MD's Desk
EMPOWER :2014-15

Once again Single - Failure - Proof Crane

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A single-failure-proof crane for Spent Fuel Storage Bay (SFSB) at NPCIL’s Kakrapar Atomic Power Plant

Crane application

This crane will be used to handle spent fuel rods in the spent fuel storage bay, where th acts as a shield to prevent radiation from entering the atmosphere as well as cools the fuel assemblies that continue to produce heat (called decay heat) for some time after removal. The bottom is equipped with storage racks designed to hold fuel assemblies. Used nuclear waste, in the form of tiny pellets, is loaded onto metal rods that are then bundled into a 'fuel assembly'. The assemblies are stored inside casements that are then submerged in cooling pools. The application of the 75/30MT single-failure-proof crane supplied by ElectroMech will be to handle these casements. Needless to say, This is a very critical application, requiring the highest levels of safety, reliability and precision.

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Crane construction

The lower block of the crane has been provided with 3 hooks - a 75MT main hook and two 40MT hooks on either side. They are positioned in such a way that the composite lifting assembly meets the requirement of single failure criteria. During regular operation, the load will be lifted by the 75MT hook and in case of failure of this hook, the load will be borne by the two 40MT hooks. This lower block gets engaged with a 3 pin arrangement to a specially designed yoke, which is a lifting attachment with 4 x 25MT hooks. This yoke will handle the spent fuel casements kept underwater.

Stringent guidelines, right from the raw material to manufacturing and testing were specified by the customer considering the critical nature of the application. Some of the special requirements for the underwater application include treating the yoke hooks with manganese phosphate and galvanising the lower block.

Design challenges

Designing a single-failure-proof crane is always a challenging task. There were a few more additional constraints while designing this crane, such as its span being only 6.8m. This demanded the trolley including redundancy machinery, safety equipment like caliper brakes and auxiliary machinery to be tightly accommodated in a crab area of 6.5m X 5.5m.

Testing

The crane underwent a rigorous 3 step testing process.

Full load and overload testing of the crane (factory testing)

The crane was tested at 100% & 125% of the full load capacity. This was based on two conditions. First, with load & overload on the 75MT centre hook and then again for the two 40MT hooks.

Testing of engagement & disengagement of the crane with yoke (factory testing)

The yoke is a critical component of this crane and its engagement & disengagement with the crane is of paramount importance. This was tested for repeatability and accuracy in the presence of the NPCIL technical team.

Overload testing of the yoke separately at 150%

As a critical link between the load and the crane, the yoke was required to be tested at 150% of the rated load. Certain constraints in the shop and the yoke being a stationary equipment with no hoisting mechanism in itself posed a major challenge for testing of the yoke. The testing was conducted by using a 200MT mobile crawler crane. The test load was lifted by suspending the yoke to its hook.

This crane was despatched after rigorous inspection and testing in our factory in the presence of NPCIL experts. They were extremely happy with the timely delivery, perfect design, quality manufacturing, high level of finishing and ultimately excellent performance during the various trials and tests. With this despatch, we are about to complete the entire order for Kakrapar Atomic Project.

We are thankful to the entire NPCIL team for their trust in our capability and providing an opportunity to prove it.