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• Neutron Shielding

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• X-Ray Shielding
• Neutron Shielding
• MRI Shielding
• NDT Shielding
• Shielding Materials

Wardray Premise provide the complete analysis and solution of Neutron and Photon shielding problems for high energy linear accelerator facilities, from definition through design, construction and installation to final testing.

Premadex^® was developed in conjunction with the Health Protection Agency specifically for neutron shielding. Typical areas of application include Particle Accelerator Facilities, Neutron Source Containers, Glovebox Construction, Nuclear Facilities, Room-Scatter Attenuation and Civil Defence.

Based on an organo-lithium salt, it is very rich in hydrogen for the most efficient neutron moderation. The lithium content, which is distributed on a molecular level for maximum effect, is adequate to prevent the significant production of secondary gamma rays.

Premadex^® is a slightly waxy, lightweight solid material. It is non-flammable, has good ageing characteristics and can be cut to shape or poured molten into prefabricated shielding assemblies.

Premadex^® is an ideal shield wherever neutrons are found.

• Room-Scatter Attenuation
• Glove Box Construction
• Accelerator Facilities
• Neutron Source Containers
• Nuclear Facilities
• Availability
• Physical Properties
• Elemental Composition

Typical building materials reflect neutrons to a high degree. For example, approximately half the number of fast neutrons striking a concrete surface will be re-emitted.

This leads to a substantial build up of scattered neutrons in a room; the intensity being inversely proportional to the internal surface area.

An appropriate surface layer of Premadex^® in a concrete room reduces the scattered neutron dose rate to around one third of its original level.

Reference Sites

These are some of the major Neutron Shielding projects that Wardray Premise have undertaken for Linear Accelerator installations:

• Christie Hospital, Manchester (two projects)
• Coventry New Hospitals.
• Ipswich Hospital (two projects)
• Mid Kent Oncology Centre (two projects)
• Mount Vernon Hospital
• Norfolk and Norwich Hospital
• Beatson Oncology Centre, Glasgow
• Walsgrave Hospital, Coventry.

Where gloveboxes are intended for handling neutron emitting radioisotopes, especially for fissionable materials, consideration must be given not only to basic shielding performance of wall materials but also to the internal scattering characteristics.

Where a critical risk is present, a lower scattered flux means greater safety. Hence the performance of Premadex^® as a neutron shielding material is complemented by its low neutron reflectivity and good thermal neutron absorption.

Its choice for glovebox shielding also combines the important benefits of simple, reliable and economical shielding design.

Particle Accelerators are used increasingly in medicine, science and industry. High-energy electron linear accelerators and cyclotrons are routinely involved in radiotherapy, isotope production, activation analysis and form the basis of many research facilities.

Premadex^® can play an important role in the solution of all radiological problems arising from neutron production within accelerator facilities.

To control neutron leakage from treatment rooms, Premadex^® can be used to line the maze entrance replacing the need for a heavy shielding door. Alternatively, when a door is necessary it can be included in the design for neutron attenuation.

Premadex^® is the most cost-effective material available for the construction of lightweight transport and storage shielding containers for highly active neutron sources such as Americium Beryllium (α,n) and Californium-252 (sf).

Its use eliminates the problem of secondary gamma rays and allows gamma shielding to be concentrated at the core of the assembly. This can result in substantial reductions in the overall weight of neutron source containers.

In the oil industry, the non-flammable nature of Premadex^® is an important safety consideration. In the offshore environment, a lightweight Premadex^® container also provides significant handling benefits.

Completed Contracts

These are some of the contracts completed for neutron source storage containers:

• British Nuclear Fuels plc
• Health Protection Agency
• Ministry of Defence
• Atomic Energy Authority
• BP Chemical Limited
• Atomic Weapons Establishment, Aldermaston
• FW Frost Limited, Norwich
• Halliburton Manufacturing and Services Limited
• Reeves Technologies Limited
• Baker Hughes Inteq Limited

Premadex^® can contribute to the safety of nuclear fission reactors in many ways. Its high attenuation and total absorption of neutrons can lead to reductions in prompt secondary gamma ray fluxes and radioactivation levels.

Simple uses include sealing ducts and penetrations where neutron scattering can be a major problem. It also offers a cost effective solution to the optimal shielding of mobile reactors.

Premadex^® is manufactured as a liquid at 95° to 100°C and can be poured at the factory directly into suitable prepared assemblies, such as glovebox panels, neutron source containers and shielding doors. Alternatively, particularly large assemblies can be filled on site by arrangement.

It is also available in block form. Standard blocks 400mm x 300mm or 280mm x 280mm, either 50mm or 75mm thick. They are easy to trim or cut to shape. Blocks can be produced in non-standard sizes to suit individual requirements.

Physical Properties
Appearance	Opaque creamy white
Coefficient of Expansion (Vol)	2-3 x 10-3K-1
Texture	Slightly waxy solid
Thermal Conductivity	0.3-0.4 W m-1 K-1
Density	1.0 g cm-3
Resistance to Acid	Excellent
Melting Point	85-90° C
Toxicity	LD50 assessed as 15g kg-1
Fire Resistance	Non-flammable
Ageing	Contains bacteriocides and antioxidants for long term stability.
Heat of Combustion	22MJ kg-1

Element	Percentage by Weight	Concentration (Atoms cm-3)
Hydrogen	11.4	6.81 x 1022
Lithium[1]	1.3	0.11 x 1022
Oxygen	39.9	1.51 x 1022
Carbon	47.4	2.38 x 1022

 

Wardray Premise Ltd.
Hampton Court Estate, Summer Road,
Thames Ditton, Surrey.
KT7 0SP, United Kingdom