Evaluation of Overall Risk Management in

Decommissioning

Sep. 11, 2018 2018 Sino-Japanese Workshop on NPP Decommissioning Technology

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Satoshi Yanagihara University of Fukui

ANDES executive director

Contents

Principle of nuclear decommissioning

Dose evaluation in decommissioning project

Basis of risk assessment

Evaluation of project risk(1) – cost over-run

Evaluation of project risk(2) – schedule slip

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Technology Deployment: Decommissioning is an aggregation of wide variety of technology. Basic knowledge is crucial including application of other areas.

Radiation Risk: Various types of radioactive materials or radioactive waste in various physical and chemical forms arise from any nuclear decommissioning activity and they pose different levels of risk.

Waste Management: Proper waste management is a key for successfully implementing a decommissioning project. Knowledge on waste management should be equipped together with nuclear decommissioning.

Project Management: Planning and evaluation of a decommission project are indispensable. The relevant methodology and tools are applicable for those in such areas of cost engineering, risk management and decision analysis.

Principle of Nuclear Decommissioning

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Decontamination of building surfaces

Radioactive waste treatment and storage

Final surval of ratioactivity

Dismantling of components

Removal of spent fules

Remote dismantling of core part

Dismantling of compnents around core part

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Typical Decommissioning Process in Reactor and Rad-waste Buildings

Time (10 -60 years)

Different kinds of risks exist in the

decommissioning process

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Risks in Decommissioning Process

IAEA, Safety Assessment for Decommissioning, Safety Reports Series No.77, 2013

Criteria for Radiation Safety

Dose limit for public around nuclear facilities Criteria for the dose limit of public in the outer area of environmental monitoring

Effective dose limit : 1mSv/year Equivalent dose for the skin : 50mSv/year Equivalent of crystalline lens : 15mSv/year

Dose limit for workers Criteria of effective dose received by radiation workers in controlled areas

One year : 50mSv Five years :100mSv Emergency :100mSv

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Dose Evaluation in Dismantling Activities

Evaluation of Public Dose

Public dose is evaluated under normal situation and accidents by applying the amount of each nuclide released into atmosphere and ocean.

External exposure Internal exposure

Evaluation of Worker Dose

Worker dose is evaluated under normal situation by applying dose rate in working area considering area characteristics, work schedule, occupational type, etc.

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Characterization of Dismantling

Work Activities (JPDR)

Work Area Dose rate differs from position to position in the area

ex. Max. 8.0mSv/h, Min. 0.2mSv/h (at service floor)

Dose rate decreases with removal of component Lower dose rate - during dismantling, post-dismantling

Work Activity Working location depends on occupational types

• Near radioactive component for cutting activity • Observation of laborer’s activities away from them etc.

Workers are exposed in limited time and activity

D&D work consists of various kinds of work activities. • Preparation, Cleaning up, Assistant Work, Entering and exiting of

controlled area etc.

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Atmosphere

Contamination Control Enclosure

Ventilation System (Building)

Leakage （Enclosure）

Inside Building

Filtering Collection

Dismantling of Equipment and Structures

Stack

Leakage （Building）

Release of Radioactive Materials to Atmosphere in Normal Situation

Release at Higher

Position

Release at Ground

Atmosphere

Filtering Collection

Ventilation System (Enclosure)

Radioactivity Particulate, Tritium, C-14

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Calculation Flow for Public Dose

Amount of radioactivity produced

Amount of radioactivity released into working area

Radioactive plume

Radioactivity in dismantling activities -Particulate radioactivity (Co-60, Eu-152 etc. ) -Gaseous radioactivity (H-3, C-14)

Deposition on the ground

Ingestion of vegetable,

milk, meet etc.

Radiation Source in Dismantling Nuclear Facilities：

Radiation from radioactive waste -Direct g-ray -Skyshine radiation

Radiation

Accumulation in seafood

External Internal

Internal

Internal External

Amount of waste arising from activities

Storage of waste

Amount of radioactivity released into environment

g-ray radiation

Skyshine radiation

External External

in Atmosphere in Ocean

Inhalation Radiation

External

Radiation

Radioactive Sea Water

swimming, Fishing

Ingestion of seafood

Emission of g-rays out of building

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Evaluation of Accident Conditions

Event Object to be Considered

Fire Filter, Solid Waste

Explosion Flammable Gas, Dynamites for Controlled Blasting

Drop Interaction of Equipment or Container and Floor or Enclosure

Clash Interaction of Dismantling Equipment and Container

Operation Mistake by Worker False Open or Close of Valve

Malfunction of Equipment

Leak of Liquid Waste, Halt of Active Equipment (Stop of Ventilation etc.), Runaway of Cutting Machine,

Loss of Electric Power etc.

Scenario of Accidents Cause of Releasing Radioactive Materials Radioactive Inventory at Accident (Transferred to Filter) Cause of Releasing Radioactive Materials

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Example of Safety Evaluation

Decommissioning plan Phase 1: Preparation for dismantling (10 years) Phase 2: Dismantling of components around core part (15 years) Phase 3: Dismantling of core part (8years) Phase 4: Demolishing of buildings (7years) Public and worker dose in Phase 1 Normal Situation • Worker Dose : 1.4 person-Sv • Public Dose : max. 6.6 μSv (individual)

Accident Condition • Public Dose : max. 0.25 μSv (individual) • Radiation release : max. 2.8 E11 Bq

Ikata NPP Unit1 (PWR: 566 MWe)

Source: SHIKOKU ELECTRIC POWER CO, INC

Risk Assessment

Risk Assessment

Identify Risk Items Quantify Risk Items Prioritize Risk Items

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Selection of possible events of unexpected occurrences or accidents

Risk for each event is defined as a function of probability and consequence

Each event is prioritize into acceptable, or unacceptable by uing risk matrix

A few examples of possible accidents or unexpected occurrences which could occur during the execution of particular tasks and which might lead to significant doses to site personnel or the public.

Identify Risk Items 1/2

Possible Unexpected Occurrence or Accidents

Fuel element dropped during handling Loss of cooling during irradiated fuel transfer Criticality of fuel storage Unexpectedly high radiation field Malfunctioning of protective equipment Malfunctioning of monitoring instruments Fire in contaminated chemical solvent Vacuum filter bag rupture

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Possible Unexpected Occurrence or Accidents (continued) Spillage of contaminated liquids Loss of essential services Local loss of contamination control Cutting equipment failure Accidental cutting of activated material Inadequate mechanical support for component being cut Oxyacetylene explosion Excessive amount of explosive charge HEPA filter failure Combustible waste fire

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Identify Risk Items 2/2

～

～

Reactor pressure vessel

Dismantling Project

Machinery around reactor

Hands-on Dismantling

Decontamination

Piping connected to RPV

Reactor internals

Post-cleanup activities

Measure for shredding contamination by vinyl sheet

Facility characterization

Setting of Local ventilation

Setting of remote systems

Remote dismantling

Radiation survey Dismantling

Measure for shredding contamination by vinyl sheet

Dismantling Setting of Local

ventilation Setting of scaffolding

Transfer of wastes

～

A

A

Example of Work Breakdown Structure

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Risk Identification

risk of schedule slip risk of radiation and industrial hazards

risk of industrial hazards

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Risk Matrix

Lik

eli

ho

od

Risk = f(probability, consequence)

HIGH RISK: not acceptable MODERATE RISK

Quantify Risk Items

Consequence

Certain Medium High Extreme Extreme Extreme

Likely Medium Medium High Extreme Extreme

Possible Low Medium Medium High Extreme

Unlikely Low Low Medium Medium High

Rare Low Low Low Medium Medium

Very Low Low Medium High Very HighLOW RISK: Acceptable

Definition Process of balancing risk with cost, schedule, and other programmatic consideration.

risk identification, risk assessment, decision-making on the disposition of risk, tracing the effectiveness of the results of the actions.

Objective

Maximizing the results of positive events and minimizing the consequences of adverse events.

Project Risk Management

Risk Management is an essential for project management.

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Risk Triangle

Technical problem

Cost over-run Schedule slip

Project management always involves risk.

Decommissioning should be accomplished on schedule, and is accomplished within budgeted cost as any engineering project do the same.

At the start of decommissioning project, there are uncertainties in each of these factors and it is important to manage the associated risk.

Risk management can help limit the potential for negative consequences arising from uncertainties and maximize the positive aspects.

In some case, technical problem may be replaced by Casualty.

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Decommissioning Cost

When planning decommissioning scenarios, all activities described in the decommissioning plan should be included in the estimation of the cost for decommissioning project.

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Level 1

Pre-decommissioning actions

Facility shutdown activities

Procurement of general equipment and material

Dismantling activities

Waste processing, storage and disposal

Site security, surveillance and maintenance

Site restoration, cleanup and landscaping

Project management, engineering and site support

Research and development

Fuel and nuclear material

Other costs

The working grout of OECD/NEA studied first the decommissioning cost. Cost items(213) are identified in hierarchy form.

Cost Groups include the followings:

Labor costs

Capital, equipment and material costs

Expenses

Contingency

OECD/NEA, International Structure for Decommissioning Costing (ISDC) of Nuclear Installations, 2012

A.L.Taboas, A.A.Moghissi and T.S.LaGuardia: The Decommissioning Handbook, ASME Press, 2004

Cost Estimation（Case Study） (1100MWe NPP)

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No Discription Likely cost ($) %

1 Spent fuel 64,312,000 15.26

2 Project management 132,812,000 31.50

3 General plant operation and maintenance 13,723,000 3.26

4 Site preparation 10,173,000 2.41

5 Asbestos removal and disposal 8,632,000 2.05

6 large component removal 6,001,000 1.42

7 Segmentation and removal of reactor vessel internals and reactor 21,877,000 5.19

8 Component and piping disposition 20,838,000 4.94

9 Contaminated building demolition 13,987,000 3.32

10 Other building building demolition 16,042,000 3.81

11 Final status survey and licence termination 2,607,000 0.62

12 Waste management 93,266,000 22.12

13 Soil remediation 742,000 0.18

14 Clean material disposition 1,087,000 0.26

15 Site restoration 15,466,000 3.67

Totals 421,565,000 100.00

OECD/NEA, ,Addressing Uncertainties in Cost Estimates for Decommissioning nuclear Facilities, NEA No.7344, 2017

Estimating Uncertainty

Triangle distribution

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OECD/NEA, ,Addressing Uncertainties in Cost Estimates for Decommissioning nuclear Facilities, NEA No.7344, 2017

No Discription Likely cost ($) % below % above Exp cost ($)

1 Spent fuel 64,312,000 5.0 25.0 68,599,467

2 Project management 132,812,000 5.0 15.0 137,239,067

3 General plant operation and maintenance 13,723,000 5.0 15.0 14,180,433

4 Site preparation 10,173,000 5.0 25.0 10,851,200

5 Asbestos removal and disposal 8,632,000 5.0 25.0 9,207,467

6 large component removal 6,001,000 5.0 25.0 6,401,067

7 Segmentation and removal of reactor vessel internals & reactor 21,877,000 5.0 75.0 26,981,633

8 Component and piping disposition 20,838,000 10.0 20.0 21,532,600

9 Contaminated building demolition 13,987,000 5.0 30.0 15,152,583

10 Other building building demolition 16,042,000 5.0 25.0 17,111,467

11 Final status survey and licence termination 2,607,000 5.0 25.0 2,780,800

12 Waste management 93,266,000 5.0 25.0 99,483,733

13 Soil remediation 742,000 10.0 35.0 803,833

14 Clean material disposition 1,087,000 5.0 15.0 1,123,233

15 Site restoration 15,466,000 5.0 20.0 16,239,300

Totals 421,565,000 5.7 26.7 451,074,550

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Description Likely costs %below %above Exp costs

Dry casks do not meet regulations 39,926,000 5.0 40.0 44,584,033

Additional ACM found post characterisation 2,158,000 5.0 20.0 2,265,900

Large component transport needs supports 2,100,000 2.0 25.0 2,261,000

Reactor vessel segments cannot be "blended" 3,282,000 5.0 30.0 3,555,500

Containment concrete shorter than expected 2,098,000 10.0 20.0 2,167,933

disposal site close/store on -site 23,317,000 5.0 25.0 24,871,467

Soil contamination deeper than mearured 742,000 10.0 25.0 779,100

Total 73,623,000 6.0 26.43 80,484,933

Risk Evaluation Results Triangle distribution

OECD/NEA, ,Addressing Uncertainties in Cost Estimates for

Decommissioning nuclear Facilities, NEA No.7344, 2017

（US $）

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Out-of-scope uncertainties

In-scope

Pro

ject

baseline e

stim

ate

Funded risk 10.6 million

Estimating

uncertainty

68.2 million

Allowances 421.6 million

Base cost

-Assumptions

-Exclusions

-Boundary

conditions

As per basis of

estimates

Risk Evaluation for Cost Over-run

OECD/NEA, ,Addressing Uncertainties in Cost Estimates for

Decommissioning nuclear Facilities, NEA No.7344, 2017

（US $）

Duration of Decommissioning Projects in Japan

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Plant Name Type Power（MWe) Cost（Oku-yen）Duration

（year）

JPDR BWR 1.5 230* 10

Tokai GCR 166 885 25

Fugen ATR** 166 750 25

Hamaoka-1 BWR 540 379 27

Hamaoka-2 BWR 840 462 27

Mihama-1 PWR 340 324 30

Mihama-2 PWR 500 359 30

Tsuruga-1 BWR 357 363 24

Shimane-1 BWR 460 382 30

Genkai-1 PWR 559 364 28

Ikata-1 PWR 566 407 40

Monju FBR 28 3,750 30

Fukushima Daiichi BWR *** 80,000 40

*: including R&D, **：Advanced Thermal Reactor, ***：Unit 1：460MWe, Unit 2-５：784MWe, Unit ６：1100MWe

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Radiological

characterization Safe enclosure

Dismantling

core part Demolition of

building structures

2016 2022 2035

Dismantling core part Dismantling core components Dismantling reactor pressure vessel Dismantling steam generator Dismantling primary system Demolishing biological shield Conditioning of dismantled waste

Building demolition

decontamination

Radiation measurement

Cancelation of controlled area

2040

Major Activities in 5 Years

Displacement of spent fuels

Rad-waste management

Decommissioning Process (Example)

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Schedule Risks on Waste Management

Radioactive waste disposal facilities should be prepared before starting dismantling of core components.

Radioactive waste will be disposed of three different disposal facilities depending of the radioactivity level.

L1: Intermediate level waste disposal L2: Low level rad-waste disposal L3: Extremely low level rad-waste disposal

Disposal depends on possibility of rad-waste disposal facilities

no L1 facility：storage（shortage of storage space） no L2 facility : storage（shortage of storage space） no L3 facility : work-stoppage (schedule delay)

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Necessary Process for Rad-waste Disposal

L1 facility

L2 facility

（quite difficult）

（experienced） （experienced）

L3 facility

（Experienced） （easy） （easy）

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Siting Licensing Construction Operation

Siting Licensing Construction Operation

Siting Licensing Construction Operation

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Risk Evaluation of Waste Disposal

Disposal facilities L1 L2 L3 L1 L２ L3

Siting 10 0 10 40 100 50

Licensing 3 3 3 90 97 97

Constraction 3 2 1 95 99 99

Transportation 3 3 2 98 95 99

34 91 48

66 9 52Possibility of disposal

Expected Year Possibility (%)*

succeed

not succeed

Evaluation of work years and possibility to complete the tasks

* Possibility is assumed by the expert judgement.

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1. Requirement of all rad-waste disposal (L1, L2, L3)

P(E) =P(E1∪E2∪E3)

=P(E1)+P(E2)+P(E3) -

(P(E1∩E2)+P(E1∩E3)+P(E2∩E3)) + 2 ⋇ P(E1∩E2∩E3)

= 0.89

P(E) ：Fault of rad-waste disposal E1: L1 waste, E2: L2 waste, E3: L3 waste

2. Requirement of rad- waste disposal for L2 and L3

P(E) =P(E2∪E3)

=P(E2)+P(E3) - P(E2∩E3)

= 0.52

P(E) ：Fault of rad-waste disposal E2: L2 waste, E3: L3 waste

Probability of Project Completion until Defined Date –case study

Summary

A safety evaluation will be made for each task associated with the reactor

or reactor systems and any other decommissioning activities which could

give rise to a significant radiological hazard.

After displacing spent fuels, radiation risk will decrease; risks of industrial

hazards will be analyzed for safety of workers.

Planning and evaluation of a decommission project are indispensable;

risk management in decommissioning project plays an important role for

completion of the planed cost and schedule.

Project risk analysis always deal with the uncertainty; cost estimation should be made with analysis of risks and uncertainty.

Proper waste management is a key for successfully implementing the

decommissioning project. The risk analysis include the process of waste

management from arising to final disposal.

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