A SURVEY OF RADIOACTIVE WASTE DISPOSAL IN IRELAND

Transcription

1 ' r. v., INIS-mf~11462 A SURVEY OF RADIOACTIVE WASTE DISPOSAL IN IRELAND N O' Donovan BSc, MB, BCh, BAO C Hone BA, MlnstP, CPhys F J Turvey CEng, FINucE, FIMarE, MIMechE December 1988 Nuclear Energy Board 3 Clonskeagh Square Clonskeagh Road Dublin 14

2 CONTENTS PAGE Introduction 1 Results 2 Summary 3 Discussion 3 Acknowledgements 4 References 4 Tables 1,2 - Questionnaire sent to Licensees 5 Table 3 - Activity of Each Isotope Disposed in Ireland Table 4 - Activity of Each Isotope Disposed to the Sewer (1987)... 7 Table 5 - Activity of Isotopes Disposed of by Incineration 8 Table 6 - Limits for Disposal of Waste without Special Control... 9 Table 7 - Limits for Disposal of Waste with Special Control 9

3 INTRODUCTION This survey was undertaken by the Nuclear Energy Board (N.E.B.) to assess the quantity of radioactive waste disposed of in Ireland and the methods used. The regulatory control of disposal is carried out on an ongoing basis by the Board's inspectors and is commented on routinely in the Board's annual report. Small quantities of radioactive material, both sealed and unsealed are imported for use in industrial, medical and laboratory applications under licence from the Board and conditions with regard to radioactive waste disposal are laid down in this licence. There is no national facility for waste disposal in Ireland and all imported sealed sources of radioactive material must be returned to the original supplier at the end of their useful life. The need for disposal of sealed sources therefore arises mainly in connection with those sources which were imported before licencing became obligatory in 1977, but is also required for those sealed sources which were purchased from manufacturers/suppliers who are no longer trading. It should be emphasised however that this survey was limited to an examination of waste arising from the use of unsealed sources. The main users of unsealed sources are radiotherapy and nuclear medicine departments of hospitals and certain laboratories, some 33 in all. These comprised 13 nuclear medicine departments and 20 other laboratories located in hospitals, third level educational establishments and commercial enterprises. Each licensee was given a questionnaire to complete and very full co-operation was obtained. See tables 1 and 2. The following details were requested. 1. List of isotopes disposed. 2. Method of disposal and the activity disposed per month via each route (i.e. sewer, incinerator, rubbish tip and returned to manufacturer). 3. Average storage period prior to disposal of the waste material. 4. The type, number, initial activity, average storage period, and method of disposal of isotope generators. Assumptions which were made when analysing the data included: a. that the total amount of administered to patients was excreted to the sewer; b. that in cases (less than 1% of total) where the method of disposal was not indicated it was assumed to be via the sewer; c. that in the case of Tc-99m administered to patients, 50% of the activity was assumed to be excreted to the sewer; d. that the amounts disposed of in one year (table 3) were 12 times the amounts disposed of per month. 5. Although the data applies only to 1987, the usage of unsealed radioisotopes is not expected to change significantly over the next five years. The 1987 data may therefore be considered typical for some years to come.

4 RESULTS An analysis of the amounts of the various radioisotopes which are disposed of as waste is given in Table 3. It can be clearly seen that by far the greatest amount of activity, (99%) is disposed of via the sewer. This is to be expected since i) most institutions do not have access to an incinerator ii) iii) iv) liquid waste miscible with water can be most conveniently disposed of via the sewer it is easier to ensure adequate dilution when using the sewer than some of the other methods of disposal users of unsealed radionuclides are reluctant to operate incinerators in built up areas, where such operation would be likely to result in objection from the local population. Disposal To Sewers The total amount of activity which is disposed of to the sewer (1987) is approximately 526 CBq per month. Table 4 gives the relative amounts of each isotope discharged in this way. Tc-99m is the isotope disposed of in the greatest quantities, amounting to 97% of the total. Its short half-life (six hours) ensures that it does not pose a significant risk to health or the environment, lodine-131, however, at 2.6% of the total, is worthy of closer attention because of its longer half-life and greater radiotoxicity. It concentrates in certain seaweeds which makes it relatively easy to monitor in the environment and to confirm that present discharges do not represent a health hazard. Gallium-67 is the third next abundant radioisotope in discharges to the sewer, accounting for a fraction of 1%, and this is followed by tritium. Though the radiotoxicity of tritium is low (Group IV) its incorporation in labelled purines and pyrimidines coupled with its long half-life (circa 12.4 years) may enhance the associated biological hazards. For this reason the use of incineration to reduce the labelled compounds to tritiated water is preferred and encouraged even when the quantities involved are small. Incineration Disposal by incineration accounts for less than 0.01% of all radioactive waste generated. The activity disposed of by this route in 1987 was approximately 517 MBq per month. This low value reflects the limited availability of suitable incineration facilities in Ireland and the fact that discharge to the sewers is both cheaper and easier for the institutions involved. Incineration, under properly controlled conditions however, does provide a safe and convenient method for disposal of non water soluble organic solvents and of contaminated material, such as tissue samples as well as solid material not suitable for discharge to the sewer. Table 5 gives the breakdown of radioisotopes incinerated and the activities involved. Tritium heads the list, amounting to 27% of the total, followed by Carbon-14 and lodine-125 at 22% each and lodine-131 at 14%. The other 15% is made up of various isotopes including S-35, Se-75, Tc-99m. Rubbish Tip Disposal of material to the rubbish tip is only permitted when the radioactive content is below the limits specified in Table 6. Material disposed of by this method mainly consisted of weakly contaminated laboratory materials. The total activity amounted to 215 MBq of which 78%, i.e. 167 MBq, consisted of tritium.

5 Isotope Generators Molybdenum-99/Fechnetium-99m generators are the mainstay of nuclear medicine departments (Ref. 2). Their storage and disposal, however, are not without problems. Of the nuclear medicine departments surveyed, 60% of them returned units to the supplier after varying periods of storage (3-6 months). In one case the units are stored for one year and then incinerated. In all other cases the cores are stored on site indefinitely. Most departments use one generator a week with an activity between GBq. The total activity used per month amounts to 1019 GBq. Assuming that all of this is administered to patients who in turn excrete 50% (rough estimate), then some 510 GBq of Tc-99m should find its way into the sewers every month (this is probably an over estimate of the actual amount discharged). Because of its short halflife (6 hours) and the extremely long half-life (hence low activity) of its decay product, this isotope poses little in the way of an environmental radiological hazard. On Site Storage Most institutions find it necessary to store contaminated laboratory ware and other contaminated material prior to disposal so that levels eventually fall below those stipulated in licences for disposal to the environment. These disposal limits are given at the end of this paper in Tables 6 and 7. This may involve storage in lead lined bins or concrete bunkers for up to 10 half-lives. In many cases, following such a storage period, activities of disposed materials are below background levels. In some departments such long term storage is not feasible because of limited space and consequently difficulties may arise in complying with the N.E.B. licencing conditions. SUMMARY A total of 526 GBq of radioactivity was disposed of per month in Ireland during 1987, amounting to 6316 GBq annually. This may be taken to be a typical annual rate for the next five years during which period usage is not expected to change. Over 99% of this is discharged to the sewers. Nuclear medicine and radiotherapy departments of hospitals are by far the largest producers of radioactive waste and most of this is discharged as patient excreta. Since these hospitals are located in the large urban centres most of the radioactive waste produced in Ireland is eventually discharged into Dublin Bay, Galway Bay and Cork Harbour. Technetium-99m accounts for 97% of this waste. Radioiodines at 2.6% form the second most abundant group of radioisotopes in the waste. All other wastes are negligible by comparison. DISCUSSION Radioactive waste disposal has been a controversial issue in recent times. This is especially true of a country like Ireland, which being non nuclear, ensures that public opinion is set firmly against the provision of a radioactive waste disposal facility. Though this view is understandable, it does not help to solve the problem of the disposal of such waste. The present system whereby most of the waste ends up in the sewers is adequate for the moment, but should there be a substantial increase in usage, then alternative means of disposal may be required. If such a situation did arise, due consideration would have to be given to the provision of a national radioactive waste storage facility and incinerator.

6 The present practice of storing solid waste on the user's premises for the long periods necessary for decay prior to unrestricted disposal is undesirable. Ideally this material should be incinerated under controlled conditions to reduce its volume, and where relevant, the concomitant biological hazard. This method of disposal is of course only acceptable if it can be carried out without causing significant atmospheric pollution from either radioactive or non radioactive products of combustion, and, if adequate facilities for handling and disposal of ash and flue filters exist. Alternatively it should be conditioned, packaged and disposed in a dedicated waste disposal site. A further problem may arise in the near future. This relates to the disposal of sealed radioactive sources. As outlined earlier, all such sources are at present returned to the original suppliers or manufacturers (none of which are located within the State) at the end of their useful life. Should this method of disposal be terminated for any reason, then the use of such sources in Ireland would be almost impossible if a disposal facility were not available. A disposal facility is also required as a final repository for redundant sealed and unsealed sources with a long half-life such as radium salts. These sources were imported by medical and educational establishments before the establishment of the Nuclear Energy Board and therefore before the present regulatory system was in force. ACKNOWLEDGEMENTS The authors would like to express their gratitude to all those institutions who cooperated in carrying out this survey. They also wish to thank the Commission of the European Communities who under its research programme on Radioactive Waste Management and Disposal supported the preparation of raw data for publication and the editing of the report. REFERENCES 1. Statutory Instruments. S.I. No. 166 of Nuclear Energy (General Control of fissile fuels, radioactive substances and irradiation apparatus) Order, (Prl. 6344) Dublin, Stationery Office. 2. O'Donovan, N., Hone, C. and Turvey, F.J. "Survey of nuclear medicine practice in Ireland." Irish journal of Medical Science. Vol. 157 (10) 1988,

7 TABLE 1 QUESTIONNAIRE SENT TO LICENSEES RADIOACTIVE WASTE DISPOSAL APPROXIMATE ACTIVITY DISPOSED OF AS WASTE (PER MONTH) ISOTOPE Total Average Activity Discharged to Sewer METHODS OF DISPOSAL Average Activity Incinerated Average Activity Disposed of to Rubbish Tip Average Activity returned to Manufacturer AVERAGE STORAGE PERIOD C-14 Co-57 Co-58 Ca-67 H Kr-85 P-32 S-35 Se75 Tc-99m TI-201 Xe-133 Others TABLE 2 ISOTOPE GENERATORS TYPE NUMBER INITIAL ACTIVITY AVERAGE STORAGE TIME METHOD OF DISPOSAL Tc-99m ln-111 Others

8 TABLE 3 ACTIVITY OF EACH ISOTOPE DISPOSED OF IN IRELAND IN 1987 MBq ISOTOPE SEWER INCINERATOR RUBBISH TIP TOTAL C Co Co Ga H Kr-85 0 P S Se Tc-99m TI Xe ln Cr Others TOTAL Note: In the case of the two institutions which did not return the questionnaire, the methods of waste disposal were assumed to be the same as those stated in the returns of institutions using the same radioisotopes under similar conditions. The amounts assumed to have been disposed of by each method were obtained by using the values quoted by the other institutions multiplied by a factor which represents the relative usage. This factor was obtained from an examination of NEB licence schedules of the two institutions in question and those which returned questionnaires.

9 TABLE 4 ACTIVITY OF EACH ISOTOPE DISCHARGED TO THE SEWER IN IRELAND (1987) ISOTOPE MBq/Month ACTIVITY DISCHARGED PER MONTH IN MBq % C-14 Co-57 Co-58 Ga-67 H Kr-85 P-32 S-35 Se-75 Tc-99m TI-201 Xe-133 ln-111 Cr-51 Others TOTAL , , ,

10 TABLE 5 ACTIVITY OF ISOTOPES DISPOSED OF BY INCINERATION (1987) ISOTOPE MBq/Month TOTAL ACTIVITY DISPOSED INCINERATION BY % C-14 Co-57 Co-58 Ga-67 H Kr-85 P-32 S-35 Se-75 Tc-99m Tl-201 Xe-133 ln-111 Cr-51 Others TOTAL

11 TABLE 6 LIMITS FOR DISPOSAL OF WASTE WITHOUT SPECIAL CONTROL Nuclide Toxicity Group Total Activity Discharged/Day (Becquerels) Activity of liquids per litre (Becquerels/litre) Activity of solids per cubic metre (Becquerels/cubic metre)* CROUP 1 5 x x x 10 3 GROUP 2 5 x x x 10 4 GROUP 3 5 x x x 10 5 GROUP4 5 x x 10 s 5 x 10' * Disposal of solid wastes without special control is subject to the additional restriction that the specific activity does not exceed 100 kbq/kg, this limit being increased to 500 kbqag for solid natural radioactive substances 1 Becquerel - 27 picocuries TABLE 7 LIMITS FOR DISPOSAL OF WASTE WITH SPECIAL CONTROL Nuclide Toxicity Group Total Activity Discharged/Day {Becquerels) Activity of liquids per litre (Becquerels/litre)* Activity of solids per cubic metre (Becquerels/cubic metre) GROUP 1 5 x x x 10" GROUP 2 5 x 10 s 5 x x 10 5 GROUP 3 5 x 10' 5 x 10 s 5 x 10' GROUP4 5 x x 10' 5 x 10 7 * In the case of liquid waste containing only lodine-125 or lodine-131 a total activity of up to 1(P Bq may be discharged/day. (i) (ii) (iii) Disposal of waste material below these limits is subject to any additional restrictions as laid down in Schedule 1 of the relevant licence. To ensure safe handling the volume of solid refuse must not be less than one tenth of a cubic metre and the activity of any single item of waste must not exceed one tenth of the values given in column 3. Excreta from individuals undergoing diagnosis or therapy with radioactive materials are exempt from these limitations.

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