IEC/IEEE 63113:2021 pdf download – 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.
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.