Measurement of Effective Delayed Neutron Fraction of VHTRC-1 Core

The authors measured the kinetic parameter beta sub(eff)/ Lambda , where beta sub(eff) represents the effective delayed neutron fraction and A is the neutron generation time, using the pulsed neutron method at the critical state of the VHTRC-1 core. The discrepancy of beta sub(eff)/ Lambda between calculation and experiment was found to be 13%. To examine the cause of this discrepancy, beta sub(eff) was measured separately at the VHTRC-1 core by using a fuel compact-Mn compact substitution technique. Calculation of the beta sub(eff) was carried out using the SRAC code with ENDF/B-IV nuclear data library. The effect of delayed neutron fraction due to the fast neutron fission was evaluated from the calculation of beta sub(eff) by means of changing the value of delayed neutron fraction to zero in SRAC's user's data file. As a result, the influence of the effective delayed neutron fraction was only 15% for the beta sub(eff). It is concluded that the delayed neutron data in EWNDF/B-IV file are validated by this integral experiment.