Advances and innovations in nuclear decommissioning11 recent experience in decommissioning research reactors

Advances and innovations in nuclear decommissioning11 recent experience in decommissioning research reactors Advances and innovations in nuclear decommissioning11 recent experience in decommissioning research reactors Advances and innovations in nuclear decommissioning11 recent experience in decommissioning research reactors Advances and innovations in nuclear decommissioning11 recent experience in decommissioning research reactors Advances and innovations in nuclear decommissioning11 recent experience in decommissioning research reactors

Advances and Innovations in Nuclear Decommissioning http://dx.doi.org/10.1016/B978-0-08-101122-5.00011-9

in stored spent fuel elements, radioactive waste from radioisotope production, and various types of active experimental facility

The designs of research reactors vary considerably, although there are some types that exist in larger numbers worldwide, such as the Argonaut (Argonne Nuclear Assembly for University Training), the TRIGA (Training, Research, Isotopes, General Atomics), and the Russian VVR (or WWR—water-cooled and moderated reactor) Depending on the planned application these types have come in a number of layouts.Research reactors are used for a wide range of activities such as core physics exper-iments, training, transmutation studies, commercial production of radioisotopes, neu-tron activation analysis, experiments involving high pressure and temperature loops for fuel and material testing, neutron scattering research, and neutron and gamma radiography In the early days a number of research reactors also played a role in the development of nuclear weapons

Many, if not most, research reactors are more than 50 years old and are ing the end of their operating lives and will require decommissioning Although the radioactive source terms within research reactors are expected to be less in radioactive inventory than in larger facilities, they may still pose significant radiological and other risks, due to aging and other issues resulting from the experimental character of their use Furthermore, many organizations decommissioning a research reactor have expe-rienced that their reactor was not “designed with a view to being decommissioned.”According to the IAEA Research Reactor Database [1] there were by Aug 2016

approach-244 operational research reactors in 55 countries; more than 150 that have been shut down or are undergoing decommissioning, and more than 350 that have been fully decommissioned Many of those decommissioned have been small facilities that were shut down and decommissioned many years ago without much reporting in public However, in recent years more information has been published about completed

decommissioning projects of research reactors, notably thanks to the efforts of the International Atomic Energy Agency (IAEA) and dedicated journals.

In Sections 11.2 and 11.3 of this chapter, examples are given of decommissioning projects in order to highlight special or common aspects, such as selection of strategy, end state, and general technical approaches to the dismantling project Elements gathered from individual reactor decommissioning experiences are summarized in Section 11.4

11.2 Ongoing or recently completed decommissioning

projects

This section does not intend to mention all projects covered by the heading But amples will be given of projects where published material has been available, and only particular aspects of each individual project will be discussed References will be given to sources of further information about the projects mentioned

ex-11.2.1 Danish Reactor 2

The Danish Reactor 2 (DR2) was the second out of three research reactors to be missioned at the Risø site in Denmark The first one was the small 2 kW DR1 that was decommissioned in 2006 DR2 was an open-tank, light water moderated and cooled reactor with a thermal power of 5 MW The reactor went critical for the first time in Dec 1958 to be used mainly for isotope production and neutron scattering experiments It was shut down in Oct 1975 for economic reasons and partially dismantled All experimental facilities were dismantled, the spent fuel elements were shipped back to the United States, and the reactor block and the cooling system were sealed Subsequently the reactor hall was used for other purposes until 1997, when a predecommissioning study was initiated in order to benefit from the fact that some members of the former operational staff were still available to con-tribute historical information This study resulted in a characterization report [2], which gave the background information for the detailed decommissioning planning that was initi-ated in 2004 after the responsibility for decommissioning of the facilities at the site had been transferred from Risø National Laboratory (RNL) to Danish Decommissioning (DD) DD

decom-is a state organization with a budget that decom-is independent of RNL’s research budgets; thdecom-is has been seen as an advantage, avoiding any prioritization between research and decommission-ing Most of the original DD staff was staff from the research facilities, but over the years many new staff members have come from outside the site, bringing in new competences.Decommissioning of the DR2 was completed in 2008; the reactor building was cleared and left for other purposes Fig. 11.1 shows a cross-section perspective of the reactor in the building as it appeared when the final decommissioning was initiated.Selection of dismantling methods started when the first overall plan was drafted for decommissioning of all nuclear facilities at the site [3] More detailed planning was made

in the decommissioning plan for DR2 put forward for approval by the nuclear regulatory authorities and when setting up the budget to be approved by the Parliament’s Finance Committee But the selection of precise approaches and tools to be used in the individ-ual dismantling operations to some extent was made during the detailed preparation of

these operations The general approach by DD is to do as much of the dismantling of active components as possible with its own staff and only to call in external contractors for work that involves little or no radioactivity This was also the case in the DR2 project where external contractors essentially were used only for concrete demolition.

Because the reactor had been shut down for 30 years when the final dismantling started the radiation levels and activity contents were moderate The highest radiation levels were of the order 40–50 mSv/h and came from steel pins in the fuel grid plate and thermocouples in the front plate of the thermal column Dismantling thus did not require the use of remote handling techniques, apart from using extension rods for tools

in certain cases, such as shown in Fig. 11.2 where the operator, using a plasma cutter mounted on a long rod, can keep a distance of a couple of meters to the radiation source

Fig. 11.1 Cross-section perspective of reactor DR2 in the building.

From N Strufe, 2009 Decommissioning of DR2 Final report DD-38 Rev.1 (ENG) Danish Decommissioning, Roskilde Available as a PDF-file from the Internet address: http://www dekom.dk/media/24133/dr%20dr2_%20final%20report_eng.pdf

The inner part of the graphite in the thermal column turned out to have accumulated some Wigner energy, and it was decided that the graphite stringers were to be annealed from the inner layer at a later stage, possibly together with graphite from the next re-actor being decommissioned, DR3.

Additional characterization was performed in order to determine how much of the biological shielding should be considered radioactive waste and how much could be cleared as ordinary industrial waste Twenty horizontal core drillings were made in the shield and used to determine the activation profile As a result the innermost 100 cm,

as illustrated in Fig. 11.3, was considered radioactive waste; that is, it above the mass specific clearance levels set by the Danish regulators

Initially it had been planned to demolish the biological shield by dry wire cutting;

DD had had a less positive experience with wet wire cutting at the DR1 But tion by hydraulic hammering was found to be the more economical solution, and the separation of radioactive and clearable concrete was still possible

demoli-A detailed description of the decommissioning of DR2 can be found in the final decommissioning report [4]

11.2.2 Korean Research Reactors KRR-1 and KRR-2

The two Korean research reactors, KRR-1 and KRR-2, were decommissioned lowing a combined decommissioning plan The two reactors were located in adjacent buildings at the KAERI’s Seoul site They were TRIGA Pool type reactors KRR-1 was

fol-a TRIGA Mfol-ark-II with fol-a fixed core, which could operfol-ate fol-at fol-a level of up to 250 kW, and KRR-2 was a TRIGA Mark III with a movable core, which could operate at a level

of up to 2000 kW KRR-1 started operation in 1962 and KRR-2 started operation in 1972; both were taken out of service in 1995 and replaced by a new and more powerful research reactor, HANARO, at the Daejeon site [5]

Fig. 11.2 Nose of thermal column being cut loose with a plasma cutter on an extension rod.

From N Strufe, 2009 Decommissioning of DR2 Final report DD-38 Rev.1 (ENG) Danish Decommissioning, Roskilde Available as a PDF-file from the Internet address: http://www dekom.dk/media/24133/dr%20dr2_%20final%20report_eng.pdf

The decommissioning project started in Jan 1997 with characterization and ing work and removal of the spent fuel to the United States Dismantling of the re-actors was carried out sequentially, starting with KRR-2 in 2001 and finishing with KRR-1, where dismantling works were completed by 2013 However, some radioac-tive waste still remains at the site and some remediation work on site and building is still pending as of Apr 2016 [6] (Figs. 11.4 and 11.5).

licens-The core structure of KRR-2 and other highly active internal components were cut into small pieces by hydraulic scissors and packed into a shielded waste cask under-water in the pool Prior to cutting the shielding concrete, all facilities embedded in the concrete, such as the thermal column and beam port tubes, were dismantled The graphite blocks, located in the thermal column near the core, were highly activated,

1000 1000

Fig. 11.3 Cross-section of DR2’s biological shield Only the crosshatched part had to be

disposed of as radioactive waste.

From N Strufe, 2009 Decommissioning of DR2 Final report DD-38 Rev.1 (ENG) Danish Decommissioning, Roskilde Available as a PDF-file from the Internet address: http://www dekom.dk/media/24133/dr%20dr2_%20final%20report_eng.pdf

914 1980

4877

844 8222

6553

956 305

Fig. 11.4 Side view of the TRIGA Mark-II type reactor.

Courtesy of S.-K Park.

T/C door Radial beam port

Bulk shielding

experimental tank

Piercing beam port

Tangential beam port

1753

305

2743 305

1753

2057 2436 2057

Thermal column

Thermalizing column core

Reflector

Fig. 11.5 Top view of the TRIGA Mark-II type reactor.

Courtesy of S.-K Park.

and a specially designed and remotely operated gripping tool was used for pulling them out The aluminum casing for the graphite was cut using a long-reach plasma arc

A core drilling machine with a 400-mm diameter diamond drill bit was used to remove the beam port pipes and the concrete around the pipes simultaneously, as shown in

Fig. 11.6 [7]

The part of the biological shield that could be considered nonradioactive waste was cut down by means of wire cutting Thereafter, a tent composed of plastic sheets was installed to cover all the activated parts and a breaker was utilized to cut the remaining concrete into pieces small enough to be packed into 4 m3 waste containers

Minimization of solid waste was an important issue in the strategy for sioning of KRR-1 and KRR-2 and was realized by repeated decontamination in order

decommis-to free release as much as possible, adhering decommis-to the clearance criteria set by the Korean regulatory authorities

It had been decided to keep the KRR-1 as a historical monument after completion

of the decommissioning However, due to the discovery of a leakage of water from the reactor pool, the plans were reviewed; it was decided to remove all radioactive material, including major parts of the biological shielding, before the building and the remaining concrete structure of the reactor could be released for unconditional access

At the moment (Apr 2016) a governmental decision still awaits regarding which nization is to be responsible for the museum

Dismantling activities began in Aug 1997 As of 2014, JRR-2 was in safe storage, awaiting the start of operation of a low-level waste repository.

The decommissioning program was divided into four major phases with the lowing major tasks:

fol-Phase 1

● Fuel elements were sent to the United States.

● Heavy water, about 16 m 3 , in the reactor tank and the primary coolant system was drained

to heavy water storage tanks.

Phase 2

● Disconnection of the reactor cooling system and sealing of the pipe ends at the reactor.

● Removal of experimental facilities and the BNCT facility.

● Sealing of all openings in the reactor body by welding plates onto them.

● Radiation monitoring tubes set up to monitor dose rate inside the reactor core during safe storage.

● Transportation of heavy water to Canada.

Phase 3

● Dismantling of the reactor cooling system

● Decontamination of the heavy water components using a heating decontamination vice, consisting of a blower, a tritium trap, and a hot air dryer This device operated with batches of max 400 kg The components were dried by hot air at 300–400°C for 2 h The contamination (maximum 750 Bq/g) of the main heavy water heat exchanger tubes was reduced to maximum 2.5 Bq/g by this method.

ulti-Fig. 11.7 JRR-2 in safe storage.

From M Tachibana, et al., 2014 Experiences on research reactors decommissioning in the NSRI of the JAEA Int Nuclear Safety J 3(4), 16–24 Available from the Internet address: http://nuclearsafety.info/international-nuclear-safety-journal/index.php/INSJ/issue/view/9

11.2.4 The IFIN-HH WWR-S

The WWR-S was a 2-MW tank-type reactor using light water as coolant, moderator, and reflector It was situated at the Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH) in Magurele near Bucharest, Romania The reactor type

is of Soviet origin and a number of similar reactors exist in the former Soviet Union and formerly associated countries The reactor was in operation from 1957 to 1997, and the decision to decommission it was made by the Romanian government in 2002

The decommissioning project started in 2010 and was carried out in three phases

Phase 1 comprised the following activities:

● Removal of materials, equipment, and nonnuclear structures that did not affect the duct of the following phases of decommissioning.

con-● Renovation of some systems preparing for the actual decommissioning activities.

● Preparing the reactor building for the work activities during the following ing phases.

decommission-Phase 2 comprised the following:

● Decontamination.

● Start of dismantling and demolition activities.

● Radioactive waste treatment, conditioning, and removal in order to obtain a progressive reduction of contaminated areas.

Phase 3 comprises the following:

● Removal of all remaining reactor materials, equipment, and components, including most support utility systems, in order to be able to utilize the building without any restrictions after decommissioning.

Prior to the start of decommissioning work the spent HEU fuel elements were patriated to the Russian Federation in Jul 2009 by air transport, the first time in the world this method was used for this kind of nuclear material The remaining LEU fuel elements were shipped back to Russia in 2012

re-Dismantling of the reactor core and segmentation of the regulation rod represented cial challenges because both were too active to be handled directly The reactor core vessel was a cylindrical aluminum vessel with a diameter of 645 mm and a height of 800 mm The dose rate at the surface was around 10 mSv/h The vessel was lifted out of the reactor and placed on a turntable in a shielded cell built up from concrete blocks in the reactor hall The core was segmented by means of a plasma cutter that was maneuvered through a narrow penetration in the shielding and surveyed by video cameras as shown in Fig. 11.8.The boron steel regulation rod was the most active component from the reactor, giving a dose rate of 3 Sv/h at a distance of 50 cm It was cut in smaller pieces directly into a shielded drum by means of shears mounted on a remotely controlled Brokk 160,

spe-as shown in Fig. 11.9

Dismantling of the reactor internals resulted in the generation of 14.724 kg of tallic waste (steel, aluminum, and copper), of which 14.542 could be released as clean

me-174 kg of aluminum and 8 kg of steel had to be disposed of as radioactive

All decommissioning activities at the reactor are scheduled to be completed in 2018 and the radioactive waste will be transferred to a newly refurbished waste-handling facility at the site The buildings are planned to be reused for a new Extreme Light Infrastructure for Nuclear Physics (ELI-NP)

Fig. 11.8 Plasma cutting of reactor core in a shielded cell.

Courtesy of C Dragolici.

Fig. 11.9 Cutting the automatic regulation rod.

Courtesy of C Dragolici.

11.2.5 NASA’s Plum Brook Reactor

The final dismantling of the Plum Brook reactor internals illustrates the fact that ferred dismantling may be complicated [9] The reactor was a 60 MWt PWR that op-erated from 1962 until 1973, when the water was drained and the facility mothballed Final dismantling of the reactor vessel internals commenced in 2003

de-Without water in the vessel to provide shielding the radiation levels at the top of the vessel were so high that even leaning over briefly to look into the vessel was out of the question Therefore, it was not possible to use tools operated with conventional long poles from above with direct visual control Instead a heavy shielded “hat” with a wall thickness of about 230 mm was placed over the reactor vessel, and via a hole in the top

of this “hat” tools at the end of long poles could be positioned vertically by means of

an electrical hoist Horizontal gripper poles were then used to manipulate the tools in the horizontal plane aided by cameras placed inside the vessel Mock-up training was used by the operators to learn this special type of working with long poles

Even after 30  years of decay the control rods exhibited exposure rates of over

10 Gy/h at contact and, therefore, needed to be sectioned remotely by means of a hydraulic shear while still inside the reactor vessel The most active sections were transported from the reactor vessel to a shielded liner during lunch break with all personnel onsite removed from the area During this operation site personnel could not exit through the portal monitors due to the increased background levels The crane operator and radiation protection personnel were the only ones in the immediate area.For this project with particularly high activity levels mock-up practicing was valu-able, saving time and exposure and helping devise optimal ways of carrying out the work During a mock-up test personnel were encouraged to stop and ask questions; and they did Sometimes this delayed the start of work, but the work was accomplished successfully because everyone was ready and understood their scope [9]

The dismantling of the Plum Brook reactor was completed in 2010, and in 2012 the building was demolished and the area remediated [10]

11.3 Planned decommissioning projects

According to the requirements and guides from the IAEA, decommissioning planning should start already from the design of a nuclear facility or as soon as possible Since most of the world’s research reactors were designed long before this requirement was formulated, few of them had a decommissioning plan in the early 2000s However, the regulators in many IAEA member states have now implemented the requirement on

a national basis, and many decommissioning plans are now being produced, both for reactors close to decommissioning and for reactors foreseen to continue operation for

a long time into future A number of examples will be given below, based on available literature However, detailed decommissioning plans are not very common in the pub-lished literature because they are considered proprietary or limited for distribution to regulators

11.3.1 Finnish Reactor 1 (FiR-1)

The FiR-1 at the Technical Research Centre of Finland (VTT) operated from 1962 to

2015 and was the only research reactor in Finland It was a 250 kW TRIGA Mk II actor, and in addition to the neutron physics applications typical for research reactors

re-it served as a training facilre-ity for personnel for the two Finnish nuclear power plants Swedish nuclear professionals also received training at the reactor Furthermore it had

a BNCT facility that was operating from the 1990s until 2012 In 2012 VTT decided

to shut down FiR-1 as soon as technically and legally justified VTT considered the reactor as “a profit unit without a strategic role for VTT,” and the income from the re-actor services no longer covered all the costs of the reactor, especially after the closure

of the BNCT facility

During 2012–13 a number of meetings were held between VTT, the regulatory authority, STUK, and the Ministry of Employment and the Economy, to which VTT belongs, in order to agree on the process of planning and implementation of decom-missioning In early 2013 the preparation of an environmental impact assessment (EIA) was initiated as one of the first steps in decommissioning planning The EIA was produced for VTT by a consultant, Pöyry Finland Oy, with expert input from VTT staff concerning radiological issues It was completed in Oct 2014 and published

in Finnish and Swedish on the home page of the Ministry of Employment and the Economy website after the ministry’s approval [11] The document is a 189-page re-port that also addresses a number of issues that often are included in a decommission-ing plan, such as an overall description of the dismantling works, radiation protection during decommissioning, and waste-handling issues

Due to the foreseen workload from decommissioning activities and a limited ber of VTT staff, it is planned to engage partners or subcontractors for most of the work Several similar reactors have been decommissioned: for instance Heidelberg 2 (HD-2) and Frankfurt 1 and 2 (FRF 1&2) in Germany, DR2 in Denmark, and KRR-1

num-in Korea Experience from those projects will be drawn upon Furthermore, the FiR-1 decommissioning could be seen as a pioneering project for domestic nuclear power utilities that will face decommissioning later on, thus making it attractive for the power utilities to take a part in the work The decommissioning of FiR-1 will be carried out under an amended operating license because the concept of a “decommissioning license” does not exist in the Finnish legislation

The decommissioning planning currently (2016) focuses on three issues: spent fuel management, procurement of dismantling planning and execution, and preparations for interim storage of the dismantling waste The fuel is subject to the return program

of the US Department of Energy (DOE), which runs until May 2019 The primary scenario for disposal of the nuclear fuel, therefore, is to send it back to the United States A secondary option would be final disposal in Finland, possibly in conjunction with fuel from the Finnish power plants However this would require relicensing of the encapsulation and spent fuel disposal facilities to be constructed in Olkiluoto on the western coast of Finland The dismantling will yield a small volume and inventory

of low- and intermediate-level waste, some tens of cubic meters Final disposal of this waste is intended to be in the waste repositories of the Olkiluoto or Loviisa NPPs An

interim storage period of about 20 years is foreseen and VTT is investigating tive locations for storage.

alterna-According to the preliminary schedule shown in the EIA, dismantling work will start by mid-2016 and finish by the end of 2018, so that the building could be released for other purposes in 2019

The following references provide further information about FiR-1 and the missioning planning: Refs [12–14]

decom-11.3.2 Greek Research Reactor 1

The Greek Research Reactor (GRR-1) is a 5 MW open pool type, light water tor designed by AMF Atomics The reactor is located on the campus of the National Centre for Scientific Research, “Demokritos” (NCSRD) in the Aghia Paraskevi dis-trict of Athens Its main experimental facilities are six beam tubes, a thermal column, a dry irradiation chamber, a pneumatic conveyor, vertical tubes and suitable baskets for irradiations, and rotating systems for uniform multiple irradiations

reac-In 2007, a decision was made to refurbish and modernize the reactor, including

a replacement of the primary cooling system The reactor has been in extended shut down since Jul 2014, and at present (May 2016) it is unclear whether the refurbish-ment plans will be carried through or the reactor will be fully decommissioned Due

to the country’s financial situation the refurbishment and modernization of the GRR-1 was stopped abruptly At the moment there is no political decision about the future of the reactor, which remains in extended shutdown

However, during the period of extended shutdown a partial decommissioning plan for dismantling of the primary cooling system was submitted and approved, and par-tial dismantling of the reactor systems carried out in accordance with the primary cooling system refurbishment project [15]

A predismantling radiological characterization of the primary cooling system by ing in-situ gamma spectrometry was carried out, as well as neutron calculations for the grid plate, control rods, and beryllium blocks Five out of six beam tubes, the control rods, the beryllium reflector blocks, and the active core supporting components (grid plate, plenum, etc.) were removed from the reactor pool and transferred to the spent fuel storage pool and other shielded storage structures Then the reactor pool and the pool cooling system were drained and a radiological characterization of the pool cool-ing system was accomplished by collection and analysis of representative samples from the internal surfaces of the systems The classification of the waste that will arise from the decommissioning of GRR-1 is based on considerations of long-term safety of waste disposal (IAEA Safety Standards Series GSG-1, Classification of radioactive waste).The decommissioning strategy is removal of all activated and contaminated parts without demolition of the biological shielding The spent fuel will be sent to the United States, according to the agreement with the DOE for shipment until 2019 The reactor building will be reused in the nuclear sector Clearance procedures will be followed for release of building structures and materials

us-In Refs [16], [17] and [18] characterization of the reactor components and systems with a view to decommissioning planning is described in detail

11.3.3 BEPO

The BEPO (British Experimental Pile Zero) at Harwell is one of many legacy facilities

in the United Kingdom that are awaiting their final decommissioning The 6 MW tor was commissioned in 1948 and used primarily for the production of radioisotopes, general irradiations, chemical engineering experiments, and as a source of neutrons for nuclear measurements The reactor had a graphite moderator and was fueled by natural or low enriched uranium and cooled by air It operated until 1968 and defuel-ing was completed the following year

reac-A program involving the removal of the chimney and restoration of the land rounding BEPO was completed in 2000

sur-Characterization of the reactor graphite core was carried out in 2014 [19] The work involved surveying around 60 of the horizontal fuel channels using a probe fitted with

a gamma sensor and a camera The probe is deployed some 10 m into the reactor using

a continuous reel of a reinforced plastic that springs into a stiff rod shape The survey information will be used to plan the decommissioning of the reactor

While BEPO was in operation, a large concrete block containing 250 tubes was used to store fuel elements and rigs from BEPO Around 175 of these tubes are over 8-m long and only 3.5 cm in diameter These storage tubes were opened in Mar 2013 for the first time since 1969, and the levels of residual radioactivity in the tubes were found to be higher than previously anticipated Because the concrete block surround-ing the storage tubes is to be demolished it was found necessary to fix the radioactivity due to the risk of fracturing the tubes during the demolition However, traditional methods to fix contamination were not considered appropriate due to the size, shape, and positioning of the tubes Instead, expanding PU foam was used with success The work was completed in Mar 2014 [20]

The BEPO reactor will remain in care and maintenance until around 2040, when the core and remaining facilities will be completely decommissioned

11.3.4 CONSORT

The UK nuclear regulator, the Office for Nuclear Regulation (ONR), in Aug 2015 approved the application to decommission the CONSORT research reactor at Imperial College London’s Silwood Park Campus in Berkshire [21]

The 100 kW reactor began operations in 1965 and was shut down in 2012 due to increasing costs and a lack of research, educational, training, and commercial use The reactor’s fuel was removed and transported to Sellafield for storage in Jul 2014.The decommissioning project will involve the removal of all radiological and non-radiological material to enable the site to be delicensed The ONR attached conditions

to the approval that the Imperial College “ensures mitigation measures are mented to minimise the environmental impact of the project.” This includes requiring Imperial College to prepare an annual environmental management plan updating on the project’s progress and reporting on the effectiveness of the mitigation measures The college must also notify the ONR in advance of any significant change to a miti-gation measure