Delphi

Introduction

For educational, training and research purposes the Department of Reactor Physics of IRI (now known as the section PNR of the R3 department) built a subcritical assembly called Delphi. This facility consists of an acrylic air-filled vessel to store the fuel and a stainless steel vessel which is filled with purified water before the start of an experiment. From bottom to top the height of the facility reaches about 250 cm, which makes it necessary to manipulate the fuel when standing on the loading platform. A tailor-made handling tool makes it possible to load the fuel pins.
Delphi will be used to train reactor operators and students. Using two He-3 proportional counter tubes, they will measure fundamental reactor physics parameters of the assembly and compare these with theory. Besides that, Delphi will be used for research on reactivity measurement methods for Accelerator Driven Systems.

Facility description

1.

168 fuel pins made of 3.8% enriched UO2 with a total length of 66.5 cm and an active length of 44 cm. The pins are positioned in a square lattice of 13x13 positions, with the central position being occupied by a water-filled tube. The pitch between the fuel pins is 23 mm, the value at which keff reaches maximum of 0.92.

2.

Stainless steel vessel with an inner diameter of 100 cm.

3.

The 252Cf-neutron source placed in a plastic capsule is stored in a stainless steel box with paraffin and B4C grains. This source has an initial strength of 18.5 MBq corresponding to a neutron emission rate of 2.4x106 s-1 and a gamma-ray emission rate of 1.3x107 s-1. Before the start of an experiment a shielding plug is removed and the source tube is lifted pneumatically. When the vessel is filled with water the source capsule can be shot in and out with air pressure.

Results



These two graphs show the results of calculations with the Monte Carlo code MCNP. The upper plot shows the inverse of the multiplication rate as a function of the fuel loading, while the lower plot shows the corresponding multiplication factor obtained by k=1-1/M. Clearly the multiplication rate is very sensitive to the position of the detector in the assembly. The distances shown in the plots are measured between the bottom of the detector and the bottom of the active fuel. The thick red line in the right plot gives the integral keff obtained by a k-code calculation.
These two graphs show the results of calculations with the Monte Carlo code MCNP. The upper plot shows the inverse of the multiplication rate as a function of the fuel loading, while the lower plot shows the corresponding multiplication factor obtained by k=1-1/M. Clearly the multiplication rate is very sensitive to the position of the detector in the assembly. The distances shown in the plots are measured between the bottom of the detector and the bottom of the active fuel. The thick red line in the right plot gives the integral keff obtained by a k-code calculation.


The position HI67_166mm was used for loading up the full 168 fuel pins for the first time. The measured multiplication factor (kmeas) obtained from the multiplication rate M corresponds within 0.3% with the calculated multiplication factor. For the fully loaded assembly the final keff reaches 0.919±0.003.


This plot gives the results of a Feynman-alpha measurement at the same position as used for the first fuel loading (HI67_166mm).

First loading experiment

At March 9, 2004, around 11:20 am, the Reactor Physics department of IRI put into operation its new sub-critical zero-power reactor, called Delphi. Under supervision of the safety authorities KFD and several VIPs (Very Interested Persons) from IRI (see figure on the left) the authors fully loaded the assembly. Besides some large pieces that were constructed outside IRI, the whole facility was designed and built in-house. A real demonstration of the technical craftsmanship present at IRI back then, and present today at RID.

 

  

 

 

Photo Gallery

Photo Gallery Delphi

Video of Delphi (1)

Video of Delphi (2)

More information

Download the poster
Poster A4, in PDF format

Download the description of Delphi
IRI-131-2003-008, in PDF format

Contact Jan Leen Kloosterman
e-mail Jan Leen Kloosterman

 

Name author: Menno Blaauw
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