Alison Turner is a department manager at a large commerical nuclear
generating plant. She is also a member of the Plant Nuclear Safety Review Committee
(PNSRC). The committee's responsibilities include reviewing and approving design changes,
procedural changes, and submittals to the Nuclear Regulatory Commission (NRC).
Today Alison finds herself in a difficult situation. PNSRC is meeting
to decide what to do about a heat exchanger problem. Routine testing on the previous
morning revealed degraded cooling water flow and high differential pressure in one of the
containment spray heat exchangers of one of the two generating units. This unit has just
returned to service after two months of repairs. Test results on the second heat exchanger
were similar. Although the other generating unit has been in continuous service, testing
reveals that its two heat exchangers are operating at less than full capacity. The most
likely cause of the problem is sand blockage on the lake water side of the four heat
After extensive analysis by engineers in the Mechanical Engineering and
Nuclear Safety & Licensing Departments, it has been concluded that the cooling water
flow falls slightly below the minimum requirement set by the technical specifications
under which the plant is licensed. Nevertheless, based on Mechanical Engineering's
analysis, Nuclear Safety & Licensing has prepared a Justification for Continued
Operation (JCO) for submission to NRC. PNSRC is now meeting to decide whether to approve
the JCO and forward it to NRC.
As Alison reviews the JCO she is uncomfortable with one assumption made
in the analysis. The analysis assumes that the heat exchangers still have 95% of their
original heat transfer capability. It is concluded that this would be satisfactory.
However, in anticipating possible accidents, Single Failure Criteria require the plant to
assume the loss of one heat exchanger. Alison wonders if, under those conditions, the heat
transfer problem would be manageable. The JCO does not discuss what might happen under
Seven members of PNSRC are present, enough for a quorum. Alison is the
least senior member present. From the outset of the meeting, committee chair Rich Robinson
has made it clear that it is important to act quickly, since any shutdown will cost the
company, and ultimately the rate payers, a lot of money in additional fuel costs.
"Repairs," he says, "might take a couple of weeks. If we don't approve
this, we may be facing a multi-million dollar proposition. Fortunately, the JCO seems
fine. What do you think?" Brad Louks and Joe Carpello immediately concur. Rich then
says, "Well, if no one sees any problems here, let's go with it." There is a
moment of silence. Should Alison express her reservations?
Alison Turner expresses her reservations. Brad Louks replies,
"We're talking about containment heat exchangers. It's an Accident Mitigation System,
and it's never had to be used here--or at any other commercial nuclear plant that we know
of, for that matter. In fact, lots of plants don't even have containment spray
systems." "Right," adds Joe Carpello, "we're ahead of the game on this
one. I don't see any problem here. Nothing's totally risk free, but we've always been
leaders in safety. Let's not get carried away with 'possibilities'."
"I don't think Alison meant to have us get carried away with
anything," Mark Reynolds interjects. "She's just wondering if the JCO should
address the question of how things would look if we lost one of the heat exchangers. How
much time would it take the Nuclear Safety and Licensing Department to make a calculation
for us--another 3 hours? It's only 1:30pm, you know." "What's the point,
Mark?" asks Joe. "Our track record is excellent, and the system is optional.
It's not as though we're taking any extraordinary risks."
Nothing further is said, and Rich Robinson calls for the vote. Though
not a committee requirement, PNSRC has always acted unanimously. It often rejects,
sometimes approves, but always unanimously. As the call goes around the room, each member
approves. The last member called on to vote is Alison. She still has serious reservations
about approving the JCO without the Nuclear Safety and Licensing Department making further
calculations. How should she vote?
Suppose Alison casts a negative vote and subsequent calculations show
that her worries were unfounded -- in the event of an accident, a single heat exchanger
would be adequate to manage any likely heat transfer problems. Would it follow that it was
wrong for her to cast a dissenting vote? [Recall that a single dissenting vote would not
defeat approval. It would only set a precedent of proceeding without unanimity.]