Question: Cumbrians Opposed to a Radioactive Environment has campaigned against all aspects of the operation of Sellafield, formally known as which worst nuclear accident in Great Britain's history, ranked in severity at level 5 out of a possible 7 on the International Nuclear Event Scale? 

Context articles: Jean McSorley
International Nuclear Event Scale
Three Mile Island accident health effects
Windscale fire
1999 Blayais Nuclear Power Plant flood
Cumbrians Opposed to a Radioactive Environment
Nuclear Accident Magnitude Scale
Kyshtym disaster
Three Mile Island accident
Andreev Bay nuclear accident

Jean McSorley is long-standing anti-nuclear campaigner, who formed the group "Cumbrians Against a Radioactive Environment" (Core) from her home town of Barrow-in-Furness, England in protest at the local Sellafield plant.
 As well as fighting compensation cases for Sellafield workers, Core took part in direct action campaigns.
 It has been incorrectly reported that they earned a string of injunctions.
[1] Neither CORE as a group, nor the individuals involved, have received injunctions; but Greenpeace – who Jean McSorley subsequently worked for - has been served with a number due to its actions against nuclear operations.
The International Nuclear and Radiological Event Scale (INES) was introduced in 1990 by the International Atomic Energy Agency (IAEA) in order to enable prompt communication of safety-significant information in case of nuclear accidents.
The health effects of the 1979 Three Mile Island nuclear accident are widely, but not universally, agreed to be very low.
 The American Nuclear Society concluded that average local radiation exposure was equivalent to a chest X-ray, and maximum local exposure equivalent to less than a year's background radiation.
 The U.S. BEIR report on the Biological Effects of Ionizing Radiation states that "[t]he collective dose equivalent resulting from the radioactivity released in the Three Mile Island accident was so low that the estimated number of excess cancer cases to be expected, if any were to occur, would be negligible and undetectable."
 A variety of epidemiology studies have concluded that the accident has had no observable long term health effects.
 One dissenting study is "A reevaluation of cancer incidence near the Three Mile Island nuclear plant" by Dr. Steven Wing of the University of North Carolina.
 In this study, Dr. Wing and his colleagues argue that earlier findings had "logical and methodological problems" and conclude that "cancer incidence, specifically lung cancer and leukemia, increased following the TMI accident in areas estimated to have been in the pathway of radioactive plumes than in other areas."
The Windscale fire of 10 October 1957 was the worst nuclear accident in Great Britain's history, ranked in severity at level 5 out of a possible 7 on the International Nuclear Event Scale.
 The fire took place in Unit 1 of the two-pile Windscale facility on the northwest coast of England in Cumberland (now Sellafield, Cumbria).
 The two graphite-moderated reactors, referred to at the time as "piles", had been built as part of the British atomic bomb project.
 Windscale Pile No. 1 was operational in October 1950 followed by Pile No. 2 in June 1951.
The 1999 Blayais Nuclear Power Plant flood was a flood that took place on the evening of December 27, 1999.
 It was caused when a combination of the tide and high winds from the extratropical storm Martin led to the seawalls of the Blayais Nuclear Power Plant in France being overwhelmed.
 The event resulted in the loss of the plant's off-site power supply and knocked out several safety-related systems, resulting in a event on the International Nuclear Event Scale.
 The incident illustrated the potential for flooding to damage multiple items of equipment throughout a plant, weaknesses in safety measures, systems and procedures, and resulted in fundamental changes to the evaluation of flood risk at nuclear power plants and in the precautions taken.
Cumbrians Opposed to a Radioactive Environment (CORE) is a non-political, non-profit organisation, located in Barrow-in-Furness, which since 1980 has campaigned against all aspects of the operation of Sellafield, formally Windscale and the site of the 1957 reactor fire.
 Issues of current interest are radioactive air and sea discharges, resultant environmental contamination, and the health detriment to local communities and wildlife.
 As well as preparing compensation cases for Sellafield workers, CORE has taken part in many direct action campaigns which have resulted in a string of injunctions.
The Nuclear Accident Magnitude Scale (NAMS) is a scale to measure the severity of a nuclear accident.
 It was proposed by the British nuclear safety expert David Smythe in 2011 as a response to the Fukushima Daiichi nuclear disaster, where the conventional International Nuclear Event Scale was used in a confusing manner.
 Furthermore, it wants to bridge the various shortcomings of INES.
The Kyshtym disaster was a radioactive contamination accident that occurred on 29 September 1957 at Mayak, a plutonium production site in Russia for nuclear weapons and nuclear fuel reprocessing plant of the Soviet Union.
 It measured as a Level 6 disaster on the International Nuclear Event Scale (INES), making it the third-most serious nuclear accident ever recorded, behind the Fukushima Daiichi nuclear disaster and the Chernobyl disaster (both Level 7 on the INES).
 The event occurred in Ozyorsk, Chelyabinsk Oblast, a closed city built around the Mayak plant, and spread hot particles over more than 20,000 sqmi , where at least 270,000 people lived, with 300 immediate deaths among the villagers nearby.
 Since Ozyorsk/Mayak (named Chelyabinsk-40, then Chelyabinsk-65, until 1994) was not marked on maps, the disaster was named after Kyshtym, the nearest known town.
The Three Mile Island accident occurred on March 28, 1979, in reactor number 2 of Three Mile Island Nuclear Generating Station (TMI-2) in Dauphin County, Pennsylvania, United States, near Harrisburg.
 It was the most significant accident in U.S. commercial nuclear power plant history.
 The incident was rated a five on the seven-point International Nuclear Event Scale: Accident with wider consequences.
The Andreev Bay nuclear accident took place at Soviet naval base 569 in February 1982.
 Andreev Bay is a radioactive waste repository, located 55 km northwest of Murmansk and 60 km from the Norwegian border on the western shore of the Zapadnaya Litsa (Kola Peninsula).
 The repository entered service in 1961.
 In February 1982, a nuclear accident occurred, a radioactive water release from a pool in building #5.
 Cleanup of the accident took place from 1983 to 1989.
 About 700,000 tonnes of highly radioactive water leaked into the Barents Sea during that time period.
 About 1,000 people took part in the cleanup effort.
 Vladimir Konstantinovich Bulygin, who was in charge of the naval fleet's radiation accidents, received the Hero of the Soviet Union distinction for his work.