CA2708902C - Candu fuel bundle loaded with burnable absorber - Google Patents

Candu fuel bundle loaded with burnable absorber Download PDF

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Publication number
CA2708902C
CA2708902C CA2708902A CA2708902A CA2708902C CA 2708902 C CA2708902 C CA 2708902C CA 2708902 A CA2708902 A CA 2708902A CA 2708902 A CA2708902 A CA 2708902A CA 2708902 C CA2708902 C CA 2708902C
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Prior art keywords
burnable absorber
fuel
power
center rod
er2c3
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CA2708902A
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French (fr)
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CA2708902A1 (en
Inventor
Gyuhong Roh
Joo Hwan Park
Won Young Kim
Jun Ho Bae
Yonghee Kim
Nam Zin Cho
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Korea Atomic Energy Research Institute KAERI
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Korea Atomic Energy Research Institute KAERI
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/30—Assemblies of a number of fuel elements in the form of a rigid unit
    • G21C3/32—Bundles of parallel pin-, rod-, or tube-shaped fuel elements
    • G21C3/326—Bundles of parallel pin-, rod-, or tube-shaped fuel elements comprising fuel elements of different composition; comprising, in addition to the fuel elements, other pin-, rod-, or tube-shaped elements, e.g. control rods, grid support rods, fertile rods, poison rods or dummy rods
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/02—Fuel elements
    • G21C3/28—Fuel elements with fissile or breeder material in solid form within a non-active casing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Monitoring And Testing Of Nuclear Reactors (AREA)

Abstract

Disclosed is a CANDU fuel bundle loaded with a burnable absorber, wherein the fuel bundle which is suitable for use in a CANDU reactor loaded with fuel having an enrichment of 0.7 ~ 3.0 wt%
and in which a plurality of fuel rods is arranged in concentric rings around a center rod is loaded with the burnable absorber so as to have a negative power coefficient, thereby improving inherent safety of the reactor. The CANDU
fuel bundle loaded with the burnable absorber includes the center rod disposed at the center of the fuel bundle and loaded with the burnable absorber and the plurality of fuel rods arranged in concentric rings around the center rod.

Description

CANDU FUEL BUNDLE LOADED WITH BURNABLE ABSORBER
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a CANDU (CANada Deuterium Uranium) fuel bundle loaded with a burnable absorber, wherein the fuel bundle which is suitable for use in a CANDU reactor loaded with fuel having an enrichment of 0.7 ¨
3.0 wt% and in which a plurality of fuel rods is arranged in concentric rings around a center rod is configured so as to have a negative power coefficient, thereby ensuring inherent safety of the reactor.
Description of the Related Art In reactors, the power coefficient (PC) is defined as the reactivity change which depends on an increase in unit power, =
and is an important core physics parameter that dominates the inherent safety of the reactor.
The power coefficient mainly results from a combination of the fuel temperature coefficient (FTC) and the coolant temperature coefficient (CTC). As such, a negative power coefficient indicates that the reactivity decreases in proportion to an increase in power, and a positive power coefficient indicates that the reactivity increases in proportion to an increase in power and thus the reactor could be unstable.
Hence, all reactors should have a negative power coefficient of an appropriate level in order to ensure inherent safety. In the case of CANDU reactors which are currently available, because the coolant temperature coefficient is innately positive, the fuel temperature coefficient should be controlled to be negative while lowering the coolant temperature coefficient so as to attain the negative power coefficient.
FIG. 10 schematically shows a conventional 37-rod fuel bundle, and FIG. 11 schematically shows a conventional 43-rod fuel bundle.
The fuel used in the CANDU reactor may be the 37-rod fuel bundle 2 as shown in FIG. 10 or the 43-rod fuel bundle 3 as shown in FIG. 11, in which a plurality of fuel rods is arranged in concentric rings around a center rod.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind the problems encountered in the related art and the present invention is intended to provide a CANDU fuel bundle loaded with a burnable absorber, wherein the fuel bundle, which is suitable for use in a CANDU reactor loaded with fuel having an enrichment of 0.7 - 3.0 wt% and in which a plurality of fuel rods is arranged in concentric rings around a center rod, includes the burnable absorber so as to have a negative power coefficient, thereby improving inherent safety of the reactor.
A first aspect of the present invention provides a CANDU
fuel bundle loaded with a burnable absorber, the CANDU fuel bundle including a center rod disposed at its center and including a burnable absorber and fuel, which are homogeneously mixed together, and a plurality of fuel rods arranged in concentric rings around the center rod.
In this aspect, the burnable absorber may be erbium, erbia (Er203) or erbium carbide (Er2C3).
In this aspect, the burnable absorber may be at a concentration of 100 wt% or less.
A second aspect of the present invention provides a CANDU fuel bundle loaded with a burnable absorber, the CANDU
' fuel bundle including a center rod disposed at its center and including a burnable absorber and fuel, which are homogeneously mixed together, and a plurality of fuel rods arranged in concentric rings around the center rod, among which fuel rods arranged in the closest concentric ring to the center rod include a burnable absorber and fuel, which are homogeneously mixed together. As such, the burnable absorber may be erbium, erbia (Er203) or erbium carbide (Er2C3)=
In this aspect, the burnable absorber mixed in the center rod, and the burnable absorber mixed in the fuel rods arranged in the closest concentric ring to the center rod, each of which is mixed with the fuel, may be at the same concentration. As such, the burnable absorber may be at a concentration of 100 wt% or less.
In this aspect, the burnable absorber mixed in the center rod, and the burnable absorber mixed in the fuel rods arranged in the closest concentric ring to the center rod, each of which is mixed with the fuel, may be at different concentrations. As such, the burnable absorber mixed in the center rod may be at a concentration of 100 wt% or less, and the burnable absorber mixed in the fuel rods arranged in the closest concentric ring to the center rod may be at a concentration of 100 wt% or less.
A third aspect of the present invention provides a CANDU
fuel bundle loaded with a burnable absorber, the CANDU fuel bundle including a center rod disposed at its center and including a core portion including a burnable absorber and a cylindrical sheath portion including fuel, and a plurality of fuel rods arranged in concentric rings around the center rod.
As such, the burnable absorber may be erbium, erbia (Er203) or erbium carbide (Er2C3).
In this aspect, the radius of the burnable absorber may be equal to or less than the radius of the fuel rods.
A fourth aspect of the present invention provides a CANDU
fuel bundle loaded with a burnable absorber, the CANDU fuel bundle including a center rod disposed at its center and including a core portion including a burnable absorber and a cylindrical sheath portion including the burnable absorber and fuel, which are homogeneously mixed together, and a plurality of fuel rods arranged in concentric rings around the center rod. As such, the burnable absorber may be erbium, erbia (Er203) or erbium carbide (Er2C3). The burnable absorber may be at a concentration of 100 wt% or less, and the radius of the burnable absorber may be equal to or less than the radius of the fuel rods.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 schematically shows a CANDU fuel bundle loaded with a burnable absorber, according to a first embodiment of the present invention;
FIGS. 2A to 2F show changes in the power coefficient at medium burnup of the CANDU fuel bundle loaded with the burnable absorber according to the first embodiment of the present invention;
FIG. 3 schematically shows a CANDU fuel bundle loaded with a burnable absorber, according to a second embodiment of the present invention;
FIGS. 4A to 4F show changes in the power coefficient at medium burnup when the burnable absorber is used at the same concentration in the CANDU fuel bundle loaded with the burnable absorber according to the second embodiment of the present invention;
FIGS. 5A and 5B show changes in the power coefficient at medium burnup when the burnable absorber is used at different concentrations in the CANDU fuel bundle loaded with the burnable absorber according to the second embodiment of the present invention;
FIG. 6 schematically shows a CANDU fuel bundle loaded with a burnable absorber, according to a third embodiment of the present invention;
FIGS. 7A to 71 show changes in the power coefficient at medium burnup of the CANDU fuel bundle loaded with erbium, erbia (Er203) or erbium carbide (Er203) that is the burnable absorber, according to the third embodiment of the present invention;
FIG. 8 schematically shows a CANDU fuel bundle loaded with a burnable absorber, according to a fourth embodiment of the present invention;
FIGS. 9A and 9B show changes in the power coefficient at W medium burnup of the CANDU fuel bundle loaded with the burnable absorber, according to the fourth embodiment of the present invention;
FIG. 10 schematically shows a conventional 37-rod fuel bundle loaded with natural U; and FIG. 11 schematically shows a conventional 43-rod fuel bundle loaded with natural U, recycled U and low-enriched U.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a detailed description will be given of embodiments of the present invention. Throughout the drawings, the same reference numerals refer to the same or similar elements, and redundant descriptions are omitted. Also in the description, in the case where known techniques pertaining to the present invention are regarded as unnecessary because they would make the characteristics of the invention unclear and also for the sake of description, the detailed descriptions thereof may be omitted.
FIG. 1 schematically shows a CANDU fuel bundle loaded with a burnable absorber, according to a first embodiment of the present invention.
As shown in FIG. 1, the CANDU fuel bundle loaded with the burnable absorber, according to the first embodiment of the present invention, includes a center rod 100 and a plurality W of fuel rods 200 arranged in concentric rings around the center rod 100.
The center rod 100, which is disposed at the center of the fuel bundle 1, may include a burnable absorber and fuel, which are homogeneously mixed together.
As such, the burnable absorber may be erbium (Er), erbia (Er203) or erbium carbide (Er2C3), and may be at a concentration of 100 wt% or less.
Meanwhile, the evaluation of the power coefficient may include lattice calculation using two-dimensional codes and core calculation using three-dimensional codes.
In the present invention, lattice calculation is carried out using the HELIOS-1.8 code developed by Studsvik Scanpower, and the library used is a nuclear cross-section library based on ENDF/B-VI in 190 neutron groups.
FIGS. 2A to 2F show changes in the power coefficient at , medium burnup of the CANDU fuel bundle loaded with the burnable absorber according to the first embodiment of the present invention.
As such, in a 43-rod fuel bundle which is a type of fuel bundle that is loadable into a CANDU reactor loaded with fuel having an enrichment of 0.7 wt%, 1.0 wt% or 3.0 wt%, when Er203 or Er2C3 that is the burnable absorber is homogeneously mixed with the fuel in the center rod 100, changes in the power coefficient are evaluated.
<TEST EXAMPLE 1-1>
The power coefficient at medium burnup depending on the amount of Er203 mixed with fuel having an enrichment of 0.7 wt%
is depicted in FIG. 2A.
Specifically, the power coefficient in the absence of the burnable absorber at 102.5% power is 0.0126 mk/% power, and the estimated discharge burnup is 6,580 MWd/tU.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 1.0 wt% Er203 results in the power coefficient being 0.0090 mk/% power and the estimated discharge burnup being 6,200 MWd/tU. Also, when about 2.0 wt%
Er203 is added, the power coefficient is 0.0036 mk/% power, and the estimated discharge burnup is 5,400 MWd/tU.
As mentioned above, in the case where the burnable absorber is homogeneously mixed in the center rod 100, the concentration of the useful burnable absorber (Er or Er203) may fall in the range of from 0 wt% to 2.0 wt%.
<TEST EXAMPLE 1-2>
The power coefficient at medium burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 0.7 wt%
is depicted in FIG. 2B.
Specifically, the power coefficient in the absence of the burnable absorber at 102.5% power is 0.0126 mk/% power, and W the estimated discharge burnup is 6,580 MWd/tU.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 1.0 wt% Er203 results in the power coefficient being 0.0090 mk/% power and the estimated discharge burnup being 5,780 MWd/tU. Also, when about 2.0 wt%
Er2C3 is added, the power coefficient is 0.0018 mk/% power, and the estimated discharge burnup is 4,870 MWd/tU.
As mentioned above, in the case where the burnable absorber is homogeneously mixed in the center rod 100, the concentration of the useful burnable absorber (Er2C3) may fall in the range of from 0 wt% to 2.0 wt%.
<TEST EXAMPLE 1-3>
The power coefficient at medium burnup depending on the amount of Er203 mixed with fuel having an enrichment of 1.0 wt%

is depicted in FIG. 2C.
Specifically, the power coefficient in the absence of the burnable absorber at 102.5% power is 0.0200 mk/% power, and the estimated discharge burnup is 16,350 MWd/tU.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 14 wt% Er203 results in the power coefficient being -0.0018 mk/% power and the estimated discharge burnup being 12,040 MWd/tU. Also, when about 100 M wt% Er203 is added, the power coefficient is -0.0344 mk/% power, and the estimated discharge burnup is 4,400 MWd/tU.
As mentioned above, in the case where the burnable absorber is homogeneously mixed in the center rod 100, the concentration of the useful burnable absorber (Er or Er203) may fall in the range of from 0 wt% to 100 wt%.
<TEST EXAMPLE 1-4>
The power coefficient at medium burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 1.0 wt%
is depicted in FIG. 20.
Specifically, the power coefficient in the absence of the burnable absorber at 102.5% power is 0.0200 mk/% power, and the estimated discharge burnup is 16,350 MWd/tU.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 14 wt% Er2C3 results in the power coefficient being -0.0018 mk/% power and the estimated discharge burnup being 11,900 MWd/tU. Also, when about 100 wt% Er2C3 is added, the power coefficient is -0.0362 mk/% power, and the estimated discharge burnup is 4,220 MWd/tU.
As mentioned above, in the case where the burnable absorber is homogeneously mixed in the center rod 100, the concentration of the useful burnable absorber (Er2C3) may fall in the range of from 0 wt% to 100 wt%.
<TEST EXAMPLE 1-5>
The power coefficient at medium burnup depending on the amount of Er203 mixed with fuel having an enrichment of 3.0 wt%
is depicted in FIG. 2E.
Specifically, the power coefficient in the absence of the burnable absorber at 102.5% power is 0.0053 mk/% power, and the estimated discharge burnup is 55,450 MWd/tU.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 25 wt% Er203 results in the power coefficient being -0.0071 mk/% power and the estimated discharge burnup being 51,290 MWd/tU. Also, when about 100 wt% Er203 is added, the power coefficient is -0.0190 mk/% power, and the estimated discharge burnup is 45,590 MWd/tU.
As mentioned above, in the case where the burnable absorber is homogeneously mixed in the center rod 100, the concentration of the useful burnable absorber (Er or Er203) may fall in the range of from 0 wt% to 100 wt%.
<TEST EXAMPLE 1-6>
The power coefficient at medium burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 3.0 wt%
is depicted in FIG. 2F.
Specifically, the power coefficient in the absence of the W burnable absorber at 102.5% power is 0.0053 mk/% power, and the estimated discharge burnup is 55,450 MWd/tU.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 25 wt% Er2C3 results in the power coefficient being -0.0071 mk/% power and the estimated discharge burnup being 51,120 MWd/tU. Also, when about 100 wt% Er2C3 is added, the power coefficient is -0.0190 mk/% power, and the estimated discharge burnup is 45,330 MWd/tU.
As mentioned above, in the case where the burnable absorber is homogenously mixed in the center rod 100, the concentration of the useful burnable absorber (Er2C3) may fall in the range of from 0 wt% to 100 wt%.
In addition, according to a second embodiment of the present invention, a CANDU fuel bundle loaded with a burnable absorber is specified below.

FIG. 3 schematically shows the CANDU fuel bundle loaded with the burnable absorber according to the second embodiment of the present invention.
As shown in FIG. 3, the CANDU fuel bundle loaded with the burnable absorber according to the second embodiment of the present invention includes a center rod 100, and a plurality of fuel rods 200 arranged in concentric rings around the center rod 100.
The center rod 100, which is disposed at the center of the fuel bundle 1, may include a burnable absorber and fuel, which are homogeneously mixed together.
As such, the burnable absorber mixed in the center rod 100 may be Er, Er203 or Er2C3.
Among the fuel rods 200, fuel rods 200 arranged in the closest concentric ring to the center rod 100, namely, fuel rods 200 of the first ring may include a burnable absorber and fuel, which are homogeneously mixed together.
The burnable absorber mixed in such fuel rods 200 may be Er, Er203 or Er2C3, which is the same as the burnable absorber mixed in the center rod 100.
Furthermore, the burnable absorber mixed in the center rod 100 and the burnable absorber mixed in the fuel rods 200 of the first ring, each of which is mixed with the fuel, may be at the same concentration. As such, the concentration of both the burnable absorber mixed in the center rod 100 and the . =
burnable absorber mixed in the fuel rods 200 of the first ring may be 100 wt% or less.
FIGS. 4A to 4F show changes in the power coefficient at medium burnup when the burnable absorber is used at the same concentration in the CANDU fuel bundle loaded with the burnable absorber according to the second embodiment of the present invention.
As such, in a 43-rod fuel bundle which is a type of fuel bundle that is loadable into a CANDU reactor loaded with fuel M having an enrichment of 0.7 wt%, 1.0 wt% or 3.0 wt%, when Er203 or Er2C3 that is the burnable absorber, which is homogeneously mixed with the fuel in the center rod 100 and the fuel rods 200 arranged in the closest concentric ring to the center rod 100, namely, the fuel rods 200 of the first ring, is used at the same concentration, changes in the power coefficient are evaluated.
<TEST EXAMPLE 2-1>
The power coefficient at medium burnup depending on the amount of Er203 mixed with fuel having an enrichment of 0.7 wt%
is depicted in FIG. 4A.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 0.1 wt% Er203 results in the power coefficient at 102.5% power being 0.0108 mk/% power and the estimated discharge burnup being 5,950 MWd/tU. Also, when =
about 0.2 wt% Er203 is added, the power coefficient at 102.5%
power is 0.0036 mk/% power, and the estimated discharge burnup is 5,190 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at the same concentration, the concentration of the useful burnable absorber (Er or Er203) may fall in the range of from 0 wt% to 0.2 wt%.
<TEST EXAMPLE 2-2>
The power coefficient at medium burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 0.7 wt%
is depicted in FIG. 4B.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 0.1 wt% Er2C3 results in the power coefficient at 102.5% power being 0.0090 mk/% power and the estimated discharge burnup being 5,940 MWd/tU. Also, when about 0.2 wt% Er2C3 is added, the power coefficient at 102.5%
power is 0.0036 mk/% power, and the estimated discharge burnup is 5,140 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at the same . =
concentration, the concentration of the useful burnable absorber (Er2C3) may fall in the range of from 0 wt% to 0.2 wt%.
<TEST EXAMPLE 2-3>
The power coefficient at medium burnup depending on the amount of Er203 mixed with fuel having an enrichment of 1.0 wt%
is depicted in FIG. 4C.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 1.4 wt% Er203 results in the power coefficient at 102.5% power being -0.0018 mk/% power and the estimated discharge burnup being 12,120 MWd/tU.
Also, when about 2.5 wt% Er203 is added, the power coefficient at 102.5% power is -0.0270 mk/% power, and the estimated discharge burnup is 7,370 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at the same concentration, the concentration of the useful burnable absorber (Er or Er203) may fall in the range of from 0 wt% to 2.5 wt%.
<TEST EXAMPLE 2-4>
The power coefficient at medium burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 1.0 wt%

=
is depicted in FIG. 4D.
Because the power coefficient decreases in proportion to an increase in the concentration of the added burnable absorber, the addition of about 1.4 wt% Er2C3 results in the power coefficient at 102.5% power being -0.0036 mk/% power and the estimated discharge burnup being 11,960 MWd/tU.
Also, when about 2.6 wt% Er2C3 is added, the power coefficient at 102.5% power is -0.0325 mk/% power, and the estimated discharge burnup is 6,190 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at the same concentration, the concentration of the useful burnable absorber (Er2C3) may fall in the range of from 0 wt% to 2.6 wt%.
<TEST EXAMPLE 2-5>
The power coefficient at medium burnup depending on the amount of Er203 mixed with fuel having an enrichment of 3.0 wt%
is depicted in FIG. 4E.
When about 20 wt% Er203 is added, the power coefficient at 102.5% power is -0.0461 mk/% power, and the estimated discharge burnup is 28,820 MWd/tU. Also, when about 40 wt%
Er203 is added, the power coefficient at 102.5% power is -0.0500 mk/% power, and the estimated discharge burnup is 19,470 MWd/tU.

As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at the same concentration, the concentration of the useful burnable absorber (Er or Er203) may fall in the range of from 0 wt% to 100 wt%.
<TEST EXAMPLE 2-6>
The power coefficient at medium burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 3.0 wt%
is depicted in FIG. 4F.
When about 20 wt% Er2C3 is added, the power coefficient at 102.5% power is -0.0443 mk/% power, and the estimated discharge burnup is 28,090 MWd/tU. Also, when about 40 wt%
Er2C3 is added, the power coefficient at 102.5% power is -0.0517 mk/% power, and the estimated discharge burnup is 18,830 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at the same concentration, the concentration of the useful burnable absorber (Er2C3) may fall in the range of from 0 wt% to 100 wt%.
On the other hand, the burnable absorber mixed in the center rod 100 and the burnable absorber mixed in the fuel rods 200 arranged in the closest concentric ring to the center rod 100, namely, the fuel rods 200 of the first ring, each of which is mixed with the fuel, may be at different concentrations. As such, the concentration of the burnable absorber mixed in the center rod 100 may be 100 wt% or less, and the concentration of the burnable absorber mixed in the fuel rods 200 of the first ring may be 100 wt% or less.
As such, in a 43-rod fuel bundle which is a type of fuel bundle that is loadable into a CANDU reactor loaded with fuel having an enrichment of 0.7 wt%, 1.0 wt% or 3.0 wt%, when Er203 W or Er2C3 that is the burnable absorber, which is homogeneously mixed with the fuel in the center rod 100 and the fuel rods 200 arranged in the closest concentric ring to the center rod 100, namely, the fuel rods 200 of the first ring, is used at different concentrations, changes in the power coefficient are evaluated.
FIGS. 5A and 5B show changes in the power coefficient at medium burnup when the burnable absorber is used at different concentrations in the CANDU fuel bundle loaded with the burnable absorber according to the second embodiment of the present invention.
<TEST EXAMPLE 2-7>
The power coefficient at 102.5% power and the estimated discharge burnup depending on the amount of Er203 mixed with fuel having an enrichment of 0.7 wt% are shown in Table 1 below.

. =

Amount of Er203 Power Coefficient Estimated ____________________________________________ at 102.5% power Discharge Burnup Center Rod First Ring (mk/% power) (MWd/tU) 0.0 wt% 0.0 wt% 0.0126 6,580 0.0 wt% 0.24 wt% 0.0036 5,100 0.1 wt% 0.2 wt% 0.0036 5,290 1.0 wt% 0.1 wt% 0.0036 5,140 2.0 wt% 0.0 wt% 0.0036 5,400 As is apparent from this table, when the concentration of Er203 of the center rod 100 is 0.1 wt% and the concentration of Er203 of the fuel rods 200 of the first ring is 0.2 wt%, the power coefficient at 102.5% power is 0.0036 mk/% power and the estimated discharge burnup is 5,290 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at different concentrations, the concentration of the useful burnable absorber (Er or Er203) may range from 0 wt% to 2.0 Wt% for the center rod 100, and may range from 0 wt% to 0.24 wt% for the fuel rods 200 of the first ring.
<TEST EXAMPLE 2-8>
The power coefficient at 102.5% power and the estimated discharge burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 0.7 wt% are shown in Table 2 below.

Power Coefficient Estimated Amount of Er2C3 at 102.5% power Discharge Burnup Center Rod First Ring (mk/% power) (mwd/tU) 0.0 wt% 0.0 wt% _________________________ 0.0126 6,580 0.0 wt% 0.24 wt% 0.0036 5,050 0.1 wt% 0.2 wt% 0.0036 5,240 1.0 wt% 0.1 wt% 0.0036 5,080 2.0 wt% 0.0 wt% 0.0018 4,870 As is apparent from this table, when the concentration of Er2C3 of the center rod 100 is 0.1 wt% and the concentration of Er2C3 of the fuel rods 200 of the first ring is 0.2 wt%, the power coefficient at 102.5% power is 0.0036 mk/% power, and W the estimated discharge burnup is 5,240 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at different concentrations, the concentration of the useful burnable absorber (Er2C3) may range from 0 wt% to 2.0 wt% for the center rod 100, and may range from 0 wt% to 0.24 wt% for the fuel rods 200 of the first ring.
<TEST EXAMPLE 2-9>
The power coefficient at medium burnup depending on the amount of Er203 mixed with fuel having an enrichment of 1.0 wt%

is depicted in FIG. 5A.
FIG. 5A shows the power coefficient at medium burnup depending on changes in the concentration of Er203 of the fuel rods 200 of the first ring under conditions in which the concentration of Er203 of the center rod 100 is 0.6 wt%.
Because the power coefficient decreases in proportion to the increase in the concentration of the added burnable absorber, when the concentration of Er203 of the center rod 100 is 0.6 wt% and the concentration of Er203 of the first ring is 1.4 wt%, the power coefficient at 102.5% power is -0.0018 mk/%
power, and the estimated discharge burnup is 12,460 MWd/tU.
The power coefficient at 102.5% power and the estimated discharge burnup when Er203 that is the burnable absorber is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring are shown in Table 3 below.

Amount of Er203 Power Coefficient Estimated _____________________________________ at 102.5% power Discharge Burnup Center Rod First Ring (mk/% power) (MWd/tU) 0.0 wt% 0.0 wt% 0.0200 16,350 0.0 wt% 3.0 wt% -0.0307 6,540 0.6 wt% 1.4 wt% -0.0018 12,460 25.0 wt% 1.0 wt% -0.0325 5,590 100.0 wt% 0.0 wt% -0.0344 4,440 ___ As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 _ =
and the fuel rods 200 of the first ring is used at different concentrations, the concentration of the useful burnable absorber (Er or Er203) may range from 0 wt% to 100 wt% for the center rod 100, and may range from 0 wt% to 3 wt% for the fuel rods 200 of the first ring.
<TEST EXAMPLE 2-10>
The power coefficient at medium burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 1.0 wt%
is depicted in FIG. 5B.
FIG. 5B shows the power coefficient at medium burnup depending on changes in the concentration of Er2C3 of the fuel rods 200 of the first ring under conditions in which the concentration of Er2C3 of the center rod 100 is 0.6 wt%.
Because the power coefficient decreases in proportion to the increase in the concentration of the added burnable absorber, when the concentration of Er2C3 of the center rod 100 is 0.6 wt% and the concentration of Er2C3 of the first ring is 1.4 wt%, the power coefficient at 102.5% power is 0.00 mk/%
power, and the estimated discharge burnup is 12,310 MWd/tU.
The power coefficient at 102.5% power and the estimated discharge burnup when Er2C3 that is the burnable absorber is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring are shown in Table 4 below.

Power Coefficient Estimated Amount of Er2C3 at 102.5% power Discharge Burnup Center Rod First Ring (mk/% power) (MWd/tU) 0.0 wt% 0.0 wt% 0.0200 16,350 0.0 wt% 3.0 wt% -0.0343 5,910 0.6 wt% 1.4 wt% 0.0 12,310 25.0 wt% 1.0 wt% -0.0344 5,110 100.0 wt% 0.0 wt% -0.0362 4,220 As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at different concentrations, the concentration of the useful burnable absorber (Er203) may range from 0 wt% to 100 wt% for the center rod 100, and may range from 0 wt% to 3 wt% for the fuel rods 200 of the first ring.
<TEST EXAMPLE 2-11>
The power coefficient at 102.5% power and the estimated discharge burnup depending on the amount of Er203 mixed with fuel having an enrichment of 3.0 wt% are shown in Table 5 below.

Amount of Er203 Power Coefficient Estimated at 102.5% power Discharge Burnup Center Rod First Ring (mk/% power) (MWd/tU) 0.0 wt% 0.0 wt% 0.0053 55,450 0.0 wt% 100 wt% -0.0486 13,370 = -20 wt% 80 wt% -0.0522 14,210 40 wt% 60 wt% -0.0503 15,950 60 wt% 40 wt% -0.0499 19,150 =
80 wt% 20 wt% -0.0433 26,800 =
100 wt% 0.0 wt% -0.0190 45,590 As is apparent from this table, when the concentration of Er203 of the center rod 100 is 80 wt% and the concentration of Er203 of the first ring is 20 wt%, the power coefficient at 102.5% power is -0.0443 mk/% power, and the estimated discharge burnup is 26,800 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at different M concentrations, the concentration of the useful burnable absorber (Er203) may range from 0 wt% to 100 wt% for both the center rod 100 and the fuel rods 200 of the first ring.
<TEST EXAMPLE 2-12>
The power coefficient at 102.5% power and the estimated discharge burnup depending on the amount of Er2C3 mixed with fuel having an enrichment of 3.0 wt% are shown in Table 6 below.

Amount of Er2C3 Power Coefficient Estimated at 102.5% power Discharge Burnup Center Rod First Ring (mk/% power) (MWditU) 0.0 wt% 0.0 wt% 0.0053 55,450 0.0 wt% 100 wt% -0.0505 12,720 20 wt% 80 wt% -0.0504 13,600 40 wt% 60 wt% -0.0520 15,330 60 wt% 40 wt% -0.0517 18,600 80 wt% 10 wt% -0.0461 26,210 100 wt% 0.0 wt% -0.0190 45,330 As is apparent from this table, when the concentration of Er2C3 of the center rod 100 is 80 wt% and the concentration of Er2C3 of the first ring is 20 wt%, the power coefficient at 102.5% power is -0.0461 mk/% power, and the estimated discharge burnup is 26,210 MWd/tU.
As mentioned above, in the case where the burnable absorber which is homogeneously mixed in the center rod 100 and the fuel rods 200 of the first ring is used at different W concentrations, the concentration of the useful burnable absorber (Er2C3) may range from 0 wt% to 100 wt% for both the center rod 100 and the fuel rods 200 of the first ring.
In addition, according to a third embodiment of the present invention, a CANDU fuel bundle loaded with a burnable absorber is specified below.
FIG. 6 schematically shows the CANDU fuel bundle loaded with the burnable absorber, according to the third embodiment of the present invention.
As shown in FIG. 6, the CANDU fuel bundle loaded with the burnable absorber, according to the third embodiment of the present invention, includes a center rod 100, and a plurality of fuel rods 200 arranged in concentric rings around the center rod 100.
The center rod 100 includes a core portion 110 and a cylindrical sheath portion 120, and may be disposed at the center of the fuel bundle 1.
In the center rod 100, the core portion 110 may include a burnable absorber, and the sheath portion 120 may include fuel.
As such, the burnable absorber included in the core portion 110 may be Er, Er203 or Er2C3, and the radius of the burnable absorber may be equal to or less than that of the fuel rods.
FIGS. 7A to 71 show changes in the power coefficient at medium burnup of the CANDU fuel bundle loaded with Er, Er203 or Er2C3 that is the burnable absorber, according to the third embodiment of the present invention.
As such, in a 43-rod fuel bundle which is a type of fuel bundle that is loadable into a CANDU reactor loaded with fuel having an enrichment of 0.7 wt%, 1.0 wt% or 3.0 wt%, when Er203, Er or Er2C3 that is the burnable absorber is separately placed in the core portion 110 of the center rod 100 and the fuel is placed in the cylindrical sheath portion 120 of the center rod 100, changes in the power coefficient are evaluated.
<TEST EXAMPLE 3-1>
The power coefficient at medium burnup depending on the radius of Er203 inserted at the core portion 110 of the center rod 100 under conditions in which fuel having an enrichment of 0.7 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 7A.
Because the power coefficient decreases in proportion to an increase in the radius of the burnable absorber inserted at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.10 cm, the power coefficient at 102.5% power is 0.0054 mk/% power, and the estimated discharge burnup is 5,370 MWd/tU. Furthermore, when the radius of the burnable absorber is 0.13 cm, the power coefficient at 102.5%
power is 0.0 mk/% power, and the estimated discharge burnup is 2,270 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er203) may range from 0 cm to 0.13 cm.
<TEST EXAMPLE 3-2>
The power coefficient at medium burnup depending on the radius of Er inserted at the core portion 110 of the center rod 100 under conditions in which fuel having an enrichment of 0.7 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 7B.
Because the power coefficient decreases in proportion to the increase in the radius of the burnable absorber inserted at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.10 cm, the power coefficient at 102.5% power is 0.0054 mk/% power, and the estimated discharge burnup is 5,160 MWd/tU. Furthermore, when the radius of the burnable absorber is 0.12 cm, the power coefficient at 102.5%
power is 0.0018 mk/% power and the estimated discharge burnup is 4,560 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er) may W range from 0 cm to 0.12 cm.
<TEST EXAMPLE 3-3>
The power coefficient at medium burnup depending on the radius of Er2C3 inserted at the core portion 110 of the center 0 rod 100 under conditions in which fuel having an enrichment of 0.7 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 7C.
Because the power coefficient decreases in proportion to the increase in the radius of the burnable absorber inserted 20 at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.10 cm, the power coefficient at 102.5% power is 0.0054 mk/% power, and the estimated discharge burnup is 5,370 MWd/tU. Furthermore, when the radius of the burnable absorber is 0.13 cm, the power coefficient at 102.5%
25 power is 0.0 mk/% power, and the discharge burnup is estimated to be 2,190 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er2C3) may range from 0 cm to 0.13 cm.
<TEST EXAMPLE 3-4>
The power coefficient at medium burnup depending on the radius of Er203 inserted at the core portion 110 of the center rod 100 under conditions in which fuel having an enrichment of 1.0 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 7D.
Because the power coefficient decreases in proportion to the increase in the radius of the burnable absorber inserted at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.33 cm, the power coefficient at 102.5% power is -0.0018 mk/% power, and the estimated discharge burnup is 11,620 MWd/tU.
Furthermore, when the radius of the burnable absorber is equal to that of the center rod 100, the power coefficient at 102.5% power is -0.0344 mk/%
power, and the estimated discharge burnup is 4,440 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er203) may range from 0 cm to equal to or less than the radius of the fuel rods.
<TEST EXAMPLE 3-5>
The power coefficient at medium burnup depending on the radius of Er inserted at the core portion 110 of the center rod 100 under conditions in which fuel having an enrichment of 1.0 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 7E.
Because the power coefficient decreases in proportion to W the increase in the radius of the burnable absorber inserted at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.3 cm, the power coefficient at 102.5% power is 0.0 mk/% power, and the estimated discharge burnup is 11,890 MWd/tU. Furthermore, when the radius of the burnable absorber is equal to that of the center rod 100, the power coefficient at 102.5% power is -0.0381 mk/% power, and the estimated discharge burnup is 4,000 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er) may range from 0 cm to equal to or less than the radius of the fuel rods.
<TEST EXAMPLE 3-6>
The power coefficient at medium burnup depending on the . =
radius of Er2C3 inserted at the core portion 110 of the center rod 100 under conditions in which fuel having an enrichment of 1.0 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 7F.
Because the power coefficient decreases in proportion to the increase in the radius of the burnable absorber inserted at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.30 cm, the power coefficient at 102.5% power is 0.0018 mk/% power, and the estimated discharge W burnup is 12,080 MWd/tU. Furthermore, when the radius of the burnable absorber is equal to that of the center rod 100, the power coefficient at 102.5% power is -0.0362 mk/% power, and the estimated discharge burnup is 4,220 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er2C3) may range from 0 cm to equal to or less than the radius of the fuel rods.
<TEST EXAMPLE 3-7>
The power coefficient at medium burnup depending on the radius of Er203 inserted at the core portion 110 of the center rod 100 under conditions in which fuel having an enrichment of 3.0 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 7G.

Because the power coefficient decreases in proportion to the increase in the radius of the burnable absorber inserted at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.30 cm, the power coefficient at 102.5% power is -0.0035 mk/% power, and the estimated discharge bUrnup is 52,470 MWd/tU.
Furthermore, when the radius of the burnable absorber is equal to that of the center rod 100, the power coefficient at 102.5% power is -0.0190 mk/%
power, and the estimated discharge burnup is 45,590 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er203) may range from 0 cm to equal to or less than the radius of the fuel rods.
<TEST EXAMPLE 3-8>
The power coefficient at medium burnup depending on the radius of Er inserted at the core portion 110 of the center rod 100 under conditions in which fuel having an enrichment of 3.0 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 7H.
Because the power coefficient decreases in proportion to the increase in the radius of the burnable absorber inserted at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.3 cm, the power coefficient at 102.5% power is -0.0053 mk/% power, and the estimated discharge burnup is 52,010 MWd/tU.
Furthermore, when the radius of the burnable absorber is equal to that of the center rod 100, the power coefficient at 102.5% power is -0.0172 mk/%
power, and the estimated discharge burnup is 45,030 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er) may range from 0 cm to equal to or less than the radius of the W fuel rods.
<TEST EXAMPLE 3-9>
The power coefficient at medium burnup depending on the radius of Er2C3 inserted at the core portion 110 of the center rod 100 under conditions in which fuel having an enrichment of 3.0 wt% is placed in the sheath portion 120 of the center rod 100 is depicted in FIG. 71.
Because the power coefficient decreases in proportion to the increase in the radius of the burnable absorber inserted at the core portion 110 of the center rod 100, when the radius of the burnable absorber is 0.30 cm, the power coefficient at 102.5% power is -0.0053 mk/% power, and the estimated discharge burnup is 52,260 MWd/tU.
Furthermore, when the radius of the burnable absorber is equal to that of the center rod 100, the power coefficient at 102.5% power is -0.0190 mk/%
_ _ =
power, and the estimated discharge burnup is 45,330 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately placed in the core portion 110 of the center rod 100, the radius of the burnable absorber (Er2C3) may range from 0 cm to equal to or less than the radius of the fuel rods.
In addition, according to a fourth embodiment of the present invention, a CANDU fuel bundle loaded with a burnable absorber is specified below.
FIG. 8 schematically shows the CANDU fuel bundle loaded with the burnable absorber, according to the fourth embodiment of the present invention.
As shown in FIG. 8, the CANDU fuel bundle loaded with the burnable absorber according to the fourth embodiment of the present invention includes a center rod 100, and a plurality of fuel rods 200 arranged in concentric rings around the center rod 100.
The center rod 100 includes a core portion 110 and a cylindrical sheath portion 120, and may be disposed at the center of the fuel bundle 1.
In the center rod 100, the core portion 110 may include a burnable absorber, and the sheath portion 120 may include the burnable absorber and fuel, which are homogeneously mixed together.
As such, the burnable absorber, which is included in the core portion 110 and is mixed in the sheath portion 120, may be Er, Er203 or Er2C3. The burnable absorber may be at a concentration of 100 wt% or less, and may have a radius that is equal to or less than that of the fuel rods.
FIGS. 9A and 9B show changes in the power coefficient at medium burnup of the CANDU fuel bundle loaded with the burnable absorber according to the fourth embodiment of the present invention.
As such, in a 43-rod fuel bundle which is a type of fuel W bundle that is loadable into a CANDU reactor loaded with fuel having an enrichment of 0.7 wt%, 1.0 wt% or 3.0 wt%, when Er203, Er or Er2C3 that is the burnable absorber is separately placed in the core portion 110 of the center rod 100 and Er203, Er or Er2C3 that is the burnable absorber is homogeneously mixed with the fuel in the cylindrical sheath portion 120 of the center rod 100, changes in the power coefficient are evaluated.
<TEST EXAMPLE 4-1>
When Er or Er203 that is a burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er203 that is the burnable absorber is homogenously mixed with fuel having an enrichment of 0.7 wt% in the sheath portion 120 of the center rod 100, changes in the power coefficient are evaluated.
Specifically, the power coefficient varies depending on the concentration of the fuel homogeneously mixed in the sheath portion 120 of the center rod 100 and the radius of the burnable absorber separately placed in the core portion 110 of the center rod 100.
The power coefficient at medium burnup depending on the radius of Er or Er203 inserted at the core portion 110 of the center rod 100 is shown in Table 7 below.

Estimated Burnable Radius of Power Coefficient Amount of Er203 at Discharge Absorber at Core at 102.5% power Sheath portion Burnup Core portion portion (mk/% power) (MWd/tU)_ 1 0.0 cm 0.0 wt% 0.0126 6,580 Er203 0.01 cm 2.0 wt% 0.0036 5,390 1 Er203 0.12 cm 0.1 wt% 0.0036 4,740 0.0 cm 0.24 wt% 0.0036 5,100 Er203_ 0.13 cm 0.0 4,540 Er 0.01 cm 0.0 wt% 0.0054 5,160 Er 0.01 cm 2.0 wt% 0.0036 5,380 Er 0.12 cm 0.1 wt% 0.0 4,470 Er 0.12 am 0.0018 4,560 As is apparent from this table, when 2.0 wt% Er203 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber (Er203) of the core portion 110 is 0.01 cm, the power coefficient at 102.5% power at medium burnup is 0.0036 mk/% power, and the estimated discharge burnup is 5,390 MWd/tU. Furthermore, when 2.0 wt%
Er203 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber (Er) of the core portion 110 is 0.01 cm, the power coefficient at 102.5% power at medium burnup is 0.0036 mk/% power, and the estimated discharge burnup is 5,380 MWd/t0.
As mentioned above, in the case where the burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er203 that is the burnable absorber is homogeneously mixed with the fuel in the sheath portion 120 of the center rod 100, the concentration of Er203 may range from 0 wt% to 2.0 wt% and the radius of the burnable absorber (Er or Er203) of the core portion 110 may range from 0 cm to 0.12 cm.
<TEST EXAMPLE 4-2>
When Er2C3 that is a burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er2C3 that is the burnable absorber is homogenously mixed with fuel having an enrichment of 0.7 wt% in the sheath portion 120 of the center rod 100, changes in the power coefficient are evaluated.
The power coefficient at medium burnup depending on the radius of Er2C3 inserted at the core portion 110 of the center rod 100 is shown in Table 8 below.

Estimated Burnable Radius of Amount of Er2C3 Power Coefficient Absorber at Core Core at Sheath at 102.5% power Discharge Burnup portion portion portion (mk/% power) (MWd/tU) 0.0 cm 0.0 wt% 0.0126 6,580 = =
Er2C3 0.01 cm 2.0 wt% 0.0036 5,390 Er2C3 0.12 cm 0.1 wt% 0.0036 4,740 Er2C3 0.0 cm 0.24 wt% 0.0036 5,100 0.13 cm 0.0 4,540 As is apparent from this table, when 2.0 wt% Er2C3 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber of the core portion 110 is 0.01 cm, the power coefficient at 102.5% power at medium burnup is 0.0018 mk/% power, and the estimated discharge burnup is 4,850 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately inserted at the core portion 110 of the W center rod 100 and Er2C3 that is the burnable absorber is homogeneously mixed with the fuel in the sheath portion 120 of the center rod 100, the concentration of Er2C3 may range from 0 wt% to 2.0 wt% and the radius of the burnable absorber (Er2C3) of the core portion 110 may range from 0 cm to 0.12 cm.
<TEST EXAMPLE 4-3>
When Er or Er203 that is a burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er203 that is the burnable absorber is homogeneously mixed with fuel having an enrichment of 1.0 wt% in the sheath portion 120 of the center rod 100, changes in the power coefficient are evaluated.
The power coefficient at medium burnup depending on the -radius of Er or Er203 inserted at the core portion 110 of the center rod 100 is shown in FIG. 9A and Table 9 below.

Estimated Burnable Radius of Amount of Er203 Power Coefficient Absorber at Core Core at Sheath at 102.5% power Discharge Burnup portion portion portion (mk/% power) (MWd/tU) 0.0 cm 0.0 wt% 0.0200 16,350 Er203 0.29 cm 3.0 wt% -0.0005 11,810 Er203 0.25 cm 5.0 wt% -0.0007 12,080 0.0 cm 25.0 wt% 1 -0.0126 9,580 Er203 0.10 cm 25.0 wt% -0.0119 9,370 Er203 0.30 cm 25.0 wt% -0.0161 8,220 j Er203 0.63325 cm -0.0344 4,440 Er 0.30 cm 0.0 wt% 0.0 11,890 Er 0.30 cm 5.0 wt% -0.0072 10,910 Er 0.30 cm 25.0 wt% -0.0181 8,050 Er 0.12 cm -0.0381 4,000 When 5.0 wt% Er203 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber (Er203) of the core portion 110 is 0.25 cm, the power M coefficient at 102.5% power at medium burnup is -0.0007 mk/%
power, and the estimated discharge burnup is 12,080 MWd/tU.
Furthermore, when 5.0 wt% Er203 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber (Er) of the core portion 110 is 0.30 cm, the power coefficient at 102.5% power at medium burnup is -0.0072 mk/%
power, and the estimated discharge burnup is 10,910 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately inserted at the core portion 110 of the _ -center rod 100 and Er203 that is the burnable absorber is homogeneously mixed with the fuel in the sheath portion 120 of the center rod 100, the concentration of Er203 may range from 0 wt% to 100 wt% and the radius of the burnable absorber (Er or Er203) at the core portion 110 may range from 0 cm to equal to or less than the radius of the fuel rods.
<TEST EXAMPLE 4-4>
When Er2C3 that is a burnable absorber is separately W inserted at the core portion 110 of the center rod 100 and Er2C3 that is the burnable absorber is homogeneously mixed with fuel having an enrichment of 1.0 wt% in the sheath portion 120 of the center rod 100, changes in the power coefficient are evaluated.
The power coefficient at medium burnup depending on the radius of Er2C3 inserted at the core portion 110 of the center rod 100 is shown in FIG. 9B and Table 10 below.

Estimated Burnable Radius of Amount of Er2C3 Power Coefficient Discharge Absorber at Core Core at Sheath at 102.5% power Burnup portion portion portion (mk/% power) (MWd/tU) 0.0 cm 0.0 wt% 0.0200 16,350 Er2C3 0.30 cm 3.0 wt% -0.0036 11,450 Er2C3 0.25 cm 5.0 wt% 0.0 11,900 0.0 cm 25.0 wt% -0.0126 9,580 Er2C3 0.10 cm 25.0 wt% -0.0145 9,150 Er2C3 0.30 cm 25.0 wt% -0.0181 8,020 Er2C3 0.63325 cm -0.0362 4,220 Specifically, the power coefficient varies depending on the concentration of the fuel homogeneously mixed in the sheath portion 120 of the center rod 100 and the radius of the burnable absorber separately placed in the core portion 110 of the center rod 100.
When 5.0 wt% Er2C3 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber (Er2C3) of the core portion 110 is 0.25 cm, the power coefficient at 102.5% power at medium burnup is 0.0 mk/% power, and the estimated discharge burnup is 11,900 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er2C3 that is the burnable absorber is homogeneously mixed with the fuel in the sheath portion 120 of the center rod 100, the concentration of Er2C3 may range from 0 wt% to 100 wt% and the radius of the burnable absorber (Er2C3) may range from 0 cm to equal to or less than that of the fuel rods.
<TEST EXAMPLE 4-5>
When Er or Er203 that is a burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er203 that is the burnable absorber is homogeneously mixed with fuel having an enrichment of 3.0 wt% in the sheath portion 120 of the center rod 100, changes in the power coefficient are evaluated.
The power coefficient at medium burnup depending on the radius of Er or Er203 inserted at the core portion 110 of the center rod 100 is shown in Table 11 below.

Estimated Burnable Radius of Amount of Er203 Power Coefficient Absorber at Core Core at Sheath at 102.5% power Discharge Burnup portion portion portion (mk/% power) (MWd/tU) 0.0 cm 0.0 wt% ' 0.0053 55,450 Er203 0.30 cm 20 wt% -0.0088 50,150 Er203 0.30 cm 40 wt% I -0.0122 48,400 Er203 0.30 cm 60 wt% -0.0139 47,130 Er203 0.30 cm 80 wt% -0.0139 46,230 Er203 0.63325 an -0.0190 45,990 Er 0.30 cm 20 wt% -0.0070 49,800 Er 0.30 cm 40 wt% -0.0122 48,160 Er 0.30 cm 60 wt% -0.0157 46,960 Er 0.30 cm 80 wt% -0.0138 46,130 Er 0.63325 an -0.0172 45,030 Specifically, the power coefficient varies depending on the concentration of the fuel homogeneously mixed in the sheath portion 120 of the center rod 100 and the radius of the burnable absorber separately placed in the core portion 110 of the center rod 100.
When 20 wt% Er203 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber (Er203) of the core portion 110 is 0.30 cm, the power coefficient at 102.5% power at medium burnup is -0.0088 mk/%

power, and the estimated discharge burnup is 50,150 MWd/tU.
Furthermore, when 20 wt% Er203 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber (Er) of the core portion 110 is 0.30 cm, the power coefficient at 102.5% power at medium burnup is -0.0070 mk/%
power, and the estimated discharge burnup is 49,800 MWd/tU.
As mentioned above, in the case where the burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er203 that is the burnable absorber is homogeneously mixed with the fuel in the sheath portion 120 of the center rod 100, the concentration of Er203 may range from 0 wt% to 100 wt%, and the radius of the burnable absorber (Er or Er203) of the core portion 110 may range from 0 cm to equal to or less than the radius of the fuel rods.
<TEST EXAMPLE 4-6>
When Er2C3 that is a burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er2C3 that is the burnable absorber is homogeneously mixed with fuel having an enrichment of 3.0 wt% in the sheath portion 120 of the center rod 100, changes in the power coefficient are evaluated.
The power coefficient at medium burnup depending on the radius of Er2C3 inserted at the core portion 110 of the center rod 100 is shown in Table 12 below.

=

Estimated Burnable Radius of Amount of Er2C3 Power Coefficient Discharge Absorber at Core Core at Sheath at 102.5% power Burnup portion portion portion (mk/% power) (MWd/tU) 0.0 cm 0.0 wt% 0.0053 55,450 Er2C3 0.30 cm 20 wt% I -0.0088 49,900 Er2C3 0.30 cm 40 wt% -0.0122 48,130 Er2C3 0.30 cm 60 wt% -0.0156 46,840____ Er2C3 0.30 cm 80 wt% -0.0173 45,960 Er2C3 0.63325 cm -0.0190 45,330 Specifically, the power coefficient varies depending on the concentration of the fuel homogeneously mixed in the sheath portion 120 of the center rod 100 and the radius of the burnable absorber separately placed in the core portion 110 of the center rod 100.
When 20 wt% Er2C3 is homogeneously mixed with the fuel in the sheath portion 120 and the radius of the burnable absorber of the core portion 110 is 0.30 cm, the power coefficient at 102.5% power at medium burnup is -0.0088 mk/% power, and the estimated discharge burnup is 49,900 MWd/tU.
3 As mentioned above, in the case where the burnable absorber is separately inserted at the core portion 110 of the center rod 100 and Er2C3 that is the burnable absorber is homogeneously mixed with the fuel in the sheath portion 120 of the center rod 100, the concentration of Er2C3 may range from 0 wt% to 100 wt%, and the radius of the burnable absorber (Er2C3) of the core portion 110 may range from 0 cm to equal to or less than that of the fuel rods.
As described hereinbefore, the present invention provides a CANDU fuel bundle loaded with a burnable absorber.
According to the present invention, the use of the CANDU fuel bundle loaded with the burnable absorber results in the negative power coefficient of the CANDU reactor because of the burnable absorber included in the fuel bundle, thus improving inherent safety of the CANDU reactor.
Although the preferred embodiments of the present invention regarding the CANDU fuel bundle loaded with the burnable absorber have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (12)

1. A CANDU fuel bundle loaded with a burnable absorber, comprising:
a center rod disposed at a center of the fuel bundle and comprising a burnable absorber and fuel, which are homogeneously mixed together; and a plurality of fuel rods arranged in concentric rings around the center rod, wherein the burnable absorber is erbium, erbia (Er2O3) or erbium carbide (Er2C3).
2. The CANDU fuel bundle as set forth in claim 1, wherein the burnable absorber is at a concentration of 100 wt%
or less.
3. A CANDU fuel bundle loaded with a burnable absorber, comprising:
a center rod disposed at a center of the fuel bundle and comprising a burnable absorber and fuel, which are homogeneously mixed together; and a plurality of fuel rods arranged in concentric rings around the center rod, among which fuel rods arranged in the closest concentric ring to the center rod comprise a burnable absorber and fuel, which are homogeneously mixed together, wherein the burnable absorber is erbium, erbia (Er2O3) or erbium carbide (Er2C3).
4. The CANDU fuel bundle as set forth in claim 3, wherein the burnable absorber mixed in the center rod, and the burnable absorber mixed in the fuel rods arranged in the closest concentric ring to the center rod, each of which is mixed with the fuel, are at the same concentration.
5. The CANDU fuel bundle as set forth in claim 4, wherein the burnable absorber is at a concentration of 100 wt%
or less.
6. The CANDU fuel bundle as set forth in claim 3, wherein the burnable absorber mixed in the center rod, and the burnable absorber mixed in the fuel rods arranged in the closest concentric ring to the center rod, each of which is mixed with the fuel, are at different concentrations.
7. The CANDU fuel bundle as set forth in claim 6, wherein the burnable absorber mixed in the center rod is at a concentration of 100 wt% or less, and the burnable absorber mixed in the fuel rods arranged in the closest concentric ring to the center rod is at a concentration of 100 wt% or less.
8. A CANDU fuel bundle loaded with a burnable absorber, comprising:
a center rod disposed at a center of the fuel bundle and comprising a core portion including a burnable absorber and a cylindrical sheath portion including fuel; and a plurality of fuel rods arranged in concentric rings around the center rod, wherein the burnable absorber is erbium, erbia (Er2O3) or erbium carbide (Er2C3) .
9. The CANDU fuel bundle as set forth in claim 8, wherein the burnable absorber has a radius which is equal to or less than a radius of the fuel rods.
10. A CANDU fuel bundle loaded with a burnable absorber, comprising:
a center rod disposed at a center of the fuel bundle and comprising a core portion including a burnable absorber and a cylindrical sheath portion including the burnable absorber and fuel which are homogeneously mixed together; and a plurality of fuel rods arranged in concentric rings around the center rod, wherein the burnable absorber is erbium, erbia (Er2O3) or erbium carbide (Er2C3).
11. The CANDU fuel bundle as set forth in claim 10, wherein the burnable absorber is at a concentration of 100 wt%
or less.
12. The CANDU fuel bundle as set forth in claim 10, wherein the burnable absorber has a radius which is equal to or less than a radius of the fuel rods.
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US9799414B2 (en) 2010-09-03 2017-10-24 Atomic Energy Of Canada Limited Nuclear fuel bundle containing thorium and nuclear reactor comprising same
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KR101101975B1 (en) * 2010-12-07 2012-01-03 한국수력원자력 주식회사 Advanced fuel bundle in candu reactor
KR101292995B1 (en) * 2011-11-03 2013-08-02 한국수력원자력 주식회사 B4C Burnable Poison for High Temperature Gas-cooled Reactor
KR101533868B1 (en) * 2012-07-24 2015-07-06 한국원자력연구원 Fuel rod layout for candu fuel bundle
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