[ RadSafe ] What is a Travelling Wave Reactor?

Sun Mar 28 22:57:36 CDT 2010

All:

      From the available info about the TWR, one 
can make some ball-park calculations.  Some 
assumptions are necessary, because better numbers 
have not, to my knowledge, been revealed.  If 
anyone has better info, please come forward.

Fact 1:  In generating 1 GWe-yr of energy, any 
nuclear reactor necessarily fissions about 1 
tonne of heavy metal, creating 1 tonne of fission products.

Fact 2:  The TWR uses metallic fuel and is cooled 
by liquid sodium.  It is based on the technology 
of the IFR  (Integral Fast Reactor), developed at 
Argonne National Laboratory in the '80s and 
'90s.  In effect, the TWR is a very large IFR (in 
size, not in GWe) that forgoes reprocessing, 
storing its fission products in the used part of 
the core (behind the traveling wave).  This 
pushes the disposal problem perhaps 60 or more 
years into the future,  Unlike the IFR, the TWR 
does not completely burn its fuel, and leaves 
behind a mixture of transuranic actinides -- 
which perhaps eventually could be recycled (not clear).

Fact 3.  In commercial readiness, the TWR is at least a decade behind the IFR.

Assumption 1:  A TWR will operate  for the 
predicted 60 years without refueling.
      At the end of its life, therefore, it will 
contain 60 tonnes of fission products mixed in 
with 240 tonnes of heavy metal (uranium and transuranics) (see below).

Assumption 2:  No net breeding.
      Once started, a TWR will presumably create 
enough fissile material (Pu-239) to sustain 
itself throughout its useful life, but no net breeding potential is claimed.

Assumption 3:  The TWR will achieve a burnup of 25%.
      This is a guess, approximately what might 
be achieved in an IFR in a single pass.  (LWRs achieve 4-5%.)

Assumption 4:  The enrichment of the initial 
critical zone is 20% (i.e., it's 20% fissile).
      This too is a guess, based on the 20% enrichment that a normal IFR needs.

Assumption 5:  The initial fissile loading is 4 tonnes per GWe.
      This is still another guess, based on the 
approximate fissile loading of an IFR core.  (An 
IFR plant also has another 4 tonnes of fissile in 
the ex-core inventory, which a TWR does not have.)

      The above facts and assumptions lead to the following conclusions:

1.  The initial core loading will consist of 300 
tonnes of heavy metal (mainly U-238 -- or could 
be Th-232): 60 tonnes destined to be burned, plus 
240 tonnes that will be left over, unused, after 60 years (Assumption 3),
      Note:  An IFR core has about 20 tonnes of 
heavy metal per GWe, and another 20 tonnes or so in ex-core inventory.

2.  The initial 4 tonnes of fissile could come 
from three sources.  (a) It can consist of excess 
weapons Pu. (b) It can be Pu recovered from LWR 
spent fuel.  Or (c), it can be 20 tonnes of uranium enriched to 20% U-235.

(a) Weapons Pu.

      The United States has about 85 tonnes of 
weapons Pu, only part of which is declared to be 
"excess" 
(<http://fas.org/sgp/othergov/doe/pu50yb.html>). 
That would be enough to prime about 10 IFRs or 20 
TWRs -- a worthwhile contribution to the 
longer-term energy supply, but not a major one.

(b)  LWR Spent Fuel.

      The United States is projected to have 
about 85,000 tonnes of heavy metal (HM) in 
commercial spent fuel 
(<http://snipurl.com/v40kv>) by 2020, containing 
perhaps 680 tonnes of fissile Pu.  That would be 
enough fissile to start up 170 TWRs or 85 
IFRs.  For talking purposes, suppose either 170 
TWRs or 85 IFRs magically spring into existence 
in 2020, and no more fissile Pu comes from LWRs, 
and also assume for a moment that enriched uranium is not available.

      Now IFRs can breed, with a doubling time of 
less than 15 years, whereas TWRs do not 
breed.  In the TWR case, therefore, the nuclear 
capacity would remain at 170 GWe from 2020 
on,  The IFRs, however, would catch up in 15 
years, reaching 170 GWe by 1035, 340 GWe by 2050, and so on.

      Fact: Every tonne of fissile invested in a 
non-breeding reactor is a tonne of fissile 
unavailable for use in a reactor type that has growth potential.

(c)  Enriched uranium.

      When the supply of fissile from LWRs is 
exhausted, the growth of a non-breeding TWR fleet 
is over unless there is some other source of 
fissile material -- and then there's no fissile 
to get a fleet of breeders going either.  As of 
now, the only other carrier of fissile material is enriched uranium.

      To get the twenty tonnes of  20%-enriched 
uranium needed to prime a TWR, one must mine 800 
tonnes of natural uranium.  The global uranium 
reserves could support a growing TWR fleet for 
perhaps a century or more, but that would mean an 
expanding worldwide enrichment capacity, to the 
distress of arms-control advocates -- a capacity 
that could be reduced and eliminated much sooner with IFRs.

                                       *     *     *     *

      Postponement of reprocessing or waste 
disposal is not an obvious advantage, and brings 
with it eventually a significant extra 
waste-management effort.  The TWR seems to have 
no significant capability that is not shared by 
the IFR, and it has a number of inherent 
disadvantages.  Moreover the IFR is almost ready 
for prime time now, whereas the TWR development 
is about where the IFR was in 1980.  Yes, there 
are non-trivial technical issues.

      Will TerraPower sell enough TWRs to recoup 
Mr. Gates' investment?  I don't know, of 
course.  But the TWR's lack of breeding alone 
makes it look like a second-best product, even if 
it can be made to work as hoped -- one that would 
have no market at all but for official failure to 
permit the IFR to come to fruition.

      That's how I see it now.  Comments and better information welcome.

      --  George Stanford
      Reactor physicist, retired

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

At 03:34 PM 3/26/2010, Brennan, Mike  (DOH) wrote:
Content-Transfer-Encoding: base64

Like I said; non-trivial technical issues.

The fuel issue will be interesting, as I also 
wonder about 60 years.  I suspect that they are 
counting on the fuel being less fussy than for a 
LWR.  The US Navy already makes fuel that they 
project for a 20+ year life, so I won't say it is 
impossible to make fuel that will last longer.

I have to admit that liquid sodium is not 
something I would feel comfortable with.  I know 
it has some neat characteristics for fast neutron 
reactors, but still; the thought of a leak causes 
certain muscles to clench.  And I agree that 
leaving fuel bathed in molten sodium for 60 years could be problematic.

On the other hand, they undoubtedly will learn 
some very cool things along the way, whether they 
make it work or not.  And I would rather have 
them answering to Bill Gates than to Congress, as 
would be the case if the research were funded by the US Government.

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu 
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Franta, Jaroslav
Sent: Friday, March 26, 2010 12:07 PM
To: radsafe at health.phys.iit.edu
Subject: Re: [ RadSafe ] What is a Travelling Wave Reactor?

UNRESTRICTED | ILLIMITÉ

<quote>
According to this presentation by Gilleland, 
"operation of a traveling wave reactor can be 
demonstrated in less than ten years, and 
commercial deployment can begin in less than fifteen years." <end quote>

This sounds awfully optimistic :  How many years 
does it take to qualify fuel that is supposed to 
remain in the reactor for 60 years ?

Right now, LWR fuel manufacturers are struggling 
with fuel qualification for rods that only stay 
in the reactor for a couple of years and have a 
burn-up of some 55 GW-days/tonne -- dozens of 
times less than fuel in the TWR concept.

There are ways to achieve extremely high fuel 
burn-up -- but NOT with solid fuel left inside a sodium reactor for decades.

Besides which, sodium-cooled reactors top out at 
a thermodynamic conversion efficiency 
considerably lower than some of these 
alternatives, due to the limited operating temperature with sodium metal.

No doubt Terapower will discover soon enough that 
just because the physics of the Travelling Wave 
Reactor can be shown to work in computer 
simulations, it doesn't mean that it can be 
developped into a useful commercial product.

Jaro
^^^^^^^^^^^^^^^^^^^^

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu]On Behalf Of Doug Aitken
Sent: March 26, 2010 2:39 PM
To: 'Brennan, Mike (DOH)'; radsafe at health.phys.iit.edu
Subject: Re: [ RadSafe ] What is a Travelling Wave Reactor?

More here!
http://earth2tech.com/2010/02/15/terrapower-how-the-travelling-wave-nuclear-reactor-works/

Regards
Doug

___________________________________
Doug Aitken
QHSE Advisor
D&M Operations Support
jdaitken at sugar-land.oilfield.slb.com
Mail: c/o Therese Wigzell,
Schlumberger,
Drilling & Measurements HQ,
300 Schlumberger Drive, MD15,
Sugar Land, Texas 77478

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