1、 American National Standard ANSI/HPS N13.45-2012 Incineration of Low-Level Radioactive Waste Approved: February 17, 2012 American National Standards Institute, Inc. Published by Health Physics Society 1313 Dolley Madison Blvd. Suite 402 McLean, VA 22101 Copyright 2012 by the Health Physics Society.
2、All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher. Printed in the United States of America ANSI/HPS N13.45-2012 iii This standard was developed under the authority of the H
3、ealth Physics Society Accredited Standards Committee (ASC) N13, Radiation Protection. The Working Group responsible for this standard had the following members: Vincent P. Williams, Chairperson (Merck LSC, liquid scintillation cocktail; BW, biological waste; CSW, combustible solid waste. Notes aDete
4、rmine whether CLW or LSC is classified as hazardous as defined by current EPA or state regulations. bCan be incinerated if a Resource Conservation and Recovery Act (RCRA) Part B permit has been obtained. cDetermine whether LSC or BW may be disposed of as though it were not radioactive. dWhen effluen
5、t concentrations approach concentration limits, activity incinerated may need to be reduced. eAqueous wastes must meet NRCs solubility criteria prior to sewer disposal. ANSI/HPS N13.45-2012 6 4.2 Classification of Wastes Characteristics of LLW to be considered in a classification scheme for incinera
6、tion should include physical form, combustibility, possibility of decomposition, and hazards other than radiological. The physical forms of LLW are generally categorized as solid or liquid. Combustibility refers to the degree of oxidation that occurs during incineration. The possibility of decomposi
7、tion is associated with biological residues, tissues, body fluids and wastes, and animal carcasses. The primary hazards other than radiological are the infectious and chemical properties of the waste. Occupational hazards associated with waste handling such as mechanical injuries, lacerations, punct
8、ure wounds, and back strains are not addressed in this standard. 4.3 Effluent Concentrations The maximum activity (Amax) for a single radionuclide that may be incinerated in a specified period of time is limited by concentration limits for radionuclides in gaseous effluent and ash or by the maximum
9、permissible dose to the nearest receptor as determined by modeling (see Section 8.2). 4.3.1 Gaseous Effluent Concentrations The following formula may be used to determine the maximum activity (Amax) that can be incinerated in one year based on a concentration limit in the gaseous effluent: Amax= CFT
10、/R (1) where: C = concentration limit averaged over 1 yr (Bq cm3)*, F = stack effluent rate (cm3s1), T = number of seconds in one year, and R = fraction of the incinerated radioactivity emitted from the stack. *Usually this value will either be specified in regulations/license conditions or can be d
11、etermined using models that calculate radiation doses to nearby residents. Although incineration of activity equal to Amaxin a single day will give the same average annual concentration as incinerating Amaxthroughout the year, an upper limit for Amaxshould be established for a single incineration cy
12、cle (e.g., 1/12th of Amax). Furthermore, the year-to-date fraction of Amaxshould be determined after each incineration cycle to ensure Amaxis not exceeded over the course of the year. Since the volume of gases released is infinitesimal compared to the volume of the atmosphere, it is assumed for purp
13、oses of this equation that the incinerator is operated continuously, regardless of the actual incinerator on-time. Therefore, T is set to be equal to the number of seconds in one year. Use of eqn (1) requires that the concentration limit be applied to the point of release (i.e., at the top of the in
14、cinerator stack). This application provides a conservative estimate because the receptor is not present at the point of release but is some distance away. Alternatively, the radiation exposure to, or the concentration limit in the vicinity of, a receptor can be used to determine the maximum activity
15、 (Amax) that can be incinerated. Section 8.2 discusses methods for determining radionuclide concentrations in the incinerator effluent. 4.3.2 Ash Concentrations The radionuclide concentration in ash will depend on the activity placed in the incinerator, the volatility of the radioactive compound, an
16、d the volume of ash produced. Generally speaking, ash that contains high concentrations of radionuclides shall be shipped to a licensed LLW disposal site as indicated in Fig. 1. Low concentrations may be disposed of in a local landfill if permitted by local and state regulations or permits. The actu
17、al disposal of ash from a LLW incinerator is beyond the scope of this standard, and readers are referred to pertinent local, state, and federal regulations, and limitations specified in the facilitys radioactive materials license (see Section 9.2). 4.3.3 Limits for Multiple Radionuclides When the LL
18、W to be incinerated contains ANSI/HPS N13.45-2012 7 more than one radionuclide, the sum of the ratios of the activity to be incinerated and the corresponding concentration limit for each radionuclide shall not exceed unity. The following formula can be used to demonstrate compliance: (Ai /Amax(i) 1,
19、 (2) where Ai is the activity incinerated for the ithradionuclide and Amax(i)is the maximum activity of the ithradionuclide that can be incinerated within a specified time period. 4.3.4 Storage for Decay Radioactive waste may be stored for decay to reduce radioactivity to levels that are ALARA. Stor
20、age of LLW for radioactive decay is an important aspect of any LLW management program. Whether a particular class of waste should be held for decay depends on quantity and radioactive half-life of the radionuclides in the waste, available storage space, and special requirements for storage such as r
21、efrigeration, shielding, appropriate ventilation, corrosion resistance, and requirements for fire protection. A thorough discussion of storage-for-decay is beyond the scope of this standard, but each institution should examine its waste types and storage capabilities to determine the quantity of LLW
22、 that should be held for decay. 4.3.5 ALARA Considerations It is important to maintain ALARA radiation exposures to radioactive waste handlers, incinerator operators, and the general public. To that end, procedures should be implemented to minimize the release of radionuclides to the environment to
23、the lowest practicable level. Such procedures may include storing short-lived radionuclides for several half-lives prior to incineration to minimize the activity released. This approach is particularly important for radionuclides for which a significant fraction is released during the incineration p
24、rocess. Decaying short-lived radionuclides usually does not come without expense. The costs associated with storage space (heating, maintenance, etc.) should be considered against the volume and total activity of short-lived radioactive waste generated. It may be cheaper and less laborious and minim
25、ize worker/public doses better by simply disposing the waste at an authorized disposal facility. Another procedure should include segregating small volumes of radioactive waste that contain high levels of activity (e.g., “stock” vials containing millicurie quantities of radioactivity). Incineration
26、of high-activity, low-volume radioactive waste results in very little volume reduction but potentially significant releases of radioactivity to the environment. 5.0 Selection of Incineration Equipment 5.1 General Once a commitment is made to incinerate LLW, it should be decided whether to use existi
27、ng equipment or to purchase new equipment. The important elements to be considered for the actual combustion process of any waste are the physical form(s) of the waste, the chemical properties and heat value (BTU content) of the various waste forms, and the volume associated with each waste form. It
28、 is these characteristics that determine the efficiency of the combustion process. 5.2 Existing Incineration Equipment Based on the results of the evaluation in Section 5.1, it may be determined that an existing incinerator can be used for some or all classes of waste generated. The practicality of
29、incinerating certain types (e.g., aqueous liquids), along with the anticipated volumes of waste, must be considered. 5.2.1 Existing Charging Systems Some incinerators are equipped with continuous feeding rams that continually feed waste into the combustion chamber. The ultimate fate of the radioacti
30、vity in the waste will affect decisions on how the incinerator should be charged. If the majority of the radioactivity is released to the atmosphere and the average concentration is less than the concentration limit, there will be no reason to segregate that type of radioactive waste from other non-
31、ANSI/HPS N13.45-2012 8 radioactive wastes. On the other hand, if the average concentration in ash makes it necessary to collect radioactive ash, separate burns (sometimes referred to as “batch burns”) will be required for radioactive waste. In the latter case, continuous feeding systems may preclude
32、 the use of such an incinerator unless the waste feed can be operated manually for batch burns. 5.2.2 Existing Ash Removal Systems A situation similar to charging systems exists with some remote ash removal systems. Batch burns may also be necessary should it be required that the ash be collected fo
33、r analysis, storage, or disposal as radioactive waste. Continuous ash removal systems may make batch-burn ash collection difficult. 5.2.3 Existing Off-Gas Treatment Systems Another feature of an existing incineration system that should be considered is the presence or absence of an off-gas treatment
34、 system (e.g., scrubber). Off-gas treatment may be required to remove certain chemical species from the effluent; however, the low levels of radioactivity found in LLW generally do not require off-gas treatment to specifically remove the radioactivity released during the incineration process. If an
35、existing incinerator is equipped with off-gas treatment, it will be necessary to evaluate the amount of radioactivity collected by the system (either in the scrubber water or fly ash from a filter arrangement) and properly dispose of any collected radioactivity or radioactive components of the syste
36、m. 5.3 Selection of New Incineration Equipment The selection of equipment for incineration of LLW requires several considerations. The radioactivity in LLW plays a limited role in determining the incinerator technology that is most appropriate for incineration of LLW. Limitations under existing syst
37、ems discussed above should be considered when selecting new incineration equipment. As of this writing, it appears that the incinerators using controlled air technology are the most economical while possessing the capability of handling most waste forms. 5.3.1 Intended Use and Volume It is typically
38、 more economical to use an incinerator on a more constant basis rather than periodically starting up and shutting down the unit (called “cycling”). Periodic cycling also tends to shorten the life of the incinerator hearth (refractory). If the volume of radioactive waste requires that the incinerator
39、 be used only one or two days per week, it may be advisable to consider incineration of both radioactive and non-radioactive wastes together or to select an incinerator with less burning capacity. It is also important to project future trends of radioactive waste generation to ensure that a given in
40、cineration capacity will not become inadequate within the lifetime of the incinerator. The incinerator manufacturer can provide an estimate of the incinerator lifetime. Projections should include the anticipated incineration of different waste types and allow for an increase in the volume of waste t
41、o be incinerated. 5.3.2 Waste Characterization It is important to perform waste characterization that includes the physical and chemical properties and the volume of each waste form. Generally, as the waste form becomes more complex, the type of incinerator required also becomes more complex (and mo
42、re expensive). For example, a rather simple incinerator is capable of incinerating contaminated laboratory refuse (e.g., bench paper and disposable gloves). However, if contaminated chemicals (e.g., scintillation fluid) or large volumes of plastic are to be incinerated, a more sophisticated incinera
43、tor may be required. Through waste character-ization, the user should compare the volumes of the different waste forms generated, the cost of an incinerator required for those waste forms, and the cost of alternative methods of disposal of the waste forms. 5.3.3 Off-Gas Treatment Generally, off-gas
44、treatment for trapping radioactivity is unnecessary. Amounts of LLW generated by medical centers, universities, and research institutions usually can be incinerated and air effluent released to the environment with appropriate monitoring and documentation of ANSI/HPS N13.45-2012 9 compliance with co
45、ncentration limits. If, however, off-gas treatment is necessary due to a particular waste form, the potential for contamination of the off-gas treatment system (e.g., scrubber water or filter train) shall be considered. Off-gas treatment systems are initially expensive and are expensive to maintain.
46、 5.3.4 Waste Charging Common methods for loading (or charging) an incinerator are batch charging the incinerator prior to start-up and adding waste during the burning cycle. Manual charging tends to be more labor-intensive and, if improperly performed, can lead to poor incinerator operation. Special
47、 waste charging systems (e.g., ram feeders) may help minimize the labor involved in charging the incinerator; however, such a system will add to the overall cost of the incineration system. If the collection of the ash is necessary for analysis, storage, or disposal as radioactive waste, it is impor
48、tant that charging be done in batches when the incinerator is to be used for both radioactive and non-radioactive wastes. 5.3.5 Ash Removal Ash removal can be performed either manually or via some type of remote ash removal system. Manual removal of ash is somewhat labor-intensive. If the ash contai
49、ns significant quantities of radioactivity, care shall be taken to avoid contamination of personnel as well as the incinerator area during the ash removal process. Remote ash removal systems help to minimize conta-mination problems; however, as with remote charging systems, the user should weigh the cost of purchasing and maintaining these systems with that of manual ash removal. If both radioactive and non-radioactive wastes are incinerated in the same unit, it may be necessary to collect radioactive ash from a given burn cycle for analysis, storage, or proper disposal. Ash remova
