GB2144899A

GB2144899A - Nuclear fuel element

Info

Publication number: GB2144899A
Application number: GB08418457A
Authority: GB
Inventors: Geoffrey Constantine
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1983-08-10
Filing date: 1984-07-19
Publication date: 1985-03-13
Also published as: GB8321491D0; GB8418457D0

Abstract

The invention provides a nuclear fuel element 10 incorporating, at one end, a guide nose 16 adapted to locate a number of canisters 26 containing a parent isotope to be irradiated by neutrons. When the fuel element 10 is loaded into the core of a nuclear reactor the canisters 26 are thus situated outside the region of the core containing the fuel, and are irradiated by neutrons in the reflector region. The canisters 26 therefore have little effect on the reactivity of the reactor. The invention also provides a method of producing isotopes by neutron bombardment, in which the parent isotope is located at an end of a fuel element 10. <IMAGE>

Description

SPECIFICATION Nuclear fuel element This invention relates to nuclear fuel elements, and to a method for producing isotopes by neutron bombardment in a nuclear reactor.

It is known to make isotopes such as iridium-192m by neutron bombardment in a nuclear reactor, one or more fuel elements from the core of the reactor being replaced with canisters of a parent isotope to be irradiated, or canisters of the parent isotope being located within a tubular fuel element.

According to the present invention, in a method for producing isotopes by neutron bombardment of a parent isotope in a core of a thermal nuclear reactor, the parent isotope is located at an end of a fuel element of the nuclear reactor, so as to be located in the reflector region outside the region of the core in which the nuclear fuel is situated.

The present invention also provides a nuclear fuel element for a thermal nuclear reactor incorporating, at one end thereof, means for locating a canister of a parent isotope.

Preferably, the locating means locates a plurality of the canisters. the canisters being held in a twisted bundle configuration about the periphery of an end portion of the fuel element.

Conventional method for neutron irradiation of samples affect the neutron flux within the core of the reactor, but the present method has little effect on the flux within the core as it utilises the thermal neutrons in the reflector peak flux below the core. Thus there is little effect on the reactivity of the reactor.

The invention will now be further described by way of example only and with reference to the accompanying drawings. in which: Figure 1 shows a side view of a fuel element; Figure 2 shows. to a larger scale. a side view of an end portion of the fuel element of Fig. 1; and Figure 3 shows a side view. partly broken away, of the end portion of Fig. 2.

Referring to Fig. 1. a fuel element 10 for use in a materials testing nuclear reactor (not shown) comprises a tubular portion 1 2 containing concentric tubes (not shown) of nuclear fuel. At one end of the tubular portion 1 2 are perforations 14, and to the other end is riveted a guide nose 1 6 of tubular form.

with a shaped bore 1 7 (see Fig. 3), the tubular portion 1 2 abutting a circumferential shoulder 1 5 on the guide nose 1 6.

Use of the fuel element 10 is in most respects conventional, the guide nose 1 6 locating at the bottom of the reactor core (not shown), the fuel element 10 being oriented vertically, and heavy water coolant liquid being introduced through the bore 1 7 of the guide nose 1 6 into the tubular portion 1 2. to emerge through the perforations 1 4 at the upper end of the fuel element 10 The surface of the bore 1 7 of the guide nose 1 6 see Fig 3) is of conventional venturi shape to assist In providing a desired coolant flow through the tubular portion 1 2 Referring to Fig. 2 which shows the guide nose 1 6 of Fig. 1 disconnected from the tubular portion 1 2. the outside of the guide nose 1 6 defines an upper and a lower rounded circumferential ridge, 20 and 22 respectively, between which is a broad circumferential groove 24. and at the lower end of the guide nose 1 6 is an end flange 1 8 with an upper face 1 9.

Sixteen cylindrical sample tubes 26 (only nine are shown in Fig. 2) are arranged in a twisted bundle configuration around the groove 24, locating in longitudinally angled holes 28 and 30 respectively through the upper ridge 20 and the lower ridge 22, and the lower ends of the sample tubes 26 abutting the upper face 1 9 of the end flange 1 8.

The sample tubes 26 are arranged in four groups of four. the angular spacing in a radical plane between the adjacent tubes 26 of one group being 20', and between adjacent groups being 30 In the 301 gaps between the groups of sample tubes 26 are four radial holes 32 (only one is shown in Fig.

2) to provide communication between the groove 24 and the bore 1 7 of the guide nose 16.

Referring also to Fig. 3. in which the sample tubes 26 are omitted, grooves 34 are defined in the outside surface of the guide nose 1 6 above the upper ridge 20. aligned with the holes 28. to enable the sample tubes 26 to be inserted into the holes 28 and 30, and as shown in Fig. 2. two semi-circular retaining collars 36 are tack-welded immediately above the upper ridge 20 after insertion of the sample tubes 26. to prevent accidental removal of the sample tubes 26. Near each end of each semi-circular retaining collar 36 is a bowed portion 38. (only two are shown in Fig. 2) about half the height of the rest of the collar 36 and bowed outwardly from the semicircular shape. When it is desired to remove the sample tubes 26 from the guide nose 1 6.

a tool (not shown) can be inserted behind each one of the bowed portions 38 in turn, and the collar 36 levered away from the guide nose 16.

In use of the fuel element 10, the sample tubes 26 containing a parent isotope such as iridium-191 or thulium- 69 are assembled into the guide nose 16 as shown in Fig. 2.

The fuel element 10 is loaded into the core of the materials testing reactor and the reactor operated in the conventional manner, each fuel element 10 producing a thermal power of about 1 MW for a period of two of three months.

After sufficient burn-up of the uranium fuel has been achieved, the fuel element 10 is unioaded from the reactor and stored for a week. The guide nose 1 6 is then disconnected from the tubular portion 1 2 of the fuel element 1 0. the retaining collar 36 is levered off and the sample tubes 26 removed from the guide nose 16.

Whilst in the nuclear reactor the sample tubes 26 are irradiated by nuetrons with an intensity of about 10,4/cm'/sec. In the case of sample tubes 26 containing iridium-i 91, the iridium-191 undergoes a neutron capture reaction to form iridium-192m. which may be used as an X-ray source. with a half-life of 74 days. In addition. further capture reactions may produce iridium-194 which is an undesirable product. but which has a half-life of only 1 9 hours, and so decays to insignificant levels during the one week storage period.

Irradiation of thulium-169 produces thu lium-170, which has a 1 28 day half-life.

It will be understood the rounded shape of the upper ridge 20 and the lower ridge 22 makes the fuel element 10 less likely to jam when inserted or removed from the reactor, but that the shapes of the upper ridge 20 and the lower ridge 22 may differ from that shown in the Figures.

It will be appreciated that the sample tubes 26 should be arranged in such a configuration as not to protrude outside the diameter of the tubular portion 1 2, and not to protrude into the bore 1 7 of the guide nose 1 6. and that the use of a twisted bundle configuration enables longer sample tubes 26 to be used than other configurations. The sample tubes 26 may however be arrange in a different configuration if desired.

The fuel element 10 has been described for use in the production of isotopes of iridium and of thulium, but may also be used in the production of other isotopes.

Claims

1. A method for producing isotopes by neutron bombardment of a parent isotope in a core of a thermal nuclear reactor, wherein the parent isotope is located at an end of a fuel element of the nuclear reactor. so as to be located in the reflector region outside the region of the core in which the nuclear fuel is situated.

2. A fuel element for a thermal nuclear reactor incorporating, at one end thereof, means for locating a canister of a parent isotope.

3. A fuel element as claimed in Claim 2, wherein the locating means locates a plurality of the canisters, the canisters being held in a twisted bundle configuration about the periphery of an end portion of the fuel element.

4. A method for producing isotopes substantially as hereinbefore described and with reference to Figs. 1, 2 and 3 of the accompanying drawings.

5. A fuel element substantially as hereinbefore described with reference to. and as shown in, Figs. 1, 2 and 3 of the accompany ing drawings.