Safety requirements for disposal of RAW

The disposal of radioactive waste is the final step in its management and one aimed at providing a permanent and final safety option. The radiation safety principles and ideas remain the same as for any other aspect of waste management, nevertheless the long timeframes involved give rise to par­ticular challenges which are given particular consideration. The interna­tional standards for the disposal of RAW were updated and agreed in 2011 [40] and provide a comprehensive set of safety requirements for all types of waste and disposal options. The standards set down clear safety objec­tives and criteria (see Box 3.3) and a number of discrete requirements to be fulfilled in order to provide for safety. As with pre-disposal management of RAW, these requirements apply to governments, regulators and opera­tors developing and operating RAW disposal facilities.

Governments are required to establish and maintain an appropriate legal and regulatory framework for safety within which responsibilities are to be clearly allocated for the siting, design, construction, operation and closure of disposal facilities. This must include: confirmation at a national level of the need for disposal facilities of different types; specification of the steps in the development and licensing of facilities of different types; a clear allocation of responsibilities, securing of financial and other resources, and provision of independent regulatory functions relating to planned disposal facilities.

The regulatory body must establish regulatory requirements for the development of different types of disposal facility for radioactive waste and set out the procedures for meeting the requirements for the various stages of the licensing process. It must also set conditions for the development, operation and closure of each individual disposal facility and carry out activities to ensure that the conditions are met.

Box 3.3 Safety objectives and criteria for disposal

Safety objective

The safety objective is to site, design, construct, operate and close a disposal facility so that protection after its closure is optimised, social and economic factors being taken into account. A reasonable assurance also has to be provided that doses and risks to members of the public in the long term will not exceed the dose constraints or risk constraints that were used as design criteria.

Criteria

(a) The dose limit for members of the public for doses from all planned exposure situations is an effective dose of 1 mSv in a year. This and its risk equivalent are considered criteria that are not to be exceeded in the future.

(b) To comply with this dose limit, a disposal facility (considered as a single source) is so designed that the calculated dose or risk to the representative person who might be exposed in the future as a result of possible natural processes affecting the disposal facility does not exceed a dose constraint of 0.3 mSv in a year or a risk constraint of the order of 10-5 per year.

(c) In relation to the effects of inadvertent human intrusion after closure, if such intrusion is expected to lead to an annual dose of less than 1 mSv to those living around the site, then efforts to reduce the probability of intrusion or to limit its consequences are not warranted.

(d) If human intrusion were expected to lead to a possible annual dose of more than 20 mSv to those living around the site, then alternative options for waste disposal are to be considered, for example, disposal of the waste below the surface, or separation of the radionuclide content giving rise to the higher dose.

(e) If annual doses in the range 1-20 mSv are indicated, then reasonable efforts are warranted at the stage of development of the facility to reduce the prob­ability of intrusion or to limit its consequences by means of optimisation of the facility’s design.

(f) Similar considerations apply where the relevant thresholds for deterministic effects in organs may be exceeded.

 

Operators of disposal facilities are responsible for the safety of the facili­ties and must carry out safety assessment and develop and maintain a safety case. They must also carry out all the necessary activities for site selection and evaluation and facility design, construction, operation, closure and, if necessary, surveillance after closure, in accordance with national strategy, in compliance with the regulatory and legal requirements.

The operator of a disposal facility must develop an adequate understand­ing of the features of the facility and its host environment and of the factors that influence its safety after closure over suitably long time periods, so that a sufficient level of confidence in safety can be achieved. Throughout the

 

process of development and operation of a disposal facility, an understand­ing of the relevance and the implications for safety of the available options for the facility must be developed by the operator for the purpose of pro­viding an optimised level of safety in the operational stage and after closure. Operators must evaluate the site and design, construct, operate and close the disposal facility in such a way that safety is ensured by passive means to the fullest extent possible and the need for actions to be taken after closure of the facility is minimised.

The host environment must be selected, the engineered barriers of the disposal facility designed and the facility operated in a manner such as to ensure that safety is provided by means of multiple safety functions, the overall performance of the disposal system not being unduly dependent on a single safety function. Containment and isolation of the waste needs to be provided by means of a number of physical barriers of the disposal system. The performance of these physical barriers must be achieved by means of diverse physical and chemical processes together with various operational controls. In addition, the capability of the individual barriers and controls together with that of the overall disposal system to perform as assumed in the safety case has to be demonstrated.

The engineered barriers, including the waste form and packaging, must be designed, and the host environment selected so as to provide contain­ment of the radionuclides associated with the waste. Containment functions must remain available until radioactive decay has significantly reduced the hazard posed by the waste, and in the case of heat generating waste, con­tainment must be available during the timeframe over which the waste is still producing heat energy in amounts that could adversely affect the per­formance of the disposal system. Disposal facilities must be sited, designed and operated in such a manner that provides features that are aimed at isolation of the RAW from people and from the accessible biosphere. The features must aim to provide isolation for several hundreds of years for short-lived waste and at least several thousand years for intermediate and high level waste. In providing isolation, consideration needs to be given to both the natural evolution of the disposal system and events causing dis­turbance to the facility. An appropriate level of surveillance and control has to be applied to protect and preserve the passive safety features, to the extent that this is necessary for them to fulfil the functions that they are assigned in the safety case for safety after closure.

In developing disposal facilities, it is important that a systematic step-by­step process is adopted. Each step must be supported, as necessary, by itera­tive evaluations of the site, of the options for design, construction, operation and management, and of the performance and safety of the disposal system.

As with pre-disposal facilities and activities, a safety case and supporting safety assessment needs to be prepared and updated by the operator, as necessary, at each step in the development of a disposal facility, during its operation and after closure. The safety case and supporting safety assess­ment must be submitted to the regulatory body for approval and must be sufficiently detailed and comprehensive to provide the necessary technical input for the regulatory process and for informing the decisions necessary at each step. The scope of the safety case for a disposal facility must include a description of all safety relevant aspects of the site, the design of the facil­ity and the managerial control measures and regulatory controls that will be applied. It must demonstrate the level of protection that will be provided for people and the environment and provide assurance to the regulatory body and other interested parties that all safety requirements will be met. The safety case and supporting safety assessment have to be documented to a level of detail and quality sufficient to inform and support decisions to be made at each step and to allow for independent review.

The site for a disposal facility must be characterised at a level of detail sufficient to support a general understanding of both the characteristics of the site and how the site will evolve over time. This needs to include its present condition, its probable natural evolution and possible natural events, and also human activities in the vicinity that may affect the safety of the facility over the period of interest. It must also show a specific under­standing of the impact on safety of features, events and processes associated with the site and the facility.

The disposal facility and its engineered barriers have to be designed to contain the waste with its associated hazard, to be physically and chemically compatible with the host geological formation and/or surface environment, and to provide safety features after closure that complement those features afforded by the host environment. The facility and its engineered barriers must be designed to provide safety during the operational period. The facil­ity must be constructed in accordance with the design as described in the approved safety case and supporting safety assessment and in such a way as to preserve the safety functions of the host environment that have been shown by the safety case to be important for safety after closure. Construc­tion activities must be carried out in such a way as to ensure safety during the operational period.

Facilities have to be operated in accordance with the conditions of the licence and the relevant regulatory requirements so as to maintain safety during the operational period and in such a manner as to preserve the safety functions assumed in the safety case that are important to safety after closure. At the end of operations, disposal facilities must be closed in a way that provides for those safety functions that have been shown by the safety case to be important after closure. Plans for closure, including the transition from active management of the facility, need to be well defined and prac­ticable, so that closure can be carried out safely at an appropriate time.

Waste packages and unpackaged waste accepted for emplacement in a disposal facility must conform to criteria that are fully consistent with, and are derived from, the safety case for the disposal facility both during opera­tion and after closure. A programme of monitoring needs to be carried out prior to, and during, the construction and operation of a disposal facility and after its closure, if this is part of the safety case. This programme must be designed to collect and update information necessary for the purposes of protection and safety. Information must be obtained to confirm the condi­tions necessary for the safety of workers and members of the public and protection of the environment during the period of operation of the facility. Monitoring also needs to be carried out to confirm the absence of any condi­tions that could affect the safety of the facility in the period after closure.

Elements of isolation can be provided by institutional control following the closure of disposal facilities, specifically those on or near to the surface (i. e., a few tens of metres). Plans need to be prepared for the period after closure to address institutional control and the arrangements for maintain­ing the availability of information on the disposal facility. These plans have to be consistent with passive safety features and must form part of the safety case on which authorisation to close the facility is granted.

In the design and operation of disposal facilities subject to nuclear safe­guards, consideration has to be given to ensuring that safety is not compro­mised by the measures required under the safeguards system. Similarly, measures must be implemented to ensure an integrated approach to safety measures and nuclear security measures.

Management systems to provide for the assurance of quality must be applied to all safety related activities, systems and components throughout all the steps of the development and operation of a disposal facility, the level of assurance for each element being commensurate with its impor­tance to safety.

The safety of existing disposal facilities developed prior to current safety standards needs to be assessed periodically until termination of the licence. During this period, the safety also needs to be assessed when a safety sig­nificant modification is planned or in the event of changes with regard to the conditions of the authorisation. In the event that any of the current safety requirements are not met, measures need to be put in place to upgrade the safety of the facility, appropriate economic and social factors being taken into account.

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