Dry-Cask Storage vs. Spent-Fuel Pools

March 20, 2011 | 7:23 pm
Lisbeth Gronlund
Former contributor

The nuclear crisis in Japan has started discussions about the safety and security advantages of storing spent fuel in dry casks (see photo) rather than spent fuel pools. UCS has long recommended that spent fuel be transferred from the pool to dry cask storage once the fuel has cooled enough, after about five years. This is a major issue in the U.S. because U.S. pools are becoming increasingly packed with spent fuel.

Here are some links for more information on this issue:

(1) Chapter 5, “Ensuring the Safe Disposal of Nuclear Waste,” from UCS’s report Nuclear Power in a Warming World (2007), which covers interim and long-term waste storage, and discusses why reprocessing is neither an effective nor desirable waste management strategy. (Note that the discussion of Yucca Mountain is out of date.)

(2) A 2003 paper Ed Lyman co-authored, followed by links to comments on the paper by the NRC, and the authors’ response:

Reducing the Hazards from Stored Spent Power-Reactor Fuel in the United States,” by Alvarez, R., Beyea, J., Janberg, K., Kang, J., Lyman, E., Macfarlane, A., Thompson, G., and von Hippel, F.N., Science and Global Security, Vol 11, 1:1-51 (2003)

Here’s the abstract of the paper:

Because of the unavailability of off-site storage for spent power-reactor fuel, the NRC has allowed high-density storage of spent fuel in pools originally designed to hold much smaller inventories. As a result, virtually all U.S. spent-fuel pools have been re-racked to hold spent-fuel assemblies at densities that approach those in reactor cores. In order to prevent the spent fuel from going critical, the fuel assemblies are partitioned off from each other in metal boxes whose walls contain neutron-absorbing boron.

It has been known for more than two decades that, in case of a loss of water in the pool, convective air cooling would be relatively ineffective in such a “dense-packed” pool. Spent fuel recently discharged from a reactor could heat up relatively rapidly to temperatures at which the zircaloy fuel cladding could catch fire and the fuel’s volatile fission products, including 30-year half-life 137Cs, would be released. The fire could well spread to older spent fuel. The long-term land-contamination consequences of such an event could be significantly worse than those from Chernobyl.

No such event has occurred thus far. However, the consequences would affect such a large area that alternatives to dense-pack storage must be examined—especially in the context of concerns that terrorists might find nuclear facilities attractive targets. To reduce both the consequences and probability of a spent-fuel-pool fire, it is proposed that all spent fuel be transferred from wet to dry storage within five years of discharge. The cost of on-site dry-cask storage for an additional 35,000 tons of older spent fuel is estimated at $3.5–7 billion dollars or 0.03–0.06 cents per kilowatt-hour generated from that fuel. Later cost savings could offset some of this cost when the fuel is shipped off site.

The transfer to dry storage could be accomplished within a decade. The removal of the older fuel would reduce the average inventory of 137Cs in the pools by about a factor of four, bringing it down to about twice that in a reactor core. It would also make possible a return to open-rack storage for the remaining more recently discharged fuel. If accompanied by the installation of large emergency doors or blowers to provide large-scale airflow through the buildings housing the pools, natural convection air cooling of this spent fuel should be possible if airflow has not been blocked by collapse of the building or other cause. Other possible risk-reduction measures are also discussed.

Review of ‘Reducing the Hazards from Stored Spent Power-Reactor Fuel in the United States’,” by the Nuclear Regulatory Commission (NRC), Science and Global Security, Vol. 11, 2-3:203-212 (2003)

Response by the Authors to the NRC Review of ‘Reducing the Hazards from Stored Spent Power-Reactor Fuel in the United States’,” by Alvarez, R., Beyea, J., Janberg, K., Kang, J., Lyman, E., Macfarlane, A., Thompson, G., and von Hippel, F.N., Science and Global Security, Vol. 11, 2-3:213-223 (2003)

(3) Ed also co-authored a paper addressing issues related to the potential effects of a radiation release from spent fuel:

Damages from a Major Release of 137Cs into the Atmosphere of the United States,” by Beyea, J., Lyman, E., von Hippel, F. N., Science and Global Security, Vol. 12:125–136 (2004)

Here’s the abstract:

We report estimates of costs of evacuation, decontamination, property loss, and cancer deaths due to releases by a spent fuel fire of 3.5 and 35 MCi of 137Cs into the atmosphere at five U.S. nuclear-power plant sites. The MACCS2 atmospheric-dispersion model is used with median dispersion conditions and azimuthally-averaged radial population densities. Decontamination cost estimates are based primarily on the results of a Sandia study. Our five-site average consequences are $100 billion and 2000 cancer deaths for the 3.5 MCi release, and $400 billion in damages and 6000 cancer deaths for the 35 MCi release. The implications for the cost-benefit analyses in “Reducing the hazards” are discussed.