The principal mission adopted for commercial SMRs has been the generation of electricity. All reactor coolant types address this mission. For those plants designed
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Table 1.2 Reactor characteristics by coolant
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Coolant
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PWR1 Light water
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BWR2 Light water
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HTGR
Helium3 Helium4
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SFR5
Sodium
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Lead6
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LFR
Lead-bismuth7
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Power (MWt/MWe)
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530/180
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750/250
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250/100
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625/283
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840/311
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700/300
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280/101.5
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Power density (kWt/liter
core)
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69
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39.5
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3.2
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6.8
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215
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116
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160
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Specific power (kWt/kg HM)
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26.8
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11.6
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89.7
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~120
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83.6
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14.5
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30.8
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Fuel geometry
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Rods
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Rods
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Pebbles
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Prismatic graphite blocks
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Rods
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Rods
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Rods
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Fuel material/cladding
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UO2/Zr-4
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UO2/Zr
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uo2/triso
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UCO/TRISO
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(U+Pu)/SS
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(U+Pu)N/SS
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UO2b/8
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Primary system temperature inlet/outlet (°C)
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295/319
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190/285
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250/750
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325/750
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360C/499C
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420/540
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340/490
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Primary operating pressure (MPa)
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14.2
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6.9
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7.0
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6.0
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0.1
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0.1
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0.1
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Secondary operating pressure (MPa)
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5.7
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NA
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13.3
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16.7
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14.7
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18
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6.7
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Plant thermal efficiency (%)
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34
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33.3
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42
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45
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37
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43a
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36.3
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1 Pers. Comm, D. Langley (mPower) to N. Todreas (MIT), Jan 2013.
2 VK-300 — Gabaraev et al. (2004); Kuznetsov et al. (2001).
3 HTR-PM — Zhang et al. (2009); Zhang (2012).
4 SC-HTGR — AREVA (2012).
5 PRISM — Triplett et al. (2012).
6 BREST — Smirnov (2012); Glazov et al. (2007)a.
7 SVBR-100 — Toshinsky and Petrochenko (2012); MOX and N fuel options proposed13.
8 Likely EP823 or EP450.
NA — Not applicable since the BWR only has a primary system.
Numerical values of characteristics are rounded.
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Table 1.3 Reactor coolant properties of significance1
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Coolant
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Water2
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Helium3
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Sodium4
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Lead4
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Lead-bismuth4
(0.445Pb-0.555Bi)
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PWR
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BWR
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Atomic weight
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18
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4
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23
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207
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208
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Phase change at 1 atm
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Melting point (°C)
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0
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NA
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98
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327
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124
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Boiling point (°C)
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100
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-267
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892
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1737
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1670
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Density, p (kg/m3)
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704.9
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754.7
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3.54
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880
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10536
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10180
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Specific heat, cp (J/kg K)
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5739
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5235
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5191
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1272
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147
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146
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Heat capacity, pcp (MJ/m3 K)
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4.05
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3.95
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0.018
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1.07
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1.55
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1.49
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Heat transfer capability
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0.543
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0.585
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0.31
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66
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15
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15
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Thermal conductivity, к (W/m K)
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3.80
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1.90
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0.65
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18.1
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2.81
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2.75
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Heat transfer coefficient (X10-4) h (W/m2 K)
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Dynamic viscosity (X104), р (kg/ms)
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0.846
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0.945
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4.0
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2.6
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20
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15
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Kinematic Viscosity (X107), v = р/р (m2/s)
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1.20
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1.26
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1.13
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2.95
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1.91
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1.47
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Thermal expansion coefficient
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326
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250
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—
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29
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11
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13
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(X105), a (1/°C)
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Prandtl number, Pr
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0.89
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0.85
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0.66
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0.005
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0.020
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0.015
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1 Typical reactor values.
2 Property values at PWR average and BWR inlet conditions from Todreas and Kazimi (2012).
3 Property values at 537 0C and 6 MPa from Petersen (1970).
4 Property values at 450 0C from Hejzlar et al. (2009).
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to be deployable to remote locations, whether placed terrestrially or dispatched as barge-mounted reactors, the added co-generation capabilities for desalinization and district heating exist. Of the water-cooled SMRs the Russian PWR and BWR systems have been designed for these additional missions. Additionally, propulsion as accomplished by Russian ice-breaker vessels using the KLT-40S reactor and its planned replacement, the RITM-200 reactor, is a further reactor mission.
The helium gas-cooled reactor can operate at high enough outlet coolant temperature, 750 °C in initial designs, to provide a process heat capability. This process heat can be used directly for various industrial processes such as shale oil recovery and the production of hydrogen by relatively high-temperature thermochemical cycles. Hydrogen production from water by electrolysis can be accomplished at the lower outlet temperature of the sodium — and lead-cooled reactors, on the order of 500550 °C, but these SMRs have not embraced this mission due to current shrinking US interest.
