Southern California Edison is seeking almost $7.6 billion from the Japanese manufacturer of the faulty steam generators that led to the permanent shutdown of the San Onofre nuclear power plant.
Edison's latest claim is at least $3 billion higher than the utility had previously sought from Mitsubishi Heavy Industries, a Tokyo-based firm that reported the latest figure in a statement Tuesday.
How much Edison wins -- if anything -- could be significant to the utility's customers.
Under a settlement agreement, state regulators assigned Edison and San Diego Gas & Electric Co. customers the responsibility to cover $3.3 billion of the shutdown costs, or 70%, even though Edison installed the troubled replacement steam generators that caused the January 2012 shutdown.
Money collected from Mitsubishi would be split 50-50 with customers, said Mindy Spatt, a spokeswoman for the Utility Reform Network.
"The more Edison gets, the more the customer gets," said Spatt, whose organization advocates for consumers before the California Public Utilities Commission.
On Monday, Edison and three other companies submitted evidence to support their case for a higher payout to the International Chamber of Commerce in San Francisco, which is serving as the arbitrator in the dispute, Mitsubishi stated.
But Mitsubishi maintains that under the agreements for development of the steam generators, its liability is limited to $137 million.
"The allegations and demands made by those parties disregard the history of the contract negotiations and performance and are factually incorrect, legally unsound, and inappropriate," Mitsubishi said in its statement.
In addition to the reported claim against Mitsubishi for almost $7.6 billion, Edison also has filed about $400 million in claims with the Nuclear Electric Insurance Limited, or NEIL, a consortium of power plant owners that provide insurance for the nation's reactors. Money recovered from NEIL would go to the benefit of Edison customers.
Scott Cunningham, an Edison spokesman, declined to comment about Mitsubishi's statement because of the ongoing arbitration that requires confidentiality. Cunningham said Edison's lawyers were determining what, if any, statement the utility would make.
The two nuclear units at San Onofre closed permanently in June 2013, a year and a half after Edison initially closed the defective steam generators. The new $680-million steam generators were found to be defective after one leaked a small amount of radiation.
FOR THE RECORD
July 28, 3:50 p.m.: An earlier version of this post said the steam generators were replaced a year and a half before the June 2013 closure. In fact, the generators were temporarily shut down a year and a half before the June 2013 closure; they were replaced prior to that.
The Utility Reform Network had supported the terms of the settlement agreement over San Onofre's closure, but last month the San Francisco consumer group asked state regulators to reopen talks on the deal. The reversal came after recent revelations of back-channel communications between regulators and utility executives.
The utilities commission has yet to rule on the organization's request. It is unclear what impact reopening the settlement talks would have on any award Edison might win in the dispute with Mitsubishi.
Follow Ivan Penn on Twitter at @ivanlpenn.