radionuclides in reactor components were simulated
by the computer codes ORIGEN-IHOT fast fission reactors and ONEDANT and
REAC-IHoT fusion reactors. Auxihary computer codes were developed to convert
the output of those three computer codes into radioactive waste parameters. The
parameters were not normaUzed to the different power levels of the compeured
reactors, but rather evaluated for these reactors as built.
The comparison of radioactive waste parameters shows that radioactive waste
from the experimental fast fission reactor may be less haizardous than that from
the experimental fusion reactor. Inclusion of the actinides would reverse this
conclusion only in the long-term. Radioactive weiste from the commerciad fusion
reactor may Jilways be less hazardous th£in that from the commercial fast fission
reactor, irrespective of the inclusion or exclusion of the actinides. The fusion
waiste would even be far less heizardous, if advanced structviral materials, like
siUcon carbide or vanadiimi alloy, were employed.
Also,
radioactive waste from the experimental fast fission reactor may be less
hazardous than that from the commercial fast fission reactor. This is a direct
consequence of the utiUzation of highly ^^^ U enriched fuel in EBR-II resulting
in a lower activation than the utihzation of uraniimi-plutonivmi-minor-actinides
fuel in IFR. Radioactive WEiste from the commercial fusion reactor may be less
hazardous than that from the experimental fusion reactor. This is a direct con-
sequence of the utiUzation of standard materials (55316) in ITER resvdting in a
higher activation than the utiUzation of Reduced Activation Materials (RAF) in
RAFHT.
The generation of High Level Radioactive Waste (HLRW) is likely not
to be avoided even for
RAFHT.
The volimie of radioactive waste from the two fusion reactors is larger than
the volvune of radioactive wEiste from the two faist fission reactors. Material
selection in the fusion reactors plays a far more important role in controlUng the
activation of the radioactive waste than it does in the fast fission reactors. If
recycUng of fusion reactor structureil materials is fovmd feasible in the future, the
volume of radioactive waste from fusion reactors will be reduced.
3