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Torness Nuclear Power Station is around 30 miles from Edinburgh.
Cannon Edinburgh Castle
According to French State owned EDF, owner-operator of the UK’s nuclear reactors, Torness nuclear power station unit one, 33 miles from Edinburgh Scotland, automatically shut down on Tuesday, 22 November, at 8.45 AM “due to an increase in seaweed levels as a result of the weather conditions in the area. We are currently monitoring the weather and the seaweed levels… We know that at certain times of year particular weather conditions in this part of the Forth Estuary can lead to increased seaweed volumes which can enter the station’s cooling water intake system. Our staff are trained to respond in this situation, and to take the plant offline if necessary. In addition, the plant’s safety systems monitor conditions like this will take the unit offline automatically, should levels rise beyond prescribed settings,…” EDF further notes that Torness has operated for 28 years, and can provide electricity to power approximately 2 million homes, (EDF should add: when it’s not blocked with seaweed and jellyfish or some other problem). See letter: https://assets.documentcloud.org/documents/3224121/Torness-Letter.pdf

Video showing Torness water outfall and explaining huge amount of water needed for cooling – about 40 cubic meters a second to operate: http://youtu.be/6orK0mshrDE (25 second video)
40 cubic meters is 40,000 liters per second. These are AGR reactors.
Video of Water Cooling System of Torness (3 min), Note extensive corrosion: http://youtu.be/-0mvpgfVq94

CC-BY-NC: Videos filmed for Fluid Mechanics Course at University of Edinburgh

Seaweed blockage of cooling water intake, at Torness Nuclear Power Station is reported to have occurred in 2006, 2013, with Jellyfish blockage occurring in 2011. Hunterston B., near Glasgow, was shutdown due to seaweed in summer of 2015. It remains a concern for Hinkley Pt. Nuclear Power Stations too, and seaweed blocked the Leningrad Nuclear Power Station water intake in October of last year (2015). Seaweed blockage occurred at a Swedish Nuclear Power Station in October of 2013. It would probably be a hazard for the proposed Moorside Nuclear Power Station, as well. Jellyfish blockage has occurred at the Diablo Canyon Nuclear Power Station in California, and in Japan.
Edinburgh skyline
Edinburgh Glasgow Hunterston B. Torness
Edinburgh is at serious risk from Torness, as well as Hunterston B, nuclear power stations. It has a population of around half a million. The region has a population of 1.3 million. https://en.wikipedia.org/wiki/Edinburgh Glasgow, also seriously endangered by Torness and Hunterston Nuclear Power Stations, has a population of 606,340 in a metro area of 2.3 million. https://en.wikipedia.org/wiki/Glasgow Together this is most of the current Scottish, non-diaspora, population, estimated at 5,373,000. https://en.wikipedia.org/wiki/Scotland The worldwide Scottish population, including diaspora, is estimated at 28 to 40 million people. https://en.wikipedia.org/wiki/Scottish_people. In short, they’ve run the majority of Scottish people off of their indigenous land only to destroy it with radioactive discharges – mostly legal for now.
The Emigrants statue in Helmsdale, Scotland, surrounded by mist at the base of the Highland Mountains, red enhanced
The Emigrants statue in Helmsdale, Scotland, red enhanced

For nuclear reactor cooling: Seawater passes through drum screens to filter smaller marine debris from the supply to the pumps downstream. The drum screens are actively cleaned via a seawater spray system to remove debris from the screen plates themselves to prevent blockage, this feature was challenged in August 2006 by seaweed (TOR01724N) and again in June 2011 by build up of jelly fish (TOR01855) which had to be manually removed and which, on both occasions, led to a trip of the reactor. The first of the drum screens was replaced in 2007 with the last of the four being replaced during this outage.” http://www.onr.org.uk/pars/2012/torness-4.pdf

In October of 2015: “The LC25 inspection examined operational records related to sea defences, groundwater borehole measurements and reactor power reduction or trip due to seaweed ingress. We noted that good local weather information is available at Torness, and suggested that Torness should consider trending these data to improve the accuracy of the design basis for external hazards. On the basis of the records sampled, we considered an IIS rating of 3 (adequate) against LC25 to be appropriate.
http://www.onr.org.uk/intervention-records/1516/torness-15-103.htm

It seems to be a concern for Hinkley Pt. Nuclear Reactors too, including the proposed one: http://www.onr.org.uk/hinkley-point-c/pre-construction-reports/onr-cnrp-ar-14-077.pdf

ONR was made aware on 1 June 2015 of the station’s decision to shut-down Reactor 3 due to severe ingress of seaweed concurrent with low tide; this ingress impacted upon the main cooling water system. The nominated site inspector’s preliminary enquiries confirmed the reactor had been safely shut-down, and safely returned to service.http://www.onr.org.uk/llc/2015/hunterston-b-2.pdf

Overnight on 23/24 May 2013 both Torness reactors were shut down due to the ingress of excessive amounts of marine debris (seaweed) into the station’s main cooling water inlet filtering systems… This investigation has also listed a number of corrective actions to be undertaken, including the review and proposal for marine defenses focused on preventing a recurrence of this type of event. The ONR site inspector will monitor progress against the closing out of these corrective actions. The ONR site inspector has also raised this matter as a regulatory issue and he will manage progress via the ONR issues data base.” http://www.onr.org.uk/llc/2013/torness-2.pdf

Shutdown after sea-water intake blockage by jellyfish – June 2011
On 28 June 2011both reactors were manually shut down due to reduced flow of sea water at intakes by a large mass of jellyfish.
“. https://en.wikipedia.org/wiki/Torness_Nuclear_Power_Station

Jellyfish force nuclear plant shutdown in Sweden
Tonnes of jellyfish clog pipes that bring in cool water to the plant’s turbines”
Posted: Oct 01, 2013 6:41 PM ET
“It wasn’t a tsunami but it had the same effect: A huge cluster of jellyfish forced one of the world’s largest nuclear reactors to shut down — a phenomenon that marine biologists say could become more common”
http://www.cbc.ca/news/world/jellyfish-force-nuclear-plant-shutdown-in-sweden-1.1875316

In 2013, “Various information sharing sessions were held which focussed primarily on the stations response to a series of vacuum maintaining unit (VMU) faults and a seaweed ingress event which occurred on 23 May 2013. The station has conducted its own investigations into both of these issues and I was generally satisfied with the corrective actions proposed. The nominated site inspector and I did make several observations regarding the seaweed ingress event requesting further consideration of how the station can improve its response to such an event, for example by taking earlier pre-emptive measures. During the inspection the station accepted these observations and committed to put in place suitable additional measures to address ONR’s observations. Following the ONR inspection the nominated site inspector received written confirmation of the proposed actions to address the observations which we judged to be satisfactory.http://www.onr.org.uk/intervention-records/2013/torness-13-006.htm

Torness (Two Advanced Gas-cooled Reactors)
3.35. On the 2 August 2006 a significant amount of seaweed caused a complete blockage of the main cooling water intake drum-screens. The event resulted in supplies of cooling water being impaired and both reactors being promptly shut down. The station took corrective action to improve the plant material condition, review and revise station procedures and provide additional training for staff responding to similar events in the future.

http://www.onr.org.uk/cns4.pdf

Complete blockage by seaweed of the main cooling water intake drum-screens is an initiating event considered in the Station Safety Report (SSR). The event resulted in supplies of main cooling water being lost for a period. As a consequence, water supplies to the reactor seawater (RSW) system, which provides a safety role, were lost for a time on one reactor and restricted on the other. The station responded to the event by shutting down both reactors within 70 minutes of receiving the first indication of impaired main cooling water flow and provided adequate post trip cooling.” (2006 report-link dead: https://en.wikipedia.org/wiki/Torness_Nuclear_Power_Station

Seaweed shuts down reactor at Leningrad nuclear plant
ST. PETERSBURG – Seaweed caused almost three days’ downtime at Unit 3 of Leningrad Nuclear Power Plant (LNPP), on the Gulf of Finland, near St. Petersburg, after a storm blew bay bottom sediments into the plant’s water intake structures, clogging the intakes that supply water to the unit’s cooling system. The blockage had to be manually removed before the reactor could resume operation.

http://bellona.org/news/nuclear-issues/2015-10-seaweed-shuts-down-reactor-at-leningrad-nuclear-plant

What do they cool the nuclear reactor with when it is blocked? Even after shutdown the nuclear reactor must be cooled. In the case of the AGRs ( e.g. Torness-Hunterston B):
As with all nuclear power stations after shutdown and fault-initiated trips the fission products still undergo radioactive decay and continue to release heat (decay heat) even after fission. Post-trip heat removal systems are provided to removal the residual heat so as to prevent the fuel overheating and damage to the reactor structures. The main functions of these systems are to firstly circulate sufficient gas coolant to transfer the heat from the fuel and elsewhere to the boilers and secondly to provide sufficient feedwater to the boilers to enable this heat to be transferred to the environment. Note that AGRs are capable of using natural circulation to prevent overheating, provided the main boilers have feedwater available.

There are two main systems for post trip cooling: these systems are arbitrarily designated ‘X’ and ‘Y’ systems. The ‘X’ system is the preferred system for cooling when the reactor is pressurised. Heat is removed from the fuel by forced circulation provided by the gas circulators operating at low speeds. The heat is removed form the reactor coolant by the decay heat boilers, or which there are four, situated directly below and separate from the main boilers in the boiler annulus.

The ‘Y’ system is used if either de-pressurisation of the reactor occurs or if the ‘X’ system fails. Heat is removed by forced circulation provided by the gas circulators operating a high speeds to compensate for the lack of pressure. The heat is removed from the reactor coolant by the main boilers fed by the emergency boiler feed system.https://nucleus.iaea. org/sites/graphiteknowledgebase/wiki/Guide_to_Graphite/
General%20Design%20and%20Principles%20of%20the%20Advanced%20Gas-Cooled%20Reactor%20(AGR).aspx

EMPHASIS ADDED THROUGHOUT.

News Reports
https://dropping.theferret.scot/torness-reactor-shut-seaweed/
https://nuclear-news.net/2016/11/23/seaweed-causes-shutdown-of-nuclear-reactor/
EDF Letter: https://assets.documentcloud.org/documents/3224121/Torness-Letter.pdf