Strategies for SGR

4.1.1. Design, design calculation, licensing

In SGRs, the tasks of special importance are design and design calculation. These activities apply for temporary equipment (such as SG rigging, devices for piping, etc.) and for permanent plant equipment including all related modifications (such as re-routing of piping, thermal insulation, steel liner of containment opening).

Piping design covered re-routing of feedwater and auxiliary feedwater, adaptation of instrumentation piping, FIG. 13. Narrow gap welding equipment installed at the mock-up.

main steam, blowdown, reactor temperature detection, drain, sampling. Design calculation basically covered analyses of structural, seismic and fluid dynamic data.

In parallel with basic engineering, the safety of all activities leading to modification of plant equipment or activities introducing a specific risk, such as handling, rigging, transportation, waste handling, is evaluated for review by the licensing authorities. These evaluations are in accordance with 10CFR50.59.

4.1.2. Scope and sequence of SGR

An SGR project includes all of the following activities [11–13]:

Fabrication of replacement SG components:

• Development of SGR technical specification;

• Consideration of potential power uprate or change in design concept, such as feeder ring versus preheater design, increased steam pressure or increased tube plugging margin;

• Consideration of design enhancements, such as electropolishing channel head, pre-service preservation of new tubing or capability for shell-side fluid circulation during wet lay-up and chemical cleaning;

• Consideration of instrumentation location changes, such as change in level tap height due to taller tube bundle;

• Design report documenting design analysis of replacement components in accordance with ASME code and/or other national jurisdictional authority;

• Design data report documenting physical capacities of replacement components (primary fluid mass, secondary fluid mass at various power levels, metal mass, weight, centre of gravity, etc.), which are used to assess impact on plant licensing basis;

• Transportation of SGR components to plant site, including ocean vessel, river barge, railroad or overland carrier.

Installation of SGR

• Metrology (usually performed with a laser templating system) of all required pipe cut locations, support interfaces and control point targets installed as 3-D reference locations, performed two cycles before replacement outage in order to impact replacement component design.

• Construction of permanent on-site storage building (‘mausoleum’) for original components (building might also function as temporary storage location for replacement components upon arrival).

• As built metrology of replacement components, construction of 3-D model, determination of critical interface coordinates, machine nozzle weld preparations on replacement components.

• Civil engineering ranging in scope from temporary movement of obstacles in component installation path to broaching concrete and steel containment building and major interior subcompartment walls.

• Creation of required site infrastructure, such as temporary cranes, lay-down platforms in containment, processing facilities for exceptionally large site labour force, etc.

• Cutting reactor coolant piping, main steam piping, feedwater piping and blowdown piping.

• Rigging and removal of original SG components and relocation to permanent on-site storage building (mausoleum).

• Decontamination of reactor coolant piping near cut ends in support of ALARA.

• Metrology survey of piping interface locations after component removal and machine piping weld prepa-rations.

• Rigging and installation of SGR components, fit-up of nozzle to pipe joints, automated narrow groove welding of all pipe joints, reconnection of component supports, NDE of all welded pipe joints.

• Replacement of SGR component thermal insulation, reinstallation and reconnection of level measurement and other instrumentation.

• Civil engineering including closing steel and concrete containment building, post-tensioning/rebinding reinforcement material, restoring interior subcompartment walls and piping to original configuration, NDE of all rewelded pipe joints.

• System leak test or hydro test of both primary and secondary systems to include all welded joints in accordance with the requirements of jurisdictional authority.

• Multiple replacement component installation during a single outage (e.g. SGRs, reactor pressurizer, reactor vessel head) is efficient but requires a high level of coordination and sharing of physical staging areas inside containment during replacement outage.

Licensing points of SGR components

• Scope of licensing effort is dependent on the extent of differences between the original SG and the SGR.

• Weight and centre of gravity – significant differences in weight and/or centre of gravity of the SGR might affect the seismic analysis of the component or the RCS loop analysis, depending on the design margin in the original licensing calculations.

• If the tube bundle size has increased, weight and centre of gravity increases might be partially offset by constructing the pressure shell and tube sheet from higher strength and thinner material.

• Fluid inventories – significant differences in either primary or secondary fluid inventories of the SGR might have an impact on the response of the SGR to design basis transients or the SGR might have an impact on the transient response of the RCS.

• Higher fluid inventories increase the mass and energy release in the event of a hypothetical pipe break, event in containment, while lower fluid inventories reduce the rate of core cooling during other design basis events.

• Primary pressure drop – significant changes in the primary pressure drop might impact the core cooling margin or core lift-off margin.

• If the SGR tube bundle is taller, adding additional tube circuits could compensate and help to maintain the original pressure drop.

• Secondary pressure drop – significant chances in the secondary pressure drop impact the SG circulation ratio, which affects the secondary fluid inventory.

• If the tube bundle is taller, increasing the width of the downcomer annulus could compensate and help maintain an adequate circulation ratio and avoid concentration of ‘foreign’ ionic species that might attack the tubes.

• In order to minimize the amount of licensing effort, the SGR needs to be as physically close to the original SG as possible.

• Uprating the power level of the plant in combination with the SGR requires additional licensing effort.

FIG. 14. Sequence for reactor coolant piping works.

4.2. OUTLINE OF SGR