backup generators, dam failure, dam tsunami, flooding, Gulf of Mexico, Hurricane Harvey, hurricane safety, nuclear backup generators, power outage, Rain, South Texas Nuclear, South Texas Nuclear Project, Storm Surge, tsunami, US NRC, US NRC hurricanes
Hurricane Harvey Updates here: http://www.nhc.noaa.gov
[Update note. The USNRC puts the nuclear units 1 and 2 at 28 ft. The newer units planned were apparently to be raised up a bit higher. Both documents still use the 1929 elevation standard not recognized by FEMA and which is a bit off due to land shift (and probably due to technology changes, as well). USNRC “STAFF ASSESSMENT OF RESPONSE TO 10 CFR 50.54(f) INFORMATION REQUEST FLOOD-CAUSING MECHANISM REEVALUATION – SOUTH TEXAS PROJECT, UNITS. 1 AND 2 DOCKET NOS. 50-498 AND 50-499” “The STP site has mainly flat topography with few gentle slopes. Elevations across the site range from 15ft (4.6 m) NGVD29 to 30ft (9.1 m) NGVD29 with plant grade of 28ft (8.53 m) NGVD29“. https://www.nrc.gov/docs/ML1425/ML14259A195.pdf ]
Hurricane Harvey’s forecast track targets a two reactor nuclear power station called the South Texas Project (STP). An internal US NRC memo leaked to the public (see below) classified it as being High on Dam Hazard Vulnerability due to the cooling pond, though they probably mean the Main Cooling Reservoir. There is-was a proposal for two more reactors at the site (STP 3 and 4). Information on the proposed reactors includes some relevant information on the site: “The STP 3 & 4 site is located 10.5 miles inland from Matagorda Bay and 16.9 miles inland from the Gulf of Mexico. It is approximately 75 miles from the Continental Shelf. The shoreline of Matagorda Peninsula along the Gulf of Mexico changes constantly, retreating landward or advancing seaward as the result of a combination of hydrologic and meteorological processes, climatic factors as well as engineering activities…. The STP 3 & 4 site is located in Matagorda County, Texas near the west bank of the Colorado River, opposite river mile 14.6. It is approximately 12 miles south-southwest of Bay City, Texas, and 8 miles north-northwest of Matagorda, Texas (Figure 2.4S.1-1). The surface elevation of the site ranges from about El. 32 to 34 ft mean sea level (MSL), which is equivalent to National Geodetic Vertical Datum of 1929 (NGVD 29), at the north boundary to between El. 15 ft to 20 ft MSL at the south boundary… A major feature of the site is the Main Cooling Reservoir (MCR), which is formed by a 12.4-mile-long earthfill embankment constructed above the natural ground surface. The MCR has a surface area of 7000 acres with a normal maximum operating level of El. 49 ft MSL. The MCR is not a safety-related facility. Makeup water to the MCR is supplied from the Colorado River and pumped into the MCR intermittently throughout the year via the Reservoir Makeup Pumping Facility (RMPF). A smaller separate cooling pond, referred to as the Essential Cooling Pond (ECP), serves as the ultimate heat sink for STP 1 & 2. The surface area of the ECP is 46 acres. (Reference 2.4S.1-1) https://www.nrc.gov/docs/ML1204/ML12048A985.pdf.
Failure of the earthen embankment, is not the only hazard, however:
“When faced with a hurricane or other foreseeable severe weather event, nuclear reactors are required to manually shut down as a safety precaution when certain conditions exist. The South Texas nuclear power station in Bay City, Texas and the Waterford nuclear power station near Baton Rouge, LA are required to shut down when hurricane force winds speeds reach 73 and 74 miles per hour, respectively. Nuclear reactor operators will also shut down the reactor in advance of the arrival of hurricane force winds. In some cases, where utilities do not have a sufficient amount of non-nuclear back-up power, this will cause a loss of electrical power before the storm even arrives.
While most nuclear reactors built in potential hurricane zones are designed to structurally withstand high winds and modest flooding, they are vulnerable to other effects of severe storms.
The most significant event is the loss of offsite power, a problem that can lead to a “station blackout.”
During operation, all atomic reactors rely upon alternating current (AC) electricity generated and transmitted from offsite sources to provide the power needed to operate the reactor’s vital safety systems. Without these systems in operation, even when the reactor is shut down, the thermally hot and radioactive fuel inside the reactor would quickly overheat and cause a nuclear meltdown.
According to U.S. Nuclear Regulatory Commission findings documented in NUREG-1150 “Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants,” station blackout is the number one contributor of risk to the public, with risk defined as a combination of probability and serious consequences.
When offsite AC power is lost due to electrical grid failure, reactors are designed to automatically switch over to required backup emergency diesel generators. These are locomotive-size, fuel-guzzling generators that provide enough power to operate a narrower but basic set of reactor safety systems. Each reactor unit is required to have at least two emergency diesel generators onsite. Should these backup generators fail due to overheating, mechanical failure or the fouling of the diesel fuel, etc. a smaller subset of vital reactor cooling instrumentation and control systems would rely upon power from large on-site battery banks. The failure of both onsite and offsite AC power supplies result in the condition known as station blackout. According to the NRC safety study, a station blackout leads to battery depletion after approximately 4 hours and sets in motion a time table where “approximately 3 hours beyond battery depletion was allowed for the restoration of AC power before core uncovery would occur.” Uncovering of the reactor core of cooling water would lead to a meltdown of the extremely hot and radioactive nuclear fuel.
However, the history of emergency diesel generators compliance with operability requirements is checkered….” Read the rest here: https://www.nirs.org/wp-content/uploads/reactorwatch/natureandnukes/nukesandhurricanes092205.pdf
Storm surge prediction for Harvey:
South Texas Nuclear site elevation maps:
More details found here: https://www.peer.org/assets/docs/nrc/12_17_13_NRC_risk_assessment.pdf
Chart found here, compliments of Greenpeace: http://environmentalarchives.com/download/2012-nrc-qualitative-preliminary-assessment-dam-hazard-vulnerabilities-operation-nuclear-power-plants-united-states/
Emphasis our own throughout.