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PostPosted: Jan 22, 2014 11:13 am 
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India's nuclear establishment had decided a long time ago to go for domestically developed PHWRs, supplemented by imported LWRs.

Recently there has been a little noticed shift, a decision to develop and build 900 MW LWRs http://asian-power.com/project/more-new ... ar-reactor

The PHWRs have gradually been upgraded from 220 MW to 500 MW (deployed) to a series of 700 MW PHWRs (to be deployed shortly).

Wondering what the reasons are for the 900 MW LWR development. The decision would be a bit unusual.. most nations have decided to domestically build either LWR or PHWR (not both)... China and Korea having thrown in with LWR after evaluating and building a couple of CANDUs, while Canada continues with CANDUs.

There are two possible reasons I can think of. What do others think? Here are my musings:

1. Limitation in scale-up capacity of PHWR: the largest PHWR built has been Darlington CANDU 880 MW. In contrast Russia's VVER is rated at 1000 MW and other LWR designs deliver 1200 MW (possibly even 1600 MW)

Is it possible that after delivering a 700 MW PHWR, India has decided it'd be too difficult or impossible to scale above 900 or 1000 MW for the future? Is there any financial or technical reason that would render the development of a 1000 MW or 1200 MW PHWR impossible or difficult.

2. A desire to replace a few of the expensive imported LWRs with cheaper domestic LWRs. But even then, why? Wouldn't it be so much easier to scale up PHWRs, with which India has so much experience, rather than develop a new technology.

It seems very expensive and strange to build both types.


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PostPosted: Jan 22, 2014 12:52 pm 
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I suspect India changed directions when Canada stopped developing new generation CANDUs. If Canada doesn't support them, why should India?

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PostPosted: Jan 22, 2014 1:45 pm 
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rban wrote:
1. Limitation in scale-up capacity of PHWR: the largest PHWR built has been Darlington CANDU 880 MW. In contrast Russia's VVER is rated at 1000 MW and other LWR designs deliver 1200 MW (possibly even 1600 MW)

Is it possible that after delivering a 700 MW PHWR, India has decided it'd be too difficult or impossible to scale above 900 or 1000 MW for the future? Is there any financial or technical reason that would render the development of a 1000 MW or 1200 MW PHWR impossible or difficult.
Scaling up Candu reactors beyond about 900MWe does have problems.
For example, the length of the pressure tubes is limited by sagging, due to the horizontal layout.
More tubes can be added, but eventually that leads to pancake-type core geometry, with increasing operating neutron flux stability issues.

However, another way to increase size is by putting two separate cores inside a single containment building......


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PostPosted: Jan 22, 2014 2:47 pm 
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rban wrote:
It seems very expensive and strange to build both types.
India seems intent on developing its own nuclear submarine fleet, with LWRs for propulsion.
That is certainly very expensive.
One way to get some return on that investment is to also build civilian LWRs.

http://timesofindia.indiatimes.com/india/Reactor-of-Indias-first-indigenous-nuclear-submarine-INS-Arihant-goes-critical/articleshow/21737816.cms?intenttarget=no


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PostPosted: Jan 22, 2014 5:03 pm 
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jaro wrote:
rban wrote:
It seems very expensive and strange to build both types.
India seems intent on developing its own nuclear submarine fleet, with LWRs for propulsion.
That is certainly very expensive.
One way to get some return on that investment is to also build civilian LWRs.

http://timesofindia.indiatimes.com/india/Reactor-of-Indias-first-indigenous-nuclear-submarine-INS-Arihant-goes-critical/articleshow/21737816.cms?intenttarget=no



This is a very interesting possibility. Worth noting that every nation which has or wants nuclear subs has gone for LWR, while Canada, which has no major military ambitions, went PHWR.


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PostPosted: Jan 22, 2014 5:15 pm 
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KitemanSA wrote:
I suspect India changed directions when Canada stopped developing new generation CANDUs. If Canada doesn't support them, why should India?



Not likely. India's reactor development is independent of CANDU; Canada stopped CANDU development due to a slow anemic Ontario economy and bleeding of tech talent... India's growing economy and hunger for power puts the country in a very different category.

CANDU will die because Canada foolishly decided to sever ties with India after the nuclear test in the 70s, which effectively slammed the door on any joint development or CANDU sales/ license revenue from India's energy sector.

A classic suicidal case of Canada cutting off her own nose to spite her face. Only side that loses is Canada, India goes off and develops her own tech and doesn't get hurt one bit.

The hostility generated ensures India buys LWRs from Russia and possibly France/USA.... they don't trust Canada enough to buy CANDUs (who knows if Liberals come back to power some day and decide to teach India a lesson in 'morality'), despite much Canadian begging and groveling.


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PostPosted: Jan 22, 2014 7:39 pm 
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The reasons given might be valid, but the main motivation is fuel. India's uranium resources are limited. All new contracts for LWR include provision of fuel for lifetime. Fuel supply is also the profitable part of nuclear business. This is despite the US reneging on supply of fuel for Tarapore BWR's. But then the US has been above the laws since the WWII.
The Russian VVER is the most competitive PWR going till the Asians rivals come up. S Korea has won the contract in the UAE but not yet completed it.
Standardization of the last design of PHWR and not going up would be good for India if the fuel supply could be ensured. LWR's are, in the words of then chairman AEC, mere 'additionalities'. India has closed cycle policy like Russia and China and used fuel is processed for fast reactors. I only wish with it could be fast MSR;s.


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PostPosted: Jan 22, 2014 10:31 pm 
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jagdish wrote:
The reasons given might be valid, but the main motivation is fuel. India's uranium resources are limited. All new contracts for LWR include provision of fuel for lifetime. Fuel supply is also the profitable part of nuclear business. s.



Jagdish, but doesn't that mean development of domestic 900 mw LWR is unwise????

First, PHWR uses natural not enriched uranium and thus, for India with limited uranium, makes more sense than LWR.

Secondly, as you noted imported LWRs come with uranium supply guaranteed, but THIS WOULD NOT necessarily apply for domestic LWRs.

Your statement "All new contracts for LWR include provision of fuel for lifetime" would not apply unless LWR was imported.

So by building domestic LWRs, India is potentially saddling herself with reactors that require more uranium and have no guaranteed supplies of said uranium. What sense does that make???

UNLESS, as discussed, the inability to scale PHWR beyond 900 mw and also the commonality with LWRs for nuclear subs.is the real reason.


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PostPosted: Jan 24, 2014 8:23 am 
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The Candu concept has the advantage that the fuel elements can be changed during operation. Hence it is the ideal concept to produce a Pu or U233* usable for government purposes.

The LWR reactor vessel is a huge piece that requires a lot of manufacturing expertise. Actually there are only a few manufacturers of LWR reactor vessels. The CANDU reactor vessel is more complex but was able to become manufactured locally.

The Candu reactor works as well without enrichment and hence local mined uranium was used during the embargo.

I think this were the main reasons for India to build Candu reactors in the past.
------------------------------------------------------------------------------------------------------------------------
On the hand heavy water costs an awful lot of money. The reactor is bigger and more complex than a LWR. The lifetime of the reactor vessel is shorter. All in all the Candu is more expensive.

I assume that India has now sufficient Pu for government purposes and does not need new capacities.

India can follow the chinese example and hence indian manufacturer learn to make large pressure vessels to make their own PWR in the future.

All in all the development seems logical.

Holger

*233U is a nice material for governmental purposes. The main disadvantage is the 232U by product.


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PostPosted: Jan 24, 2014 1:11 pm 
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Sagging and such are hardly issues, just increase the number of spacers, slightly increase pressure tube thickness, etc. Very easy to do. Coal supercritical steam boilers use ridiculously long supercritical water tubing, all over the place. It makes CANDU look easy.

If any reactor is scaleable its a pressure tube reactor, and the economies of scale should scale up to much larger sizes than PWRs. With PWR at some point the vessel thickness and bulk becomes a very serious quality control and manufacturing issue, as well as containment issue. Pressure tubes avoid that. Break area stays the same, when a tube ruptures it acts like a pressure fuse so more than 1 tube rupture is not a plausible event with proper design.

Even refuelling machine duty could stay the same with slightly enriched fuel and flux would be much flatter producing more power per tube on average.

So I think it is quite strange that large pressure tube reactors aren't more popular.


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PostPosted: Jan 24, 2014 4:04 pm 
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Cyril R wrote:
Sagging and such are hardly issues, just increase the number of spacers, slightly increase pressure tube thickness, etc. Very easy to do
Spacers are used between the calandria tubes and the pressure tubes carrying the heavy uranium fuel bundles, to avoid contact between the tubes -- which was found to be an important factor in blister formation and eventual PT cracking.
There are no spacers between the calandria tubes, so the sagging of PTs is transferred to the CTs, and the whole core eventually sags.
Increasing PT thickness would probably mean increasing the CT size as well, if the same size gas annulus is to be maintained.
A larger CT size means less space between them for things like the liquid zone control rods, the shutoff rods, the secondary shutdown system injecting gadolinium nitrate, and all the reactivity instrumentation.
Basically the whole reactor would have to be redesigned.
Putting two cores next to each other in a single RB would not entail any significant core redesign - only some PHT layout and fuelling machine track adjustments.

If a core redesign is deemed warranted, then a better solution is to orient the fuel channels vertically, so as to do away with the sagging issue completely.
Doing that has a big impact on the fuelling system -- but is resolved if we change to fluid fuel.


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PostPosted: Jan 24, 2014 4:17 pm 
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HolgerNarrog wrote:
The Candu concept has the advantage that the fuel elements can be changed during operation. Hence it is the ideal concept to produce a Pu or U233* usable for government purposes.
No it isn't "ideal". Far from it:
The fuelling system works very slowly relative to the rate of fuel bundle transfer that would be required for weapons material production.
It has been theorized that a small part of a Candu core could be refuelled quickly by the existing system, to get the appropriate Pu quality.
But this sort of operation would eventually impact operation of the reactor as a whole, as the majority of the fuel is left unshuffled.
Besides that, it would significantly increase the required supply of fresh fuel, which would of course be a dead giveaway for unauthorized use, and quickly result in suspension of uranium fuel deliveries.
As a matter of historic record, no Canadian supplied Candu plants have been used for military Pu production, thanks to bilateral agreements stipulating IAEA inspections.


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PostPosted: Jan 25, 2014 4:57 am 
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jaro wrote:
Cyril R wrote:
Sagging and such are hardly issues, just increase the number of spacers, slightly increase pressure tube thickness, etc. Very easy to do
Spacers are used between the calandria tubes and the pressure tubes carrying the heavy uranium fuel bundles, to avoid contact between the tubes -- which was found to be an important factor in blister formation and eventual PT cracking.
There are no spacers between the calandria tubes, so the sagging of PTs is transferred to the CTs, and the whole core eventually sags.
Increasing PT thickness would probably mean increasing the CT size as well, if the same size gas annulus is to be maintained.
A larger CT size means less space between them for things like the liquid zone control rods, the shutoff rods, the secondary shutdown system injecting gadolinium nitrate, and all the reactivity instrumentation.
Basically the whole reactor would have to be redesigned.


I don't see it. The calandria tubes are really thin and could easily be a few millimeters thicker. A much tighter pitch is possible as shown by the ACR-1000, which means regular CANDU has no trouble at all. In fact most newer CANDU proposals use a thicker calandria tube to prevent calandria tube failure in case of a pressure tube leak.

Redesign in any case would be very modest, for example wire wrap to "web" the calandria tubes together, would be a very simple design change.

Quote:
Putting two cores next to each other in a single RB would not entail any significant core redesign - only some PHT layout and fuelling machine track adjustments.


Good point. Why is that not popular then?

I highly doubt that there are sound technical reasons why larger CANDUs are not more popular.


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PostPosted: Jan 25, 2014 4:59 am 
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The last CANDUs in Canada were built at a time when ~700MWe was a very respectable unit size.

There have been few built since apart from some plants in China and South Korea that appear to be economically operated technology testbeds and thus were built to be as similar to Canadian reactors as possible to reduce design risks.

ACR was proposing to move to 1000MWe unit size.


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PostPosted: Jan 25, 2014 1:10 pm 
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Cyril R wrote:
The calandria tubes are really thin and could easily be a few millimeters thicker. A much tighter pitch is possible as shown by the ACR-1000, which means regular CANDU has no trouble at all. In fact most newer CANDU proposals use a thicker calandria tube to prevent calandria tube failure in case of a pressure tube leak.
The ACR design was mainly to reduce costly heavy water inventory.
Besides reducing the calandria size by using a tighter pitch, it also changed PHT to light water and fuel from NU to LEU.
I saw a good deal of the design work and co-authored one of the many design reports (not reactor core related).
As noted earlier, the tighter lattice causes all sorts of problems: The ACR design had to scrap the liquid zone control system, since it would simply not fit between the calandria tubes. Control rods also had to be redesigned, along with the GdNO3 secondary shutdown system.
CAD studies showed that retubing of the ACR would be considerably more difficult than standard Candu, due to the tight lattice.
Finally, although the LEU fuel would provide higher burnup, the overall uranium utilization would be quite a bit lower than Candu NU.
The development work stopped when AECL was sold to SNC-Lavalin. Nobody is ever going to build an ACR.
Romania wants to build two more Candu-6's and Argentina has been talking about another Candu project for some time.
India's 700MWe PHWRs are - co-incidentally? - similar to the EC6 units built in China.


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