The STP reactors are cooled by a 7,000 acre channeled reservoir surrounded by a earth/cement embankment. The top of the embankment wall is 67-feet above mean sea level. The reactor complex is situated below on a grade of 29-feet above mean sea level.The South Texas Project nuclear power station near Bay City, Texas has not yet dodged a bullet from a very powerful Hurricane Harvey. The hurricane battered the Texas Gulf Coast region from August 25 to August 30, 2017 finally dumping an all time record 50-inches of rainfall flooding the Houston metropolitan area 112 miles to the northeast of the reactors before moving on. At publishing time, the Colorado River is cresting over its banks at 47' feet, three feet above flood stage (44 feet), at the gauging station at Bay City on August 31, 2017. The Colorado runs adjacent to the East of the reactor site. But the operators are still projecting that the flood water will not impact the reactor site. The South Texas nuclear power station has remained at full power throughout the hurricane and tropical storm. The reactor site never experienced sustained winds over 73 miles per hour that would have triggered an Emergency Action Level requiring the reactor to shut down. Given the unique cooling system, projections for flooding are a much more vague criteria left to the operator's discretion. The reactor site at no time during the storm lost offsite power from the electric grid that provides electricity to 100% of reactor safety and cooling systems. Loss Of Offsite power (LOOP) would have automatically shut down the reactors. With the loss of offsite power, nuclear power stations have back up emergency power systems, like emergency diesel generators, which provide electricity to a vital subset of those reactor safety and cooling. A "SCRAM" however leaves operators with an extremely hot reactor core to be cooled on narrower safety margins.
Beyond Nuclear and Texas watchdog groups Sustainable Energy & Economic Development (SEED) Coalition and the South Texas Association for Responsible Energy have called upon the U.S. Nuclear Regulatory Commission and the operators of the South Texas nuclear power plant to put the reactors into "its safest condition, cold shutdown" in advance of predicted flood waters that prompted Bay City authorities to declare a "mandatory evacuation" before emergency evacuation routes flooded, including those for a radiological emergency at the South Texas nuclear station. The Bay City mandatory evacuation order was later lifted and modified to a "voluntary evacuation."
The unprecedented rainfall in the region broke a U.S. continental record. The groups had warned that the NRC and the South Texas Nuclear Operating Corporation have previously recognized that there is a credible threat from a nuclear accident initiated by a breach in a 12-mile long perimeter embankment wall that surrounds the 7,000 acre Main Cooling Reservoir for the two reactors.
A closer look at the cooling water intake (right) and discharge piping (left) system from the reservoir down to the reactor below.
The Main Cooling Reservoir's embankment contains the all important reactor cooling water behind an earth and cement wall, the top of which is 65- to 67-feet above mean sea level. The nuclear power station is situated below, at 29-feet above mean sea level. The normal maximum operating water level in the reservoir is 47-feet above mean sea level. The rain has ceased as the hurricane is now downgraded to a tropical storm that has moved on to Louisiana.
Throughout the storm, the NRC and South Texas Project did not publicly post any information on the status of the changing water level within the reservoir despite the unprecedented rainfall that has inundated the region.
Similarly, as for any of the many inherently dangerous industries concentrated on the Texas Gulf Coast, the public watchdog groups maintain that the call for shutting down the reactors in advance of this powerful storm, if given the opportunity, is the prudent action when the nuclear reactors, regardless of design, can be secured in the safest and most stable condition, cold shutdown. This is one of the major lessons to be learned from the Fukushima Daiichi nuclear disaster in Japan.
UPDATE: Beyond Nuclear questioned the NRC on the compliance of continued operation of South Texas with the potential closing of radiological emergency evacuation routes The NRC Public Affairs Office responded, "On August 30, 2017, FEMA has concluded that offsite radiological emergency preparedness remains adequate to provide 'Reasonable Assurance' and that appropriate measures can be taken to protect the health and safety of the public in a radiological emergency at the South Texas Project. At this time, FEMA is not initiating actions to conduct a Disaster Initiated Review of offsite issues within the South Texas Project 10-mile emergency planning zone."