Failure Mode and Reliability Study for Electrical Facility 1

FAILURE MODE AND RELIABILITY STUDY FOR ELECTRICAL FACILITY

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 Failure Mode and Reliability Study for Electrical Facility 2

Failure Mode and Reliability Study for Electrical Facility

Introduction

The article titled, "Failure mode and reliability study for Electrical Facility of the High-

Temperature Engineering Test Reactor" was inspired by the launching of a new plant of design

of Gas Turbine High-Temperature Reactor for cogeneration to enhance the industrial application

of High-Temperature Gas-cooled Reactors. High-Temperature Engineering Test Reactor

(HTTR) technology will be employed to structure, construct, operate the new plant to ascertain

long-lasting high efficiency and safe operation since the technology is already prevailing. The

key safety and economic concerns encompassing the initiative is the test program for electricity

and hydrogen cogeneration covers, and the examination of the pairing between the nuclear

reactor and the non-nuclear installation. Safety and failure mode elements of the nuclear and

non-nuclear systems are the key determinants of the reliability of the entire plant. Consequently,

a unified system of licensing and risk assessment will be incorporated to respond to the safety

concerns of both chemical and nuclear components of the plant.

Evaluation of different aspects of power systems has been given greater attention than

studies relating to failure mode and reliability of HTTR Electrical facility. Detection,

prioritization, and curbing of systems and processes’ potential failure are typically determined

using Failure Mode and Effect Analysis (FMEA). However, FMEA has been advancing since its

initial use by the aerospace industry in the 1960s. The chief problems have been inadequate

operating skills and experience, trustable input data, and a lack of an appropriate approach for

passive systems analysis. Nevertheless, the lack of trustworthy data input has been partially

solved for the recently built nuclear reactors by using the Bayesian inference, which has been
 Failure Mode and Reliability Study for Electrical Facility 3

successfully utilized in the Chinese High Flux Engineering Test Reactor (HFETR). Generally,

the probability of greater improvements in the safety and reliability of emerging reactor

technologies can be anticipated following the great strides being made about incorporating

artificial intelligence.

Objectives

The prime goal of this work is to determine the frequency of outages of HTTR-based

cogeneration plant posed by the failures of the HTTR Electrical Facility aided by the following

objectives:

To examine the modes of failure of the system based on the rate of occurrence and rigorousness

using the Failure Mode and Effect Analysis (FMEA) approach.

To frame an FMEA-based technique for progressive monitoring of failure modes with a focus on

identifying the most impactful failures that must be dealt with extreme accuracy.

To evaluate the impact of design improvements on the system reliability through comparing the

frequency of failure for the standard system design and its modified version

To investigate the effect of the aging incident on the system reliability by relating the first and

the last year of operation of the system failure

Main Findings

The main findings are based on the objectives stipulated above. For example, based on

average failure rates, the findings indicate a substantial improvement in first-year system

reliability from 0.5 to 0.7. Furthermore, integration of an extra inverter D in the Uninterruptible

AC power System improves its reliability from 0.76 to 0.94, whereas the reliability of offsite
 Failure Mode and Reliability Study for Electrical Facility 4

power heightens from below 0.96 to above 0.99 when incorporated with Secondary Commercial

Line (Kowal and Torabi, 2021, p. 7). Contrarily, regarding failure rate uncertainties, the results

do not show a continuous characteristic since the calculations were based on multiple points. The

reliability data was obtained from the NRC NUREG/CR-6928 in the United States, which

provided the average values and the Probability Density Functions (PDF) of the failure rate

component using a Gamma distribution model. However, a failure rate of fifty of the improved

system configuration, 3.0E-05, is more than twice lower than that of the standard design (6.6E-

05). On the contrary, the results of the aging phenomena are established based on busbar joints,

electrical cables, transformers, circuit breakers, and disconnectors. The components’ lifespans

are reported to influence the failure rate of the systems. In this regard, evaluation of components’

lifespans distribution can avail insights regarding the time dependence of the failure rate using

statistical data from operating experience and accelerated aging tests.

Reliability Concepts Studied

A system is a combination of a network of components structured to suit a specific design

to operate in the desired way. However, the reliability of such a system hinges upon the types,

quantities, and dependability of its components, which collectively gives insight into the ability

of the entire function to function under specific conditions for a specific period. As a result,

reliability brings up the concepts of availability, testability, and maintenance to determine the

overall cost-effectiveness of a system. Availability denotes the period for which a system can

function effectively which is achieved through testability which entails assessing the system

including its components to determine the time that the system can reliably operate (Karim and

Islam, 2019, p. 161). Conversely, maintainability denotes maintenance actions that are

undertaken when a system is found to have faults that would hinder it from operating within the
 Failure Mode and Reliability Study for Electrical Facility 5

predetermined time and under the specified conditions (Aven, 2017, p. 5). In this regard,

availability, testability, and maintenance are part of reliability system engineering concepts

studied and considerably rely on each other as discussed above.

Methodology

FMEA and gradual screening approach constitute the prime methods employed in the

analysis of HTTR-based cogeneration plant’s reliability. FMEA methodology is employed to

identify and evaluate events that can result in inadequate power of the HTTR Electrical Facility,

including occurrence, severity, and detection ratings. As a result, FMEA is a straightforward

method for assessing and improving a system targeting to identify where a failure can occur, its

probability of arising, and the extent of the outcomes of the failure. Contrarily, the gradual

screening methodology focused on the potential agents of failure and their greatest severe

consequences. However, it incorporated the Risk Priority Number (RPN), which is a

mathematical multiplication of severity, frequency, and detection, to aid in the prioritization of

the identified potential causes of failure. A two-dimensional risk matrix was then introduced

portraying the total failure modes accompanied by an explicit frequency and severity. The risk

matrix avails grounds for the continuous monitoring of the failure modes. In this regard, FMEA

and the gradual screening approach constitute the prime methodologies employed to determine

the reliability of the HTTR-based cogeneration plant based on failure rate.

Applications to the Reliability Systems

Reliability in engineering systems is applicable in determining potential failures and their

causes, the rate of occurrence, and mitigation measures to counter them. Examples of causes of

failure that reliability systems can detect include poor design, the sophistication of equipment,
 Failure Mode and Reliability Study for Electrical Facility 6

incorrect manufacturing techniques, human errors (Sunilraj and Eswaramoorthy, 2016, p. 2).

Furthermore, by supporting the formulation of a systematic and effective maintenance plan and

providing insights into maintenance operations at the equipment level, reliability systems help to

avoid superfluous preventative maintenance tasks (Sunilraj and Eswaramoorthy, 2016, p. 3).

Reliability systems also avail quantitative assessment of how diverse maintenance tasks can

impact performance at the system level by allowing modeling and comparison of different

maintenance strategies which give results at the components and plant level. They can also

reinforce the integration efforts of various functional aspects in the process industry, including

lean manufacturing philosophy such as TPM (Aven, 2017, p. 5). Moreover, reliability systems

permit adequate evaluation of policies and resources such as spare parts and crews, and layout of

the plant before undertaking integration efforts, enabling engineers, operators, and maintenance

personnel to make informed decisions to realize the goals of a plant. In this regard, reliability

systems play a considerable role in identifying potential failures and suitable mitigation measures

by facilitating the determination of how diverse maintenance tasks can impact performance and

enabling engineers, operators, and maintenance personnel to make informed decisions regarding

plant operation.

Interpretation and Analysis

Reliability systems engineering allows quantification of output and performance by

incorporating the aspect of time, probability, intended function, and operating conditions.

Consequently, the function of reliability hinges upon time and other aspects of the plant

including, the aging phenomena of the busbars and disconnectors. Besides, the numerical

probability that illustrates the reliability of a facility should be a value between one and zero. For

instance, from the article, the integration of an extra inverter D in the Uninterruptible AC power
 Failure Mode and Reliability Study for Electrical Facility 7

System improved its reliability from 0.76 to 0.94, whereas the reliability of offsite power

heightened from below 0.96 to above 0.99 when incorporated with Secondary Commercial Line

all of which are values between zero and one. The higher the value of the numerical probability

values the higher the availability time of operation of the respective system. For example, a

system whose reliability is 0.9999 means that the system is subject to failure for only 52 minutes

in a whole year. The reliability value in terms of numerical probability guides the detection of

possible reliability issues by giving insight into the most suitable maintenance schedule.

Consequently, reliability systems engineering is a crucial aspect in systems’ management by

facilitating systematic employment of the most appropriate engineering practices and techniques

to achieve optimum operation of a system cost-effectively.

Discussion

The FMEA findings presented above were initial reliability calculations conducted on the

HTTR Electrical Facility based on one year of progressive functioning. Contrarily, the FMEA-

based gradual screening approach was employed to choose failure modes that needed to be

excepted from quantitative assessment and those that could be evaluated based on uncertainty

and aging impacts. The gradual screening approach is advantageous over FMEA since the

failures of the higher risk priority are arrived at with greater precision. Reliability was then

compared based on two design options, including the standard one and the improved

configuration in which secondary commercial offsite power line and inverter D were

incorporated as modifications (Kowal and Torabi, 2021, p. 7). The FMEA study conducted for

the standard design with secondary commercial offsite power line showed the highest Risk

Priority Number which is a vital comprehension because the Loss of Offsite Power is recognized

as the most dangerous among all Anticipated Operational Occurrences (AOOs) of an HTTR,
 Failure Mode and Reliability Study for Electrical Facility 8

especially in the aspect of heat removal in the reactor core (Kowal and Torabi, 2021, p. 7).

However, the results of the study conducted in this paper should not be applied in other

locations, but should be replaced with site-specific information when executing HTTR in a

particular location to account for the site’s unique factors such as environmental conditions.

Conclusion

Unified systems of licensing and risk assessment are vital in plants to address the safety

concerns of both chemical and nuclear components of the plant, including HTTR Electrical

Facilities. Furthermore, enhancing reliability is crucial to reduce the frequency of outages of

HTTR-based cogeneration plants posed by the failures of the HTTR Electrical Facility, which

the article sought to tackle as its main objective. Subsequently, FMEA and gradual screening

approach methodologies were employed in the analysis of HTTR-based cogeneration plant’s

reliability. The results indicated that reliability engineering systems give significant insights into

the availability and maintenance of systems, rendering availability and maintainability concepts

part of reliability engineering. Generally, reliability systems play a significant role in identifying

potential failures appropriate mitigation measures by facilitating the determination of how

various maintenance tasks can impact performance and enabling engineers, operators, and

maintenance personnel to make informed decisions.

Summary Paragraph

I have learned that system reliability, which can be achieved using FMEA and the

gradual screening approach, is vital in preventing or minimizing the possibility of failures. Tests

regarding the reliability of a system give insight into the suitable implementation of maintenance

and enhance the availability of the system. For example, the numerical value of probability for
 Failure Mode and Reliability Study for Electrical Facility 9

system reliability provides the time in which a system can operate without experiencing failures.

Once this time is established, engineers, operators, and maintenance personnel can come together

and develop an informed maintenance schedule or make decisions about modifications that can

be integrated to improve availability and reduce the frequency of maintenance to heighten

productivity. In this regard, I have learned that conducting adequate tests on a system to

determine its reliability gives more accurate insights into its availability and the most economical

maintenance schedule to achieve an overall cost-effective operation of an entire plant. The

knowledge about FMEA and the gradual screening approach will be useful in that identifying

possible failures in design projects that I will held responsible. They will aid me in breaking

down designs into components and then critically analyze each to determine events of failure,

producing reliable designs.

References

Aven, T., 2017. Improving the foundation and practice of reliability engineering. Proceedings of

the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 231(3),

pp.1-11.

https://www.researchgate.net/publication/315978919_Improving_the_foundation_and_pr

actice_of_reliability_engineering/link/58ed4ff50f7e9b37ed14e6c5/download

Karim, M.R. and Islam, M.A., 2019. Reliability and Survival Analysis. Springer Singapore.

https://sci-hub.se/10.1007/978-981-13-9776-9

Kowal, K. and Torabi, M., 2021. Failure mode and reliability study for Electrical Facility of the

High Temperature Engineering Test Reactor. Reliability Engineering & System Safety,

210, p.1-11. https://sci-hub.se/10.1016/j.ress.2021.107529

Sunilraj B. A and Eswaramoorthy M. 2016. Application of reliability engineering: A detailed

study. International Journal of Engineering Research and Technology (IJERT) ICRET,

4( 21), p.1-3. https://www.ijert.org/research/application-of-reliability-engineering-a-

detailed-study-IJERTCONV4IS21059.pdf