TYPES OF WATER REACTORS

1. PWR - PRESSURIZED WATER REACTORS
- these are reactors cooled & modulated by high pressure liquid water. they are the majority of current reactors, & are generally considered the safest & most reliable technology currently in large scale deployment, although 3 mile island is a reactor of this type. this is thermal neutron reactor design, the newest of which are Advanced Pressurized Water Reactor.

2. BWR - BOILING WATER REACTOR
- these are reactors cooled & moderated by water, under slighlty lower pressure. the water is allowed to boil in the reactor. the thermal; efficiency of these reactors are higher, simpler, potentially more stable & safe. these reactors make up a substantial of modern reactors. this is thermal neutron reactor design. the newest of Advanced Boiling Water Reactor & economic simplified boiling water reactor.

3. PHWR - PRESSURIZED HEAVY WATER REACTOR
- this is Canadian design, these reactors are heavy-water cooled & moderated pressurized water reactors, instead of using a single large pressure vessel as in a PWR, the fuel is contained in hundreds of pressure tubes. these reactors are fuelled with natural uranium & are thermal neutron design. PHWR can be refueled while at full power. this have been built in Canada, Argentina, China, India, Pakistan, Romania, South Africa.

4. RBMK - REAKTOR BOLSHOY MOSHCHNOSTI KANALNIY (high power channel reactor)
- a Soviet Union design , built to provide plutonium as well as power. RBMK are water cooled with a graphite moderator , are in some respects similar to CANDU in that they refuelable on-load & employ a pressure tube design instead of a PWR-style pressure vessel. RBMKs were very unstable & too large to have containment buildings making them dangerous in the case of accident.

THE CHERNOBYL PLANT HAS 4 RBMK REACTORS :
1. AGCR - Advanced Gas Cooled Reactor
2. GCR - Gas Cooled Reactor
3. Monju
4. Aqueous Homogeneous Reactor.

ADVANCED REACTORS :
- integral fast reactor
- pebble bed reactor
- high temperature gas cooled reactor
- SSTAR - small, sealed, transportable autonomous reactor.
- suboritical
- thorium based reactor

GENERTION IV REACTORS :
* gas cooled fast reactor
* lead cooled fast reactor
* moltan salt reactor
* sodium-cooled reactor
* super critical water reactor.