A method for determining a maintenance cycle of a high-temperature gas-cooled reactor nuclear island instrument control device

Abstract

The present application belongs to the technical field of high temperature gas cooled reactor nuclear island instrument control equipment operation and maintenance, and particularly relates to a high temperature gas cooled reactor nuclear island instrument control equipment overhaul cycle formulation method. The method comprises the following steps: step 1: nuclear island instrument control equipment importance classification; step 2: equipment reliability rating; before the first operation of the unit, the equipment quality reliability rating is performed according to the continuous operation time of 98% of the qualified rate before instrument calibration adjustment and the annual average number of faults; step 3: equipment overhaul cycle formulation; and step 4: equipment overhaul cycle dynamic adjustment strategy. The present application has the beneficial effect of reducing the frequency of shutdown, and in the entire operation cycle, the planned shutdown time + unplanned shutdown time can be directly reduced, and the annual average power generation or gas supply of the unit is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of operation and maintenance technology of instrumentation and control equipment in high-temperature gas-cooled reactor nuclear island, and specifically relates to a method for determining the maintenance cycle of instrumentation and control equipment in high-temperature gas-cooled reactor nuclear island. Background Technology

[0002] High-temperature gas-cooled reactors (HTGRs) are considered the most promising fourth-generation reactors due to their broad commercial application prospects in combined heat and power (CHP) and high-temperature process heat, possessing enormous development potential. However, compared to mainstream pressurized water reactors, their construction cost per unit power is higher, putting them at a disadvantage in terms of economics.

[0003] Unlike pressurized water reactors, which must be shut down for refueling when fuel burnup reaches the design depth, high-temperature gas-cooled reactors are designed for continuous online refueling. Therefore, the maintenance cycle of the equipment will affect the frequency of overhauls and the number of startups and shutdowns, thus affecting the unit's operation and maintenance costs and economic benefits.

[0004] Currently, the maintenance principles for the instrumentation and control system equipment of high-temperature gas-cooled reactor nuclear island mainly have the following problems: 1. There is a lack of a quantitative decision-making tool for the maintenance cycle of instrumentation and control equipment specific to the characteristics of high-temperature gas-cooled reactor (HTGR) technology. Due to the lack of operational data, the maintenance cycle of instrumentation and control equipment in newly built HTGR units is generally based on the operating experience of traditional pressurized water reactor units or general industrial standards. This leads to unreasonable equipment maintenance cycles, increased workload for personnel maintenance, and higher economic costs.

[0005] 2. The existing maintenance cycle of the nuclear island instrumentation and control system of high-temperature gas-cooled reactors mostly adopts a fixed periodic mode, which fails to reflect the inherent safety characteristics of high-temperature gas-cooled reactors; it does not fully consider the reliability differences of the corresponding instrumentation and control system equipment; and it lacks sufficient analysis of the severity of the consequences of a first-level failure under the severity level of the operating conditions, thus failing to achieve the optimal allocation of operation and maintenance resources. Summary of the Invention

[0006] The purpose of this invention is to provide a method for determining the maintenance cycle of instrumentation and control equipment in the nuclear island of a high-temperature gas-cooled reactor. The problem this patent aims to solve is to provide a decision-making tool for determining the maintenance cycle of instrumentation and control equipment in the nuclear island of a high-temperature gas-cooled reactor.

[0007] The technical solution of the present invention is as follows: A method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor nuclear island, comprising the following steps: Step 1: Classification of the importance of nuclear island instrumentation and control equipment; Step 2: Equipment reliability rating; Before the unit's first operation, the equipment quality reliability rating is conducted based on the continuous operating time with a pass rate of 98% before instrument calibration and adjustment, and the average number of annual failures. Step 3: Establish equipment maintenance cycles; Step 4: Dynamic adjustment strategy for equipment maintenance cycle.

[0008] Step 1 includes: Step 11: Compile a complete equipment list; Based on the high-temperature gas-cooled reactor process flow, safety analysis report, and process system control instructions, the equipment of the nuclear island instrumentation and control system was reviewed, and a list of equipment to be evaluated was formed for all field instruments, transmitters, sensors, controllers, cabinets, and network equipment involved in monitoring, control, and protection. Step 12: Classify equipment importance; Equipment importance is categorized into four classes: A, B, C, and D.

[0009] In step 12, Class A equipment refers to equipment with single-point sensitivity. This means that a single equipment failure can lead to power plant shutdown, outage, power reduction, or significant power fluctuations. Equipment whose failure of a single piece of equipment will result in any of the following consequences is identified as Class A equipment: (a) Causes automatic or manual reactor shutdown or machine stoppage; (b) Causes power disturbances with an amplitude ≥10%FP; (c) Equipment that is not scheduled to enter the down mode due to operational restrictions, and cannot be repaired online or within the time limit; (d) It is impossible to perform maintenance online, and the failure of the equipment makes it impossible for the unit to maintain long-term stable operation.

[0010] In step 12, Class B equipment refers to equipment other than Class A equipment. Equipment whose failure in a single unit could lead to the loss or degradation of critical functions supporting nuclear safety or generator power generation at the power plant is classified as Class B equipment. Equipment whose failure in a single unit would result in any of the following consequences is identified as Class B equipment: (a) Causes power disturbances with an amplitude <10%FP; (b) Equipment that can be repaired online and can be repaired within the time limit when entering the down mode without being subject to unplanned operational restrictions; (c) A reduction in redundant equipment that could lead to reactor shutdown, outage, or power reduction, including single-channel logical trips; (d) Loss of redundancy in the security system; (e) Security system starts; (f) Unable to control critical reactor safety functions; (g) The ability to shut down or maintain a shutdown state and remove residual heat is reduced; (h) Emergency operating procedures cannot be executed; (i) It cannot prevent or mitigate the release of radioactivity outside the containment; (j) is a high-risk equipment.

[0011] In step 12, Class C equipment refers to equipment whose failure consequences do not meet the classification criteria for critical equipment, but whose failure would make the increase in personnel safety, industrial safety, environmental safety, or radiation safety hazards unacceptable. If a single equipment failure occurs, any of the following consequences will occur. Equipment other than Class A and Class B equipment is classified as Class C equipment. (a) This leads to a reduction in redundancy in critical systems or a decrease in the depth of defense in depth; (b) Causes unacceptable chemical, radioactive, or environmental hazards; (c) If the unplanned entry into the operating restriction conditions does not require a mode reduction, or if the mode reduction requirement can be waived through alternative means; (d) Promotes the failure of other critical equipment or is detrimental to their operation, but does not cause the immediate failure of the critical functions of the critical equipment; (e) Causing delays or obstruction of timely maintenance of critical equipment; (f) Leads to an unacceptable increase in repair, replacement, or operating costs; (g) Equipment subject to regulations such as industrial safety regulations; (h) Equipment with scarce spare parts, long purchase cycles, or high value; (i) Equipment that causes the loss of important alarms or makes it impossible to monitor operating parameters, increasing the burden on operators; (j) Equipment for refueling or changing materials, or equipment that affects the critical path of the overhaul; (k) Emergency preparedness and emergency response equipment.

[0012] In step 12, D-class devices refer to all devices that do not meet the identification criteria for classes A, B, and C.

[0013] Step 4 includes establishing equipment performance criteria and testing parameters within the analysis and evaluation cycle, and adjusting the maintenance cycle based on the analysis and evaluation conclusions. Specifically, this includes: Step 41: Establish performance criteria and monitored parameters; For important systems and key equipment, performance criteria and monitored parameters are established, and reliability analysis and evaluation are conducted on operational quality indicators, the number of defects, and trends of change within the analysis and evaluation cycle. Step 42: Dynamically adjust the strategy; Based on the analysis and evaluation results, when the rating is Level 1 for a continuous period, the original maintenance cycle will be extended, but not exceeding the longest maintenance cycle of the same equipment level. When the rating is Level 3 for a continuous period, the original maintenance cycle will be shortened by half a cycle. If the pre-adjustment pass rate of equipment of the same type and model from the same manufacturer is lower than 80% within the original maintenance cycle, the originally determined maintenance cycle will be shortened by half a cycle. For equipment of the same type and model from the same manufacturer, if the pre-adjustment pass rate is greater than 95% or above within the original maintenance cycle, the original maintenance cycle shall be extended, but the extended maintenance cycle shall not exceed the longest maintenance cycle of the same equipment class.

[0014] The beneficial effects of this invention are as follows: the design feature of the high-temperature gas-cooled reactor, which allows for continuous online refueling without shutting down the reactor, reduces downtime caused by maintenance and repairs, directly and significantly improving economic efficiency. The conventional overhaul shutdown cycle for nuclear power units is approximately 40-60 days. Reducing the frequency of shutdowns directly reduces both planned and unplanned downtime throughout the entire operating cycle, significantly increasing the unit's average annual power generation or gas supply. With improved reliability, extending the frequency of maintenance and repairs reduces labor costs and also lowers spare parts purchase and storage costs. Furthermore, the subsequent refinement of maintenance and repair cycles provides a foundation for the transformation of nuclear power plants towards higher safety, higher efficiency, lower cost, and intelligent and sophisticated operations. Attached Figure Description

[0015] Figure 1 The present invention provides a method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor nuclear island, with a flowchart.

[0016] The diagram shows: 1. Classification of the importance of nuclear island instrumentation and control equipment; 2. Complete equipment list; 3. Single failure consequence analysis; 4. Classification conclusions; 5. Equipment reliability rating; 6. Continuous operating time of instruments; 7. Average number of failures per year; 8. Equipment rating; 9. Equipment maintenance cycle formulation; 10. Equipment importance classification results; 11. Reliability rating results; 12. Testing cycle; 13. Evaluation cycle; 14. Dynamic adjustment strategy for equipment maintenance cycle; 15. Establishment of performance criteria and testing parameters; 16. Dynamic adjustment strategy. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] This invention provides a method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor (HTGR) nuclear island. First, the instrumentation and control equipment is categorized and classified by importance, and its reliability is rated to determine the maintenance cycle for the instrumentation and control system and equipment. Subsequently, performance monitoring of the instrumentation and control equipment is conducted within the predetermined cycle, and the maintenance cycle of the instrumentation and control system and equipment is dynamically adjusted as appropriate. This ensures that the maintenance cycle adjustment strategy meets the actual situation and operational requirements of the equipment. This not only facilitates the scheduling of maintenance windows between different modules, improving the overall unit availability and external heating stability, but also reduces the operation and maintenance costs of the HTGR unit, thus improving its economic efficiency.

[0019] A method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor nuclear island includes the following steps: Step 1: Classification of the Importance of Nuclear Island Instrumentation and Control Equipment Step 11: Compile a complete equipment list; Based on the high-temperature gas-cooled reactor process flow, safety analysis report, and process system control instructions, the equipment of the nuclear island instrumentation and control system was reviewed. A list of equipment to be evaluated was compiled for all field instruments, transmitters, sensors, controllers, cabinets, and network equipment involved in monitoring, control, and protection. This list serves as the basis for all subsequent analyses.

[0020] Step 12: Classification of Equipment Importance Equipment importance classification is primarily based on deterministic analysis of the consequences of a single equipment failure. It can also be supplemented by probabilistic methods and engineering judgments, taking into account factors such as inherent equipment reliability, operating environment, and frequency of operation. To avoid discrepancies in classification results for equipment with similar functions and types, the equipment's failure state is generally considered according to the most severe scenario during classification.

[0021] The importance of equipment can be categorized as follows: Class A equipment, also known as critical components, refers to equipment with single-point sensitivity. A failure in a single piece of this equipment can lead to power plant shutdowns, outages, reduced power output, or significant power fluctuations. Equipment whose failure in a single piece of equipment will result in any of the following consequences can be identified as Class A equipment: (a) Causes automatic or manual reactor shutdown or machine stoppage; (b) Causes power disturbances with an amplitude ≥10%FP; (c) Equipment that is not scheduled to enter the down mode due to operational restrictions, and cannot be repaired online or within the time limit; (d) It is impossible to perform maintenance online, and the failure of the equipment makes it impossible for the unit to maintain long-term stable operation.

[0022] Category B equipment: refers to equipment other than Category A equipment, where a single equipment failure could lead to the loss or degradation of critical functions supporting nuclear safety or generator operation at the power plant. Equipment whose failure in a single unit would result in any of the following consequences can be identified as Category B equipment: (a) Causes power disturbances with an amplitude <10%FP; (b) Equipment that can be repaired online and can be repaired within the time limit when entering the down mode without being subject to unplanned operational restrictions; (c) A reduction in redundant equipment that could lead to reactor shutdown, outage, or power reduction, including single-channel logical trips; (d) Loss of redundancy in the security system; (e) Security system starts; (f) Unable to control critical reactor safety functions; (g) The ability to shut down or maintain a shutdown state and remove residual heat is reduced; (h) Emergency operating procedures cannot be executed; (i) It cannot prevent or mitigate the release of radioactivity outside the containment; (j) is a risk-critical (high-risk) equipment (excluding Class A equipment).

[0023] Class C equipment: Also known as critical equipment, this type of equipment, while not meeting the criteria for critical equipment, would cause unacceptable increases in personnel safety, industrial safety, environmental safety, or radiation safety hazards if it failed. This also includes equipment worthy of preventative maintenance. Any equipment other than Class A and Class B equipment whose failure in a single instance would result in any of the following consequences is classified as Class C equipment.

[0024] (a) This leads to a reduction in redundancy in critical systems or a decrease in the depth of defense in depth; (b) Causes unacceptable chemical, radioactive, or environmental hazards; (c) If the unplanned entry into the operating restriction conditions does not require a mode reduction, or if the mode reduction requirement can be waived through alternative means; (d) Promotes the failure of other critical equipment or is detrimental to their operation, but does not cause the immediate failure of the critical functions of the critical equipment; (e) Causing delays or obstruction of timely maintenance of critical equipment; (f) Leads to an unacceptable increase in repair, replacement, or operating costs; (g) Equipment subject to regulations such as industrial safety regulations; (h) Equipment with scarce spare parts, long purchase cycles, or high value; (i) Equipment that causes the loss of important alarms or makes it impossible to monitor operating parameters, increasing the burden on operators; (j) Equipment for refueling or changing materials, or equipment that affects the critical path of the overhaul; (k) Emergency preparedness and emergency response equipment.

[0025] Class D equipment: also known as general equipment, does not require separate identification. All equipment that does not meet the identification conditions of Class A, Class B and Class C is general equipment.

[0026] Based on the above principles of importance classification, the following preliminary classification conclusions can be drawn by classifying the instrumentation and control system equipment of the high-temperature gas-cooled reactor. Category A equipment: All instrumentation and control equipment related to unit safety in high-temperature gas-cooled reactors is equipped with four-channel redundancy. When a single channel fails, the system is degraded but does not affect the normal operation of the unit. Therefore, there is no Category A equipment.

[0027] Class B Equipment: The following systems' equipment is classified as Class B equipment based on the above principles; Safety-grade thermal process measurement system, protection system, post-accident monitoring system, and nuclear island main feedwater system Class C Equipment: The following systems' equipment is classified as Class C equipment based on the above principles; Plant water system, equipment cooling water system, nuclear island main steam system, primary loop pressure relief system, main helium blower system, reactor pressure vessel system Class D equipment: Since Class D equipment does not require preventive maintenance, corrective maintenance is usually performed when it fails, so no maintenance cycle is specified for it.

[0028] Step 2: Equipment Reliability Rating Before the unit's initial operation, equipment reliability can be rated based on the continuous operating time with a 98% pass rate before instrument calibration and adjustment, and the average number of annual failures. Refer to the table below for details: Step 3: Establish Equipment Maintenance Cycle Note: C represents the overhaul cycle of the nuclear power unit. Step 4: Dynamic Adjustment Strategy for Equipment Maintenance Cycles Based on the table above, establish an analysis and evaluation management procedure for various types of instrumentation and control equipment. During the analysis and evaluation cycle, set equipment performance criteria and testing parameters, and adjust the maintenance cycle according to the analysis and evaluation conclusions.

[0029] Step 41: Establish performance criteria and monitored parameters For important systems and critical equipment, performance criteria and monitored parameters must be established to facilitate reliability analysis and evaluation of operational quality indicators, number of defects, and trends during the analysis and evaluation cycle.

[0030] Step 42: Dynamically Adjust the Strategy Based on the analysis and evaluation, when the rating is consistently Level 1, the originally determined maintenance cycle can be appropriately extended, but it should not exceed the longest maintenance cycle among equipment of the same level. When the rating is consistently Level 3, the originally determined maintenance cycle should be shortened by half a cycle.

[0031] If the pre-maintenance pass rate of equipment of the same type and model from the same manufacturer is lower than 80% within the original maintenance cycle, the originally determined maintenance cycle should be shortened by half a cycle.

[0032] For equipment of the same type and model from the same manufacturer, if the pre-adjustment pass rate is greater than 95% or above within the original maintenance cycle, the original maintenance cycle may be appropriately extended. However, the extended maintenance cycle should not exceed the longest maintenance cycle among equipment of the same class.

[0033] In addition, without affecting the safe operation of the unit, maintenance and repair can be carried out one by one during operation to improve operational reliability, reduce the workload of overhaul shutdowns for maintenance and repair, and shorten the shutdown time.

[0034] Example: Step 1: Classify the importance of nuclear island instrumentation and control equipment. Specifically, based on documents such as the high-temperature gas-cooled reactor process flow, safety analysis report, and process system control specifications, 2. compile a complete equipment list. 3. Analyze the consequences of single equipment failure using deterministic methods, and combine inherent equipment reliability, operating environment, and operating frequency with probabilistic methods and engineering judgments to classify equipment importance. 4. Obtain a graded conclusion based on the equipment classification principles.

[0035] The second step combines the continuous operating time of 6 instruments (with a pass rate of 98% before instrument calibration and adjustment before the first operation), the average number of failures over 7 years, and the equipment rating to complete the reliability rating of 5 equipment.

[0036] Step 3: 9. Establish equipment maintenance cycle, and complete 13. Evaluation cycle based on 10. Equipment importance classification results, 11. Reliability rating results, and 11. Test cycle.

[0037] Step 4, 14. Dynamic Adjustment Strategy for Equipment Maintenance Cycles: Based on the results of the assessment cycle (13), 15. Establish equipment performance criteria and testing parameters to facilitate reliability analysis and evaluation of operational quality indicators, the number of defects, and trends within the assessment cycle (13). Based on the assessment conclusions, 16. Develop a dynamic adjustment strategy.

[0038] The above specific implementation methods have fully verified the feasibility and engineering practical value of the method described in this invention. This invention provides a decision-making tool for determining the maintenance cycle of nuclear island instrumentation and control equipment in high-temperature gas-cooled reactor (HTGR) engineering. It is applicable to the dynamic adjustment of the maintenance cycle of HTGR instrumentation and control systems and equipment, facilitating the arrangement of maintenance windows between different modules, improving overall unit availability, reducing HTGR unit operation and maintenance costs, and enhancing unit economic efficiency. All variations and modifications to the method described in this invention should be considered within the scope of this invention.

Claims

1. A method for determining a maintenance cycle of instrumentation and control equipment in a high temperature gas cooled reactor nuclear island, characterized in that, Includes the following steps: Step 1: Classification of the importance of nuclear island instrumentation and control equipment; Step 2: Equipment reliability rating; Before the unit's first operation, the equipment quality reliability rating is conducted based on the continuous operating time with a pass rate of 98% before instrument calibration and adjustment, and the average number of annual failures. Step 3: Establish equipment maintenance cycles; Step 4: Dynamic adjustment strategy for equipment maintenance cycle.

2. The method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor nuclear island as described in claim 1, characterized in that, Step 1 includes: Step 11: Compile a complete equipment list; Based on the high-temperature gas-cooled reactor process flow, safety analysis report, and process system control instructions, the equipment of the nuclear island instrumentation and control system was reviewed, and a list of equipment to be evaluated was formed for all field instruments, transmitters, sensors, controllers, cabinets, and network equipment involved in monitoring, control, and protection. Step 12: Classify equipment importance; Equipment importance is categorized into four classes: A, B, C, and D.

3. The method of claim 2, wherein the method further comprises: determining the instrumented equipment maintenance period based on the instrumented equipment maintenance period and the instrumented equipment maintenance period of the reference nuclear island. In step 12, Class A equipment refers to equipment with single-point sensitivity. This means that a single equipment failure can lead to power plant shutdown, outage, power reduction, or significant power fluctuations. Equipment whose failure of a single piece of equipment will result in any of the following consequences is identified as Class A equipment: (a) Causes automatic or manual reactor shutdown or machine stoppage; (b) Causes power disturbances with an amplitude ≥10%FP; (c) Equipment that is not scheduled to enter the down mode due to operational restrictions, and cannot be repaired online or within the time limit; (d) It is impossible to perform maintenance online, and the failure of the equipment makes it impossible for the unit to maintain long-term stable operation.

4. The method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor nuclear island as described in claim 2, characterized in that: In step 12, Class B equipment refers to equipment other than Class A equipment. Equipment whose failure in a single unit could lead to the loss or degradation of critical functions supporting nuclear safety or generator power generation at the power plant is classified as Class B equipment. Equipment whose failure in a single unit would result in any of the following consequences is identified as Class B equipment: (a) Causes power disturbances with an amplitude <10%FP; (b) Equipment that can be repaired online and can be repaired within the time limit when entering the down mode without being subject to unplanned operational restrictions; (c) A reduction in redundant equipment that could lead to reactor shutdown, outage, or power reduction, including single-channel logical trips; (d) Loss of redundancy in the security system; (e) Security system starts; (f) Unable to control critical reactor safety functions; (g) The ability to shut down or maintain a shutdown state and remove residual heat is reduced; (h) Emergency operating procedures cannot be executed; (i) It cannot prevent or mitigate the release of radioactivity outside the containment; (j) is a high-risk equipment.

5. The method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor nuclear island as described in claim 2, characterized in that: In step 12, Class C equipment refers to equipment whose failure consequences do not meet the classification criteria for critical equipment, but whose failure would make the increase in personnel safety, industrial safety, environmental safety, or radiation safety hazards unacceptable. If a single equipment failure occurs, any of the following consequences will occur. Equipment other than Class A and Class B equipment is classified as Class C equipment. (a) This leads to a reduction in redundancy in critical systems or a decrease in the depth of defense in depth; (b) Causes unacceptable chemical, radioactive, or environmental hazards; (c) If the unplanned entry into the operating restriction conditions does not require a mode reduction, or if the mode reduction requirement can be waived through alternative means; (d) Promotes the failure of other critical equipment or is detrimental to their operation, but does not cause the immediate failure of the critical functions of the critical equipment; (e) Causing delays or obstruction of timely maintenance of critical equipment; (f) Leads to an unacceptable increase in repair, replacement, or operating costs; (g) Equipment subject to regulations such as industrial safety regulations; (h) Equipment with scarce spare parts, long purchase cycles, or high value; (i) Equipment that causes the loss of important alarms or makes it impossible to monitor operating parameters, increasing the burden on operators; (j) Equipment for refueling or changing materials, or equipment that affects the critical path of the overhaul; (k) Emergency preparedness and emergency response equipment.

6. The method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor nuclear island as described in claim 2, characterized in that: In step 12, D-class devices refer to all devices that do not meet the identification criteria for classes A, B, and C.

7. The method for determining the maintenance cycle of instrumentation and control equipment in a high-temperature gas-cooled reactor nuclear island as described in claim 1, characterized in that, Step 4 includes establishing equipment performance criteria and testing parameters within the analysis and evaluation cycle, and adjusting the maintenance cycle based on the analysis and evaluation conclusions. Specifically, this includes: Step 41: Establish performance criteria and monitored parameters; For important systems and key equipment, performance criteria and monitored parameters are established, and reliability analysis and evaluation are conducted on operational quality indicators, the number of defects, and trends of change within the analysis and evaluation cycle. Step 42: Dynamically adjust the strategy; Based on the analysis and evaluation results, when the rating is Level 1 for a continuous period, the original maintenance cycle will be extended, but not exceeding the longest maintenance cycle of the same equipment level. When the rating is Level 3 for a continuous period, the original maintenance cycle will be shortened by half a cycle. If the pre-adjustment pass rate of equipment of the same type and model from the same manufacturer is lower than 80% within the original maintenance cycle, the originally determined maintenance cycle will be shortened by half a cycle. For equipment of the same type and model from the same manufacturer, if the pre-adjustment pass rate is greater than 95% or above within the original maintenance cycle, the original maintenance cycle shall be extended, but the extended maintenance cycle shall not exceed the longest maintenance cycle of the same equipment class.

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