Fuel rod cladding, fuel rod and fuel assembly

Abstract

Systems for controlling and protecting nuclear reactors. A drive of an emergency safety rod of a nuclear reactor includes an electric drive, a reduction gear, and a rack-and-pinion gear. The electric drive contains a contactless electric motor based on permanent magnets, which is installed in the housing of the electric drive with a motor rotor position sensor, and a reduction gear for changing the rate of rotation of the electric drive. A toothed rack is installed along the axis of the rack-and-pinion gear in order to provide for the reciprocating motion of a system absorber rod connected thereto. A toothed electromagnetic clutch having a contactless current supply is installed on an inner shaft of the rack-and-pinion gear, enabling the rigid and simultaneous mechanical coupling of half-couplings, and the drive contains a reverse-motion coupling, a rack-separation spring and toothed rack position sensors.

Claims

1. A fuel rod assembly, comprising: a fuel rod; wherein the fuel rod includes a cladding; wherein the cladding includes a weldless, solid-rolled tubular element with spiraled ribs located on an outer surface of the fuel rod and is made of chrome silicon steel with a ferrite grain size of less than 0.0336 mm; wherein an opening angle of each rib is between 30 and 40 and a cross-sectional shape of the rib is a trapezoid with rounded corners at a top portion of the trapezoid and with smoothed corners at a base portion of the trapezoid; wherein the fuel rod is sealed at ends thereof and nuclear fuel is placed inside the cladding; wherein each rib has a height of at least 0.75 mm and a wall thickness of a maximum of 0.6 mm; wherein the trapezoid has a curvature radius of 0.2-0.35 mm; wherein the trapezoid has a fillet radius of 0.55-0.9 mm; wherein the fuel rod assembly is operable to be used in a reactor with a heavy liquid metal coolant, wherein the heavy liquid metal coolant includes lead or a lead-bismuth mixture.

2. The fuel rod assembly according to claim 1, wherein the cladding is made of steel with a chromium content between 10 wt % and 12 wt % and a silicon content between 1.0 wt % and 1.3 wt %.

3. The fuel rod assembly according to claim 1, wherein the cladding has four spiraled ribs that are equally spaced apart.

Description

LIST OF FIGURES

(1) The claimed invention is illustrated by drawings, where FIG. 1 shows the cladding appearance, FIG. 2 shows the cladding cross-section, FIG. 3 shows the rib cross-section.

IMPLEMENTATION OF THE INVENTION

(2) The items are as follows:

(3) 1. FR cladding.

(4) 2. Spacing spiral ribs.

(5) 3. Rounded corner at the rib top.

(6) 4. Smoothed corner at the rib bottom.

(7) The cladding 1 (see FIG. 1-FIG. 2) is a solid-rolled tubular element with spacing spiral ribs 2 located on the outer surface of the cladding 1.

(8) The cladding 1 is made of chrome silicon steel of the ferritic-martensitic grade with ferrite grain size of not less than 7 under GOST 5639 and has an outer crest diameter between 9.8 mm and 13.5 mm, the thickness of the cladding is between 0.38 mm and 0.55 mm, the cladding internal diameter is between 7.2 mm and 11.2 mm, the inner and outer surface roughness does not exceed Ra=1.2 m under GOST 2789.

(9) In the preferred embodiments, steel 16H12MVSFBR-SH (EP823-SH) is used as the chrome silicon steel of ferritic-martensitic grade. This steel has the following composition, wt %: carbon 0.14-0.18, silicon 1.0-1.3, manganese 0.5-0.8, chrome 10.0-12.0, nickel 0.5-0.8, vanadium 0.2-0.4, molybdenum 0.6-0.9, tungsten 0.5-0.8, niobium 0.2-0.4, boron 0.006 (as per calculation), cerium <0.1 and the remainder is iron.

(10) In terms of service properties (high resistance to vacancy swelling, low rate of radiation creep, high corrosion resistance in lead-bismuth), steel EP823-SH is the most suitable material for FR claddings of reactors with a heavy liquid metal coolant.

(11) The number of ribs mat vary.

(12) In the preferred embodiment of the invention, the cladding includes 4 ribs.

(13) Each rib 2 (see FIG. 3) protrudes above the cladding and is a trapezoid with rounded peaks and rounded corners at the base 6 (fillet) in cross-section. The rib opening angle is between 22 and 40, in the most preferred embodiments, between 30 and 40.

(14) Such rib configuration ensures manufacturability of the FR cladding, allows to reduce the core hydraulic resistance and intensifies heat exchange processes due to the easier HLMC flow along the ribs. In addition, design of the ribs with rounded peaks and fillets at the interface with the cladding allows to decrease stress concentrations and risk of defects at the rib base due to the mode of production and subsequent operation of FR, and, therefore, to eliminate corrosion damage of FR.

(15) The preferred cladding parameters are as follows:

(16) cladding wall thickness of maximum 0.6 mm, preferably 0.4 mm;

(17) rib height 7 between 0.55 mm and 0.85 mm, preferably 0.75 mm;

(18) opening angle between 22 and 40, preferably 30;

(19) corner curvature radius 3 at the top 9 between 0.2 mm and 0.35 mm, preferably 0.2 mm;

(20) fillet radius 4 at the bottom between 0.55 mm and 0.9 mm, preferably 0.7 mm.

(21) Ribs 2 are equally spaced, each one is spiraled with a pitch between 450 mm and 1000 mm, preferably 750 mm. Preferably, the cladding 1 is made with left-hand winding of ribs.

EMBODIMENT EXAMPLE

(22) A tube with 4 spiral ribs was fabricated by cold rolling of billets made of steel EP823-SH for manufacture of the fuel claddings.

(23) The cladding crest diameter is 13.5 mm, cladding wall thickness is 0.4 mm, cladding inner diameter is 11.2 mm. The ribs have a height of 0.75 mm, rib half-height width is 0.75 mm, rib height-to-thickness ratio is 1.85 mm. The cross-section of the rib was a trapezoid with rounded corners at the trapezoid top with a curvature radius of 0.2 mm, fillet radius of 0.7 mm. The rib opening angle was 30. The ribs were spiraled with a pitch of 750 mm (left-hand winding).

(24) Nuclear fuel based on uranium dioxide was placed in the manufactured cladding and the manufactured FRs were sealed with upper and lower tail pieces (plugs).

(25) To complete the fuel assembly, the assembled FRs were installed in the frame structure with the spacing on a rib-to-rib basis and attached in the upper, intermediate and lower grid mounted on the frame structure. The resulting assembly was installed in the reactor.

(26) The invention allows to manufacture a cladding with ribs as a single unit, and to reduce the probability of defects in stress concentration spots, which ensures stable heat and corrosion resistance in contact with the HLMC at operating temperatures.

(27) The invention allows to implement spacing of adjacent fuel rods (rib-to-rib) between the upper and lower support (for FR) spacer grids of the FA, spacing with reflector and FA support elements (which allows to simplify the FA design) and to ensure long-term stability in the HLMC medium (lead, eutectic alloy of lead and bismuth), subject to appropriate HLMC process (about 75,000 hours), temperature and dose limits for FR cladding.