On 25/02/2021 22:55, Steve Walker wrote:
On 25/02/2021 21:00, newshound wrote:


Chernobyl was not a mistake, it was known bad design, there was
reliance on operators to avoid a particular operating regime due to
that design constraint, there was no safety system to prevent such
operation and someone chose to carry out an unauthorised test, within
that regime, outside even the test's pre-determined parameters.


I don't like the term "bad design". I'm not sure it is possible to
design and build anything useful that does not have some limitation
The operators got confused and took it outside its clearly defined
permissible envelope. Rather like putting a 747 into a vertical dive,
and then trying to pull out at 600 knots. When our experts looked at
the RBMK in the 1970's they decided it would not have been licensable
in the UK presumably because of the lack of interlocks to prevent it
being taken beyond the safe envelope. But as we have seen recently
with the Max 8, safety system design can be cocked up too.

No. It was not the lack of interlocks. It was the basic design of the
reactor. It is nothing like Western reactors - part of it being designed
to use hundreds and hundreds of small pipes, able to be welded by pretty
well any old welder, instead of properly coded welders for the job.

That's an example of *good* design, in the context of the former soviet
union and their shortage of electrical power. That let them build the
complicated bits in a factory and assemble them on-site with
"shipbuilding" technology. And also to "scale" the plant. Welds didn't
fail either, until they were massively overstressed by the power
transient from getting the physics wrong.


The
design was known to a) increase power output as the control rods were
inserted, b) take too long to insert the rods and

These points only apply IF you drive it outside the envelope

c) a single failure
could cause damage to nearby channels, defeating the concept of being
safe with two failures (Western licensing would have required more anyway).

I've already pointed out that it would not be licenced in the UK. But
then neither are some Russian aircraft.


Plus the Soviet Union did not even require any containment around the
reactor.

Rather like Magnox and AGR plant, in fact.


They knew it was unsafe, but did nothing about it. After Chernobyl, they
did make some changes to improve safety - making the basic design safer.
Changes that they could have done years earlier, but no-one dared to
speak out against higher power.

All technology is potentially unsafe. The issue is, getting the balance
of risk against benefit.

UK companies in the nuclear industry have a policy that anyone - no
matter if they a Nuclear Safety Engineer or a humble labourer, can stop
any job at any time if they think that there is danger ... even if that
job is nothing to do with them, but they are just passing by and see
something.

Sort of true. But I am not sure whether the standard western trope about
authority in the Communist block is quite right. Certainly the
*penalties* for, say, a factory manager if a worker dies there can be
much more severe in the west.

Also, it wasn't an unauthorised test; but it had not been reviewed as
carefully as it would have been in the UK.

At the time it took place, it was not authorised at higher levels IIRC,
only locally and the test began despite being far outside the parameters
stated as required for the test and well into the danger zone - so it
*was* unauthorised.

No, it *was* authorised; just implemented badly.