The main purpose of the burst can detection (BCD) equipment is to provide early warning to the reactor operator of the presence of a failed fuel can. Sam­ples of reactor coolant are withdrawn from various sampling points and monitored врйіеск for increases in their fission product level relative to background level which normally remains reasonably constant. Sur­face uranium contamination (usually 3 mg/element) left on the magnox can during manufacture releases fission products into the gas circuit, the level of which is used as a reference standard.

Ideally the data provided by the BCD gear should give the reactor operator sufficient time to check for authenticity, i. e., to confirm that the count is not a ‘spurious’ reading caused by plant malfunction.

1.7.1 Fuel

The uranium fuel rod is clad in a magnox can sealed at both ends by welding (Fig 2.22) which:

• Prevents the escape of fission products released during burn-up into the reactor coolant gas in which their activity is a health hazard and restricts main­tenance work on plant.

• Prevents the ingress of the reactor coolant CO; which causes severe corrosion of the fuel rod, lead­ing to oxide build up.