ACR-1000 – the AECL Design

July 30, 2008 — David Jackson

Timing is everything – not only in comedy but also in life. I leave it to you to decide whether they are one and the same thing.

It’s unfortunate for AECL that the AP1000 and EPR are so far ahead of the ACR-1000 in their development. As noted in previous posts, EPR reactors are being built in Finland and France and construction of the first AP1000 design has just started in China with orders on the books from two US utilities.  It appears that the ACR–1000 design is not yet complete and the final design will not be ready for construction until 2012.

This timing means that there will be real construction and operating experience for both its competitors before construction even starts on the first ACR-1000.

This reactor will be heavy-water moderated and light-water cooled with a design power of 1,050 MW (electrical).  Precise details of the design are either not publicly available or haven’t been fixed yet.  For example, there is an optimisation process between the burnup (energy produced from a given quantity of fuel), CVR (void reactivity) and fuel enrichment (percentage of uranium in the fuel that is uranium-235).  In the past AECL has been reluctant about specifying an exact enrichment for ACR fuel.  I’ve heard 2.1% but I have also been told other numbers.

There are several design options that could be used to reduce costs and enhance performance compared to previous CANDU reactors. For example, it is likely that new fuel will be used. The CANFLEX fuel bundle has 43 fuel elements, instead of 37, and has been undergoing tests for several years. The elements have two different diameters and projections to improve the heat transfer into the reactor coolant. Using slightly-enriched uranium fuel will yield more power from each fuel channel giving a smaller reactor core and other reactor systems could also be scaled down. A smaller and simpler reactor should reduce maintenance and capital costs.

As noted in an earlier post, a CANDU 6 reactor requires 265 Mg (metric tons) of heavy water for its moderator and 192 Mg for its coolant, a total of 460 Mg per reactor. The ACR-1000 as currently envisaged will require 250 Mg, all for its moderator but none for its coolant which will be light water. This even though the ACR-1000 has significantly higher output power, 1050 MW (e), versus an average of 640 MW (e) for the CANDU 6. This again represents a substantial capital cost reduction.

However, like its CANDU predecessors, the ACR-1000 will require replacement of its pressure tubes after thirty years.  This would extend its life by another 30 years but still would require a major expenditure even if the projected one year time frame for refurbishment could be maintained.   

The ACR-1000 has the possibility to be an excellent next step in the evolution of the CANDU design. We will only know when the first ACR-1000 is built and operated.

Privately many familiar with the Canadian nuclear industry dismiss the ACR-1000 as a viable contender for Ontario’s new reactors simply because it is so far behind its competitors. I think that’s a shame on patriotic grounds even though Canadians generally don’t like flag waving. On the other hand, as a citizen of Ontario who fully expects a reliable and sufficient electricity supply I would be very nervous about staking the future on the success of the ACR-1000.      

 

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AP1000 – the Westinghouse Entry

July 14, 2008 — David Jackson

“You can be sure if it’s Westinghouse”

The old advertising slogan from the 1950’s still contains a grain of truth. However, the Westinghouse of today is very different from the old company with several changes of ownership over the intervening years. At the moment the majority shareholder of Westinghouse Nuclear is Toshiba who purchased it from British Nuclear Fuels in 2006 who had purchased it from CBS in 1996 and so on.

Nevertheless, Westinghouse in its various incarnations can claim to have designed or built about half of the world’s nuclear power plants including many now operating in the US, France and Japan, an impressive record.

The AP1000 is a pressurized water reactor (PWR) moderated and cooled by light (normal) water using enriched uranium fuel.  It belongs in the same class of reactors as the AREVA EPR but with a net electrical power of 1100MW compared to 1600 MW of the EPR.

Personally, I find a lot to like in the design philosophy of the AP1000. The designers to the extent possible use components already tested and operating in existing reactors. In addition to having established suppliers, this also facilitates experience-based prediction of the operational characteristics of these components, information critical for convincing Probabilistic Risk Assessment of system safety. This key factor accounts for the AP1000 design being so far along in the US and European licensing processes.

Another design emphasis is on making the reactor simpler that its predecessors. For example, the AP1000 claims to use 50% fewer safety-related values, 89% less piping, and 85% less cabling.  That appeals to me on the grounds that the fewer components there are, the less there are to go wrong. Both Maintenance and construction should be easier.  

The AP1000 incorporates several “passive safety” features meaning that the reactor can make use convection and other natural phenomena to deal with accident scenarios. This used to be called “inherent safety” but this expression to my mind in the same class as “unsinkable ship” has thankfully passed into history as has the Titanic.

As noted elsewhere on this blog, Westinghouse has concluded a deal for two AP1000 reactors for South Carolina. Construction in China on the first AP1000 started in February this year. It is being constructed by a Chinese utility using technology transferred from Westinghouse and is expected to go into operation in 2013. This is an impressive schedule and it remains to be seen if the reactor can be built on time and on budget.

There was a rumour around a few months ago that Westinghouse was less interested than it might be in the Canadian market because it wished to concentrate on the US market. The forgings shortage and the fact that they were the only reactor vendor to show up at the Polish Engineers in Canada session in spite of the Ontario government gag order have been mentioned in support of this speculation.  I hope the rumour is false because from what I know at this point the AP1000 looks to be an excellent reactor.

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The AREVA EPR– the French Reactor

July 6, 2008 — David Jackson

The AREVA EPR is one of the three contenders listed in the Ontario RFP and perhaps, a candidate for the reactors under discussion in Alberta and Saskatchewan and maybe for new reactors at Bruce Power if that occurs.  The second New Brunswick reactor will undoubtedly be an AECL product, most likely the first ACR-1000 but I can only hope they will choose an EC-6.

So what does EPR stand for? Well strangely enough it means one thing in Europe (European Pressurized Reactor) and another in the US (Evolutionary Pressurized Reactor) although apparently they are talking about exactly the same reactor design.  Apparently, the AREVA marketing department has concluded that confusion might still arise and they push the expression “US EPR” to drive the point home that their reactor is not merely a European artefact. It’s not clear what they believe is the best name choice for Canada.  

That may be typical of government owned companies. Well over 80% of AREVA is owned by the government of France with some minority interest by Siemens and others.  From recent episodes concerning takeover bids for other companies and the recent announcement of a second EPR for France, it’s clear that the CEO of AREVA takes direction on important issues directly from the President of France. One would think that fact alone might hamper AREVA’s reactor sales in the United States but probably not in Canada where we are more accustomed to state-owned companies such as AECL for example.

Most of the power reactors in France are actually Westinghouse designs but the last four French reactors completed by 2000 were designed by Framatome (since absorbed into AREVA) and form AREVA’s main experience in reactor design with a lesser contribution from Siemens experience with German reactors in the more  distant past.

The EPR is a light (ordinary) water reactor using it both for moderation and coolant. Its fuel is enriched uranium with up to 5% uranium-235. In those respects, it is generically similar to its Westinghouse rival, the AP1000. However, one area in which it is very different is its power output, 1,600 MW (e) (electrical) compared to a powers of about 1,100 MW (e) for the AP1000 and 1,050 MW (e) for the AECL ACR-1000. The EPR is a more powerful unit than its rivals which is advantageous in terms of brute power production but could be a disadvantage in flexibility for deployment on the Ontario grid where an EPR would roughly be the equivalent of two Darlington reactors.

In my opinion the design appears to have become overly complex by attempting to address a great many issues at the same time. For example, it has a complex containment system consisting of a steel shell attached to a concrete shell presumably to harden the reactor against an aircraft strike. By now even the least sophisticated terrorists have realized that driving an aircraft into a reactor containment structure is unlikely to lead to the havoc they would wish to create. In some sense the old aphorism that   “generals always prepare for the last war” seems to apply to the EPR.

To counter an accident in which a hot reactor core of molten fuel might burrow into the earth, the notorious “China Syndrome”, the EPR has a “core catcher” consisting of a concrete basin specially designed to prevent this happening. Other features are separate compartments for the heat transport (coolant) pumps and a pool of water at the base of the reactor.

It seems that these special features may have caused some of the delays and cost overruns experienced during the construction of the first EPR at Olkiluoto, Finland which is already 25-50% over budget and more than two years behind schedule. Problems in welding the steel containment shell and pouring concrete to the required specifications for the core catcher are reported to have been problems.  The second EPR being built at Flamanville Normandy is also having some construction problems but apparently less severe than in Finland showing that AREVA is well on the learning curve.

Difficulties in constructability are just one class of the teething problems to be expected in bringing any new complex engineering design into operation and probably will be typical of all three of the so-called Generation 3 reactors under consideration in Canada. The AREVA projects are simply the furthest along whereas the first AP1000 has just started construction and the ACR-1000 has at least another four years to go before a construction start can be made. 

Although I have my own personal misgivings, the EPR would likely prove to be an adequate reactor for use in Canada.

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