CHAPTER 6: SAMG for SFP and shutdown cases

SAMG for Spent Fuel Pool (SFP) and shutdown cases

IAEA SSG-54 requires that SAMG address not only at-power conditions, but also damage to the reactor core during shutdown states, and damage to fuel in the spent fuel pools. For example:

SSG-54, 2.11:
“The accident management programme should address all modes and states of operation and all fuel locations, including the spent fuel pool, and should take into account possible combinations of events that could lead to an accident.”

SSG-54, 2.37:
“Accident management guidance should be considered for any specific challenges posed by shutdown plant configurations and large scale maintenance. The potential for damage to fuel in the reactor core and in the spent fuel pool, and in on-site dry storage if applicable, should also be considered in the accident management guidance. As large scale maintenance is frequently carried out during planned shutdown states, the protection of workers should be a high priority of accident management.”

SSG-54 3.105:
“All significant sources of radioactive material in the plant, including the reactor core and spent fuel pools, and the occurrence of accidents in all relevant normal operating and shutdown states (including open reactor or open containment barriers) should be addressed.”

Therefore, the steps outlined earlier in this module must also consider these operating states and fuel locations.

During shutdown, there are two distinct periods: one with the RPV still closed and one with the RPV opened.

For the time the RPV is still closed, the SAMG will be closed to the at-power SAMG. For the time the RPV is open, different entry criteria may be needed. Because often the entry condition for the SAMG is linked to the Core Exit Temperature (CET), which is not available at an open RPV. In such condition, the containment radiation may be an appropriate entry condition, best preceded by an entry on low pool level.

A first priority in the shutdown mode is to stop all work and remove all people from working sites that may develop elevated radiation levels. As also the containment may be opened (hatch opened), a direct follow-up priority is to close the containment. Note that this may be a complex and time consuming period (~3 hours).

For the SFP, it may happen that it is located inside containment, which may then activate SAMG as in the case of an open RPV. Where it is located in an auxiliary building, entry into SAMG may be linked to radiation levels, best preceded by an entry on low pool level.

Available strategies have been discussed in Module 2.