installation of horizontal biological shielding · pdf fileinstallation of horizontal...

INSTALLATION OF HORIZONTAL BIOLOGICAL SHIELDING

AT THE DRY STORAGE UNIT 3A AT ANDREEVA BAY:

PROBLEMS AND SOLUTIONS

IAEA CEG Workshop, 26 - 27 April 2012, Helsinki

Implementation of International Nuclear Legacy Programmes in Russia

IAEA CEG Workshop

Radiological Improvements to DSU 3A

26 – 27 April 2012, Helsinki2

Outline of presentation

• Background to DSU 3A at Andreeva Bay

• Installation of the temporary cover in 2004

• Development of the design for HBS

• Installation of HBS over DSU 2A and 2B

• Problems and solutions with implementing the design over DSU 3A

• Measures to address predicted exposure to personnel

• Unexpected findings during work implementation

• Results of the work

• Radiation safety

• Conclusions

IAEA CEG Workshop



Background - Andreeva Bay - North West Russia

• Derelict former Soviet Navy base,

40 kilometres from Norwegian border

• 22,000 Spent Nuclear Fuel assemblies

(~30 tonnes, ~6 tonnes U 235)

• Currently stored in three monolithic

reinforced-concrete tanks of approximately

20 metres in diameter, commonly known as

Dry Storage Units DSU 2A, DSU 2B and

DSU 3A)

• Each tank contains ~1000 x 250mm diameter pipes (cells) up to 5m long which are

surrounded with concrete

• Tanks converted to SNF storage under emergency conditions

DSU 3A

DSU 2A

DSU 2B

IAEA CEG Workshop



Background - Andreeva Bay - SNF

• DSU 3A contains water with traces of fuel and chloride -

highly contaminated with deposits over cell walls and over

the DSU surface

• Strategy for long term management of SNF: to prepare the

DSU area for future construction of B153, remove the SNF

from Andreeva Bay and send to Mayak for reprocessing

(agreed by stakeholders in 2007)

Cell flooded

Corroded canister head Deformed canister lid Canister covered by debris

Photos looking down the cell

at the SNF canisters head

IAEA CEG Workshop



Condition of DSU 3A (1999-2005)

3 6 12 24 48 96 192 384 768 1536 3072

Peak radiation EDR

3 mSv/h over concrete beams

42 mSv/h under concrete beams

1999 2005Stabilisation of radiation

levels since installation of

temporary cover in 2004

Effective Dose Rate (EDR) over concrete beams in µSv/h

IAEA CEG Workshop



Physical condition of DSU 3A (2005-2009)

Above concrete beams in DSU 3A

View under the temporary weatherproof cover

View of the Interspace

between the top of the

DSU and the underside

of the existing concrete

beams

IAEA CEG Workshop



Project Objective: Radiological improvements to DSU 3A

The aims of the project were to lower the radiation levels over DSU 3A

• To provide a safer environment for construction of the DSU Enclosure

• To provide a removable shielding that can be remotely handled and replaced

during retrieval of the SNF

IAEA CEG Workshop



Design and procurement of Horizontal Biological Shielding

Trials to confirm design parameters

Trials to test handling techniques

Optimal sizing for cell coverage

Installation

frame

Edged with a stepped

profile to make an

effective biological shield

IAEA CEG Workshop



Condition of DSU 2A before

horizontal shielding in 2008

Shielding installation

Completed in 2009

µSv/h

µSv/h

Installation of HBS on DSU 2A

IAEA CEG Workshop



Installation of HBS on DSU 2B

• Effective Dose Rate (EDR) reduction factors achieved� 50 – 100 for DSU 2A using 75mm thick steel � 100 – 350 for DSU 2B using 120mm thick steel

• Dose rate normalised for routine operations (<6 µSv/h)

• Installation of shielding was carried out semi-remotely using Bobcat ®

DSU 2B after installation of shielding 2009DSU 2B before installation of shielding 2008

IAEA CEG Workshop



Advanced procurement of main equipment for DSU 3A

HIAB long reach crane with different grabs for

• Lifting concrete slabs onto waste trolley

• Lifting large debris into containers

• Recovery of the BROKK in case of failure

• Placing light weight covers (caps) over cells

• Placing horizontal biological shielding

BROKK 90 remote manipulator with tools for

• Cutting asphalt

• Jack hammer separation of concrete slabs

• Grab for lifting small debris

• Operating vacuum cleaner to sweep up

dust and debris up to 50mm

BROKK and HIAB

Remotely operable equipment with long

procurement lead times was ordered in

advance, prior to completion of the design

IAEA CEG Workshop



Basis of the design solution

Arrangement of sanitary

and process control

modules according to the

design in 2008 by Onega

Some assumptions made early on

during the design phase were later

found to be unreliable

Brokk module

Hiab module

SRW module

Ventilation module

Control room

Sanitary sluice

DSU 3A

IAEA CEG Workshop



Contractual arrangements

• Implementation Contract placed with the Kurchatov Institute on September 2009

• Six parts of the Work Breakdown Structure (WBS):

• WBS1 Documentation and project management of the contractor

• WBS2 Performance trials to demonstrate methodology on a mock-up of DSU 3A at Yellow Hill

• WBS3 Procurement of the process modules, sanitary control and equipment

• WBS4 Site preparation to raise the height of the temporary cover and install the modules

• WBS5 Active operational phase to demolish the concrete slabs, remove the debris and install

biological shielding

• WBS6 Close-out works to remove temporary structures and install a smaller cover over DSU 3A

• Time pressure – the project was on the critical path for construction of the

DSU Enclosure and ultimately retrieval of the SNF from the DSUs

ID Task Name

1 WBS 1: Documentation and management

2 WBS 2: Mock-up facility and trials

3 WBS 3: Procurement & assembly of modules

4 WBS 4: Site preparation

5 WBS 5: Active operation phase

6 WBS 6: Close-out works

1

2

3

4

5

6

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1

2010 2011 2012

IAEA CEG Workshop



Challenge: High radiation field during preparatory work

EDR distribution at a height of 0.1m from the cover

Layers of

concrete beams

Concrete beam

supports

underneath

Assumptions about the radiation source term were

needed to calculate thickness of shielding.

Factors of EDR reduction required

over the concrete beams

IAEA CEG Workshop



Confirmation of EDR during early work (WBS 1)

The calculations of EDR were sensitive to the source model and assumptions.

Original calculations indicated a significant collective dose of 1.7 man Sv.

IAEA CEG Workshop



Changes implemented at the Preparatory Stage (WBS 4)

Problems and solutions

1. Steel plates were laid over the

concrete beams to provide

supplementary shielding as an

additional safety measure during

the preparatory work (WBS 4)

2. Trials confirmed that the HIAB

boom deflected more than

calculated. The roof needed to be

raised by 1.8 metres.

3. The method of raising the height

of the roof was changed. The

KPM 40 crane was used instead

of jacks.

4. The control room module was

placed in different location to

reduce exposure to workers.

Revised Arrangement

IAEA CEG Workshop



Challenges during demolition of concrete beams (WBS 5)

1. The brittleness of the concrete beams caused unintentional fragmentation of the waste.

2. A diverse range of wastes and oversized items was discovered after removal of beams.

3. Support columns were bedded on mortar creating bulges on the surface of the DSU.

4. The main equipment was unsuitable to remove large quantities of rubble.

5. The main equipment could not efficiently retrieve waste that had fallen into the cells.

6. The main equipment occasionally failed or was damaged, temporarily stopping all work.

7. The vacuum cleaner frequently clogged with larger pieces of rubble.

8. The quantity of ILW was higher than predicted.

9. Unaccounted waste was discovered between the inner and outer block work walls

IAEA CEG Workshop



Overcoming the difficulties during the active work (WBS 5)

IAEA CEG Workshop



Radiation level during placement of HBS (WBS 5)

Effective monitoring

of progress

IAEA CEG Workshop



Discovery of heavy contamination around the DSU

The gamma camera was used to locate hot spots and could

easily assess the effectiveness of remedial measures

IAEA CEG Workshop



Remedial measures to achieve EDR target (WBS 5)

Target EDR <12 µSv/h

1. Removal of heavily

contaminated soil and

debris from around the

outside of the DSU.

2. Localisation of major

gamma sources on and

outside the tank using

available shielding

materials.

3. Decontamination of HBS

surface on the tank.

4. Radiological

measurements on the

tank, determination of the

achieved EDR value.

19.01.2012

IAEA CEG Workshop



Radiation levels during remedial works (WBS 5)

Before and after

additional shielding

IAEA CEG Workshop



Radiological Improvement results achieved

Achieved EDR was better than the target of <12 µSv/h

IAEA CEG Workshop



Size reduction of the roof (WBS 6)

100 Te

mobile

crane

IAEA CEG Workshop



Radiation safety during implementation

• Both the individual and collective doses to personnel were closely

monitored. Measures taken to reduce dose were effective.

• Work was performed according to the principles of ALARA (As Low

As Reasonably Achievable).

IAEA CEG Workshop



Conclusions

• The aims of the project were achieved

• Horizontal biological shielding is installed over the DSU 3A

• The new cover over the DSU enables the DSU Enclosure to be

constructed safely, ultimately leading to retrieval of the SNF

• The average EDR is 7.44 µSv/h over the tank and 15 µSv/h

around the tank

• Optimisation of the technology helped to minimise exposure of

personnel to radiation

• Problems were overcome mainly through the ingenuity and hard

work of the contractors involved

• Experience using remotely operable equipment with video

systems can be employed for future phases of the work at

Andreeva Bay

IAEA CEG Workshop



Thank you for your attention.

Any questions?

Спасибо за внимание.

Вопросы?

Nick McAtamney

Ник МакАтамни

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