atw - International Journal for Nuclear Power | 11/12.2019


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atw Vol. 64 (2019) | Issue 11/12 ı November/December



Task Information

and Requirements

Task to Consider

Working Time

Teamwork and



Task Support

Workplace Factors

Hazard Identification

Expected PSFs

2 Task Analysis

Task Analysis (TA) is the initial step in the case of human

error assessment. It provides the characteristics of different

tasks, their vulnerabilities, and properties by understanding

the objectives, performance methods, scopes of

the tasks, and procedures involved [6]. In addition, TA

helps eliminate the conditions that can cause errors before

they occur by providing detailed information about the

tasks as well as other information for predicting and

preventing errors.

2.1 TA Method

Although several TA methods exist, considering the

physical characteristics (complexity) and Human Machine

Interface (HMI) aspect (using remote devices) of the

decommissioning activities, we utilized the Hierarchical

TA (HTA) method.

HTA is a systematic and detailed TA method that is used

to achieve task objectives. It is appropriate for not only

identifying detailed task configuration and conditions, but

also expressing complex task steps as a simple, hierarchical

structure. Furthermore, the HTA method was used because

it can easily describe the characteristics of the work

involved and identify significant information about the


| Tab. 1.

Details of tasks to be performed for TA.

• Task influencing factors

(cutting size, number of cutting operations, precision, etc.)

• Task output requirements

• Record feedback to indicate adequacy of action taken

• Alarms and warnings

• Actions to be taken

• Equipment needed (type, size, performance,

required utility, equipment usage constraint, etc.)

• Task frequency and required accuracy

• Physical position of the operator

(standing, sitting, squatting, etc.)

• Biomechanics

• Movement

(lifting, pushing, rotating, pulling, swaying, etc.)

• Force required

• Unit working time based on “work contents”

• Additional work hours taking into account “work support”

and “workplace environmental conditions”

• Number of work shifts and workers per work shift

• Cooperation required between the teams performing

the work

• Personal communication for monitoring or

taking control actions

• Cognitive workload

• Physical workload

• Overlap of task requirements (serial versus parallel task


• Special and protective clothing for work

• Job aids, procedures, or reference materials needed

• Required auxiliary tools and equipment

• Ingress and egress paths to the work site

• Workspace required to perform the task

• Typical workplace environmental conditions

(e.g. lighting, temperature, noise, etc.)

• Work breaks taking into account “work support” and

“ workplace environmental conditions”

• Identify work-related hazards,

e.g. potential personal injury hazards

Examples include:

• Stress

• Time pressure (critical path operations)

• Extreme environmental conditions

• Reduced staffing

HMI, communication and decision making processes, as

well as possible accidents. The HTA method involves

describing the manner in which tasks need to be performed

after establishing their overall objectives and classifying

them into their sub-tasks [6].

Using a tabular format to perform HTA allows one to

express complex tasks that require significant skill in a

suitable manner, because one can include detailed notes, if

necessary. In this study, we comprehensively reviewed

various items, such as HMI, Communication, Time, and

Accident, for the decommissioning activity in a tabular

format; this is shown in Table 1 [5].

2.2 Target Decommissioning Activity for TA

In general, one of the most challenging tasks during plant

decommissioning is believed to be the removal of the

highly radioactive internal components of the reactor pressure

vessel (RPV); this is true for Kori Unit 1 as well. In

addition, another reason that this is one of the most

difficult activities is because these radioactive components

must be dismantled and cut underwater owing to the

severe radiological conditions of the RPVI components

[7-8]. Therefore, it is recommended that the reactor

internals be removed as early as possible in the plant

dismantling sequence, so that these water systems and

their associated support systems can be released for

decommissioning, which minimizes the costs associated

with maintaining these systems in operation after

permanent plant shutdown [8].

The cross-section of the RPV with the primary internal

components at Kori Unit 1 is shown in Figure 2. As can be

seen from the figure, the internal structures adjacent to the

core barrel active region are the most highly activated, and

in most cases, include intermediate level waste components

that might require removal prior to the disposal of the

remainder of the RPV and reactor internal components

[7]. Thus, in this study, this RPV internal segmentation

activity is selected from among the various dismantling

activities in Kori Unit 1.

Furthermore, in this study, the TA was performed for

the most complex and highly radioactive RPVI cutting task

among various disassembly activities by using the HTA

method. The sequence of operations for each sub-activity

in this target task is listed in Table 2.

2.3 TA Results

The TA for the RPVI Dismantling Activity was performed as

per the activities listed in Table 2 based on the items listed

in Table 1. In our study, this analysis was performed for

each of the 10 sub-activities. The summary of the TA for

the RPVI Dismantling Activity is given as follows.

p In general, in the decommissioning of nuclear power

plants, the cutting of parts in the RPVI is the most

complicated and difficult task during the dismantling

process. Therefore, the influence on the internal factors

of the workers was evaluated in order to have a relatively

high value in terms of operator internal response.

p This kind of dismantling operation, which is complex

and requires accuracy and reliability, is significantly

influenced by the internal and external characteristics

of the worker. Therefore, sufficient education and

training is required. However, as the driving principle

and operation method of these cutting equipment and

accessories ( cutting equipment, remote control device,

display, auxiliary equipment, etc.) are not complicated

and operation is relatively simple, an operator is not

required to have considerable experience in using them.


Development of Performance Shaping Factors for Human Error Reduction during Reactor Decommissioning Activities through the Task Analysis Method ı Byung-Sik Lee, Hyun-Jae Yoo and Chang-Su Nam

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