High bum-up core

PNC also developed a type of 316 stainless steel with significantly increased high temperature creep strength and low swelling properties by adding small amounts of phosphorus, boron, titanium and niobium to conventional SUS 316 stainless steel. The low-swelling PNC 316 steel used in Monju will be applicable to 90,000 MWd/t in the initial core and 130,000 MWd/t in a high bum-up core. It is a top performer compared with similar materials that have been developed around the world. A fuel pin behavior analysis code (CEDAR) was also developed by PNC to evaluate the behavior of the fuel pins in Monju. 

Fuel and Core Design -24M Fuel Cycle -High Bum-up Fuel -MOX Core Design - 18 Month fuel cycle - 30% MOX design cap. - Change to 24 Month Cycle if necessary - Long term R D item... 

The EFR core has been designed to have a high bum-up (20% heavy atoms) and long residence time in < der to minimise the fuel cycle cost and leacmr outage time fcH r elling. 

To suppress initial reactivity of the core, gadolinium (Gd203) is used in the fuel pellets as a burnable poison. The enrichment distribution in the CCR bundle is optimized to flatten the local power. The CCR core has several control cells where the control rods are inserted during operation. To minimize neutron leakage from the core, fuel assemblies with high bum-up fuel are shuffled to the periphery of the core. These design aspects are similar to the approach used in current BWRs. 

In order to confirm the irradiation performance and thus to anticipate the feasibility of reaching on fast core structures high bum-up and high temperature, 912Cr-ODS... 

The MBRU-12 has maintained a conservative approach, providing for the shuffling of fuel under a closed guard vessel cover, which could help achieve early market availability. The 4S reactor, however, incorporates a small-diameter core of high neutron leakage rate with moving reflector control of bum-up reactivity loss, as a way to assure negative sodium void worth under all conditions. The reflector in the 4S is located outside the core and the power control is executed via the feedwater control from the steam-water power circuit. Some further related R D is required on these features (ANNEX XIV). 

It contains two kinds of fuel assemblies with different plutonium enrichments, the more highly enriched core fuel assemblies being located on the outside to levelize the output power (Fig. 3.4). The initial bum-up will be 80,000 MWd/t (average for discharged fuel assemblies). 

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