GB 15146.9-1994 Nuclear criticality safety of fissile materials outside the reactor. Performance and inspection requirements for nuclear criticality accident detection and alarm systems
Some standard content:
National Standard of the People's Republic of China
Nuclear criticality safety for fissile materialsoutside reactor
Performance and testing requirementsfor nuclear criticality detection and alarm systemsGB 15146.9--94
This standard is equivalent to the international standard ISO7753 (1987) "Nuclear energy-Performance and testing requirements for criticality accident detection and alarm systems".
1 Subject content and scope of application
This standard specifies the performance and testing requirements for criticality accident detection and alarm systems. This standard applies to all operating places or facilities related to uranium, enriched uranium and other fissile materials where criticality accidents may occur. This standard does not apply to facilities such as reactors or critical assemblies where the operating instruments already meet the requirements of this standard. This standard mainly deals with systems sensitive to radiation rates. The specific characteristics of the criticality accident alarm system shall meet the requirements of GB12787. 2 Reference standards
GB12787 Criticality accident alarm equipment
3 Terms
3.1 Criticality accident criticality accident Energy release event caused by unexpected self-sustaining or divergent neutron chain reaction. 3.2 Minimum criticality accident of concern Minimum criticality accident that the criticality accident alarm system must detect. In this standard, the minimum criticality accident of concern is defined as: under unshielded conditions, the total absorbed dose of neutrons and radiation caused in free air 2m away from the reaction object within 60s is 0.2Gyl.
Note: 1) Studies on previous criticality accidents have shown that if a criticality accident occurs, its radiation intensity generally exceeds the value of 0.2Gy; of course, for criticality accidents that are unlikely to occur in practice and whose power increases very slowly, the radiation intensity may not reach this value. 3.3 Independent areas individual areas
Can be regarded as areas that are unrelated to each other. That is, there is no mutual exchange of materials between such areas; the minimum spacing between materials in adjacent areas is 10 cm, and the average surface density of fissile materials in the area is less than 50 g/m. 4 General Principles
4.1 Overview
Approved by the State Administration of Technical Supervision on December 22, 1994 and implemented on October 1, 1995
GB15146.9-94
Any place where it is confirmed that the installation of a criticality accident alarm system can reduce the overall risk probability must install such a system. At the same time, the possible hazards caused by false alarms of the system must be considered.
4.2 Limitations and general requirements
4.2.1 In an independent area, any operation involving a total amount of more than 700g235U, 520g233U, 450g ring of fissile isotopes or 450g of any combination of these isotopes must evaluate the necessity of installing a criticality accident alarm system. At the same time, during operation, when there are moderators or reflectors that are more effective than water, care must be taken to consider the contribution of these media to reactivity. 4.2.2 According to the provisions of the various clauses of this standard, for places where the maximum foreseeable criticality accident dose in free air will not exceed 0.12Gy, a criticality accident alarm system may not be installed. When making such an estimate, it can be assumed that the maximum total number of fissions of the corresponding external reactor event is not greater than 2×1019.
4.3 Detection
In the area required to be covered by the criticality accident alarm, means must be provided to detect excessive radiation dose or dose rate and issue a signal for personnel to evacuate.
4.4 Alarm
4.4.1 The sound alarm signal must have special sound characteristics and the volume emitted must be strong enough so that all personnel in the area to be evacuated can hear the alarm. The alarm signal must last at least until all personnel who should evacuate can evacuate to the assembly point. 4.4.2 The size of the alarm trigger point must be appropriately selected so that the alarm system can detect the minimum critical accident of concern and minimize the probability of false alarms caused by non-critical accidents. 4.4.3--Once a critical accident is detected, an alarm signal for personnel evacuation must be issued immediately. 4.4.4 After the alarm signal is issued, even if the radiation level at the accident site has dropped below the alarm trigger point, the alarm signal must continue until it is manually reset. The manual reset switch must be located outside the evacuation area and equipped with a device to prevent unauthorized persons from activating the reset switch. 4.4.5 In areas with high background noise levels, the alarm system should be equipped with a visual alarm signal. 4.5 Reliability
4.5.1 Special attention must be paid to reducing the occurrence of false alarms. The ways to reduce this are: a. Improve the reliability of each channel of the alarm system; b. It is more desirable to use two or more channels to respond together to trigger the alarm. In a system using redundant channels, when any channel fails, the critical accident alarm system must still meet the detection criteria specified in Article 5.2 and should issue a fault indication signal, but cannot trigger an alarm.
4.5.2 Means should be provided to test the response capability and effectiveness of the alarm system. Such testing should not trigger the evacuation of personnel. 4.5.3 For places where fissile material operations are to continue when the external power supply is cut off, the critical accident detection and alarm system must be equipped with an uninterruptible power supply; otherwise, such operations should be carried out under the supervision of portable instruments. 4.5.4 Under strong radiation exposure of up to 10°Gy/h, the detectors of the alarm system must still be able to work normally. The inspection of the detector performance should be carried out in accordance with the provisions of GB12787.
5 Alarm system design criteria
5.1 System reliability
The design of the alarm system should be as simple as possible as long as reliable alarms can be ensured and false alarms can be avoided. 5.2 Detection criteria
The design of the criticality accident alarm system must ensure that the minimum criticality accident of concern can be detected instantaneously. 5.3 Instrument response
In the design of radiation detectors, it can be assumed that the minimum duration of the radiation transient process is 1ms, and the design must ensure that the criticality alarm system can respond to the radiation transient process with this duration. 5.4 Alarm trigger point
In order to minimize the occurrence of false alarms, the setting value of the trigger alarm should be high enough, but it must meet the detection criteria specified in Article 5.2. An indication signal indicating which detection channel is triggered must be provided. 5.5 Detector layout
The installation position and spacing of the detectors should be appropriately selected to avoid the shielding effect of large equipment or materials. The spacing between the detectors must be considered based on the selected alarm trigger point and detection criteria. The calculation method of the detector detection range is shown in Appendix A (reference). 5.6 Inspection
5.6.1 The response performance of the instrument to radiation must be checked regularly to ensure that the instrument continues to work properly. For systems with redundant channels, the performance of each channel must be inspected. The inspection method should comply with the provisions of GB12787. The inspection cycle can be determined based on experience and needs, but it should be inspected at least once a month. Inspection records must be maintained and saved. 5.6.2 The entire alarm system must be inspected regularly. The sound signal generator should be inspected at least once a quarter, and it must be determined through on-site monitoring that the volume of the alarm sound is higher than the background noise level in the area where personnel should evacuate. When doing this type of inspection, the relevant personnel who will be affected must be notified in advance to avoid misunderstandings. 5.6.3 If any performance abnormality is found during the inspection, corrective measures must be taken immediately. 5.6.4 Detailed procedures must be formulated to minimize the number of false alarms during the inspection process and ensure that the system is restored to normal working condition immediately after the inspection is completed.
5.6.5 When the criticality accident alarm system needs to be shut down for a period of time due to maintenance or other reasons, the management department of the nuclear facility must be notified in advance.
A1 Assumptions
GB15146.9-94
Appendix Abzxz.net
Relationship and calculation of effective radius of detector and alarm trigger point (reference)
Making some appropriate assumptions can simplify the calculation of effective radius of detector at any given alarm trigger point. These basic assumptions are as follows:
a. The system must respond to the minimum critical accident of concern. b. The detector is a rate meter.
c The accident can be a fast transient process occurring in non-moderated and non-reflective fissile metal materials, or a fast transient process or self-sustaining fission reaction process occurring in moderated fissile materials. d. The response coefficient of the alarm system detector to the fast transient process should be at least 1/2500 of the actual dose rate. Assume that the fast transient process has a pulse width of 1 ms or wider.
e. The radiation intensity of the ray is inversely proportional to the square of the distance from the source, and it is assumed that the attenuation coefficient of the ray in air is 3 at longer distances. (This value is greater than the actual attenuation coefficient at all distances of interest). f. For fast transient processes in non-moderated, non-reflecting metal devices, the ratio of neutron dose to dose is assumed to be 12. This ratio is derived from the following critical reaction results, that is, two very similar critical measurements were carried out in a 239Pu metal system with local reflection. The total number of fissions produced by the fast transient process is 3×1015; the neutron dose at a distance of 1.8m from the center of the reaction is equal to 0.51Gy, and the ? dose is equal to 0.051Gy. Therefore, for a completely naked 239Pu metal system, the ratio of neutron dose to dose can be assumed to be 12. Based on this assumption, in the neutron and mixed fields 2m away from the accident center, the assumed total radiation dose of 0.2Gy is equal to 0.185Gy and the dose is equal to 0.015Gy. (These doses correspond to 1.86×1015 fissions.) g. For those fission devices with moderation, the ratio of neutron dose to dose is assumed to be 0.3. This assumption is based on the results of the simulation experiment of the Y-12 accident. When the Y-12 simulated accident ran for 42 minutes at a sustained fission rate of 9.5×1012 fissions per second, the neutron dose measured at 1.9m from the center of the simulated accident was 0.47Gy, and the dose was equal to about 1.6Gy. Therefore, for a device similar to the Y-12 system, at 2m from the center of the accident, the neutron dose is equal to 0.047Gy and the dose is equal to 0.153Gy in the assumed total radiation dose of 0.2Gy. (These doses correspond to 2.2×1015 fissions.) Calculation of the effective action radius of the A2 detector
Using the above assumptions, for any selected alarm trigger point, the maximum distance between the relevant detector and the potential accident point (i.e., the effective action radius) can be calculated. Taking the fast transient in the fully exposed metal ball system as an example, the response of the detector at a distance of T is: =DX
wherein: T - the response of the detector, Gy/ms; α - the distance from the accident center, a=2m; ×
D is the absorbed dose rate at a point a away from the accident center, Gy/ms; r - the effective action radius of the detector, m,
dair - the attenuation coefficient of free air, dair=3, see Article A1; ε - the response coefficient of the alarm system to the fast transient process, e-1/2500, see Article A1. Assuming that the alarm starting point is 5×10-4Gy/h, then: 194
pr 240m
GB15146.994
5×10-40.015×3.6×106×
Table (A1) gives the calculated values x
Table A1 Calculated values of effective action radius (+) under three types of power surges Power surge type
Transient process without moderation and without skin-gold device Transient process of moderation device
Steady-state process of moderation device
rT.=5X10-Gy/)
It can be clearly seen from the results given in Table (A1) that for the steady-state process of the moderation device, the effective action radius of the detector is the smallest, and this is generally always the case. For this extreme case, according to the detection criteria of this standard, the relationship curve between the alarm trigger point and the effective action radius of the detector can be drawn, as shown in Figure A1. The data used is based on the calculation results of this extreme case of the steady-state process of the moderator. For those places where two coincidences are required to trigger the alarm and the failure of any channel will not affect the continued operation of the system, when the alarm trigger point is set to 5×10-4Gy/h, three detectors should be required to be set within a radius of 150m from each point in the operating area. li
Effective action of the detector is light, m
Relationship curve between the alarm trigger point and the effective action radius of the detector for the alarm system using a dose rate meter T
B1 General
GB15146.9—94
Appendix B
Emergency plan
(reference)
The setting of the critical accident alarm system itself means that the probability of such accidents cannot be ignored. Therefore, appropriate emergency plans should be formulated for such accidents and their possible consequences. This appendix lists the items that should be considered when developing such plans. B2 Evacuation Routes
Evacuation routes should be clearly identified in the emergency plan. Evacuation routes should be the quickest and most direct routes, where practicable. Evacuation routes should be clearly marked.
B3 Assembly Points
A designated assembly point should be established for evacuees and should be outside the evacuation area. B4 Headcounts
There should be a method to confirm that all evacuees have left the accident area. B5 Training and Drills
Personnel should be trained in evacuation methods and all personnel should be familiar with evacuation routes and assembly points. New personnel should be promptly educated and drilled. Emergency drills should be conducted at least once a year and the facility's emergency plan should be improved accordingly. Such emergency drills should be announced in advance.
B6 Emergency Procedures
Emergency procedures should be developed in advance and approved by the facility's competent authority. The expected emergency response units should be informed of the scenario design of the drills and assisted in developing appropriate emergency response procedures. These departments include both on-site and off-site departments. B7 Medical preparation
Pre-arrangements should be made for the care and treatment of injured and exposed personnel. The possibility of personnel being contaminated by radionuclides should be considered. B8 Personal dosimetry
The emergency plan should include procedures for personal dosimetry and rapid identification of exposed personnel. B9 Radiation monitoring
Instruments and procedures for measuring radiation levels after critical accidents should be provided. A command center should be established to control overall information communication. 196
Additional notes:
This standard was proposed by China National Nuclear Corporation. GB15146.9-94
This standard was drafted by the China Institute of Atomic Energy. The main drafters of this standard are Jiang Dexi and Zhang Xiaojian. 1972×1015 fissions. ）A2 Calculation of effective action radius of detector
Using the above assumptions, for any selected alarm trigger point, the maximum distance between the relevant detector and the potential accident point (i.e., effective action radius) can be calculated. Taking the fast transient in the fully exposed metal ball system as an example, the response of the detector at a distance of is: T, =DX
Where: T——response of the detector, Gy/ms; α——distance from the accident center, a=2m; ×
D absorbed dose rate at a distance from the accident center, Gy/ms; r-effective action radius of the detector, m,
dair——attenuation coefficient of free air, dair=3, see A1; ε——response coefficient of the alarm system to the fast transient process, e-1/2500, see A1. Assuming that the alarm starting point is 5×10-4Gy/h, then: 194
pr 240m
GB15146.994
5×10-40.015×3.6×106×
Table (A1) gives the calculated values x
Table A1 Calculated values of effective action radius (+) under three types of power surges Power surge type
Transient process without moderation and without skin-gold device Transient process of moderation device
Steady-state process of moderation device
rT.=5X10-Gy/)
It can be clearly seen from the results given in Table (A1) that for the steady-state process of the moderation device, the effective action radius of the detector is the smallest, and this is generally always the case. For this extreme case, according to the detection criteria of this standard, the relationship curve between the alarm trigger point and the effective action radius of the detector can be drawn, as shown in Figure A1. The data used is based on the calculation results of this extreme case of the steady-state process of the moderator. For those places where two coincidences are required to trigger the alarm and the failure of any channel will not affect the continued operation of the system, when the alarm trigger point is set to 5×10-4Gy/h, three detectors should be required to be set within a radius of 150m from each point in the operating area. li
Effective action of the detector is light, m
Relationship curve between the alarm trigger point and the effective action radius of the detector for the alarm system using a dose rate meter T
B1 General
GB15146.9—94
Appendix B
Emergency plan
(reference)
The setting of the critical accident alarm system itself means that the probability of such accidents cannot be ignored. Therefore, appropriate emergency plans should be formulated for such accidents and their possible consequences. This appendix lists the items that should be considered when developing such plans. B2 Evacuation Routes
Evacuation routes should be clearly identified in the emergency plan. Evacuation routes should be the quickest and most direct routes, where practicable. Evacuation routes should be clearly marked.
B3 Assembly Points
A designated assembly point should be established for evacuees and should be outside the evacuation area. B4 Headcounts
There should be a method to confirm that all evacuees have left the accident area. B5 Training and Drills
Personnel should be trained in evacuation methods and all personnel should be familiar with evacuation routes and assembly points. New personnel should be promptly educated and drilled. Emergency drills should be conducted at least once a year and the facility's emergency plan should be improved accordingly. Such emergency drills should be announced in advance.
B6 Emergency Procedures
Emergency procedures should be developed in advance and approved by the facility's competent authority. The expected emergency response units should be informed of the scenario design of the drills and assisted in developing appropriate emergency response procedures. These departments include both on-site and off-site departments. B7 Medical preparation
Pre-arrangements should be made for the care and treatment of injured and exposed personnel. The possibility of personnel being contaminated by radionuclides should be considered. B8 Personal dosimetry
The emergency plan should include procedures for personal dosimetry and rapid identification of exposed personnel. B9 Radiation monitoring
Instruments and procedures for measuring radiation levels after critical accidents should be provided. A command center should be established to control overall information communication. 196
Additional notes:
This standard was proposed by China National Nuclear Corporation. GB15146.9-94
This standard was drafted by the China Institute of Atomic Energy. The main drafters of this standard are Jiang Dexi and Zhang Xiaojian. 1972×1015 fissions. ）A2 Calculation of effective action radius of detector
Using the above assumptions, for any selected alarm trigger point, the maximum distance between the relevant detector and the potential accident point (i.e., effective action radius) can be calculated. Taking the fast transient in the fully exposed metal ball system as an example, the response of the detector at a distance of is: T, =DX
Where: T——response of the detector, Gy/ms; α——distance from the accident center, a=2m; ×
D absorbed dose rate at a distance from the accident center, Gy/ms; r-effective action radius of the detector, m,
dair——attenuation coefficient of free air, dair=3, see A1; ε——response coefficient of the alarm system to the fast transient process, e-1/2500, see A1. Assuming that the alarm starting point is 5×10-4Gy/h, then: 194
pr 240m
GB15146.994
5×10-40.015×3.6×106×
Table (A1) gives the calculated values x
Table A1 Calculated values of effective action radius (+) under three types of power surges Power surge type
Transient process without moderation and without skin-gold device Transient process of moderation device
Steady-state process of moderation device
rT.=5X10-Gy/)
It can be clearly seen from the results given in Table (A1) that for the steady-state process of the moderation device, the effective action radius of the detector is the smallest, and this is generally always the case. For this extreme case, according to the detection criteria of this standard, the relationship curve between the alarm trigger point and the effective action radius of the detector can be drawn, as shown in Figure A1. The data used is based on the calculation results of this extreme case of the steady-state process of the moderator. For those places where two coincidences are required to trigger the alarm and the failure of any channel will not affect the continued operation of the system, when the alarm trigger point is set to 5×10-4Gy/h, three detectors should be required to be set within a radius of 150m from each point in the operating area. li
Effective action of the detector is light, m
Relationship curve between the alarm trigger point and the effective action radius of the detector for the alarm system using a dose rate meter T
B1 General
GB15146.9—94
Appendix B
Emergency plan
(reference)
The setting of the critical accident alarm system itself means that the probability of such accidents cannot be ignored. Therefore, appropriate emergency plans should be formulated for such accidents and their possible consequences. This appendix lists the items that should be considered when developing such plans. B2 Evacuation Routes
Evacuation routes should be clearly identified in the emergency plan. Evacuation routes should be the quickest and most direct routes, where practicable. Evacuation routes should be clearly marked.
B3 Assembly Points
A designated assembly point should be established for evacuees and should be outside the evacuation area. B4 Headcounts
There should be a method to confirm that all evacuees have left the accident area. B5 Training and Drills
Personnel should be trained in evacuation methods and all personnel should be familiar with evacuation routes and assembly points. New personnel should be promptly educated and drilled. Emergency drills should be conducted at least once a year and the facility's emergency plan should be improved accordingly. Such emergency drills should be announced in advance.
B6 Emergency Procedures
Emergency procedures should be developed in advance and approved by the facility's competent authority. The expected emergency response units should be informed of the scenario design of the drills and assisted in developing appropriate emergency response procedures. These departments include both on-site and off-site departments. B7 Medical preparation
Pre-arrangements should be made for the care and treatment of injured and exposed personnel. The possibility of personnel being contaminated by radionuclides should be considered. B8 Personal dosimetry
The emergency plan should include procedures for personal dosimetry and rapid identification of exposed personnel. B9 Radiation monitoring
Instruments and procedures for measuring radiation levels after critical accidents should be provided. A command center should be established to control overall information communication. 196
Additional notes:
This standard was proposed by China National Nuclear Corporation. GB15146.9-94
This standard was drafted by the China Institute of Atomic Energy. The main drafters of this standard are Jiang Dexi and Zhang Xiaojian. 1979-94
This standard was drafted by the China Institute of Atomic Energy. The main drafters of this standard are Jiang Dexi and Zhang Xiaojian. 1979-94
This standard was drafted by the China Institute of Atomic Energy. The main drafters of this standard are Jiang Dexi and Zhang Xiaojian. 197
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