Project Description

Project Details

Client: Dounreay Site Restoration Ltd.

Services Provided


Structural Design & Analysis

Pipe Stress

Active Transfer Line:

This project involved an analysis of a duplex pipe system which spanned between two buildings on a lead shielded bridge using Caesar II software.

Load cases considered were normal operating plus fault condition from a seismic event for a 1 in 10,000 year Design Base Earthquake loading (0.14g) and Cliff edge (0.196g).

The system consisted of a duplex pipe where the primary line was guided within the secondary containment line. It was a gravity flow system with design pressure of 6 Bar (g) designed to ASME B31.3 for category M fluids. Operating temperature ranged from -13.2 degrees Celsius to 40 degrees Celsius.

Analysis included both duplex pipe and supporting structure to correctly model the dynamic behaviour of the combined system. Seismic analysis was carried out via model analysis and Response Spectra. A PD5500 check was carried out on the nozzle connection to the transfer pot vessel.

The FE model included a detailed representation of the steelwork supporting structure that spans between the two buildings, as well as the lead shielding that surrounds the duplex pipe system. The dynamic behaviour of the combined structure was then assessed to calculate the natural frequencies, prior to Morson Projects undertaking Response Spectrum analysis and combining the modes by the SRSS method to determine the loading under the DBE and Cliff Edge events.

Reaction Vessel Sample Lines:

The reaction vessel sample line and vessels had been out of operation for 20 years, the scope of the work was to review the existing pipework and vessel structure to determine if the system could be returned to service and shown to be compliant with the modern design standard.

Activities included:

  • Analysis of pipe system to include pumps, vessels and supporting structure.
  • System analysed under Normal Operating and Seismic loads.
  • Fluidic pump to transfer the sample liquor between vessels, rated at 6 Bar (g).
  • Pipework forms the containment boundary and must withstand normal and fault conditions without causing breach.
  • Vessel vented to atmosphere subject to temperature range of -5oC to 100oC.
  • Seismic analysis of combined pipe system, equipment and supports to 1 in 1,000 year event (0.054g) plus seismic margin event (0.076g)
  • System assessed to ASME B31.3 category M fluid.
  • Vessel nozzles checked to PD5500.

In order to carry out a representative assessment of the pipe system pumps, vessels and the supporting structure was included in the Caesar II model. The dynamic behaviour of the combined system was analysed to calculate the major modes of the combined structure, prior to Morson Projects undertaking Response Spectrum analysis and combining the modes by the SRSS method to determine the loading under the DBE and Cliff Edge events. The forces, stresses and displacements from the combined Normal Operating and Seismic load case were checked against the design requirements of ASME B31.3, In addition to the code compliance checks Morson Projects  reviewed the pipe support locations and made recommendations on changes to support locations which would improve the compliance of the system and also provided additional justification and acceptability for continuing use when regions of slight overstress were calculated by referring out to the ASME III NC class 2 components design code.