Induced nuclear reactions: processes – systems – and elements – Fuel component structure – Plural fuel segments or elements
Reexamination Certificate
1998-05-22
2001-07-17
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Fuel component structure
Plural fuel segments or elements
C376S170000, C376S267000, C376S419000, C376S447000
Reexamination Certificate
active
06263038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nuclear reactor core arrangement. More particularly, this invention relates to a nuclear reactor core arrangement which is adapted to combust plutonium along with uranium fuels and which utilizes a plurality of fuel assemblies that include mixed-oxide (MOX) fuel rods.
2. Discussion of the Related Art
The Department of Energy (DOE) has a large excess of plutonium resulting from the retirement of nuclear weapons and is considering options for its disposal. One option recommended by the National Academy of Sciences (NAS) for the disposal of the excess weapons-grade plutonium is conversion to spent fuel. In this approach, the excess weapons plutonium is converted to plutonium oxide (PuO
2
) and used in a mixed oxide (PuO
2
—UO
2
) form without reprocessing as fuel for existing nuclear reactors. This results in a spent fuel form which is “proliferation resistant” and that meets the “spent fuel standard” which is recommended by the NAS and which is being used by the DOE.
However, this mixed oxide (MOX) approach requires: 1) conservative, realistic core performance characteristics which are similar to those for current uranium core designs; 2) that the technique minimize licensing risks by avoiding any erosion of safety margins compared to those for currently licensed conventional uranium core designs; 3) that impacts on plant operation be minimized or totally avoided; and 4) that the energy extracted from the MOX fuel be maximized, thus providing the best economics.
Accordingly, ground rules were established by the DOE in light of the above objective. Namely, it is required that:
There is no mixing of MOX and burnable absorber in the same fuel rod. This allows manufacture of lead test assemblies in existing European MOX fuel fabrication facilities.
The fuel and core designs are developed using existing fuel and core design methodologies.
The equilibrium cycle core design characteristics using MOX matches current uranium oxide (UO
2
) reload core design characteristics as much as possible.
The cycle length of the MOX core design is essentially the same as that of the UO
2
core design.
There is no significant (if any) plant modifications necessary.
There is no significant impact on plant systems or operation.
Plant parameters should remain within existing plant technical specifications to the greatest extent possible.
Accordingly, there exists a need for a nuclear core arrangement which can used in existing facilities and which enables an acceptably high throughput of plutonium in the form of MOX, while remaining within the above constraints.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a novel core design that allows the use of mixed oxide (MOX) fuel containing weapons-grade plutonium in an existing nuclear reactor.
Another object of the present invention is to provide a novel reload core design that enables the disposal of a large quantity of weapons-grade material in existing nuclear reactors with no significant plant modifications or impact on plant systems or plant operation.
Another object of the present invention is to provide novel core designs for pressurized water reactor which uses MOX fuel, which maximizes the loading and throughput of weapons-grade plutonium and which is capable of disposing of a predetermined amount of weapons-grade plutonium in a given number of years of plant operation.
Another object of the present invention is to provide a novel reload MOX core design that has essentially the same cycle length and combustion characteristics as existing UO
2
core designs.
Another object of the present invention is to provide a novel core design that would ensure that fuel assemblies can be manufactured in existing MOX fuel fabrication facilities and meet the requirement that the MOX and a burnable absorber are not present in the same fuel rod.
Another object of the present invention is to provide a novel reload MOX core design that will allow plant parameters to remain within the existing plant technical specifications to the greatest extent possible.
In brief, in order to achieve the above objects and to use up the above mentioned stockpile of weapons-grade plutonium, the plutonium is converted into a mixed oxide (MOX) fuel form wherein it can be disposed in a plurality of different fuel assembly designs. Depending on the equilibrium cycle that is required, a predetermined number of one or more of the fuel assembly types is selected and arranged in the core of the reactor in accordance with a selected loading schedule. Each of the fuel assemblies is designed to produce different combustion characteristics whereby the appropriate selection and disposition in the core enables the resulting equilibrium cycle to closely resemble that which is produced using conventional urania fuel. The arrangement of the MOX fuel and burnable absorber rods within each of the fuel assemblies, in combination with a selective control of the amount of plutonium which is contained in each of the MOX rods, is used to tailor the combustion characteristics of the assembly.
More specifically, a first aspect of the invention resides in a fuel assembly for use in a nuclear reactor comprising: a plurality of MOX fuel rods; and a plurality of burnable absorber rods; each of the MOX fuel rods and each of the burnable absorber rods being disposed at a predetermined location within the fuel rod assembly.
A second aspect of the invention resides in an equilibrium cycle core arrangement of a nuclear reactor comprising: a plurality of fuel assembly types, each type comprising: a plurality of MOX fuel rods, and a plurality of burnable absorber rods, each of the MOX fuel rods and each of the absorber rods being disposed at a predetermined location within a rod matrix for that type; wherein each fuel assembly type has a different number of MOX fuel rods and burnable absorber rods, respectively.
A further aspect of the invention resides in a nuclear reactor core comprising a first predetermined number of mixed oxide (MOX) fuel assemblies which are arranged in a predetermined pattern in the core; each of the fuel assemblies being selected from a plurality of different fuel assembly designs wherein the MOX fuel is arranged differently and which, when arranged in the predetermined pattern, combust to produce an equilibrium cycle which is essentially the same as an equilibrium cycle produced using fuel assemblies containing only urania fuel.
Another aspect of the invention comes in a method of fueling a nuclear reactor comprising the steps of: loading a first group of fresh unburnt MOX fuel rod assemblies into a first set of predetermined positions in a core of the reactor, in accordance with a predetermined location schedule; loading a second group of MOX fuel rod assemblies which have been burned once, into a second set of predetermined positions which are selectively arranged in the core with respect to the first set of predetermined positions, in accordance with the predetermined location schedule; and loading a third group of MOX fuel rod assemblies which have been burned twice, into a third set of predetermined positions which are selectively arranged in the core with respect to the first and second set of predetermined positions, in accordance with the predetermined location schedule.
An important feature of the above method comes in the step of selecting the first group of fuel rod assemblies so as to comprise one or more of a plurality of predetermined octantly symmetrical assembly designs which each contain different amounts of plutonium and/or wherein the plutonium is distributed between the fuel rods of the assembly in a manner wherein an equilibrium cycle for the core exhibits a predetermined relationship with a predetermined equilibrium cycle produced using urania fuel.
Another important feature of the above method comes in the step of distributing the amount of plutonium which is contained in the fuel rods of each of the plurality of octantly symmetrical assembly des
Kantrowitz Mark L.
Rosenstein Richard G.
Carone Michael J.
CE Nuclear Power LLC
Crenshaw, Jr. Henry T.
Kananen Ronald P.
Keith Jack
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