Reactor Parameters from Neutron and Gamma-Ray Noise Measurements

Rossi-alpha auto- and cross-correlation measurements on a large subcritical assembly using an in-core neutron detector and in-core and ex-core photon detectors are reported. The correlation amplitude and the main relaxation constant were determined in each measurement. The relaxation constants ( = 4090 1/sec) and the nine relative correlation amplitudes obtained were used to determine four space damping factors and some basic parameters describing the sources of correlated fluctuations.By utilizing some basic fission parameters (⟨v⟩, ⟨v²⟩, spontaneous fission probability) and the effective multiplication factor (k = 0.788) from pulsed-neutron source measurements or from computations, estimates for the prompt-neutron lifetime (l = 53.2 µsec), the equivalent number of free neutrons (⟨y₀⟩= 5.24) in the reactor, the mean fission rate (α_f⟨y₀⟩ = 73 800 1/sec) and the efficiency (€_nl = 8.1 × 10^-4) of the neutron detector could further be determined.The results verify the applicability of the gamma observation technique in reactor noise measurements as a substitute and a complement to noise measurements via neutron detection.