TABLE. 12. Emergency Classification for Light Water Reactors in Operating, Standby or Hot Shutdown Mode
For the following entry conditions: | Declare a general emergency if: | Declare a site area emergency if: | Declare an alert if: |
Critical safety function impairment |
Failure to stop nuclear reaction1 | Failure to scram when above 5% power [or insert site specific power level]2 and any of the following: or or or | Failure to scram when above 5% power [or insert site specific power level] and abnormal conditions indicate that an automatic or manual scram is necessary | Failure to fully shut down (increasing neutron flux)3 as part of normal shutdown with sufficient heat removal available (ultimate heat sink available and sufficient) |
Inadequate core cooling — vessel level4 | Vessel water level is, or is projected to be, below top of active fuel for more than 15 min | Vessel water level is or is projected to be below top of active fuel | Vessel water level decreasing over a longer time period than expected while systems are responding as designed |
Notes about level measurement: Pressurized water reactor pressurizer levels may not be valid indicators of vessel water level under accident conditions Pressurized water reactor water levels measured in the vessel can have considerable uncertainties (30%) and should only be used for trend assessment Boiling water reactor high dry well temperature and low pressure accidents (e.g. LOCAs) can cause the water level to read erroneously high
| Vessel water level is or is projected to be below top of active fuel and any of the following: or or Note: Imminent reactor coolant system or containment boundary failure might be considered as additional criteria.5 | | |
Inadequate core cooling — core temperature6 | Core exit thermocouple reading greater than 800oC | Core exit thermocouple reading greater than 650oC | Core exit thermocouple reading greater than 370oC |
Inadequate core cooling — decay heat removal (considering the operations of pumps, piping, heat exchangers, heat sinks, power supply, auxiliary fluid) | | Actual failure or projected long term failure of the ability to remove decay heat to the environment, potentially affecting the ability to protect the core | Unavailability of the normal feedwater system for decay heat removal7 |
Pressurized water reactor — abnormal primary system temperature (inadequate core cooling) Note: Temperature should be measured in the vessel. Most pressurized water reactors have core exit thermocouples to measure temperatures in the vessel. Use the average of the highest four core exit thermocouple readings. If there is water flow, the hot leg temperature (Thot) could be used if core exit thermocouples are not available, although this indication is less prompt.8 For boiling water reactors there are no instruments that provide a valid reading of core temperature. | Pressurized water reactor — negative cooling margin on the basis of Fig. 7 or primary system temperature exceeds scale for more than 15 min [or insert site specific time for core damage following a loss of coolant accident] and any of the following: or or Note: Imminent reactor coolant system or containment boundary failure might be considered as additional criteria.10 | Pressurized water reactor — negative cooling margin on the basis of Fig. 7 for more than 15 min [or insert site specific time that core damage is possible following a loss of coolant accident] | Pressurized water reactor — primary system pressure and temperature indicate negative cooling margin on the basis of Fig. 7 for more than 5 min Note: Negative cooling margin is read as soon as the system temperature is higher than the saturation temperature at the set pressure of the reactor coolant system safety valves.11 |
Loss of AC or DC power sources | Actual or projected loss of all AC or DC power needed for operation of safety systems and their supporting systems is likely for more than 45 min [or insert site specific time required to uncover core for more than 15 min] Loss of all AC or DC power needed for safety systems operation and any of the following: or or | Actual or projected loss of AC or DC power needed for operation of safety systems and their supporting systems for more than 30 min [or insert site specific time required to uncover the core] | AC or DC power needed for operation of safety systems and their supporting systems is lost or reduced to a single source |
Conditions of an unknown cause affecting safety systems | | | Conditions which are not understood and which could potentially affect safety systems |
Loss of or degraded control of safety systems including post-accident instrumentation12 | Unavailability of safety system instruments or controls in the control room and remote control locations and any of the following: or or | Unavailability of safety system instruments or controls in the control room for more than 15 min and major transient in progress potentially affecting the ability to protect the core | Unreliable functioning of several safety system instruments or controls in the control room for more than 15 min |
Loss of fission product barriers |
Major increased risk of damage to the core or spent fuel Note: Core damage can occur if the core is uncovered for more than 15 min. | Loss for more than 45 min of all the systems required to protect the core or spent fuel [or insert site specific time required to uncover core for more than 15 min] | Failure of an additional safety system component will result in uncovering of the core or spent fuel | Actual or predicted failures leaving only one train to prevent core damage, spent fuel damage or a major release |
High 131I concentration in the primary coolant Note: Coolant samples should not be taken if they will result in high individual doses. Use only concentrations from samples taken after the start of the event Coolant concentrations may not be representative Assumes the core may not be coolable after 10% melt
| 131I concentration is greater than [insert site specific values for release of 10% of core inventory] | 131I concentration is greater than [insert site specific value indicating release of 20% of the gap inventory] | 131I concentration is greater than [insert site specific value 100 times the technical specifications or other operational limits] |
Confirmed core damage | [Insert site specific readings from postaccident sampling system13 indicating release of 20% of gap inventory14] | [Insert site specific readings from postaccident sampling system indicating release of 1% of gap inventory] | |
Primary system leak | Primary system leak requiring all normal and high pressure emergency core coolant systems to maintain primary system water level15 and any of the following: or or Note: Imminent containment boundary failure might be considered as an additional criterion16. | Primary system leak for more than 15 min requiring all normal and high pressure emergency core coolant systems to maintain primary system water level [insert site specific indicators] | Primary system leak rate for more than 15 min greater than 2% of normal full power feedwater flow17(for boiling water reactor refer to the reactor coolant inventory control system) [insert site specific indicators — as an alternative, reference to normal charging flow might be made] |
Primary system leak directly to atmosphere, such as: Pressurized water reactor: steam generator tube rupture Boiling water reactor: main steam isolation valve failure outside of containment A leak with a failure of the containment to achieve isolation A plant with no containment
| Primary system leak directly to the atmosphere and any of the following: or or | or | Pressurized water reactor: primary system leak to the secondary system requiring continuous operation of more than the usually operating20charging pumps to maintain primary system water level Boiling water reactor: main steam isolation valve failure without loss of integrity of steam piping to turbine and/or condenser21 |
Radiation levels |
Effluent release rates greater than 100 times the release limits | Effluent monitor readings for more than 15 min greater than [insert site specific list of effluent monitors and readings indicating that in 1 hour the off-site doses will be greater than the intervention levels for urgent protective actions, assuming average meteorological conditions] | Effluent monitor readings for more than 15 min greater than [insert site specific list of effluent monitors and readings indicating that in 4 hours the off-site doses will be greater than 0.10 of the intervention levels for urgent protective actions, assuming average meteorological conditions] | Effluent monitor readings for more than 15 min greater than [insert site specific list of effluent monitors and readings indicating 100 times the release limits] |
High radiation levels in the control room or other areas requiring continuous access for safety system operation and maintenance Note: Inconsistent monitor readings could result from incomplete mixing, a failed monitor or irradiation from a contaminated system nearby. Monitors may show high, low or centre range if they fail. Readings can be confirmed using hand held monitors outside the area. | Radiation levels greater than 10 mSv/h | Radiation levels greater than 1 mSv/h potentially lasting several hours | Radiation levels greater than 0.10 mSv/h potentially lasting several hours |
High radiation levels in areas requiring occasional occupancy to maintain or control safety systems | Radiation levels greater than 100 mSv/h potentially lasting several hours | Radiation levels greater than 10 mSv/h potentially lasting several hours | Radiation levels greater than 1 mSv/h potentially lasting several hours |
Elevated containment (for boiling water reactors, dry well)22 radiation levels Note: Inconsistent monitor readings could result from incomplete mixing or a failed monitor or irradiation from a contaminated system nearby23. Monitors may show high, low or centre range if they fail. Readings can be confirmed using hand held monitors outside the containment | Containment radiation levels greater than 5 Gy/h [or insert site specific reading indicating release of greater than 20% gap inventory] | Containment radiation levels greater than 1 Gy/h [or insert site specific reading indicating release of greater than 1% gap inventory] | Containment radiation levels increase more than 0.10 mGy/h [or insert site specific reading indicating release of greater than 10% coolant inventory] |
Unplanned increase in plant radiation levels | Multiple plant radiation monitors show an unplanned or unpredicted increase by a factor of 100 or more and any other indication of actual core damage | Multiple plant radiation monitors show an unplanned or unpredicted increase by a factor of 100 or more and a major transient is in progress potentially affecting the ability to protect the core | Multiple plant radiation monitors show an unplanned or unpredicted increase by a factor of 100 or more |
High ambient dose rates at or beyond24 the site boundary | Ambient dose rates at or beyond the site boundary greater than 1 mSv/h [or insert the site specific operational intervention level for evacuation; see Procedure B1 in Ref. [27]] | Ambient dose rates at or beyond the site boundary greater than 0.1 mSv/h [or insert one tenth of the site specific operational intervention level for evacuation; see Procedure B1 in Ref. [27]] | Ambient dose rates at or beyond the site boundary greater than 10 μSv/h [or insert site specific reading indicating 100 times the background] |
Security events, fires, explosions, toxic gas releases, natural and other events |
Security event (intruder or malicious act) | Security event resulting in loss of the ability to monitor and control safety functions needed to protect the core | Security event resulting in damage or impaired25 access to safety systems | Security event with potential to affect safety system operation, or uncertain security conditions |
Fire or explosion (including turbine failure) | | | Fire or explosion potentially affecting areas containing safety systems |
Toxic or flammable gases including, for boiling water reactors, hydrogen in the dry well26 | | Flammable gas concentrations that prevent control or maintenance of safety systems | Toxic or flammable gases in the plant |
Evacuation of the main control room27 | | Neither the main control room nor the emergency control room is habitable | Plant can be controlled from emergency control room |
Major natural disaster such as: | | Major natural events resulting in damage or impaired30 access to safety systems and/or decay heat removal systems or affecting their long term operation | Major natural events that threaten the plant such as: |
Loss of communications31 | | | Events resulting in actual or potential loss of communications to the site for a long period of time |
Plant shift supervisor’s opinion | Conditions that warrant taking urgent protective actions off the site | Conditions that warrant preparing the public to implement urgent protective actions or Conditions that warrant taking protective actions on the site | Abnormal conditions that warrant obtaining immediate additional assistance for the on-site operations staff or Abnormal conditions that warrant increased preparedness on the part of off-site officials |
Spent fuel pool events |
Abnormal refuelling or spent fuel conditions | Fully drained pool containing more than one third of a core removed from the reactor within the past 3 years or Radiation level in pool area greater than 3 Gy/h | Water level below top of irradiated fuel or Radiation level in pool area greater than 30 mGy/h | Loss of ability to maintain water level above spent fuel or Damage to spent fuel or Loss of ability to maintain pool water temperature below 80°C32 |