Congress Approves Yucca Nuclear Project

WASHINGTON (Reuters) ^ | July9 | WASHINGTON (Reuters)

[chimera]

I would agree with reprocessing waste, but that it is not inconsistent with building the facility at Yucca Mountain.

Absolutely correct. If reprocessing were revived at some point, and Yucca Mountain were constructed and in operation, there is no reason why spent fuel could not be diverted to the reprocessing site(s), and Yucca left with whatever inventory it had up to that point. It would also be useful for storage of non-useful wastes from the reprocessing facility. The nature of those is different from spent fuel, so you'd likely have an intermediate step of stabilization and immobilization, but the half-lives (and IHI) would be different for those materials. Physical half-life is much less than for spent fuel, so YM would certainly be adequate, as now envisioned, for storing those materials based on that criterion.

[drmatt]

You still can't dismiss the possibility that a relatively small, dedicated group of people could successfully remove a canister or two, open the canister (by cutting some welds), remove the fuel rods, and chemically separate the plutonium. This group may or may not have bomb-making capability - if not, they could likely find a market for the plutonium. What is the probability that this scenaio would occur - it's probably very low. But risk is not determined just from the probability of occurrence, but also from the consequences of occurrence. And the potential consequences of a sufficient quantity of weapons-usable plutonium in the wrong hands would be enormous. The two scenarios that I've discussed in this thread (1) repository flooding and (2) long-term proliferation risks (the "plutonium mine") would likely fall into the category of low-probability, high-consequence events. There are also other scenarios (e.g. "repository criticality") that I haven't discussed. But it is often a judgement call to define just how low the probability would be, particularly when you have to consider time periods of tens of thousands of years. A legitimate question from the NRC (or more likely, from organized intervenors) during the licensing process could be along the lines: "You state that the probability for such-and-such scenario is very low and below the design basis. What is the basis for assigning this low probability, and what are the consequences of this scenario if it did occur?" If the consequences are very high, then your stuck with defending an estimate of the probability of occurrence, which can be extremely hard to do when you have to consider time periods of tens of thousands of years.

The bottom line is that unprocessed, light-water reactor spent fuel rods are a very poor waste form for permanent disposal in a geologic repository, with the potential to cause high-consequence scenarios. Yucca Mountain should not be a permanent repository for unprocessed light water reactor spent fuel - rather it should be a centralized, monitored retrievable storage facility. Eventually, the spent fuel should be chemically separated into plutonium, minor actinides, uranium, and fission products. The plutonium and minor actinides should be deep-burned in advanced reactors to eliminate their potential for proliferation. With a deep-burn fuel cycle, the revenues from electricity generated by these advanced reactors should more than pay for the treatment process. The uranium, which constitues 95% of the waste (by weight) can be recycled into the nuclear fuel cycle or disposed as low-level waste. The fission products can be encapsulated within ceramic coatings that have a corrosion resistance of 100,000 years or more (based on mineral analogues). When the NRC or the intervenors ask their questions, the answer will be along the lines: "We have considered these scenarios. Because of the fact that we have separated and destroyed the fissile material, and because the remaining waste is encapsulated by ceramic materials, the consequences of these scenarios are negligible."

[chimera]

The bottom line is that unprocessed, light-water reactor spent fuel rods are a very poor waste form for permanent disposal in a geologic repository, with the potential to cause high-consequence scenarios. Yucca Mountain should not be a permanent repository for unprocessed light water reactor spent fuel - rather it should be a centralized, monitored retrievable storage facility.

An MRS facility certainly makes sense from a technical and resource utilization viewpoint. As I recall the MRS concept was floated for a time prior to the YM decision, and the opposition from the pols and various assorted wacko groups was even more vociferous than for YM at this stage. Why? Because the MRS is perceived by the wackos as being beneficial to the industry, whereas YM, while beneficial in the sense of answering the "what do we do with the waste" boogeyman they always bring up, is perceived as less beneficial because it closes the door on commercial reprocessing.

So while MRS makes sense, the reality is that the political system may not allow it, but will allow a permanent repository. It may not be the best thing to do, but may be the best we can do under the present circumstances. It will do some good in the sense of keeping LWR technology viable by defusing the wackos' argument about "nobody knows what to do with the waste". If YM is operational, we will know what to do with the waste, even if it isn't the best thing to do from a technical, economic, or strategic viewpoint. But we may not have any choice.

So, we have reached a point of agreement. I like that. Gives me the warm and fuzzies. In the interests of fairness and trying to see the other side of the coin, I understand what you are saying about the diversion risks. I will respectfully agree to disagree on the "plutonium mine" hazard scenario and its relative probability of occurrence and possible consequences. I just think it is a less likely scenario than you do. Repository siting and construction, the design and fabrication of the canisters (BTW, you probably can't break them open at the welds, because with existing joining technology it is possible to make the weld zones stronger than the native metal), the allowance of conservative design margins and assumptions in the risk analyses, all lead me to think reasonable steps have been taken to reduce that risk. And, from my (numerous) dealings with the NRC, I think they will take a "reasonable person" approach and give lower weight to less likely scenarios when it comes to making a licensing decision.

So, any other loose ends to tie up in this discussion?

[drmatt]

I agree for the most part with your interpretation of the politics, but there is a little bit of momentum these days to re-visit alternatives to direct disposal of unprocessed LWR spent fuel. In fact, I am presently working on a DOE-funded project to develop transmutation fuels - so even DOE is not putting all of their eggs in one repository.

With regard to MRS, Yucca Mountain (as presently designed) will in effect be an MRS facility for at least the first 100 years or so after it opens. That's because the current design requires the drift tunnels to be actively ventilated for 60 years, otherwise fuel inside the canisters would overheat. Natural ventilation is then relied upon for another 40 years or so. So there are no plans to backfill the tunnels (which I think enhances somewhat long-term proliferation risks). DOE adopted this design because the unventilated, backfilled repository was limited to a very sparse loading of about 4 canisters per acre, because of the decay heat load of the spent fuel and its impact on the structural integrity of the tunnels. When you look at all the extraordinary measures DOE has adopted in order to try and make this repository design work (million dollar canisters, titanium rock/drip shields, adding neutron poison to the canisters, active ventilation, etc.) it becomes increasingly obvious (at least to me) that unprocessed LWR spent fuel is just not the right thing to leave in the ground.

Thanks for the give and take - it's been a good discussion.