1. Equipment should be reviewed from the point of view of
providing information to operators to help them prevent accidents and to
cope with accidents when they occur. Included might be instruments that
can provide proper warning and diagnostic information; for example, the
measurement of the full range of temperatures within the reactor vessel
under normal and abnormal conditions, and indication of the actual
position of valves. Computer technology should be used for the clear
display for operators and shift supervisors of key measurements relevant
to accident conditions, together with diagnostic warnings of conditions.
In the interim, consideration should be given to requiring,
at TMI and similar plants, the grouping of these key measurements,
including distinct warning signals on a single panel available to a
specified operator and the providing of a duplicate panel of these key
measurements and warnings in the shift supervisor's office.
2. Equipment design and maintenance inadequacies noted at
TMI should be reviewed from the point of view of mitigating the
consequences of accidents. Inadequacies noted in the following should
be corrected: iodine filters, the hydrogen recombiner, the vent
gas system, containment isolation, reading of water levels in the
containment isolation, reading of water levels in the containment
area, radiation monitoring in the containment building, and the
capability to take and quickly analyze samples of containment
atmosphere and water in various places. (See recommendation
A.7.) :
3. Monitoring instruments and recording equipment should be
provided to record continuously all critical plant measurements and
conditions.
4. The Commission recommends that continuing in-depth
studies should be initiated on the probabilities and consequences
(on-site and off-site) of nuclear power plant accidents, including the
consequences of meltdown.
a. These studies should include a variety of small-break j
loss-of-coolant accidents and multiple-failure accidents,
with particular attention to human failures.
b. Results of these studies should be used to help plan for
recovery and cleanup following a major accident.
c. From these studies may emerge desirable modifications in
the design of plants that will help prevent accidents and mitigate
their consequences. For example:
(i) Consideration should be given to equipment that would
facilitate the controlled safe venting of hydrogen gas from the
reactor cooling system.
(ii) Consideration should be given to overall gas-tight
enclosure of the let-down/make-up system with the option of
returning gases to the containment building.
d. Such studies should be conducted by the industry and
other qualified organizations and may be sponsored by the restructured
NRC and other federal agencies.
5. A study should be made of the chemical behavior and the
extensive retention of radioactive iodine in water, which resulted in
the very low release of radioiodine to the atmosphere in the TMI-2
accident. This information should be taken into account in the studies
of the consequences of other small-break accidents.
6. Since there are still health hazards associated with the
cleanup and disposal process, which is being carried out for the first
time in a commercial nuclear power plant, the Commission recommends
close monitoring of the cleanup process at TMI and of the transportation
and disposal of the large amount of radioactive material. As much data
as possible should be preserved and recorded about the conditions within
the containment building so that these may be used for future safety
analyses.
7. The Commission recommends that as a part of the formal
safety assurance program, every accident or every new abnormal event be
carefully screened, and where appropriate be rigorously investigated, to
assess its implications for the existing system design, computer models
of the system, equipment design and quality, operations, operator
training, operator training simulators, plant procedures, safety
systems, emergency measures, management, and regulatory requirements.
