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Light water graphite reactor LWGR

A light water graphite reactor (LWGR) uses light water as coolant and graphite as moderator. 7 are operating worldwide, totalling 7.0 GW gross, out of 34 units of this type on record.

Operating
7
7.0 GW gross
Under construction
0
Planned
0
Retired
22
Steam Graphite corevertical pressure tubes Turbineto grid Direct cycle — one loop
Graphite moderates, water cools. Decoupling the two allows on-load refuelling and very large cores.

A graphite block moderates while light water in vertical pressure tubes boils and feeds the turbine directly. Decoupling moderator from coolant allows on-load refuelling and very large single units without a heavy forged pressure vessel. The RBMK is the only commercial implementation and carried a positive void coefficient at low power — the condition central to the 1986 Chernobyl accident. Surviving units were retrofitted; the type is being retired and none are under construction.

Advantages
  • Decoupling moderator from coolant allows on-load refuelling and very large single units
  • No heavy pressure vessel required, so a large reactor could be built without forging capacity
  • Uses only slightly enriched fuel
Drawbacks
  • Positive void coefficient at low power — the condition central to the Chernobyl accident
  • No full containment building in the original design
  • Very large graphite core is difficult to inspect and its ageing sets the plant's life
  • No unit has been built since 1986 and the type is being retired
Design basis
CoolantLight water
ModeratorGraphite
Fuel formSlightly enriched uranium dioxide in pressure tubes
Typical enrichment2–2.6% U-235
Where they operate
Russia7

Model lines

ModelOperatingUnits on record
RBMK-1000 7 13
RBMK — 6
EGP-6 — 4
RBMK-1500 — 2
AMB-200 — 1
AMB-100 — 1
AM-1 — 1

Operating LWGR units

UnitCountryGross MWOnline
Kursk nuclear power plant 1-3 Russia 1,000 1984
Kursk nuclear power plant 1-4 Russia 1,000 1986
Leningrad nuclear power plant 1-3 Russia 1,000 1980
Leningrad nuclear power plant 1-4 Russia 1,000 1981
Smolensk nuclear power plant 1-1 Russia 1,000 1983
Smolensk nuclear power plant 1-2 Russia 1,000 1985
Smolensk nuclear power plant 1-3 Russia 1,000 1990

Sources