James Hall was almost 12 years into a 22-year-minimum non-parole period for a murder in 2006 when the latest offending occurred in 2017.

Imposing sentence in the District Court on Thursday, Judge Gordon Barrett said the guard had gone into Hall's cell to speak about a prison-related matter.

Hall closed the door behind her and after some conversation, it was then that he committed the two acts of rape.

"She froze and complied with your demands because she feared the more that she fought, the more you would fight," Judge Barrett told the 33-year-old.

"She knew something of the circumstances of the offending which saw you in prison."

Judge Barrett said the woman suffered only minor physical injuries, but had endured significant mental anguish.

"She is filled with self-blame for trusting you and for putting herself in a position of being vulnerable," he said.

In his earlier verdict after a trial by judge alone, Judge Barrett said he found Hall's account of the incident to be "entirely false" but described the victim's evidence as "detailed, nuanced, consistent, credible and truthful".

In her victim impact statement the guard said having to relive the incident during the trial had "almost broken me" and going to work was now "overwhelming".

"I don't feel safe to walk among prisoners anymore," she said.

Judge Barrett said it was likely Hall would spend the rest of his jail sentence in a high-security facility after offending against a woman who was just carrying out her job in prison.

He imposed a head sentence of seven-and-a-half years for the two rapes and added five-and-a-half years to Hall's existing non-parole period, taking it to 27-and-a-half years.

Australian Associated Press