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 Post subject: " Candu still can do "
PostPosted: Jul 28, 2010 9:25 am 
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A plug for CANDU-thorium near the end of this article....
Quote:
Candu still can do;
Don't throw out the valuable Candu baby with the AECL privatization bathwater

National Post, 28 July 2010
Jan Carr
Financial Post
Canadians have a lot riding on the impending privatization of Atomic Energy Canada Ltd. (AECL). We need to wind down our ownership in a fashion that ensures we continue to benefit from AECL's unique CANDU technology and that requires distinguishing the institutional history of the nuclear industry from its accomplishments and potential.
It is hard to imagine a more difficult company for shareholders to love than AECL. It has been dogged by a long and continuing series of commercial disappointments from cost overruns on power plants to spectacular failures in the production of medical isotopes. It has become a thorn in government's side through its sometimes ill-timed requests for substantial funding. But much of this results from flaws in AECL's mandate and the way it is financed.
The common element of the cost overruns is that they all occurred in Canada, while AECL projects overseas have been completed early and under budget. It is reasonable to ask therefore whether the Canadian model of having provincially owned utilities using public money as the developer-owner of nuclear power stations is part of the problem. After all, these same utilities encounter similar scheduling and budget problems on non-nuclear projects, such as the delays and almost doubling in cost of the new diversion tunnel now under construction at Niagara Falls.
The medical isotope business clearly has problems bigger than AECL. While Chalk River's 50-year-old reactor has accounted for half the world's isotope supply, it should be noted that the other half came from reactors that are just as old. The price of medical isotopes on the world market must be unsustainably low -- what else can explain several decades of no investment in new production facilities anywhere in the world? Somehow in the distant past, AECL seems to have got stuck in the role of a charity -- subsidizing the cost of half of the world's nuclear medical procedures, courtesy of Canadian taxpayers.
There are problems of AECL's making, to be sure, but many for which it is blamed result from the environment in which it works. It has a dysfunctional corporate structure -- basically that of a government department attempting to undertake three disparate businesses. AECL's responsibilities include operating a public research laboratory, manufacturing medical isotopes and engineering electrical generating equipment, all within a budgeting process synched to government, and not business, timetables.
Institutional issues can be fixed through reorganization and privatization, which the government has committed to doing, by splitting off the power reactor business from the balance of AECL and privatizing it under the working name of CANDU Inc. This business has significant potential for Canada's industrial and economic policies, and also our standing in the world as a nation contributing to global peace and stability.
CANDU Inc. anchors an industry of some 150 individual companies collectively employing 30,000 people. This is the Canadian nuclear industry -- a major employer of skilled men and women that is already in place and includes not only prized manufacturing jobs, but also encompasses the high-tech and knowledge industries in which we see our future. While some of these companies and jobs could survive the migration of CANDU Inc. overseas, more will be gained by privatizing in a fashion that keeps the anchor company here at home.
AECL's unique reactor technology provides Canada with geopolitical leverage that supports all our instincts as a nation that works for global harmony. CANDU nuclear technology is less fussy than others about the type of fuel it uses. Its usual fuel is natural uranium, which avoids the need for the nuclear enrichment process all other reactor designs require. Enrichment is the key step en route from peaceful nuclear uses to military uses and is central to international non-proliferation efforts. CANDU technology facilitates the use of nuclear energy in a way that does not enhance military involvement and in so doing reduces polarization in global politics.
CANDU reactors can also be designed to use thorium instead of uranium. Compared with uranium, thorium is more plentiful and more evenly distributed throughout the world. Chasing scarce and distant oil to fuel local economies has contributed to many armed conflicts and much international friction. India and China in particular have large quantities of thorium that might allow those enormous and rapidly developing economies to meet some of their burgeoning energy requirements from local non-emitting sources. Indian and Chinese success in this can only have a positive impact on global security in the decades ahead.
Canada's nuclear technology is an asset that can benefit the world while contributing to our national industrial and economic strategies. For this to happen, AECL needs to be reorganized and privatized in a thoughtful and strategic manner, and not in frustration by a disenchanted owner.

Jan Carr is a corporate director and former chief executive of the Ontario Power Authority.


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PostPosted: Jul 28, 2010 12:28 pm 
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Besides the reorganization suggested, the AECL should look at AHWR300-LEU. The fuel concept is an eye opener. Th-20%LEU can be a high burn up fuel for all solid fueled reactors.
After a long time interest by South Korea and Canada, it is the Chinese who are using the DUPIC technique.
The Canadians should also borrow, use and return the US SNF after using it in a set of CANDU reactors along the 48 latitude and sell the power to the USA.


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PostPosted: Jul 29, 2010 11:03 am 
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I personally love the CANDU reactor and wish we had some in the United States.

DUPIC is only part of what these reactors can do.


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PostPosted: Aug 02, 2010 8:43 pm 
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NNadir, are there any cheap tweaks that can be done to the existing base CANDU design (a la loading RMBK reactors with SEU instead of NU) to reduce its void reactivity below zero and thus make it legal to build south of the border?

I think the main attraction of DUPIC in the People's Republic of Soviet Yankeestan would be the 'no net "waste" production' aspect - am I barking up the wrong tree?

What else can CANDU do? (time to groan at the lame pun :lol: )

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PostPosted: Aug 02, 2010 10:32 pm 
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Alex Goodwin wrote:
NNadir, are there any cheap tweaks that can be done to the existing base CANDU design (a la loading RMBK reactors with SEU instead of NU) to reduce its void reactivity below zero and thus make it legal to build south of the border?

I think the main attraction of DUPIC in the People's Republic of Soviet Yankeestan would be the 'no net "waste" production' aspect - am I barking up the wrong tree?

What else can CANDU do? (time to groan at the lame pun :lol: )


I would direct this question to Jaro, who started this thread. He (or she) is far and away the expert on heavy water moderated reactors here.

My first guess would be "add plutonium." (One can see more here: Positive Void Coefficient, CANDUs.)

I'm a fan of plutonium of course, not that this makes me a bad guy. Other things make me a bad guy.

CANDU's are known for producing low burn-ups, but MOX/Th might make for a whole other situation being obtained.

However as I understand it, the type of cladding used currently, and the lack of a significant plenum in the fuel rods, draws some limitations to burn up.

But again, Jaro is the expert here on CANDUs and prehaps he or she will respond in better detail


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PostPosted: Aug 03, 2010 5:25 am 
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What the hell, let's have a bang at it.

Jaro, how would the dupic cycle alter the CANDU's void coefficient?

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PostPosted: Aug 03, 2010 12:14 pm 
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Alex Goodwin wrote:
how would the dupic cycle alter the CANDU's void coefficient?

Definitely in a good way -- ie. reducing it significantly.

The details are spelled out nicely in Jeremy's FAQ post, referenced by NNadir:
NNadir wrote:
My first guess would be "add plutonium." (One can see more here: Positive Void Coefficient, CANDUs.)

As stated in the linked text, in addition to Pu, an increase in U enrichment above natural level (NU = 0.71% U235) has a similar effect.
The U235 content of LWR SNF varies between 0.8% to 1.0% (by weight) -- this would end up in the DUPIC fuel, along with about 0.8% fissile Pu (or ~1.15% total Pu).

I would also add that there has been much interest in the potential capital-cost reduction by replacing the D2O coolant with H2O and by reducing the overall inventory of D2O (such as by using a smaller lattice pitch and overall calandria size).
This is much tougher to achieve, since the void coefficient with H2O coolant in the fuel channels can be a lot worse, than the classic CANDU design (as a numerical example, the void reactivity of a standard CANDU lattice, 28.575 cm pitch, with H2O PHT, is +70 mk, whereas going from NU to SEU only reduces that to about +67 mk; ....by contrast, reducing lattice pitch from 28 cm to 20 cm reduces void reactivity to ZERO, with the same fuel channels etc.).

From "Reactor Physics of NG CANDU" by Chan, P.S.W., Tsang K.T., Buss, D.B. (Proceedings of the Twenty Second Annual Conference of the Canadian Nuclear Society. Toronto, June 2001) :
Quote:
4.0 Comparison of NG CANDU with Other Reactor Designs
Figure 3 compares the NG CANDU reference lattice with the NU CANDU lattice, the
Japanese FUGEN reactor lattice, and the UK SGHWR lattice. The NG CANDU, the FUGEN
reactor and the SGHWR are all channel-type reactors that use H2O as coolant and D2O as
moderator. FUGEN and SGHWR are vertical reactors with boiling H2O coolant. NG CANDU
is a horizontal reactor with pressurized H2O coolant. All three reactor-designs suppress the
coolant-void reactivity by reducing the moderator-to-fuel volume ratio. Furthermore, all three
designs use relatively large calandria tubes to fine-tune this ratio.
FUGEN and the SGHWR use different methods to achieve slightly negative coolant-void
reactivity. The SGHWR used interstitial floodable moderator-displacing tubes to achieve a very
low moderator-to-fuel volume ratio at a relatively large lattice pitch of 26 cm. FUGEN uses
Mixed Oxide (MOX) fuel, with sufficient plutonium content to give a slightly negative
coolant-void reactivity at a lattice pitch of 24 cm
.


In more general terms, an inherent reactivity characteristic of CANDU reactors is a positive void reactivity coefficient, which leads to a power increase following a large LOCA.
For comparison, light water reactors are susceptible to reactivity increases when the coolant density in the reactor increases. This effect can occur if a pipe breaks on the secondary side of the steam generator in the case of a pressurized water reactor, or if steam flow out of the piping is suddenly interrupted in the case of a boiling water reactor.
The discharged secondary side coolant removes heat and causes the primary reactor coolant temperature to decrease, resulting in a power increase due to the negative coolant temperature coefficient.
The rate of power increase is governed by the rate of coolant expulsion, which depends not only on the size of the pipe break but also on the assumptions regarding the closure of fast-acting main steam isolation valves and the shutoff of feed-water to the steam generators. Modern light water reactor analyses assume that both of these beneficial actions take place. If they did not, the speed of the calculated positive power transient would be significantly higher.

Another inherent characteristic of CANDU design is its longer neutron lifetime.
CANDU reactors have a small power coefficient. As a result they can be shut down easily and quickly by small changes of control absorber level.
In contrast, light water reactors have a large power coefficient and so require a large amount of control movement to render the reactor safe after a postulated initiating event (or PIE, as defined in IAEA Safety Standard NS-R-1)

The Doppler effect (decreased power change rate due to increased fuel temperature) is very important in limiting power changes if the prompt neutron lifetime is short as it is in a light water reactor, and less important if the prompt neutron lifetime is long as it is in the CANDU system, thereby allowing more time for control response.
Doppler feedback is the only effective means of controlling power rise in a light water reactor if reactivity exceeds the “cliff-edge” of prompt criticality. …..due to its long neutron lifetime, a CANDU reactor is not nearly as sensitive to this condition, since engineered control action is still effective within a limited range above prompt criticality.


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lattice_configurations_of_HW_reactors_NU-NG-Fugen_SGHWR.jpg
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PostPosted: Aug 03, 2010 8:27 pm 
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In the AHWR design, the positive void coefficient is balanced by part use of Th-Pu fuel. In the LEU version, the Th-19.75%LEU fuel is recommended. These tricks could work for CANDU/PHWR too. The latter fuel will give a high burn up too. LEU requirement in PHWR will be lower than 22% of AHWR due to higher neutron economy. Light water could be used as coolant with 22% LEU.


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