Radwaste management: deep geological repositories

Could WIPP replace Yucca Mountain?

13 September 2011

The 2010 decision by the?US Department of Energy to abandon the Yucca Mountain repository for high-level radioactive waste is still being played out. Yet in May the Blue Ribbon Commission on America’s Nuclear Future said that the need for a disposal solution is ‘inescapable,’ and that a mined repository is the most promising option. Could an expansion of the operating Waste Isolation Pilot Plant be a viable alternative to Yucca Mountain? By Christopher Timm and Jerry Fox

WIPP is located in southeastern New Mexico near Carlsbad, NM. The disposal area of WIPP is situated approximately 655 meters (2150 ft) underground; mined into the middle of a 610 m (2000 ft) thick salt formation deposited 250 million years ago. The repository consists of surface facilities, the primary one being the Waste Handling Building, four vertical shafts drilled into the salt formation and a series of eight disposal areas called panels (Figure 1). In 1992, the Land Withdrawal Act (LWA) [1] established that the combined volume of transuranic (TRU) waste allowed at WIPP must be less than or equal to 175,564 m3 (6,200,000 ft3) with a disposal limit for remote-handled TRU waste of 7,080 m3, with the remainder contact-handled TRU waste.

The Yucca Mountain repository is located in a volcanic tuff mountain in the SW Nevada desert about 161 km (100 mi) northwest of Las Vegas, Nevada. It is the proposed disposal site for up to 77,000 metric tons of radioactive waste (primarily commercial and defence spent fuel (SNF) and high-level radioactive waste (HLW) presently in storage nationwide at commercial reactors and Department of Energy (DOE) sites. It arose from the 1982 Nuclear Waste Policy Act [2].

The major difference between them is the geology. Salt is relatively plastic and will creep in to close any mined out openings relatively quickly, while openings in tuff will maintain their shape and volume much, much longer. As a result, retrieval of the radioactive waste is feasible from Yucca Mountain for hundreds of years, while upon placement of waste into WIPP, retrieval of waste is only possible for three to four years at best after placement [3].


The history of both WIPP and Yucca Mountain can be traced back to 1956, when the National Academy of Sciences recommended deep geological disposal of long-lived radioactive waste from nuclear reactors, suggesting that buried salt deposits and other rock types be investigated for permanent repositories [4].

In 1970, the Atomic Energy Commission issued a report that indicated the primary choice for a deep geological disposal was salt beds [5]. Salt deposits were preferred for disposal of radioactive wastes based on a number of characteristics. Physically and geologically, the attractive properties of salt deposits include:

  • Good structural properties, with a compressive strength and radiation-shielding properties similar to concrete
  • Bedded salt deposits are completely free of circulating ground waters and are isolated both above and below from underground aquifers by essentially impermeable rock formations, such as shale
  • Salt generally exists in areas of low seismicity
  • Any fractures that might develop are healed by plastic deformation and recrystallization of the salt
  • Salt thermal properties are better than those of most other rock types
  • Salt is relatively inexpensive to mine.

In 1972, after a salt mine near Lyons, Kansas was ruled out after the discovery of many abandoned and poorly-closed oil exploration boreholes, the local, state and federal politicians representing the Carlsbad area all came forward to the AEC in favour of locating the disposal site in southeastern New Mexico, initially in an abandoned potash mine. The offer was accepted and DOE proceeded to investigate the general area to the east of Carlsbad to determine whether the potash mines or underlying salt formations were suitable for location of a waste repository. The investigations determined that the Salado Formation in that area was sufficiently thick and geologically stable and had a sufficiently large horizontal area with undisturbed integrity (no boreholes puncturing the formation) to warrant the issuance of a draft EIS in 1979. That EIS proposed that WIPP be considered for disposal of both defence-related and commercial high-level waste and storage of spent nuclear fuel [6].

However as a result of objections by the State of New Mexico and assorted citizen groups, the original mission of WIPP as authorized by Congress in 1979 was only as a research and development facility to study the feasibility of disposal of defence-related radioactive waste in salt beds. The Record of Decision for the EIS that was issued by the DOE, (the successor to the AEC) in 1981 concentrated on potential disposal of TRU radioactive waste but did also include an intent to conduct experiments with the disposal of defence generated HLW, and the construction of WIPP proceeded.

In that same timeframe, the resistance to WIPP by other entities in New Mexico, in particular the anti-nuclear groups became very active. Somewhat surprisingly, the congressman representing the district that contained Los Alamos National Laboratory, the state environmental department and attorney general were equally against the location of WIPP in New Mexico. As a result, several lawsuits were filed and an agreement was reached in 1981 that effectively limited WIPP limited to the disposal of defence-related transuranic waste only. The construction of WIPP and the evaluation of its acceptability as a radioactive waste disposal facility continued despite continuous attempts by various opponents to stop the project. Those attempts, plus some safety and environmental concerns, led to a declaration by the Secretary of Energy in 1989 that the opening of WIPP would be delayed indefinitely [7]. The WIPP programme was restructured and that declaration was withdrawn a few months later. This led to a subsequent lawsuit in 1991 by the State of New Mexico to stop shipments to WIPP. Nevertheless, Congress made the determination to proceed with WIPP via the Land Withdrawal Act of 1992, as amended [1]. This led to the certification of WIPP by the Environmental Protection Agency (EPA) in 1998 and the disposal of the first TRU waste in WIPP in March 1999.

Partly as a result of the limitations put on WIPP in 1979, Congress passed the Nuclear Waste Policy Act (NWPA) in 1982 that set in motion a nationwide search for a new site for the deep geologic disposal of high-level radioactive waste and spent nuclear fuel. This act ultimately led to Yucca Mountain [2] (see also NEI February 2009, pp20-1).

Research and development

Following radwaste disposal experiments in the 1950s and 1960s [5], a continuing investigation and R&D programme focused on the WIPP site began in 1975 and lasted until the submission of the certification application to the EPA in 1996 [9]. The principal technical issues addressed by that programme included:

  • The interaction of transuranic wastes with the salt environment including assessment of potential degradation mechanisms and the impact on the repository and radionuclide isolation
  • The interaction of thermal and radiation fields from heat producing wastes with the salt environment and the impact on the waste form encapsulating materials
  • Prediction of the response of the host rock to both the ambient conditions upon excavation and the enhanced deformation anticipated with heat-producing waste forms
  • Characterization of the potential for radionuclide migration in the WIPP environment
  • Characterization of the properties of the host rock for permeation of gases or liquids
  • Assessment of the potential for mobilization of natural fluids in the salt and the subsequent interaction with waste containers
  • Quantification of the technology for sealing man-made penetrations into or near the storage horizons
  • Demonstration and certification of safe operational techniques and appropriate design assumptions.

The foundation for the effectiveness of disposal of HLW and SNF at WIPP has already been established. Subsequent to the opening of WIPP, investigative work has continued to improve the overall understanding of how salt reacts to the heat and radioactivity emitted from TRU wastes, affects of other emissions from the waste containers (such as volatile organic compounds) on the repository, the geotechnical impact of major openings on the salt formation, the performance assessment, and operational procedures.

The other aspect of the R&D necessary for disposal of HLW and SNF is the waste packaging, transportation, and handling requirements. Those requirements have been extensively researched during the development of Yucca Mountain [10] and the appropriate systems, equipment and processes developed. Those systems, equipment and processes would serve as a more than adequate baseline for any modifications necessary for disposal in salt.


If WIPP is to be expanded for the disposal of HLW (and SNF if reprocessing is continued to be blocked in the USA) by use of the current facilities or co-locating a new disposal facility in the land withdrawn for WIPP, multiple issues would have to be addressed, many of which are discussed below.


The land withdrawal area for WIPP is a square measuring 6.44 km (4 mi.) on each side for a total area of 41.4 km2 (16 mi.2) and the active disposal area covers approximately 2.59 km2 (1 mi.2) in the middle of the withdrawn area with the surface facilities only covering approximately 0.13 km2 (0.05 mi.2 ) [11]. The area required for the same capacity for high-level waste and SNF disposal as was planned for Yucca Mountain is approximately 0.32 km2 (0.125 mi.2) for the surface facilities and 0.8 km2 (0.3 mi.2 ) of subsurface facilities [10].

The repository portion of Yucca Mountain is planned to include approximately 64.4 km (40 mi) of railroad lines [12]. However, it is doubtful whether the design of a HLW/SNF repository in salt would use the same disposal approach – rail lines – because of the difference in geological properties between salt and tuff. Since the load bearing properties of salt are substantially less than those of tuff, the underground area for a HLW/SNF repository in salt would be substantially greater than the Yucca Mountain plan. Even so, there should be sufficient area to locate a separate HLW/SNF repository in the land withdrawal area of WIPP since the thickness of the Salado Formation would allow for more than one disposal level for HLW/SNF.

The geological characterizations of the WIPP land withdrawal area and the surrounding area indicate that a location south or east of the current WIPP facility would be preferable for two reasons. First, either location avoids a possible solution front that was identified early in the WIPP siting process. Second, they minimise the impact to the near surface hydrogeology associated the possible release pathways to either potable water aquifers (there are none nearby) or to Nash Draw, an intermittent stream to the west of the WIPP site.

A review of the current WIPP configuration (Figure 1, p22), indicates that expansion to the east would be the easiest should a decision be made to use as much of the existing shaft and underground facilities as possible. Also, should an increase of the capacity of the HLW/SNF repository be required above the 77,000 tons of nuclear waste currently authorized, as has been stated by DOE, the thickness of the Salado Formation would accommodate the construction of more than one disposal level in the repository – an option that had been explored earlier for WIPP [11].

The presence of oil or gas wells or other natural resource mining activities that may have resulted in breaches of the Salado Formation could expedite or facilitate the entry of water or brine into the formation and consequent interaction with radioactive waste disposed therein. Since WIPP was initiated, there has been a substantial increase in the oil and gas exploration and extraction activities in the Delaware Basin, where WIPP is located, so many of the previous areas that were undisturbed now have been drilled through. Although there has been increased borehole drilling in the environs of WIPP, as reflected by the increased deep borehole drilling density reported in the 2009 recertification application to EPA [13], the integrity of the Salado Formation under the 41.4 square kilometer (16 square miles) land withdrawal area has not changed since drilling is not allowed within that area. In fact, close surveillance is kept of any drilling within one mile of the WIPP boundaries so it would be relatively easy to expand the land withdrawal area up to 64.7 km2 (25.mi.2) and maintain the formation integrity required. This is allowed by 40CFR191, which allows expansion of up to 100 km2 (roughly 38.6 mi.2) [14]. Of course, it would require an amendment of the Land Withdrawal Act (PL 97-102) [1].

Waste handling facilities

There are two major issues with using the existing WIPP facilities to transfer and dispose of HLW/SNF. First, while the Waste Handling Building at WIPP is equipped with a hot cell, the handling plan for Yucca Mountain indicates as many as four hot cells would be needed since the radioactive waste would be received in both canistered and uncanistered shipments and would consist of multiple forms and sizes of containers that would have to be transferred into waste packages for disposal [10]. Therefore, it is probable that the WIPP hot cell does not have either the equipment or capacity or meet the current DOE safety requirements for the handling of HLW containers or SNF canisters. A second but equally critical issue is the ability of the Waste Shaft to handle the HLW/SNF waste packages. The WIPP waste shaft car is 9.1 m (30 ft) high by 3 m (10 ft) wide by 4.6 m (15 ft) deep and can carry a payload of 45 tons [11]. The proposed HLW/SNF waste package size is 3.7-5.5 m (12-18 ft) long by 1.5-1.8 m (5-6 ft) in diameter and the maximum weight of a waste package with a full load of either HLW or SNF is expected to be 54.25 tons [10]. A HLW/SNF waste package that is 5.5 m (18 ft) long would have to be lowered into the repository via the WIPP Waste Shaft in a vertical position, which would require special rigging for transfer into and out of the car. Also, the current waste shaft would not be able to transfer the heavier HLW/SNF waste packages, which are projected to be 90% of the HLW/SNF volume designated for Yucca Mountain.

There are major operational health and safety differences between WIPP and Yucca Mountain, primarily derived from the larger diversity of the radioactive waste types to be managed at Yucca Mountain versus WIPP. WIPP basically had four waste forms – contact handled TRU and TRU mixed waste and remote handled TRU and TRU mixed waste [11]. Those four waste forms are characterized and containerized at the generator sites and are prepared for disposal in one waste handling building. For Yucca Mountain, the operational plan is to receive six waste streams in different forms of canisters. To prepare those waste streams for disposal in the appropriate containers (the Transportation, Aging and Disposal Containers) will require eight separate facilities, most of which are planned for remote handling of the waste – effectively large hot cells. The HLW and SNF will be transferred into waste packages, which are essentially 1.5-1.8 m (5-6 ft) diameter cylinders ranging from 3-6 m (10-20 ft) long and weighing up to 50 tons for final emplacement. The surface temperature of the waste packages will range from 60°C to 200°C. However, the surface dose rate of the waste packages will be at or below the contact handled limit [15]. Thus, the major health and safety differences are the greater number of waste forms and the heat and radiation levels of those waste forms. While the WIPP waste handling building was designed to handle some forms of HLW, it was not designed to handle the variety that Yucca Mountain is designed to manage.


The major transportation routes to WIPP have already been established, as shown in Figure 2 [11]. If a HLW/SNF repository was co-located at the WIPP site, additional truck transportation routes would be required to serve the commercial nuclear facilities located in south Texas, Florida, the upper Midwest and along the eastern seaboard. These potential routes had already been identified in the Yucca Mountain Nevada EPA documents.

Transport by rail to the WIPP site would use much of the basic rail network proposed for Yucca Mountain via the Texas-Pacific and BNSF railroads with the addition of BNSF routes from the Midwest and Union Pacific routes through Texas to that network. Additionally, rail transport to the WIPP site would require the restoration of the rail spur line that extended from the mainline of the BNSF near Loving, Texas to the WIPP site during the period of construction of WIPP in the 1990s [11].


In terms of regulation, the site would have to demonstrate that it could meet the EPA disposal standards (40CFR191) [16] and certification requirements (40CFR194) [17]. The primary issue here is whether the EPA standards for WIPP (40CFR191) or for Yucca Mountain (40CFR197) would be applicable. There is a significant difference between them: the EPA standards for WIPP require that the annual cumulative dose rate from any releases be less than 0.15 mSv/year for 10,000 years after closure; the Yucca Mountain standards include a dose limit of 1 mSv/year between 10,000 years and 1 million years [18]. However, it is significant that 40CFR191 is applicable to any radioactive waste disposal facility operated by DOE, while 40CFR197 is Yucca Mountain-specific.

The site would also have to receive a Resource Conservation and Recovery Act (RCRA) [19] disposal permit modification from the New Mexico Environment Department. It also may be necessary for the Nuclear Regulatory Commission to issue it a licence depending on how the enabling legislation is worded. (EPA currently is the certifier for WIPP per the LWA, but the NRC is the licensing agency for high-level waste/SNF repositories).

If the disposal would be in the current WIPP facilities, then a major modification to the WIPP Hazardous Waste Facility Permit (HWFP) issued by the New Mexico Environment Department would be required since the high-level waste would be disposed in different containers than currently identified in the HWFP and there may be hazardous materials in the high-level waste identified for disposal at Yucca Mountain other than those approved for disposal as mixed waste in WIPP. In addition, if the existing facilities were used, then authorization could be accomplished by relatively minor modifications to the Land Withdrawal Act (recognizing that nothing related to nuclear waste disposal in the US that requires Congressional action is ever minor). That would leave EPA as the regulatory agency and 40CFR194 as the certifying process. However, should a new disposal facility be proposed to be constructed and operated within the withdrawn land area (new waste handling building, shafts and underground workings) then it appears that only the NRC licence would be required based on the licensing history for Yucca Mountain.

While the US currently does not have a SNF recycling programme, that possibility is currently being considered by the Blue Ribbon Commission established by president Barack Obama to make strategic nuclear energy recommendations. If it opts for a closed-fuel-cycle option that includes reprocessing, then storage of SNF in a salt formation is not a viable option. Regardless of fuel cycle strategy, however, some existing HLW will require permanent disposal, it said.

Author Info:

Christopher M. Timm, PE and Jerry V. Fox, PhD, PE, PECOS Management Services, 2418 Juan Tabo NE, Albuquerque, New Mexico 87112


A review of the scientific, engineering, and operational factors associated with the development and management of a HLW/SNF repository on or in the vicinity of WIPP leads to the following conclusions:
1. The Salado Formation that contains the WIPP repository is equally suited for disposal of HLW and SNF (if reprocessing is not planned) in terms of geology, hydrogeology, and physical, chemical and radiological interactions with the HLW/SNF waste packages. However, it is not recommended for storage of SNF that is planned to be reprocessed.
2. A separate HLW/SNF disposal facility would be required to be constructed to accommodate the diversity of the HLW/SNF waste forms, the increased handling requirements, and the size and weight of the HLW/SNF waste packages (which precludes the use of the existing underground repository for the disposal of those waste packages).
3. There is sufficient space within the land withdrawn for WIPP (16 square miles) to co-locate a HLW/SNF repository with WIPP. In fact, many of the WIPP surface facilities and infrastructure could be shared with the HLW/SNF disposal facility.
4. The preferred location for the HLW/SNF underground repository would be to the south or to the east of the WIPP repository.
5. Transportation of HLW/SNF to the WIPP site would be facilitated in that the basic network of rail and truck routes is already established and the rail spur that served WIPP during construction could be restored.

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Map of WIPP repository Map of WIPP repository
Figure 2: WIPP truck transportation routes showing DOE facilities from which waste will be collected Figure 2: WIPP truck transportation routes showing DOE facilities from which waste will be collected

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