Why The Permian Basin May Not Be The Best Place To Store Nuclear Waste
Originally published on Forbes.com on April 3
The US Nuclear Regulatory Commission (NRC) has evaluated a proposal by Holtec International to build a storage site for radioactive nuclear waste in New Mexico, and determined that a license can be issued.
Last Monday, the attorney-general for New Mexico filed a lawsuit against the NRC intended to block the project because it would endanger the environment, residents, and nearby industries like agriculture and oil and gas production.
One of the risks evaluated by NRC is earthquakes. But earthquakes are often associated with oil and gas production, and the proposed Holtec site is close to thousands of new oil and gas wells in the Delaware basin. This deserves a closer look.
Earthquakes in Permian basin.
Figure 1. Earthquakes greater than magnitude 3 in Permian basin from January 2018 through March 2021 (39 months). Source: USGS.
The earthquake swarm just south of Carlsbad is about 60 miles from the proposed Holtec site, shown by a blue star in Figure 1. Holtec presented a map that showed major geologic structures (faults, etc) close to the edge of the basin, and the swarm in Figure 1 appears to overly a dense part of the structures.
The swarm contains maybe 100 quakes of magnitude greater than 3. The biggest quakes were a 5.0 on 26 March 2020 and a 4.5 magnitude on 17 March 2021.
Only one quake greater than magnitude 3 occurred in this location in the 3-years before 1 January 2019. So this swarm started fairly suddenly in January 2019. A swarm such as this may be triggered by drilling new disposal wells or by a high-pressure plume of wastewater hitting a fault line after spreading slowly over time.
A swarm of earthquakes that appears fairly suddenly adds to the uncertainty of predicting the safety of a proposed nuclear waste storage in an oil and gas field, especially a giant field like the prolific Delaware basin in New Mexico.
So-called induced earthquakes like this caused serious concern in Oklahoma starting in 2009 and reaching a peak in 2015 when 887 quakes occurred in one year (six times more than occurred in California).
They were caused by spreading wastewater injected at the bottom of disposal wells.
Previous earthquakes have been felt and studied in the unconventional Dagger Draw oilfield in New Mexico. This is a carbonate zone on the left edge of the Delaware basin but in New Mexico not Texas (Figure 3).
Again, wastewater injection into deep formations close to basement granite rock was the cause of the earthquakes. At Dagger Draw a fluid plume from several disposal wells spread sideways about 10 miles before intersecting a deep fault line which triggered the earthquakes.
With this background, we take a look at the risks that Holtec examined in their proposal to NRC.
Holtec’s proposed nuclear waste repository.
The proposed repository for spent nuclear fuel from nuclear reactors bears the name Consolidated Interim Storage Facility (CISF). “Interim” refers to a plan that this will be temporary to be used only until a permanent repository is constructed at a yet-to-be-decided location in the US.
How much nuclear waste? A nuclear reactor typically generates about 2,000 tons of radioactive uranium waste per year. Altogether, about 83,000 tons of spent fuel are stored at temporary sites in over 30 US states. Phase 1 of the proposed project would transport and store in New Mexico about a tenth of this amount.
Phase 1 of the nuclear storage would constitute 500 modules (Figure 2) each containing one in-ground cylindrical canister that is packed with spent uranium nuclear material.
Figure 2. Artist’s layout of CISF containing about 500 modules, with canister shown in inset. Source: US Nuclear Regulatory Commission. Source NRC.
But additional phases could be built out to 10,000 modules. This raises an obvious concern: will CISF in New Mexico end up becoming the permanent storage site for US nuclear waste?
The site would be situated in southeastern New Mexico, midway between Carlsbad and Hobbs. There are thousands of oil wells in the vicinity (Figure 3).
What are the risks?
NRC’s Review Process has studied the proposal and determined that a license can be issued. The proposal included a comprehensive Safety Analysis and EIS (Environmental Impact Statement).
Risks that were evaluated included radiation contamination by (1) transport of storage casks by trucks and rail. Each steel-welded canister is encased in a steel and concrete cask for transporting. But truck accidents can occur, especially as highways are getting clogged by increasing numbers of ordinary semi-trailers.
Other risks at the CISF site included (2) failure of storage canisters, (3) potential sinkholes opening up, (4) playa lakes and aquifer contamination, (5) earthquake damage.
The danger of produced water in the Delaware basin.
It appears this was not examined specifically, but disposal of produced water can and often does cause induced earthquakes.
There are thousands of oil and gas wells in the Delaware basin (Figure 3). It has been reported that for each barrel of oil there are 4 barrels of salt water produced (a different observer reported a ratio of 5-10.) The ratio was 10 in Oklahoma when the earthquake swarms started over there. The basin, New Mexico portion, produced about 1 million bopd for each of the past three years, so this would give at least 4 million bwpd (barrels of water per day) for each of those 3 years. This is a lot of water to dispose.
Figure 3. Wells drilled in Wolfcamp formation (left) and Bone Spring formation (right). Star is CISF site. Rectangle is earthquake swarm. Source: EIA.
Disposal wells are the cheapest way to get rid of the produced water. In the Delaware, oil production has increased by more than 4 times since 2009, and so wastewater disposal has increased in concert.
Wastewater injection can lead to an unstable subsurface and rapid changes in induced earthquakes (Figure 1.)
The scene is gradually changing due to recycling of produced water – an alternative to disposal wells. According to the same report, five new water recycling plants will be commissioned by 2022, to complement 90 smaller-scale recycling facilities that have come into existence since 2015.
The risk of earthquake damage.
Earthquakes are often triggered in the basement rock which lies deeper than the oil and gas zone, but faults that trigger earthquakes can lie at any level (shallow or deep) and can sometimes be several miles away from the disposal wells (Link dated June 18, 2015).
So is there a risk of a large earthquake that could damage the canisters of hot radioactive material and allow it to leak out of the CISF storage site?
For comparison, the largest three of the Oklahoma earthquakes – two of magnitude greater than 5 – caused significant damage to surface buildings.
The following suggest it is difficult to rule out a future earthquake of magnitude greater than 5 that could reach the proposed nuclear storage site in Figure 3: (1) the continuing disposal of produced water in the Delaware (with a high water/oil ratio over half of the ratio in Oklahoma), (2) the uncertain timing and location of the earthquake swarm of Figures 1, 3 which popped up in the last couple of years, and (3) the occurrence of a magnitude 5 quake in that recent swarm.
Earthquake safety analysis at CISF site.
The potential damage of an earthquake to the CISF site was evaluated by Holtec. The evaluation classifies an earthquake as caused by movements in the mantle of the earth. This wording does not specify induced earthquakes due to oil and gas operations, which occur in the crust not the mantle.
It’s unclear whether earthquakes in the crust of magnitudes 5 or greater (as have occurred in the Delaware basin) were considered in the safety analysis of the CISF site.
The conclusion of the CISF evaluation was that the “Design Basis Earthquake will not affect the safe operation of HI-TRAC CS.”
A deeper look.
A deeper look into the safety analysis document states:
A major site of earthquake activity within 200 miles was located in west Texas southeast of the CISF site. This “is hypothesized as being a result of fluid pressure build-up from fluid injection.” In other words, earthquakes caused by oil and gas disposal of wastewater.
This location had to be in the Midland basin, near the towns of Midland and Odessa (Figure 1). It seems the safety analysis, and the earthquake predictions, were done by Holtec before thousands of shale-oil wells were drilled and fracked in the Delaware basin right next door to the CISF site (Figure 3). In fact, one graphic of earthquake probability was dated in 2009.
One takeaway is that oil and gas operations that trigger earthquakes down below may not be an ideal neighbor to nuclear waste storage sites up above – at least in the Permian desert of New Mexico.