<p>Using salt domes in which to store nuclear waste has been considered in the USA and Germany. These two countries have potentially suitable salt domes.</p>
<p><a href="https://www.ncbi.nlm.nih.gov/books/NBK208696/" rel="noreferrer"><strong>Factors in favor of salt domes</strong></a> are (Sect 12 of the reference):</p>
<ul>
<li>Salt is already mined from such domes in the USA. The voids left
behind provide reduce the cost of nuclear waste storage. The cost of
producing the voids is absorbed by corporations mining the deposit
for salt. The nuclear waste disposing entities spend less money
digging fewer holes.</li>
<li>Salt deposits are geologically stable, having existed for millions of
years.</li>
<li>More so in the USA, the geological setting of the deposits is also
secure. The salt domes are in regions with low seismicity.</li>
<li>In bedded salt deposits the overlying strata such as limestone and
dolomite provide truss-like support to the overburden. The
possibility of roof collapse causing the release of radioactive
materials stored under these conditions appears very small but merits
verification.</li>
<li>Salt is a good thermal conductor and will supposedly dissipate the
heat from the nuclear waste. I would be more comfortable with this
reason if the containers of nuclear waste were placed directly into
specially sized holes within the salt domes, where the containers are
in maximum direct contact with the salt. If the containers of nuclear
waste are simply placed in within the air space of the underground
chamber the waste must first heat the air which then heats the walls
of the salt chamber. The dissipation of heat takes longer.</li>
<li>Salt domes are only secure if they are mined by mechanical means:
drilling and blasting or grinding. Salt domes mined by aqueous
methods - dissolving the salt with water and removing the salt as
brine produces underground chambers with no internal support, such as
pillars or human installed rock or cable bolts which reinforce the
walls and ceiling of underground chambers. Such chambers would be
unsuitable and could be prone to collapse.</li>
</ul>
<p><strong>Issues with using salt domes</strong> to store nuclear waste:</p>
<ul>
<li><p>Salt is generally regarded as being self healing. Any small cracks
that may develop within the salt deposit will close. This applies to
small cracks, but may not apply to very large cracks.</p>
</li>
<li><p>Salt domes are generally considered to inhibit the flow of fluids
through them. However, under conditions of high temperature and
pressure, as exists deep underground, <a href="https://www.popsci.com/storing-nuclear-waste-in-salt-deposits-isnt-as-secure-as-youd-think/" rel="noreferrer">salt can become more
porous</a> allowing more fluids to pass through it. This can be
problematic if in flowing water was to pick up radioactive material
and start spreading it around the region of the salt dome.</p>
</li>
<li><p>The nature of the nuclear waste to be stored needs to be considered.
Salt domes would be better at storing solid waste. Some waste is
liquid which can more easily contaminate storage area via leaks and
spills. Such waste would need to be thickened so it contained 35
percent solids.</p>
</li>
<li><p>If high level nuclear waste is to be stored, the amount of heat
generated would be 1 - 3 Btu/h per US gallon (278.7 - 836.1 J/L). An
acre-foot (1233.48 m<sup>3</sup>) of such waste would produce 1 MBtu
per hour (1055 MJ per hour). The equivalent of burning 700 lb (317.5
kg) of coal.</p>
</li>
</ul>

CC BY-SA 4.0
2022-07-15T13:28:46.127Z
I'm not sure about the very last calculation: Energy density of coal=24 MJ/kg, so 44kg/hour to give 1055MJ/hr - an order of magnitude difference.  I haven't checked the conversion from non-SI
Chris H
CC BY-SA 4.0
2022-07-15T13:39:38.873Z
Isn't "Salt domes are only secure if they are mined by mechanical means" an 'issue' rather than a factor in favour of salt domes? (Or at least neutral rather than a posivite?)
Pharap
CC BY-SA 4.0
2022-07-15T13:52:56.057Z
Seems like all that heat it generates would be ripe for energy generation - If you put a geothermal plant on top of your disposal site maybe?  Allows the site to still be useful for more than just hazardous material storage.  Any safe way to take advantage of that?
Darrel Hoffman
CC BY-SA 4.0
2022-07-16T14:55:30.427Z
It is unclear how the heat generation is specifically a problem for salt domes: Are they better heat insulators than other geological formations?-- Another issue I'm missing in the downsides is the corrosiveness of hot salt, at least in the presence of humidity. So *if* water seeps in somehow it will compromise the containers faster than other environments. Not sure about the chemistry of dry hot salt and metal/glass containers.
Peter - Reinstate Monica
CC BY-SA 4.0
2022-07-16T15:07:48.483Z
After reading up some it seems that the plan for the German salt storage in Gorleben was to actually flood it intentionally ("we cannot keep it dry anyway") which would start corroding the barrels and lead in geological time, together with geological pressure, to their complete destruction and contamination of the site. The long-term containment would be purely by geological barriers. (I suppose that that's also the case in other geological formations, over geological times, so corrosion may be irrelevant as a specific salt dome issue.)
Peter - Reinstate Monica
CC BY-SA 4.0
2022-07-14T13:32:35.213Z
2022-07-14T16:44:54.400Z
2022-07-14T16:44:54.400Z
Fred
<p>Hi Salt domes have formed over a period of several million years. These salt domes are usually also very well sealed against water by a protective layer (Anhydrite) (salt dissolves in water and if the salt dome were not dry it would not exist). These drying conditions, in addition to an already existing infrastructure through salt mining, are the reason why salt domes are used as nuclear repositories.</p>
<p>Have a Look: <a href="https://www.sciencedaily.com/releases/2020/04/200429075857.htm" rel="noreferrer">https://www.sciencedaily.com/releases/2020/04/200429075857.htm</a></p>
<p><a href="https://i.sstatic.net/2yxE4.png" rel="noreferrer"><img src="https://i.sstatic.net/2yxE4.png" alt="enter image description here" /></a></p>
<p>Source: <a href="https://antisocialnetwork-2labz.blogspot.com/2017/04/rock-salt-for-dummies-freelance-files_15.html" rel="noreferrer">https://antisocialnetwork-2labz.blogspot.com/2017/04/rock-salt-for-dummies-freelance-files_15.html</a></p>

CC BY-SA 4.0
2022-07-16T15:20:51.410Z
Ironically, the blogspot article you link to disses the actual popular science article in https://sciencing.com/rock-salt-formed-7192004.html as bad, half-assed writing.
Peter - Reinstate Monica
CC BY-SA 4.0
2022-07-14T08:06:44.060Z
2022-07-14T08:16:36.323Z
2022-07-14T08:16:36.323Z
Weiss
<p>I keep reading that final storage sites for nuclear waste are being built in salt domes. In the case of the German Gorleben project, the salt domes <a href="https://www.base.bund.de/SharedDocs/Pressemitteilungen/BASE/EN/2021/0917_gorleben.html" rel="nofollow noreferrer">were determined to be unsuitable</a> after prolonged investigation.</p>
<p>Regardless of the Gorleben case, why are salt domes preferred?</p>

CC BY-SA 4.0
2022-07-16T20:35:52.507Z
Could you make at least some of that clear? When you keep reading whatever, why leave out the details about salt in storage sites?
Robbie Goodwin
<geology><uranium><hazardous><ionizing-radiation>
Why are salt domes suitable for the final disposal of nuclear waste?
Weiss
# Why are salt domes suitable for the final disposal of nuclear waste?

(Asked by: username_0 on 2022-07-14)

I keep reading that final storage sites for nuclear waste are being built in salt domes. In the case of the German Gorleben project, the salt domes [were determined to be unsuitable](https://www.base.bund.de/SharedDocs/Pressemitteilungen/BASE/EN/2021/0917_gorleben.html) after prolonged investigation.

Regardless of the Gorleben case, why are salt domes preferred?

**Tags:** geology, uranium, hazardous, ionizing-radiation

> **Comments:**
> **username_1**: Could you make at least some of that clear? When you keep reading whatever, why leave out the details about salt in storage sites?  

---

## 2 answers

### Answer by username_0 on 2022-07-14. Score: 10 | Accepted answer

Hi Salt domes have formed over a period of several million years. These salt domes are usually also very well sealed against water by a protective layer (Anhydrite) (salt dissolves in water and if the salt dome were not dry it would not exist). These drying conditions, in addition to an already existing infrastructure through salt mining, are the reason why salt domes are used as nuclear repositories.

Have a Look: <https://www.sciencedaily.com/releases/2020/04/200429075857.htm>

[![enter image description here](https://i.sstatic.net/2yxE4.png)](https://i.sstatic.net/2yxE4.png)

Source: <https://antisocialnetwork-2labz.blogspot.com/2017/04/rock-salt-for-dummies-freelance-files_15.html>

> **Comments:**
> **username_6**: Ironically, the blogspot article you link to disses the actual popular science article in https://sciencing.com/rock-salt-formed-7192004.html as bad, half-assed writing.  

---

### Answer by username_2 on 2022-07-14. Score: 22

Using salt domes in which to store nuclear waste has been considered in the USA and Germany. These two countries have potentially suitable salt domes.

[**Factors in favor of salt domes**](https://www.ncbi.nlm.nih.gov/books/NBK208696/) are (Sect 12 of the reference):

* Salt is already mined from such domes in the USA. The voids left
  behind provide reduce the cost of nuclear waste storage. The cost of
  producing the voids is absorbed by corporations mining the deposit
  for salt. The nuclear waste disposing entities spend less money
  digging fewer holes.
* Salt deposits are geologically stable, having existed for millions of
  years.
* More so in the USA, the geological setting of the deposits is also
  secure. The salt domes are in regions with low seismicity.
* In bedded salt deposits the overlying strata such as limestone and
  dolomite provide truss-like support to the overburden. The
  possibility of roof collapse causing the release of radioactive
  materials stored under these conditions appears very small but merits
  verification.
* Salt is a good thermal conductor and will supposedly dissipate the
  heat from the nuclear waste. I would be more comfortable with this
  reason if the containers of nuclear waste were placed directly into
  specially sized holes within the salt domes, where the containers are
  in maximum direct contact with the salt. If the containers of nuclear
  waste are simply placed in within the air space of the underground
  chamber the waste must first heat the air which then heats the walls
  of the salt chamber. The dissipation of heat takes longer.
* Salt domes are only secure if they are mined by mechanical means:
  drilling and blasting or grinding. Salt domes mined by aqueous
  methods - dissolving the salt with water and removing the salt as
  brine produces underground chambers with no internal support, such as
  pillars or human installed rock or cable bolts which reinforce the
  walls and ceiling of underground chambers. Such chambers would be
  unsuitable and could be prone to collapse.

**Issues with using salt domes** to store nuclear waste:

* Salt is generally regarded as being self healing. Any small cracks
  that may develop within the salt deposit will close. This applies to
  small cracks, but may not apply to very large cracks.
* Salt domes are generally considered to inhibit the flow of fluids
  through them. However, under conditions of high temperature and
  pressure, as exists deep underground, [salt can become more
  porous](https://www.popsci.com/storing-nuclear-waste-in-salt-deposits-isnt-as-secure-as-youd-think/) allowing more fluids to pass through it. This can be
  problematic if in flowing water was to pick up radioactive material
  and start spreading it around the region of the salt dome.
* The nature of the nuclear waste to be stored needs to be considered.
  Salt domes would be better at storing solid waste. Some waste is
  liquid which can more easily contaminate storage area via leaks and
  spills. Such waste would need to be thickened so it contained 35
  percent solids.
* If high level nuclear waste is to be stored, the amount of heat
  generated would be 1 - 3 Btu/h per US gallon (278.7 - 836.1 J/L). An
  acre-foot (1233.48 m3) of such waste would produce 1 MBtu
  per hour (1055 MJ per hour). The equivalent of burning 700 lb (317.5
  kg) of coal.

> **Comments:**
> **username_3**: I'm not sure about the very last calculation: Energy density of coal=24 MJ/kg, so 44kg/hour to give 1055MJ/hr - an order of magnitude difference.  I haven't checked the conversion from non-SI  
> **username_4**: Isn't "Salt domes are only secure if they are mined by mechanical means" an 'issue' rather than a factor in favour of salt domes? (Or at least neutral rather than a posivite?)  
> **username_5**: Seems like all that heat it generates would be ripe for energy generation - If you put a geothermal plant on top of your disposal site maybe?  Allows the site to still be useful for more than just hazardous material storage.  Any safe way to take advantage of that?  
> **username_6**: It is unclear how the heat generation is specifically a problem for salt domes: Are they better heat insulators than other geological formations?-- Another issue I'm missing in the downsides is the corrosiveness of hot salt, at least in the presence of humidity. So *if* water seeps in somehow it will compromise the containers faster than other environments. Not sure about the chemistry of dry hot salt and metal/glass containers.  
> **username_6**: After reading up some it seems that the plan for the German salt storage in Gorleben was to actually flood it intentionally ("we cannot keep it dry anyway") which would start corroding the barrels and lead in geological time, together with geological pressure, to their complete destruction and contamination of the site. The long-term containment would be purely by geological barriers. (I suppose that that's also the case in other geological formations, over geological times, so corrosion may be irrelevant as a specific salt dome issue.)  

---

