NTS shielding assessors were asked to provide an assessment to justify the shipment of 120 UX-30B transport packages on board a PNTL vessel. Timescales were short plus the vessel had only previously been licensed to carry 40 of the packages.

The solution 

The customer quickly confirmed that the source within the UX-30B package was unirradiated material (no radionuclides associated with recycled material) and so had a relatively low source strength. This meant a simple analytical approach would be enough to demonstrate compliance. The main concern was for the dose rates in the occupied areas of the ship. Even though each package contained significantly less source than the ships were designed to handle, there were many more packages than the ship was originally designed to transport.

We took an analytical approach based on each package having a standard surface source distribution equivalent to the dose rate measurements provided by the customer. By using this source analysis and calculating the distance fall-off from all sources to various locations on the ship, we were able to demonstrate that the dose rate criteria would still be met.

The outcome 

The analytical approach we took enabled us to quickly demonstrate the proposed shipment was acceptable from a dose and regulatory perspective and on a timeframe to meet the customer’s needs.

We have encoded the solution so that if a similar situation arises we can produce results with the same speed and agility. This case study demonstrates our flexible approach. While we have expertise in assessments running detailed computer codes e.g., MCBEND, MCNP and Attila, we are also able to devise simpler solutions specific to a customer’s challenge.