From: redin@lysator.liu.se (Magnus Redin)
Newsgroups: sci.energy,sci.environment
Subject: Re: Nuclear madness (Extremely safe nuclear power)
Date: 13 Sep 1996 23:11:57 GMT

hatunen@netcom.com (DaveHatunen) writes:

>In article <51c1ls$5bu@newsy.ifm.liu.se>,

>> Uhh, you buy them from Sweden? *ducks flying tomatoes*
>>
>> Start with a company with a good track record, let it set up a
>> division that is very open about its design and procedures, let it
>> complete or make a new design with those goals in cooperation with
>> teams that carefully have studied how other nuclear powerplants has
>> worked out.  (GNU nuke? ;-) )

> Um. Now, here in the USA, exactly how do we do that? Does the
> federal government look around for a company with a good track
> record (a rare bird indeed) and point to it to take over with an
> exclusive government contract? Does it mandate the private utilities
> to use this firm or else?

Collect a pool of investors and choose to invest in the company best
suited to build a publically acceptable powerplant.

> One of the BIG problems in the hayday of American nuke construction
> was that an entire inustry sprang up without any experienced
> personnel available, for all practical purposes. The contractors
> used had vast experience in construcition of skyscrapers and
> shopping malls, and very little in nuclear construction. Huge
> numbers of piping and support designers were required, and there
> just weren't that many of them around. Contractors were hiring warm
> bodies off the street and hanging the title "engineer" on them.

Thats lunacy. Why dident the early companies that did have some
experience sell standardised units that could be put together by less
skill lokal people? Would that not have been an very obvious way to
make lots of money for the manufacturers that had skill and the
utilities that would have gotten plants on time and within
specifications?

> As for Swedish skill, one can't help wondering how much average
> skill they would have had if they had built near 100 plants in a
> decade or so.

There wre one small heavy water moderated plant built in the late
fifties if I remeber right. It had some intresting failures, they got
mechanical vibrations in the core that cracked the fuel elements and
they tried to coat the tubes with teflon to lessen the friction of the
water. The teflon was softened by the neutron radiation and clogged
pumps, etc and this helped to start a new research field into nuclear
chemistry. ;-) There were a larger heavy water plant built but it was
never commisioned, the rumour have it that the oldest professor were
not comfortable with the calculations. These reactors were intended to
use non enriched uranium and were part of the secret nuclear weapons
program.

The development program leading to usefull reactors were started 1962
and the first design, the one of a kind Oskarshamn 1 was finished in
1968 and comissioned 1971. It is a 440 MW BWR that now has had its
reactor vessel renovated. (By people working inside it in light
clothes. ) The second example of the first BWR generation were the 750
(now 781) MW Ringhals 1. After the first two related one of a kind
plants they tried to standardise the design and 1966 to 1972 they
designed a 570 MW reactor of wich thre were built. The third
generation were of two kinds one 900 MW of wich two were built in
Sweden and one 660 MW of wich two were built in Finland. The fourth
kind designed 1973-1980 were a 1060 MW design of wich two were built.

Had we built a hundred reactors there would have been more of each
generation.

The fourth BWR generations design were developed into a fift design
completed 1986-1990 with an 840 MW and a 1140/1300 MW type. That
design is gathering dust in ABB:s archives. :-(

>> It could perhaps pay off to use a radically simplified and ultra
>> secure design like PIUS that doesent relie on any active systems for
>> nuclear safety. Then it wont matter as much if any valves, pumps,
>> computers, etc breaks down or if the operators go nuts.

> Yeah...

Oh yeah! (Includes an old post)

Another foolproof reactor I find much more promising is ABB:s PIUS
reactor. It is a PWR completely without active security systems.

It has a 3300 m3 reactor vessel built out of prestressed concrete 7-10
m thick. Near the bottom of the reactor vessel there is a small tank
containing the core with fuel elements simmilar to the usual US PWR:s
but shorter. At the bottom of the core vessel there is a bundle of
about 1 m long tubes open at both ends. Above the core there is a
riser for the hot water and near the top of the reactor vessel there
is another bundle of vertical tubes connected to the riser at the top
of the tubes and open to the reactor vessel at the bottom. The riser
then goes to a set of four steam generators, then to the circulation
pumps and then back with another pipe to the bottom of the small core
vessel.

The reactor vessel is filled with borated water.

When it is at rest water is heated by the heat generated by
radioactive decay in the core. It raises thru the raiser and goes out
into the reactor vessel thru the upper bundle of open tubes (The upper
density lock). At the same time there is cooler bottom water sucked
thru the tube bundle at the bottom of the core vessel into the core.
This system has no pumps or valves at all and can run indefinately
untill the water somehow escapes.

In the reactor vessel there are four heat exchangers whose tubing
enters from the top. (There are no perforations at all in the sides or
bottom of the core vessel. ) Those four heat exchangers are connected
to four small cooling towers integrated into the top of the reactor
building. They carry the rest heat and they heat leakage from the core
during operation to the ambient air. There are no pumps in this
system, the water heated in the heat exchangers rises due to its
higher density up into the cooling towers where the heat is carried to
the air naturally circulating thru them. Then the chilled water falls
down to the bottom of the heat exchangers to be heated again. This
system has no pumps or valves at all and can run indefinately untill
the water somehow escapes.

When the reactor is started the circulation pumps in the steam
generators are started forcing a circulation thru the steam
generators. Then the water in the inner circulation is diluted with
destilled water so that the nuclear reacton can start in the core now
free of the high boron concentration.

It is a delicate control process to keep the pumps running at the
right speed. If it fails and they run to quick removing more heat then
what is generated in the core or to slow not removing heat fast enough
the ballance in the density locks (Those bundles of open tubes) is
disturbed and borated water from the reactor vessel enters the inner
circulation shutting down the nuclear reaction.

There are a few more tricks in the design. The steam generator is used
to break any siphoning from the reactor vessel if there is a leakage
in the steam generators at the side of the reactor vessel.

This means that if any active system fails in any way so that to much
or to little power is generated the reactor shuts itself down withouth
any active systems at all. And then it chills itself indefinately
withouth any active systems at all.

It has a second ultimate security system. If the cooling tower system
is grossly damaged, like in a war, the reactor vessel volume is
designed so that it takes a week for the water to boil off before the
core is exposed and the core cladding cracks releasing volatile
elements in the fuel.

Its safe for everything except an accident that cracks the 7-10 m
thick prestressed concrete vessel with its double stainless steel
cladding.

Another nice feature is that the prestressed concrete vessel is
designed so that the steel cables holding it together can be removed
and inspected.

Since is are no active security system and the generated effect is
controlled only by pumpspeed and boron content there are no control
rods, redundant safety coolant pumps, redundant safety grade diesel
generators, redundant safety grade control systems, safety grade
valves, etc, etc. Lots of very expensive equipment that is not needed
to be bought or maintained. Lots of saved money and things that cant
fail since they are not there.

It is also designed to be build from scratch in three years instead of
the usual five saving intrest money.

It is probably very hard for it to fail in such a way that the system
is damaged so much that it need expensive repairs. This means that the
owners of a PIUS reactor are safe from the kind of capital loss that
hit the ownerd of the TMI plant.

It has two drawbacks, it dosent use its fuel as efficient as other
reactors since it works at a lower temperature and the concrete vessel
is fairly expensive due to its size.

Some data about the proposed PIUS design:

Thermal power					2000 MW
Electrical power at 15 C coolant temperature	640 MW
Number of 18x18 fuel elements			213
The cores active height				2,5 m
The cores equivalent diamater			3,76 m
Mean heat load on the fuel elements		11,9 kW/m
Mean heat density				72 kw/l
Core inlet temperature				260 C
Core outlet temperature				290 C
Preassure					9 MPa
Mass flow thru the core				13 000 kg/s
Mean fuel use					45 500 MWd/ton
Fuel enrichment					3,5%
The reactor vessels inner diamtere		12 m
The reactor vessel volume			3300 m3
The reactor vessels unperforated volume		3000 m3
The reactor vessel height			44m
The reactor vessel wall thickness		7-10 m
Number of steamgenerators and circulation pumps	4

Reference: ABB technical publications no 2 1990


Regards,


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Magnus Redin  Lysator Academic Computer Society  redin@lysator.liu.se
Mail: Magnus Redin, Björnkärrsgatan 11 B 20, 584 36 LINKöPING, SWEDEN
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