Should a desalination project be near a nuclear plant?

By William Simpson, especially for CalMatters

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San Luis Obispo County is exploring the construction of a large seawater desalination plant along its 90-mile coastline to provide a drought-resilient water supply for 16 partner water agencies. One leading option involves twinning or expanding the plant at or near Diablo Canyon, California’s last operating nuclear power plant.

Desalination is extremely energy intensive. Reverse osmosis systems — which force seawater through membranes to filter out salt — typically require 4,000 to 5,000 or more kilowatt-hours of electricity per acre-foot of water produced. (An acre foot is the amount of water needed to cover an acre of land under one foot of water.)

With California’s grid already under stress, providing reliable power is a major challenge. Proponents argue that using Diablo Canyon offers clear advantages. The plant already operates a small on-site desalination facility that produces up to 1.5 million gallons per day.

Nuclear reactors provide stable 24/7 baseload power at very low marginal cost – sometimes described as almost ‘free’ to use on site. Electricity is zero carbon and using existing infrastructure would significantly reduce costs and new demand on the electricity grid.

Last month, the U.S. Nuclear Regulatory Commission approved 20-year license renewals for Diablo Canyon’s two units, potentially extending operations through 2044 and 2045. Although state law currently limits operations to 2030, the federal approval leaves longer-term options open.

This path carries significant risks. Critics argue that economic pressures and concerns about the reliability of the electric grid should not be prioritized over public health, safety and the environment.

The Diablo Canyon reactors are 1980s-era Westinghouse pressurized water reactors located in a highly seismic coastal area. The Diablo Canyon plant is located near multiple active faults, including the Hosgri Fault, which is 3 miles offshore, and the Shoreline Fault, which is less than a mile away.

Independent experts and advocacy groups such as Mothers for Peace warn that the seismic analyzes may underestimate the combined danger of simultaneous fault ruptures that could cause more ground motion than the plant is designed to withstand. A major earthquake during continued operation could potentially trigger a Fukushima-scale accident affecting the Central Coast and parts of Southern California.

In 2011, in Fukushima, Japan, a magnitude 9.0 earthquake and subsequent tsunami damaged a nuclear plant, releasing radioactive material into the environment and prompting tens of thousands to evacuate.

A major problem at Diablo Canyon is the fragility of the reactor vessel, particularly in Unit 1, which was built with defective material. Decades of neutron radiation can make a steel pressure vessel brittle, increasing the risk of cracking or failure during a seismic event or rapid cooling. Critics, including UC Berkeley-affiliated experts, say the Nuclear Regulatory Commission granted exemptions to Diablo Canyon without enough long-term data.

The plant’s cooling system draws in 2 billion to 2.5 billion gallons of seawater daily and discharges it approximately 20 degrees warmer. This process kills billions of fish larvaeplankton and marine organisms per year.

It also degrades an estimated 14 square miles of coastal habitat—an area the size of San Luis Obispo. Environmental groups, including the California Coastkeeper Alliance, call it one of the most destructive coastal operations in the state.

Expanded operation would also generate and store more high-level radioactive waste at a seismically active site without a permanent repository. Critics worry about corrosion of the plant’s dry containers in the salty coastal air and potential seismic damage to its spent fuel pools.

Plant expansion is also economically controversial. Some analyzes put the total cost by 2045 at $20 billion to $45 billion, including possible disaster or retrofit costs. Critics argue that PG&E increased costs of providing government subsidieswhile safer renewable energy and storage alternatives receive less attention.

The DESAL Feasibility Study in San Luis Obispo County is evaluating multiple sites, technologies and energy sources, including possibly combining desalination with planned offshore wind activity in Morro Bay. However, the periodicity of the wind makes it less suitable for a facility that needs to operate at high capacity around the clock.

Public hearings were held last month, but no final decisions were made. Whether a nuclear desalination plant moves forward will depend on technical, economic and environmental findings, as well as public input and policy.

Proponents say it’s a pragmatic solution to drought-resistant water using reliable, low-carbon energy. Critics see expanding an aging nuclear plant in an earthquake-prone country as an unacceptable risk.

The lessons of Fukushima serve as a reminder of what can happen when risks are underestimated.

This article was originally published on CalMatters and is republished under Creative Commons Attribution-NonCommercial-No Derivatives license.