Overview of ICRP Approach to Waste Management

Transcription

1 Overview of ICRP Approach to Waste Management Christepher McKenney 1 & Francois Besns 2 1 U.S. Nclear Reglatory Commission (NRC), USA 2 Institte for Radiological Protection and Nclear Safety (IRSN), France

2 Overview The Three Fndamental Radiological Protection Principles The Principle of Jstification The Principle of Optimisation of Protection The Principle of Application of Dose Limits The Three Exposre Sitations Planned exposre sitations Emergency exposre sitations Existing exposre sitations Application to near srface disposal 2

3 The Principle of Jstification Any decision that alters the exposre sitation shold do more good than harm. (ICRP 103) Radioactive waste management and disposal operations are an integral part of the practice that generated the waste. They are not a free-standing practice that needs its own jstification. The jstification shold be reviewed periodically as new information arises. 3

4 Principle of Optimisation of Protection The likelihood of incrring exposre, the nmber of people exposed, and the magnitde of their individal doses shold be all kept as low as reasonably achievable, taking into accont economic and societal factors. (ICRP 103) A key principle giding the application of the ICRP system of protection of the ICRP system of protection to the disposal of radioactive waste. Practical considerations inclde the se the sorce-specific dose constraints, and to define and implement a process to enhance the isolation and containment capabilities throgh siting, design, constrction, and operational considerations. At a national policy level, decisions shold consider optimisation in its broadest sense when decisions are taken on the nmber and type of disposal facilities to develop. 4

5 Principle of Application of Dose Limits The total dose to any individal from reglated sorces in planned exposre sitations other than medical exposre of patients shold not exceed the appropriate limits specified by the Commission. (ICRP 103) The Commission recommends a dose constraint of 0.3 msv per year for normal exposre sitations, or a risk constraint of 10-5 per year for potential exposre sitations for members of the pblic. In evalating doses to the pblic, the Commission recommends the se of the representative person. (ICRP 101 and ICRP 103) When dealing with radiological protection post-closre in the distant ftre, the representative person is hypothetical and shold se present day data. 5

6 Protection of the Environment Protection of the environment is the aim of preventing or redcing the freqency of deleterios effects on fana and flora to a level where they wold have negligible impact on the maintenance of biological diversity, the conservation of species, or the health stats of natral habitats, commnities and ecosystems. (ICRP 103) Recommend sing the Reference Animals and Plants approach to evalate the ecosystem resilience. Provides additional lines of reasoning on the impacts of releases from the disposal site over time. For waste disposal and long-term frames, evoltion of the biosphere is likely, ths ftre possible scenarios may need to be created with stakeholders to evalate sensitivity and ncertainty. 6

7 Planned Exposre Sitations Sitations involving the deliberate introdction and operation of sorces of exposre Althogh the sitation is planned -> exposres are not necessarily anticipated or planned to occr! If exposres are anticipated, they are called normal exposres. They are virtally certain to occr and have a magnitde which is predictable, albeit with some ncertainty. If exposres cold occr bt are not anticipated to occr, they are called potential exposres. These are sitations that are the reslt of an nexpected evoltion or an accident in the system. 7

8 Emergency Exposre & Existing Sitations Emergency Exposre Sitations reslt from a loss of control of a planned sorce (e.g., an accident), or from any nexpected sitation (e.g., a malevolent event), which reqire rgent action to avoid or redce ndesirable exposres. Existing Exposre Sitations reslt from sorces that already exist when a decision to control them is taken (e.g., sorces of natral radiation, past activities, or after emergencies). 8

9 Application to Waste Disposal The process of siting, designing, constrcting, operating, and closing a near-srface disposal facility is a planned exposre sitation. There is an obligation to ensre an optimized level of protection dring both the operational and post-closre phases. Decisions on siting, design, waste inventory and operations all inflence the optimization of the system. While a planned exposre sitation, exposres from the disposal facility to the pblic are not planned to occr as sch. One design goal is to prevent and avoid exposres to the extent possible, both in the operational phase and in the post-closre phase. 9

10 Application to Waste Disposal (cont d post-closre) The facility relies largely on passive systems for its isolation and containment, especially in the long term. As time passes, radioactive decay will be decreasing the hazard of the waste, while the level of isolation and containment may decrease de to deterioration or becase of distrbing events or intrsion events. There is no certainty that sch exposre will occr and there is a range of possible doses that cold occr. Ths, these are potential exposres. 10

11 Application to Waste Disposal (cont d post-closre constraints) For evalating the post-closre period, it is generally sefl to dis-aggregate the probability and dose for those scenarios and events with probabilities less than 10-3 and se the 0.3 msv per year dose constraint. For lower probability scenarios and events in the postclosre period, aggregate the probability and dose to se the 10-5 risk constraint. Very low probability scenarios have likely been exclded by the se of siting and design criteria. Hman intrsion evalation are assessed to comply with a 20 msv per year dose constraint. All of these constraints are sbject to frther optimization! 11

12 Application to Waste Disposal (cont d operations) Dring the operational phase of a disposal facility, both normal exposres and potential exposres shold be considered. The range of scenarios shold be relevant to the range of activities at the site, which cold lead to potentially emergency exposre sitations for certain events (e.g., if waste processing for high-activity sorces was co-located with the disposal facility). The exposres dring operations consider both workers and pblic. 12

13 Application to Waste Disposal (cont d- existing sitation?) Near srface disposal facilities are at varios phases of development and operation in nmeros contries. These are planned exposre sitations as they are being sited, nder design, nder constrction, in operation or closed and nder some degree of reglatory control. One type of an existing sitation wold be sites developed otside of the reglatory control, sch as legacy mining waste sites. Another type wold be where a major nexpected deviation from the planned fnctioning of control by the reglatory athority occrs, sch as a breakdown of civil society de to war, political pheaval or widespread natral disaster. The reglatory athority wold tilize optimization for the decisions to be taken to bring the facility nder reglatory control. 13

14 Smmary (1) Waste disposal facilities are planned exposre sitations. Jstification of waste disposal is a reqired part in jstifying the practice generating the waste. The combination of siting, design, and operations optimize the post-closre performance. Exposres in the post-closre period are potential exposres and are not planned to occr. Exposres shold be constrained below 0.3 msv per year for dose or 10-5 per year for risk constraints. Where probability of sitations cannot be reliably assessed, a disaggregated approach (separate evalation of probability and dose) is applied. 14

15 Smmary(2) Indicative probability of occrrence of conditions, events and processes casing exposre Circmstances Reqirement Design basis 1 Circmstances that are expected to occr dring the development, operation and after closre Design basis 10-1 to 10-3 Incidents, accidents and events that are likely to arise from time to time dring the period of development, operation and after closre Assessed to comply with dose constraints 0.3 msv. Considered in optimisation. Assessed to comply with dose constraints 0.3 msv. Considered in optimisation. Design basis 10-3 to 10-6 Accidents / incidents / distrbing events that cold occr bt are not expected to occr dring the period of development and operation and for a period of a few hndred years after closre Assessed to comply with risk constraints Considered in optimisation. Or emergency reference levels Design basis Assmed 1 after licence termination and zero before Hman intrsion Assessed to comply with intrsion criteria 20 msv. Considered in optimisation. Otside design basis < 10-6 Extreme bt nlikely events Demonstrated to be otside scope of assessment. Not considered in optimisation. 15

16 Smmary (3) Dose assessments in the long term are necessarily associated with large ncertainties and ths shold be considered as indicators of the radiological impact. The comparison of calclated dose and risk with constraints or reference vales is a way to check if the system can reasonably meet the protection targets and criteria bt nmerical compliance with dose criteria alone shold not compel acceptance or rejection of a disposal facility. Optimisation of protection is a jdgmental process on the qality of design and management principle. Optimisation is central to the demonstration that radiation protection principles are met and has to be nderstood in the broadest sense as an iterative, systematic, and transparent evalation of options for enhancing the protective capabilities of the disposal facility and for redcing impacts (radiological and others). Optimisation also shold be considered within the context of the broader national waste management policy and strategy when deciding the type and location of disposal facilities considering both radiological impact and non-radiological aspects. 16