Re: UCS- NRC Relies on Falsified Safety Studies

["Thomas E. Potter" <pottert@erols.com>]

I seem to remember reading news accounts of this "study" and being

struck by the low

quality of this effort, even assuming it was only a propaganda effort.

It has "summer

intern with other priorities" written all over it.



Many of the assertions are plainly unsupportable.  Others simply

demonstrate a complete

failure to understand what a probabilistic risk assessment is.



Consider the UCS assertion that nuclear plant risk assessments are

really not risk assessments

because potential accident consequences are not evaluated. Here the term

accident

consequences is intended to mean health and economic consequences.  This

assertion

ignores the fact that different risk assessments have different

objectives that may involve

other consequences.  For example, risk assessments focused on reducing

the probability

of core melt need not look at consequences beyond core melt.



Even if one is interested in health consequences, complete assessment of

the risk of health

or economic consequences is usually not necessary.  Probabilistic

assessment of these

consequences was commonly performed in the first decade or so of power

reactor PRAs.

After a number of these assessments it became very clear that health and

economic

consequence risk was closely connected to containment performance.  If

the containment

fails early in the scenario, consequences tend to be relatively severe.

If the containment fails

late in the scenario, consequences are relatively minor.  If the

containment does not fail, the

consequences are miniscule.  Carrying the probabilistic analysis through

to consequences

does not add much in the way of information.



The UCS assertion that accident probability calculations rely on

assumptions that

contradict actual operating experience is strange, given that the

primary purpose of PRAs

is to assess risk by systematic examination of operating experience.  A

large part of the

effort goes to building an experiential database of component and system

performance.

To the extent that this experience is affected by regulatory compliance

or violation, by

aging effects, by design flaws or successes, or other factors, the

effects of those factors

are incorporated in the assessment.  To assert otherwise is absurd.



The UCS assertion that reactor pressure vessels are assumed to be

fail-proof, even though

embrittlement forced the Yankee Rowe nuclear plant to shut down is

misleading in several

respects.  It is true that low probabilities are assigned to scenarios

in which reactor vessels

fail catastrophically.  This is sound for vessels with adequate

ductility. The assertion suggests

that somehow vessels will lose their ductility irreversibly and without

detection.  This

suggestion fails to acknowledge that ductility is monitored througout

the life of each vessel,

and that embrittlement, once detected, is readily restored by annealing

the vessel.



The UCS "study" makes much of apparent discrepancies between PRAs

without making

much of an effort to understand them.  It should not be surprising that

identical plants in

different settings or operated by different entities with different

procedures should have

different risk profiles.  Risk is dependent not just on the plant but on

external factors, such

as reliability of off-site power, and performance of operators.



There are only two ways we can assess nuclear power plant risk.  We can

divine it

or we can analyze it systematically.  In pretty much rejecting PRA, UCS

would have us

divine it.  Actually, they would have us have them divine it.  I'll take

my chances with PRA.

We cannot analyze risk perfectly, of course.  There is a limit to which

we can know what

we don't know.  And we will make mistakes, of course.  But, thanks to

the systematic

approach, some of these can be identified and corrected.



Operating history strongly indicates that we are managing this

technology adequately.

Continued reasonable efforts at improvement are desirable, if only to

hold complacency

at bay. But perfection, unattainable in any case, is unnecessary.  While

we need to be

somewhat mindful of our critics because they are rarely always or

completely wrong,

we should not allow ourselves to be unduly distracted.



The UCS attack on PRA opens with a description of the consequences of

the Chernobyl

accident.  What it fails to recognize is that a PRA is exactly what

Chernobyl needed.



Thomas Potter



---------------------

Norm Cohen posted:



Date: Wed, 20 Mar 2002 22:15:25 -0500

From: Norman Cohen <ncohen12@comcast.net>

Subject: UCS- NRC Relies on Falsified Safety Studies



HI all,

The URL below leads to both the Executive Summary and a link to the

entire report.  reactions welcomed.



http://www.ucsusa.org/energy/nuc_risk.html



Norm.



Summary of the USC study from the link given by Norm:



          The Union of Concerned Scientists (UCS) examined how nuclear

plant risk

          assessments are performed and how their results are used. We

concluded that the

          risk assessments are seriously flawed and their results are

being used inappropriately

          to increase -- not reduce -- the threat to the American

public.



          Nuclear plant risk assessments are really not risk assessments

because potential

          accident consequences are not evaluated. They merely examine

accident probabilities

          -- only half of the risk equation.



          Moreover, the accident probability calculations are

          seriously flawed. They rely on assumptions that contradict

actual operating

          experience:



            The risk assessments assume nuclear plants always conform

with safety

          requirements, yet each year more than a thousand violations

are reported.



            Plants are assumed to have no design problems even though

hundreds are reported

          every year.



            Aging is assumed to result in no damage, despite evidence

that aging materials

          killed four workers.



            Reactor pressure vessels are assumed to be fail-proof, even

though embrittlement

          forced the Yankee Rowe nuclear plant to shut down.



            The risk assessments assume that plant workers are far less

likely to make

          mistakes than actual operating experience demonstrates.



            The risk assessments consider only the threat from damage to

the reactor core

          despite the fact that irradiated fuel in the spent fuel pools

represents a serious health

          hazard.



          The results from these unrealistic calculations are therefore

overly optimistic.



          Furthermore, the NRC requires plant owners to perform the

calculations, but fails to

          establish minimum standards for the accident probability

calculations. Thus, the

          reported probabilities vary widely for virtually identical

plant designs. Four case studies

          clearly illustrate the problem:



            The Wolf Creek plant in Kansas and the Callaway plant in

Missouri were built as

          identical twins, sharing the same standardized Westinghouse

design. But some

          events at Callaway are reported to be 10 to 20 times more

likely to lead to reactor core

          damage than the same events at Wolf Creek.



            The Indian Point 2 and 3 plants share the same Westinghouse

design and sit side

          by side in New York, but are operated by different owners. On

paper, Indian Point 3 is

          more than 25 percent more likely to experience an accident

than her sister plant.



            The Sequoyah and Watts Bar nuclear plants in Tennessee share

the same

          Westinghouse design. Both are operated by the same owner. The

newer plant, Watts

          Bar, was originally calculated to be about 13 times more

likely to have an accident

          than her sister plant. After some recalculations, Watts Bar is

now only twice as likely

          to have an accident.



            Nuclear plants designed by General Electric are equipped

with a backup system to

          shut down the reactor in case the normal system of control

rods fails. On paper, that

          backup system is highly reliable. Actual experience, however,

shows that it has not

          been nearly as reliable as the risk assessments claim.



          To make matters worse, the NRC is allowing plant owners to

further increase risks by

          cutting back on tests and inspections of safety equipment. The

NRC approves these

          reductions based on the results from incomplete and inaccurate

accident probability

          assessments.





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