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Spectrum measurements in the ZENITH plutonium core 7 using a neutron chopper

Abstract

As part of the experimental programme on the first plutonium loading of ZENITH (Core 7) a series of measurements was carried out with the neutron chopper on a beam emerging from the core centre. The general experimental programme on the two ZENITH plutonium cores has been covered elsewhere. Core 7 had a carbon/Pu239 atomic ratio of 2666 and a steel/Pu239 ratio of 76.8, giving an absorption cross-section at 2200 m/sec. of 0.31 barns/carbon atom. The fuel was in the form of 'spikes' of 0.020 in. thick Pu/Al alloy sheathed in 0.020 in. aluminium, the isotopic composition of the plutonium being 97.4% Pu239, 2.55% Pu240 and 0.1% Pu241. The overall layout of the reactor core and reflector is shown in the vertical section through the reactor vessel and the plan view. The core consists of a vertical array of 235 cylindrical graphite sleeves of outer diameter 7.37 cm into each of which a cylindrical graphite box may be loaded. Sunning longitudinally inside the box are six parallel grooves which act as locations for the edges of either the Pu/Al spikes or graphite dummies of the same external dimensions. Each groove accommodates two spikes end-to-end, with a small graphite spacer between to  More>>
Authors:
Barclay, F R; Cameron, I R; Pitcher, H H.W.; Symons, C R [1] 
  1. General Reactor Physics Division, Atomic Energy Establishment, Winfrith, Dorchester, Dorset (United Kingdom)
Publication Date:
May 15, 1964
Product Type:
Technical Report
Report Number:
AEEW-R-374
Resource Relation:
Other Information: Country of input: International Atomic Energy Agency (IAEA); 10 refs, 17 figs, 2 tabs
Subject:
22 GENERAL STUDIES OF NUCLEAR REACTORS; ABSORPTION; ALUMINIUM; CYLINDRICAL CONFIGURATION; ENERGY SPECTRA; FUEL ELEMENTS; GRAPHITE; HEAT EXCHANGERS; HEAT TRANSFER; LENGTH; NEUTRON CHOPPERS; NEUTRONS; NITROGEN; PLUTONIUM; PLUTONIUM 239; PLUTONIUM 240; PLUTONIUM 241; REACTOR CORES; STAINLESS STEELS; WELDING
OSTI ID:
20885080
Research Organizations:
United Kingdom Atomic Energy Authority, Reactor Group, Winfrith (United Kingdom)
Country of Origin:
United Kingdom
Language:
English
Other Identifying Numbers:
TRN: GB07A0174050551
Availability:
Also available from H.M. Stationery Office
Submitting Site:
GBN
Size:
42 pages
Announcement Date:
Jul 14, 2007

Citation Formats

Barclay, F R, Cameron, I R, Pitcher, H H.W., and Symons, C R. Spectrum measurements in the ZENITH plutonium core 7 using a neutron chopper. United Kingdom: N. p., 1964. Web.
Barclay, F R, Cameron, I R, Pitcher, H H.W., & Symons, C R. Spectrum measurements in the ZENITH plutonium core 7 using a neutron chopper. United Kingdom.
Barclay, F R, Cameron, I R, Pitcher, H H.W., and Symons, C R. 1964. "Spectrum measurements in the ZENITH plutonium core 7 using a neutron chopper." United Kingdom.
@misc{etde_20885080,
title = {Spectrum measurements in the ZENITH plutonium core 7 using a neutron chopper}
author = {Barclay, F R, Cameron, I R, Pitcher, H H.W., and Symons, C R}
abstractNote = {As part of the experimental programme on the first plutonium loading of ZENITH (Core 7) a series of measurements was carried out with the neutron chopper on a beam emerging from the core centre. The general experimental programme on the two ZENITH plutonium cores has been covered elsewhere. Core 7 had a carbon/Pu239 atomic ratio of 2666 and a steel/Pu239 ratio of 76.8, giving an absorption cross-section at 2200 m/sec. of 0.31 barns/carbon atom. The fuel was in the form of 'spikes' of 0.020 in. thick Pu/Al alloy sheathed in 0.020 in. aluminium, the isotopic composition of the plutonium being 97.4% Pu239, 2.55% Pu240 and 0.1% Pu241. The overall layout of the reactor core and reflector is shown in the vertical section through the reactor vessel and the plan view. The core consists of a vertical array of 235 cylindrical graphite sleeves of outer diameter 7.37 cm into each of which a cylindrical graphite box may be loaded. Sunning longitudinally inside the box are six parallel grooves which act as locations for the edges of either the Pu/Al spikes or graphite dummies of the same external dimensions. Each groove accommodates two spikes end-to-end, with a small graphite spacer between to avoid welding together of the spike sheaths when heated. Lateral spacers of graphite or stainless steel fill the five spaces between the six spikes or dummies. The total length of the plutonium-loaded core region is 140 cm, the ends of the element forming graphite reflectors of length 53 cm. In Core 7 each fuel element contained 10 Pu-Al spikes. The fuel elements are arranged in a triangular lattice of pitch 7.62 cm to form the reactor core, of diameter 1.23 m. A radial graphite reflector approximately 1 metre thick surrounds the core and is separated from it by an annular lampblack thermal barrier, contained within graphite tiles, which reduces heat transfer from the core. The reactor can be heated by circulation of nitrogen through a 250 kW heater below the core. The nitrogen flows upwards through the core in the interstitial channels between the elements and then,after mixing with cooler nitrogen in a plenum above the core, flows down through channels in the side reflector. This heating system in principle permits independent variation of the core and side reflector temperatures. Although the plant is capable of operating at core temperatures of up to 800 deg. C, a restriction to 420 deg. C was imposed in the present experiments to avoid possible damage to the fuel. The theoretical treatment of the ZENITH plutonium cores relied on a calculation using the Winfrith DSN program to deal with the spatial and energy distribution of neutrons below 1.5 eV in the fuel cell. The comparison of the measured spectrum with that given by DSN provided a test of the method of calculation, and in particular of the graphite scattering model. The. detailed comparison with theory was complicated by the necessity of accounting adequately for the radial fine structure of the spectrum emergent from the source element, taking into consideration the spatial response function of the chopper and associated collimating system. Some consideration was given to the possibility of providing a source element of simpler geometry than the normal fuel element (e.g. a homogeneous cylindrical spine with fuel, absorber and moderator surrounded by an outer sleeve of graphite) but difficulty then arises in the specification of the fuel content of the spine region in order to match the absorption characteristics of the standard element. It was consequently decided to employ the normal heterogeneous source element and to use the theoretical model to predict the detailed structure of the emergent team. (author)}
place = {United Kingdom}
year = {1964}
month = {May}
}