Trouble is brewing at Britain's nuclear reprocessing plant

Britain's huge nuclear reprocessing plant at Sellafield (formerly known as Windscale) is in trouble. Its supposedly fail-safe arrangements for averting radiation accidents have been proved seriously defective, and the government is insisting on a complete review of safety standards at the plant, which is the largest discharger of radioactivity in the Western world.

Sellafield's worst mishap produced nuclear contamination of a long stretch of Cumbrian coastline. The area is located near the pipe through which effluent from reprocessing equipment flows into the Irish Sea.

British Nuclear Fuels, the company running Sella-field, was forced to admit the accident was the result of ''misunderstanding between managers,'' who took a full week to admit the beach was contaminated. BNF may face prosecution for the accident.

Earlier, a television program drew attention to the high incidence of leukemia in a village near Sellafield. A special inquiry into the program's claims is under way.

The government has had to press BNF hard to take steps to upgrade Sellafield's safety standards. At first the company denied that a serious problem existed.

The trouble at Sellafield has come at a bad moment for the government. The plant reprocesses spent fuel from Magnox first-generation nuclear power stations. It also stores spent fuel from second-generation stations in Britain, other European countries, and Japan, and stockpiles plutonium for military purposes.

Prime Minister Margaret Thatcher is a strong advocate of both nuclear power stations and British-made nuclear weapons. The difficulties at Sellafield hit at the heart of her forward nuclear planning.

The Sellafield facility is large and includes much aging reprocessing equipment. The government has decided that safety standards have been allowed to fall.

Attention was drawn to the spillage by the environmental group Greenpeace, which was later fined (STR)50,000 (some $75,000) for trying to interfere with the BNF pipeline. Greenpeace complained it had been unfairly treated.

Although BNF rejected allegations linking Sellafield with the incidence of leukemia, Mrs. Thatcher decided an eminent physician should conduct an urgent inquiry. Over the Christmas and New Year period 25 miles of coastline near Sellafield will remain closed.

Sellafield has been the center of criticism in the late 1970s, when BNF was accused of lax handling of radioactive materials. It tried to tighten up safety standards and went ahead with a reconstruction program.

Government officials concede there will always be a public-relations problem at Sellafield. Only sweeping changes in the senior personnel running the plant, they say, will convince people that a new and genuine effort to avoid mishaps is being made. It is thought that early in 1984 a major management shakeup will be initiated.