The highly active waste liquor (HAL) arising from the reprocessing of nuclear fuel continues to generate heat due to the decay of fission products. Prior to verification it is stored in stainless steel tanks equipped with multiple cooling coils and a jacket. If the cooling system completely failed, the liquor would eventually boil, leading to the possible release of radioactive material. The cooling water is normally recirculated through mechanical draught cooling towers and make-up water comes from a nearby lake. In the event of a complete failure of the cooling tower based supply, a connection can be made to enable cooling water to be pumped from a local river using portable fire pumps. No other pipework is required for this operation; a direct connection is made to the jacket and coils. A spare tank in always kept on standby so that, in the event of cooling coil or jacket failure, the contents can be transferred via a valve and a diverter using a steam powered ejector (no electricity needed). This complete standby system is tested once every month. Using the data given below, produce a fault tree and estimate the annual frequency of boiling of the HAL. If the end result is unacceptable, what steps would be recommended to improve the system? Item Failure rate, /yr Tank cooling jacket and coil) 1 x 10* Tank valve (HAL outlet) 4 x 10 Water pipework (cooling system) 1 x 104 Spare tank 1 x 10* Transfer steam supply 2 x 107 Steam pipework 1 x 103 Ejector 2 x 10-3 Diverter 4 x 103 Cooling tower system (mechanical) 4 x 10* Normal cooling water supply (lake) 1 x 105 Electricity supply 1 x 106 Item Unavailability on demand Fire pump 4 x 103 River water 1 x 10'3 Item Error probability Connection error (fire hoses) 1 x 10 e