U.S. Sen. Barbara Boxer called for an investigation Wednesday into whether Southern California Edison, the operator of the San Onofre nuclear power plant, knew about major problems with steam generators that later experienced a radiation leak.

A 2012 report by Mitsubishi Heavy Industries found that it and Edison were “aware of serious problems with the design of San Onofre nuclear power plant’s replacement steam generators before they were installed,” Boxer (D-Calif.) and Rep. Ed Markey (D-Mass.) wrote in a letter to Allison Macfarlane, chairman of the U.S. Nuclear Regulatory Commission.

“Further, the report asserts that SCE and MHI rejected enhanced safety modifications and avoided triggering a more rigorous license amendment and safety review process.”

“We believe this alarming Report raises serious concerns about SCE’s and MHI’s past actions,” the lawmakers continued. “Safety, not regulatory short cuts, must be the driving factor in the design of nuclear facilities, as well as NRC’s determination on whether Units 2 and 3 can be restarted.”

A probe of the issue by the commission is likely, given that Boxer chairs the Senate Environment and Public Works Committee, which oversees the commission.

NRC spokeswoman Lara Uselding wrote in an email Wednesday that the commission will reply to Boxer’s letter “in the normal course of business.” An Edison spokeswoman didn’t return a message seeking comment.

The inquiry could set back Edison’s efforts to restart part of the plant, which has been shut down since a small radiation leak last January 2012.

That leak was caused by a design flaw in replacement steam generators, which did not undergo a thorough independent analysis by the NRC because Edison asserted during the approval process that the new generators wouldn’t create a greater safety risk than the old ones. The generators were built by Mitsubishi Heavy Industries.

Boxer’s concerns come at a sensitive time for the utility, which is seeking federal approval to restart one of San Onofre’s two reactors for a trial run at reduced power. The utility has insisted that running the plant at 70 percent power would be perfectly safe.

Questioning Edison’s credibility has been a central theme of anti-nuclear activists, who claimed the company risks public safety by putting profits ahead of important protection measures.

Edison has strenuously disputed those claims, saying safety is its No. 1 priority.

Under federal law, a nuclear plant’s operator is responsible for evaluating proposed design changes to the plant. A thorough review by the NRC, which regulates nuclear plant safety in the United States, typically isn’t required unless the company running the plant determines that the changes bring an added safety risk.

Boxer’s letter in many ways echoes concerns raised last spring by nuclear expert Arnie Gundersen that Edison deceived federal regulators.

Gundersen, a former nuclear industry executive, found that the utility added hundreds of tubes to the generators and made other significant changes, yet represented them as “like for like” replacements.

“By misleading the NRC on the true nature of the replacement, Edison fooled the NRC into giving a rubber stamp and not conducting a thorough NRC review and approval process,” Gundersen wrote in a March 2012 report commissioned by the environmental group Friends of the Earth.

Edison has issued a broad denial of assertions that it misrepresented the replacement generators during the federal review.

“At all times during the steam generator replacement process, and the ongoing outages in Unit 2 and 3, SCE has provided open and transparent information to the Nuclear Regulatory Commission,” the company wrote in a statement last spring.

However, the utility didn’t respond to several follow-up queries after Voice of OC requested a timeline of when it told regulators about specific changes like the additional tubes.

What is known is that in a key presentation early in the review process, Edison omitted certain changes.

A 2006 presentation by Edison to the NRC, billed as an overview of its plans for the replacement generators, neglected to mention key modifications, such as removal of the stay cylinder, which Gundersen describes as “the main structural pillar” in the generator.

That presentation was missing from the official meeting minutes until Voice of OC reported in May that the NRC couldn’t offer a concrete reason why it was not there. The record was then released the next business day.

As the outage passes the one-year mark, Edison continues to spend hundreds of millions of dollars running a plant that doesn’t produce electricity, making costly repairs and finding replacement power.

You can reach Nick Gerda at ngerda@gmail.com, and follow him on Twitter: @nicholasgerda.

Since you've made it this far,

You are obviously connected to your community and value good journalism. As an independent and local nonprofit, our news is accessible to all, regardless of what they can afford. Our newsroom centers on Orange County’s civic and cultural life, not ad-driven clickbait. Our reporters hold powerful interests accountable to protect your quality of life. But it’s not free to produce. It depends on donors like you.

Join the conversation: In lieu of comments, we encourage readers to engage with us across a variety of mediums. Join our Facebook discussion. Message us via our website or staff page. Send us a secure tip. Share your thoughts in a community opinion piece.