Lead filling is a process in which lead is introduced into a container designed to contain radioactivity and/or store radioactive materials. Depending upon the container’s geometry, the lead application process can be carried out in various ways, including lining with sheet lead, lead bricks and casting molten lead.
Canada Metal is a leader in this field and its expertise is sought from the design phase through completion to ensure the feasibility and methodology of the lead filling operation.
A prime example of the company’s expertise was demonstrated when it was asked to fill several (18) vessels of different configurations with lead. Upon completion, the vessels were to be RT tested for porosity.
Two of the vessels required approximately 43,000 lbs. of lead shielding each, using a continuous pour. Canada Metal accomplished this, with zero porosity in the 7+ inches of lead filling.
In another example, the company was tasked to provide lead shielding, with the additional assurance of adhesion of the lead to the base metals of at least 50% of the “wetted surface” area. Complicating matters further, two metals were involved, each having distinct heat coefficient transfer properties. After some experimentation, Canada Metal was able to guarantee adhesion to a minimum of 75% of the wetted surface, as confirmed by Ultrasound Testing (UT).
Understanding Ultrasound Testing (UT) and Radiation Testing (RT)
Through its established affiliations with certified testing companies, Canada Metal is able to offer in-house UT and RT testing of its lead filling. In addition, if defects such as porosity or non-adhesion are discovered during the testing process, Canada Metal guarantees that they will correct the condition at no additional cost to the client.
Both UT and RT testing are used to ensure the integrity of the lead filling operation. RT testing is a method of using a radioactive source on one side of the lead lining coupled with measuring the level of radioactivity on the opposite side. Prior to testing, the acceptable threshold of radiation is calculated taking into account the thickness of the container walls and the thickness of the lead.
UT testing is a method of finding voids by moving a UT head over the area to be tested. Before testing, the acceptable area of hollow space is calculated taking into account the thickness of the container walls. In both UT and RT, a grid is drawn on the container and each grid is numbered. The reading at each grid is noted and if the reading surpasses the acceptable level, a repair procedure is prepared and must be approved prior to effecting the repairs.
Keep in mind that UT testing is not used to find voids in the lead, but rather to determine whether the lead has adhered to the wetted surface. Once the poured lead solidifies, it typically shrinks away from the container wall. The slight resulting gap is generally ignored; however, when the specification calls for adhesion, UT testing is used to ensure that the finished product meets the mandated criteria.
Lead Filling Standards for the Nuclear Industry
For lead shielding applications within the nuclear industry, there are minimum standards that are governed by various authorities. While they may be modified to suit a particular piece of equipment or installation, these standards are strict and must be adhered to. The quality of lead is also specified and Canada Metal uses only lead that meets or surpasses ASTM B29 14 L50021 for purity.
What to Look for in a Lead Filling Service Provider
For potential purchasers of lead filling services, it is important to be sure that the lead shielding operation is carried out by a reputable, reliable, qualified and experienced company. Most importantly, purchasers need to choose a company with an unblemished track record for quality and performance.
Look for a market leader such as Canada Metal, a company that brings decades of experience to address the unique challenges and the precise requirements of the nuclear industry.