TV

How secret race to develop ‘The Bomb’ affected those involved

Rachel Brosnahan is developing a rep for playing characters with a secret.

The 24-year-old actress had a break-out turn on “House of Cards” as Rachel Posner, a reformed call girl with incriminating knowledge of Frank Underwood’s (Kevin Spacey) misdeeds.

Now she’s starring in the new WGN America period drama “Manhattan” (premiering Sunday at 9 p.m.) as Abby Isaacs, the wife of a scientist staffed on the top-secret project to build the first atomic bomb during World War II. But despite the themes of secrecy and the political undertones of each series, Brosnahan says her characters are very different.

“Both women are quite resilient and I think that’s as far as the similarities go,” she tells The Post from Santa Fe, NM, where “Manhattan” is filming its 13-episode first season.

Though the series is set against the historical backdrop of the Manhattan Project in Los Alamos, NM, in 1943, “Manhattan” will focus on the secrets and lies that follow the scientists and their families living in this isolated community. For Abby and husband Charlie (Ashley Zukerman) — who can’t tell his wife about his classified job — those lies will begin to create a rift in their marriage.

“The weight of this secret begins to pull them apart and it’s hard when they begin to lead individual lives and grow so drastically apart — how do you come back together? Abby and Charlie’s story really looks at what happens when lying becomes the norm,” Brosnahan says.

Abby develops secrets of her own as she gets a job and gains independence dealing with the harsh realities of her new life — a trajectory that convinced the actress she wouldn’t be playing just another housewife.

“I really didn’t want to be an appendage to another character,” says Brosnahan, who initially wanted the smaller role of Helen, the project’s lone female scientist.

“She becomes so much stronger and [creator Sam Shaw and director Thomas Schlamme] let me know that, and I couldn’t wait to get into the skin of this character. It was scary that it is so different from anything I’ve been doing and I’m still a little scared about it coming out.”

Brosnahan says recurring roles on “House of Cards” and “The Blacklist” helped prepare her for “Manhattan,” though shooting on location in Santa Fe has been a big difference.

The show took over an abandoned burn hospital to re-create Los Alamos, and the cast and crew has had to deal with the unpredictable New Mexico weather — including hail, rain and wind so strong the actors could barely walk in it. “We’re actually dealing with the elements as they come,” she says. “The wind and the dust is all real and it’s something that really informed these people in these ‘scenes’ in their real lives. I think it adds another layer of authenticity.”