Multi-jacket liquid nitrogen ice plug freezing method for nuclear power plant pipeline maintenance

Abstract

The invention belongs to the technical field of nuclear power plant pipeline freezing, and discloses a multi-jacket liquid nitrogen ice plug freezing method for nuclear power plant pipeline maintenance, the configuration parameters of ice plug jackets are determined according to pipeline parameters, and the jackets are arranged in a series connection or parallel connection mode to realize freezing; the total length recommendation value of the jackets is obtained according to the pipe diameter checking standard, after the total length is determined, the number of the jackets and the length of gaps are calculated, the gaps are distributed, and when the parallel ice plug jacket mode is adopted, the length of the jackets of all branches is determined according to the branch pipe diameter checking standard by adding the branches, and the number and the pipe diameter of the branches are configured. The freezing time of the ice plug is shortened, meanwhile, the size of the closed ice plug is increased, the freezing efficiency is improved, and energy conservation and efficiency improvement are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear power plant pipe freezing, and particularly relates to a multi-jacket liquid nitrogen ice plug freezing method for nuclear power plant pipe maintenance. BACKGROUND

[0002] The stability of a nuclear power plant unit during operation is crucial for the nuclear power plant, but certain equipment problems may still occur during operation. In order to reduce unnecessary cost increase caused by unit shutdown maintenance, an ice plug freezing isolation technology is used to isolate the maintenance section. The principle is to use the low temperature of liquid nitrogen to freeze the pipe of the freezing section, so as to form an ice plug in the pipes before and after the isolation section, thereby isolating the pipes.

[0003] At present, the main freezing method used by the nuclear power plant is single-jacket ice plug freezing, that is, two jackets are used before and after the isolation section to achieve isolation. Although this method is simple, it has the following disadvantages:

[0004] Firstly, when the required freezing section length is long, the freezing time caused by the single jacket is long, and the ice plug cannot be quickly frozen to have a certain bearing capacity.

[0005] Secondly, due to the long length of the single jacket, the liquid nitrogen needs to be diffused inside the single jacket, and the cooling effect on the pipe wall cannot be quickly achieved, resulting in a large consumption of liquid nitrogen.

[0006] Thirdly, in order to ensure that the ice plug can bear a certain water impact, more liquid nitrogen needs to be introduced or the freezing length needs to be increased to increase the ice plug adhesion capacity, thereby causing a large consumption of liquid nitrogen. SUMMARY

[0007] The purpose of the present application is to provide a multi-jacket liquid nitrogen ice plug freezing method for nuclear power plant pipe maintenance, which solves the problem of limited use range of single jacket. By studying the freezing performance of multi-jacket under different pipe diameters, different flow rates and different heat loads, the advantages of multi-jacket compared with single jacket in freezing speed, freezing depth and temperature field distribution are determined, thereby expanding the applicability of ice plug technology under a larger range of engineering conditions.

[0008] In order to achieve the above purpose, the present application provides the following technical solution:

[0009] A multi-jacket liquid nitrogen ice plug freezing method for nuclear power plant pipe maintenance, the configuration parameters of the ice plug jacket are determined according to the pipe parameters, and the jacket arrangement is implemented in series or parallel mode to realize freezing;

[0010] When the ice plug jacket is used in series, the total length recommended value of the jacket is obtained according to the pipe diameter D, the total length LN is determined, the number of jackets N and the gap length L are calculated, and the gap is distributed.

[0011] When the ice plug jacket is in parallel, by adding a branch, according to the branch pipe diameter dn, the length Ln of each branch jacket is determined according to the standard, and the number n and the pipe diameter of the branch are configured.

[0012] As an implementable way, the ice plug jacket in series includes:

[0013] S11: According to the pipe diameter D of the factory maintenance pipeline, the recommended range and recommended value of the total length of the jacket are obtained;

[0014] S12: The total length of the jacket is selected as LN according to the recommended value of the total length of the jacket obtained;

[0015] S13: The number of jackets N and the length of a single gap L are preliminarily determined according to the pipe diameter D of the factory maintenance pipeline;

[0016] S14: According to the total length LN, the number of jackets N and the distribution of the length of a single gap L.

[0017] As an implementable way, in S13, the number of jackets is N, and the selected range is:

[0018] When D≤300mm, N=1~2;

[0019] When 300<D≤600mm, N=2~4;

[0020] When 600<D≤800mm, N=3~6.

[0021] As an implementable way, in S13, the gap length L is selected in the range of:

[0022] When LN≤600mm, N≤2, 10mm≤L≤60mm;

[0023] When 600mm<LN≤1200mm, N≤4, 10mm≤L≤50mm;

[0024] When 1200mm<LN≤1600mm, N≤6, 10mm≤L≤40mm.

[0025] As an implementable way, a pipeline with a nominal diameter of 300mm is selected, the total length of the jacket is in the range of 485.85~809.75mm, the recommended length is 600mm, LN=600mm is selected, the number of jackets is selected as N=1~2, and the gap length is selected in the range of 10mm≤l≤60mm.

[0026] As an implementable way, a pipe with a nominal diameter of 500 mm is selected, the total length of the jacket is in the range of 762-1270 mm, the recommended length is 1000 mm, LN is selected as 1000 mm, the number of jackets is selected as N=2-, and the gap length is selected in the range of 10 mm≤l≤50 mm.

[0027] As an implementable way, the parallel ice plug jacket mode includes:

[0028] S21: adding a branch to the pipe;

[0029] S22: selecting the number n of branches according to the pipe diameter D of the pipe in the factory;

[0030] S23: determining the pipe diameter dn of each branch according to the number of branches;

[0031] S24: obtaining the recommended range and recommended value of the total length of the jacket on each branch according to the pipe diameter dn of the branch;

[0032] S25: selecting the total length of the jacket as Ln according to the recommended value of the total length of the jacket.

[0033] As an implementable way, in S21, the branch is added to the pipe by welding or grafting.

[0034] As an implementable way, in S22, the number n of branches is selected in the range of D / 200 mm≤n≤D / 100 mm.

[0035] As an implementable way, in S23, dn is a standard pipe diameter≤D / n.

[0036] Compared with the prior art, the multi-jacket liquid nitrogen ice plug freezing method for pipe maintenance of a nuclear power plant has the following beneficial effects:

[0037] The application not only shortens the freezing time of the ice plug, but also increases the volume of the closed ice plug to improve the freezing efficiency and achieve energy saving and efficiency increase.

[0038] The application can select an ice plug application method according to actual needs.

[0039] The application can adjust the number and form of jackets according to the actual pipe diameter requirements, so as to realize the regulation and control of freezing time, pressure-bearing capacity, etc., and thus achieve the effect of energy saving and efficiency increase.

[0040] The application can adjust the number of branches according to the actual pipe diameter requirements, so as to realize the effect of N times flow reduction, thereby realizing fast ice formation, and thus achieving the effect of energy saving and efficiency increase. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the technical description.

[0042] Figure 1 The flowchart of the ice plug jacket application mode in series provided by the present application;

[0043] Figure 2 The ice plug jacket in series provided by the present application;

[0044] Figure 3 The flowchart of the ice plug jacket application mode in parallel provided by the present application;

[0045] Figure 4 The ice plug jacket in parallel provided by the present application. DETAILED DESCRIPTION

[0046] The following will be further described in detail through specific embodiments.

[0047] As shown in Figures 1 to 4 , the present application provides a multi-jacket liquid nitrogen ice plug freezing method for nuclear power plant pipeline repair, the configuration parameters (such as total length, number or branch planning) of the ice plug jacket are determined according to the pipeline parameters (such as pipe diameter D), and the jacket arrangement is implemented in series or parallel to achieve efficient freezing. When the ice plug jacket in series is used, first, the recommended value of the total length of the jacket is obtained by searching the standard according to the pipe diameter D, after the total length LN is determined, the number of jackets N and the gap length L are calculated, and the gaps are distributed. When the ice plug jacket in parallel is used, by adding branches, the jacket length Ln of each branch is determined by searching the standard according to the branch pipe diameter dn, and the number of branches n and the pipe diameter are configured. Both of the two ways realize the temporary plugging of the pipeline by forming ice plug through the heat absorption of liquid nitrogen vaporization in the jacket.

[0048] As shown in Figure 1 and Figure 2 , the ice plug jacket application steps in series include:

[0049] S11: According to the pipe diameter D of the plant repair pipeline, the recommended range and value of the total length of the jacket are obtained by searching the table or searching the industry standard NB / T 20551-2019;

[0050] S12: The total length of the jacket is selected as LN according to the recommended value of the total length of the jacket searched out;

[0051] S13: The number of jackets N and the single gap length L are preliminarily determined according to the pipe diameter D of the plant repair pipeline;

[0052] S14: According to the total length LN, the number of jackets N and the single gap length L, the length of each gap is distributed.

[0053] In S13, the number of jackets is N, and the selected range is:

[0054] When D≤300mm, N=1~2;

[0055] When 300<D≤600mm, N=2~4;

[0056] When 600<D≤800mm, N=3~6.

[0057] In S13, the gap length L is selected in the range of:

[0058] When LN≤600mm, N≤2, 10mm≤L≤60mm;

[0059] When 600mm<LN≤1200mm, N≤4, 10mm≤L≤50mm;

[0060] When 1200mm<LN≤1600mm, N≤6, 10mm≤L≤40mm.

[0061] Alternatively, a pipe with a nominal diameter of 350mm is selected. According to industry standards, the total length of the jacket is in the range of 533.4~889mm, and the recommended length is 700mm, so LN=700mm is selected. The number of jackets is selected in the range of: 2~4, and the gap length is selected in the range of: 10mm≤L≤50mm.

[0062] As shown in Figure 3 and Figure 4 The parallel ice plug applying step includes:

[0063] S21: adding a branch to the pipe by welding or grafting;

[0064] S22: selecting the number n of branches according to the pipe diameter D of the factory maintenance pipeline;

[0065] S23: determining the pipe diameter dn of each branch according to the number of branches;

[0066] S24: obtaining the recommended range and recommended value of the total length of the jacket on each branch according to the pipe diameter dn of the branch from the table or industry standard NB / T20551-2019;

[0067] S25: selecting the total length of the jacket as Ln according to the recommended value of the total length of the jacket found.

[0068] In S22, the number n of branches is selected in the range of: D / 200mm≤n≤D / 100mm.

[0069] In S23, dn is the standard pipe diameter ≤D / n.

[0070] Optionally, a pipe with a nominal diameter of 500 mm is selected. The number of branches, n, is selected within the range of 2.5 ≤ n ≤ 5. In this case, n = 3, 4, or 5 can be selected based on the operational difficulty and requirements. In this case, the pipe diameters dn of each branch are DN150 mm, DN125 mm, and DN100 mm, respectively. According to industry standards, the total jacket length ranges are 252.45–420.75 mm, 211.95–353.25 mm, and 171.45–285.75 mm, respectively. Ln = 300 mm, 250 mm, and 200 mm are selected respectively.

[0071] Example 1

[0072] Select a pipe with a nominal diameter of 300mm and choose the series connection method. According to industry standards, the total jacket length ranges from 485.85 to 809.75mm, with a recommended length of 600mm. Select LN = 600mm. The number of jackets should be selected from N = 1 to 2. The gap length should be selected from 10mm ≤ l ≤ 60mm.

[0073] As shown in Table 1, the number of jackets was selected as 1 or 2, and the gap length was selected as 20mm and 60mm. The ice volume is shown in Table 1. After using the number of jackets and the gap length within the range shown above, the ice plug volume formed by freezing with a single jacket was significantly improved, achieving the goals of energy saving, efficiency improvement and increased pressure resistance.

[0074] Table 1. Ice plug volume ratio for DN300mm pipes with different jacket types.

[0075]

[0076] As shown in Table 1, this embodiment presents data on the ice plug volume ratio of DN300 mm pipes with 1 to 2 jackets and 20 to 60 mm gap lengths. It can be clearly seen that by using different numbers of jackets and gap lengths within the ranges shown above, the ice plug volume formed by freezing with a single jacket is significantly increased, achieving the goals of energy saving, efficiency improvement, and enhanced pressure resistance.

[0077] Example 2

[0078] Select a pipe with a nominal diameter of 500mm and choose the series connection method. According to industry standards, the total jacket length ranges from 762 to 1270mm, with a recommended length of 1000mm; therefore, select LN = 1000mm. The number of jackets should range from N = 2 to 4. The gap length should range from 10mm ≤ l ≤ 50mm.

[0079] As shown in Table 2, the number of jackets was selected as 2, 3, or 4, and the gap length was selected as 20mm and 50mm. The ice volume is shown in Table 2. After using the number of jackets and the gap length within the range shown above, the ice plug volume formed by freezing with a single jacket was significantly increased compared with that formed by single-jacket freezing, thus achieving the purpose of energy saving, efficiency improvement, and increased pressure bearing capacity.

[0080] Table 2. Ice plug volume ratio for DN500mm pipes with different jacket types.

[0081] Pipe diameter / mm Number of jackets Gap length / mm Ice plug volume ratio DN 500 2 20 100.00％ DN 500 2 50 105.46％ DN 500 3 20 157.19％ DN 500 3 50 162.29％ DN 500 4 20 172.47％ DN 500 4 50 177.15％

[0082] As shown in Table 2, this embodiment presents data on the ice plug volume ratio of DN500 mm pipes with 2 to 4 jackets and 20 to 50 mm gap lengths. It can be clearly seen that by using the number of jackets and gap lengths within the range shown above, the ice plug volume formed by freezing with a single jacket is significantly increased, achieving the goals of energy saving, efficiency improvement, and enhanced pressure resistance.

[0083] Example 3

[0084] Select a pipe with a nominal diameter of 700mm and choose the series connection method. According to industry standards, the total jacket length ranges from 1066.5 to 1777.5mm, with a recommended length of 1400mm. Select LN = 1400mm. The number of jackets should range from N = 3 to 6. The gap length should range from 10mm ≤ 1 ≤ 40mm.

[0085] As shown in Table 3, the number of jackets selected were 3, 4, 5, and 6, and the gap lengths were 20 mm and 40 mm. The ice volume is shown in Table 3. After using the number of jackets and the gap length within the range shown above, the ice plug volume formed by freezing with a single jacket was significantly increased, achieving the goals of energy saving, efficiency improvement, and enhanced pressure resistance.

[0086] Table 3. Ice plug volume ratio for DN700mm pipes with different jacket types.

[0087] Pipe diameter / mm Number of jackets Gap length / mm Ice plug volume ratio DN 700 3 20 100.00％ DN 700 3 40 101.90％ DN 700 4 20 115.16％ DN 700 4 40 117.12％ DN 700 5 20 119.42％ DN 700 5 40 120.07％ DN 700 6 20 121.81％ DN 700 6 40 123.20％

[0088] As shown in Table 3, this embodiment presents data on the ice plug volume ratio of DN700 mm pipes with 3 to 6 jackets and 20 to 40 mm gap lengths. It can be clearly seen that by using the number of jackets and gap lengths within the ranges shown above, the ice plug volume formed by freezing with a single jacket is significantly increased, achieving the goals of energy saving, efficiency improvement, and enhanced pressure resistance.

[0089] Example 4

[0090] Select pipes with a nominal diameter of 300mm and choose a parallel connection method. The number of branches, n, should be within the range of 1.5 ≤ n ≤ 3. In this case, n = 2 or 3 can be selected based on the operational difficulty and requirements. The pipe diameters dn of each branch are DN150 mm and DN100 mm, respectively. According to industry standards, the total jacket length ranges are 252.45–420.75 mm and 171.45–285.75 mm, respectively. Select Ln = 300 mm and 200 mm, respectively.

[0091] The freezing time is shown in Table 4. After adopting the parallel method, the time required to form an ice plug is greatly reduced compared with the single-jacket freezing method, thus achieving the goals of energy saving, efficiency improvement and increased pressure resistance.

[0092] Table 4 Freezing schedule for DN300mm pipes under different application methods

[0093] Pipe diameter / mm Number of branches Freezing time / s DN 300 1 10819 DN 500 2 9563 DN 500 3 8790

[0094] This application proposes application schemes for different pipe diameters. In practice, operators can choose the application method and select the number of jackets and gap length within the specified range to perform ice plugging operations, thereby controlling the freezing time, pressure bearing capacity, etc.

[0095] The above description is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application.

Claims

1. A multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair, characterized by, According to the pipeline parameters, the configuration parameters of the ice plug jacket are determined, and the jacket arrangement is implemented in series or parallel to achieve freezing; When the ice plug jacket in series is adopted, the total length of the jacket is recommended according to the standard, the total length LN is determined, the number of jackets N and the gap length L are calculated, and the gaps are distributed; When the ice plug jacket in parallel is adopted, the branch is added, the jacket length Ln of each branch is determined according to the standard, and the number of branches n and the pipe diameter are configured.

2. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 1, wherein, The ice plug jacket in series includes: S11: According to the pipe diameter D of the factory maintenance pipeline, the recommended range and value of the total length of the jacket are obtained; S12: The total length of the jacket is selected as LN according to the recommended value of the total length of the jacket obtained; S13: The number of jackets N and the single gap length L are preliminarily determined according to the pipe diameter D of the factory maintenance pipeline; S14: The gap length is distributed according to the total length LN, the number of jackets N and the single gap length L.

3. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 2, wherein, In S13, the number of jackets is N, and the selection range is: When D≤300mm, N=1~2; When 300<D≤600mm, N=2~4; When 600<D≤800mm, N=3~6.

4. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 2, wherein, In S13, the gap length L, the selection range is: When LN≤600mm, N≤2, 10mm≤L≤60mm; When 600mm<LN≤1200mm, N≤4, 10mm≤L≤50mm; When 1200mm<LN≤1600mm, N≤6, 10mm≤L≤40mm.

5. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 2, wherein, Select the pipeline with a nominal diameter of 300mm, the total length of the jacket is 485.85~809.75mm, the recommended length is 600mm, LN=600mm is selected, the number of jackets is selected as N=1~2, and the gap length is selected in the range of 10mm≤l≤60mm.

6. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 2, wherein, Select the pipeline with a nominal diameter of 500mm, the total length of the jacket is 762~1270mm, the recommended length is 1000mm, LN=1000mm is selected, the number of jackets is selected as N=2~, and the gap length is selected in the range of 10mm≤l≤50mm.

7. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 1, wherein, The ice plug jacket in parallel includes: S21: Adding a branch to the pipeline; S22: The number of branches n is selected according to the pipe diameter D of the factory maintenance pipeline; S23: The pipe diameter dn of each branch is determined according to the number of branches; S24: The recommended range and value of the total length of the jacket on each branch are obtained according to the pipe diameter dn of the branch; S25: The total length of the jacket is selected as Ln according to the recommended value of the total length of the jacket.

8. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 7, wherein, In S21, the branch is added to the pipeline by welding or grafting.

9. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 7, wherein, In S22, the number of branches n is selected in the range of D / 200mm≤n≤D / 100mm.

10. The multi-jacketed liquid nitrogen ice plug freezing method for nuclear power plant pipe repair of claim 7, wherein, In S23, dn is the standard pipe diameter ≤D / n.

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