Are we paying too much to reduce radiological risk?

In 2000, the DoE budget request to Congress included $5.9 billion for Environmental Management (EM) and $154 million for Environmental Safety and Health (ES&H). The former includes all clean-up activities for past defence activities. The latter deals primarily with workers’ safety and health. However, EM also has some expenditures related to worker safety.

There have been several studies discussing DoE-generated risks to budget proposals and expenditures. However, these have dealt with the subject in a general way, and have not directly related expenditures to total risks of a DoE site or sites.

The axes of risk

While there are many DoE documents that deal with risk, their relative size and relationships are often confused. One of the reasons is the different conceptual axes of Nevada Test Site (NTS) risk. Three of these are shown in Figure 1. While some of the details deal only with the NTS, the methodology can easily be extended to most sites.

The vertical dimension shows the eight major categories of NTS risks. They include:

•Contaminated soils, mostly from above-ground tests.

•Radioactive waste management sites, mostly for low-level wastes.

•Underground test areas.

•Transportation risk (mostly of low-level waste from other sites).

•Radiological and chemical risks to workers.

•Occupational injuries to workers, other than radiological or chemical.

•Large accidents, such as aircraft hitting certain facilities.

•Present measured or estimated risks off-site.

The horizontal dimension is the time scale, shown as present and future. Present refers to data that are reasonably current. Some NTS documents estimate risks as far as 10,000 years into the future. The future is defined as 100 years from now. This is consistent with statements made in the NTS Environmental Impact Statement.

A third dimension is that of off-site and on-site risks. Radioactive waste management sites, far above the water table, will produce only on-site risks for the foreseeable future. Others, such as transportation risks, will be mostly off-site, taking place far from the NTS.

The eight categories of risk, along with two possibilities for both location and time, generate a total of 32 possible combinations. However, only 14 have risks substantially above zero.

All the rest have zero or close to zero risk, based on present understanding. For example, there is no workers’ risk, either radiological and chemical or accidental, off-site. Since it is assumed that the NTS will cease operation and have all barriers removed (a highly conservative assumption) in about a century, there are no workers’ risks in the future.

Additional risks

There are at least two other sources of additional risks that are not estimated here. The NTS contains about 1500 abandoned and inactive facilities, structures and disposal sites. About 740 do not have latitude or longitude locations. Given these unknowns, it is difficult to make even elementary estimates of risk for these sites.

Exhaust emissions health effects are not estimated for on-site construction and mobile sources emissions. On-site and off-site emissions total in the hundreds of tonnes annually.

Issues not addressed

There are many issues that are not dealt with here, for space reasons. Some of them are: cost/benefit analysis of risk and risk regulations; the proposed adjacent Yucca Mountain repository for high-level nuclear wastes; and ecological risk assessment.

Uncertainties

There are many uncertainties in measuring or calculating NTS risks. Some NTS data are classified, and unavailable for public scrutiny. For example, the so-called underground source term, that is, the amount and location of radionuclides as residue from underground tests, is secret. Given little knowledge of this source term, there are considerable uncertainties about the risks associated with underground test areas. Even if the source term was known and published, the geology and hydrology of the NTS may still contain many unknowns. Exactly how fast and in which direction(s) the water flows may not be known with certainty for years, if ever. Thus the risk to off-site populations will remain uncertain.

Conservatism and risks

A conservative approach is taken towards many of the radiological risks discussed below. To ensure that these risks are not inadvertently underestimated, risks are sometimes overestimated. This is usually undertaken in response to regulations that specify this conservative approach. The EIS notes, for example: “For conservatism in the performance assessment (of radioactive waste management sites), site recognition and passive barriers are considered to be lost after institutional control (is not in place...”

Other risk estimates, such as those dealing with workers’ occupational risks, were calculated using standard industrial statistics. No extra conservatism is built into this data. Thus the data is a combination of both conservative and realistic assumptions.

Major sources of risk

Total fatalities per year are shown in Figure 2 for the four largest sources, over all combinations of locations and time. The largest is risk to workers from sources other than radiological or chemical. About one-third less is transportation off-site, almost completely non-radiological. A factor of about 30 lower is transportation on-site, again almost completely non-radiological. The lowest of the four, about a factor of 100 lower than the largest, is workers risk due to radiological and chemical sources. Results confirm the EIS statement: “human health risks ... (are) expected to be dominated by occupational injuries to workers engaged in activities such as construction, maintenance, excavations etc.”

However, the EIS did not compare all sources of risk, and did not evaluate risks beyond the year 2006. There are a number of observations to be made. These include:

•The total number of fatalities is relatively small, of the order of 0.5 per year. Present NTS-associated fatalities are about 0.008% of Nevada deaths in 1996.

•The rankings have little correlation with the risk perceptions of Nevadans. Respondents in a survey of 1200 citizens regarded transportation of high-level waste as the greatest source of NTS risk, but such transportation does not exist. Storage of low-level radioactive waste, the second highest perceived risk, does take place. However, minimum and maximum latent cancer fatalities (LCFs) from this source range between 1-7% of the lowest column in the figure.

•Groundwater contamination, taken here to mean tritium from underground test areas, was fifth on the respondents’ scale. Minimum and maximum LCFs from this source were essentially zero and 30% of the lowest column in the figure. Clearly, adequate risk information has yet to be transmitted to Nevadans.

•The absolute differences between risk values are greater than is apparent from the logarithmic scales.

•By far the largest proportion of risks are due to accidents, as opposed to radiological or chemical sources. The three largest sources of risk – workers occupational, transportational off-Site and transportational on-site – fall into the former group.

Although public concerns about radiological risk naturally centre on hazards off-site, the largest source of radiological hazard is to workers.

Figure 3 shows the proportions of total NTS accidental deaths and LCFs. Risks are dominated by workers’ occupational and transportation off-site accidental deaths.

All other sources of fatalities are small by comparison.

Relating risks to expeNditures

For the NTS, budgets requests for Defence Environmental Restoration and Waste Management for 2000 were $90.2 million; for Environmental, Safety and Health $2.4 million. As previously noted, there is probably some overlap in the subjects dealt with by the two organisations.

To relate risks to expenditures quantitatively, a number of simplifying assumptions must be made.

•Environmental Restoration and Waste Management is assumed to deal with radiological risks, and Environmental Safety and Health is assumed to deal with non-radiological risks.

•Only fatalities are considered here. Non-fatal cases, such as accidents and genetic effects, can also be evaluated using this methodology.

•Only the maxima of each range of fatalities are considered. More statistical analysis, taking account of minima, distributions, etc, can also be performed.

•The four combinations of risks – present on- and off-site, and future on- and off-site, are combined here.

The results are shown in Figure 4. At the NTS at least, expenditures per fatality are about 5000 times greater for radiological than for non-radiological deaths.

The total risks

The total risks of a sample DoE site, the NTS, have been calculated. Although DoE concentrates most of its risk-reduction measures on radiological sources, results indicate that by far the largest proportion of risk derives from non-radiological sources. Expenditures per estimated death are vastly higher, of the order of four orders of magnitude, for radiological as opposed to non-radiological risks.