CANADA: 'Hydro Power is breaking our hearts'

Karl Johanson karljohanson at shaw.ca
Fri Jul 23 12:25:17 EST 2004


"Ian St. John" <istjohn at noemail.ca> wrote in message
news:74kLc.19731$Gf7.711290 at news20.bellglobal.com...
> Fresno Farms wrote:
> > Ian St. John:
> >
> >> Hydro power can still be useful in selected areas
> >
> > If so, Canada or Alaska would be the place.
> >
> >> where there is a large
> >> reservoir, mostly with little vegetation, such as at boulder dam.
> >> But even that should be considered. Do we REALLY need a hydro dam
> >> just to maintain the patterns of the past or could we replace it
> >> with a similarly
> >> cost nuclear power.
> >
> > Nuke power, at full project cost including plant
> > decommishioning and 20,000 years of storage is currently
> > an economic bust.
>
> Lie. The cost of decommisioning and storage is factored in during the
> operating lifetime. The fanciful costs are always a result of someone
trying
> to ensure an unreasonable level of absolute proof or 'what if' scenario.

And by holding the emission standards to levels which, if applied to all
energy types,  would effectively kill coal, oil, natural gas, geothermal &
biomass, all of which emit radioactive materials into the environment.

>The
> best situation is one with reprocessing in which the depleted fuel is
> extracted for its fissionables and used again, leaving very little waste
for
> the power. And as most of the radioactivity of the 'spent fuel' is due to
> short lives actinides, the fuel activity decays rapidly.
>
> A rational approach to risk management would consider that the fuel is
> 'safe' when it is no more hazardous than the original ore.
>
> > Large scale solar (such as being considered in
> > Sacremento and SF, are economically competative
> > with new (hugely expensive) hydro in California.
>
> In desert terrain, sure. The drought is part of the problem. The dams were
> built under the assumption of a stable climate ( gee, imagine that ) and
the
> current climate change is making them very poor investments.
>
> > I'm not familiar with the Canadian economics.
>
> I imagine so. The best green energy in Canada is wind power (competitive
in
> many locations ) and geothermal using heat pumps to extract heat from old
> mines. http://town.springhill.ns.ca/geotherm1.htm. However, our primary
> green energy is nuclear with natural uranium ( not enriched ). The
> advantages are
>
> 1: no downtime for refueling
> 2: slow warmup and cooldown ( allowing more time to check things out in a
> crisis )
> 3: no enrichement of the fuel needed
> 4: ability to burn many fuels including mixed oxides to utilise old
> plutonium from bombs.
> 5: unmatched record for uptime ( up until lately,which is mainly due to
them
> being pushed past their design lifetimes).

Other advantages of the Candu include:

>From http://www.nuclearfaq.ca/cnf_sectionD.htm#q
"D.1     Why is the CANDU design one of the safest in the world?

The CANDU system is a strong example of safety through both engineered
redundancy and passive design. The core has numerous triple-redundant
detectors that feed to two logically, conceptually and physically separate
shutdown systems (shut-off rods and high-pressure poison injection). Each
system is capable of shutting down the core within 2 seconds following a
LOCA ("Loss-of-Coolant Accident" -- the design-basis accident for CANDU
reactors), without credit given to operator intervention. See the next FAQ
for a more detailed discussion of the engineered CANDU safety systems.

In addition to engineered safety systems, CANDU reactors have a number of
inherent safety features that distinguish it from other reactor designs
(e.g. PWRs, BWRs):


The subdivision of the core into two thermalhydraulic loops (in most CANDU
designs), and hundreds of individual pressure tubes within each loop,
localizes a LOCA (Loss-of-Coolant Accident) to one small region of the core,
and reduces the reactivity effect of a LOCA accordingly. Furthermore, the
two core-passes per loop mean that only a quarter of the core would likely
suffer a mismatch between heat generation and removal under such conditions
(and only the highest-power fuel elements within this one-quarter-core
region).

The large-volume, low-pressure, low-temperature moderator surrounding the
pressure tubes acts as a heat sink in large LOCA scenarios, rendering
negligible the risk of "fuel meltdown". The moderator, in turn, is
surrounded by a thick light-water shield tank (used for biological and
thermal shielding) which can also act as a heat sink in severe accident
scenarios.

The moderator also provides a low-pressure environment for the control rods,
eliminating the "rod-ejection" scenarios considered in PWR safety analyses.
In addition, the location of neutronics measurement devices in the moderator
avoids subjecting this equipment to a hot, pressurized environment.

Heavy-water neutron kinetics is slower by several orders of magnitude than
light-water kinetics, reducing the discontinuity between prompt and delayed
kinetic behaviour, and making control easier.

Criticality of CANDU fuel bundles in light water is impossible, avoiding one
concern of severe accident analyses that light-water reactors must contend
with. Furthermore, since the geometry of the CANDU core is near optimal from
a reactivity standpoint, any rearrangement under severe accident conditions
ensures shutdown.

On-power refuelling means that the power distribution reaches an equilibrium
within a year of start-up, and remains virtually unchanged for the reactor's
operating life. This greatly simplifies the analysis of core behaviour as a
result of postulated accidents.

On-power refuelling also allows defective fuel to be detected and removed
from the core, reducing the contamination of the reactor coolant piping and
simplifying maintenance.

The low excess reactivity of the CANDU core leads to relatively low
reactivity worth of the control devices, limiting the potential severity of
postulated loss-of-regulation accidents.

The positioning of the steam generators well above the core promotes natural
thermosyphoning (i.e. movement due to the coolant's own density
differences), which can remove decay heat if shut-down cooling is lost. At
the same time, the large amount of small-diameter piping in the feeder
network acts as a natural "radiator" under such conditions.

This significant amount of inherent, or "passive", safety in the CANDU
system, in conjunction with fast-acting, robustly engineered safety systems
and backup safety systems, is the reason why a complex technology like
nuclear power can be one of the safest and most reliable energy options
available."






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