Determination of large negative reactivity by integral versions of various experimental methods.

Abstract

The large negative reactivity is measured in Semi·Homogeneous Experimental facility (SHE). Experimental methods are Sjostrand's pulsed neutron, source multiplication and rod drop methods beside revised King-Simmons' pulsed neutron methods. Neutron detectors are placed at various points in the core region for multi-points measurement.Usual one-point reactor model analysis resulted in the reactivity values, strongly dependent on the detector position with the increase of subcriticality. In addition, disagreements between the used experimental methods are also pointed out.In order to overcome these difficulties due to the spatial higher harmonics and the kinetic distortion in the neutron flux distribution, an integral version analysis is applied, in which use is made of multi-points reactor model. In the analysis, space integration of the neutron counts obtained throughout the core region is made with weights of the adjoint function of fast neutrons, calculated using the two-or three-dimensional diffusion code. The negative reactivity values determined by the integral version analysis agreed well with each other within the uncertainty of -5% in the reactivity range down to -50 dollars.It is concluded that all the experimental methods are adequate for precise determination of the large negative reactivity of reactor provided that the integral version analysis is utilized or that correction is made for the change of the neutron generation time using precise calculation.

Effects of Spatial Harmonics on Thermal Neutron Spectra Measured by Time-of-Flight Method

“…A straight collimator of B 4 C consisting of a 80 em long resin path of 4 em inside diameter is placed in such position as to let only the reentrant hole be visible from the detector bank. This bank is made up of an array of four 2.54 em diameter 15 em active length stainless steel 3 He detectors (Reuter-Stokes P4-0806-264) filled to 10 atm.…”

Experimental Verification and Analysis of Neutron Streaming Effect through Void Holes for Control Rod Insertion in HTTR.

“…The holes were provided to simulate the parallel void holes of the control rod columns of the HTTR core. The void reactivity worths were determined by the revised King-Simmons' pulsed neutron method which was developed by some of the authors< 16 l. In this method, the reactivity values obtained by well-known King-Simmons' formula< 17 l is corrected for the change of the neutron generation time. Theoretical analysis was also performed with the SRAC code system.…”