In This Issue
Fall Bridge: A Panoply of Perspectives
September 22, 2014 Volume 44 Issue 3

Disposal of US Spent Nuclear Fuel

Friday, September 12, 2014

Author: Salomon Levy

The disposal of all US spent nuclear fuel (SNF) is the responsibility of the federal government. That decision was made in the 1950s by the Atomic Energy Commission and it still applies.

In 1976, however, US presidential candidates agreed that separation of plutonium (Pu) from SNF should be deferred indefinitely because of proliferation concerns, and that policy was implemented as a presidential order in April 1977. The result is that the commercial SNF inventory continues to grow; when storage capacity is exceeded, it will be shifted to interim storage facilities, and the US government will pay for those storage costs from its receipt of $1 per megawatt-hour of contained SNF energy for disposal.

Background

US history with plutonium started with the decision to produce it for nuclear bombs at Hanford and Savannah River in the early 1950s. The required Pu separation process produced extensive volumes of liquid high-level waste (HLW) that were stored in tanks and were rather costly to maintain to prevent leakage.

In the late 1970s the availability of low-cost uranium encouraged US electrical nuclear power plants to use once-through fuel cycles for economic reasons; the resultant SNF is stored in water pools at the plant to handle its decay heat until it can be turned over to the government for disposal. That disposal was anticipated to be in deep geological repositories (DGRs) after appropriate approvals of their safety. But no DGR has been implemented and the US SNF stockpile continues to grow at the rate of about 2,000 metric tons per year, with requirements for storage depending on the government timing for its disposal.

Radioactive Content

Over the years the radioactivity of US nuclear power plant fuel has increased significantly both to reduce electrical generation costs and to achieve the current ability to generate about 20 percent of the nation’s electricity. I remember that at the first commercial nuclear boiling water reactor (BWR), Dresden 1 (1960–1978), SNF radioactivity was limited to 5,000 megawatt-days per metric ton for safety reasons. In contrast, pressurized water reactor (PWR) fuel is now discharged with radioactive content or exposure in excess of 50,000 megawatt-days per metric ton of SNF.

Figure 1

The high radioactivity content in SNF relative to the natural radioactivity of uranium is plotted in Figure 1 (Cherry et al. 2014), showing that the ratio will approach the value of 1 only after 100,000 to 1,000,000 years. However, accepted engineering practice is to suspect all long-term predictions beyond 10,000 years because their uncertainties increase with time and become too large to be trusted.

It is important to note that Figure 1 does not apply to all US discharged power plant SNF because radioactive contents vary with plant operating conditions and how the fuel was used. Also, there are amounts of SNF discharged from the earliest operating plants or discharged prematurely (for a variety of reasons) that may have ratios of radioactive content to that of natural uranium much closer to 1 after about 10,000 years. The disposal of these amounts of SNF in DGRs may be worth pursuing even though approval by some of the involved parties may be difficult. Such attempts are urged and recommended both to establish and address opposition views and to get early experience with SNF disposal in DGRs.

Disposal Options

SNF could be reprocessed to obtain its Pu and usable uranium (U) for reuse or turned over to the US government for disposal after adequate removal of its decay heat. The United States tested the closed fuel cycle approach to reprocessing SNF, recycling Pu, and reusing the U fuel, as illustrated in Figure 2. Reloads were carried out for both BWRs and PWRs but discontinued because they could not compete with the once-through fuel cycle.

Figure 2

At Savannah River the HLW is separated into two streams: the highly radioactive products (primarily strontium and cesium) and the remaining low-level waste. The radioactive products are to be combined with glass-forming material to produce a glass molten mixture that is solidified into stainless steel canisters for eventual disposal in DGRs.

Liquid metal fast breeder reactors (LMFBRs) were once considered an attractive nuclear alternative and a major US Department of Energy (DOE) program was carried out at the Idaho National Laboratory, where two experimental breeder reactors (EBRs) operated successfully. That program included the coupling of EBR-2 to light water reactors (LWRs) and the development of a pyro-processing technology to deal with LMFBR spent fuel disposal. However, the program was abandoned because the LMFBR electricity production costs were judged excessive and not able to compete with LWR-produced electricity. The United States is participating in an LMFBR program in South Korea but with no intent to restart such an effort in this country.

Figure 3

France is the world leader among nations in avoiding underground Pu disposal. For example, AREVA, a French nuclear power engineering company, can operate with a full core of mixed Pu-U fuel and use an advanced fuel assembly (named CORAIL) that is capable of multiple Pu recycling. The anticipated results of these efforts are depicted in Figure 3, which shows the projected French Pu inventory with different reload strategies. However, it is important to note that France can pursue any Pu strategy it desires because its charges for electricity are determined by the government and not subject to competition as they are in the United States. In other words, US Pu recycling must be able to compete with nonnuclear generation of electricity, and that objective is not readily satisfied.

Regulatory Delays

The US Nuclear Regulatory Commission (USNRC) review of disposal safety at Yucca Mountain has been restarted by the courts and the findings will be of great interest when published. While it would be inappropriate to predict the USNRC conclusions, it is worthwhile to recall that DOE was originally assigned responsibility in 1982 and that Yucca Mountain was selected because it was judged the best available site. Years have passed and nearly $18 billion has been spent to justify the site’s safety—which has already been established by an independently reviewed, published total system project analysis.

I believe the potential USNRC comments can be satisfactorily addressed, but the challenge is in getting the government to proceed with SNF disposal instead of continuing to delay. A preliminary approach should be developed and needs for legal and technical personnel identified. The program will face opposition from the current president and the Senate while having the support of the House and nuclear plant owners. It is hoped that a meeting of the opponents could be arranged to find a compromise and to avoid another intervention by the courts.

A logical compromise might be to agree on limited SNF disposal at Yucca Mountain with the provision to remove the SNF if the release of radioactivity exceeds agreed-upon levels. Some benefits in terms of roads and construction may be needed and Nevada technical personnel should be welcome to participate in the safety evaluations and to voice their concerns.

Conclusions

Disposal of SNF from the earliest operating plants and of SNF discharged prematurely should be pursued at Yucca Mountain. Safety documents should be submitted to the US Nuclear Regulatory Commission for review and approval. If the process is denied or stopped, appeal to the courts should follow to secure disposal.

The process should be extended to other SNF starting with the lower fuel exposures and expanding to cover all SNF.

SNF owners need to have strong legal and technical teams to support this process and ensure its success.

Reference

Cherry JA, Alley WM, Parker BL. 2014. Geologic disposal of spent nuclear fuel: An earth science perspective. The Bridge 44(1):51–59.

About the Author:Salomon Levy (NAE) is president of S. Levy and Associates in San Jose.