Radioactive Incident Monitoring Network (“RIMNET” – UK)

One of the lesser known networks in the United Kingdom is Radioactive Incident Monitoring Network or “RIMNET.” This network was set up in 1986 following the accident at the Chernobyl nuclear station in the Ukraine as part of the National Response Plan.

Rimnet is designed to monitor radiation dose across the entire United Kingdom (a map of all sites can be found here [PDF]) and relayed to a computer in London at the Department for Energy and Climate Change for near-immediate alerts to rises in radioactivity. It is managed by the Met Office. There are 92 sites spread across the UK in all areas both close to major cities, in rural areas and near or in MoD properties.

Rimnet was developed in three stages:

  • An initial system, RIMNET Phase 1, was installed in 1988 as an interim solution
  • The Phase 2 system operated until January 2005
  • Phase 3 went live in 2006

There was a detailed article in the journal Radiation Protection Dosimetry in 1993 detailing Phase 2 (Radiat Prot Dosimetry (1993) 50 (2-4): 171-176.) (see

The article gave a technical summary of the systems in use:

System Configuration
Monitors Type: Geiger-Muller
Measurement range: background to 3 mGy.h -1
Temperature –20oC to +40oC
Windspeed: up to 100 knots
Humidity up to 95%
Main CDF (“Central Database Facility” Configuration: two Digital VAX clustered processors
RIMNET workstation terminals, System Manager console and data storage
Communication Links Combination of leased lines, public data network (packet switched network for PCs), local Ethernet connections

In some ways RIMNET was a civil companion to the UK Warning and Monitoring Organisation before it was disbanded in 1991. However by Phase 2 of RIMNET it was much more sophisticated in collecting and transmitting radiation doses than the UKWMO ever was. RIMNET consisted of 90+ collection sites, fully automated than did not need personnel to man them. RIMNET, now at Phase 3, continues to monitor for radiation levels to this day.



SL-1– One of America’s Worst Nuclear Accidents

On 3rd January 1961 America suffered one of its worst nuclear accidents at the SL-1 experimental nuclear reactor at Idaho Falls, Idaho.

The accident killed the three men on duty, two almost immediately and one shortly after. The cause was a prompt criticality accident, a control rod in the reactor was removed too far causing a sudden surge in power.The power surge was later established to have jumped to 10 gigawatts in less than 4 milliseconds causing the water coolant surrounding the reactor core to form a water hammer and cause the entire pressure vessel, weighing 11.7 tonnes, to jump more than 9 feet.

The SL-1 disaster is important in many respects because it demonstrates human inability to confront the dangers of nuclear power, our creeping complacency towards the energy being unleashed and not to truly learn from these accidents.

In many respects SL-1 was an accident waiting to happen; the reactors were not inside true containment buildings, the reactor design allowed this accident to happen and its arguable whether the crew was experienced to enough to supervise the running of a nuclear reactor.

America, and most of the world’s nuclear powers had already experienced nuclear accidents before the one at SL-1. There was the disastrous fire at Pile no. 1 at Windscale in 1957 in the UK which revealed just how much wasn’t understood about nuclear power, there was also the Kyshtym disaster in the USSR when the cooling system for a tank of highly radioactive waste failed resulting in an explosion, also in 1957. Against this background of disasters, two young men in their mid 20s and a 22 year old trainee were allowed to operate the SL-1 reactor.

Further reading:

  • Idaho Falls: The Untold Story of America’s First Nuclear Accident, William McKeown (not strictly the “first” accident, a criticality accident killed Harry Daghlian in December 1945 with what became known as the “demon core”)
  • Final report of SL-1 recovery operation, General Electric Company Idaho Test Station SL-1 Project, U.S. Atomic Energy Commission. Idaho Operations Office
  • Video: SL-1 The Accident: Phases I and II, U.S. Atomic Energy Commission at the Internet Archive