ML20203C656
| ML20203C656 | |
| Person / Time | |
|---|---|
| Issue date: | 12/12/1997 |
| From: | Birmingham J NRC (Affiliation Not Assigned) |
| To: | Essig T NRC (Affiliation Not Assigned) |
| References | |
| PROJECT-693 NUDOCS 9712150380 | |
| Download: ML20203C656 (6) | |
Text
..
j.* aeg k
UNITED STATES 3-y j
NUCLEAR REGULATORY COMMISSION WASHINGTON D.C. 30eeH001
%*****/
December 12, 1997 HEMORANDUM T0: Thomas H. Essig. Chief Gener'.c Issues and Environmental Projects Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation FROM:
Joseph L. Birmingham Project Mana er
/ Agb Generic Issues and Environmental ProjectsBranch Division of Reactor Program Management Office of Nuclear Reactor Regulation
SUBJECT:
SUMMARY
OF PUBLIC MEETING WITH THE BABC0CK AND WILCOX OWNERS GROUP (B&WOG) TO DISCUSS BORON PRECIPITATION AND DILUTION CONCERNS On November 18 19. 1997, the U.S. Nuclear Regulatory Commission (NRC) staff met with representatives of the B&W Owners Group regarding concerns for boron precipitation and dilution following a loss of-coolant accident (LOCA).
The first concern is that, following a LOCA. the concentration of boron inside the vessel may increase to the point of saturation and the boron precipitate out of solution potentially blocking flow past the fuel rods.
The second concern is that, following a small break LOCA (SBLOCA), steam, low in boron concentration, would travel up the hot leg. condense in the stea? generator, and subsequently reenter the vessel causing a return to criticality.
The NRC was represented by members of the Reactor Systems Branch. the Quality Assurance. Vendor Inspection and Maintenance Branch, and the NRC B&WOG Project Manager. The B&WOG was represented by personnel from three member utilities and Framatome Technologies Inc. (FTI).
The NRC opened the meeting by stating that a primary goal of the meeting was to obtain a clear understanding of the safety significance of the issues and the methods used to prevent their occurrence or to mitigate the consequences gpG of their occurrence.
FTl briefed the NRC on the two issues including when the concerns were first reported to the NRC and to the B&WOG member utilities.
The boron dilution concern was first reported to the B&WOG member utilities by i
Preliminary Safety Concern (PSC) 8 81 in 1981 and was thought to be resolved gCQ in 1985.
In 195s. a concern arose that a pump bump or natural circulation I
could cause a return to criticality.
The NRC was notifiea of the concern by
_.m OMV FM*98### EbH,"
,7..El.lM.((.lJll 93](cb3>
e x
Q (h50]
~^
W
December 12, 1997 T.
Essig 2-letter JHT/95 79, dated July 31. 1995. The boron precipitation concern was was reported to B&WOG member utilities by PSC 2 91, dated November 1. 1991 and by a followup letter dated November 7. 1991. The NRC was notified by letter JHT/91-186 dated November 7. 1997.
In its discussion of boron precipitation. FT! indicated that the breaks of concern for the lowered loop plants were limited to cold leg breaks occurring between the reactor coolant pumps and the vessel at an elevation below the centerline of the cold leg pipe junction with the vessel.
Other breaks result in the reactor vessel vent valves being effective for about a month following full power operation.
Breaks at about 0.05'ft result in one low pressure injection (LPI) pump being able to keep up with the break flow rate at 72 psig. With breaks smaller than 0.05'ft. the reactor coolant system (RCS) remains pressurized with one LPI pump running or, if the RCS is depressurized the RCS will refill.
FTI calculated the probability for a 4
break of this size occurring in this location to be less than 10.
fil discussed two active methods for boron control to meet the requirements of 10 CFR 50.46.
The two methods were dump-to sump (DTS) and auxiliary pressurizer spray (APS). The DTS method controls boron concentration by dumping some reactor coolant with d high baron concentration to the containment sump via the decay heat removal dropline.
This allows reactor coolant with a lower boron concentration to enter the vessel and fuel area.
The APS method controls boron by injecting approximately 100 gallons per minute of coolant lower in boron through the hotleg via the pressurizer, and into the reactor vessel to dilute coolant inside the vessel.
The pressurizer spray flow rate is acccmplished by throttling one train of low-pressure injection. A third active method. hot leg injection, routes coolant up the decay heat drop line into the hotleg. All three methods can be failed simultaneously by power failure at one electrical bus before any method is initiated, for the DTS method of boron control. FTI indicated it was important that the operators know when to initiate DTS, are able to initiate DTS from a control area, and are able to measure the effect on boron concentration.
FTI indicated that the integrity of the sump screens and plant-specific parameters of temperature and pressure were a consideration for some plants.
For the APS method of boron control. FTl indicated it was important that.the operators know when to initate APS and are able to know the effect on boron concentration.
~
3 December 12, 1997 T. Essig As an additional means of preventing boron precipitation. FTl discussed the existence of gaps between the hotleg nozzle and the reactor vessel internals.
i FTI had performed bounding calculations showing that the hotleg nozzle gap forms as the reactor vessel internals cool and that sufficient coolant flows-through the gap to prevent boron precipitation in the reactor vessel. The B&WOG had previously forwarded FTl calculation 51 1266113 00, which summarized calculations of core boron concentrations in B&W designed plants under post LOCA conditions.
FTl 51 1266113 00 included an analysis of the formation
't of the hotleg nozzle gaps and their effect on boron concentrations after a LOCA.
In its discussion of boron dilution, FT! stated that during recovery from a SBLOCA. a plant may spend time in boiler / condenser mode of cooling and a substantial amount of cooler deborated water could accumulate in the steam generator and the reactor coolant pump (PCP) suction piping.
If, after this accumulation. a RCP is started or bumped or natural circulation initiates, the concontration of boron in the water entering the core may not be sufficient to prevent a return to criticality.
FTl discussed the parameters that affect this event.
The parameters included; fuel enrichment, power history of the plant prior to the event, the amount of low boron coolant accumulated in the steam generator, and the concentration of boron inside the vessel (this is affected by the concentration of boron in the emergency core cooling system water injected into the vssel).
FTl discussed calculations performed to bound this event. The calculations indicated that, depending on the specifics of a plant, a recriticality could occur in this event but would be limited primarily by the Doppler coefficient of the fuel. This recriticality was not expected to cause fuel damage.
FTI indicated that, for plants with highly enriched cores, the concentration of boron in the water injected by the emergency core cooling system may need to be increased to ensure a prompt cessation of the recriticality.
During the FTl presentations, the NRC asked about the initiating conditions and assumptions used for the calculations, the affect of plant parameters on t
the outcome of the events.:the operator actions required and the time needed to implement them, alternative methods of control, and the probability of success or failure. The NRC indicated it would issue a status letter for the questions on boron precipitation sent to the Owners Group on June 25. 1996.
Regarding boron dilution, the NRC requested that FTl provide a status letter
. _ = - -
Ag-s> tem-+
y sqe,.
y m + 9s tie s..w.qnr.m.
g-e-y,,
.,,y,--y,,-
,,--,-y.w,y-p
-peyar,m-,
,,~m-m.--
m.
m
. - = _. -._
December 12, 1997 T.
Essig 4-to the NRC by the end of December 1997 and submit interim calculations by the end of January 1998 (On December 3,1997 FTl notified the NRC that the status letter would be provided after December 1997).
Names of the meeting participants are attached.
Project No. 693
Attachment:
As stated cc:
Mr. Robert W. Keaten, Chairman Mr. Michael E. Henshaw, Chairman B&WOG Executive Comittee B&WOG Analysis Committee GPU Nuclear Corporation Duke Energy Co.. EC08H One Upper Pond Road PO Box 1006 Parsippany, NJ 07054 Charlotte NC 28201-1006 Mr. Robert Schomaker, Manager Framatome Technologies Inc.
PO Box 10935 Lynchburg VA 24506 0935
December 12. 1997 T.
Essig 4
to the NRL oy the end of December 1997 and submit interim calculations by the end of January 1998 (On December 3,1997. FTl notified the NRC that the status letter would be provided after December 1997).
Names of the meeting participants are attached.
Project No. 69,'
Attachment:
As stated cc:
Mr Robert W. Keaten Chairman Mr. Michael E. Henshaw, Chairman B&WOG Executive Committee B&WOG Analysis Committee GPU Nuclear Corporation Duke Energy Co., EC08H One Upper Pond Road PO Box 1006 Parsippany, NJ 07054 Charlotte, NC 28201-1006 Mr. Robert Schomaker, Manager framatome Technologies Inc.
PO Box 10935 Lynchburg. VA 24506-0935 DISlRIBUTION:
Central File TAttard PUBLIC OGC PGEB r/f ACRS SRXB r/f WLyon HQMB r/f GCwalina JBirmingham EWeiss E-Mail S. Collins J. Roe
- f. Miraglia R. Wessman R. Zimmerman T. Collins B. Sheron DOCUMENT NAME: G:\\JLB\\ BORON. SUM OfflCE PGEB:0 RPM ()LA SC/PGEB;0 RPM BC/PGEB:0 RPM NAME JBirmingh$m:sw FAN >
TEssig @
DATE 12/ /0 /97 12/ / 0/97 12/ /b/9Y Y OFFICIAL RECORD COPY
i r
MEETING ATTENDEES NOVEMER 18 19, 1997. LYNCHBURG, VA uta OReauru0N J, KLINGENFUS FRAMATOME TECHNOLOGIES J. J. CUDLIN FRAMATOME TECHNOLOGIES BERT M. OVNN FRAMATOME TECHNOLOGIES B0B SCH0 MAKER FRAMATOME TECHNOLOGIES l
PAUL V. FLElllNG FLORIDA POWER CORPORATION KEVIN CAMPBELL FLORIDA POWER CORPORATION M. E. HENSHAW DUKE POWER JOHN LINK GPU NUCLEAR BILL MCSORLEY GPU NUCLEAR i
GORDON WISSINGER FRAMATOME TECHNOLOGIES l
CHERYL WARRt.N FRAMATOME TECHNOLOGIES GARY HAYNER FRAMATOME TECHNOLOGIES EO KANE FRAMATOME TECHNOLOGIES WARREN LYON NRC\\NRR\\DSSA\\SRXB ERIC WEISS NRC\\NRR\\DSSA\\SRXB TONY ATTARD NRC\\NRR\\DSSA\\SRXB GREG CWAllNA NRC\\NRR\\ DISP \\HQMB JOSEPH BIRMINGHAM NRC\\NRR\\DRPM\\PGEB P
k l
Attachment
-n
,_.--m,.,
w
.w-.-
3y7
-