IEC IEEE 63113 pdf – Nuclear facilities – Instrumentation important to safety – Spent fuel pool instrumentation
5 Functional requirements Spent fuel pools within the scope of this document shall be provided with monitoring instrumentation that enables the plant staff to recognize the following conditions.
a) Thermodynamic conditions in the pool. Pool thermodynamic conditions may be determined by measurement of pool temperature. Higher than normal temperatures may indicate an abnormally high rate of pool water evaporation. Normal temperatures in combination with unexpected loss of inventory may indicate that the pool is leaking.
b) Maximum water level. Pool inventory has approached the point where there is a risk of water overflowing the top of the pool. c) Minimum water level for moving fuel. Pool inventory less than this level would be insufficient to comply with accident analysis assumptions of iodine decontamination factors following a fuel handling accident.
d) Minimum active cooling water level. Pool inventory has approached the point where there is a risk that operation of the normal fuel pool cooling system cannot be supported.
e) Minimum shielding water level. Pool inventory has approached the point where the coolant cannot provide substantial shielding for a person standing on the spent fuel pool operating deck.
f) Top of fuel water level. Pool inventory has reached the point where the fuel remains covered but actions to implement make-up water addition should no longer be deferred.
g) Air dose rate above the pool. Gamma radiation dose rates in the pool building are at a level that indicates that significant loss of shielding has occurred. Functional requirements for conditions a), d), e), f) and
g) are intended to monitor design extension conditions that do not involve fuel damage. There is reason to believe that information about those conditions will enable the operators to restore pool cooling before fuel in the pool is damaged. Nevertheless, provisions should 2 also be made to enable the plant staff to recognize the following severe accident conditions:
h) Fuel damage water level. Pool inventory has approached the point where fuel damage is expected.
i) Bottom of fuel water level. Pool inventory has reached the point where air cooling is the dominant cooling mechanism for the fuel. When functions to detect conditions
i) are implemented they shall comply with the requirements given in this document. In this document the term “spent fuel pool monitoring instrumentation” refers to any monitoring instrumentation that is specifically intended to detect one or more of the conditions listed above. Annex A provides further discussion of conditions a) through i) above and the spent fuel pool monitoring instrumentation functions intended to detect these conditions. It also gives a diagram showing an example of how the measurements might physically relate to each other and the spent fuel pool itself. The specific values corresponding to the above conditions shall be determined based upon plant-specific design information. Instruments that are intended to detect conditions a), d), e) and f) shall accurately indicate the water level when the water is both below and above its saturation temperature. Instruments that are intended to detect conditions a), b), and c) are meant for use in plant operational states. Instruments that are intended to detect conditions a), d), e), f), and g) are meant for use during accident conditions to alert operators to situations that may jeopardize the cooling of spent fuel under DEC.
Instruments that are intended to detect conditions g), h), and i) are meant for use during severe accident conditions to alert the operators to situations that may immediately result in or have already resulted in fuel damage. A spent fuel pool that contains two or more sections that are connected by normally open gates may be treated as a single spent fuel pool. If the isolable sections of the pool are not used for long-term storage of significant quantities of fuel (as defined by local regulations), sensors for level and temperature monitoring channels shall be located in the main pool. Administrative provisions shall be put into place to ensure that these instruments are operable before pools are isolated from each other.