EBR-II REACTOR PHYSICS BENCHMARK

In September of 2014, Dr. Pope was awarded a three-year $400,000 grant from the U.S. Department of Energy to prepare an Experimental Breeder Reactor II reactor physics benchmark evaluation. The project developed a reactor physics benchmark evaluation of the Experimental Breeder Reactor II (EBR-II) suitable for inclusion in the International Reactor Physics Experiment Evaluation Project (IRPhEP) handbook. EBR-II was a sodium-cooled, metal fueled, fast neutron spectrum reactor with a thermal power rating of 62.5 MW. The benchmark evaluation focused on the reactor core configuration associated with EBR-II Run 138B. This reactor configuration was selected for reactor physics benchmark evaluation because it was used for several important experiments associated with the Shutdown Heat Removal Test program. These tests investigated the behavior of the reactor under severe accident scenario conditions including loss of primary coolant flow without reactor scram and loss of reactor heat sink without reactor scram.

The two tests performed during EBR-II Run 138B were a loss of flow without SCRAM Test and a loss of heat sink without SCRAM Test.  The loss of flow test is done to test how the reactor would "coast down" with out SCRAMing in the event that we lost our pumps. The key steps in this test are to establish full power, insert special SCRAM protection for the test, bypass the loss of flow SCRAMs, and finally turn off the the pumps and see how the reactor acts. Fig. 2 is a graph of the temperature of the reactor as it is "coasting" back to operational temperatures.  This test showed part of the inherent safety of the reactor.

The loss of  heat sink test is to see how the reactor acts when the secondary loop stops moving. The secondary loop is there to take heat from the reactor and transfer that heat to an evaporator for the purpose of boiling water to create steam, as seen in Fig 4.  If the second loop stops flowing we lose the sink that sucks up a lot of the heat of the reactor.  The key steps in this test are to establish full power, "stop" flow in the secondary loop, and monitor the passive power reduction and the leveling of the tank temperature. Fig 3 shows the temperatures of verious parts of the tank and how they level off when we lose our heat sink. 

An MCNP6 model of the reactor has been assembled. The model is very detailed with each fuel element in the reactor individually described. The input file for the MCNP6 model used 267,521 lines. An in-house code was developed to prepare the input files, execute MCNP, and extract the results (MICKA). Fig 1 shows a cross section of the reactor MCNP6 model.

The benchmark was included in the International Reactor Physics Experiment Evaluation Project (IRPhEP) handbook.

Students who have worked on this project include Ed Lum, Bilguun Byambadorj, Shawn Seegmiller, Quinton Beaulieu, and Jordan Sheppard.