[ RadSafe ] Accelerated weathering of borosilicate glass

[Brennan, Mike (DOH)]

Hi, Dan.

First, I am glad that we agree that it is better to make fuel out of the
weapons grade Pu than it is to declare it to be waste and make a problem
out of it.  I agree that it will not provide a significant amount of the
fuel needed by existing, let alone possible new reactors, but the point
is to change if from something that can be used in nuclear weapons into
something that can't.  Burning it in a reactor will do quite nicely.

Second, I am not a particular fan of Yucca Mountain.  I believe that the
whole "unsolvable spent fuel crisis" is false, created by the political
maneuverings of people who are anti-nuke for emotional reasons, and who
care not a whit if science and logic are for or against them.  I
personally believe that spent commercial fuel should be reprocessed, so
the isotopes that are responsible for it being radioactive for "hundreds
of thousands of years" can be removed and used to make power.  

I recognize that often to speed things up for modeling factors have to
be adjusted.  I also recognize that this does not always work, and
frankly, I see some issues with the modeling described here that makes
me wonder about how good it is.  A wind tunnel model of a house exposed
to a 100 mph wind for one hour does not tell you much about what will
happen to the real house when exposed to a 1 mph wind for 100 hours.
Doing the experiment with the exterior sheathing removed from the model
doesn't improve the quality of the information the test provides,
either.

>1) Stability of man-made tunnels (e.g. mine adits) Collapse of tunnel
systems, regardless of engineering, will occur over time, and perhaps
100-300 years would be sufficient for collapse. I've seen adits that
are/were 100 years old and they are at least 75% collapsed.  Much
depends on the strength of the rock, stress caused by the removal of
rock for the tunnel, stress from thermal effects from increased local
temperature.  The "shields" that drain water away from the canisters
(condensed from the thermal effects of the fuel on water-bearing
minerals) then are no longer effective.  Thus "no credit" is a good
assumption.

Indeed, the tunnels can and probably will collapse at some time.  It
would seem to me, however, that the amount of force that can be brought
to bear on the canisters is very dependent on the size and shape of the
chambers they are put into.  It shouldn't be terribly hard to force from
above would tend to vector around rather than through the canisters.  Be
that as it may, if the "shields" that drain water away are no longer
effective, then any water that enters the chamber pools there, and does
not flow across the glass at high pressure.

>2) Water of Mineralization
Aside from the water that is naturally present from the hydrogeologic
setting, minerals frequently contain some water of mineralization, that
when heated, give off this water initiating thermal decomposition of the
mineral.
These minerals include authigenic clays formed naturally by
decomposition of the aluminosilicates in the host rock.  Water of
mineralization is usually yielded-up at reasonably low temperatures.
Given the significant heating by the assembled waste canisters, this
water will condense and cause the zone to become quite "wet", thus
encouraging early corrosion in the canisters.
This has been demonstrated at Yucca Mountain.  The point is, the zone
around the canisters will be wet, perhaps not "saturated", but certainly
dripping wet.

If the water is coming out of minerals, isn't it fairly saturated in a
number of soluble compounds?  While I think that the amount of heat and
the length of time the heat will be produced is often exaggerated, let's
go with the idea that the canisters are hot, and mineral rich water is
dripping onto them.  Wouldn't that tend to evaporate some of the water,
leaving the minerals behind, and eventually coating the canister in
rock?  Even if it doesn't deposit rock, the model would be enhanced by
an estimate of how long water dripping on the canisters would take to
breach all the layers to the glass.  My guess is that it would be a fair
bit of time.

>3) Chemistry of water
Water naturally reacts with CO2 and the minerals present to form a
solution in equilibrium with the mineral phases present as well as the
gas phases such as oxygen. This solution causes corrosion to occur in
the canisters.
I'm not sure how much "credit" is given to the canisters themselves, but
I imagine that they would be fairly well corroded after only a few
hundred years, directly exposing the fuels themselves.  Thus over tens
of thousands of years to be modeled, "no credit" is a good assumption to
make for the canisters.

There are a fair number of metals that corrode and form a patina, which
in turn prevents or retards further corrosion.  The original discussion
was about glass with Pu in it, but if you wish to discuss spent fuel, I
would remind you that the fuel is in ceramic pellets inside of special
cladding, both of which were designed to survive high temperatures and
flowing water, and for BWR reactors, the interface between boiling water
and steam.  Pretty robust stuff.

>4) Smectite Characteristics
Decomposition of the borosilicate glass forms a smectite mineral.  This
is a general category of clays that are montmorillonites.  These are
generally
(Na,Ca)0,3(Al,Mg)2Si4O10(OH)2.n(H2O) in composition with lots of room
for additions of some cations such as bivalent iron.  Features of
smectite chemistry are that 1) they tend to be authigenic or formed from
mineral precursors that are undergoing weathering and 2) they can
alternately swell and shrink on exposure to moisture and can therefore
rupture containers as they swell.  They also adsorb and desorb
materials.  I would imagine that from alpha recoil and radiation damage,
the borosilicate glasses would tend to decompose faster than the modeled
equivalent.  The accelerated decomposition by placing 6 atm pressure was
probably just that: An accelerated test to establish the weathered
products. But I would expect that following corrosion of the canister,
the glass, having sustained significant radiation damage would weather
to smectite fairly readily.
Adsorption / desorption of Pu and other R/Ns would follow in the
leachate water.

I don't know what the effect of the radiation energy on the glass would
be: that would be an interesting experiment itself.  I differ to your
greater knowledge concerning the decomposition products of the glass.  

>5) Poor management, poor engineering, bad QA, etc.
I don't quite understand your point, but it seemed more of a rant than
reasoned.  The facility would be, at some point, allowed to settle into
the natural system, meaning collapse of tunnels, etc.  Yucca Mountain is
only "retrievable" storage up to a point in time.

Having seen more than just a couple of "experiments" where it was
concluded beforehand that the result would show that the proposed action
was unacceptable, and where the assumptions kept getting "adjusted"
until the desired results were achieved, I am suspicious whenever
something like this.  I would equally be suspicious if DOE said that
they hadn't tested their containers under scenarios that were likely to
happen, but they were pretty sure there was no problem.

>6) Source Term
The flux of R/Ns out of the canisters and into the natural system
provides input into the other models.

GIGO.  This is a reason for being more realistic at this stage of the
modeling, not less.  Given that for spent fuel the activity drops pretty
fast, the longer the engineered systems hold out, the less radioactive
material is available to be removed.  As for the canisters of Pu laced
glass: the flux out is 0.0 until they are breached and a flow path is
established.  Assuming the obstacles out of existence doesn't work when
DOE wants to do it in favor of Yucca Mountain; it shouldn't work against
Yucca Mountain, either.  

But be all that as it may:  Even if this experiment is completely
reasonable and accurate, it STILL doesn't show that there is a risk to
the public from using Yucca Mountain, and there isn't a hint as to how
using Yucca Mountain to store (or dispose of) spent fuel is more
dangerous to the public than leaving it where it is now.  

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Dan W McCarn
Sent: Wednesday, August 29, 2007 6:10 AM
To: radsafe at radlab.nl
Subject: RE: [ RadSafe ] Accelerated weathering of borosilicate glass

Hi Mike:

Just to advance a few points:

The geochemical experiments were conducted under pressurized conditions
to accelerate weathering effects in order to determine the likely
outcome of canister / borosilicate glass weathering. This is a common
technique for investigating potential outcomes for mineral phases - to
expose them to leaching solution under various thermodynamic conditions
and observe the outcome. The leachate and mineral phases present (clays
& borosilicate
glass) are then modeled with a geochemical code with an appropriate
thermodynamic database.  If possible, the kinetics of the reaction are
estimated to better understand the ultimate outcome of source term
release.

Ultimately, the effectiveness of the repository lies in the geology,
geochemistry and hydrology, not in "man-made" barriers.  That is why the
"base case" for the repository assumes "no credit" from the engineered
barriers.

1) Stability of man-made tunnels (e.g. mine adits) Collapse of tunnel
systems, regardless of engineering, will occur over time, and perhaps
100-300 years would be sufficient for collapse. I've seen adits that
are/were 100 years old and they are at least 75% collapsed.  Much
depends on the strength of the rock, stress caused by the removal of
rock for the tunnel, stress from thermal effects from increased local
temperature.  The "shields" that drain water away from the canisters
(condensed from the thermal effects of the fuel on water-bearing
minerals) then are no longer effective.  Thus "no credit" is a good
assumption.

2) Water of Mineralization
Aside from the water that is naturally present from the hydrogeologic
setting, minerals frequently contain some water of mineralization, that
when heated, give off this water initiating thermal decomposition of the
mineral.
These minerals include authigenic clays formed naturally by
decomposition of the aluminosilicates in the host rock.  Water of
mineralization is usually yielded-up at reasonably low temperatures.
Given the significant heating by the assembled waste canisters, this
water will condense and cause the zone to become quite "wet", thus
encouraging early corrosion in the canisters.
This has been demonstrated at Yucca Mountain.  The point is, the zone
around the canisters will be wet, perhaps not "saturated", but certainly
dripping wet.

3) Chemistry of water
Water naturally reacts with CO2 and the minerals present to form a
solution in equilibrium with the mineral phases present as well as the
gas phases such as oxygen. This solution causes corrosion to occur in
the canisters.
I'm not sure how much "credit" is given to the canisters themselves, but
I imagine that they would be fairly well corroded after only a few
hundred years, directly exposing the fuels themselves.  Thus over tens
of thousands of years to be modeled, "no credit" is a good assumption to
make for the canisters.

4) Smectite Characteristics
Decomposition of the borosilicate glass forms a smectite mineral.  This
is a general category of clays that are montmorillonites.  These are
generally
(Na,Ca)0,3(Al,Mg)2Si4O10(OH)2.n(H2O) in composition with lots of room
for additions of some cations such as bivalent iron.  Features of
smectite chemistry are that 1) they tend to be authigenic or formed from
mineral precursors that are undergoing weathering and 2) they can
alternately swell and shrink on exposure to moisture and can therefore
rupture containers as they swell.  They also adsorb and desorb
materials.  I would imagine that from alpha recoil and radiation damage,
the borosilicate glasses would tend to decompose faster than the modeled
equivalent.  The accelerated decomposition by placing 6 atm pressure was
probably just that: An accelerated test to establish the weathered
products. But I would expect that following corrosion of the canister,
the glass, having sustained significant radiation damage would weather
to smectite fairly readily.
Adsorption / desorption of Pu and other R/Ns would follow in the
leachate water.

5) Poor management, poor engineering, bad QA, etc.
I don't quite understand your point, but it seemed more of a rant than
reasoned.  The facility would be, at some point, allowed to settle into
the natural system, meaning collapse of tunnels, etc.  Yucca Mountain is
only "retrievable" storage up to a point in time.

6) Source Term
The flux of R/Ns out of the canisters and into the natural system
provides input into the other models.

7) MOX Fuels
At last something that we can agree on!  I would certainly hope that MOX
reactor fuels will used to dispose of weapons-grade material, thus
converting them to energy and making the material useless for weapons
following discharge from the reactor.  Although the MOX fuels from
weapons don't make that much dent in the reactor-related requirements
(perhaps 5% for 20 years?), it seems the right thing to do.

Dan ii

Dan W McCarn, Geologist
Houston and Albuquerque

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Brennan, Mike (DOH)
Sent: Monday, August 27, 2007 11:51
To: radsafe at radlab.nl
Subject: RE: [ RadSafe ] Accelerated weathering of borosilicate glass

First of all, I have to say that I am not in favor of disposal of
weapons grade Pu: I believe it should be used as fuel in reactors, and
be a resource rather than a waste.  Be that as it may, and acknowledging
that I don't know more about this experiment than what is mentioned in
this abstract, I do know a modest amount about the way they plan to
dispose of things at Yucca Mountain, and as an ex-submariner, I have a
fair understanding of the behavior of water under pressure.

So, as I understand it, the glass containing the waste is inside an can,
which is inside a canister, which is inside a chamber, which is inside
the Mountain.  The outside of the Mountain (and any man-made tunnels and
spaces within it) is presumably at one atmosphere pressure.  With the
possible exception of the glass and the can, there is presumably a gap
of some size between the exterior of one layer of containment and the
interior of the one that contains it (the canisters, for example, are
not fit into the rock with no space around them.  If any of these
assumptions are wrong or unreasonable, please let me know.

Now, while I do not agree that the protection of the canister and the
can should be discounted, any more than I agree that the
geologic/climatic changes needed to have pressurized water coursing
through the heart of the mountain should be assumed, I will leave those
for the moment.  I will not concede, however, my long held belief that
pressurized water flows from a point of higher pressure to a point of
lower pressure via the path of least resistance.  Water may flow into
dead end spaces while the pressure in that space is less than the
pressure of the flow, but when it equalizes the water pools and the flow
goes elsewhere.  When the flow reaches a space at a lower pressure the
stream drops to that pressure until it can flood it enough to build up
the pressure.  If the space is open to the atmosphere that never
happens, and the movement of the water is dictated by gravity.

Given that, I have to say that I can't envision any set of
circumstances, up to and including an earthquake that collapses the
mountain, in which the path of least resistance for a 6 atmosphere
stream of water is into the chamber, into the canister, into the can,
across the glass, out of the can, out of the canister, and out of the
chamber.  

So this experiment seems to require poor management, poor engineering,
bad QA, seismic and climatic changes of epic proportions, and selective
suspension of the laws of physics.  

And the ironic thing is that even given all of that, they still can't
build a scenario in which someone is harmed, because the amount of water
needed to weather the glass would dilute the material to infinitesimal
levels by the time it could get to where someone could drink it.