Assessment of the Fingerprinting Method for Verification of Spent Fuel in MACSTOR KN-400 CANDU Spent Fuel Dry Storage

摘要

Wolsong site in republic of Korea currently has four CANDU reactors. Spent fuel bundlesdischarged from the reactors are transferred to an interim dry storage facility after a few years ofcooling in the water pool. However, the site does not have enough space for further extension ofits existing interim storage facility. Hence, Korea Hydro and Nuclear Power has built a newmodular type of dry storage facility, MACSTOR KN-400, which has the capacity to store up to24000 CANDU spent fuel bundles. The safeguards regulations of the IAEA demand an effectivemethod of spent fuel verification at the MACSTOR KN-400 storage facility in the event of anyloss of continuity of knowledge. Central and corner structures of the MACSTOR KN-400 alongwith the re-verification tube were modeled using the radiation transport code, MCNP. Centraland corner structures have different types of re-verification systems. Both, gamma and neutronsimulations were carried out using these MCNP models developed for the MACSTOR KN-400.CANDU spent fuel bundles with a burnup of 7.5 GWD/t (burnt at specific power of 28.39 MW/t)and 10 years cooling time were considered for the radiation source term. MCNP gammatransportsimulations were done by including a CZT detector inside the re-verification tube.Gamma-transport simulations for different spent fuel diversion scenarios were carried out. It wasobserved that for diversion scenarios wherein most of the bundles are removed from the innerportions of the basket (opposite side of the collimator to the re-verification tube), it was difficultto conclude whether diversion has taken place based on the change in gamma radiation signals.Similarly neutron transport simulations were also carried out by including a helium-3 detectorinside the re-verification tube. Results obtained from neutron-transport simulations for variousspent fuel diversion scenarios were encouraging and indeed indicated higher sensitivity fordiversion of fuel bundles. The study concludes that as the fingerprinting method based ongamma signals alone does not adequately protect diversion of fuel bundles inside baskets,alternative fingerprinting method such as the one with neutron signals should be explored.