woodplc.com

ALARPing Risk Reduction Measures: Better quantification for better results

Presented by

Jack Davy and David Craig of Wood

Stuart Turner of EDF Energy

2

Introduction

EDF Energy is part of EDF Group

and is one of the largest energy

companies in the UK, supplying

around 5 million residential and

business accounts with electricity

or gas.

We produce around one-fifth

(20%) of the nation’s electricity

and that makes us the largest

supplier by volume - something

we’re really proud of.

EDF Energy employs over

13,500 people across the UK.

• 7 Advanced Gas-cooled

Reactor (AGR) power stations

• 1 Pressurised Water Reactor

(PWR) power station

• Combined generation

capacity of 8,918 MWe

• All located on estuarine or

open coasts

• All lower tier COMAH

establishments

EDF Energy UK nuclear power plant

(NPP) fleet

Fuel Oil

• Providing an

essential back

up electrical

supply.

• Also used for

the generation

of auxiliary

steam,

vaporisation of

CO2 and some

other heating

and ventilation

Ammonia

• Primarily for

boiler feed

water

treatment to

avoid acidic

conditions

thereby

minimising

corrosion.

Sodium

Hypochlorite

• Dosed into the

incoming

cooling water

to mitigate

efficiency

reductions in

condenser and

circulating

water system

plant due to

biofouling.

Hydrazine

• Used as an

oxygen

scavenger to

control

concentrations

of dissolved

oxygen

thereby

minimising

corrosion.

Typical NPP COMAH substances

The process

6

CDOIF and CA Guidance on ERA and

ALARP

28/05/20197

EDF Energy approach to ERA

► In 2014, the COMAH Competent Authority (CA) requested EDF Energy

undertake Environmental Risk Tolerability Assessments based on previously

submitted PHR scenarios using the CDOIF ERA methodology.

► In 2015, the first Phase 1 report was submitted which assessed MATTE potential

for all receptor types demonstrating that the risk was bounded by potential

effects on surface water due to the characteristics of these NPP sites.

► In 2016, the CA agreed streamlining of method to a bounding S-P-R linkage of:

Liquid Dangerous Substances

↓Surface Drainage

↓Surface Water Type Receptors

EDF Energy approach to ERA

Phase 1

Part 1

• EDF Energy assessment with support from an Independent Marine Biology

specialist contracted to provide conservative high-level consequence assessment

reports for Surface Water type receptors avoiding the need for detailed

monitoring beyond the screening intent of this stage.

Phase 1

Part 2

• Risk assessment specialists from Wood contracted to support failure frequency

and risk assessment stage of work adding external challenge and experience.

• Positive feedback received from Competent Authority concerning approach to

assessments including format of output.

Phase 2

• Compliance against HSE Technical Measures

• ALARP Assessment of the key scenarios for each station

• Calculation of benefits based on reduction in aggregated risk against agreed

event ‘costs’ (£1-100M)

When writing this paper, we asked

ourselves?

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

10

►Does use of this approach give a meaningful output?

►Does it provide decision-making output when the answer is

not obvious?

► Is it effective in considering combinations of measures which

may be interdependent?

►Can it generate options to reduce risk which

►Are logical and make “engineering sense”?

►Allow the best options to be prioritised?

Case studies

11

Station 1 – simple example

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

12

►Workshop identified 46 potential improvement options and

screened in 12 for further assessment (4 reducing FO risk and 8

on the hypo system).

►Sodium hypochlorite system

► All releases are MATTE B but a release outside the bund goes direct

to marine receptor.

► 8 options assessed – 7 of these were not grossly disproportionate –

option with the greatest absolute risk reduction selected due to

HSE guidance.

“The option, or combination of options which achieves the lowest level of residual risk should be implemented, provided grossly disproportionate costs are not incurred”

Station 1 – simple example

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

13

►Two Independent systems with dominant risks.

Off loading area

Station 2 – Targeted effective measures

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

14

►Workshop identified 56 potential improvement options and

screened in 10 for further assessment (2 reducing FO risk and 8

on the hydrazine system).

►Hydrazine system

► Lots of options – obvious from MJS that multiple measures needed.

► 8 options assessed – some options were mutually exclusive and others

options became disproportionate when initial measures implemented.

► Option 48 preferred for higher benefit for lower CAPEX. If implemented,

makes Option 38 grossly disproportionate.

Description

CAPEX

Before other

measure

After other

measureRisk

ReductionMJS

Risk

ReductionMJS

38 Double walled pipework £25k 2.88E-5 £389k 3.17E-7 £4.3k

48 Secondary containment

around pipework £10k 3.17E-5 £428k 2.88E-7 £3.8k

Station 2 – Targeted effective measures

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

15

►The approach to ALARP gives increased clarity in choosing

between options

►Hydrazine system

► Assumption that options 7 (FO) and 48 already to be implemented

► Following implementation of initial measures, the MJS and DF

factors should be recalculated.

► Option 42 was not initially GD (and preferable to Option 41 in

isolation) but becomes GD when others implemented

Option. Description CAPEXInitial

MJS

Revised

MJS

Grossly

Disproportionate

41Replace plastic IBCs with

steel£10 k £34 k £23 k No

42Use of dedicated delivery

vehicle£50 k £61 k £41 k Yes

Station 2 – Targeted effective measures

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

16

►Two different systems focus of ALARP study

►Hydrazine – dominant risks – multiple release cases

► Pipe between bund and processing

► IBC type

Station 3 – Global measures

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

17

►Site only held fuel oil in MATTE quantities

►No scenarios dominate the risk

Station 3 – Global measures

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

18

►Fuel oil systems

► Workshop identified 32 potential improvement options and

screened in 4 for further assessment.

► Site wide fuel oil MJS ~£180k

► Options are not independent – implementation of any option

reduces the benefit of all remaining options

►Result of assessment: Option 8 is the most-favoured by CBA but

Option 7 was implemented given operational constraints

(nuclear safety case)

Option

No.

Description CAPEX Benefit Remaining MJS

2 Alarm on bulk tanks £50k £109k £70k

3 Sump level alarm £40k £141k £38k

7 Oil on Water alarm £50k £170k £10k

8 Oil on Water trip £70k £173k £7k

19

Lessons learned

Inputs, communication and efficiency

► Initial supporting guidance was limited for the whole process

► Pragmatic & engaged regulators were essential

► Centralised Project Management with consistent lead roles

aided consistency

► Risk Assessment processes developed in a ‘proportionate’ way

without which the project would have been driven to an

unsustainable level of detail thus delaying the implementation

of any outcome enhancements.

The challenge that continues is to embed consideration of

environmental risk tolerability within the modification process

Lessons about the ALARP Process

Lessons learned from ALARP assessment

Add a coloured

transparent

segment and

caption if

required.

Delivering on

our promises

21

►ALARP process can work well using CA fundamental approach

but the differences of environmental risk must be considered.

► Must use appropriate inputs (generic event costs) and

proportionate level of detail – expert judgement & sensitivity

analysis

► Must consider all significant Major Accidents (MAH and MATTE)

and all significant receptors

► Must consider the aggregated effects of risk reduction

► Important to consider the interaction and inter-dependency of

measures

►Use of different metrics can be used to prioritise measures and

combinations of measures

ALARP process can effectively be transferred in environmental risk

and produce clear prioritized risk reduction measures.

Thanks for listening

Any questions?

22

woodplc.com