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Additional Explanation:
This standard was proposed by National Technical Committee on Nuclear Energy of Standardization Administration of China.
This standard was developed by Beijing Institute of Nuclear Engineering (BINE).
This standard is formulated by reference to American National Standard ANSI/ANS 57.7-1988.
Safety Design Guidelines for Away-from-reactor Storage Pool Used for Spent Fuel
1 Subject Content and Application Scope
This standard specifies mandatory criteria and basic requirements for ensuring the nuclear safety during the design of away-from-reactor storage pool used for spent fuel (hereinafter referred to as away-from-reactor pool).
This standard is applicable to the safety design of away-from-reactor storage pool used for UO2 spent fuel unloaded from light water reactor and cooled for more than five years.
This standard is not applicable to the safety design of pool at reactor.
2 Normative References
GB 8703 Regulations for Radiation Protection
GB 15146.8 Nuclear Criticality Safety for Fissile Materials Outside Reactors - Part 8: Criticality Safety Criteria for the Handling Storage and Transportation of LWR Fuel Outside Reactors
GBJ 204 Code for Construction and Acceptance of Reinforced Concrete Engineering
GBJ 205 Code for Construction and Acceptance of Steel Structure Engineering
EJ 724 Criteria for Fire Protection of Nuclear Fuel Reprocessing Plant
EJ 849 Design Rules for Radiation Safety of Nuclear Fuel Reprocessing Plant
3 Terms
3.1
away-from-reactor storage pool (hereinafter referred to as away-from-reactor pool)
spent fuel storage pool set beyond the boundary of reactor plant area, generally used for receiving and storing spent fuels from several reactors
3.2
fuel unit
object treated as single article during operation, storage or transport; it may be single fuel element, fuel assembly, spent fuel in tank or a batch of fuel elements that are packed together
3.3
storage basket
metal member with opening used for transferring and storing one or more spent fuel units
3.4
storage cell
metal member set in pool and used for supporting and maintaining fuel unit so that the fuel unit is in sub-critical state during storage
3.5
basket bracket
metal member set on pool bottom or wall and used for supporting storage basket and enabling the storage basket to keep the fuel in it in sub-critical state under any circumstances
3.6
design basis accident
those accident conditions of away-from-reactor pool for which corresponding measures are taken in design according to the determined design criteria
Examples:
a. nuclear criticality accident;
b. loss of pool water-cooling function;
c. container falling;
d. design basis earthquake occurring.
4 General Safety Criteria
4.1 Main safety objective
Main safety objective is ensure the irradiation borne by working personnel, the public and environment in all operation states and accident conditions does not exceed the limit value specified by the nation, and implement the principle "as low as reasonably achievable" in design.
4.2 Safely principle
Comply with the principle "safety first". In-depth defense shall be reflected and multilevel protection shall be provided in design so as to ensure the normal operation of away-from-reactor pool, prevent accident and limit accident development and consequence.
4.3 Overall basis of safety design
Safety design of away-from-reactor pool must comply with those specified in relevant laws, regulations and standards of the nation as well as this standard.
4.4 Quality assurance
As for buildings/structures, systems and components which are important for the safety of the away-from-reactor pool, they shall be graded by safety function, and matched quality assurance requirements for them realizing safety function importance must be proposed.
4.5 Protection against site feature and natural events
4.5.1 The mutual influence between the away-from-reactor pool and the environmental factors of its plant site (e.g., population, meteorology, hydrology, geology, earthquake and other relevant facilities) must be considered.
4.5.2 As for buildings/structures, systems and components which are important for the safety of the away-from-reactor pool, that they still maintain safety function in possible natural events related to the plant site (e.g., earthquake, tornado, lightning, hurricane, flood, tsunami, lake surge, debris flow, etc.) must be taken into consideration in design. The strength of various natural events possibly occurred shall be determined so as to determine the design basis of item important to safety. Because the data sources of most serious natural event are uncertain and the time period for accumulating the data is limited, proper margin shall be remained for the design when taking into account the most serious natural event in plant site and its surrounding area.
4.6 Fire and explosion protection
As for buildings/structures, systems and components important for safety, their design must ensure that they still maintain safety function in fire and explosion accidents.
4.7 System safety design
Systems for handling, transferring and storing spent fuel must be designed together with their auxiliary systems so that they are able to carry out the following actions in operation state or accident conditions:
a. Preventing accidental nuclear criticality accident from occurring;
b. Preventing personnel from suffering overdose irradiation;
c. Preventing uncontrolled release of radioactive substance from exceeding permissible limit;
d. Preventing stored fuel and item important to safety from being seriously damaged.
4.8 Human error
Human factors engineering shall be considered, especially operation control and limit of systems and components important for safety. Necessary measures shall be taken to improve automatic response to operation, prevent manual misoperation as well as automatically correct and compensate after manual misoperation.
4.9 Maintenance
Minimum maintenance principle shall be implemented. As for items that must be maintained, necessary measures shall be provided so that it is convenient for maintenance personnel to approach, and it is ensured that irradiation suffered and radioactive substance ingested by the maintenance personnel comply with the principle "as low as reasonably achievable".
4.10 Emergency capability
Emergency measures, withdrawal routes and communication with existing emergency organization and agency outside the plant (e.g., hospital, fire protection organization，public security organization, etc.) shall be considered.
4.11 Decommissioning
Convenient decontamination and safe decommissioning of all systems of away-from-reactor pool must be considered in design.
5 Basic Requirements of Safety design
5.1 Basic function of facility
Basic function of facility is the safe and intermediate storage and management of spent fuel, and the specific functions are as follows:
a. Safely receiving and long unloading of spent fuel between transport container and vehicle;
b. Preparation before unloading the spent fuel from transport container;
c. Underwater unloading of spent fuel transport container;
d. Safe storage of unloaded spent fuel in pool;
e. Fill the stored spent fuel into container and transport it outward or directly transfer it to reprocessing plant for treatment, if necessary;
5.2 Sealing function of facility
The integrity of primary barrier of stored spent fuel shall be ensured, and secondary barrier shall be provided to ensure the sealing function of facility and prevent radioactive substance from being released to surrounding environment in an uncontrolled way.
5.2.1 Primary barrier
It refers to the spent fuel cladding. Measures for fuel acceptance inspection, filling the failed fuel into box, storage environment, safe transfer of container, decay heat outward conduction, pool water cooling and purification, etc. shall be taken to reduce cladding damage. And measures for sealing the failed spent fuel shall be taken.
5.2.2 Secondary barrier
Multiple secondary barriers shall be arranged.
5.2.2.1 Spent fuel is stored in pool; in normal state, the water in the pool always maintains the level specified in design to ensure the radiation safety of the operation personnel.
5.2.2.2 The pool shall be designed into reinforced concrete integral structure with stainless steel cover.
5.2.2.3 The followings shall be arranged for the water in the pool:
a. Pool water preparation and replenishment system with sufficient multiplicity;
b. Pool water cooling system;
c. Pool water purification system that can remove radioactive substances and other impurities in the pool water both in normal state and accident conditions;
d. Collection and return system for leak pool water.
5.2.2.4 Radioactive waste collection and disposal: ensure that various radioactive wastes generated by facilities are released into environment in a controlled way.
5.2.2.5 The plant shall be of four-zone arrangement, and people flow and air flow in the plant and each zone shall be controlled.
5.2.2.6 General ventilation shall be arranged for plant, and different ventilation rate and negative pressure shall be arranged for each zone; the airborne radioactive substance shall be filtered through process waste gas purification system or vented exhaust and released into the environment in a controlled way.
5.3 Receiving and outgoing system of container
5.3.1 Plant layout
It shall be meet the following requirements:
a. It is capable of accommodating various transport containers and their transport vehicles to be received (or sent out); the received (or sent out) quantity every day matches with the design capacity of the facilities, and, where necessary, proper temporary storage zone of container shall be arranged.
b. Air brake shall be arranged at the entrance of plant where transport vehicles enter into so that the air in the plant is prevented from diffusing outside the plant when transport vehicles enter into the plant.
5.3.2 Crane for transferring transport container
It is one of the equipment of the facilities which is important for safety, of which the design requirements are as follows:
a. It shall be so designed that it is of Grade 1 in nuclear safety function grade, Category I in seismic category and Grades A and B in quality assurance grade.
b. Hoisting capacity: normally, it shall be adapt to the maximum load of the maximum transport container expected to be received (or sent out); it is able to stop at certain position without working but never causing heavy object-falling fault under all design loads (including design seismic load).
c. Motion direction: it is able to move in four directions in the vertical plane.
d. Motion range: within the range for transferring the transport container but not passing through over the spent fuel storage zone.
e. Safety devices: safety devices that can resist damages from such external events as overload, overspeed, overtravel, fault of mechanical components and parts and electrical elements, manual misoperation and earthquake as well as corresponding fault alarm devices shall be equipped, and they shall be designed according to the principle of single fault.
f. Manipulation and control: crane may be operated manually or remotely. Synchronous monitoring device for main hook position and load, hoist spool and its motor as well as motor/limit switch of cross beam lifting appliance and force-limiting device shall be arranged. Gantry and trolley of crane cannot move together with the lifting mechanism.
g. Where necessary, microcomputer control systems for crane automatic positioning, automatic operating and automatic lifting may be arranged.
h. Safety-related crane structure and its support system shall be so designed that falling accident will not occur when they are bearing various loads and in the condition of power failure due to accident. Means indicating whether the lifting appliance is in lifting state as well as overload interlocking device shall be provided for the crane so that it can lock by itself in case of overload.
i. Necessary maintenance inspection facility shall be provided in design; lifting appliance shall be so designed that it facilitates decontamination and inspection.
1 Subject Content and Application Scope
2 Normative References
3 Terms
4 General Safety Criteria
5 Basic Requirements of Safety design
Annex A (Informative) Schematic Diagram for the Technology Process of the Away-from-reactor Storage Pool Used for Spent Fuel
Annex B (Informative) Recommended Physical-Chemical Properties of the Pool Water
Annex C (Informative) Conservative Rate of Generation for Decay Heat of Pressurized Water Reactor Spent Fuel
Annex D (Informative) Typical Dose Rate
