South Carolina authorities are investigating charges that highly radioactive spend nuclear fuel rods have been buried illegally and in a potentially dangerous way at a Barnwell, S.C., low-level nuclear waste dump.

Sources said the U.S. Department of Justice has joined in the investigation to check allegations that state officials are involved.

Susan Byers Lott, a former accountant for the dump site operator, Chem-Nuclear Systems Inc., told state investigators last month that 26 shipments of spent fuel from Boston Edison's Pilgrim nuclear power plant were buried at Barnwell between mid-1977 and January 1978.

Two other utilities also sent spent fuel to Barnwell, while other nuclear facilities routinely sent banned nuclear wastes and other prohibited material, Lott alleged.

She said Boston Edison was billed for a surface radiation level on the shipments of 17,000 to 20,000 rem per hour, a level that would be fatal to humans.

Spokesmen for both Boston Edison and Chem-Nuclear denied the charges, pointing out that spent fuel radiation levels are generally much higher, Walter Salvi of Boston Edison said the utility had shipped used fuel channels, part of the support and tubing inside a nuclear power plant core, during the period in question, and that such channels would have exhibited the 17,000-20,000 rem level. Shipments of such channels would be within the law.

There is "absolutely no truth" to Lott's charges that the shipments involved spent fuel rods, Salvi said, adding that "all the fuel that came into that plant is still in that plant."

Spent nuclear power plant fuel is classified as high-level waste and must be kept isolated from the environment for hundreds if not thousands of years. It is beginning to pile up in the temporary "swimming pool" storage tanks at each of the nation's 70 operating reactors.

Several utilities, although not Boston Edison, have said they may have to shut reactors down in the next decade if a solution to the storage problem is not found. Controversial legislation is now pending in Congress that would establish a variety of approaches to dealing with it.

Burial of such waste anywhere would violate "a whole host of rules" and would lead to revocation of licenses for both Chem-Nuclear and any utility involved, plus possible criminal charges, according to Nuclear Regulatory Commission enforcement chief Victor Stello.

Lott, 31, made her charges under oath in a Feb. 8 meeting with South Carolina law enforcement and health officials.

According to a transcript of the meeting obtained by The Washington Post, Lott said she helped draw up a contract between Chem-Nuclear and Boston Edison in 1977 for the disposal by burial of 26 loads of spent fuel rods.

The company, she said, ran tests to make sure it could unload safely the hot cargo from special cylindrical casks that workers called "silver bullets." In an interview, Lott said she saw all the shipments arrive at the rate of one or two a week.

"Each cask has a motor on the end to cool the rods inside, and they were mounted on sort of steel sawhorses on the back of the truck and covered with a wire mesh." Lott said Tri-State Motor Transit of Joplin, Mo., a licensed nuclear carrier, brought in the shipments.

Each load was accompanied by a Radiological Survey Report (RSR) form that is part of Chem-Nuclear's billing system, and all the RSRs listed spent fuel rods as the cargo, Lott testified.

Lott said she was responsible for billing customers and was given all the RSRs to file for that purpose. However, the RSRs for the 26 shipments from Boston Edison were missing from the files obtained from Chem-Nuclear by the state attorney general's office, she said.

She pointed out staple holes and upside-down and backward forms that she said indicated the remaining papers had been gone through hastily before being turned over to the authorities.

Low-level waste is generally defined as anything not either spent fuel or the waste that is separated from the fuel. "There are things that are called low-level wastes that do exhibit high levels of radiation," explained Dale Smith, chief of the Nuclear Regulatory Commission low-level facility licensing operation.

Lott, who worked at Chem-Nuclear four years, was fired in October 1978 after filling a sex discrimination complaint with the Equal Employment Oportunity Commission. A year later, she charged that Chem-Nuclear was illegally receiving quantitites of liquid radioactive waste and had buried at least three tanker trucks -- cab, wheels and all -- that were too contaminated to save.

Assistant State Attorney General Richard Wilson began an investigation of those charges in late November and has included the spent fuel burial allegation into the probe. He said a report would be made sometime this month.

Lott was asked during the Feb. 8 deposition-taking if she might have mistaken contracts involving used control rods or spent fuel racks for one involving rods. She said she knew the difference.

Control rods are moved between fuel rods to increase or reduce the nuclear chain reaction, and spent fuel racks hold the used rods in their swimming pool storage area. Both are highly radioactive on removal from the reactor, but the levels drop off quickly. Normally they are stored on-site for a year or so in order to cool off before shipment to Barnwell.

Boston Edison spokesman Salvi said the company may have sent spent fuel racks and control rods to Barnwell, but it would have been during the last six months of 1978 and not during 1977.

Lee Hebberd, Chem-Nuclear's site manager at Barnwell, said fuel rods were "just something we don't take." The company has always abided by NRC rules on what may be buried at Barnwell, he said.

In an interview, Lott said she and her family have received threatening phone calls and suffered attempted breakins at their house trailer home in Denmark, S.C., since the state investigation began. She recently lost another job as a cashier in a small grocery store, allegedly in a financial retrenchment, she said.

She and her attorneys have asked state authorities to seek immunity for her from prosecution in return for testimony on what she said was her knowledge of under-the-table payments between various utilities and Chem-Nuclear officials.