Almost half a million pounds has been spent cleaning the cells of dissident republicans engaged in a dirty protest at Maghaberry Prison.
Justice minister David Ford said the £446,913 had been paid to external companies which have been carrying out work at the high security jail in Co Antrim.
A further £55,738 has been used to buy supplies such as a specialist industrial absorbent, said the minister.
More than 40 dissident republicans including John Paul Wootton and Brendan McConville who were convicted of the murder of police constable Stephen Carroll in 2009, have been segregated and are held at Maghaberry's Roe House.
Just over 30 are involved in a no wash dirty protest smearing excrement on the walls and floor of their cells as well as emptying urine into the prison landings.
The protest, which started last May, is in opposition to strip searches. Inmates want electronic scanning devices to replace what they claim are humiliating full body searches. Prisoners have also accused the authorities of reneging on an agreement which was signed in August 2010 after months of talks with mediators.
This week, a group calling itself the new IRA claimed responsibility for the murder of 52-year-old prison officer David Black and linked his shooting to the ongoing protest.
Information on the cell cleaning costs was released in response to a written question from SDLP MLA Pat Ramsey.
Mr Ramsey, who has visited Roe House as part of an SDLP delegation, said: "The amount of money that has been spent on cleaning could be better spent on a scanner which I would hope would resolve the current protest at Roe House."
Finlay Spratt, chairman of the Prison Officers' Association, said: "It is terrible conditions for the staff who have to work in the prison but, it just shows that the dedication and commitment they have. People in other industries would simply not work in those types of conditions, but what choice do prison officers have? If they don't do it there would be nobody to look after the prisoners."