CN113449990A

CN113449990A - Method for evaluating shutdown safety risk during overhaul period of nuclear power station

Info

Publication number: CN113449990A
Application number: CN202110726105.5A
Authority: CN
Inventors: 王俊鹏; 马文奇; 何江华; 栾永刚; 李明; 胡俊锋; 田华宁; 朱志斌; 于炳瀛; 许礼伦
Original assignee: Shandong Nuclear Power Co Ltd
Current assignee: Shandong Nuclear Power Co Ltd
Priority date: 2021-06-29
Filing date: 2021-06-29
Publication date: 2021-09-28

Abstract

The invention discloses a shutdown safety risk evaluation method during the overhaul period of a nuclear power station, which establishes a shutdown safety risk evaluation system during the overhaul period of the nuclear power station through each evaluation criterion of safety functions provided by the shutdown safety risk evaluation method, is used for identifying and quantifying the redundancy degree and the risk level of the safety functions of the nuclear power station at each stage of the overhaul, distinguishes the risk levels through colors, evaluates the overall influence of each activity of the overhaul on the safety functions, and has clear, quantitative and visual indication on each safety function overall risk condition of each working window. The risk evaluation can be carried out on the mutual influence among the activities of the overhaul in the overhaul preparation stage, the overall influence of the activities of the nuclear power station on the key safety function during the overhaul is recognized in advance, the nuclear safety risk working condition exists during the overhaul, and the nuclear power station personnel are guided to adjust the plan in advance according to the evaluation result to avoid the high risk working condition, so that the overall risk of the overhaul is controllable.

Description

Method for evaluating shutdown safety risk during overhaul period of nuclear power station

Technical Field

The invention relates to a shutdown safety risk evaluation method during the overhaul period of a nuclear power station.

Background

At present, the nuclear power station in China generally adopts a three-level risk analysis method for the safety risk analysis of overhaul to control the safety risk of overhaul. The first-level risk analysis is risk analysis of a working bag preparation layer, the second-level risk analysis is to analyze the interrelation between overhaul activities on the basis of the first-level risk analysis to ensure that the project can be carried out safely and orderly, and the third-level risk analysis is to analyze the risks possibly encountered in the whole overhaul from an overhaul comprehensive layer on the basis of the first-level risk analysis and the second-level risk analysis. The evaluation mode of the nuclear safety risk during the overhaul period can only analyze the correlation between overhaul activities by depending on the experience of power station personnel, has no judgment basis, and cannot quantify the degree of the risk.

Considering that the safety function of the power station may be challenged due to mutual influence among various works because the configuration of the power station is different from the normal operation period and is continuously changed along with the process of overhaul, a large number of systems/equipment are quitted to operate, a large number of pre-maintenance and test works need to be executed and the like during the overhaul period of the nuclear power station, the overhaul plan needs to be evaluated before the overhaul work starts, the mutual relation among various overhaul activities is analyzed, and the safety function is ensured not to be challenged. It is known that a power station develops similar overhaul nuclear safety risk management software to perform nuclear safety risk analysis, see published patent CN111798005 (a development method of a nuclear power plant overhaul nuclear safety risk management tool). The method needs the power station to develop corresponding software for matching analysis, and the software calculation is also based on the result after personnel evaluation as input and is also considered as the evaluation judgment process in essence. Compared with the method, the method is simple and easy to implement, intuitive and understandable, software support is not needed, and all power station personnel can directly evaluate and analyze the overhaul plan according to the evaluation criterion.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: and analyzing and controlling the shutdown safety risk during the overhaul period of the nuclear power station.

In order to solve the problems, the technical scheme of the invention is to provide a shutdown safety risk evaluation method during the overhaul period of a nuclear power station, which is characterized by comprising the following steps:

step 1, determining key safety functions to be considered in shutdown working conditions during overhaul of a nuclear power station: determining key safety functions to be considered during the overhaul of the power station according to the fuel cladding, the pressure boundary of the reactor coolant system and the safety functions to be considered of the integrity of the containment during the shutdown of the nuclear power station, wherein the key safety functions to be considered comprise reactivity control of fuel in a reactor core, reactor core cooling, power supply availability, water charge control of the reactor coolant system and the containment, and SFP cooling of a spent fuel pool and SFP water charge of the spent fuel pool when spent fuel exists in the spent fuel pool;

step 2, analyzing system equipment influencing the functions of each key safety function, wherein:

a system device for affecting a reactivity control function, comprising: the boron concentration of the reactor coolant system RCS is greater than the mode 6 non-xenon boron concentration, the number of available reactivity control runners, no fuel movement, the hoisting of the internals and the change activity of the control rod trip/coupling core, and the minimum available number of source range instruments;

the system equipment for influencing the core cooling function comprises: the number of available steam generators SG, the liquid level of a refueling water pool, a row of normal shutdown cooling systems RNS can be used for exporting the waste heat of the reactor core, a second row of normal shutdown cooling systems RNS can be used for exporting the waste heat of the reactor core, and the liquid level of a reactor coolant system RCS is higher than the operation liquid level for reducing the water loading;

the system equipment for influencing the power supply availability function comprises: an independent off-plant power supply can supply power to the depth defense bus, a second independent off-plant power supply can supply power to the depth defense section bus, a standby diesel engine A can supply power to a nuclear island medium-voltage bus 1 section ES-1 bus, and a standby diesel engine B can supply power to a nuclear island medium-voltage bus 2 section ES-2 bus;

system equipment for effecting a reactor coolant system water charge control function includes: in the mode 5, the liquid level of the RCS of the reactor coolant system is more than 20%, the refueling water pool is full of water, the liquid level of the RCS of the reactor coolant system is higher than the running liquid level of the reduced water charge amount, and the quantity of available water sources for the RCS water replenishing of the reactor coolant system is less than the quantity of the water sources;

the system equipment for influencing the containment function comprises: a containment closed state, a containment personnel gate available, a containment isolation function available, a containment alternate boundary operation with a containment closed time less than an in-containment steam generation time, an RCS complete and at least one steam generator SG available, a containment recirculation cooling system VCS or a passive containment cooling system PCS available for containment cooling;

the system equipment for influencing the SFP cooling function of the spent fuel pool comprises: the number of usable rows of the spent fuel pool cooling system SFS, at least two power supplies for supplying power to the usable spent fuel pool cooling system SFS pump, at least 1 row of normal shutdown cooling system RNS for cooling the spent fuel pool SFP and two rows of the plant water system SWS/equipment cooling water system CCS;

the system equipment for influencing the SFP water capacity function of the spent fuel pool comprises: the liquid level of the spent fuel pool is normal, at least 1 boronized water source chemical and volume control system CVS can be used for supplementing water to the SFP of the spent fuel pool, an additional boronized water source spent fuel cleaning pool CWP or a spent fuel loading pool CLP can be used for supplementing water to the SFP of the spent fuel pool, a desalination system DWS can be used for supplementing water to the SFP of the spent fuel pool, a passive containment cooling water tank PCCWST or a passive containment cooling auxiliary water tank PCCAWST can be used for supplementing water to the SFP of the spent fuel pool, and the residual heat of a reactor core is less than 7 MW;

step 3, formulating each key safety function evaluation standard: the evaluation standard is formulated on the basis of ensuring the redundancy of each key safety function at any time of overhaul, divided into four risk levels of high, medium, low and no risk according to the reserved redundancy, and identified by four colors of red, orange, yellow and green;

and 4, performing risk evaluation on the determined overhaul plan: before overhaul is started, after an overhaul plan is determined, evaluating the overhaul plan according to the key safety function evaluation standard made in the step 3, wherein the evaluation takes the overhaul plan time as an axis, dividing the overhaul stage into a plurality of evaluation platforms according to the overhaul process, evaluating each key safety function on each evaluation platform one by one, and making an evaluation result into a shutdown safety function evaluation summary table taking the time as the axis;

and 5, according to the evaluation result in the step 4, making a risk control measure: if the high risk, namely the red working window, is evaluated in the step 4, the overhaul plan must be adjusted before the overhaul is started, and the work affecting the key safety function is adjusted to other working windows; if the mid-risk, i.e. the orange working window, is evaluated, control measures for the risk condition must be made before major repair begins to ensure that the major repair working risk is controllable.

Preferably, the evaluation criteria in step 3 include:

reactivity control evaluation criteria:

when the boron concentration of the RCS of the reactor coolant system is more than that of the mode 6 without xenon, the RCS can be scored by 1, otherwise, the RCS can not be scored;

the number of available reactivity control boron injection flow channels is 1 minute per hour, and 2 minutes are obtained for two or more;

1 point is obtained when no fuel moves, the reactor internals are hoisted, and the control rod tripping/interlocking reactor core changes the activity, otherwise, no point is obtained;

at least one source range meter can be used for 1 point, at least two source range meters can be used for 1 point in the mode 6, and the source range meters can not be used for scoring in the reverse direction;

core cooling evaluation criteria:

the number of the available steam generators SG is 1 when the number is 1, and 2 when the number is 2;

when the reloading pool is full of water, the item is scored as 1, otherwise, the item is not scored;

the RNS of the normal shutdown cooling system can be used for obtaining 1 point when the waste heat of the reactor core is derived, otherwise, the RNS does not obtain the point;

the RNS of the second row of normal shutdown cooling systems can be used for obtaining 1 point when the waste heat of the reactor core is derived, otherwise, the RNS does not obtain the point;

the RCS liquid level of the reactor coolant system is 1 point when the RCS liquid level is higher than the operation liquid level for reducing the water loading, otherwise, the RCS liquid level is not scored;

evaluation criteria of power supply availability:

the independent off-plant power supply can be rated as 1 when supplying power to the depth defense bus, otherwise, the power is not rated;

the second independent power supply can obtain 1 point when supplying power to the depth defense section bus, otherwise, the power supply does not obtain the point;

the standby diesel engine A can obtain 1 point when supplying power to a 1-section ES-1 bus of the nuclear island medium-voltage bus, or else, the standby diesel engine A does not obtain the point;

the standby diesel engine B can obtain 1 point when supplying power to the 2 sections of ES-2 buses of the nuclear island medium-voltage bus, or else, the standby diesel engine B does not obtain the point;

water content evaluation criteria:

mode 5 and when the RCS liquid level of the reactor coolant system is more than 20%, 1 score is obtained, otherwise, no score is obtained;

when the reloading pool is full of water, the user can score 1, otherwise, the user can not score;

1 minute is obtained when the quantity of the RCS water replenishing available water source of the reactor coolant system is 1, and 2 minutes is obtained when the quantity of the RCS water replenishing available water source is more than or equal to 2;

and (4) evaluating the containment vessel:

the score of 1 is obtained when the containment vessel is in a closed state, otherwise, the score is not obtained;

the containment personnel gate can be used for 1 point, otherwise, the containment personnel gate can not be used for scoring;

the score of 1 is obtained when the containment isolation function is available, otherwise, the score is not obtained;

the point is 1 when the containment is operated instead of the boundary and the closing time of the containment is less than the generation time of steam in the containment, otherwise, the point is not scored;

a reactor coolant system RCS is complete and at least one SG is available for a score of 1, otherwise no score is obtained;

the VCS or the PCS can be used for scoring 1 point when the containment is cooled, or else, the VCS or the PCS does not score;

the cooling evaluation standard of the spent fuel pool is as follows:

1 point is obtained when the number of available rows of the spent fuel pool cooling system SFS is 1, and 2 points are obtained when the number of available rows is 2;

when at least two paths of power supplies supply power to an available SFS pump of the spent fuel pool cooling system, the power is divided into 1 point, otherwise, the power is not divided into points;

at least 1 column of normal shutdown cooling systems RNS can be used for obtaining 1 point when cooling the spent fuel pool SFP, and otherwise, the RNS does not obtain the point;

if the two rows of the SWS/CCS are available, the score is 1, otherwise, the score is not obtained;

the evaluation standard of the water content of the spent fuel pool is as follows:

when the liquid level of the spent pool is normal, the spent pool is divided into 1 point, otherwise, the spent pool is not divided into points;

the CVS of the at least one boronized water source chemical and volume control system can be used for obtaining 1 point when the spent fuel pool SFP is replenished with water, and otherwise, the CVS does not obtain the point;

the additional boronized water source spent fuel cleaning pool CWP or spent fuel loading pool CLP can be used for 1 point when SFP water replenishing is carried out, otherwise, no point is obtained;

the desalination system DWS can be used for obtaining 1 point when the spent fuel pool SFP replenishes water, otherwise, the water is not obtained;

the passive containment cooling water tank PCCWST or the passive containment cooling auxiliary water tank PCCAWST can be used for supplementing water to the spent fuel pool SFP, when the residual heat of the reactor core is less than 7MW, the PCCWST does not need to be used for cooling the reactor core, and can be used for scoring 1 point when a cooling water source is provided for the spent fuel pool, otherwise, the score is not obtained.

Preferably, in the evaluation process of the reactivity control, a redundancy score of 0-1 corresponds to a high risk, a redundancy score of 2 corresponds to a medium risk, a redundancy score of 3-4 corresponds to a low risk, and a redundancy score of 5 corresponds to no risk;

in the evaluation process of the reactor core cooling, when the redundancy score is 0-1, high risk is corresponded, when the redundancy score is 2, medium risk is corresponded, when the redundancy score is 3, low risk is corresponded, and when the redundancy score is 4-5, no risk is corresponded;

in the evaluation process of the power supply availability, when the redundancy score is 0-1, high risk is corresponded, when the redundancy score is 2, medium risk is corresponded, when the redundancy score is 3, low risk is corresponded, and when the redundancy score is 4, no risk is corresponded;

in the water content evaluation process, when the redundancy score is 0-1, high risk is corresponded, when the redundancy score is 2, medium risk is corresponded, when the redundancy score is 3, low risk is corresponded, and when the redundancy score is 4, no risk is corresponded;

in the evaluation process of the containment, when the redundancy score is 0, high risk corresponds to, when the redundancy score is 1, medium risk corresponds to, when the redundancy score is 2-3, low risk corresponds to, and when the redundancy score is 4-5, no risk corresponds to;

in the evaluation process of the spent fuel pool cooling, when the redundancy score is 0-2, high risk is corresponded, when the redundancy score is 3, medium risk is corresponded, when the redundancy score is 4, low risk is corresponded, and when the redundancy score is 5, no risk is corresponded;

in the evaluation process of the water filling amount of the spent fuel pool, a high risk corresponds to a redundancy score of 0-1, a medium risk corresponds to a redundancy score of 2, a low risk corresponds to a redundancy score of 3, and no risk corresponds to a redundancy score of 4-5.

Compared with the prior art, the invention has the beneficial effects that:

the invention relates to a shutdown safety evaluation method based on risk evaluation management, which determines a system/equipment with a safety function guaranteed by theoretical analysis of various safety functions of a power station, works out an evaluation standard from the perspective of guaranteeing the redundancy degree of the safety functions, carries out risk evaluation on a overhaul plan according to the evaluation standard after the overhaul plan is determined, identifies the overhaul risk, and prepares control measures in advance according to the evaluation result. The method comprises the steps of establishing a shutdown safety risk evaluation system during the overhaul of the nuclear power station through each evaluation criterion of the safety function provided by the shutdown safety risk evaluation method, identifying and quantifying the redundancy degree and the risk level of the safety function of the nuclear power station at each stage of the overhaul, distinguishing the risk levels through colors, and analyzing the overall influence of each activity of the overhaul on the safety function, so that a clear, quantitative and visual indication is provided for each safety function overall risk condition of each working window.

The invention can carry out risk evaluation on the mutual influence among the activities of the overhaul in the overhaul preparation stage, identify the total influence of the operations of the nuclear power station on the key safety function in the overhaul period in advance and the nuclear safety risk working condition existing in the overhaul period, guide the personnel of the nuclear power station to adjust the plan in advance according to the evaluation result to avoid the high-risk working condition or make effective measures on the working condition with reduced safety margin, ensure that the overhaul activities do not cause the challenge to the reactor core safety, and ensure that the overall risk of the overhaul is controllable.

The method has the advantages of simplicity, easiness, no need of software support and capability of evaluating the overhaul plan by all power station personnel according to the determined evaluation standard. For the same pile type, after the determined evaluation standard, the pile type can be repeatedly used before and during each overhaul. The related personnel who participate in the overhaul evaluate the whole overhaul plan, so that the power station personnel can deeply know the overhaul work risk to be started and the mutual influence of various works, and the overhaul risk is controllable after the risk working condition is adjusted or a correction measure is made according to the evaluation result.

Detailed Description

In order to make the invention more comprehensible, preferred embodiments are described in detail below.

The invention relates to a nuclear power station overhaul nuclear safety risk evaluation method based on risk evaluation management.

According to the fuel cladding, the pressure boundary of a reactor coolant system, the safety function of the integrity of a containment vessel which needs to be considered during the shutdown period of the nuclear power plant and the domestic and foreign industry experience, the key safety functions during the overhaul period of the nuclear power plant are considered to comprise:

when the fuel is in the core:

reactivity control

Core cooling

Availability of power supply

Reactor coolant system water charge control

Safety shell

When the spent fuel exists in the spent pool:

SFP (spent fuel pool) cooling

SFP water content

And analyzing system equipment influencing the functions of each key safety function, and formulating each safety function risk evaluation table by considering the technical characteristics of the AP1000 power station. The risk evaluation matrix of each safety function makes an evaluation standard according to the following principle, and the risk degree is sequentially distinguished by four colors of red, orange, yellow and green from high to low according to the score of each safety function:

red: the non-redundant equipment ensures the key safety function, the red working condition is forbidden to enter, and if the red risk occurs in the shutdown safety evaluation of the planned work during the overhaul period, measures are immediately taken or the plan is adjusted to degrade the risk.

Orange color: the equipment for ensuring the key safety function has the minimum number of redundant columns available (1 column), the planned orange risk work should develop an emergency plan to make a compensation measure for losing the redundant equipment, and if the shutdown safety evaluation for the planned work during the overhaul period has an unplanned orange risk, the measure should be immediately adopted to degrade the risk to the green and yellow risk levels.

Yellow: the equipment redundancy margin drops but there is still sufficient redundancy to guarantee critical safety functions, allowing planned or unplanned entry into the yellow risk level.

Green: all systems that guarantee critical safety functions are available.

The evaluation criteria for each safety function are described below:

and (3) reactivity control:

when the material is fully discharged, the reactivity control is not applicable any more;

when the boron concentration of the RCS is more than that of the mode 6 without xenon, the score is 1, otherwise, the score is not obtained;

the number of available reactivity control (boron injection) flow channels is 1 minute per hour, and 2 minutes are obtained for two or more;

when the reactor core changes activities such as no fuel movement, hoisting of the reactor internals, release/coupling of control rods and the like, the score is 1, otherwise the score is not obtained;

at least 1 source range meter is available (at least two source range meters are available in mode 6) a score of 1 is given, and no score is given otherwise.

Cooling the reactor core: (modes 1-6)

The available SG is 1 when the number is 1 and 2 when the number is 2;

the RNS in one row can be used for deriving the residual heat of the reactor core to obtain 1 score, otherwise, the RNS does not obtain the score;

the second row of RNSs can be used for obtaining 1 point when the waste heat of the reactor core is derived, otherwise, the RNSs do not obtain the points;

the RCS liquid level is 1 point when the RCS liquid level is higher than the running liquid level for reducing the water content, otherwise, the RCS liquid level is not scored.

Power supply availability: (all modes)

the standby diesel engine A can obtain 1 point when supplying power to the ES-1 bus, otherwise, the standby diesel engine A does not obtain the point;

the standby diesel engine B can be scored 1 point when supplying power to the ES-2 bus, and otherwise, the standby diesel engine B is not scored.

Water content: (modes 1-6)

1 is scored when the mode 5 and the RCS liquid level is more than 20 percent, otherwise, no score is scored;

the RCS liquid level is 1 point when the water loading is reduced and the running liquid level is not marked otherwise;

the available water source quantity of RCS water supply is 1 time and 1 minute, and the available water source quantity is 2 time and 2 minutes when the available water source quantity is more than or equal to 2.

Containment vessel: (modes 1-6)

RCS act and at least one SG gets 1 score when available, otherwise not get score;

the VCS or PCS may be used to score 1 when the containment is cool, otherwise it does not score.

Cooling a spent fuel pool: (all modes)

The number of available rows of SFS is 1 to obtain 1 point, and the number of available rows of SFS is 2 to obtain 2 points;

when at least two power supplies supply power to the available SFS pump, the power is divided into 1 point, otherwise, the power is not divided into no points;

at least 1 row of RNSs can be used to score 1 for cooling SFP, otherwise no score;

the SWS/CCS two columns get 1 point when available, otherwise no point is given.

Water content of spent fuel pool: (all modes)

at least 1 boronized water source (CVS) can be used for SFP water replenishment to score 1, otherwise no score is obtained;

additional boronized water sources may be scored 1 for SFP refill (CWP or CLP), otherwise not;

DWS can be used for scoring 1 when SFP water replenishing, otherwise, no score is obtained;

PCCWST or PCCAWST can be used for 1 point when SFP water replenishing (the residual heat of a reactor core is less than 7MW) is carried out, otherwise, no point is obtained.

According to the design functions of each system of the nuclear power station and the principle of ensuring the redundancy degree of each safety function, the risk evaluation tables of each safety function during the overhaul period are formulated as follows:

TABLE 1

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

And grading the level of the risk degree of each key safety function according to the level of the redundancy score, manufacturing a shutdown safety function evaluation summary table taking time as an axis, and evaluating and controlling the shutdown safety risk during the overhaul period of the nuclear power station according to the change condition of each safety function taking time as an axis in the evaluation process.

The risk evaluation work takes the planned overhaul time as an axis, and each safety function needs to be evaluated in each time period from the beginning of overhaul to the end of overhaul. In any time period of the manually divided overhaul plan, for each evaluation standard of any safety function, when the evaluation table requirements are met, scoring is carried out, when the evaluation table requirements are not met, scoring is not carried out, and after the total score in each time period is calculated, the risk grade is determined by referring to the last two columns of the evaluation table.

After the risk evaluation of the overhaul plan is completed, the overhaul plan is adjusted according to the evaluation result, the red risk working condition which is evaluated is adjusted to be a lower risk working condition, the orange risk working condition which is evaluated is adjusted to be the lower risk working condition or an emergency plan is developed to make a compensation measure for losing redundant equipment, and the risk controllability in the overhaul process is ensured.

The summary table of the shutdown safety function evaluation in this embodiment is as follows, wherein the letters G/Y/O/R represent the risk levels green, yellow, orange, and red, respectively.

Table 8.

Claims

1. A shutdown safety risk evaluation method during the overhaul period of a nuclear power station is characterized by comprising the following steps:

2. The method for evaluating the shutdown safety risk during the overhaul of the nuclear power plant as claimed in claim 1, wherein the evaluation criteria in the step 3 comprise: