Annals of Nuclear Energy 37 (2010) 888–893

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Annals of Nuclear Energy

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Development of a standard communication protocol for an emergencysituation management in nuclear power plants

Man Cheol Kim a,*, Jinkyun Park a, Wondea Jung a, Hanjeom Kim b, Yoon Joong Kim b

a Integrated Risk Assessment Center, Korea Atomic Energy Research Institute, 150, Deokjin-dong, Yuseong-gu, Daejeon 305-353, Republic of Koreab YGN Nuclear Power Division Training Center, Korea Hydro and Nuclear Power Company, 517 Kyemari, Hongnong-eup, Yeongkwang-gun, Chonnam 513-880, Republic of Korea

a r t i c l e i n f o

Article history:Received 18 February 2009Received in revised form 23 December 2009Accepted 3 January 2010Available online 15 April 2010

0306-4549/$ - see front matter � 2010 Published bydoi:10.1016/j.anucene.2010.01.003

* Corresponding author. Fax: +82 42 868 8256.E-mail address: charleskim@kaeri.re.kr (M.C. Kim)

a b s t r a c t

Correct communication between main control room (MCR) operators is an important factor in the man-agement of emergency situations in nuclear power plants (NPPs). For this reason, a standard communi-cation protocol for the management of emergency situations in NPPs has been developed, with the basicdirection of enhancing the safety of NPPs and the standardization of communication protocols. To vali-date the newly developed standard communication protocol, validation experiments with 10 licensedNPP MCR operator teams was performed. From the validation experiments, it was found that the useof the standard communication protocol required more time, but it can contribute to the enhancementof the safety of NPPs by an operators’ better grasp of the safety-related parameters and a more efficientand clearer communication between NPP operators, while imposing little additional workloads on theNPP MCR operators. The standard communication protocol is expected to be used to train existing NPPMCR operators without much aversion, as well as new operators.

� 2010 Published by Elsevier Ltd.

1. Introduction

When an emergency situation occurs in a nuclear power plant(NPP), main control room (MCR) operators are required to managethe emergency situation to prevent the occurrence of an accidentfrom the emergency situation. An example of the failure of MCRoperators in properly managing an emergency situation is theThree Mile Island Unit 2 (TMI-2) accident.

The management of emergency situations in NPPs is mainlyguided by emergency operating procedures (EOPs). After theTMI-2 accident, the symptom-based EOPs have been widely usedto enhance the safety of NPPs through a reduction of operators’workload under emergency situations (Park et al., 2001). Underthe emergency situations, the SRO make decisions and providecommands to other MCR operators based on EOPs and the informa-tion from other MCR operators. For this reason, the correct com-munication between the SRO and MCR operators is crucial in themanagement of emergency situations in NPPs.

As mentioned by Ujita et al. (1992) and Ujita et al. (1995), theperformance of MCR operators in emergency situations in NPPs isstrongly affected by not only the cognitive process of each opera-tor, but also by communications and collaboration among opera-tors. Sasou et al. (1993) indicated that the variables ‘‘decisionmaking” and ‘‘communication” were the main factors whencharacterizing a team’s behavior. Reinartz and Reinartz (1992)

Elsevier Ltd.

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mentioned that verbal communications among MCR operators isnot only a mechanism by which teamwork functions, but also animportant clue in understanding the intermediate cognitive pro-cesses of MCR operators. After the observation and evaluation oftwo crew members by eight domain experts in a combat informa-tion center, Rouse et al. (1992) categorized the identified problemsinto three categories and found that communication-related prob-lems took up more than half of all the problems (52% and 57%).

The importance of communications can also be found in large-scale investigations on the operational events with human errorsin NPPs. Sträter (2003) investigated 232 operational events withhuman errors in German NPPs and found that roughly 10% of theoperational events with human errors included communicationproblems as the major important contributor to the event. Hirotsuet al. (2001) investigated 193 operational events with human er-rors among a total of 885 operational events occurring at JapaneseNPPs and found that about 13% of the operational events with hu-man errors were caused by problems in written communicationsand about 5% of the operational events with human errors werecaused by problems in verbal communications. These theoreticalobservations and operational experiences lead us to conclude thatif we can reduce these communication errors, we can significantlyreduce the amount of human errors in safety–critical systems suchas large-scale chemical plants and nuclear power plants.

In the computer science field, a protocol is a set of rules forexchanging information between computers. If we extend thisconcept to human operators in NPPs, a communication protocolcan be defined as a set of rules for exchanging information between

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human operators. For example, when the senior reactor operator(SRO) of an operator team asks the turbine operator (TO) ‘‘whatis the steam generator level?” for many cases the turbine operatoris expected to answer not only the value of the steam generator le-vel, but also the trend of the steam generator level.

Usually, each operator team develops its own communicationprotocol, and the members of each operator team become veryaccustomed to it. But, there have been a lot of concerns as towhether the intentions of a speaker are always properly deliveredto a listener, because the rules for exchanging information betweenoperators are learned implicitly through working as a team. Inother words, the rules for exchanging information are not explicitlyspecified or taught to the operators. For example, even thoughthere are two kinds of steam generator levels, narrow range (NR)and wide range (WR), SROs usually do not specify which steamgenerator level they are asking. Because the required steam gener-ator level is situation-dependent, sometimes TOs have to decidewhich steam generator level to report. This concern becomes moreserious when the speakers and listeners experience a high level ofstress in emergency situations.

From the observations on the communications of NPP MCRoperators during the management of simulated emergency situa-tions, it was found that different operator teams have differentcommunication protocols. Some instructors in a nuclear trainingcenter also expressed their concerns on the possible chances ofoperator’s confusion or misunderstanding of SRO’s orders whenan operator of a team is working in another operator’s team as asubstitute. This concern comes from the fact that different operatorteams develop their own communication protocols, and thereforesometimes these communication protocols are not completelycompatible with each other.

One countermeasure for the diversity in the communicationprotocols among MCR operators is a standardization of these com-munication protocols. After analyzing the initiating speech and re-sponse speech interactions of 10 flight crews (each crew consists oftwo pilots), Kanki et al. (1989) found that the communication pat-terns of high performance crews are more homogeneous than thoseof low performance crews, and the homogeneous pattern can besummarized as: captains give more commands than the averageand first officers respond with more acknowledgements than theaverage. The interpretation of this homogeneity is that the high per-formance crews established a standard form of communication andtherefore, they could interact in more predictable ways. From a casestudy on a high-reliability army armored brigade, Zohar and Luria(2003) found that that most of task-related interactions were basedon script language (i.e., verbs and action phrases signifying partic-ular meta-scripts and relevant contingencies). The interpretationfor this result is that standardized communications among opera-tors can increase the predictability of the communications and re-duce the possibilities of a confusion or misunderstanding, andtherefore ultimately increase the performance of a team.

For these reasons, we developed a standard communicationprotocol for emergency operations in a type of NPPs. Even thoughthe target plants of this study were one type of NPPs, we believethat the general principles for developing standard communicationprotocols can be applied to other safety–critical systems such aslarge-scale chemical plants and other types of NPPs.

2. Development of a standard communication protocol

2.1. Theoretical backgrounds

For a standard communication protocol to be effective, it shouldbe developed in a way that it can contribute to the enhancement ofthe performance of operators. Many researches have been con-

ducted to establish the relation between the communications ofhuman operators and the performance of them. Some researchersfound the number of overt communications is, at least partly, re-lated to the performance of human operators [To find related liter-atures, refer to Bowers et al. (1998)]. Bowers et al. (1998) foundthat high performance crews revealled more acknowledgements.From one of our previous researches (Kim et al., 2007), it is be-lieved that NPP operator teams with a higher performance showa higher completeness for the sentences of their communications.

2.2. Effects of an abstraction hierarchy level and an engineeringdecision level

To establish the ways in which a high quality communicationcan be achieved, we also investigated the relation between twolevels (abstraction hierarchy level and engineering decision level)and the performance of MCR operators. The abstraction hierarchylevel (AHL) describes the levels of knowledge or information re-lated to the problem space that should be considered to performa response action described in the procedures. From the viewpointof a communication quality, it can be assumed that the lower AHLthe sentence of a speaker conveys, the clearer the listeners under-stand the original intention of the speaker. The four levels of theAHL are as follows (Park et al., 2008):

(1) Component function level (CF): response actions that can beperformed with considerations of the function or status ofa single component.

(2) System function level (SF): response actions that can be per-formed with considerations of the functions or status ofmore than two components.

(3) Process function level (PF): response actions that can be per-formed with considerations of the functions or status ofmore than two systems.

(4) Abstraction function level (AF): response actions that can beperformed with considerations of the functions or status ofmore than two processes.

The engineering decision level (EDL) describes the level of cog-nitive resources that are required to establish the decision criteriafor the response actions described in the procedures. From theviewpoint of a communication quality, it can be assumed thatwhen a speaker conveys a sentence that requires a lower EDL,the listeners find it easier to understand the original intention ofthe speaker. The four levels of the EDL are as follows (Park et al.,2008):

(1) ED-1: when simple comparisons between clear criteria andthe plant status or plant parameters specified in a responseaction are required.

(2) ED-2: when generalizations or comparisons between refer-ence information and the plant status or plant parametersare required (e.g. comparison of trends).

(3) ED-3: when the establishment of proper decision criteria forthe plant status or plant conditions are required using theknowledge acquired through training or experience.

(4) ED-4: when proper decisions should be made without prede-fined or given decision making criteria.

Based on the above assumptions and some previous researchresults, it seems that the higher the sum of the AHL and the EDLof operators’ communication, the lower the performance of theoperators. Considering the fact that the performance time is in gen-eral considered to have a negative correlation with the perfor-mance of the operators, we made the following hypothesis.

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Hypothesis I. The sum of the AHL and the EDL of operators’communication has a positive correlation with the performancetime for a task.

Fig. 1 shows the relation between the sum of AHL and EDL ofoperator’s communication and the performance time for a task.From Fig. 1, it can be found that for the diagnosis tasks with lower(AH + ED) levels, the performance time is lower, which means ahigher performance of the MCR operators. Even if Fig. 1 cannot pro-vide a formal statistical proof for Hypothesis I, we think it providesa guide for the development of a standard communication protocolnecessary for the management of emergency situations in NPPs.

2.3. Candidate protocols and review by field experts

Based on theoretical backgrounds, we developed five differentcandidate standard communication protocols. One of the five can-didate protocols was the most typical communication protocol ofNPP MCR operators. The five candidate protocols were reviewedby several instructors of a nuclear training center, and the reviewresults were taken into consideration to develop a prototype stan-dard communication protocol. Fig. 2 shows the developed standardcommunication protocol for the reactivity control task, as anexample. Conventionally, many SROs simply ask ROs ‘‘is the reac-tor shut down?” The standard communication protocol requiresSROs to ask two questions, ‘‘RO, is the reactor power is decreasingand the startup rate (-)?” and ‘‘RO, are all the control rods in-serted?” to clearly check the three specific symptoms of reactorshutdown. The EDL of the conventional communication protocolis evaluated as ED-2, whereas the EDL of the standard communica-tion protocol is evaluated as ED-1. In this way, the introduction ofthe standard communication protocol can reduce the EDLs.

2.4. Some issues related to a standard communication protocol

During the development of a prototype standard communica-tion protocol, several issues were raised. In the process of resolvingthese issues, we applied two basic principles for the developmentof the standard communication protocol, which were an enhance-ment of the safety of NPPs and the standardization of communica-tion protocols, whenever a decision making process is necessary.Some of the issues and our decisions are described below:

Fig. 1. A comparison of the performance time with the sum of an AHL and EDL forthree diagnosis tasks described in the EOP of an NPP.

– To emphasize the safety aspect, the steps in EOPs are reflectedin the standard communication protocol as much as possible,instead of simplifying or omitting some overlapped steps.

– When an SRO gives an order to an operator, he/she is requiredto call the corresponding operator first to obtain the operator’sattention. Normally, without specifically calling the operator,the corresponding operator receives the order of the SRO,but for enhancing the safety of NPPs, specifically identifyingan operator when the SRO gives an order will increase the reli-ability of the information on the plant.

– If an SRO needs information on both the value and the trend ofa plant parameter, the SRO is required to specifically requestboth the value and the trend of the plant parameter, insteadof assuming that simply requesting information on a plantparameter will provide him/her with both the value and thetrend of the plant parameter.

– Additional information in EOPs is reflected in the standardcommunication protocol, in an attempt to increase the safetyof NPPs. For example, in the step ‘‘Establish a sufficient feed-water supply to more than one steam generator,” SROs arerequired to check on two detailed conditions that should besatisfied for a satisfaction of the step. This decision comesfrom the fact that sentences with a lower EDL will lead to ahigher performance due to less chances for confusion.

3. Validation of the standard communication protocol

3.1. Validation environment

To validate the developed standard communication protocol,we performed validation experiments. 10 NPP MCR operator teamsfrom four NPPs with similar reactor types participated in the vali-dation experiments. We will call the four NPPs as NPP 1, NPP 2,NPP 3 and NPP 4. Each operator team was asked to perform themanagement of a simulated emergency situation with their owncommunication protocols (conventional protocol) first, and thento perform the management of another simulated emergency situ-ation with the standard communication protocol. The simulatedemergency situations were one of the following:

– Loss of coolant accident (LOCA).– Steam generator tube rupture (SGTR).– Loss of all feedwater (LOAF).– Excessive steam dump event (ESDE).

Table 1 shows the assignment of simulated emergency situa-tions to the NPPs and the protocols, and Table 2 shows some statis-tics for the assignment of the simulated emergency situations forthe validation experiments. It should be noted that the assignmentof the simulated emergency situations shown in Table 1 is not bal-anced well, as shown in Table 2. In fact, we developed a well-bal-anced initial assignment plan for the validation experiments, butvarious external factors such as the education and training planof the utility company forced us to change the initial assignmentplan. Because those external factors are hard to control, well-bal-anced experiments will always be a big challenge.

Each of 10 NPP MCR operator team is asked to manage one ofthe four simulated emergency situations with their own communi-cation protocol and then manage one of other simulated emer-gency situations with the standard communication protocol.After performing the management of emergency situations, theoperators were asked to answer a questionnaire. Each NPP MCRoperator team answered to the nine questions, six questions forNASA-Task Load Complexity (TLX) and three questions for evaluat-

Fig. 2. Part of the standard communication protocol.

Table 1Assignment of accident situations for the validation experiments.

Conventional protocol Standard protocol

1 NPP 3 SGTR LOCA2 NPP 4 SGTR SGTR3 NPP 1 LOCA SGTR4 NPP 2 ESDE LOAF5 NPP 3 SGTR LOAF6 NPP 4 LOCA ESDE7 NPP 1 ESDE SGTR8 NPP 2 LOAF LOCA9 NPP 3 SGTR ESDE10 NPP 4 ESDE LOCA

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ing some characteristics related to the safety of NPPs. NASA-TLX isproposed as a multi-dimensional rating scale in which informationabout the magnitude and sources of six workload-related factorsare combined to derive a sensitive and reliable estimate of work-load (Hart and Staveland, 1998). NASA-TLX is considered to beone of the most widely used methods of measuring subjectiveworkload. Even if the three questions do not have a theoretical ba-sis, they are selected to directly ask the participants of the experi-ments of some characteristics related to the safety of NPPs.

3.2. Comparison of the performance time

Fig. 3 shows a comparison of the performance time for the diag-nosis tasks during the management of emergency situations. FromFig. 3, it can be found that the performance time when the stan-dard communication protocol was used, is usually longer for all

Table 2Some statistics for the assignment of the simulated emergency situations for the validatio

Conventional protocol Standard prot

SGTR LOCA ESDE LOAF SGTR L

NPP 1, 2 0 1 2 1 2 1NPP 3, 4 4 1 1 0 1 2Protocol sum 4 2 3 1 3 3

four simulated emergency situations when compared to the per-formance time when the conventional protocols of the operatorswere used. If we take the following facts into account, it can be saidthat this longer performance time was expected before the valida-tion experiment started.

– In case of the standard communication protocol, the sentencesbecome longer to accomplish the basic direction of enhancingthe safety of NPPs and the standardization of communicationprotocols. For example, the SROs always had to call the operatorfirst when they requested information or give orders. In the con-ventional protocols, they simply request information or giveorders without explicitly calling the operator.

– The operators first encountered the standard communicationprotocol right before they are asked to use it. Therefore, theoperators were not accustomed to the standard communicationprotocol when compared to the conventional communicationprotocol that they were accustomed to.

The fact that the use of the standard communication protocolrequires more performance time is acceptable because the MCRoperators could finish the diagnosis task in less than the predefinedrequired time (10 min) on average, no matter whether the conven-tional communication protocol is used or the standard communi-cation protocol is used.

3.3. Comparison of workloads

Fig. 4 shows a comparison of the workloads of operators, eval-uated by using NASA-TLX. As can be seen in Fig. 4, the workload

n experiments.

ocol NPP sum

OCA ESDE LOAF SGTR LOCA ESDE LOAF

0 1 2 2 2 22 1 5 3 3 12 2 7 5 5 3

Fig. 3. A comparison of the performance time for the diagnosis tasks of theemergency situations.

892 M.C. Kim et al. / Annals of Nuclear Energy 37 (2010) 888–893

when the standard communication protocol is used is about 4.4%higher on average than the workload when the conventional proto-cols are used. If we consider the fact that the operators were notaccustomed to the newly developed standard communication pro-tocol and the standard communication protocol has a more com-plex structure for accomplishing the basic direction of enhancing

Fig. 4. A comparison of the workload

Fig. 5. A comparison of some character

the safety of NPPs and the standardization of communication pro-tocols, it can be said that the introduction of the standard commu-nication protocol did not significantly change the workload of theoperators during an emergency situation management. For thisreason, we expect that the standard communication protocol canbe accepted by NPP MCR operators without much aversion.

3.4. Comparison of safety-related characteristics

Fig. 5 shows a comparison of some characteristics related to thesafety of NPPs evaluated by using the three questions in the ques-tionnaire that the authors prepared. The three questions are thesituation awareness (SA) on safety parameters, efficiency, and clar-ity, and they are developed to estimate the effectiveness of thestandard communication protocol with respect to both the reduc-tion of the possibilities of human error and the increase in the po-tential to recognize essential information. As can be seen fromFig. 5, the three characteristics related to safety when the standardcommunication protocol was used were evaluated to be about13.2% higher on average when compared to the same three charac-teristics when the conventional protocols were used. It means thatwhen the standard communication protocol was used, the opera-tors could grasp the safety-related parameters better and commu-nicate with each other more efficiently and more clearly. For this

s evaluated by using NASA-TLX.

istics related to the safety of NPPs.

M.C. Kim et al. / Annals of Nuclear Energy 37 (2010) 888–893 893

reason, it can be said that the standard communication protocolwill contribute to enhancing the safety of NPPs.

4. Discussion

One advantage that should be emphasized in the validationexperiments is the fact that the experiments are performed with li-censed NPP MCR operator teams and the feedback is received fromthem. But, one shortcoming of the validation experiments is thatthe number of participating NPP MCR operator teams is not big en-ough to draw statistically valid results. But, it should be noted thatthe validation experiment with licensed NPP MCR operator teamsto the scale that statistically valid results can be drawn is alwaysa big challenge.

From the works of Kanki et al. (1989) and Zohar and Luria(2003), it was expected that the standard communication protocolwill enhance the performance of NPP MCR operator teams. Thiswork provides an experimental basis for such an expectation.

The experimental results show that the workload is about 4.4%higher but the characteristics related to the safety of NPPs areabout 13.2% higher when the standard communication protocolis used. Even though it is hard to say the results are statistically va-lid due to the insufficiency of the number of participated NPP MCRoperator teams, it can be said that the experimental results showthe effectiveness of the standard communication protocol.

5. Conclusions

To enhance the safety of NPPs in emergency situations by mak-ing the communications between MCR operators in NPPs clearer,we developed a standard communication protocol for NPPs, withthe basic direction of enhancing the safety of NPPs and the stan-dardization of communication protocols. After developing five can-didate protocols, these candidate protocols were reviewed by fieldexperts and the review results were reflected in the developmentof the standard communication protocol in this study. To verifythe newly developed standard communication protocol, a valida-tion experiment was performed. In the validation experiment, 10NPP MCR operator teams were asked to perform the managementof simulated emergency situations with a conventional protocol(the protocol that they were used to) and the standard communi-cation protocol. Even though it was found that the use of the stan-dard communication protocol required more time, it was alsofound that the use of the standard communication protocol couldcontribute to the enhancement of the safety of NPPs, while impos-ing almost the same amount of workload on NPP MCR operators.The newly developed standard communication protocol can beused for not only the training of new NPP MCR operators, but also

training existing NPP MCR operators to gradually change theircommunication protocol practices to the developed standard com-munication protocol. By reducing the human error possibilitiesduring the management of emergency situations, the standardcommunication protocol is expected to contribute to enhancingthe safety and performance of NPPs.

Acknowledgements

This work was partly supported by Nuclear Research & Devel-opment Program of the National Research Foundation of Korea(NRF) grant funded by the Korean government (MEST) (grant code:2010-0001029).

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