CA1100649A - Method for savings in nuclear reactors by using beryllium embedded fuels - Google Patents
Method for savings in nuclear reactors by using beryllium embedded fuelsInfo
- Publication number
- CA1100649A CA1100649A CA265,989A CA265989A CA1100649A CA 1100649 A CA1100649 A CA 1100649A CA 265989 A CA265989 A CA 265989A CA 1100649 A CA1100649 A CA 1100649A
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- CA
- Canada
- Prior art keywords
- beryllium
- fuel
- rod
- rods
- reactor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE:
The effect of the (n,2n) reactions of beryllium when exposed to fast neutrons having energies at or above the (n,2n) threshold for beryllium is utilized to achieve reactivi-ty increases with at least one beryllium rod properly embedded in a bundle-type fuel element. The reactivity increases are obtained by positioning the beryllium rod at regions of the reactor where the neutrons are fast with the amount of inserted beryllium being such that the volume ratio of beryllium to beryllium and fuel is of about 5.3% when the reactor is moderated with heavy water or the volume ratio of beryllium to fuel is of about 8.2% when the reactor is moderated with light water.
Such reactivity advantageously be employed to reduce the amount of heavy water moderator inventory in a heavy water reactor or to relax the requirement of uranium enrichment in a light water reactor.
The effect of the (n,2n) reactions of beryllium when exposed to fast neutrons having energies at or above the (n,2n) threshold for beryllium is utilized to achieve reactivi-ty increases with at least one beryllium rod properly embedded in a bundle-type fuel element. The reactivity increases are obtained by positioning the beryllium rod at regions of the reactor where the neutrons are fast with the amount of inserted beryllium being such that the volume ratio of beryllium to beryllium and fuel is of about 5.3% when the reactor is moderated with heavy water or the volume ratio of beryllium to fuel is of about 8.2% when the reactor is moderated with light water.
Such reactivity advantageously be employed to reduce the amount of heavy water moderator inventory in a heavy water reactor or to relax the requirement of uranium enrichment in a light water reactor.
Description
The present invention relates generally to a method for saving in nuclear reactors and more particularly to method by embedding or inserting beryllium (or its compounds) into the fuel bundle of nuclear reactors to reduce the in~entory of D2O
in a heavy water reactor or to relax the requirement of uranium enrichment in a light water reactor and the resulting fuel ele-ments.
Having low (n,2n) threshold and extremely small neutron capture cross sections, the beryllium can be used in a reactor as not only a good neutron moderator but also a fast neutron mul-- tiplier. With one or several beryllium rods properly embedded in a bundle-type fuel element at regions where the neutron spec trum is as hard ~or fast) as possible, the (n,2n) reactions in beryllium can be effectively utilized to take part of the neutron slowing down function and also to achieve some additional neutron multiplication. ~ecause of these kwo fast effects, the lattice pitch (and thus the D2O inventory) of a heavy water reactor fuel cell can be reduced by properly embedding beryllium rods in the uel without diminishing the neutron multiplication factor. In the case of light water reactors, a properly beryllium embedded fuel element of lower enriched uranium can be made to have the - same neutron multiplication as that of a higher enriched one.
Reactors, such as CANDU, employing heavy water modera-tion are attractive because of their ability to use natural ura-nium as the feed fuel. The lattice pitch needed for such D2O
reactors, however, is usually large as compa~ed to other types ;~
of reactors, resulting in a big core and large inventory of the heavy water moderator which is quite costly. A significant part of the capital cost of a heavy water reactor is for the D2~ in-ventory~
As for light water reactoxs, it is well known that only enriched uranium fuels can make the reactor critlcal.
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.
However, if the uranium enrichment of the fuel can be reduced without decreasing the overall neutron multiplication effect, the fuel cost of this type of reactors will be more economic than that of the existing ones.
The present invention proposes to properly embed a light element such as beryllium (or its compounds), which has low (n,2n) threshold and extremely small fast and thermal neutron capture cross sections with good neutron slowing down power~
in nuclear fuel bundles to partially slow down the fast neutrons by (n,2n) reactions in the beryllium before the neutrons trans-port into the moderator region and get thermalized there into thermal neutrons. One extra neutron is gained in the meantime from each of these reactions. Because of the fast e-Efect of beryllium and its negligible capture of both fast and thermal neutrons, the neutron multiplication factor of a nuclear fuel element can thus be enhanced by properly inserting beryllium rods into the fuel element. Since (n,2n) reactions can be induced only b~y neutrons having energies not less than the threshold, the beryllium rods should be placed at positions i~side the fuel bundle where the neutron spectrum is as hard as possible in order to effectively utilize the fast effects.
However, because of the inferior moderating power of Be as compared to D2O, it is necessary to take into consideration not only the position but also the amount of inserted beryllium in order to beneficially utilize the beryllium (n,2n) effects.
In a heavy water moderated reactor, this amount should be such that the volume ratio of beryllium to beryllium and fuel is of about 5.3%.
In a light water moderated reactor, this amount should be such that the volume ratio of beryllium to fuel is of about 8O2%.
In thedrawings:
; -2-.
.
Fig. 1 is a cross-sectional plan view of a typical fuel element used in the Douglas Point pressurized heavy water reactor (CANDU-PHW).
Fig. 2 is a modification of the fuel element of Figure 1 according to one aspect of the present invention.
Fig. 3 is a plot of the neutron multiplication factor versus lattice pitch for a Douglas Point pressurized heavy water reactor type (CANDU-PHW~ fuel element of Figures 1 and 2 . ,.~., , Fig. 4 is a graph showing the neutron multiplication factors when the coolant is changed from D20 to H20 for the , fuel element of Figure 2 and a similar fuel e~ement containing _ _ . . .
an unfuelled .
, . . .. ., ,; .. ... .
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, .. . .
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tubular central supporting rod (the data point in Fig. 4) -to simulate the fuel element used in a CANDU type boiling light water reactor tCANDU-BLW).
Fig. 5 is a cross~sectional plan view drawing of a fuel ele-ment as used in another CANDU-P~IW reactor, the Pickering Genera-ting Station, modified in accordance with the present invention.
Fig. 6 shows the reactivities of the fuel element of Figure 5 compared with that of a typical Pickering Gen~rating Station heavy water reactor type fuel element.
Fig. 7 is a cross-sectional plan view of a fuel element of the present invention for light water reactors.
Fig. 8 is a graph of reactivity versus uranium enrichment for the fuel element shown in Figure 7 with a square lattice pitch of 9.5 cm.
Fig. 3 shows the neutron multiplication factor versus latti-ce pitch as calculated by a Monte Carlo code, H~COR-SAFE, for a typical CANDU l9-rods fuel element (Fig. 1) used in the Douglas Point Nuclear Power Station in Canada~ In the original Douglas Point fuel element (Fig. 1). all 19 rods are made of natural UO2 with Zircaloy-2 cladding and the square lattice pitch is 22~86 cm. In the proposed fuel element of the present invention in-cluding a beryllium-containing rod (Fig. 2), the central rod is replaced by a Zircaloy~2 sheathed beryllium rod of the same siæe.
The square lattice pitch of the fuel element is varied. The cal-culated results as given in Fig. 3 show that the berryllium~embedd-ed fuel element of the present invention (Fi~, 2) with a pitch of 22 cm has about the same neutron multiplication value as that of the original Douglas Point fuel element (Fig. 1). A reduction of 0,86 cm in pitch here is equivalent to saving of about 9% of ~` 30 the D~O moderator inventory.
As a second example (not shown) of the use of an (n,2n) scatterer in the heavy water reactor fuel, the coolant of the 6~
above mentioned fuel element (of the type shown in Figure 1) is changed from D2O to H2O and the central fuel rod is replaced by an unfuelled tubular central supporting rod with the lattice pitch of the fuel element enlarged to about 27 cm to simulate a CANDU-BLW fuel such as that used in the Gentilly Nuclear Power Station in Canada. The reactivities calculated by Monte Carlo m thod for this fuel element with and without the central tubu-lar tie-rod replaced by a beryllium rod of the same size are shown in Figure 4. It may be seen from Figure 4 that by insert-in~ a beryllium rod in the center of the fuel element, the lat-tice pitch can be reduced by about 2 cm without a decrease in reactivity, thus giving a saving of approximately 16.5% of the D2O moderator inventory in this instance.
Fig 5 is a drawing of the CANDU 2~-pins fuel element as used in the Pickering Generating Station in Canada with twel-ve additional beryllium rods embedded at the positions shown.
From the calculated results of reactivity as given in Figure 6, it may be seen that with the twelve beryllium rods embedded in the fuel the pitch can be reduced from the original 28.58 cm to 27.4 cm without diminishing the reactivity of the original no-beryllium-embedded fuel. This, in turn~ yields a saving of about 9.78% of the D2O moderator inventory.
For light water reactors, in order to simplify the cal~
culations by Mo~te Carlo method, a concentrically arranged fuel element may be utilized~ Fig. 7 gives an example of the propo-sed LWR tlight water reactor) fuel element with beryllium rods inserted therein. Each fuel element consists of a bundle of 19 enrichod Uo2 fuel rods and 6 smaller beryllium rodsO Here, the fuel rod dimension was set to be the same as that of a typical boiling water reactor IBWR). To illustrate the results that can be obtained by inserting beryllium rods into the fuel ele-ment as shown in Figure 7, reactivity calculations wePe done .
for the fuel element contAining fuels with various uranium en-richment values and the results were plotted in Figure 8. The uranium enrichment chosen for ~he fuel element with the six beryllium rods removed was 1.95 weight percent of U which is typical for a boiling water reactor. A square lattice pitch of 9.5 cm was used in the Monte Carlo calculations here. It is seen from Figure 8 that the uranium enrichment value of a fuel element containing beryllium rods as shown in Figure 7 can be lessened by about 0.1 weight percent as compared with and still yields the same neutron multiplication factor as compared to the fuel without beryllium embedded~
Although the fuel elements of Fig.'s 1, 2, 5 and 7 have been shown and described in terms of their components and cross-sectional plan views, it will be understood to those skilled in the art that the construction and structural details of the fuel elements and the reactors in which they are used is otherwise conventional and within the skill o the art.
The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms described, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention.
~ ' .~
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.
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in a heavy water reactor or to relax the requirement of uranium enrichment in a light water reactor and the resulting fuel ele-ments.
Having low (n,2n) threshold and extremely small neutron capture cross sections, the beryllium can be used in a reactor as not only a good neutron moderator but also a fast neutron mul-- tiplier. With one or several beryllium rods properly embedded in a bundle-type fuel element at regions where the neutron spec trum is as hard ~or fast) as possible, the (n,2n) reactions in beryllium can be effectively utilized to take part of the neutron slowing down function and also to achieve some additional neutron multiplication. ~ecause of these kwo fast effects, the lattice pitch (and thus the D2O inventory) of a heavy water reactor fuel cell can be reduced by properly embedding beryllium rods in the uel without diminishing the neutron multiplication factor. In the case of light water reactors, a properly beryllium embedded fuel element of lower enriched uranium can be made to have the - same neutron multiplication as that of a higher enriched one.
Reactors, such as CANDU, employing heavy water modera-tion are attractive because of their ability to use natural ura-nium as the feed fuel. The lattice pitch needed for such D2O
reactors, however, is usually large as compa~ed to other types ;~
of reactors, resulting in a big core and large inventory of the heavy water moderator which is quite costly. A significant part of the capital cost of a heavy water reactor is for the D2~ in-ventory~
As for light water reactoxs, it is well known that only enriched uranium fuels can make the reactor critlcal.
, ,~Y
.,: . ~;
.
However, if the uranium enrichment of the fuel can be reduced without decreasing the overall neutron multiplication effect, the fuel cost of this type of reactors will be more economic than that of the existing ones.
The present invention proposes to properly embed a light element such as beryllium (or its compounds), which has low (n,2n) threshold and extremely small fast and thermal neutron capture cross sections with good neutron slowing down power~
in nuclear fuel bundles to partially slow down the fast neutrons by (n,2n) reactions in the beryllium before the neutrons trans-port into the moderator region and get thermalized there into thermal neutrons. One extra neutron is gained in the meantime from each of these reactions. Because of the fast e-Efect of beryllium and its negligible capture of both fast and thermal neutrons, the neutron multiplication factor of a nuclear fuel element can thus be enhanced by properly inserting beryllium rods into the fuel element. Since (n,2n) reactions can be induced only b~y neutrons having energies not less than the threshold, the beryllium rods should be placed at positions i~side the fuel bundle where the neutron spectrum is as hard as possible in order to effectively utilize the fast effects.
However, because of the inferior moderating power of Be as compared to D2O, it is necessary to take into consideration not only the position but also the amount of inserted beryllium in order to beneficially utilize the beryllium (n,2n) effects.
In a heavy water moderated reactor, this amount should be such that the volume ratio of beryllium to beryllium and fuel is of about 5.3%.
In a light water moderated reactor, this amount should be such that the volume ratio of beryllium to fuel is of about 8O2%.
In thedrawings:
; -2-.
.
Fig. 1 is a cross-sectional plan view of a typical fuel element used in the Douglas Point pressurized heavy water reactor (CANDU-PHW).
Fig. 2 is a modification of the fuel element of Figure 1 according to one aspect of the present invention.
Fig. 3 is a plot of the neutron multiplication factor versus lattice pitch for a Douglas Point pressurized heavy water reactor type (CANDU-PHW~ fuel element of Figures 1 and 2 . ,.~., , Fig. 4 is a graph showing the neutron multiplication factors when the coolant is changed from D20 to H20 for the , fuel element of Figure 2 and a similar fuel e~ement containing _ _ . . .
an unfuelled .
, . . .. ., ,; .. ... .
,, .. , .. - . 1 _ .
, .. . .
, .
i ~ :
' ~ .
. , , , '~.' ,,, ~ . ' ' :
;4~
tubular central supporting rod (the data point in Fig. 4) -to simulate the fuel element used in a CANDU type boiling light water reactor tCANDU-BLW).
Fig. 5 is a cross~sectional plan view drawing of a fuel ele-ment as used in another CANDU-P~IW reactor, the Pickering Genera-ting Station, modified in accordance with the present invention.
Fig. 6 shows the reactivities of the fuel element of Figure 5 compared with that of a typical Pickering Gen~rating Station heavy water reactor type fuel element.
Fig. 7 is a cross-sectional plan view of a fuel element of the present invention for light water reactors.
Fig. 8 is a graph of reactivity versus uranium enrichment for the fuel element shown in Figure 7 with a square lattice pitch of 9.5 cm.
Fig. 3 shows the neutron multiplication factor versus latti-ce pitch as calculated by a Monte Carlo code, H~COR-SAFE, for a typical CANDU l9-rods fuel element (Fig. 1) used in the Douglas Point Nuclear Power Station in Canada~ In the original Douglas Point fuel element (Fig. 1). all 19 rods are made of natural UO2 with Zircaloy-2 cladding and the square lattice pitch is 22~86 cm. In the proposed fuel element of the present invention in-cluding a beryllium-containing rod (Fig. 2), the central rod is replaced by a Zircaloy~2 sheathed beryllium rod of the same siæe.
The square lattice pitch of the fuel element is varied. The cal-culated results as given in Fig. 3 show that the berryllium~embedd-ed fuel element of the present invention (Fi~, 2) with a pitch of 22 cm has about the same neutron multiplication value as that of the original Douglas Point fuel element (Fig. 1). A reduction of 0,86 cm in pitch here is equivalent to saving of about 9% of ~` 30 the D~O moderator inventory.
As a second example (not shown) of the use of an (n,2n) scatterer in the heavy water reactor fuel, the coolant of the 6~
above mentioned fuel element (of the type shown in Figure 1) is changed from D2O to H2O and the central fuel rod is replaced by an unfuelled tubular central supporting rod with the lattice pitch of the fuel element enlarged to about 27 cm to simulate a CANDU-BLW fuel such as that used in the Gentilly Nuclear Power Station in Canada. The reactivities calculated by Monte Carlo m thod for this fuel element with and without the central tubu-lar tie-rod replaced by a beryllium rod of the same size are shown in Figure 4. It may be seen from Figure 4 that by insert-in~ a beryllium rod in the center of the fuel element, the lat-tice pitch can be reduced by about 2 cm without a decrease in reactivity, thus giving a saving of approximately 16.5% of the D2O moderator inventory in this instance.
Fig 5 is a drawing of the CANDU 2~-pins fuel element as used in the Pickering Generating Station in Canada with twel-ve additional beryllium rods embedded at the positions shown.
From the calculated results of reactivity as given in Figure 6, it may be seen that with the twelve beryllium rods embedded in the fuel the pitch can be reduced from the original 28.58 cm to 27.4 cm without diminishing the reactivity of the original no-beryllium-embedded fuel. This, in turn~ yields a saving of about 9.78% of the D2O moderator inventory.
For light water reactors, in order to simplify the cal~
culations by Mo~te Carlo method, a concentrically arranged fuel element may be utilized~ Fig. 7 gives an example of the propo-sed LWR tlight water reactor) fuel element with beryllium rods inserted therein. Each fuel element consists of a bundle of 19 enrichod Uo2 fuel rods and 6 smaller beryllium rodsO Here, the fuel rod dimension was set to be the same as that of a typical boiling water reactor IBWR). To illustrate the results that can be obtained by inserting beryllium rods into the fuel ele-ment as shown in Figure 7, reactivity calculations wePe done .
for the fuel element contAining fuels with various uranium en-richment values and the results were plotted in Figure 8. The uranium enrichment chosen for ~he fuel element with the six beryllium rods removed was 1.95 weight percent of U which is typical for a boiling water reactor. A square lattice pitch of 9.5 cm was used in the Monte Carlo calculations here. It is seen from Figure 8 that the uranium enrichment value of a fuel element containing beryllium rods as shown in Figure 7 can be lessened by about 0.1 weight percent as compared with and still yields the same neutron multiplication factor as compared to the fuel without beryllium embedded~
Although the fuel elements of Fig.'s 1, 2, 5 and 7 have been shown and described in terms of their components and cross-sectional plan views, it will be understood to those skilled in the art that the construction and structural details of the fuel elements and the reactors in which they are used is otherwise conventional and within the skill o the art.
The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms described, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention.
~ ' .~
:
.
3a . :
Claims (6)
1. In a heavy water moderated nuclear reactor fuelled with natural uranium and having rods of nuclear fuel arranged in a plurality of fuel bundles, the improvement comprising at least one beryllium-containing rod inserted into at least one fuel bundle and positioned at regions thereof where the neutrons are fast, with the amount of inserted beryllium being such that the volume ratio of beryllium to beryllium & fuel is of about 5.3%, so as to obtain a reactivity increase, such reactivity increase resulting from the effect of the (n,2n) reaction of beryllium when exposed to fast neutrons having energies at or above the (n,2n) threshold for beryllium, said effect slowing down the fast neutrons and achieving a gain in neutron mul-tiplication due to the release of one extra neutron from each (n,2n) reaction.
2. The heavy water moderated nuclear reactor of claim 1, wherein said at least one fuel bundle consists of 19 fuel rods with one rod in the center and has a predetermined lattice pitch of 22.86 centimeters, said central fuel rod being replaced by said at least one beryllium-containing rod, the lattice pitch of the resulting fuel bundle being thus reduced to 22 centimeters without substantially detrimentally affecting the neutron multiplication value of the reactor.
3. The heavy water moderated nuclear reactor of claim 1, wherein said at least one rod comprising beryllium is disposed in an interstitial space between the fuel rods to replace some D2O in said at least one fuel bundle and is so positioned therein as to obtain reactivity increase.
4. The heavy water moderated nuclear reactor of claim 1, wherein said reactor is cooled with light water (such as Gentilly-1) and said at least one fuel bundle contains 18 fuel rods about an unfuelled tubular central tie rod and has a predetermined lattice pitch of about 27 centimeters, said cen-tral unfuelled rod being replaced with said at least one beryl-lium-containing rod, the lattice pitch of the resulting fuel bundle being thus reduced to about 25 centimeters without sub-stantially detrimentally affecting the neutron multiplication value of the reactor.
5. In a light water moderated nuclear reactor having rods of nuclear fuel comprising enriched uranium arranged in a plurality of fuel bundles, the improvement comprising at least one beryllium-containing rod inserted into at least one fuel bundle at some light water region and positioned at regions thereof where the neutrons are fast with the amount of inserted beryllium being such that the volume ratio of beryllium to fuel is of about 8.2 % so as to obtain a reactivity increase, said reactivity increase resulting from the effect of the (n,2n) reaction of beryllium when exposed to fast neutrons having energies at or above the (n,2n) threshold for beryllium, said effect slowing down the fast neutrons and achieving a gain in neutron multiplication due to the release of one extra neutron from each (n,2n) reaction.
6. The light water moderated nuclear reactor of claim 5, wherein said fuel bundle consists of 19 fuel rods with one rod in the center, said fuel rod having a radius of 0.626 centimeter, and six beryllium-containing rods having a radius of 0.32 centimeter, said beryllium containing rods being inserted into six interstitial spaces between the fuel rods so as to obtain a reactivity increase.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA265,989A CA1100649A (en) | 1976-11-18 | 1976-11-18 | Method for savings in nuclear reactors by using beryllium embedded fuels |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA265,989A CA1100649A (en) | 1976-11-18 | 1976-11-18 | Method for savings in nuclear reactors by using beryllium embedded fuels |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1100649A true CA1100649A (en) | 1981-05-05 |
Family
ID=4107315
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA265,989A Expired CA1100649A (en) | 1976-11-18 | 1976-11-18 | Method for savings in nuclear reactors by using beryllium embedded fuels |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1100649A (en) |
-
1976
- 1976-11-18 CA CA265,989A patent/CA1100649A/en not_active Expired
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