E&T spoke to Steve Frishman, a geologist at the head of the Agency for Nuclear Projects office at the Office of the Governor of the State of Nevada and a man who has been involved in the Yucca Mountain project since the beginning, about why the nuclear waste repository has failed to meet expectations.
After almost 25 years in the planning and almost £90 billion wasted, the United States has abandoned its plans for a high level nuclear waste storage facility at Yucca Mountain. The site in Nevada 100 miles north west of Las Vegas and adjacent to the Nevada Nuclear Test Site was designated in the 1987 Nuclear Waste Policy act as the national repository for HLW. The Department of Energy (DoE) was to begin accepting spent fuel there in 1998, but a series of delays and legal challenges made that impossible.
In 2009 President Barack Obama announced that the site was no longer an option and proposed to eliminate all funding for the project. A decision that to all intents signals the death knell for the costly project and raises the question, was it ever a viable option? One man that believes that it was doomed from the start was Steve Frishman, a geologist and head of the Agency for Nuclear Projects office at the Office of the Governor of the State of Nevada.
E&T: What was the original plan for high level nuclear waste (HLW) storage at Yucca Mountain?
Steve Frishman: “It follows the idea of deep geologic disposable. There is a ridge just off the south west corner of the Nevada test site, which is volcanic rock. Originally they were going to build a vertical shaft down to a level about 300 metres below the top of the ridge and from there do a series of tunnels or drifts as exploratory work in order to get all the physical characteristics and to work out the hydrology, as this is all above the water table, which is a unique situation for what is being looked at anywhere else in the world.
E&T: It seems that the project is unlikely to go ahead, but can you tell me what’s been built up to now?
SF: “They have built an exploratory U-shaped tunnel that goes almost horizontally in Yucca mountain and then runs along at the level at which the waste would be disposed, this has ramps that comes back out. It is a total of about 5 miles long and its going into Yucca Mountain at about a 2 per cent gradient, down to the level where waste would be which is about a mile and half. There is about a two mile long run in at that level where waste would be, and they have built drifts that branch off of that.
“Then there is about a mile and a half coming back out so the U-shape is a mile and a half on the two sides and two miles on the long run at the depth where the waste would be. They have another exploratory tunnel that goes off at a slightly higher level which is primarily a research thing that have nothing to do with the disposal of waste, but because the rocks we dipping it was a way to look at a larger geologic sections so you could see the all of the type of rock that the waste would be involved with. The U-shaped tunnel called the Exploratory Studies facility, or ESF, would be the place where they started the drifts for waste emplacement. In other words they would take off from that, and the U-shape would be an access drift.
E&T: I understand that water and the water table presented a particularly thorny problem at the site?
SF: “The reason for this is that the water table is very deep under Yucca Mountain, about 6-800 metres below the top of the mountain. So understanding the unsaturated zone, meaning the zone above the water table, is unique in term of trying to do a very detailed analysis because it is just something that has never been done before.
“Unsaturated zone work is well known by soils hydrologists, but looking at deep unsaturated zone hydrology is unknown in itself as this has never been taken up because no one has ever needed to do it before there was no reason to do it.
“For mining you deal with what you have. You have a resource and work out the safest way to get to the resource, but in this case trying to characterise the hydrology and geology is something that’s never been done and whole new approaches had to be figured out.”
E&T: This talk of rainfall is somewhat surprising given that we are talking about a desert region?
SF: “We’re in dry climate so the rainfall is only on the order of 6-8 inches a year but, at the same time, we’re in an area which is prone to episodic precipitation which gives very large amounts of rain in very short periods of time so. We are now trying to understand what happens with episodic rainfall and that is something that came very late to the way the DoE was looking at the scenario.
“Up until 1995 they thought that because there is such little rainfall and because we are so far above water table that any precipitation will infiltrate slowly into the rock.
E&T: How does the type of rock formation affect the way that water flows through it?
SF: “The rock transmits water in two ways. The reason that I discuss water so much when talking about geological storage is that if the waste is going to escape from the site, then water will be vehicle.
“Until 1995 the DoE worked on a hydrological model that said the infiltration would be very slow because water would be moving through the pore space in the rocks. Above the water table the rock will be 80-90 per cent saturated; meaning 80-90 per cent of the pore space has water in it. What they were ignoring in that was that the rock is pretty heavily fractured.
“If you have precipitation on the surface, we at the state maintained that the easiest way the water was going to travel was through these fractures; but the department said there was no evidence of this. In 1995 they finally analysed some samples that they had collected over the years and realised that water has the capability of moving through Yucca Mountain very rapidly and moving through the fractures.
E&T: Did this information cause a change of thinking from the DoE?
SF: The info that finally got them to understand that fracture flow is a very important part of the hydrology is that they had built their explorative facility underground to the level in which they would store the waste and when taking samples from this tunnel they found amounts of chlorine 36. There is a small amount of chlorine 36 that is generated in the atmosphere, but if the ratio of 35 to 36 is higher than that that would be generated in the atmosphere then it must have come from atmospheric weapons testing.
“They found excess amounts at the level that they would expect to place waste and had to start looking at how that had got there, and obviously this comes from the water coming in through the fractures and means episodic flow becomes a real issue. That changed the whole way that they store waste at Yucca Mountain for waste isolation.
E&T: How did this change the strategy?
SF: “The initial plan was to put the waste it into the rock in the unsaturated zone and because the water moves very slowly through the system there was little danger of any of it contacting the waste, dissolving it and moving it to the water table and then having it move in the ground water to a place where it become accessible in the environ.
“The water table down gradient from Yucca Mountain becomes very shallow in the valley and that water is used for irrigation for water for farming and drinking. The biggest dairy in the state is situated there and uses the water, so the first place you could see contamination is through irrigation in the valley and water for human and stock consumption.
“The question then becomes not whether Yucca Mountain will start to leak, but how fast it will begin to leak. This is the basis of the current argument.
Once they accepted that water could move very rapidly through the systems we have used the DoE's own models to discover how quickly that could actually be, and it could be in less than a thousand years.”
E&T: Given these adverse conditions is it not somewhat surprising that the DoE pushed ahead with the scheme?
SF: “The department’s response to that instead of saying ‘new information has told us this is not workable’ they went looking for ways to delay the release. They began looking for a metal container to hold the waste, which has high corrosion resistance. This turned out to be a problem because first of all it’s difficult to figure out the chemistry of the water that would come into contact with this supposedly corrosion resistant metal. Part of the reason it’s difficult to figure that out is that the waste will generate a lot of heat.
E&T: I understand that you are not very happy with the DoE’s experiments into these containers?
SF: “The DoE has carried out some fairly short term corrosion experiments in some pretty benign conditions. They are testing a Nickel alloy that has been in use for about 20 years primarily as flasks for highly oxidising acids; it’s never been tried as a long term corrosion resistant material.
“They carried out the main corrosion experiments for about five years. They submerged the material in water, which was of a chemistry they assumed to be representative. They then extrapolated it out and came up with the idea that the thickness of this metal ought to last thousands and thousands of years in that environment.
E&T: Doesn’t this change the whole concept that was originally laid out for the storage facility?
SF: “Yes it does. Instead of relying on the geology of the system to maintain isolation they were going to use a metal alloy to delay the release. All that happens with that delay is that you allow for the decay of fission products like strontium 90 and caesium 137 – these have half lives of about 30 years, so these would be gone to all intents and purposes in 3-500 years anyway. But the rest of the actinides are still there.
“The original idea for deep geological disposal is that you need very long isolation in order to deal with isotopes such as plutonium which has a half life of about 25 thousand years. And that’s the real danger. It’s the very long lived isotopes we’re worried about.
E&T: So instead of geological storage they were relying on the containers?
SF: “They now have this metal container, where there is some controversy over how corrosion resistant this really is. The state on Nevada have sponsored corrosion experiments on the same material which show that waste containers using that alloy under some slightly different assumptions about the chemistry of the water that contacts them may last a few hundred to a thousand years rather than hundreds of thousands of years.
“They then thought about looking at the idea of defence in depth, meaning if one system fails then you should have another system with effectively provides some redundancy. They then came up with the idea of putting drip shields over the top of these containers, the waste containers would placed horizontal in the drifts on pallets so that if you had a waste emplacement drift that was 1km long you would have these 16-18ft waste containers lined up on pallets along these drifts and the idea was to put a drip shield along the top of this line of waste containers.
“This becomes their main point in defending the idea that Yucca mountain can contain waste, so rather than the geology doing the work they have come up with this elaborate engineering logic to make it happen.”
E&T: How would you say the problems at Yucca Mountain have left other geological storage plans around the globe?
SF: “The approaches that have been taken in countries like Sweden and Finland are looking at geological disposal at entirely different directions. What they are looking at is first understanding that water will be the release mechanism and trying to look at whether you have a geologic setting that would make it incredibly difficult for radioactive waste to be released into the environment even if waste was to come into contact with it.
“One of the reasons why Yucca Mountain has been a controversial issue for so long is because the federal government is trying to force an unwelcome situation, and every other country that is trying to deal with nuclear waste has decided or found out the hard way that you can’t force this on anybody. France have had to re-do their programme, the United Kingdom had to re-do their programme and Sweden figured out the hard way that you can’t force it on anybody and the US is the last place that the forcing option is still alive and it is on its deathbed right now.”
E&T: I was surprised to learn that the state of Nevada was opposed to the project from the start?
SF: “We have a political issue, but even though the president has said Yucca Mountain cannot go ahead and is not an option we’re still in the licensing process because that hasn’t been stopped. We in Nevada have filed 225 contentions, contentions meaning technical objections to the licence applications, and we actually filed a few more, but it is totally unprecedented that over 95 per cent of the contentions that we have filed have actually been accepted for hearing. Usually any proceedings for nuclear power plants will have 25 or 30 technical objections and of those maybe 2 or 3 are accepted for hearing.