Protection Against Extreme External Events Like Fukushima
Through smart construction, NuScale's SMR is designed to protect itself against climate, cyber and physical threats. Its main intent is to protect the public, workers, and the environment if an extreme event occurs. For example:
- Integral reactor design eliminates interfacing pipes and pumps that could potentially fail
- Vacuum inside containment provides significant unique safety advantages in the event of a severe accident
- Large reactor pool, in which the modules are submerged, provides assured access to ultimate heat sink and radiation shielding under all conditions
- Passive safety systems provide stable long-term cooling without a need for electrical power or makeup water
- Unlimited coping period for Fukushima-like events
- Below-grade location of NuScale Power Modules™ (NPM) provides additional safety and security
- No Design Basis Accident can cause core to uncover
- Smaller source term per reactor and longer time periods of potential release
- Core damage frequency (CDF) 10-10 per module year for internal events at full power
- Seven layers of defense (four more than conventional reactors)
- Deeply embedded spent fuel pool with four times the water volume per MWt of conventional nuclear reactors
Possibility of Core Damage Significantly Reduced
The safety of the plant is enhanced due to a number of key features, such as a simplified design, inherent cooling capabilities, passive engineered safety features, and lower core power density. In the extremely unlikely event that a NuScale core is damaged, consequences would be well below the threshold to warrant off-site evacuations.
No Safety‐Related Backup Power
NuScale conducted a review of the Fukushima Daiichi event which included an earthquake followed by a tsunami that destroyed back‐up power for decay heat removal. The most significant safety‐related change to the NuScale design post‐Fukushima was eliminating the need for DC power to actuate DHRS and ECCS. There was also significant economic benefit in this design change. The NuScale Power Modules (NPM) are now designed so that no operator or computer actions, no AC or DC power, and no addition of water is needed to ensure fuel cooling for an unlimited period of time.
Increased Seismic Resiliency
The NuScale ultimate heat sink resides inside a Seismic Category I reactor building capable of withstanding a Fukushima‐type seismic event, hurricanes, tornadoes, and floods. The reactor building is designed for input spectra with peak accelerations of 1.15 g (1078 gal) for frequencies ranging from 3‐12 Hz. This is greater than the maximum ground acceleration observed during the Fukushima event.
Prolonged Spent Fuel Pool Cooling Capability
NuScale spent fuel resides below ground in a stainless steel‐lined concrete pool that serves as the ultimate heat sink. On loss of all AC and DC power, the spent fuel remains cooled and safe for 5 months (150 days) without the need to add water.
External Accessibility for Pool Refill
One of the challenges to cooling the Daiichi spent fuel pool was the difficulty in adding water to the spent fuel pool (i.e., located on top level above ground). The NuScale design has external fire connections to permit refill of the spent fuel pool and reactor building pool while maintaining personnel safety.
Air‐Cooled Condensers for Inland Siting
The NuScale design permits the use of air‐cooled condensers for inland siting of a plant instead of an ocean front that may be susceptible to tsunamis.
We have taken every precaution and the utmost care to ensure our reactors are as safe as possible on all fronts, now and for the future.