If you want to understand why Toshiba Corp. is about to report a multi-billion dollar write-down on its nuclear reactor business, the story begins and ends with a onetime pipe manufacturer with roots in the swamp country of Louisiana.

The Shaw Group Inc., based in Baton Rouge, looms large in the complex tale of blown deadlines and budgets at four nuclear reactor projects in Georgia and South Carolina overseen by Westinghouse Electric Co., a Toshiba subsidiary.

On Tuesday, Toshiba is expected to announce a massive write-down, perhaps as big as $6.1 billion, to cover cost overruns at Westinghouse, which now owns most of Shaw's assets. The loss may actually eclipse the $5.4 billion that Toshiba paid for Westinghouse in 2006 and has forced the Japanese industrial conglomerate to put up for sale a significant stake in its prized flash-memory business. Toshiba had to sell off other assets last year following a 2015 accounting scandal.