Radiological Hazard Assessment and tiny 'hot' particles
Because of the permitted discharges and unpermitted leaks from the Hinkley A and B stations last century, the mud is known to be contaminated with a wide range of nuclear fission products including plutonium and uranium, as confirmed in NRPB M-173 and by later by gamma spectrometry. Contamination is shown in the later official RIFE reports and in the recent (2021) independent testing funded by the STOP HINKLEY group.
A major problem with official radiological assessments is an over-arching assumption that most exposures are from external sources. They "average" the radiation over a large volume of soil (or mud or sand, etc) and assume that you are just fairly close-by. The only internal exposure that is usually considered is radioactive iodine (which causes thyroid cancer) and, as it gets into milk, many thousands of gallons of milk have been thrown away after nuclear accidents. It is also considered for internal radiotherapy doses, but not usually for 'Radioactively hot particles' in our environment.
Radiation exposure refers to any situation in which body tissue is exposed to ionising radiation. When we consider the concept of radiation exposure it is important to bear in mind not just the type of radiation that is being emitted (e.g. alpha, beta or gamma and their energy), but also the route by which that radiation enters the body. A commonly held image of nuclear (ionising) radiation is that it strikes the outside of the body - in what's known as external exposure. However the radioactive material also has the ability to deposit its energy in our internal organs through the process of inhalation, ingestion, injection, and absorption - what is termed internal exposure. This exposes our internal cells to high levels of repeated attacks and can often lead to cancer.
Alpha-emitting radioactive microparticles, which are known to have passed through the 5-micron filters at Hinkley Point are invisible to the normal tests used by government agencies. Such particles are known to cause cancers and mutations when they get into the human body.The Welsh Senedd asked for a direct test for alpha-emitters and the charity Children With Cancer proposed use of cheap CR-39 detectors developed at Bristol University and special software that can identify the tracks from americium, plutonium and uranium micro-particles. Despite NRW putting this to EDF they refused, backed by the government's CEFAS.
Even the flawed TR-534 Cefas analysis process showed that the top layer (of up to 1 metre) of dredged matter probably contains almost all the 239Pu (plus 238Pu and 240Pu and 241Am) at an under-estimate of about 1 Bq/kg dry weight (Table 24, pages 22-23).
Although this would, on a land-fill site, be classified as
Very Low Level Radioactive Waste, when the dredged matter contains vast numbers of microscopic highly radioactive particles mixed in with mud and fine silt, it is absolutely not appropriate to re-suspend these in a sea estuary that has high tidal flows, winds, and populated areas along the coasts of the Severn estuary.
Firstly, in TR-534, Cefas "averaged" the 239Pu radioactivity in their samples from all depths tested which immediately reduced the level by a factor of 6-fold. Then they do not assess the 'hot particles' that can be individually inhaled or ingested and irradiate the body from inside. Instead they average the radioactivity within the total bulk of the sampled sediment.
The TR-534 Figure 5,
Assessment of dose to individual members of crew and the public arisinguses average activities. These conveniently give exposure values external radiation for individual members of the crew and public below the de minimis criteria of 10 μSv/year (individual doses) and 1 manSv/year (collective dose), respectively. So, they conclude that the dredged material is
not radioactive (!!!) under current law.
So that's ok then? We do not think so.
Downloads and a more technical radiation assessment page.