ADVANCED STUDIES ON GAMMA BLINDNESS, HIGH RESOLUTION HYBRID MASS ALPHA STPECTROSCOPY/EXTRACTION AND NEUTRON DETECTION WITH CTMFDS

The primary focus of this thesis pertains to R&D results associated with deploying tensioned

metastable fluid detector (TMFD) technology for monitoring of spent nuclear fuel

(SNF) for actinide content from their neutron emissions while under extreme photon backgrounds

(> 150 Gy/h), as may be expected within a hotcell. Traditional state-of-the-art

neutron detectors such as 3He and BF3 based systems are well-known to be dysfunctional

under such conditions, despite having pulse-shaped discrimination capabilities that allow

them to differentiate photons vs. neutrons. The aim of this thesis was to test the ‘gamma

blind’ ability of the centrifugally tensioned metastable fluid detector (CTMFD) based system,

to monitor for actinide generated neutrons despite the anticipated high intensity gamma

background, a goal which was successfully accomplished. Methods, designs, and experimental

procedures are discussed for successful neutron monitoring from an Americium-Beryllium

neutron source, as well as results showing no hindrance to neutron detection capability at

modest negative pressure states through 150 Gy (15 kRad) accumulated gamma dose.

A secondary focus was the ability of the TMFD based systems to perform alpha spectroscopy

on closely separated (<10 keV) alpha particle emissions from 239Pu and 240Pu

isotopes. Due to the closely spearated alpha decay energies, this feat could previously only

be perfromed by tedious and expensive mass-spectrometry based systems. Instead, a wet

chemistry apporach for detecting trace (? 10−3 Bq/mL) quantity alpha radiation with high

alpha energy resolution (<10 keV) was developed and validated using the CTMFD system.

Using this technique, mixtures containing samples of 239Pu:240Pu with activity concentrations

ranging in ratio from 1:0 to 0:1 were able to be identified within ±12% accuracy.

Lastly, successful assessments were conducted for detecting neutron emissions from a 1

Ci Plutonium-Beryllium source under a variety of shielded configurations using a CTMFD

and a 3He based Ludlum 42-49BTM detector. Concrete, lead, and water shielding materials

of thicknesses ranging from 0 to ?30 cm were placed as shielding material, with the

CTMFD configured only for fast energy neutron detection. Monte Carlo N-Particle Transport

(MCNP) code-based simulations were performed for derivation of the neutron energy

spectrum incident on the detectors to compute sensitivity estimates. At 0.6 MPa (6 bar) negative pressure, the CTMFD was determined to offer up to 7 times higher sensitivity vs the

Ludlum 42-49B, though further increasing the negative pressure state to 1.1 MPA (11 bar)

exponentially increases the sensitivity to offer 100+ times higher sensitivity for the CTMFD

vs the Ludlum 42-49B.