1. Nuclear Reactors Chapter 4

2. Nuclear Reactors Categories Breeder or Converter or Burner
Coolant {water, heavy water, gases, liquid metal}
Moderator {water, heavy water, graphite}
Boiling water or pressurized water systems

3. Nuclear Reactors Neutron Balance in Thermal Reactors Notes:
63 – 5 = 58 n produce Pu-239
78-63 = 15 n produce U- 236
59-32 – 17 n produce Pu-240
In steady – state ~ 32% of
energy is produced by
Pu fissions.

4. Nuclear Reactors Neutron Balance in Fast Reactors Notes:
Fuel is typically 20% Pu and 80% depleted U.
Bulk of fissions from Pu
Pu created > Pu consumed since: 116 n absorbed in Pu,
but: 134 – 13 = 121 produce
Pu-239.
4. Thus Rx “breeds” fissile Pu 239

5. Nuclear Reactors Light Water Reactors
The most widely used electricity producing reactors in the world today are thermal reactors that are moderated, reflected and cooled by ordinary (light) water (H20).
2. Two Main Types
-Boiling water reactors (BWR)
-Pressurized water reactors (PWR)

6. Nuclear Reactors Light Water Reactors
Advantages
- Abundant supply of water.
- well known properties
- cheap cost
Disadvantages
- Water has high vapor pressure, requiring high pressure operation.
- Water has a large cross- section of absorption for neutrons. Therefore it is not possible to fuel a light water reactor with natural uranium. The fuel must always be enriched to some extent.

7. Nuclear Reactors
Pressurized Water Reactors

8. Nuclear Reactors Pressurized Water Reactors- Coolant Path

9. Nuclear Reactors Pressurized Water Reactors- Coolant Path
Components

10. Nuclear Reactors Pressurized Water Reactors- Reactor compartment

11. Nuclear Reactors Pressurized Water Reactors
Flow paths
Components
One of 1st reactor designs
Standard for Naval vessels
3. Requires steam generator (next slide)to produce steam for turbines.

12. Nuclear Reactors Pressurized Water Reactors- The Steam Generator
Steam flow path
Feed water path
General chemistry
(pH, phosphates)
Components

13. Nuclear Reactors Pressurized Water Reactors- The Pressurizer
Components
Down power Tc (I), Coolant Expands, Pzr level (I), Pzr Pressure (I), Spray valve opens, Steam condenses, Pzr Pressure (d), limiting the Pressure surge.
Up Power Tc (d), coolant contracts, Pzr level (d), Pzr pressure (d), water flashes to steam, Pzr pressure (I)

14. Nuclear Reactors Pressurized Water Reactors- The Pressurizer

15. Nuclear Reactors Pressurized Water Reactors- The Fuel
-Slightly enriched 2-5 w/o U-235
-Fuel pellets of UO2 black ceramic looking
-Pellets 1cm x 2cm
-Loaded into Zircaloy tubes (low Σa)
-Zircaloy is alloy of zirconium + tin + iron + chromium
-Rods arranged as cluster or assembly
Other arrangements possible, such as fuel plates vice rods.

16. Nuclear Reactors AP 1000

17. Nuclear Reactors AP 1000 Westinghouse Electric Design Generation III +
PWR
2 Loops
~1000 MWe

18. Nuclear Reactors
Boiling Water Reactors

19. Nuclear Reactors Boiling Water Reactors BWR Advantages:
Direct cycle, no secondary loop
Less mass flow rate since coolant water is permitted to
absorb latent heat and sensible heat.
Can operate at lower pressure ~ 900 psi
{not zero/ atmospheric pressure since
1. high temp required to drive turbines
2. high pressure prevents wall dryout}
Lower pressure mean thinner pressure vessel
and less expensive components.
BWR Disadvantages:
Radioactive coolant throughout engine room
Shielding and containment larger
Lower power density – need larger core and PV then PWR

20. Nuclear Reactors
Boiling Water Reactors

21. Nuclear Reactors Heavy Water Reactors
A heavy water (D2O) where D = H2 , can operate on
natural uranium because the absorption cross section
of deuterium for thermal neutrons is very small.
D2O is also less effective in moderating neutrons than
H2O. Therefore neutrons lose less energy per collision
and travel farther before reaching thermal energies. The
core of a heavy water reactor is considerably larger than
a LWR.

22. Nuclear Reactors Heavy Water Reactors
H2 is a rare isotope of H. ~ 150 ppm
It contains 1 n and 1 p, instead of just 1 p.
3. D2O was discovered by American Harold Urey in 1931,
for which he received the 1934 Nobel prize in chemistry.
D2O is 10% heavier than H2O
It is 3x worse at slowing neutrons
It is 600x worse at absorbing neutrons
Can extract D20 from H20 is a multistage process.

23. Nuclear Reactors Heavy Water Reactors
CANDU Reactor – Canada Deuterium Uranium reactor

24. Nuclear Reactors Heavy Water Reactors
CANDU Reactor – Canada Deuterium Uranium reactor

25. Nuclear Reactors Heavy Water Reactors
CANDU Reactor – Canada Deuterium Uranium reactor

26. Nuclear Reactors Heavy Water Reactors
CANDU Reactor – Canada Deuterium Uranium reactor
To avoid a large pressure vessel it uses pressurized tube concept.
Rx consists of a large tank called a calandria filled with D2O
moderator at atmospheric pressure.
Tank is penetrated by hundreds of horizontal tubes containing
the fuel. The D2O coolant flows through the tubes at high pressure
(~1500 psi) and does NOT boil.
Thus by pressurizing the coolant rather than the whole reactor
a large pressure vessel is avoided.
Because of lower pressure (than conventional PV), the tubes
can not be raised to high enough temperature to steam at same
temp as light water reactors. The result is plants are less efficient
(~28-30%).
Plant reactivity is controlled by absorber rods, and light water
compartments.

27. Nuclear Reactors Breeder Reactors
Four Types
Liquid Metal Cooled Fast Breeder Reactor. LMFBR
Gas Cooled FBR
Molten Salt BR
Light Water BR
Only LMFBR is only one significantly commercialized
anywhere in world.
Operates on U -> Pu fuel cycle
fueled with Pu isotopes
blanketed with U 238 natural or depleted.
No moderator since we want fast neutrons

28. Nuclear Reactors Breeder Reactors
Four Types
Use sodium coolant because
Excellent heat transfer
Non corrosive
High plant temperatures
High power density
Disadvantage of Sodium coolant
Sodium reacts violently with water
High melting point (98 C) need heated piping.
Forms β and ϒ emitters (radioactive) most plants
use two loop system to prevent radioactive sodium
from entering S/Gs.

29. Nuclear Reactors Breeder Reactors