Task 4

"A compilation and assessment of the engineering and nuclear performance of the various concepts proposed for neutron-source applications including fusion, fission and accelerator systems."

Table of Contents

  1. Introduction

  2. Design options

  3. Performance metrics

  4. Fission options
    1. IFR
    2. HTGR
    3. PbBi reactor

  5. Fusion options
    1. Molten salt
    2. HTGR
    3. DD fuelling

  6. Accelerator options
    1. HTGR core
    2. Liquid metal core
    3. Aqueous blanket

  7. Observations

Total length: ~20 pages


Introduction

Most of the performance parameters are dominated by blanket and fuel cycle choices, and to a lesser extent the source of neutrons

  • The absence of criteria to judge the value of different levels of performance makes comparisons inconclusive


    Fuel Cycle Options

    Feedstock
    • Weapons material (239Pu) as sole source
    • Fission waste as sole source
    • Weapons material as makeup feed
    • Minor actinides only (no Pu or U in feedstock)

    Disposition scenario

    • Power producing mode (high conversion ratio)
    • Moderate destruction mode (conversion ratio of 0.5-1)
    • Maximum destruction mode (non-uranium fuel, high burnup reactivity loss)
    • Pu denaturing (i.e., producing radioactive byproducts that contaminate the Pu)

    Processing mode

    • batch vs. continuous processing
    • once-through vs. multiple recycle


    Engineering Concepts Previously Considered

    TypeCoolant/moderatorFuelBreeder/target
    Fission
    IFR
    Nametallic
    HTGR
    Hecoated oxide
    Heavy metal
    PbBi
    Fusion
    molten salt
    self-cooledPuFFlibe
    HTGR
    HeoxideLi oxide
    Accelerator
    Na option
    NaW
    PbBi option
    PbBiPbBi
    Aqueous
    D2O oxide W/Pb suspension
    "Non-aqueous"
    He/graphitemolten saltliquid Pb
    HTGR
    Hecoated oxide


    Key Neutronic Performance Parameters

    • Conversion ratio (ratio of production to destruction of actinides)
    • Peak and average 239Pu discharge burnup (MWd/g)
    • Consumption rate (kg/yr)
    • Loading rate (kg/yr)
    • Discharge fraction of 239Pu
    • Fraction of original Pu destroyed
    • Fission-to-capture ratio
    • External neutron source strength (MW)

    Engineering Performance Parameters

    • Power density (linear power, surface heat flux, volumetric heating)
    • Fluence limits and lifetime
    • In-system inventory of 239Pu and total actinides
    • Time dependence and spatial nonuniformity of blanket behavior


    Example: Na-cooled integral fast reactor

    • Metallic fuel, relatively hard spectrum
    • Multiple recycling of the fuel is used to allow complete actinide destruction
    • Burnup of ~10% per pass is achieved
    • The minimum 239Pu fraction achieved is ~50%
    conventionalmoderate burnerpure burner
    Conversion ratio1.15*0.540
    TRU** consumption rate (kg/yr)-33*110231***
    Peak discharge burnup (MWd/g)0.1510.1600.334
    Average discharge burnup (MWd/g)0.1070.1180.450
    Burnup reactivity loss (%Dk)0.032.93.2
    Fuel cycle length (months)231212
    Equilibrium discharge %239Pu635852
    239Pu inventory (tonnes)1.812.144.52
    Heavy metal inventory (tonnes)22.713.97.47

    Thermal power: 840 MW per module
    Peak allowable fast fluence: 3.8x1023 n/cm2 (cladding limited)

    * could be tailored for TRU consumption =0
    ** TRU=transuranic
    *** 231 kg/yr ~ 1 g/MWd = maximum achievable


    Example: HTGR

    • GA PC-MHR
    • Pu oxide fuel in multiple layers of pyrolytic carbon and SiC
    • Use of a burnable poison to enable high once-through burnup (Er2O3)
    • Relatively soft spectrum (peak at ~0.1 eV)
    • Several scenarios considered: "Pu spiking", "spent fuel" level of irradiation, and maximum "Pu destruction"

    Processing modeonce-through, no recycle
    Thermal power450 MW per module
    TRU consumption rate (kg/yr)250
    Peak discharge burnup (MWd/g)0.785
    Average discharge burnup (MWd/g)0.590
    Fuel cycle length (months)36
    .
    239Pu burnup90-95%
    Total Pu burnup65-72%
    Discharge 239Pu fraction<30%
    Peak fast fluence (goal)4.2x1025 n/cm2


    Preliminary Conclusions

    1. There are many different transmutation fuel cycles and many different blankets proposed, each having its own unique characteristics.

    2. There is no established set of criteria for transmutation reactors. Point-design comparisons are tied to authors' assumptions and are inconclusive. Most concepts could be re-optimized under a different set of assumptions.

    3. Most performance parameters are more dependent on blanket and fuel cycle choices than the source of neutrons.

    4. The most fundamental distinction between these systems is whether or not an external source of neutrons is provided - i.e., critical vs. subcritical blanket operation. With an external neutron source and no requirement for criticality, deeper burnup is possible without fuel recycling.

    5. Both fusion and accelerators provide external sources. If depth of burnup is the chief reason for using an external source, then accelerators are likely to be superior to DT fusion because the need to breed tritium restricts the depth of burnup for fusion systems. We should consider DD.

    6. Subcritical assemblies offer operating advantages over critical assemblies. Spectrum-related performance differences are probably secondary in importance; fast-flux fission cores can perform pretty well.

    7. Operating a subcritical assembly starting from an initial loading to complete burnup implies a very wide range of operating conditions. A combination approach, in which only the latter stages of burnup are achieved using an external neutron source, offers a sensible alternative.