- A detail study of a Loss of Coolant Accident (LOCA) in a Pressurized
Water Reactor was conducted in order to estimate the consequences
of the accident using the computer simulation code EMERALD.
An effort was undertaken to modify the EMERALD code and to make
it operable on the OSU CYBER computer because this program was too
large to run on the present OSU system. This modification was done
by breaking EMERALD up into two separate codes, which were called
IODINE and NOBLGS, each of which was then small enough to run on the
OSU computer. The combination of output results generated by IODINE
and NOBLGS gives the same results as EMERALD.
For this analysis, two release models, differing in the amount
of radioactivity which would be released following a LOCA, were
considered. Calculations were performed using the IODINE and NOBLGS
programs for both of the release models. In these calculations, three
major factors were varied to verify the effect of each on the LOCA.
They were the primary containment leak rate, spray removal rate, and
the atmospheric dilution factors. A set of calculations was carried
out to show the effect of the primary containment leak rate in case
of an accident. A significant reduction in off-site doses would result
in the situation where the containment does not fail. For example, the
total whole body and total thyroid doses, at the plant exclusion
boundary, are reduced by a factor of about 290 and 190, respectively,
in the case where the primary containment remains intact (normal leak
rate) compared to the situation where the containment fails, assuming
every other factor is unchanged.
Studies were also undertaken to illustrate the dependence of the
thyroid exposure on the spray removal rate. Higher doses would result,
following a LOCA, for the situation with no spray system operating.
For instance, an increase in thyroid dose by a factor of about 16.5
was obtained for the case with no spray as compared to the case when
the spray operates at full capacity, assuming the containment remains
intact for all periods after the accident. Furthermore, the dependency
of the meteorological conditions on the off-site exposures due to a
LOCA was studied. As expected, the more unfavorable meteorological
conditions give higher dose rates. For example, the total thyroid and
total whole body doses for all periods at the plant exclusion boundary
increase by a factor of about 360 and 730, respectively, when the most
unfavorable meteorological conditions, rather than the actual on-site
atmospheric conditions, were used.