Don't feed us seaweed, Eskom

South Africa must be able to trust Eskom's information on our nuclear power plant

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13/03/2020 07:16:07

                                                                                                                                                                                                            Don't feed us seaweed, Eskom

                                                                                                                                                                                                            Reliable, timely information from Eskom is essential to restore public trust in this essential utility.

                                                                                                                                                                                                            This was underlined by the incident at Koeberg this week, when one of the two nuclear reactor units went off after an incident involving a sea-water pump. The unit is expected to be back online on Sunday.

                                                                                                                                                                                                            The incident was marred by confused messages from Eskom about what had happened.

                                                                                                                                                                                                            When unit 1 went offline on Tuesday evening, resulting in stage 4 loadshedding, Eskom said it was due to a fault with the sea-water pump that cools the reactors and emphasised there was no risk as it had nothing to do with the reactor. There was no explanation for why the fault with a single pump would put the entire unit out of operation.
                                                                                                                                                                                                            Koeberg is a nuclear power station, so we all get understandably edgy when something goes wrong.

                                                                                                                                                                                                            Then on Thursday it emerged that there had been nothing wrong with the water pump and it did not have to be repaired.

                                                                                                                                                                                                            The real situation was revealed by energy expert Chris Yelland, who now also acts as an energy advisor to OUTA.

                                                                                                                                                                                                            Yelland said, in a series of tweets early on Thursday, that the pump did its job and cut out as a safety precaution. Eskom has not contradicted Yelland on this.

                                                                                                                                                                                                            Yelland believed there had been an internal breakdown in communications in Eskom rather than deliberate misinformation to the public.

                                                                                                                                                                                                            There has been confusion over why the unit is still offline, with no clear explanation from Eskom.

                                                                                                                                                                                                            The NNR told OUTA late on Thursday that it has not issued any directive to Koeberg to keep the unit off.

                                                                                                                                                                                                            This is what the NNR told OUTA: “The NNR was notified by Koeberg of the unit 1 trip. This is not a nuclear safety incident and therefore there are no safety concerns. The NNR inspectors are monitoring the situation closely. At this stage the NNR has not imposed any regulatory directives on this matter.”

                                                                                                                                                                                                            The public needs to know what is happening. “We want to see the NNR report on this incident as soon as possible. We want to know why it happened and how it was addressed,” says Liz McDaid, OUTA’s Portfolio Manager for Energy.

                                                                                                                                                                                                            “South Africa needs an NNR that can act without fear or favour. It needs to be well resourced to be able to respond quickly. In the past the NNR has had to step in to shut down the NTP facility at NECSA due to safety protocol breaches,” says McDaid.

                                                                                                                                                                                                            “While it’s good that the NNR has responded, we believe that informing the public timeously is also critical. OUTA contacted the NNR on Tuesday and we received an update late on Thursday. The NNR has not issued any public statement and we have asked for the report which details the causes of the maintenance failure.”

                                                                                                                                                                                                            Eskom has to be transparent and accountable and prove credible to the public. We are still waiting.

                                                                                                                                                                                                            We want to be sure that information from Eskom to the public is reliable. This is particularly important when dealing with a nuclear reactor.

                                                                                                                                                                                                            “The public must be able to trust Eskom information on nuclear power,” says McDaid. “A nuclear power station is very different from a coal-fired power station.”

                                                                                                                                                                                                            We’d like to be sure that there is sufficient built-in redundancy in critical systems at Koeberg, so that if something like a pump goes off there’s a back-up that takes over immediately.

                                                                                                                                                                                                            This incident also raises concerns about routine maintenance at Koeberg. Eskom has previously assured us that maintenance there is run according to a rigorous schedule, as it’s a nuclear power plant. We’d like to be sure of that.

                                                                                                                                                                                                            Here’s what Chris Yelland has established about what happened at Koeberg

                                                                                                                                                                                                            On 10 March, the 930MW Unit 1 nuclear reactor at the Koeberg power station was manually shut down by the operators, in line with the reactor operating procedure, as a result of the increasing temperature on the secondary side of the plant. This resulted in the Stage 2 loadshedding at the time increasing to Stage 4.

                                                                                                                                                                                                            Each of the two 930MW Units at Koeberg has three sea-water circulating pumps for the tertiary cooling water circuits at the power station, which would normally ensure there is adequate redundancy.

                                                                                                                                                                                                            Normally each reactor can operate at full rated output with two of the three sea-water circulating pumps in operation, and at 60% of rated output if only one of the three sea-water circulating pumps is in operation.

                                                                                                                                                                                                            In this instance, one of the sea-water circulating pumps was undergoing maintenance, and the second had tripped due to the low water level in the suction inlet pit. The third sea-water circulating pump was operating normally.

                                                                                                                                                                                                            The low water level in the suction inlet pit was caused by an ingress of excessive marine life and other debris to the inlet drum screen. The drum screen motor had tripped due to high torque caused by the detritus, which in turn resulted in the low suction pit water level.

                                                                                                                                                                                                            As indicated above, the nuclear reactor should have been able to operate at 60% of rated output in these circumstances. However, due to degraded heat removal (or cooling) capability of the tertiary cooling circuit heat exchanger, temperatures did not stabilise sufficiently, even when operating at this reduced output. This then required the manual shut-down of the Unit 1 nuclear reactor.

                                                                                                                                                                                                            The degraded heat exchanger in the tertiary cooling loop was in need of maintenance despite the recent extended shut-down of Unit 1 for refuelling and deep level maintenance in November 2019. Following this shut down, Unit 1 was returned to service on 6 January 2020.

                                                                                                                                                                                                            The excess marine life and debris has since been cleared off the drum filter, and it is now back in service. The water level in the suction pit has sufficiently recovered, and the associated sea-water circulating pump has been put back in service, and no anomalies have been noted. This pump was not damaged as previously advised by Eskom.

                                                                                                                                                                                                            The required technical assessments and regulatory approvals have been obtained to start-up and safely return the Koeberg Unit 1 back on the grid.  The current projected synchronisation date is Sunday 14 March. 

                                                                                                                                                                                                            Picture: GroundUp

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