Health Physics Pergamon Press 1975. Vol. 29 (September), pp. 389-392. Printed in Northern Ireland
INCINERATION OF ANIMAL RADIOACTIVE WASTE: A COMPARATIVE COST ANALYSIS* WINBORN D. GREGORY and H. DAVID MAILLIE The Univcrsity of Rochester, Health Physics Division, 260 Crittenden Blvd., Rochester, New York 14642
(Received 2 December 1974; accepted 22 Janwry 1975) Abstract-Incineration of radioactive waste has been found to be an excellent method for reducing both the bulk and the handling problems associated with the use of animals in a research institution. A cost analysis has been made at the University of Rochester for the incineration of certain wastes as compared to the cost of land burial. I n determining the feasibility of incineration for a radioisotope the major factors to be considered are the activity, half-life, and maximum permissible air concentration of the isotope and the size of the carcass in which it is incorporated. Comparative examples are given for several specific isotopes in use at this institution. Environmental factors are also considered. INTRODUCTION
used for biological research where tracer quantities of radioisotopeshave beeninjected and found to be an excellent method for reducing the animals have been sacrificed at some time both the bulk and the handling problems after injection. The carcasses are individually associated with the use of animals in a research bagged and segregated into freezers according institution. Federal regulations (10CFR20.305) to the half-life. A tagging system is used to do not allow incineration as a means of disposal identify the date they may be incinerated. The except by special exemption. Any application freezers are also used to store those carcasses for an exemption to incinerate radioactive that may not be incinerated but must be shipped materials must include a justification for this out for land burial. means of disposal. There are three major factors The incinerator used is a Kellogg-Man which are important to this justification. The crematory type unit with a combustion rate of most important is environmental, but this is the 501b/hr. An exemption has been granted to most difficult to approach. The second is the incinerate radioactive materials since 1968. logistics of holding and shipping animal car- Currently, permission has been given to incasses, and the third factor is that of expense. To cinerate 23 different isotopes at certain fixed a health physics unit supporting an educational limits based on the maximum permissible coninstitution, cost can be, but should not be, the centration (MPC) in air for each isotope. most important factor. Permission has been granted to exceed the MPC A cost analysis has been made at the at the mouth of the stack by a factor of 10 University of Rochester for the incineration of during any single burning. A special variance certain wastes as compared to the cost of land was granted for lZ5Iand lS1Ito exceed MPC by burial. I n general, incineration has a cost a factor of 20. The calculations for the amount advantage, but this is dependent on the radio- burned at one time are also based on the isotope and the size of the animal carcass in assumption of 100% of the radioisotope going which it is incorporated. up the stack. A 30-min burning period is assumed. This is considered to be the average FACILITIES Animal carcasses are accumulated in six time it takes to burn an animal carcass. A large chest type freezers. The animals have been dog takes about 1 hr to be consumed while rats take only 15 min. Over a 30-min burn* This paper is based on work performed under ing period, the total volume of air flowing contract with the U.S. Atomic Energy Commission up the stack is 8.5 x 10*ml. This volume is at the University of Rochester Atomic Energy Project multiplied by 10 x MPC to give the pCi and has been assigned Report No. UR-3490-643.
INCINERATION of radioactive waste has been
I N C N R A T I O N OF ANIMAL RADIOACTIVE WASTE
amount that may be incinerated in one burn period. For example, iron-59 has an MPC of 2 x 10-8 pCi/ml. The calculation results in an amount of 17 pCi that may be put into the incinerator in a single one-half-hourperiod. The limit of pCi[yr of each isotope is a self-imposed restriction, but takes into consideration the MPC and the anticipated use of the isotope. A calculation of the per cent of the MPC for the year is also made for each isotope. This is based on a 40-hr work week for a total air flow of 3.53 x 101aml/yr. For those isotopes known to remain in the ash, a stainless steel box is used to hold the ashes. They are later transferred to a 55-gal drum and shipped for land burial.
Table 2. Isotopes m.th short half-lifr Isotope
of (HPC). for Year
1 x lo-1o
a x lo-'
stored until the level is low enough to incinerate. Although chromium-51 may be burned in larger quantities due to the high MPC, the short half-life makes it feasible to store this isotope for radioactive decay before incinerating. Dog carcasses weighing 40-50Ib and containing up to 50 pCi of chromium-51 were brought for disposal at the rate of one per week. UNIT COSTS In a 6-month period taken for evaluation, this The cost analysis in this paper is based on gas resulted in 26 dogs which would have filled at consumption, freezer costs, man-hours, and least six 55-gal drums. The cost for this is shipping costs. Since the incinerator is used for shown in Table 3. For this one example the normal incineration at other times, no deyearly savings from incineration would amount preciation or capital expenses were considered to over $700. Also, depending on the frequency in this analysis for the facility itself. Table 1 of land burial shipments, more freezer space shows the basic breakdown of costs so that would be required in holding animals for a variable expenses may be changed to meet shipment, than if they could be incinerated on one's o w n situation. a regular basis. The next category of half-lives include those EXAMPLES isotopes listed in Table 4. From experience, it Carcasses containing short half-life material has not been practical to hold any of these are easily handled by storage and incineration. The only limiting factor is the amount of isotopes longer than three half-lives. For 1261 freezer space available. In Table 2 there are this would be a 6-month storage period and four isotopes with short half-lives listed as would be given an upper limit of 10,uCi that examples. Chromium-51, with a half-life of would be held for incineration. Anything over 27.8 days, is the cut-off point used. Any this limit would not even be considered. Also, reasonable activity of these isotopes may be if the animal carcasses are small, it is not practical to incinerate each one individually. A 4-month study was made of a collection of Table I , Basir fir cost analysis carcasses containing iron-59. There were GAS CONSUMPTION bundles of rats (up to 10 rats each and originally
1.040 cu. Pt./Rr Hatvral Gae $0.170 per 100 Cu. I t .
Table 3. Dogs withchromium-51 (Etmluationpniod: 6 months)
FREEZER S T O W E power conemption 2000 kwlnear Electricity $0.03 per kW Freezer Capacity: 25.3 Cu. Pt. COBt on New Freezer: $259.00 Ass10 Year L i f e Time
Land Burial unit cost
Reconditioned NIT 17A. 55 'Allan Drum $10.00
Shipping Chergca Service - $46.00
U n d Burial of Drums
Freezer Use @ 45 Cu. Pt.
1Incineration unit cost
Ash D i s p o s a l
W. D. GREGORY and H. D. W I L L I E Tnble 6 . Isotopes with long knlf-l$e
Tnble 4. Isotopes with medium half-Iifi of ( M m a far Year
3 5 ~
containing 80 pCi per bundle), rabbit carcasses, and some bags of plastic vials containing extracted tissues. The total weight of this collection was 205 lb and one 55-gal drum would have held the entire lot. They were, however, held for decay down to 17 pCi and were incinerated in 37 half-hour burn periods throughout the 4-month period. This is one 17-pCi package per burn period. An analysis of the cost is given in Table 5. It would have cost $16.55 more to ship for land burial. In practical terms this is equivalent to incineration in cost, but it is a good-example of the break-even point due to the size of the pa.ckage that is incinerated. From this example it may be concluded that anything smaller than a package of about 10 rats or a rabbit carcass may become more expensive to incinerate. Of course, this depends on the activity limit for incineration and the activity in each carcass. The third category of radioisotopes are those with long half-lives. A few examples of these are given in Table 6. It will be noted that tritium and carbon-14 may be incinerated in IargepCi quantities. For this reason it is economically feasible to dispose of small animals as well as large ones by charging the incinerator with up to the pCi limit that is allowed to be burned at one time. A 3 months evaluation for tritium and carbon-14 is shown in Table 5 . Corcasses containing 6w1-59 (Eunluntion period: 4 months) Land Burial UDit Land
Burial of O r m a
Table 7. There is no ash handling problem since nearly 100% of both isotopes would go up the stack (BUSHand HUNDAL, 1973). The other radioisotopes in this category, as represented by calcium-45 and cadmium-109, have low incineration limits and half-lives of such length that it is not feasible to store these for radioactive decay. Therefore, it is not economically advantageous to incinerate these isotopes if the carcasses contain above the incineration limit or if the animals are small. ENVIRONMENTAL IMPACT
No attempts have been made to measure the release of radioactivity from incineration. Perhaps this should be the next step. From a mathematical standpoint the concentration at the outlet of the stack does not exceed 10 x MPC based on the limits per burning period. Calculations (CEMBER,1969) have been made to estimate the activity in the air at ground level. Using an emission rate of 100mCi/yr (the maximum amount that is anticipated to be burned in a year), the maximum ground level concentration is 1.7 x pCi/cm3. This is lower than the MPC for a mixture of isotopes by a factor of about a thousand. Most of the 100 mCi is attributable to tritium and carbon-14 which are minimum hazard isotopes. Tabla 7 . Cnrcnssrs contnining tritium and cnrbon-14 (Evaluation period 3 month) land Burial
rncineration unit cost
1ncineracion unit cost
Freezer use @ 8 Cu. Ft.
Freezer Use @ 8 Cu. Ft. Natural Gas
INCINERATION OF ANIMAL RADIOACTIVE WASTE
An unknown factor to consider is the possible Another problem with land burial is the reconcentration of these incinerated radio- logistics of shipping frozen animal carcasses. isotopes in the environment. This is known to Arrangements must be made for definite and occur with fallout from a nuclear bomb (RITCHIE immediate shipment, and the barrels cannot be and MCHENRY, 1973) and studies are conducted packaged ahead of time. If the shipment is around nuclear power plants (CULLITON, 1973). delayed before burial, there is the risk of rupture Since there are no agricultural activities in the of the drum. immediate vicinity of the incinerator the CONCLUSION greatest hazard would be due to inhalation in From the examples given in this paper it nearby occupied areas. should be clear that incineration as a means of On the other hand, land burial is also becoming a touchy subject. Most of the attention waste disposal can be advantageous on a cost is being focused on spent fuel from reactors, but basis. The factors which limit the amount of often all waste is affected by the decisions incineration are the activity, the half-life, the pertaining to high level waste. In fact, our low- MPC in air, and the size of the animal carcass. level waste is buried at the same burial site Incineration may be a direct environmental as a reactor’s so-called low-level waste. At the detriment, but, realistically, it is doubtful that Moorehead, Kentucky, burial grounds, it was there is any real hazard from the small amounts reported (FRY,1969) that in 1967 the burial of that are permissible to incinerate. solid waste with low hazard potential was at the REFERENCES rate of 200,000 ft3/yr with an average activity BUSH D. and HUNDAL R. S., 1973, Health Phys. 24, of 4 Ci/ft3. Our waste does not approach this 564. level of activity and realistically should be CEMBERH., 1969, Introduction fo Health Physics considered in a separate category. The point is (Oxford: Pergamon Press). that land burial space is being wasted by burying CULLITON M. A., 1973, Radiat. Data Rebts 14, 145. low level activity that could be handled better RITCHIE J. C. and MCHENRY J. R., 1973, Radiat. through incineration. By low level is meant less Data Reps 14,727. than 100 pCi/ft3. FRY M., 1969, Am. J. publ. Hlth 59,448.