Fuel bundle

Rodgers, J. T., and R. G. Rosehart, 1969, Turbulent Interchange Mixing in Fuel Bundles, Trans. Conf. Applied Mechanics, University of Waterloo, Waterloo, Canada. (App.)... 

Uranium dioxide for use in nuclear fuel must be produced to a stringent specification so that it can be pressed into pellets and sintered at high temperature in hydrogen to produce dimensionally stable, crack-free UO2 pellets with a density typically 97% of theoretical. The fuel pellets are loaded into zirconium alloy tubes, welded closed and assembled into fuel bundles. 

This paper is concerned primarily with the application of chemistry to the control of radioactive waste products from the use of nuclear energy. As far as immediate effects are concerned, nuclear power from uranium is a particularly clean energy source (1). The radioactive waste prpducts are well contained within the used fuel bundles. Since some constituents of the radioactive wastes take almost a thousand years to decay to an innocuous level and a few persist for many millennia, e.g. we have to ensure... 

Fuel Channel. A fuel channel encloses the fuel bundle. The combination of a fuel bundle and a fuel channel is called a fuel assembly. See Fig. 6,... 

The channel is a square-shaped tube fabricated from Zircaloy 4. The outer dimensions arc 5,518 inches (14 centimeters) by 5,518 inches (14 centimeters) by 166,9 inches (424 centimeters) long, The reusable channel makes a sliding seal lit on the lower tie plate surface. It is attached to the upper tic plate by the channel fastener assembly, consisting of a spring and a guide, and a cap screw secured by a lock washer. The fuel channels direct the core coolant flow through each fuel bundle and also serve to guide the control rods. 

The disposal concept is based on cooling of spent fuel bundles for 30-40 years whereafter they are encapsulated into iron-copper canisters. The canisters would be deposited into a network of tunnels, in crystalline bedrock at the depth of 400-700 meters, and isolated from the rock by a layer of bentonite clay. After operational period, all imdergroimd spaces would be backfilled and sealed and the above groimd buildings demolished. The disposal concept is illustrated in Fig. 1. 

However, the international developments in the fuel cycle area, such as partitioning and transmutation technology, are followed and regularly assessed in Finland. The long storage period before permanent disposal leaves the various spent fuel management options open. The disposal concept is retrievable, thus recovery of the disposed spent fuel bundles is feasible in case that imforeseen reasons for that emerge in a later phase. 

Fuel bundles have been declad by transverse sawing with a hacksaw blade operated under water to provide cooling and prevent zircaloy fires. The preferred saw consists of a hardened tool-steel cutting edge welded to a tough-steel blade [H2]. More fines are produced than in shearing. 

Figure 10.5 Stepped blade used for shearing metal-clad uranium oxide fuel bundles. (From J. T. Long, Engineering for Nuclear Fuel Reprocessing, Cordon Breach, New York, 1967, with permission.)...

D. C. Groeneveld and W. W. Yousef, Spacing Devices for Nuclear Fuel Bundles A Survey of Their Effect on CHF, Post CHF Heat Transfer and Pressure Drop, Proc. ANSIASMEINRC Information Topical Meeting on Nuclear Reactor Themtal-Hydraulics, Nuclear Regulatory Commission/CP-0014 (2) 1111-1130,1980. 

C) isostatic (100-300 MPa) conqtression to surround the fuel bundles by a homogoieous, dense ceramic material, like corundum (microcrystalline AI2O3) or graphite. Since corundum and gr hite are natural minerals, the long term resistance should be very high, even against water. 

The application of the mixed uranium-plutonium fuel in power reactors requires assurance of safe transport of semifinished items, fuel elements, and fuel bundles (FB). To research various aspects of safety, it is necessary to take into account that the thermal and radiation characteristics and criticality parameters of MOX fuel are higher than the characteristics of fuel on a basis of uranium dioxide. 

Sources of radiation in fresh fuel are plutonium isotopes, products of decay of the plutonium isotopes, and impurities of products of fission in the regenerated plutonium. As a result, the gamma and neutron radiation dose on a surface of fresh fuel bundles generated by fuel from weapon plutonium exceeds by more than an order of magnitude the appropriate dose capacity for FB from uranium fuel. Moreover, capacity of dose on a surface of FB with regenerated plutonium exceeds on an order of magnitude the dose capacity for FB with weapons plutonium. 

Besides, surfaces of FB and the fuel elements can be polluted by plutonium. The level of heat release for FB made of weapon plutonium is essentially higher than that for FB made from uranium (in the latter, heat release is practically absent). For example, heat release of FB of reactor BN-600 reaches 20 watts and that in FB of reactor VVER-1000 reaches 130 watts. The heat release of fuel bundles with regenerated or recycled reactor-grade plutonium is several times higher. 

Spent fuel bundles with fuel from power (i.e., reactor-grade) plutonium, which were stored for 1-3 years, are characterized by a heat release approximately 70% higher than those with uranium dioxides. The heat release from fuel bundles made of weapon plutonium is approximately 30% higher than that of FB with uranium [1]. 

To manufacture fuel bundles with mixed fuel, it is necessary to ensure transport of semifinished items (powder or tablets). The analysis performed of the fleet of casks in Russia determined that, among packages for transportation of semifinished items of MOX fuel, packages TUK-29 and TUK-30 have the most acceptable parameters. 

VVER-1000 REACTOR FUEL ELEMENTS AND FUEL BUNDLES... 

At the moment, there are no transport packages in Russia that are suitable for the transportation of fuel elements and fuel bundles of reactor VVER-1000 with fresh mixed fuel. VNIPIET has performed design studies for such packages and appropriate auxiliaries. The work was conducted in two directions ... 

Cask TK-S8 for transport of samples of fuel elements and fuel bundles (10-20 FBs/year) ... 

Transportation of fuel elements in both types of packages is carried out in a technological canister. Structure, size, and design of the canister are analogous to that of the fuel bundle. Capacity of the canister is up to 180 fuel elements or rods. 

Technologies of operation with both types of packages are similar to each other. Design of both packages presupposes remote loading and unloading of fuel bundles and the possibility of unloading them under water. 

Unloading of fresh MOX fuel bundles in nuclear power plants (NPP) can be carried out by various methods ... 

Unloading FBs without immersion of a package into a pool using a protective reloading device. The two last variants can be applied for loading of sample fuel bundles. 

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