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ReportDOI

A simplified model of decontamination by BWR steam suppression pools

01 May 1997-

AbstractPhenomena that can decontaminate aerosol-laden gases sparging through steam suppression pools of boiling water reactors during reactor accidents are described. Uncertainties in aerosol properties, aerosol behavior within gas bubbles, and bubble behavior in plumes affect predictions of decontamination by steam suppression pools. Uncertainties in the boundary and initial conditions that are dictated by the progression of severe reactor accidents and that will affect predictions of decontamination by steam suppression pools are discussed. Ten parameters that characterize boundary and initial condition uncertainties, nine parameters that characterize aerosol property and behavior uncertainties, and eleven parameters that characterize uncertainties in the behavior of bubbles in steam suppression pools are identified. Ranges for the values of these parameters and subjective probability distributions for parametric values within the ranges are defined. These uncertain parameters are used in Monte Carlo uncertainty analyses to develop uncertainty distributions for the decontamination that can be achieved by steam suppression pools and the size distribution of aerosols that do emerge from such pools. A simplified model of decontamination by steam suppression pools is developed by correlating features of the uncertainty distributions for total decontamination factor, DF(total), mean size of emerging aerosol particles, d{sub p}, and the standard deviation of themore » emerging aerosol size distribution, {sigma}, with pool depth, H. Correlations of the median values of the uncertainty distributions are suggested as the best estimate of decontamination by suppression pools. Correlations of the 10 percentile and 90 percentile values of the uncertainty distributions characterize the uncertainty in the best estimates. 295 refs., 121 figs., 113 tabs.« less

Topics: Aerosol (51%)

Summary (1 min read)

Introduction

  • Sufficient energy can be imparted to the suppression pools that temperatures rise to near the boiling point.
  • Each of the important uncertainties identified in Chapters 111 and IV is characterized by a parameter that arises in the model used to predict source term attenuation.
  • As mentioned above, aerosol-laden gases may be injected into steam suppression pools by way of quenchers or large diameter downcomers or horizontal vents.
  • Results of the uncertainty analyses are used to formulate simplified expressions for aerosol removal by suppression pools.
  • It does appear that there can be important differences in the suppression pool designs even within a particular class of boiling water reactor containment types.

A. Mark I Suppression Pools

  • The internal diameter of the torus is about 472 cm. 9 3 There are 12 discharge lines from safety relief valves on the reactor coolant system that go to 'T' quenchers in the suppression pool.
  • The 'T' quencher has two arms constructed from 30-cm-diameter schedule 80 piping.

cm in diameter.

  • The venting arrangement from the Mark I drywell to the suppression pool is complicated and not well described in the readily accessible literature.
  • There are eight vents symmetrically arrayed around the drywell.
  • Typically, these vents are 206 cm in diameter.
  • The vents connect to a header about 145 cm in diameter within the pool.
  • There are 96 downcomers from this header.

B. Mark 11 Suppression Pools 9 3

  • Vent lines from the reactor coolant system discharge to 'T' quenchers in this pool.
  • The 'T' quenchers are rather similar to those used in Mark I suppression.

Steam

  • Vertical downcomer pipes connect the Mark 11 drywell to the suppression pool.
  • There are variations in the designs of these pipes.

Mark 111 Suppression Pools

  • The Mark 111 suppression pool is an annulus surrounding the base of the drywell .
  • There are eight quenchers fed by lines from 20 relief valves on the reactor coolant system as shown in Figure 6 [12].
  • The quenchers used in the Mark 111 suppression pools are called X-quenchers and are shown in Figure 7 .
  • The next layer of vents have centerlines 340 cm below the low water level.

D. Conclusions

  • The details of suppression pool construction vary among classes of plants and even within each particular class of plant.
  • In the case of the Mark I and Mark I1 designs, the vents are downcomers.
  • It appears that a single, simplified model of aerosol removal by steam suppression pools can be defined for gas injection through all types of quenchers.
  • Only the depth of submergence is a significant difference among the various containment types.
  • Injection through vents in Mark I. and Mark 11 containment types can be treated with the same .model.

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