Comment by cjslep | Hacker News Reader

Comment by cjslep | Hacker News Reader

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I think this article is very well-written overall. However, there are still a point that could use clarification.

> During a routine test on April 26, 1986, reactor Number 4 at the Chernobyl Nuclear Power Plant experienced a power surge that triggered an emergency shutdown. It did not work.

Calling the incident a routine test greatly mischaracterizes what they were doing. This wasn't some sort of daily safety checklist test nor a safety margin test, this was a full-blown experiment. Yes, like a science lab experiment, but with a fully fueled commercial RBMK reactor. This is important because the author falsely makes routine nuclear powerplant operation seem unsafe.

To properly characterize the experiment on fair grounds it is nice to mention that the experiment they wanted to test is started by carrying out a simulated emergency shutdown. This is huge. You don't call an emergency shutdown of a gigantic plutonium-making-machine "routine" (Note: RBMKs have a thermal power output on the high side). However, the bigger problem was that the authorities running this experiment treated it exactly the same way the author did.

If the authorities did care, they would have properly trained the night shift personnel with the experiment (or delayed the experiment altogether). The fact that the experiment continued with the night shift that was poorly trained for the experiment operations points to a "this is routine and should not be a big deal" vibe of whoever was in charge. I dislike how nowadays others (such as the the author) looking into the reactor accident keep espousing this giant red flag.

It wasn't actually any science experiment, merely an engineering step to improve the emergency process, and not even performed for the first time:

https://www.oecd-nea.org/rp/chernobyl/c01.html

"The Unit 4 reactor was to be shutdown for routine maintenance on 25 April 1986. It was decided to take advantage of this shutdown to determine whether, in the event of a loss of station power, the slowing turbine could provide enough electrical power to operate the emergency equipment and the core cooling water circulating pumps, until the diesel emergency power supply became operative. The aim of this test was to determine whether cooling of the core could continue to be ensured in the event of a loss of power.

This type of test had been run during a previous shut-down period, but the results had been inconclusive, so it was decided to repeat it. Unfortunately, this test, which was considered essentially to concern the non-nuclear part of the power plant, was carried out without a proper exchange of information and co-ordination between the team in charge of the test and the personnel in charge of the operation and safety of the nuclear reactor. Therefore, inadequate safety precautions were included in the test programme and the operating personnel were not alerted to the nuclear safety implications of the electrical test and its potential danger."

Of course, in hindsight it is obvioust that it was poorly executed. But it's not surprising that they were more relaxed doing the procedure for the second time, and again, during "the routine maintenance shutdown."

I'd take issue with the idea that there was no/minimal coordination with the reactor operators.

In fact, the issue that made the turbine spindown test such a disaster for Chernobyl was the extended amount of time and number of power excursions that that reactor (not non-nuclear) operators had spent trying to setup for the initial conditions of the turbine test.

The test had been intended for the afternoon shift, and required reactor power and steam output to be set within a prescribed band before the test. The operators duly setup these initial conditions, but then the regional electrical control center unexpectedly asked Chernobyl-4 to remain online (instead of shutting down as planned) to service electrical demands.

The reactor operators then resumed power operations and tried to re-establish test conditions at the end of their shift when they received permission to shutdown. But this shift from power operations to low power back to power operations and back again to low power induced xenon transients, and an extremely unusual and dangerous control rod configuration, all in an effort to establish the nuclear parameters to run the non-nuclear test.

And then they turned over to the evening shift as if they were handing over a set of car keys for a company sedan, an evening shift that had not been expecting the test (though by this point the conditions were such that either shift would have caused the reactor accident IMHO, assuming no one made the brave call to abort the test completely).

I'm willing to grant that professional nuclear testing groups were not actually involved in the design and implementation of the test, but it's simply not true that this was the result of a bunch of steam plant engineers running a test that was felt to be non-nuclear in nature. The nuclear reactor operators were deeply involved in setup and spent almost the entirety of a shift setting up for this test, and had plenty of opportunity throughout to evaluate the possible reactor plant response to their actions.

In fact had the test simply been to take a reactor operating at power and to spontaneously trip the steam supply valve to the turbines the accident would never have happened, even without coordinating with the reactor operators first. In the actual event the closure of the steam valve was simply the non-nuclear nudge that finally tipped off a disaster laboriously arranged during a full shift by nuclear reactor operators, operators who should have known better just from first nuclear principles.

Also, the experiment's requirement lead into the operators disabling almost every single safety mechanism. The automated systems disallowed the actions they were trying to do, so they disconnected most important security measures.

Operating like that you can make even hydroelectric power station extremely deadly, and kill a lot of people.

Is there are a good article or book describing this, i.e. that they disabled safety mechanisms. I'd like to read more about it.

I can recommend Atomic Accidents: A History of Nuclear Meltdowns and Disasters: From the Ozark Mountains to Fukushima by James Mahaffey - it has a chapter on Chernobyl and goes into a fair amount of details:

http://www.amazon.com/Atomic-Accidents-Meltdowns-Disasters-M...

This is an excellent piece that goes into some detail:

https://leatherbarrowa.exposure.co/chernobyl

They were doing things in their routine. Thus it's routine.

You're misrepresenting things.

No, the actions leading up to the explosion were anything but normal and routine. The operators went far outside the safety envelope of the reactor by deliberately disabling the mechanisms designed to prevent mishaps.

Chernobyl was caused by irresponsible and reckless behavior. You can't paint this as everyday operation, it's not even close.

I could write "Conduct improv brain surgery on the guy sitting next to me" in my daily planner and it doesn't make it routine. Calling a knife a fork doesn't make it so, and calling something routine that isn't likewise doesn't make it so.

If you conducted brain surgery on the guy next to you routinely then it makes it routine. Even if it's a really silly thing to do.

You could not be more wrong. The circumstances leading to the Chernobyl accident were exceptional and unusual by any measure.

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