|
|
|
Engineering Services/Nuclear:
MPR BWR ECCS Suction Strainer Services
MPR's Nuclear Experience
Background
USNRC Bulletin 96-03 requires that operators of Boiling Water Reactors (BWRs) evaluate the adequacy
of their existing Emergency Core Cooling System (ECCS) strainers following a postulated pipe break
inside the Drywell. These strainers take suction from a "Suppression Pool" (Torus, for Mark I
Containments) which is designed to remove energy from the Drywell following a postulated pipe break.
The concern raised in Bulletin 96-03 is that insulation (both fibrous and reflective metal type) and
other debris will be transported from the Drywell into the Torus, and will block the strainer
openings and reduce the ECCS pumps' NPSH below required.
Experience
MPR has been following this industry issue since inception, including client representation at BWR
Owners Group ECCS Suction Strainer committee meetings. In addition to our familiarity with work
being performed in the industry, MPR has considerable experience with Mark I Toruses and ECC Systems.
Such work includes:
- Mark I Containment Long-Term Program—MPR served as a Mark I utility's technical
lead for this program. MPR performed structural analyses for all torus structural components and
attached piping, and design work for modifications required to meet Mark I LTP stress criteria.
These modifications included re-design of the suction strainers and SRV spargers.
- Determination of Replacement Strainer Acceptable Size and Weight—MPR re-evaluated
original structural analyses for a Mark I containment to calculate the maximum size and weight
replacement strainers that could be installed without exceeding Mark I stress criteria for torus
nozzle penetrations, transitions, attached piping, and ring girders (for ring girder supported
strainers).
- Evaluation of ECCS Strainer Options—MPR evaluated the several options for resolving
Bulletin 96-03 available to a Mark I plant. This evaluation included: 1) debris source term and
transport definition, in accordance with guidance from the BWR Owners Group Utility Resolution
Guide, 2) scoping strainer sizing calculations and design basis NPSH margin calculations, 3)
scoping stress analyses of torus stresses with potential new suction strainers, in accordance with
Mark I criteria, and 4) cost benefit evaluations of various options for resolving Bulletin 96-03
issues.
- Torus De-Sludging Engineering Support—MPR provided engineering support for a torus
de-sludging effort conducted during a recent outage. This work included outage hydraulic analyses
and testing of the proposed filter system. Working with the Utility Desludge Team, the desludging
system was effectively optimized, which resulted in a successful torus desludging without generation
of any filter waste.
Services
MPR can provide engineering support for resolution of Bulletin 96-03 to Mark I Containment plants in
several areas:
- Independent reviews of replacement strainer plans, including debris loadings (amount of
insulation, corrosion products, etc.) postulated for strainer design, NPSH margin calculations, and
strainer hydrodynamic loading analyses.
- Structural analyses to show that replacement strainers will not result in stresses in torus
penetrations, attached piping (TAP), or torus attached structures (if not a "bolt-on" strainer) that
exceed Mark I LTP acceptance criteria.
- Design of specialized strainer-to-suction piping attachments for plants without one-for-one
bolted flange connections.
- Modification engineering design packages for strainer installation.
Contact
For further information on the BWR ECCS suction strainer or other engineering services provided by MPR, please contact
Caroline Schlaseman, PE or
Bill McCurdy, PhD.
More MPR Nuclear Experience
The following pages provide insight on our experience in a few of MPR's nuclear D&D projects:
|