Another Rare M2.1 Earthquake Hits Near Pilgrim Nuclear Power Station, Massachusetts


A M2.1 earthquake struck North Plymouth, Massachusetts, on December 3, 2019, at 4:29 p.m. local time, at a depth of 5.5 miles (8.9 km). 

Officials say that the Pilgrim Nuclear Power Station hasn’t felt it, but all around Pilgrim, people reported loud bang and rumbling.

A M2.1 earthquake hit near Pilgrim nuclear plant in Plymouth in Massachusetts on December 2 2019, A M2.1 earthquake hit near Pilgrim nuclear plant in Plymouth in Massachusetts on December 2 2019 map, A M2.1 earthquake hit near Pilgrim nuclear plant in Plymouth in Massachusetts on December 2 2019 concerns
A M2.1 earthquake hit near Pilgrim nuclear plant in Plymouth in Massachusetts on December 2, 2019. Map via USGS

The rare earthquake was reported more than 40 times on the USGS website.

According to officials, the earthquake was not felt at Pilgrim Nuclear Power Station. The spokesman of the company said the plant and spent fuel pool weren’t affected.

But all around Pilgrim, social media was abuzz with reports of a loud bang and rumbling.

Several reports came from people living three to five miles of the plant. Rumblings were also felt in Plymouth Center.

One person described it as a “thundering” sound, another saying it “rattled glasses on a rack.”

The New Quake Raises Issues

Did Holtec share seismic readings it took at the plant with state agencies?

Can the crane used to hoist radioactive fuel assemblies from the spent fuel pool into storage casks handle earthquake activity?

This new tremor raises issues and officials have no answers.

U.S. Nuclear Power Plant Requirements

U.S. nuclear power plants are built to withstand a broad spectrum of environmental hazards, including earthquakes.

The NRC requires that safety-significant structures, systems and components be designed to take into account the most severe natural phenomena historically reported for the site and surrounding areas.

The NRC then adds margin to predicted ground motions to provide for additional robustness and to account for any limitations on historical data.

In other words, U.S. plants are designed to be safe based on historical environmental data, including the area’s predicted maximum credible earthquake.

pilgrim nuclear plant earthquake
A M2.1 earthquake hit near the Pilgrim nuclear power plant on December 3, 2019. Picture:, public domain via Wikipedia

The NRC requires nuclear power plants to maintain operating seismic monitors on site

When an earthquake occurs, data recorded by the plant’s seismic instrumentation is used by the operators to make a rapid determination of the degree of severity of the event, including the need to shut down the plant when Operating Basis Earthquake (OBE) levels are exceeded.

The data, coupled with plant walkdowns, or visual assessments, is used to make the initial determinations of whether the plant must be shut down, if it has not already been shut down by the plant operators or the perturbations resulting from the seismic event.

Here is a pdf containing all requirements of a nuclear plant in the USA.

Nuclear Regulatory Commission spokesman Neil Sheehan about the pilgrim event

In the case of Pilgrim, the plant no longer has an operating reactor. As such, the primary focus of safety is on the spent fuel pool and dry cask storage facility.

Both are designed with a high degree of robustness and capable of withstanding the levels of earthquake activity discussed above.

The earthquake activity reported in Massachusetts on Tuesday would not have approached a level of concern for either the spent fuel pool or the dry casks at the plant.

The NRC could dispatch an inspector to the site to independently verify the safety of the pool and dry casks if we had any safety concerns regarding either. Again, that is not the case with respect to this seismic activity. [MV Times, USGS]

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