Safely Providing Base Load Power
TerraPower is committed to the safety of our design. Our design features meet current regulatory requirements for nuclear reactor safety with the additional benefits of innovative passive safety features. Current analyses have been conducted according to requirements by the International Atomic Energy Agency (IAEA), and U.S. codes and standards such as those of the U.S. Nuclear Regulatory Commission (NRC), American Society of Mechanical Engineers (ASME) and Institute of Electrical and Electronics Engineers (IEEE). As the design progresses, we continue to work with regulators to define safety criteria appropriately. The traveling wave reactor (TWR) is a Generation IV reactor, of which a key characteristic is the use of passive safety features to mitigate accident scenarios. TerraPower has taken this further in that the TWR can perform its safety function indefinitely with no offsite power. In addition, the design has features that allow it to withstand many “beyond design basis accidents.” That is, accident scenarios currently considered so improbable that it is unnecessary to allow for them in the reactor design.
Some of the key safety features of the TWR:
- As a pool-type reactor, it allows for a large heat sink, thereby slowing the accident scenario considerably because of the time required for the coolant to heat up.
- The TWR uses metallic fuel that has significantly less retained energy than equivalent oxide fuel (i.e., less energy to be absorbed in an accident).
- It eliminates hydrogen-producing materials, such as those created in LWRs when fuel temperatures reach 1,200 degrees Celcius and water reacts with zirconium.
- The TWR incorporates inherent safety features that can shut the reactor down without using control rods.
- Its passive independent residual heat removal systems do not rely on electricity, but rather use natural circulation and coolant to air heat exchangers.
The TWR does not require prompt operator actions to put the reactor in a safe shutdown condition. Using the laws of physics, the plant will shutdown automatically without the need for human intervention in the case of a natural disaster. The TWR is not a pressurized system and overheating accidents like Fukushima cannot occur. In the event of a shutdown, no on-site or off-site power is required to remove passive decay heat. The plant is designed to withstand natural phenomena (earthquakes, floods, tsunamis, etc.) with equipment configured to eliminate the risk of common fault failures. For the balance of the plant, the TWR is essentially the same as current reactors. Modern safety analyses using probabilistic risk assessment show that this reactor design is significantly safer than current reactors. Because the TWR is a pool-type, sodium-cooled reactor, accidents play out over hours and days rather than the seconds and minutes in a typical light water reactor (LWR). Certain types of severe accidents for LWRs, such as a loss of coolant accident (LOCA), cannot occur in a TWR. This is because the reactor operates at essentially atmospheric pressure. Therefore, a rapid depressurization accident, such as an LOCA, cannot happen.