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There are two reasons the U.S. Navy Nuclear Propulsion Program has a spotless record with regard to reactor accidents: fail-safe plant design, and a highly educated and trained force of enlisted nuclear operators.I was one of those operators, an Engineering Laboratory Technician. Part of my job description—in addition to being a mechanical engineroom watchstander—was to monitor the radiologic safety of the ship and crew. (For the other Nukes reading this, I realize this is an oversimplification, but I don't want to get into the weeds with a lengthy explanation of Chem/Radcon etc.)This is a cutaway illustration of a Los Angeles-class attack submarine:That space forward of the engine room (about midships) is the Reactor Compartment. While its design and layout are classified, all U.S. Navy nuclear plants operate on the same principle. The reactor plant, though complex, is only used to heat and circulate water at very high temperature and pressure. This heat source replaces the combustible fuels used in traditional boilers. The steam generators, (odd how the Navy names things after what they do, isn't it?) through which the reactor coolant water circulates, generate steam that drives turbines in the engine room for propulsion and electrical power. To prevent radiological contamination, the high-pressure/temperature water in the reactor plant never comes in direct contact with the water that is used to generate steam, and never enters the engine room.The reactor compartment “walls” are also incredibly thick, and are composed of materials (varying thicknesses of steel, lead, water, and plastics) that attenuate the different types of radiation emitted by an operating reactor. This shielding is so effective that in four years of mainly standing watch in Engine Room Forward (about thirty feet from the reactor vessel), I received a lower dose of ionizing radiation than you would on an average trans-continental flight, or from a year on the beach.Another duty I had was to perform daily monitoring of the reactor coolant. This was both proactive (to ensure the chemical conditions in the reactor plant were ideal to minimize corrosion and therefore prevent leaks) and reactive (monitoring for fission products that would indicate a fuel element failure had occurred). I also made daily surveys of compartments adjacent to the reactor using portable detecting equipment to look for both streaming and particulate radiation. Never once did I find elevated levels.The crew on submarines is highly trained and constantly drilled on the actions they would take if this monitoring did reveal a radiologic hazard, or if there were a coolant or steam leak. The training and drills are frequent and intense enough that personnel respond immediately and thoroughly to any situation that might hazard the ship or crew.Training and vigilance minimize the chance that a radiological incident might occur on board. Should the worst-case scenario happen, the design of engineering systems and the actions of the crew ensure a high probability that both the ship and personnel survive.Part of the culture that is instilled and reinforced from the first day of nuclear training is that the crew are the ship. All of the safe designs, advanced technology and preventive measures mean nothing without men and women of diligence and integrity to operate the vessel. Being part of the Engineering Department on two submarines is one of my proudest accomplishments.If it tells you anything about the safety of the propulsion plants in U.S. Navy subs, some of the best sleep I ever got was on high-speed runs across the Pacific Ocean, with the reactor operating at full power for days on end.

https://www.facebook.com/188872144758/posts/10157814811434759/Constructors completed the track laying on the eastern extension section of Beijing Subway Line 7 in June 2019.China’s first subway line runs through the heart of Beijing and opened in 1969 after years of debate, to ferry soldiers from their barracks on the outskirts to the city center. The first line, known as Line 1, didn’t open to the public until 1980s. The second subway system, in Tianjin, wouldn’t debut until 1984. Prior to 1990s, subway construction in China was a slow-moving process. However, in the following 30 years, China’s growth in the transportation sector is impressive. Subway lines in China are being built at an incredible rate and the subway system has gone from covering three cities in 1990 to 33 cities in 2019.As of June 2019, 33 Chinese cities have subways, 21 of which entered the rail transit era in the last 10 years. Thirteen of the 33 cities ran lines exceeding 100 kilometers. According to data from 21 Data News Laboratory, the total operating mileage of the subway lines in China was about 4,600 kilometers.In terms of the operational subway mileage, Shanghai ranks top with the mileage of 670 kilometers, followed by Beijing (617 km), Guangzhou (474 km), Shenzhen (286 km) and Wuhan (264 km).If we change the criteria, the ranking changes as well. Beijing ranks top in terms of both the daily volume of passenger transport of 11.48 million, followed by Shanghai, Guangzhou, Shenzhen and Chengdu. Beijing also leads all the other Chinese cities with 20 subway lines. In April 2019, the average daily subway passengers volume in 12 cities exceeded 1 million.It is not an exaggeration to state that, if a subway system in the international metropolis, such as Beijing and Shanghai, collapses for a single day, it would bring the entire city to a grinding halt. The rail transit network eases the traffic congestion in such cities and is vital for such large cities. It will continue to remain so.In 2015, China’s National Development and Reform Commission issued a document which regulated that subway’s load capacity should not be no less than 7,000 passengers per kilometer per day. However, a survey about the subway operation in 29 cities in April this year showed that the subway passenger transport intensity (per kilometer per day) in six cities, including Kunming, Ningbo, Xiamen, Dongguan, Guiyang and Urumqi, was under 7,000.

Although the written history of California is not long, records of earthquakes exist that affected the Spanish missions that were constructed beginning in the late 18th century. Those records ceased when the missions were secularized in 1834, and from that point until the California Gold Rush in the 1840s, records were sparse. Other sources for the occurrence of earthquakes usually came from ship captains and other explorers. For the period 1850–2004, there was about one potentially damaging event per year on average, though many of these did not cause loss of life or property damage. The earliest known earthquake was documented in 1769 by the Spanish explorers and Catholic missionaries of the Portolá expedition as they traveled northward from San Diego along the Santa Ana River near the present site of Los Angeles.[1][2]The few damaging earthquakes that occurred in the American Midwest and the East Coast were well known (1755 Cape Ann, 1811–12 New Madrid, 1886 Charleston), and it became apparent to settlers that the earthquake hazard situation was much different in the West. While the 1812 Wrightwood, 1857 Fort Tejon, and 1872 Lone Pine shocks were only moderately destructive in mostly unpopulated areas, the 1868 Hayward event affected the thriving financial hub that is the San Francisco Bay Area, with damage from Santa Rosa in the north to Santa Cruz in the south. By this time, scientists were well aware of the threat, but seismology was still in its infancy. Reactions following destructive events in the late 19th and early 20th centuries included developers, press, and boosters minimizing and downplaying the risk out of fear that the ongoing economic boom would be negatively affected.[3][4]California earthquakes (1769–2000)According to seismologist Charles Richter, the 1906 San Francisco earthquake moved the United States Government into acknowledging the problem. Prior to that, no agency was specifically focused on researching earthquake activity. The United States Weather Bureau did record when they happened and several United States Geological Survey scientists had briefly disengaged from their regular duties of mapping mineral resources to write reports on the New Madrid and Charleston events, but no trained geologists were working on the problem until the Coast and Geodetic Survey was made responsible after 1906. The outlook improved when professor Andrew Lawson brought the state's first monitoring program online at the University of California, Berkeley in 1910 with seismologist Harry Wood, who was later instrumental in getting the Caltech Seismological Laboratory operational in the 1920s.[3][5]Early developments at the Caltech lab in Pasadena included an earthquake observation network using their own custom built short period seismometers, the Richter magnitude scale, and an updated version of the Mercalli intensity scale. In 1933, the Long Beach earthquake occurred in a populated area and damaged or destroyed a large number of public school buildings in Long Beach and Los Angeles. Some decades later, the 1971 San Fernando earthquake affected the San Fernando Valley north of Los Angeles. In both cases, the perception of those involved with policy making in California was changed, and state laws and building codes were modified (but not without much debate) to require commercial and residential properties to be built to withstand earthquakes. Higher standards were established for fire stations, hospitals, and schools and construction of dwellings was also restricted near known active faultsList of earthquakes in California - Wikipedia