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 The Case of the Radioactive Pillow

The Reactor Facility that was Built at Columbia University  but Never Used

The Decay-In-Storage Room at the Einstein College of Medicine

Freeze-Drying as a Potential Mean for Waste Handling of Animal Carcasses Containing Radioactive Material

The Decay-In-Storage Room at the Einstein College of Medicine
By George Hamawy and Carl Passler

In anticipation of the closing of the last remaining radioactive waste burial site at Barnwell, S.C., to out-of-compact waste, the Albert Einstein College of Medicine decided to start a decay-in-storage room to handle its radioactive waste. The college is a medical school, graduate school, and medical research institution with approximately 400 research laboratories, of which 140 use radioactive material for research. All the college's affiliated hospitals are at different locations, and their radioactive waste is handled separately.

 storage room before operation
Storage room before operation
8 months later
8 months later
The first task was to estimate the size of the area needed to handle the radioactive waste, which, contrary to general belief, was found to be relatively small. We also found that the accumulated waste volume will reach a maximum size and stabilize at that level after an elapsed period of approximately 3 years.

WASTE GENERATION

Our records indicated that during 1992 we had shipped for burial 100 drums (55 gallons or 7.5 feet3 each) of compacted solid dry waste. That is 750 ft3 of compacted solid dry waste. Since our compaction ratio was 2:1, the actual volume was 1500 ft3. All radioactive liquid waste, excluding sink disposal and decay, was solidified and treated as solid waste. The solidified liquid constituted about 5 percent of the dry solid waste. The liquid scintillation drums were handled differently, and their disposal was not affected by the Barnwell site closure.

The distribution of radioactivity by isotopes used in 1992 is shown in table 1.
MAXIMUM VOLUME TO BE STORED

To estimate the size of the area required for sroring the radioactive waste, we made the following assumptions.
  1. Isotope usage will continue at the same rate in the future.
  2. The annual volume of waste generated for each isotope is proportional to the amount of activity during that period. Table 2 shows the annual volume of waste generated in 1992.
  3. We must store the waste being generated by the long-lived isotopes carbon 14 and hydrogen 3 until an alternative method of disposal is devised, sometime within the next 10 years.
  4. The waste is being successfully segregated by isotope.
  5. After a storage period of 10 half-lives for each isotope, the waste can be considered nonradioactive and can be removed from the waste area.

Table 1 - Distribution of Annual Isotope Usage (1992)
Isotope
 Amount (Ci)
 Percentage
Phosphorus 32
 1.84
 43
Sulfur 35
 1.10
 26
Iodine 125
 0.38
 9
Chromium 51
 0.35
 8
Hydrogen 3
 0.59
 14
Carbon 14
 0.02
 <1

Because the minimum storage period is 10 half-lives of the isotope being stored (set by article 175 of the New York City Health Code), the maximum accumulated volume of waste to be stored for each isotope is the amount that is being generated during that period of time for each isotope.  In other words, for isotopes whose 10-half-life period is less than a year, the maximum accumulated waste volume is less than the annual waste volume generated. When that period is longer than a year, the maximum accumulated waste volume is larger than the annual waste volume generated. The maximum accumulated volume of waste for each isotope and the aggregate amount, excluding the long-lived isotopes, are shown in figure 1.

The waste generated by the use of hydrogen 3 is largely in low-activity liquid form, while the solid waste volume is small. A large percentage of hydrogen 3 waste will be disposed of as liquid waste.
Table 2 - Annual Volume of Solid Radioactive Waste Generated by Isotope (1992)
Isotope
 Volume of Waste (ft3)
Phosphorus 32
 645
Sulfur 35
 390
Iodine 125
 135
Chromium 51
 120
Total:
 1290
The long-lived solid waste (hydrogen 3 and carbon 14) will be compacted and stored until a disposal site is established. The total volume of this kind of long-lived waste is approximately one 55-gallon drum of compacted dry solid waste annually.

AREA REQUIRED

The maximum accumulated waste volume was calculated to be 1880 cubic ft (fig. 1).To estimate the size of the area that will be required to store this amount of waste, we assumed the following conditions:
  1. The waste will be stored in boxes measuring 19 by 19 by 26 in. (approximately 5 ft3).
  2. The boxes will be stacked three high.
  3. The boxes will be in rows that are spaced to allow for traffic and easy access.
If we stack the boxes three high to a height of 6.5 ft, the solid area required is approximately 300 ft2. Since we require space between the rows, a conservative  estimate would be to double the solidarea to a required storage area  of 600 ft2.
figure 1
Figure 1
 
LOCATION

The following criteria were used to select an appropriate location for the storage room.

  1. The room must be centrally located for easy access from various buildings of the college.
  2. The room must have easy access to the outside for shipping the decayed waste.
  3. The room must be somewhat isolated from the busy traffic of college personnel.
  4. The room must satisfy the size requirements and be in compliance with all pertinent codes and regulations.
We investigated several available locations within the college and selected a room in the basement of one of the buildings that meets all the selection criteria. The dimensions of the room are approximately 30 by 17 ft.

ROOM PREPARATION

The storage room was prepared for accepring waste for decay by implementing the following room modifications.
  1. An area monitor with an alarm system was installed inside the room. 
  2. The floor was covered by an enamel surface without seams.
  3. A sprinkler system was installed.
  4. A systemof pallets divided the room into different sections for each isotope's waste storage.
  5. An elaborate system of recording waste information was devised, The data are recorded both electronically and manually.
The room was prepared for rhe storage operation and began to accept waste for decay in May 1994.  The Barnwell burial site closed its doors to waste from our New York area in June 1994.

WASTE COLLECTION

Segregated radioactive solid waste was collected from users and transported to the decay-in-storage room. All pertinent information was logged in, and the waste bags were inspected and packed in boxes. Informational labels were affixed to each box.

The storage period of 10 half-lives was calculated, and the date of probable disposal was marked on a long-term wall calendar.

After the elapsed storage period, the boxes were checked for radiation, and all the data on monitoring, inspection, and contents were kept for reference.  The box was then disposed of as nonradioactive waste after the radiation safety officer's approval.

POSTOPERATION

Eight months after the start of the operation, the volumeof accumulated radioactive waste ro be handled and stored in the storage room was even smaller than anticipated (figure 2).

Some of this volume reduction was attributed to the following factors
  1. An intensive campaign was launched within the college for minimizing radioactive waste generation.
  2. Laboratories were charged a fee for the use of the storage room to encourage the minimization of waste.
  3. Laboratories were encouraged to store their short-lived waste for decay within their respective laboratories rather than in the storage room. Several laboratories chose this option.
CONCLUSION

The first thought when considering a decay-in-storage room is that the area required will be very large, but the actual size of the area is relatively small.  Excluding the long-lived radioactive waste, it is assumed that the volume of accumulated waste will increase gradually and reach its maximum volume 3 years after the storage starting date (the period required for sulfur 35 decay, the isotope with the longest half-life of our decayable waste).  After this elapsed period, the total waste volume will remain stable with no appreciable increase, and no additional storage area will be required.
figure 2
Figure 2



The Authors

George Hamawy is the radiation safety officer at Albert Einstein College of Medicine in the Bronx, New York.  He received his education at New York University and Hunter College and has been working with radioactive materials for the last 25 years.

Carl Passler is the assistant radiation safety officer at Albert Einstein College of Medicine.  He received his training in the U.S. Navy serving on a nuclear submarine for 6 years.
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