INL's nuclear research and development and maintenance work lend themselves to myriad challenges in the health and safety realm.
The nuclear site in eastern Idaho where the Idaho National Laboratory (INL) is located was once home to the world’s first electricity-producing nuclear facility and first liquid-metal-cooled reactor. More than 50 different reactors have been housed at the site over its lifetime.

The site’s long history also includes the commissioning and activation of the Hot Fuels Examination Facility (HFEF). Originally designed to handle pre- and post-irradiated reactor fuel for examinations and experiments within an argon-filled “hot cell”—a containment designed to protect workers from radioactivity and other hazards by allowing operators to work with remotely handled tools using windows for visibility—HFEF currently performs experiments on post-irradiated fuel. These efforts allow scientists to better understand characteristics that, among other things, can be exploited to develop accident-tolerant nuclear fuels.
Imagine that your daily work is looking into a hot cell that is 30 feet wide by 70 feet long and 25 feet tall (see Figure 1). To perform experiments on post-irradiated fuel, you must utilize remotely handled tools that resemble robot arms, extend through the four-foot-thick concrete walls, and mirror the commands and controls in your hand (which remains in a safe environment outside the cell). The work being performed can range from the manipulation of items larger than paint cans to items one-eighth of an inch in size.
Despite a long history of great accomplishments, HFEF had never before removed and replaced a hot cell window until October 2016. The replaced window was leaking mineral oil, which is required to maintain transparency in a window made of several slabs of thick leaded glass. Without the mineral oil, the window cannot provide the visibility necessary for work to continue. THE WINDOW INL’s nuclear research and development and maintenance work lend themselves to myriad challenges in the health and safety realm. The replacement of this hot cell window, initially installed circa 1975, demonstrated the complex health and safety challenges that the operations and maintenance staff can face.
The job involved hazards that include, but were not limited to, the following:
  • high noise
  • radiation/contamination
  • manual material handling
  • silica exposure
  • lead handling
  • heavy lifting, hoisting, and rigging
  • elevated working surfaces
Protecting workers from these hazards required personal protective equipment (PPE) and the design of a specialized ventilation system and specialized containment.

HFEF includes fifteen windows arrayed along the four sides of the cell wall. Each window is several layers of thick leaded glass, 4 feet deep, 3 feet tall, 4 feet wide, and weighs roughly 14,000 pounds. Mineral oil is used to fill voids between the layers of glass for optical clarity. The windows are contained inside steel frames that utilize lead wool and lead sheeting to seal small gaps between the frame and window and are held in place by high-density, lead-painted grout (219 lb/ft3). The windows themselves are divided into three separate pieces: the “A slab,” the “B slab,” and the tank unit. These comprise several layers of glass and mineral oil. The A slab is the radiologically contaminated side of the window—the side facing the interior of the hot cell, with its high-radiation fields.
The A slab of the window to be replaced was changed out in late 2015. The tank unit and B slab were designed to be removed as a single unit (see Figure 2); however, for this job, they were eventually separated.
Removal of the window included the following tasks:
  • placement of a shield inside the hot cell (to reduce any potential radiation from sources in the cell)
  • removal of electrical and mechanical interferences
  • removal and draining of radiologically contaminated mineral oil contained within the window
  • establishment of a containment tent
  • removal of all grout
Windows are designed to be as thick as the hot cell wall to provide protection from radiation, contamination, and other hazards within the cell. For additional protection when the window was removed, a 9,000-pound steel shield was held in place by a crane on the inner side of the hot cell. The outer side of the window was covered with plywood to prevent accidental striking of the window.
The Challenges of Repairing a Specialized Nuclear Containment
Hot Cell
Window to the
Disadvantages of being unacclimatized:
  • Readily show signs of heat stress when exposed to hot environments.
  • Difficulty replacing all of the water lost in sweat.
  • Failure to replace the water lost will slow or prevent acclimatization.
Benefits of acclimatization:
  • Increased sweating efficiency (earlier onset of sweating, greater sweat production, and reduced electrolyte loss in sweat).
  • Stabilization of the circulation.
  • Work is performed with lower core temperature and heart rate.
  • Increased skin blood flow at a given core temperature.
Acclimatization plan:
  • Gradually increase exposure time in hot environmental conditions over a period of 7 to 14 days.
  • For new workers, the schedule should be no more than 20% of the usual duration of work in the hot environment on day 1 and a no more than 20% increase on each additional day.
  • For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% of the usual duration of work in the hot environment on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
  • The time required for non–physically fit individuals to develop acclimatization is about 50% greater than for the physically fit.
Level of acclimatization:
  • Relative to the initial level of physical fitness and the total heat stress experienced by the individual.
Maintaining acclimatization:
  • Can be maintained for a few days of non-heat exposure.
  • Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.
  • Can be regained in 2 to 3 days upon return to a hot job.
  • Appears to be better maintained by those who are physically fit.
  • Seasonal shifts in temperatures may result in difficulties.
  • Working in hot, humid environments provides adaptive benefits that also apply in hot, desert environments, and vice versa.
  • Air conditioning will not affect acclimatization.
Acclimatization in Workers