Friday, 15 October 2010

Oldbury visit part two

Continuing on with some more on the recent tour of Oldbury nuclear power station that I recently participated in. If you missed part one please take a look here.

The next part of the power station I want to discuss I find particularly interesting. The reactor pressure vessel. It is actually constructed of pre-stressed concrete. I believe this was the first reactor to be constructed in this way. The approach seems to have been very successful as Oldbury's sister reactor Wylfa was also constructed using this method as were the later AGR (Advanced Gas Cooled Reactor) designs.

In the image below you can see one of the areas known as a stressing gallery. What you can see here are the ends of the steel pre-stressing "tendons" as they emerge from within the concrete of the reactor pressure vessel.

Upper stressing gallery  (Photo Credit: Magnox North Ltd)

What the photograph does not show is how hot it was here! It felt to be at least 35 degrees C. A member of staff mentioned that it had been as warm as 47 degrees in recent days in this area. It's not surprising considering this is as close as somebody can get without actually being IN the reactor core.  

It may be helpful to refer to the cutaway drawing of  the similar Wylfa reactors. The cutaway and 104 others can be found at the New Mexico Digital Collection. Even if you don't take a look at the cutaways now I urge you to bookmark it for later as they really are an excellent way to get a good feel for the layout of various reactors.

Next up on the tour was the spent fuel pond. Once fuel elements have completed their stay in the reactor they require many months of cooling as the continued decay of fission products produces heat. Used fuel elements are removed from the reactor core and transferred down into the fuel storage pond. This is done via various chutes which deliver the fuel elements to the fuel pond area of the facility.

Fuel storage pond  (Photo Credit: Magnox North Ltd) 
Following a storage period in the fuel ponds the fuel elements are loaded into specialized fuel transport flasks and sent off site for disposal/storage. These flasks are rather large and are very well shielded.

Fuel transport flask  (Photo Credit: Magnox North Ltd) 

The final area of the tour was a gas recirculator hall. The Magnox type reactor (as are the newer AGRs) are cooled with Carbon Dioxide gas. Large fan like circulators are used to maintain an adequate flow of coolant gas throughout the core. Unfortunately I cannot locate any images of the circulators or the drive motors. I will attempt to locate some more information on the gas circulators. Needless to say this area was also fairly warm but was very noisy due to the circulator motors.

It's worth remembering that these reactors were operating before humankind set foot on the Moon. Thinking of the lifespan of these reactors in those terms really puts in perspective the kind of things that have already been accomplished with nuclear power.

Lookout for details of my visit to the Imperial College London CONSORT research reactor facility and a look at a very interesting future reactor concept in future posts.

Tuesday, 5 October 2010

Oldbury visit part one

Oldbury Power Station  (Photo Credit: Magnox North Ltd)

I was recently fortunate enough to participate in a tour of Oldbury nuclear power station.

Commissioned in 1967 I believe that Oldbury is the oldest serving nuclear power station in the world (if not the oldest operating power plant in the world?).

Oldbury along with its sister reactor Wylfa on Anglesey are unique among currently operating reactors. In particular Oldbury was the first reactor in the world to have a prestressed concrete pressure vessel.

The heart of Oldbury is its two gas cooled (by carbon-dioxide), graphite moderated reactor piles. These of course exist for the sole purpose of heating the coolant gas so it can pass through boilers (which are actually located within the reactors pressure vessels) and produce steam for the business end of things, the turbines.

Both of Oldbury’s turbines are located in a single large turbine hall. This is first area that I was shown on the tour of the plant.

Oldbury turbine hall
(Photo Credit: Magnox North Ltd source)

Sadly photographs of the site were not permitted so I will have to fill in with publicly available resources. There is an excellent panoramic view of the turbine hall found here. What you can’t see in the panorama that you can see on the photograph above (apologies for the small size!) is that the turbines and generators are located above the ground level of the hall. This creates a split level arrangement that allows pipework etc to come up from below ground level to the turbines.

The turbine hall itself is not adjoined to the reactor buildings so the steam pipes come via underground service tunnels.

Aerial view of site with Turbine hall and reactors highlighted.
(Photo Credit: Google Earth)

The level of noise inside the turbine hall was incredible despite only one turbine operating at the time. We were of course wearing hearing protection but it was still fairly loud despite this. Another immediate impression was that despite the age of the plant and that it clearly was 1960s equipment everything appeared to be very well maintained and in extremely good condition. I was very surprised by the very high level of cleanliness.

Next stop was into the reactor buildings proper.

Prior to entering this area staff are required to collect and wear a very modern personal dosimeter. These are electronically booked out with a personal pin code. I presume that this forms some kind of automated dosage monitoring and probably allows all kind of exposure statistics to be produced.

We took a lift to pretty much the top of the reactor buildings and were given of an overview of the site. The exact spot can be seen here.

I was the shown the refuelling control room where the giant fuelling machine is driven. As the reactor core is under pressure (around 24 bar), the refuelling machine needs to operate at the same pressure to permit refuelling.  

The refueling machine at Oldbury.
(Photo Credit: Magnox North Ltd)

The refuelling machine runs along rails so that it can position itself on the pile cap in order to access the reactor below. The top of the reactor pile begins 12 meters below the pile cap as can be seen in the image below (it’s the open white tiled area). Also note how clean everything looked. It really does look this good in person!

Reactor pile cap. The refueling machine is also seen to the left of the image.
(Photo Credit: Magnox North Ltd)

The MAGNOX fuel elements are stacked 8 rods high inside the the graphite core and each element/rod is around 1 metre in length and are perhaps 3-4 centimeters wide (excluding the fins). This is quite a contrast to say fuel assemblies in a modern water cooled reactor which consist of bundles of dozens of thin rods. Un-enriched uranium metal fills each element.

Each reactor contains approximately 26,000 MAGNOX fuel elements within 3308 graphite channels. Fuel elements often spend many years in the reactor with some elements reportedly have been in the core for upto 13 years.

The MAGNOX name comes from the material that the uranium fuel is encased in. Essentially a non oxidising Magnesium alloy hence the name Magnesium Non-Oxidising (or MAGNOX).

The refuelling machine extends a ‘grabber’ down into the graphite pile that grabs the top of a MAGNOX fuel element. Note in the image below you can see an indentation at the end of the fuel element. The other end of the element is somewhat pointed so it fits into the indentation on the rod above.

Example of a typical MAGNOX fuel rod.
(Photo Credit: NDA Insight Stakeholder newsletter)

The image below shows an Oldbury MAGNOX fuel element shown inside a graphite block representative of what is found in the Oldbury reactor. The fins not only provide a larger surface area for heat transfer but also position the element within the graphite channels within the reactor. This permits the CO2 gas to circulate past the element.

Oldbury MAGNOX fuel element in graphite brick.
(Photo Credit: Prof. B Marsden, University of Manchester, NGRG)

As seen below thousands of graphite bricks were assembled to form the reactor pile.

Oldbury graphite pile during construction.
(Photo Credit: Prof. B Marsden, University of Manchester, NGRG)

Finally for this installment at least I must mention the visitors room at the plant. Still on site is a room with various educational displays and a fantastic 3D plastic model of the reactor. This room was used to educate visiting groups of school children on the basics of nuclear fission and how the power station operates. The room had some great large child friendly fission graphics all over the floor and i’m sure any inquisitive child would have enjoyed them. It was a little sad to see it dormant as school tours are no longer permitted post 9/11.

This makes me consider the wider aspect of educating and inspiring school children about this sort of thing.

That’s about it from my Oldbury visit for the moment but I shall write some more in the coming days.

Rather than reproducing various facts and figures here I direct you you to the operators site here.

Last but certainly not least, a big thanks to the friendly and super professional folks at Magnox North who took the time to provide the tour and make it possible. 

Saturday, 2 October 2010

Upcoming visit to Oldbury nuclear power station

Oldbury Power Station (Photo: David Bowd-Exworth)

 Next week I am fortunate enough to be participating in a tour of Oldbury nuclear power station. In the post 9/11 world, tours are not easily obtained so many thanks to the people at Magnox North who operate the site for this opportunity.

I will write in detail about the visit once it has taken place.

I have a number of things I want to ask during the tour however please get in touch via the comments section if anybody would like me to ask anything specific.

Being a graphite moderated gas cooled reactor it will be a real treat to see up close as, water moderated/cooled reactors are by far the more common type worldwide.

Oldbury is one of the first generation of UK power reactors and was commissioned in 1967. This power station is forty-three years old! To date its generated 122 TWh with an 81% load factor.

Let's think about this some more. This single facility for the last forty-three years has generated enough electricity to provide for the electrical needs of 2 million Britons; and it did it 81% of the time!

It has done this, quietly, safely and without emitting millions of tonnes of CO2 into the atmosphere.

If a forty-three year old power station can continue to generate safely in the year 2010, stop and consider what the third generation AP1000 and EPR (the two models that will probably be constructed here in the UK) will be capable of. I plan to write something of a summary comparison between the two reactor designs as they are both very interesting but very different in their design philosophies.