Application of flow testing and analysis
technology to risk assessment for plantmaintenance management
Shun WatanabeCentral Research Institute of Electric Power Industry
International Symposium: Risk‐based Management of Energy Infrastructure
November 10, 2023 @Katahira Campus, Tohoku University

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Number of inspections in JAPANESE light water reactors

Number of weld line

100000
10000
1000
100
102000PWR2PWR4
PWR6
PWR8
PWR10
PWR121500
1000
50002004

1BWR
PWR
Number of inspection per 1 light water reactor*( *Reference: “JNES‐RE‐2012‐0003” )PWR1PWR3
PWR5
PWR7
PWR9
PWR112500Number of inspection

Total of weld line
Number of weld line to be inspected

2006

2008

2010

2012

2014

years
Number of inspection at periodic inspection in Japanese PWR*
( *Reference: Press release of Japanese power utilities ) Several safety related systems were added to the plants through the processof the new regulatory requirements in Japan.
 However, the number of components to be inspected will increase even more
after the plant restart. (This is already a large amount.) Effective measure will be required to command maintenance activities byreasonably assigning limited resource.
2“Maintenance significance” in JAPANESE code
Maintenance target

Maintenance significanceACorrection measures

P

Maintenance planning
Maintenance method
・Time based
・Condition based・Breakdown maintenanceJudgment

Classification ofsafety importanceClass 1, 2, 3

Risk assessmentby PRA

Quantitative assessment(Core damage frequency etc.)

Supply reliability
Operating experience

DC

Consideration

Maintenance operation

Operational safety

Outcome evaluation

Ambient impact

Consideration by organizational
engineered judgment

These considerations areNOT quantified.

Maintenance flow and definition of maintenance significance in Japanese code*(*Reference: “Code for Maintenance at Nuclear Power Plants, JEAC4209”)

 The Japan Electric Association, “Code for Maintenance at Nuclear Power Plants”
 It is available for Japanese utilities to select the maintenance method according
to “maintenance significance” of the object.
 Some of the maintenance significances (supply reliability, operating experience,operational safety and ambient impact) are not quantified yet.
3The pipeline where “maintenance significance”
is NOT effective in the present code The pipeline in the turbine building (BOP : Balance of Plant) Classification of safety importance for most of these pipelines isassigned to “class 3” or “non‐class”.
 It is difficult to acquire meaningful evaluation results by “the risk
assessment (PRA)” because these pipelines hardly affect the coredamage frequency.
 The number of the pipelines to be inspected is still large and“time‐based maintenance” is almost applied as the maintenancemethod.
It is important to improve the maintenance framework of the BOP
depending on quantification of the impact to the supply reliability andthe operational safety etc. as the maintenance significance.
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To introduce the matrix of the maintenance significanceHighmaintenance significancePipe failure impact( Fluid leakage risk )Reference: S. Watanabe, et al., CRIEPI report L16001, 2017.

【Rank B1】
Amount of inspection resources“Middle”【Rank A】
Amount of inspection resources“High”【Rank C】
Amount of inspection resources“Low”【Rank B2】
Amount of inspection resources“Middle”

Low
maintenance significancePipe failure probability

 In order to quantify the maintenance significance, the matrix which defined by“pipe failure probability” and “pipe failure impact” was introduced.
 Through the matrix, the new maintenance ranking is possible to be considered
for the BOP pipelines where the classification of safety importance is low.
(Amount of inspection resource indicates inspection method, frequency etc.）5

To quantify the parameter of the matrix
Reference: S. Watanabe, et al., CRIEPI report L16001, 2017.

Pipe failure probability(Pipe failure mode)

Fluid leakage behavior（Leakage amount, temperature,pressure and diffusion area)
Impact to surrounding
equipment

Impact to function offailure pipe lineP

Impact tooperational safety

 In order to quantify “pipe failure probability”, a variety of pipe failure mode areevaluated by using the plant database and analysis tools.
 In order to quantify “pipe failure impact”, fluid leakage behavior due to pipe
failure is evaluate by the experiment (Main topic in this presentation).
 And also, impact of fluid leakage to function of failure pipeline, surrounding
equipment and operational safety must be considered.
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Objectives in this presentation
 Optimization of maintenance management in systems with low
safety significance and quantification of maintenancemanagement risks for this purpose.
 Quantification of the impact on maintenance management, including worksafety in the event of piping damage
 Evaluation of Pipe Damage Probability Considering Deterioration Events inLow‐Class Piping

 This presentation will focus on "Quantification of Failure Effects"
as a study utilizing flow testing and flow analysis.
 Evaluation of jetting behavior and influence range by flow experiment andflow analysis
 Work Safety Indexing Initiatives
7Reference: S. Watanabe, et al., CRIEPI report L16001, 2017.

Experimental equipment①②Pressure≦2.0MPaG, Temperature≦210℃
 The condition of pressure and temperature were set based on the condition of “balanceof plant (BOP)” in Japanese NPPs.
 It is possible to inject water or steam into the fluid injection room from the horizontal
nozzle (①) or the vertical nozzle (②). Flow visualization measurement is conducted byusing the high‐speed video camera and the laser through the optical window.
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Geometry parameter of the pipe opening area
Guillotine breakPossible to replace
PinholeCrack
1mm

Nozzles are installed at the room wall

 It is possible to simulate various
geometry of opening area as the pipe
failure mode for 50mm and under of pipe
diameter.
 In order to conduct the fluid leakage
experiment, the parameter of theopening area was set to crack, pinhole
and guillotine break.

Pipe failure mode

Parameter

Crack (length)

10, 20, 30 and 40 mm

Pinhole3, 6, 9, 12 and 15 mm

Guillotine break

15A, 25A, 40A and 50A

Reference: S. Watanabe, et al., CRIEPI report L16001, 2017.
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Measurement of high‐pressure water splash behavior
Experiment
Wu et al （1983）
Reitz et al （1982）
Syakouchi（2004）

GravityθNozzle outlet（Guillotine break: 16.1mm）

107
Ⅰ
106

100mm

Atomization

GravityWe

105Nozzle outlet（Guillotine break: 12.7mm）

Ⅱ

104

100mm

Wind induced

103
Ⅲ

102

Gravity

Rayleigh

101
102

103

105

104

106

Nozzle outlet（Pinhole: 9mm）

107

100mm

Re

Experimental conditions and jet flow
visualization results
Reference: S. Watanabe, et al., Transactions of the JSME, No. 20‐00109, 2020.
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Measurement of dispersal behavior of high‐pressure
steam and flushing steam Visualized imaging of high‐temperature, high‐pressure jets
 Steam jets have a narrow adiabatic expansion region and diffuse as a free jet near
the nozzle.
 Flushing jets* have a wider adiabatic expansion region and a wider diffusion
range than steam jets. (*High‐temperature water jet with phase change due todepressurization and boiling)θθAdiabatic expansion area is wide due todepressurization boiling, No free jet near
the nozzle

The adiabatic expansion region is narrow, and the flow
is generally diffused as a free jet in the vicinity of thenozzle. Diffuse as a free jet in the vicinity of the nozzle

Flushing jet spreading behavior

Steam jet spreading behaviorReference: T. Yuasa, et al., Transactions of the JSME, No. 22‐00157, 2022.
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Analytical model of heat conduction in human skin The human body's skin consists of three layers: epidermis, dermis, and subcutaneous tissue*1.
 Values specified in ISO13506*2 are used for thermal conductivity and volumetric heat capacity.
 Only the skin depth direction is considered (one‐dimensional model)
heat conduction equation
𝜕 𝑇𝜌𝑐 𝜏𝜕𝑡

𝜕𝑇𝜕𝑡

0.08 mm 1.5 mm

3 mm
Skin depthdirection x [mm]

𝜕 𝑇𝜅
𝜕𝑥

Heat transfer coefficient h(t)・Fluid temperature：50～210℃
・Room temperature：25℃

Epidermis
・κ1：0.616 W/m・K
・Cv1：4.16 MJ/m3・K・ρ1：1000 kg/m3

Temperature boundary（Body temperature：36℃）

Dermis・ κ2：0.598 W/m・K
・ Cv2：4.02 MJ/m3・K・ ρ2：1000 kg/m3

Subcutaneous fat
・ κ3：0.366 W/m・K
・ Cv3：2.29 MJ/m3・K・ ρ3：1000 kg/m3*1：Yamada, 2018., Watanabe, 2023. *2：ISO13506, 2017.

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Results of heat conduction analysis on human skin
 Initial skin temperature: 36 ℃, fluid temperature: 100 ℃, heattransfer coefficient: 1,000 W/m2‐K
 Exposure time: 1 sec (after 1 sec, cooling by 25 ℃ air)
Cooling by air（5 W/m2 K）
100
Skin surface

Skin temperature [℃]90Room temperature

Epidermis‐dermis

80

Dermis‐subcutaneous tissue

70
60
50
40
30
2001Time t [s]23Reference: S. Watanabe, et al., 2023.
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Results of burn severity evaluation
 Minor burns on the epidermis only are first‐degree burns, second‐degreeburns reach the dermis, and third‐degree burns reach the subcutaneous tissue.
 The following model equation can be used to evaluate indices related to theseverity of burns.
 Ω is calculated as the integral value when T > 273.15+44 K.

Damage integral Ω

1.0E+06

𝜕Ω𝜕𝑡𝐴𝑒𝑥𝑝∆𝐸𝑅𝑇

Cooling by air
5 W/m2 K

1.0E+04
Third degree heat injury
1.0E+02
Second degree heat injury
1.0E+00
First degree heat injury
1.0E‐02
012Time t [s]3Reference: S. Watanabe, et al., 2023.
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Conclusion
 In order to quantify the maintenance significance, the matrix which
defined by “pipe failure probability” and “pipe failure impact” wasintroduced. Through the matrix, the new maintenance ranking ispossible to be considered for the pipeline where the classificationof safety importance is low (=BOP pipeline).
 The research project plan for the optimization of the maintenanceframework of BOP in Japanese NPPs was drawn up. And theexperimental facility was constructed to evaluate the fluid leakage
behavior as fundamental data for “pipe failure impact”.
 By using this facility, it is able to conduct the test of the jet whichleaked from various flaw geometries of the piping. And basic data
related to flow leakage and diffusion from the small diameter pipe
was obtained.

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