can keep removing decay heat after reactor shutdown. Negative temperature coefficients in the moderators and the fuels keep the fission reactions under control, causing the reaction to slow as temperature increases. Some SMRs may need an active cooling system to back up the passive system, increasing cost. Additionally, SMR designs may have less need for containment structures. Some SMR designs bury the reactor and spent-fuel storage pools underground. Smaller reactors would be easier to upgrade. SMRs maintain core cooling with a passive safety system which eliminates the need for pressure injection systems. With a passive safety system, emergency AC power sourced from a diesel generator is not required for core cooling. A passive safety system is simpler, requires less testing, and does not lead to inadvertent initiation. SMRs do not require an active containment heat system due to passive heat rejection out of containment and a containment spray system is not required. An emergency feedwater system is not necessary for SMRs, allowing for core heat removal and enhancing safety. SMRs featuring water and sodium coolants increase reactor safety through their ability to withhold byproducts of the fissile fuel introduced into the coolants during a severe accident. This characteristic of a SMR allows for the ability of a SMR to mitigate the release of fissile material, contaminating the environment, in the event of a failure to maintain containment of nuclear material occurred. Some SMR designs feature an integral design of which the primary reactor core, steam generator and the pressurizer are integrated within the sealed reactor vessel. This integrated design allows for the reduction of a possible accident as radiation leaks can easily be contained. In comparison to larger reactors having numerous components outside the reactor vessel, this feature drastically increases the safety by decreasing the chance of an uncontained accident. Furthermore, this feature allows many SMR designs bury the reactor and spent-fuel storage pools underground at the end of their service life therefore increasing the safety of waste disposal. Flexibility of SMR Small nuclear reactors, in comparison to conventional nuclear power generation plants, offer many advantages due to the flexibility of their modular construction. This flexibility in the modularity of a SMR system allows for additional units to be incrementally added in the event load on the grid increases. Additionally, this flexibility in a standardized SMRs design revolving around modularity allows for rapid production at a decreasing cost following the