Update to SSG and residents from Dungeness B
We recognise the importance of keeping local communities updated with activities at our power stations, and following some noise caused by one of our reactors coming offline we wrote to residents of Dungeness and members of the Site Stakeholder Group to apologise and let them know the reason why.
Please find a copy of the letter below.
Dear Dungeness resident,
I would like to apologise for any disturbance you may have experienced as a result of Reactor 21 coming offline at 00.00 Thursday morning.
The reactor came offline, which means it stopped generating power, due to an issue with a conventional valve as we were raising the power levels from the planned refuelling outage. As a result steam was released from the vents (the steam is from pure water) which can make a loud noise. This can sometimes be alarming for people not familiar with nuclear power station but it is perfectly normal and expected. I would like to stress that the reactor shut down and cooled safely, which is our overriding priority when a reactor goes offline.
I’ve included a short explanation of why the steam being released creates a noise below. And our doors are open to any member of the public who wishes to take a tour and learn more about how nuclear energy is generated.
Please do not hesitate to contact me should I be able to provide any further information, and I apologise again for the noise during the night.
Martin B Pearson
Why is steam released and why does it create a noise?
All power stations use a source of heat to turn water into steam. The steam is used to turn a turbine which generates electricity. In nuclear power stations the heat is created from the fission reaction inside the reactor.
When we stop the fission reaction, i.e. when the reactor is shut down, the steam is no longer used for generation and so is exhausted via the safety relief valves. There is a loud noise due to the large volume of steam escaping, like a kettle boiling but on a much bigger scale.
Instead of the steam rotating the turbine, it builds up until there is enough pressure to open the safety relief valves. The steam pressure is over 162 bar (=2350PSI) to open the valves. To put this into context – average car tyre pressure is 32 PSI, so the pressure is over 70 times that in a car. Atmospheric pressure is around 15 PSI so it is about 160 times greater than atmospheric pressure. By the time the steam comes out, the pressure has dissipated so it will be about the same as atmospheric pressure.
If a reactor trips at full load, that means it was generating 550MW (around enough for 750,000 homes), so sometimes the steam release can take a while for all the steam to discharge.
Afterwards, the reactor continues to cool down. We then enter what is known as a “shutdown state” until we are ready to start up again.