Monitoring the contents of a container by ultrasonic means

Induced nuclear reactions: processes – systems – and elements – Testing – sensing – measuring – or detecting a fission reactor... – Leak detection

Reexamination Certificate

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C376S251000, C376S252000, C376S253000, C376S272000, C376S450000, C376S245000, C073S024010, C073S570500, C073S597000, C073S602000, C073S603000, C073S632000

Reexamination Certificate

active

06680994

ABSTRACT:

BACKGROUND OF THE INVENTION
1. The Field of the Invention
This invention relates to apparatus and methods for monitoring, non-intrusively, the contents of a container containing fluid. The invention relates particularly, but not exclusively, to a method of non-intrusively monitoring the gaseous contents of a container in order, for example, to confirm the composition or purity of the gas within the container.
2. The Relevant Technology
It is often important to be able to monitor and confirm the composition or purity of gas contained within a container in order to monitor possible events, such as corrosion of the container, or to detect a leakage of the gas contained within the container or the leakage of a gas into the container. This may be particularly important when the gas or other contents of the container are toxic or in some other way harmful.
The invention therefore has particular application in, for example, the nuclear industry where the storage of radioactive substances requires continual or periodic monitoring of storage conditions to confirm continuous safe storage.
It may also be useful to non-intrusively monitor the contents of a container holding hazardous fluid or solid in the form of, for example, flammable, biological or pharmaceutical materials.
The invention may also be useful in monitoring the contents of containers in the vicinity of potentially hazardous processes such as in the operation of high voltage switch gear where gas within containers provides electrical insulation for the switchgear.
Known methods and apparatus for monitoring the gaseous contents of a container in order to confirm the composition of the gas within the container require penetration of the container in order to sample the gas contained within the container or in order to introduce a sensor into the container.
A problem with such known methods and apparatus is that because it is necessary to penetrate the container, there is a risk that leakages from the container occur around the area where penetration has taken place. Such systems, in seeking to establish that no leakage is occurring have to generate a potential site for leakage. This is technically undesirable and a potential problem with regulatory authorities.
Spent nuclear fuel is highly radioactive and it is necessary to appropriately deal with the fuel to ensure that the radioactive spent fuel does not contaminate the environment.
There is a requirement to be able to safely store spent nuclear fuel for an intermediate period known as “interim storage” which period may be prolonged if required, pending a decision as to whether reprocessing or disposal of the fuel is to be undertaken. Spent fuel is typically stored within a sealed container during such storage.
Typically, a container suitable for interim storage of spent fuel comprises a canister made of pressure vessel grade steel within which the spent fuel is held. The canister incorporates radioactive shielding in its lid. Once the canister has been filled with spent fuel, it is fitted with a lid and welded. The final welding of the lid seals the fuel. The lid of the canister will typically have a double seal. Prior to final sealing of the lid, the canister is filled with helium so that the spent fuel is held in a sealed container in a helium atmosphere.
To provide further radiation shielding the canister is placed in a concrete storage cask which is also fitted with a lid. The canister may be positioned within a concrete cask such that there is a space between the canister and the cask. The cask has inlet ports at the bottom and outlet ports at the top so that air may flow within the concrete cask in order to cool the canister.
The concrete outer cask provides shielding for both gamma and neutron radiation and protection against external hazards.
It is desirable to be able to, from time to time, monitor the contents of the canister in order to ensure that no untoward reactions are occurring within the canister. Such checks would also indicate the continued integrity of the fuel cladding in the canister.
A known method of monitoring spent fuel within a sealed canister or dual purpose metal cask involves opening the sealed canister to examine the fuel and the atmosphere surrounding the fuel known as the cover gas within the canister.
A disadvantage with this known method is that there is a risk of contamination to the surroundings and the facilities required are extensive and expensive. In addition, it is neither easy nor practical to be able to continuously monitor the canister and contents thereof using such a method.
A second known method of monitoring spent fuel within a canister is through use of an installed penetration by which it is possible to attach instrumentation to measure the pressure or quality of the cover gas over the spent fuel or the seal interspace gas. Measurement of such gases will provide information relating to the chemical composition of the cover gas in the canister.
A disadvantage of this known method is that the presence of the penetration prejudices or degrades the integrity of the containment barrier of the canister thus providing a potential leak which could lead to radioactive contamination.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a method for non-intrusively monitoring the contents of a sealed container comprising steps of:
transmitting an ultrasonic signal through a wall of the container into the contents of the container, receiving a signal from within the container, and analysing the received signal thereby deducing the composition of the contents of the container. This can thus be achieved without having to unseal the container.
According to a second aspect of the present invention there is provided apparatus for non-intrusively monitoring the contents of a sealed container the apparatus comprising:
transmitter means for transmitting an ultra-sonic signal through a wall of the container into the contents of the container;
receiving means for receiving a signal from within the container;
analysing means for analysing the received signal thereby deducing the composition of the contents of the container.
By means of the present invention it is possible to measure at intermittent intervals the quality of the atmosphere within a container.
The canister may be a substantially gas tight canister. The canister may be a metal canister, for instance of carbon steel or stainless steel.
The canister may be formed of a body and one or more lid elements. The one or more lid elements may be sealed to the body in use. Preferably a first lid is provided, together with a second outer lid. Preferably the first lid is received within the opening to the canister. The first and/or second lid may rest on one or more internal lips provided by the canister. The one or more lid elements may be welded to the body. The welds may provide a gas tight seal between a first lid and the canister and a second lid and the canister.
Preferably the canister has the general form of a right cylinder. Preferably the lids are provided on the top end of the canister, most preferably within the profile of the side wall of the canister, such that an end wall of the side wall is exposed.
Preferably the canister contains spent nuclear fuel rods or other irradiated nuclear material.
The canister may be provided with an internal gas pressure of greater than ambient, a positive pressure. The positive pressure may be at least 1.1 atmospheres, more preferably at least 1.2 atmospheres. Preferably the gas in the canister is substantially helium.
Preferably the canister is provided within a further container in use. The outer container may be a cask, for instance a concrete cask. Preferably the internal configuration of the outer container generally matches the outer configuration of the canister.
The outer container may be provided with a lid to seal the body of the container following insertion of the canister.
Preferably the outer container is provided with a supply of cooling gas to its interior. Preferably the cooling ga

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