阅读说明：本技术 一种核电厂氢气***性气体环境分区方法 (Method for partitioning hydrogen explosive gas environment of nuclear power plant ) 是由 陈琳 刘文华 王乐 高鸽 彭洁 张璐 刘政 谢维 于 2019-09-23 设计创作，主要内容包括：本发明涉及一种核电厂氢气爆炸性气体环境分区方法,包括：(1)分析核电厂核岛厂房的含氢系统,按房间范围确定氢气爆炸性气体环境危险区域；(2)确定所述危险区域内氢气的释放源和释放等级；(3)进行氢气爆炸性气体环境危险区域的预划分；(4)进行通风条件分析,在所述预划分的基础上调整氢气爆炸性气体环境危险区域的划分结果；(5)根据爆炸性气体环境的持续时间,对氢气爆炸性气体环境危险区域的分区进行修正。本发明综合考虑了氢气释放源的释放速率、通风条件和持续时间等条件对氢气爆炸性气体环境分区的影响情况,简单科学,可操作性强。(The invention relates to a method for partitioning an explosive gas environment of hydrogen in a nuclear power plant, which comprises the following steps: (1) analyzing a hydrogen-containing system of a nuclear island plant of a nuclear power plant, and determining a dangerous area of the hydrogen explosive gas environment according to the room range; (2) determining a release source and a release level of hydrogen in the hazardous area; (3) pre-dividing dangerous areas of the hydrogen explosive gas environment; (4) analyzing ventilation conditions, and adjusting the partitioning result of the hydrogen explosive gas environment dangerous area on the basis of the pre-partitioning; (5) and modifying the subarea of the dangerous area of the explosive gas environment of the hydrogen according to the duration time of the explosive gas environment. The method comprehensively considers the influence of the conditions of the release rate, the ventilation condition, the duration and the like of the hydrogen release source on the hydrogen explosive gas environment partition, and is simple, scientific and strong in operability.)

1. A method for partitioning an explosive gas environment of hydrogen in a nuclear power plant comprises the following steps:

(1) analyzing a hydrogen-containing system of a nuclear island plant of a nuclear power plant, and determining a dangerous area of the hydrogen explosive gas environment according to the room range;

(2) determining a release source and a release grade of the hydrogen in the hydrogen explosive gas environment dangerous area;

(3) pre-dividing dangerous areas of the hydrogen explosive gas environment;

(4) analyzing the ventilation condition, and adjusting the partitioning result of the dangerous area of the hydrogen explosive gas environment on the basis of the pre-partitioning according to the analysis result;

(5) and modifying the subarea of the dangerous area of the explosive gas environment of the hydrogen according to the duration time of the explosive gas environment.

2. The nuclear power plant hydrogen explosive gas environment zoning method according to claim 1, characterized in that: in the step (1), the dangerous area of the hydrogen explosive gas environment is determined by combing the purpose and the drainage path of the hydrogen in the nuclear island plant.

3. The nuclear power plant hydrogen explosive gas environment zoning method according to claim 1, characterized in that: the release source in the step (2) refers to a position or a place where substances capable of forming explosive mixtures can be released, and the release source of hydrogen in the nuclear power plant comprises hydrogen-containing equipment, a flange, a valve and a joint; the release sources are divided into a continuous release source, a primary release source and a secondary release source according to the release frequency and the release duration of the combustible substances, wherein,

the continuous-stage release source is a release source which can continuously release or expect long-term release;

the primary release source is a release source that is expected to be released periodically or occasionally during normal operation;

secondary sources of release are sources of release that are not expected to release during normal operation, and only occasional and short-term releases when they occur.

4. The nuclear power plant hydrogen explosive gas environment zoning method according to claim 3, characterized in that: the pre-division in the step (3) is to pre-divide the area with the continuous-level release source into 0 areas, the area with the first-level release source into 1 areas and the area with the second-level release source into 2 areas according to the grade of the hydrogen release source.

5. The nuclear power plant hydrogen explosive gas environment zoning method according to claim 1, characterized in that: the analysis of the ventilation conditions in step (4) takes into account both the assessment of the ventilation rating and the division of the effectiveness of the ventilation, the assessment criteria of the ventilation rating being as follows:

when assuming the volume V_ZLess than 0.1m³Or less than the actual volume V₀1% of the total volume of the hazardous area is considered to be equal to V for high-level ventilation_Z；

If the volume V is assumed_ZGreater than the actual volume V₀Low-level ventilation;

assumed volume V_ZThe middle-level ventilation is positioned between the two air inlets;

the hypothetical volume V_ZThe calculation formula of (a) is as follows:

in the formula:

c- -number of fresh air replacements per unit time;

dV₀dt — total flow rate of fresh air through the volume under consideration;

f- -ventilation quality coefficient;

V₀-considering the total volume provided by the actual ventilation in the vicinity of the release;

(dV/dt)_min-minimum volumetric flow rate of fresh air;

(dG/dt)_max-the maximum release rate of the release source;

LEL_m-lower explosion limit;

k- -safety factor applicable to lower explosion limit;

t- -ambient temperature.

6. The nuclear power plant hydrogen explosive gas environment zoning method according to claim 5, characterized in that: the effectiveness of ventilation is divided into the following three levels:

good: ventilation is continuously present;

in general: during normal operation, the presence of ventilation is expected, allowing short, infrequent discontinuous ventilation to occur;

difference: ventilation that does not meet "good" or "general" standards is not possible, but long periods of discontinuous ventilation are not expected.

7. The nuclear power plant hydrogen explosive gas environment zoning method according to claim 1, characterized in that: in the step (5), after the release source stops releasing, the average concentration is required to be from the initial value X₀Down to k times LEL_mThe duration t of (a) is calculated as follows:

in the formula:

c- -number of fresh air replacements per unit time;

f- -ventilation quality coefficient;

LEL_m-lower explosion limit;

k- -safety factor applicable to lower explosion limit;

X₀-initial concentration of combustible substance;

for the situation that the duration time t of the explosive gas environment existing in the room obtained by the calculation is several hours, the situation cannot be degraded into a non-explosive gas dangerous environment, and the original regional division is maintained; for rooms with a duration t of no more than 1 hour, a non-explosive gas environment can be degraded.

Technical Field

The invention belongs to an explosive gas atmosphere analysis technology, and particularly relates to a method for partitioning an explosive gas atmosphere of hydrogen in a nuclear power plant.

Background

The safety is a life line for guaranteeing the development of nuclear power, the development of the nuclear power must be established on the basis of safety, and the operation experience of the nuclear power station at home and abroad for decades shows that: an explosion inside a nuclear power plant poses a significant potential threat to nuclear power plant safety, and the possibility of an explosion occurring extends throughout the life cycle of the nuclear power plant. According to the statistics of the Electric power research Institute (Electric power research Institute), the frequency of fire and explosion in the nuclear power plant is 0.14 times/(heap year) from 1991 to 2008, and the relatively high frequency is not negligible. Also, serious internal explosive events can cause nuclear accidents, and many significant nuclear accidents that have historically been associated with internal combustible explosions. Therefore, internal explosions have become one of the most immediate threats to nuclear power plant safety. In this context, several advanced nuclear power countries have been developing studies on explosions caused by combustible leakage inside nuclear power plants and their complex causes, possibly with serious consequences.

The hydrogen system is used as an important component of a gas system of a nuclear power plant and plays an important role in safe and stable operation of the nuclear power plant. Meanwhile, hydrogen dissipated by a hydrogen system of the nuclear power plant during normal operation is one of main reasons for causing fire and explosion inside the nuclear power plant, and explosion of the hydrogen can seriously threaten the nuclear safety. In 2011, the fukushima nuclear power station in 3 months and days has serious consequences because of nuclear leakage caused by hydrogen explosion caused by earthquake and tsunami. This fact has strengthened the understanding of the importance of the nuclear industry to the safety and control of hydrogen in nuclear power plants. The 2012 national energy agency starts research and development projects on handling over-design basis accident safety technologies of nuclear power plants under construction comprehensively, and researches on aspects including distribution and control of hydrogen of the nuclear power plants are carried out so as to promote improvement of nuclear power safety.

However, the research on hydrogen fire and explosion of nuclear power plants in China starts late, relatively complete analysis principles and methods are formed only by analyzing and evaluating a containment hydrogen concentration control system under serious accidents at the present stage, and systematic research on the aspects of explosive gas environment zoning of hydrogen and explosion prevention of related equipment is not developed for domestic nuclear power plants. Other industrial fields (such as petroleum, chemical industry, thermal power and the like) have corresponding explosive gas environment analysis methods, and the national standard explosive environment part 14: the site-classified explosive gas atmosphere (GB 3836.14-2014) also relates to concepts related to partitioning of an explosive gas atmosphere, but due to the special environment of a nuclear power plant, the site conditions to be considered are more complicated, and the national standard GB3836.14-2014 does not provide method steps that can be directly partitioned according to the executed hydrogen explosive gas atmosphere, so that the method cannot be directly applied to the field of nuclear power hydrogen explosion protection, and researchers are required to further perfect the relevant method for partitioning of the hydrogen explosive gas atmosphere and optimize and improve the method according to the actual nuclear power plant.

Disclosure of Invention

The invention aims to provide a method for analyzing the hydrogen explosive gas environment of a nuclear power plant in a partitioned manner, which comprehensively considers the influence of the conditions such as the release rate, the ventilation condition, the duration and the like of a hydrogen release source on the hydrogen explosive gas environment partition, is simple and scientific and has strong operability.

The technical scheme of the invention is as follows: a method for partitioning an explosive gas environment of hydrogen in a nuclear power plant comprises the following steps:

(1) analyzing a hydrogen-containing system of a nuclear island plant of a nuclear power plant, and determining a dangerous area of the hydrogen explosive gas environment according to the room range;

(2) determining a release source and a release grade of the hydrogen in the hydrogen explosive gas environment dangerous area;

(3) pre-dividing dangerous areas of the hydrogen explosive gas environment;

(4) analyzing the ventilation condition, and adjusting the partitioning result of the dangerous area of the hydrogen explosive gas environment on the basis of the pre-partitioning according to the analysis result;

(5) and modifying the subarea of the dangerous area of the explosive gas environment of the hydrogen according to the duration time of the explosive gas environment.

Further, according to the method for partitioning the hydrogen explosive gas environment of the nuclear power plant, in the step (1), the dangerous area of the hydrogen explosive gas environment is determined by combing the use and the drainage path of the hydrogen in the nuclear island plant.

Further, in the method for partitioning the explosive gas environment of hydrogen from a nuclear power plant as described above, the release source in step (2) refers to a location or a place where a substance capable of forming an explosive mixture can be released, and the release source of hydrogen from a nuclear power plant includes a hydrogen-containing device, a flange, a valve, and a joint; the release sources are divided into a continuous release source, a primary release source and a secondary release source according to the release frequency and the release duration of the combustible substances, wherein,

the continuous-stage release source is a release source which can continuously release or expect long-term release;

the primary release source is a release source that is expected to be released periodically or occasionally during normal operation;

secondary sources of release are sources of release that are not expected to release during normal operation, and only occasional and short-term releases when they occur.

Further, in the method for partitioning the hydrogen explosive gas environment of the nuclear power plant as described above, the pre-division in the step (3) is to pre-divide the region where the continuous-stage release source exists into 0 region, the region where the first-stage release source exists into 1 region, and the region where the second-stage release source exists into 2 regions according to the grade of the hydrogen release source.

Further, in the method for partitioning the hydrogen explosive gas environment of the nuclear power plant as described above, the analysis of the ventilation conditions in the step (4) is considered from the evaluation of the ventilation grade and the effectiveness division of the ventilation, and the evaluation criteria of the ventilation grade are as follows:

when assuming the volume V_ZLess than 0.1m³Or less than the actual volume V₀1% of the total volume of the hazardous area is considered to be equal to V for high-level ventilation_Z；

If the volume V is assumed_ZGreater than the actual volume V₀Low-level ventilation;

assumed volume V_ZThe middle-level ventilation is positioned between the two air inlets;

the hypothetical volume V_ZThe calculation formula of (a) is as follows:

in the formula:

c- -number of times(s) fresh air is displaced (charged) per unit time^-1)；

dV₀Dt — total flow rate of fresh air through the volume under consideration;

f-ventilation quality coefficient, the value range is from f 1 (ideal state) to 5 (air flow is blocked);

V₀-considering the total volume (controlled by the factory) provided by the actual ventilation in the vicinity of the release, the invention is considered according to the engineering practice as the volume of the room in which the source of the release is located;

(dV/dt)_minminimum volumetric flow rate of fresh air (volume per unit time, m)³/s)；

(dG/dt)_maxMaximum release rate of the source of release (mass per unit time, kg/s), maximum release rate of hydrogen (dG/dt)_maxCalculated as three times the hydrogen release rate dG/dt during normal operation, excluding the amount released upon rupture due to a catastrophic event;

LEL_mlower explosion limit (mass per unit volume, kg/m)³) The lower explosion limit of hydrogen was 4% by volume fraction, that is, 0.0034kg/m³；

k- -safety factor applicable to lower explosive limits, with typical values:

k is 0.25 (continuous stage and stage 1 release);

k is 0.5 (2-level release);

t- -ambient temperature (K).

Further, the effectiveness of ventilation is divided into the following three levels:

good: ventilation is continuously present;

in general: during normal operation, the presence of ventilation is expected, allowing short, infrequent discontinuous ventilation to occur;

difference: ventilation that does not meet "good" or "general" standards is not possible, but long periods of discontinuous ventilation are not expected.

Further, in the method for partitioning the explosive gas environment of hydrogen in a nuclear power plant as described above, in the step (5), the average concentration is required to be from the initial value X after the release of the release source is stopped₀Down to k times LEL_mThe duration t of (a) is calculated as follows:

in the formula:

c- -number of times(s) fresh air is displaced (charged) per unit time^-1)；

f-ventilation quality coefficient, the value range is from f 1 (ideal state) to 5 (air flow is blocked);

LEL_mlower explosion limit (mass per unit volume, kg/m)³) The lower explosion limit of hydrogen was 4% by volume fraction, that is, 0.0034kg/m³；

k- -safety factor applicable to lower explosive limits, with typical values:

k is 0.25 (continuous stage and stage 1 release);

k is 0.5 (2-level release);

X₀initial concentration of combustible substance, in the present invention, the leaked gas is considered to be pure hydrogen, X₀Taking 100 percent;

for the situation that the duration time t of the explosive gas environment existing in the room obtained by the calculation is several hours, the situation cannot be degraded into a non-explosive gas dangerous environment, and the original regional division is maintained; for rooms with a short duration t (typically no more than 1 hour), a non-explosive gaseous environment may be degraded.

The invention has the following beneficial effects: the method for partitioning the hydrogen explosive gas environment of the nuclear power plant can be used for evaluating the type of the hydrogen explosive gas environment dangerous area of the nuclear island factory building by combining the actual situation of the nuclear power plant and comprehensively considering the aspects of analysis of a hydrogen release source, influence of ventilation conditions, duration calculation and the like. The method lays a foundation for the assessment and control of the hydrogen explosion risk of the nuclear power plant, and also provides an important reference for the improvement of the fireproof and explosion-proof design of the nuclear power plant. Based on the research of the hydrogen explosive gas environment partition of the nuclear power plant, the research work of explosive gas environment partition and explosion-proof design of other hazardous gases can be further developed, the design level of internal explosion protection of the nuclear power plant is improved, and the safety of the nuclear power plant is improved. Meanwhile, the explosive gas environment partition can effectively distinguish the areas where the explosion-proof electrical equipment and the non-electrical equipment need to be arranged, so that the equipment cost is reduced on the whole, the economy is improved, the explosion-proof types of the electrical equipment and the non-electrical equipment are determined, and the method has practical operation significance for equipment purchase. The method is simple to operate, and an analysis conclusion can be quickly obtained without complex modeling.

Drawings

FIG. 1 is a flow chart of a method for partitioning an explosive gas environment of hydrogen in a nuclear power plant according to the present invention.

Detailed Description

The invention is described in detail below with reference to the figures and examples.

The invention provides a method for partitioning an explosive gas environment of hydrogen in a nuclear power plant, which comprises the following steps of:

(1) determining an analysis Range

The analysis range of the dangerous area of the hydrogen explosive gas environment is comprehensively determined by comparing the technology and the economy according to the grade and the position of a release source, the property of combustible substances, ventilation conditions, obstacles, production conditions and operation experience. According to the actual condition of the nuclear power station, only a hydrogen-containing system of a nuclear island plant of the nuclear power station needs to be analyzed, and the division of the explosive gas environment danger area related to hydrogen according to the room range is considered.

Hydrogen leakage is likely to occur at hydrogen-containing positions such as hydrogen-containing equipment, flanges, valves, joints and the like arranged in the nuclear island plant of the nuclear power plant and the hydrogen is gathered to form an explosive gas environment, so that a dangerous area of the hydrogen explosive gas environment can be determined by combing the purpose and the drainage path of the hydrogen in the nuclear island plant.

(2) Hydrogen leak release source grading

The basic work for determining the type of hydrogen explosion hazard zone is to identify the source of release of hydrogen and to determine the level of release. The release source refers to a position or a place where substances capable of forming explosive mixtures can be released, and the release source of hydrogen in the nuclear power plant mainly comprises hydrogen-containing equipment, flanges, valves, connectors and the like. Hydrogen-containing welded pipes and the like are not considered as a release source because they do not release to the atmosphere.

The release source can be divided into a continuous release source, a primary release source and a secondary release source according to the release frequency and duration of the combustible substance. The release source rating should comply with the following regulations:

a) the continuous-stage release source should be a continuous release or a release source that is expected to release over a long period of time. The following can be classified as a sequential stage release source:

-the surface of the combustible liquid in the fixed-roof tank not covered with inert gas;

the surface of combustible liquids in direct contact with air, oil, water separators, etc.;

vapour vents and other orifices that release combustible gases or combustible liquids into the space, often or for long periods of time.

b) The primary release source should be one that is expected to release periodically or occasionally during normal operation.

The following may be classified as a primary release source:

seals for compressors and valves, etc. that release combustible materials during normal operation;

-a drain on the container containing the combustible liquid, where, in normal operation, when the water is drained, it is possible to release combustible material into the space;

-a sampling point which, in normal operation, will release combustible material into the space;

pressure relief valves, vents and other orifices that release combustible material into the space during normal operation.

c) Secondary sources of release should be sources of release that are not expected to release during normal operation, and only occasional and short-term releases when they occur. The following can be classified as a secondary release source:

during normal operation, no seals of the pump, compressor and valves releasing the combustible substance can appear;

flanges, connections and pipe joints which, in normal operation, cannot release combustible substances;

safety valves, vents and other orifices which, in normal operation, cannot release combustible substances into the space;

a sampling point which, in normal operation, cannot release combustible substances into the space.

In the above definitions of the primary release source and the secondary release source, both release scenarios are specified during normal operation.

According to the technological characteristics of a drought system of a nuclear island plant of a nuclear power plant and the leakage rate of related equipment, hydrogen-containing equipment, flanges, valves and the like can be generally divided into two-stage release sources. In the analysis process, the method provided by the invention assumes that the leaked gas is only hydrogen, does not consider inert gases such as nitrogen and the like, and is more conservative than the actual situation.

(3) Pre-partitioning of hazardous areas of hydrogen explosive gas environments

The division of the explosion hazard zone should be determined according to the level of the release source and the ventilation condition. The area with continuous level release source can be divided into 0 area, the area with first level release source can be divided into 1 area, the area with second level release source can be divided into 2 areas, on the basis, the division result of the relative explosion danger area can be adjusted according to the analysis of the ventilation condition.

(4) Analysis of aeration conditions

Flammable gases or vapors released into the atmosphere can be diluted in air by means of escape or diffusion until their concentration is below the lower explosive limit, without exception to hydrogen. Ventilation, i.e., air flow, enables fresh air to displace the atmosphere surrounding the release source to facilitate the escape of flammable gases. The ventilation rate is proper, and the persistence of the explosive gas environment can be avoided, so that the division of the explosion danger area is influenced.

The effectiveness of the ventilation to control the diffusion and duration of the explosive gas environment of hydrogen depends on the level of ventilation, the effectiveness of the ventilation, and the design of the ventilation system. Venting, while not effective in preventing the formation of an explosive environment, can avoid an explosive environment for extended periods of time.

The analysis of the ventilation conditions should take into account both the assessment of the ventilation rating and the division of the effectiveness of the ventilation.

The ventilation grade is divided into three types of high-grade ventilation, medium-grade ventilation and low-grade ventilation. Determining the ventilation level requires calculating the assumed volume V at each source of release_ZAccording to V_ZWith the actual volume V₀The ventilation grade can be evaluated according to the relation. The specific evaluation criteria are as follows:

a) when V is_ZLess than 0.1m³Or less than V₀1% of (a), high Ventilation (VH), the volume of the hazard zone is considered to be equal to V_Z；

b) If V_ZGreater than V₀Low grade Ventilation (VL);

c)V_Zlocated between the two, is the medium Ventilation (VM).

Assumed volume V_ZHas a crucial role in the assessment of the ventilation rating, V, depending on the value of the safety factor k_ZRepresents exceeding the Lower Explosive Limit (LEL)_m) 0.25 times or 0.5 times the volume of the average concentration of the combustible gas or vapor. To determine the hypothesisVolume V_ZIt is necessary to determine first the minimum volumetric flow rate (dV/dt) of fresh air that dilutes the release of a given combustible substance to a prescribed concentration below the lower explosive limit_minThis parameter can be calculated by:

in the formula:

(dV/dt)_minminimum volumetric flow rate of fresh air (volume per unit time, m)³/s)；

(dG/dt)_maxMaximum release rate of the source of release (mass per unit time, kg/s), maximum release rate of hydrogen (dG/dt)_maxCalculated as three times the hydrogen release rate dG/dt during normal operation, excluding the amount released upon rupture due to a catastrophic event;

LEL_mlower explosion limit (mass per unit volume, kg/m)³) The lower explosion limit of hydrogen was 4% by volume fraction, that is, 0.0034kg/m³；

k- -safety factor applicable to lower explosive limits, with typical values:

k is 0.25 (continuous stage and stage 1 release);

k is 0.5 (2-level release);

t- -ambient temperature (K).

Assumed volume V_ZIs inversely proportional to the ventilation frequency C of the room where the releasing source is located, and the resistance generated during the air flow may cause poor ventilation in partial area of the place, resulting in V_ZIncrease so that V is calculated_ZAnd a ventilation quality coefficient f is required to be introduced for correction, and a specific calculation formula is as follows:

in the formula:

c- -number of times(s) fresh air is displaced (charged) per unit time^-1)；

dV₀Dt — total flow rate of fresh air through the volume under consideration;

f-ventilation mass coefficient, ranging from f-1 (ideal state) to 5 (air flow is obstructed).

V₀The invention takes into account the volume of the room in which the source of the release is located, according to the actual engineering considerations, taking into account the total volume (controlled by the factory) provided by the actual ventilation in the vicinity of the release.

The effectiveness of ventilation, which may reduce the level of explosion hazard in indoor locations, also affects the existence or formation of explosive gaseous environments. Therefore, when determining the zone type, the effectiveness of ventilation also needs to be considered.

The ventilation effect is divided into the following three levels:

-good: ventilation is continuously present;

- -in general: in normal operation, ventilation is expected to exist. Allowing short, infrequent discontinuous ventilation to occur;

-difference: ventilation that does not meet "good" or "general" standards is not possible, but long periods of discontinuous ventilation are not expected.

In the rooms with independent ventilation systems of the nuclear power plant, the ventilation conditions are considered to be good according to the definition.

(5) Adjusting partitioning of hazardous areas of hydrogen explosive gas environment

Because the explosion danger level of indoor place can be reduced to effectual ventilation, on the basis of the presorting of hydrogen explosive gas atmosphere danger area, through the analysis of ventilation condition, can adjust regional division, carry out the division of the explosive gas atmosphere danger area in the room of release source place according to table 1 in this embodiment.

Table 1: influence of independent ventilation on zone type

(6) Modification of hydrogen explosive gas environment zoning

The duration of the explosive gas environment has a significant impact on the classification of the hazardous area. For the explosive gas environment, the environment is only a place with short existence time and can be degraded into a non-explosive gas dangerous environment, and the area with longer duration can not be degraded. Therefore, under the condition that the duration time of the explosive gas environment existing in the room is calculated to be several hours, the explosive gas environment cannot be degraded into a non-explosive gas dangerous environment, and the original regional division is maintained; for rooms of shorter duration (typically no more than 1 hour), a non-explosive gaseous environment may be degraded.

After the releasing source stops releasing, the average concentration is required to be from the initial value X₀Down to k times LEL_mThe duration t of (a) is calculated as follows:

in the formula:

X₀initial concentration of combustible substance, in the present invention, the leaked gas is considered to be pure hydrogen, X₀Taking 100 percent.

The method for partitioning the hydrogen explosive gas environment of a nuclear power plant according to the invention is described below by means of a specific example.

(1) Determining an analysis Range

In certain nuclear power engineering, hydrogen provided by a hydrogen station arranged outside a nuclear island plant is injected into a volume control box of a chemical and volume control system (RCV) to perform a chemical control function, then is processed by a nuclear island drainage exhaust system (RVD), a boron recovery system (ZBR), a waste gas treatment system (ZGT) and other process systems, and is discharged into a nuclear auxiliary plant ventilation system (VNA) at a safe concentration far lower than the lower explosion limit after being monitored and detected by a nuclear sampling system (RNS). According to the hydrogen application and the evacuation path, under the normal operation condition, the engineering nuclear island plant has hydrogen leakage and explosion risks, and rooms needing further explosive gas environment analysis are mainly part of rooms located in a nuclear auxiliary plant (NX), a nuclear fuel plant (KX) and a reactor plant (RX).

(2) Hydrogen leak release source grading

The hydrogen-containing equipment, flanges and valves contained in these rooms are divided into secondary release sources according to the process characteristics of the engineering chemical and volume control system (RCV), the nuclear island hydrophobic exhaust system (RVD), the boron recovery system (ZBR) and the waste gas treatment system (ZGT) and the leakage rates of the associated equipment.

(3) Pre-partitioning of hazardous areas of hydrogen explosive gas environments

The room in which the secondary release source is present is pre-divided into the hydrogen explosive gas atmosphere 2 zone.

(4) Analysis of aeration conditions

Taking the N212 room of the NX factory building as an example, the room is a pipe gallery and is provided with a plurality of pipelines, valves and sampling ports of an RCV system, the release rate and the grading of the release source of the hydrogen in the room are shown in the table 2, and the maximum release rate (dG/dt) of the hydrogen when the room normally operates can be calculated by the table_maxIs 4.97E-10 kg/s.

TABLE 2 Hydrogen release source, level of release source and release rate for normal operation of N212 room of certain nuclear power plant

By consulting the ventilating system manual of the NX factory building, the number of times of ventilation and air exchange of the room is 15.4 times/h, the ventilation quality coefficient is 1, the ambient temperature is 298.15K, and the minimum volume flow rate (dV/dt) of the fresh air in the room can be calculated according to the formula (1)_minIs 3.01E-07m³And s. On the basis of the above, the assumed volume V of hydrogen gas release can be calculated according to the formula (2)_ZIs 6.98E-05m³Much less than 0.1m³And the room volume V₀And 1% of the total ventilation level, the ventilation grade of the room is high-grade ventilation according to the judgment criterion, and the ventilation effectiveness is good.

(5) Partitioning of hydrogen explosive gas environment

According to the analysis method in table 1, the room is classified into the explosive gas atmosphere 2 zone, the level of the release source is 2, the ventilation level is high, and the ventilation effectiveness is good.

(6) Modification of hydrogen explosive gas environment zoning

According to the duration calculation formula (4), the duration t of hydrogen diffusion in the room can be calculated to be 0.25 h. Since the duration is less than 1h, the room should be modified to a non-explosive gas environment according to the analysis method of "modification of the partition of the hydrogen explosive gas environment".

According to the analysis method, the rooms in which hydrogen-containing equipment, valves, flanges and the like are located in the nuclear island plant of the target nuclear power plant are analyzed according to the grade of the release source and the ventilation condition, and the total number of the rooms divided into 2 areas of the explosive gas environment is 24 after the calculation result of the duration is corrected.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.