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FYI
----- Original Message -----
From: Ted Rockwell
Sent: Friday, February 14, 2003 5:53 PM
Subject: [MbrExchange] ALARA as a detriment Friends:
Some of you may be interested in a note I just received from a colleague who was working as an outside contractor at Davis-Besse. It illustrates one of the major drawbacks in the Precautionary Principle--the idea that certain outcomes are so intolerable that one must pay almost any price to avoid them. We have tended to treat ALARA that way. Art Upton and others tell me, "You may well be right, that there is no harm at low levels. But we just want to be conservative." That type of "conservatism" does not always lead to lower risk. ________________________________ Hi Ted. I know you consider that ALARA can add unnecessary costs to operating nuclear power plants. Here is another arrow for your quiver. The industry is familiar with the Davis-Besse story. Years ago, a small leak developed in a reactor vessel head pipe penetration. The leaking reactor coolant, borated water, is highly corrosive to carbon steel materials and was particularly corrosive at the interface between the penetration weld material, Inconel 600, and carbon steel head material. Over the years, the amount of leakage grew as evidenced by the amount of
boric acid crystals collected on the head of the reactor vessel. This amounted
to hundreds of pounds of crystalline boric acid on the head, and hundreds of
pounds more which was released as vapor and collected throughout the
containment vessel, particularly in the air handling units. The amount of
head corrosion also was increasing, but the plant operators were not aware of
this. The head was finally inspected in the spring of 2002. The inspection
revealed a hole which had penetrated through all of the carbon steel head
material down to the thin stainless steel liner, which protects the reactor
vessel from the reactor coolant.
The plant shut down, and is still not operating in the spring of 2003. The details of this incident are available at the NRC's website, www.nrc.gov, and the links to Davis Besse show the magnitude of the issue. This event could have been avoided if an inspection had been performed, either preemptively based on French operating experience, or soon after the plant operators were aware that a leak existed. An obvious question is why such an inspection was not performed, particularly since the requirements of ASME Section XI require an inspection if pressure boundary leakage is suspected. Two primary factors were involved. One was the plant operators desire to maintain a high rating from INPO (Institute for Nuclear Plant Operations). One of the major factors INPO uses in judging how well a plant is being operated is low collective dose. The collective dose for the entire nuclear industry, as well as for individual plants, is published each year to show how well the industry is doing. The second, and related factor, was ALARA. The concept of minimizing all radiation dose was so firmly ingrained at the plant and enforced by the Radiation Control department, that the ISI (In Service Inspection, the program which executes the inspections for ASME Section XI) engineers who could have performed a meaningful inspection were not allowed near the reactor vessel head. The personnel dose resulting from such an inspection would have been well within the regulatory limits, and within the even lower limits imposed by the plant operators. However, the inspection was delayed for years in order to minimize exposure. Hundreds of millions ($350+)of dollars later, the plant operators certainly regret their strong adherence to ALARA and the INPO low dose rating criteria in this case. ____________________________________________ Ted Rockwell _______________________________________________ MbrExchange mailing list MbrExchange@list.ans.org |