high temperature heat, is to adopt cogeneration, maintaining consistent output, while diverting otherwise unneeded heat to an auxiliary use. District heating, desalination and hydrogen production have been proposed as cogeneration options. Overnight desalination requires sufficient freshwater storage to enable water to be delivered at times other than when it is produced. Membrane and thermal are the two principal categories of desalination technology. The membrane desalination process uses only electricity and is employed the most out of the two technologies. In the thermal process, the feed water stream is evaporated in different stages with continuous decreases in pressure between the stages. The thermal process primarily uses thermal energy and does not include the intermediate conversion of thermal power to electricity. Thermal desalination technology is further divided into two principal technologies: the Multi Stage Flash distillation (MSF) and the Multi Effect Desalination (MED). Waste One study reported that some types of SMR could produce more waste per unit of output than conventional reactors, in some cases more than 5x the spent fuel per kilowatt, and as much as 35x other waste products, such as active steel. Neutron leakage rates were estimated to be higher for SMRs, because in smaller reactor cores, emitted neutrons have fewer chances to interact with the fuel. Instead, they exit the core, where they are absorbed by the shielding, turning it radioactive. Reactor designs that use liquid metal coolants also become radioactive. Another potential issue is that a lower fraction of the fuel is consumed, increasing waste volumes. The potentially increased diversity of reactors may require accordingly diverse waste management systems. A report by the German Federal Office for the Safety of Nuclear Waste Management found that extensive interim storage and fuel transports would still be required for SMRs. A repository would still be required in any case. Many SMR designs are fast reactors that have higher fuel burnup, reducing the amount of waste. At higher neutron energy more fission products can usually be tolerated. Breeder reactors "burn" , but convert fertile materials such as into usable fuels. Some reactor designs utilise the thorium fuel cycle, which offers significantly reduced long-term waste radiotoxicity compared to the uranium cycle. The traveling wave reactor immediately uses fuel that it breeds without requiring the fuel's removal and cleaning. Safety Some proposed SMRs use cooling systems that use thermoconvection – natural circulation – to eliminate cooling pumps that could break down. Convection