01 How It Works
PHWR/CANDU reactors use heavy water - water where hydrogen atoms are replaced by deuterium - as the moderator. Heavy water absorbs fewer neutrons than ordinary water, meaning the reactor can sustain a chain reaction with un-enriched natural uranium. Horizontal pressure tubes carry coolant through the heavy water moderator. The unique feature: the reactor can be refuelled while at full power, with no shutdown required.
02 Pros & Cons
โ Advantages
- Runs on natural uranium - no enrichment facility needed
- On-power refuelling - very high capacity factor
- Can burn thorium, MOX, and other fuels
- Excellent neutron economy
โ Disadvantages
- Heavy water is very expensive to produce
- Heavy water must be kept leak-free (tritium hazard)
- More complex fuel channels than solid-core designs
- Large reactor building footprint
03 Specifications
THERMAL EFFICIENCY~31%
OPERATING TEMP~290ยฐC
PRESSURE~100 bar
FUELNatural UOโ (0.7%)
FUELNatural UOโ (0.7%)
COUNTRIESCanada, India, South Korea, China, Pakistan, Romania, Argentina
04 Did You Know?
India has a major PHWR programme as it cannot easily access enrichment services due to nuclear non-proliferation restrictions. Canada's CANDU reactors have achieved over 90% capacity factors - among the highest in the world.