Advances and innovations in nuclear decommissioning13 recent experience in environmental remediation of nuclear sites

Advances and innovations in nuclear decommissioning13 recent experience in environmental remediation of nuclear sites Advances and innovations in nuclear decommissioning13 recent experience in environmental remediation of nuclear sites Advances and innovations in nuclear decommissioning13 recent experience in environmental remediation of nuclear sites Advances and innovations in nuclear decommissioning13 recent experience in environmental remediation of nuclear sites Advances and innovations in nuclear decommissioning13 recent experience in environmental remediation of nuclear sites Advances and innovations in nuclear decommissioning13 recent experience in environmental remediation of nuclear sites

Advances and Innovations in Nuclear Decommissioning http://dx.doi.org/10.1016/B978-0-08-101122-5.00013-2

13

Recent experience in

environmental remediation

of nuclear sites

P.M Booth

Hylton Environmental, Cheshire, United Kingdom

13.1 Introduction

Contamination of the ground and groundwater on nuclear sites might result from his-torical as well as current practices and incidents Such incidents might include leaks from buildings and tanks, spills during the transportation of materials, leaks from his-torical waste disposal trenches, and as a consequence of cross-contamination from poorly designed boreholes Due to the potential risk to human health or the environ-ment from such contamination it may be necessary to remediate specific areas of the site in order to control or eliminate this risk

The IAEA has defined remediation as “the process whereby any measures that may

be carried out to reduce the radiation exposure from existing contamination of land ar-eas through actions applied to the contamination itself (the source) or to the exposure pathways to humans” [1]

Because of the complex and historical nature of many nuclear sites and the wide variety of materials handled, any potential contamination may be radiological or non-radiological in nature, and often a combination of both

As a nuclear licensed site moves toward the end of its lifecycle decommissioning activities are likely to accelerate, although it should be recognized that decommis-sioning is not undertaken exclusively upon a site’s closure There are examples where decommissioning activities will occur in parallel to ongoing site operations, especially

at sites with a long historical legacy (Sellafield in the United Kingdom for example) Remediation is invariably an expensive exercise so it is necessary to understand the drivers for carrying out such work as well as the potential options available to meet any required remediation or dose targets The drivers to undertake remediation might include site delicensing, meeting a desired end state, offsite migration of contami-nants, stakeholder pressures, or it may form part of the site’s overall decommissioning strategy Adopting a sustainable remediation approach, especially in countries with limited available funding, might be necessary In such instances it is important to set and agree upon required cleanup targets prior to the commencement of any work so that regulatory and, in many instances, public approval can be acquired A remediation program should be well planned and designed around a sound understanding of the site and its immediate environment, usually though the prior production of a concep-tual site model

Understanding a site’s lifecycle and how the two complementary activities of de-commissioning and remediation might interact is therefore important As mentioned previously, a remediation program might form part of the decommissioning or site re-lease strategy but it may also be required as a standalone activity without any decom-missioning taking place at the site The timing of any remediation program therefore needs to correlate with both the drivers and the other potential activities being carried out at the site

While the primarily focus of this chapter will be to highlight examples of where remediation has been carried out on nuclear licensed sites that are also undergoing decommissioning it will also discuss why in some instances remediation is currently being undertaken without the presence of decommissioning activities

13.2 Environmental remediation within the

decommissioning lifecycle

A nuclear site has a well-established lifecycle commencing with planning/design/con-struction, through operation and then ultimately decommissioning as it moves towards its eventual closure As Fig. 13.1 shows, environmental remediation can take place throughout the operating lifetime of a site and often during or after decommissioning Decommissioning itself usually takes place after the cessation of site activities, but because many sites have a long operating lifetime it is not uncommon to see decom-missioning activities being carried out in parallel with some of these operations The Sellafield site in the United Kingdom, for example has a wide range of legacy facilities that will take time to decommission However, there is the potential that if they are left untouched they will result in some safety and environmental challenges in the near future In instances like this it is undoubtedly prudent to implement some focused decommissioning as soon as is feasible

The decommissioning process also revolves around a lifecycle with the following types of activity shown in Table 13.1 below

Plan

Initial site characterization

and selection of remediation

criteria

Life cycle of facility and activity—prevention and preparedness based

Life cycle of a remediation—existing contamination based

Implementation of the remediation plan

Postremediation management Identification of remediation options

and their optimization, followed by subsequent development and approval of the remediation plan Design Construction Commissioning Operation Decommissioning

Fig. 13.1 Remediation within a site’s lifecycle.

Figure courtesy of the IAEA.

Many factors need to be considered when determining the timing of environmental remediation within both the site and its decommissioning program lifecycles In many instances, before the advent of physical decommissioning and demolition activities, it might be necessary to demonstrate that an understanding of any surface or below-ground contamination is already in place This baseline understanding allows a site to verify that any subsequent decommissioning activities are not leading to further ground con-tamination A soil sampling and/or groundwater monitoring program followed by the production of a conceptual site model is invariably utilized to provide such verification There may, in some instances, be very little reason to perform environmental re-mediation adjacent to or under a facility until the entire decommissioning process is complete The decommissioning activities themselves might cause ground contami-nation, which will then necessitate a further phase of remediation If a facility is still standing there are likely to be a number of access issues Firstly, an inability to gain access underneath or adjacent to a facility will reduce the confidence in the overall site characterization and thus potentially lead to an incorrect remedial approach Secondly, most if not all facilities have a safety case associated with them, which might preclude certain activities like the drilling of boreholes, the injection of materials, or the utiliza-tion of remedial techniques that cause vibrautiliza-tion

The actual approach chosen for site remediation has to take into consideration the extent of the contamination, the site location, and the desired end state or cleanup cri-teria Removal of all contamination may not necessarily be the optimum or most prac-tical solution The objective of remediation is to reduce doses to exposed individuals

or groups of individuals, to avert doses to such groups or individuals in the future, and

to reduce or prevent the environmental impact [2] Some remediation approaches are passive, while others are more active or may involve actual intervention Remediation can also be carried out in-situ or ex-situ

Remedial approaches generally fall into three main categories [3]:

l Removal of contamination to a more suitable location (a disposal or storage site for example).

l Containment of the contamination on-site.

Dilution of the source of contamination.

Design, construction, and start-up phase Initial Decommissioning Plan

Operating Phase Update Decommissioning Plan

Finalize Safe Enclosure Plan Prepare Shutdown Plan Transition Phase Source term reduction and waste conditioning

Prepare Site Preparation Plan and S&M Plan Preparation Phase Site preparation and initial dismantling

Deferred Dismantling Period Update Final Decommissioning Plan

Surveillance and maintenance Decontamination and Dismantling Phase Decontamination and dismantling activities Final Phase Final survey and license termination

There are essentially two end members to the remediation spectrum The first re-volves around the complete removal of all contaminated material This approach can clearly be both expensive and time consuming and additionally relies on the avail-ability of waste disposal systems to take the contaminated material At the other end

of the scale monitored natural attention can prove to be a viable strategy especially at sites where institutional control is likely to remain in force for many years after the cessation of site activities With such an approach a site can take advantage of natural attenuation and dilution The choice of approach and the timing therefore has to un-derpin the nature of the problem, the drivers for undertaking the remediation, and the agreed end state of the site Sustainable and optimized solutions are often encouraged

As highlighted in Section 13.1 there will also be many instances when remediation work will be required irrespective of a site’s decommissioning activities If we con-sider a nuclear site through its lifecycle there are many opportunities for activities or incidents to lead to the contamination of ground and groundwater Common causes of contamination might include the following:

l Leaks from buildings and facilities.

l Leaks from surface storage compounds.

l Poorly performing waste disposal sites.

l Spills during the transportation of materials.

l Leaks from underground pipes.

l Aerial dispersion from stacks and incinerators.

l Past practices of allowing liquids to evaporate from hardstands.

l Cross-contamination of aquifers resulting from poorly designed boreholes.

l Dispersion of material during the decommissioning of facilities.

There are therefore many drivers to undertake remediation without or prior to de-commissioning activities in order to reduce hazards to workers, the public, and the environment

13.3 Selected case studies on environmental remediation

projects

This section will provide some examples of where environmental remediation needed

to be considered on nuclear licensed sites in conjunction with the planned decom-missioning program Each of the four examples demonstrate that the specific drivers for undertaking the remediation influenced how such activities linked into the site’s decommissioning strategy, specifically the timing and adopted approach

13.3.1 Hanford river corridor completion strategy

The Hanford site, located in Washington State, United States covers an area of 1518 sqkm (or km2) Its original remit was to produce plutonium for national defense, and activities sup-porting this were carried out between 1943 and the late 1980s In 1989 plutonium produc-tion ceased and the site focused more on waste management and environmental restoraproduc-tion

The site cleanup consists of three major components: the river corridor, the central plateau, and the tank wastes, with each component presenting a complex and challeng-ing undertakchalleng-ing involvchalleng-ing multiple projects and requirchalleng-ing many years and billions of dollars to complete [4]

This case study will focus on the river corridor portion of the site, which is ap-proximately 570 sqkm (or km2) in area and includes the south shore of the Columbia River This area of the site houses nine former plutonium production reactors, solid and liquid waste disposal sites, and support facilities There are therefore a variety

of contaminated land challenges These challenges are not just radiological in nature (strontium, uranium) because hexavalent chromium resides in groundwater at levels over ten times above the drinking water standard Cleanup of the river corridor has been one of the site’s primary priorities since the 1990s and groundwater contami-nation continues to threaten the Columbia River The overall challenges in this area relate to both decommissioning and remediation and it is recognized that the two ac-tivities need to be carefully coordinated

The major challenges include the following:

l Remove, treat, and dispose of K Basin sludge.

l Place surplus production reactors into interim safe storage until final disposal.

l Prevent hexavalent chromium from impacting the Columbia River.

l Achieve strontium-90 river protection goal.

l Remediate the 300 area uranium plume.

l Demolish and close the 324 Building.

l Remediate 618-10/11 burial grounds.

The strategy for achieving the cleanup of the river corridor was set out in 2010 with the vision that the majority of the work would be complete by the end of 2015 (rec-ognizing that some work elements would still be outstanding) Remedial approaches incorporating cleanup levels for both soil and groundwater were set prior to tackling the remediation These cleanup levels cover the above/below-ground structures as well

as the land itself, and they aim to provide adequate protection to human health and the environment in addition to allowing the land to be reused in line with the Hanford

being carried out adjacent to the Columbia River and Fig. 13.3 depicts pump-and-treat remediation in the river corridor area

It was deemed crucial that the cleanup approach included the many facilities and waste disposal areas With the size of the area and the many decommissioning and remediation subprojects occurring in parallel, it was important to adopt a ho-listic and joined up approach This would maximize worker safety and limit further ground and groundwater contamination

Importantly, it was recognized that historical groundwater plumes (tritium, iodine, and nitrates) from the central plateau area of the site had not only reached the river corridor area, but also the Columbia River itself Although contamination levels had decreased over time through natural attenuation, remedial activities focused on the plateau area will additionally and importantly restrict future plumes impacting on the river corridor area A series of key performance measures (to have ideally been

achieved by 2015) were set and demonstrate the interaction between decommissioning and environmental remediation activities:

l Nine production reactors were to be demolished, cocooned, or dispositioned.

l Facilities to be demolished (522).

l High nuclear hazard facilities or waste sites to be remediated (20).

l Hot cells to be removed (20).

l Waste sites to be remediated (995).

l Waste and debris to be removed, treated, and disposed of (16.8 million tons).

This case study demonstrates that at a large complex site like Hanford it was cru-cial on the one hand to logically compartmentalize the site but also be aware of the effects each region might have on the other and therefore adopt a holistic remediation strategy Close interaction between the various decommissioning and environmental

Fig. 13.2 Cleanup work adjacent to the Columbia River.

From Mark Triplett, Pacific Northwest National Laboratory.

Fig. 13.3 Pump-and-treat remediation within the river corridor.

From Mark Triplett, Pacific Northwest National Laboratory.

remediation subprojects and activities was also imperative to maximize efficiency and funding, and facilitate a reduction of potential increased contamination

13.3.2 ANL building 330 facility decontamination and demolition

project

Building 330 on the Argonne National Laboratory (ANL) site was built in 1954 to accommodate the Chicago Pile 5 (CP-5) reactor The site is located 27 miles southwest

of downtown Chicago and is surrounded by both rural and populated areas The role

of this particular reactor was to produce neutrons and gamma rays for experiments as well as to serve as a training facility Building 330 was taken out of service in 1979 and

a year later all nuclear fuel and heavy water was transported to the Savannah River site

in South Carolina The facility then spent the next 12 years in a dry lay-up condition prior to a period of decontamination and dismantling between the years 1992–2000 [6] The following objectives were set out for the decontamination and demolition program:

l Remove all hazardous and asbestos-containing materials.

l Remove all interior mechanical, electrical, architectural systems and components and phys-ical structures.

l Package and transport waste materials to approved disposal facilities.

l Conduct a final status survey.

l Backfill the excavated area up to the surrounding grade level.

l Install an impermeable asphalt barrier cap.

l Reseed the site with groundcover plantings.

l Release the site for use under Argonne’s continued scientific research and development mission.

This phase of the work commenced in 2009, but following the removal of the majority of building debris and excavation of foundations, radiological monitoring detected elevated gamma levels beneath where the E wing had resided A further char-acterization was therefore undertaken in 2011 that identified some discrete areas of

Cs137 within soil samples Localized soil removal was undertaken in order to remove these areas of contamination

The final status survey for the Building 330 footprint area was undertaken in May 2011 and was designed and conducted in accordance with Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) guidance The survey comprised surface gamma scans and the collection and analysis of soil samples Some small areas of contaminated soil in excess of the Cs137 criterion remained, but the contractor concluded that the results demonstrated that aver-age concentrations appeared to satisfy the previously established project criteria However, because there was no established elevated measurement comparison (EMC) for use when derived concentration guideline levels (DCGLs) were ex-ceeded, the site administrators felt there was no MARSSIM technical basis to support the conclusion reached The in-house ANL team (based on the site history and the results of previous investigations) subsequently developed a list of likely contaminants (Tc99, Am241, Ba133, c14, Cs137, Sr90, Pu238, and Pu239/240) and DCGLs for potential reuse of the site When the DCGLEMC was applied to the sample re-sults (thus comparing the elevated readings to the release criteria) it was deemed that the release criteria had been met

An independent verification survey was also undertaken but those responsible for this survey did not have sight of the original contractor report during that time The indepen-dent survey concluded that three of nine survey units did not meet the established release limit for Cs.137 It was therefore recommended that this material should not be reused as backfill material They additionally recommended that further remediation should be undertaken or the material could only be released if agreed restrictions to its use were

in place Figs. 13.4 and 13.5 show site characterization and soil removal around B330.

Once ANL and USDOE were satisfied with the confirmatory radiological surveys, approval was given to backfill the excavated area This was undertaken by placing clean borrowed soil into the excavation, capping with an asphalt cap, and then covering the disturbed areas with topsoil and seeding them The completion of the project allowed USDOE to issue an unrestricted use designation for the site, and the establishment of

Fig. 13.4 Site characterization around B330 at ANL’s Chicago site.

From Larry Moos, Argonne National Laboratory.

Fig. 13.5 Site characterization and soil removal around B330 at ANL’s Chicago site.

From Larry Moos, Argonne National Laboratory.

DCGL values for the primary contaminant of concern allowed the area to be reused in line with ANL’s mission of delivering innovative research and technology

In terms of lessons learned, if an approach had been adopted that minimized or eliminated the spread of contaminated materials to other parts of the excavation, this might have reduced the requirement for further remediation and reduced delays and expense to the contractors during the final status survey The contractors’ final status survey report could have been prepared, thoroughly reviewed, and provided to the independent varication survey team prior to their arrival on-site This would have fa-cilitated any issues being resolved before the independent verification was undertaken Because the soil residing below the building was only assessed and remediated many years after the demolition work, different contractors were utilized This in turn led

to additional costs in relation to many of the project components like mobilization, project management, project controls, and field inspectors

13.3.3 The Windscale trenches

The Sellafield site is located on the northwest coast of England in West Cumbria The industrial history of the site is both varied and complex, with the initial activities com-mencing in 1941 It was originally developed as a Royal Ordnance Factory for the production of trinitrotoluene (TNT) but following cessation of this activity at the end

of World War Two the site was cleared (1946) The following year the government ac-quired the site in order for it to be the location for Britain’s plutonium production plant

In the early 1950s, the world’s first civil nuclear power generation reactors (Calder Hall) were constructed and the site has been developed and expanded ever since With the exception of a prototype reactor built in the 1960s, this further expansion was pri-marily in support of the reprocessing of spent nuclear fuel and the temporary storage of solid and liquid reprocessing wastes prior to their vitrification, encapsulation, and more permanent storage Fig. 13.6 shows a historical photograph of the trenches Please note the proximity to other facilities within this compact area of the site

Fig. 13.6 Historical photo of the Windscale trenches at Sellafield.

Photo courtesy of Sellafield Ltd.

For many years Sellafield has undergone extensive phases of decommissioning This decommissioning work continues today and takes place alongside the site’s existing operations Owned by the Nuclear Decommissioning Authority (NDA) the Sellafield site’s legacy ponds and silos remain their greatest decommissioning challenge, and therefore priority, across their entire estate The NDA’s overall strategy remains to de-commission all their sites as soon as reasonably practicable, taking account of lifecycle risks to people and the environment and other relevant factors [7] Although their pref-erence is for continuous decommissioning it is recognized that on some occasions there may be clear benefits to be had from deferring this kind of work Such an approach may, for example, allow a site operator to take benefit from radioactive decay or natural attenuation when considering future risk to human health and the environment

The Windscale Trenches within the central part of the site (separation area) were the primary on-site disposal facility for solid radioactive wastes in the 1950s These unlined trenches are thought to contain wastes that would today be categorized as low-level waste (LLW) Much of the original radioactive inventory is thought to be tritium associated with furnace liners and filters disposed following the 1957 Windscale fire It

is likely, however, that other fission products and actinides will be present in addition

to a range of nonradiological components There is also a reasonable possibility that small amounts of short-lived intermediate-level waste (ILW) may have been disposed Around 40%–50% of the area associated with the trenches was partially reprofiled (to enhance surface drainage) and capped with tarmac The remaining uncapped areas were either vegetated or covered with hard-core or tarmac, but not really with any specific regard for protection of the trench wastes

Tritium contamination is observed offsite in springs on the nearby beach in a direc-tion that is broadly consistent with the direcdirec-tion of groundwater flow to the southwest

of the facility Although the tritium is likely to be associated with a number of sources

in the separation area it is believed that releases from the trenches are likely to contrib-ute to the observed concentrations Modeling studies suggest that the offsite impacts

of any future releases from the trenches will continue to be negligible However, the conceptual understanding that underpins the modeling studies suggests it is likely that there might be a continual release from the trenches to groundwater if some form of intervention was not considered This is due to the flow of meteoric water through the trenches and the associated release of radionuclides (including less mobile fission products and actinides) and other contaminants

From the site operators’ perspective there are clear drivers that revolve around demonstrating optimization in how the trenches are managed Such drivers include liability management and the development of robust management plans Nuclear reg-ulatory drivers are also clearly crucial (Nuclear Site License Conditions 32 and 34),

as are environmental regulatory requirements (i.e., those relating to the Groundwater Directive) So even though the offsite risks are considered to be low, the potential for uncontrolled release of contaminants from the trenches to the unsaturated zone and underlying groundwater requires the identification of an appropriate, proportionate management strategy to control any migration

The site operators therefore decided to hold a stakeholder workshop in order to consider potential management options for the trenches [8] The workshop’s main