Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 86-63
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
August 6, 1986
Information Notice No. 86-63: LOSS OF SAFETY INJECTION CAPABILITY
Addressees:
All pressurized water nuclear power reactor facilities holding an operating
license or a construction permit.
Purpose:
This notice is to alert recipients to a potentially significant problem
pertaining to the loss of safety injection (SI) capability as a result of
common-mode failure of SI pumps from crystallization of boric acid. The NRC
expects that recipients will review this notice for applicability to their
facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities. However, suggestions contained in
this notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Related Documents:
AEOD Engineering Evaluation Report E606: "Loss of Safety Injection
Capability at Indian Point Unit 2," May 1986.
NRR Generic Letter 85-16: "High Boron Concentrations," August 23, 1985.
NRC "Report to Congress on Abnormal Occurrences," NUREG-0090, Vol. 8, No. 2,
November 1985.
Description of Circumstances:
On December 28, 1984, during operations to top off the ECCS accumulators,
the licensee at Indian Point Unit 2 observed discharge pressure to two SI
pumps to drop from 1100 psig and 1500 psig, respectively, to about 700 psig
corresponding to accumulator pressure. These pumps were secured from
operation. The third SI pump could not be manually started. The licensee
declared all the safety injection (SI) pumps inoperable and manually tripped
the reactor. The malfunction of the pumps was apparently caused by boric
acid crystallization blocking pump suction and by possible gas binding of
the pumps.
Two parallel, leaky valves in the discharge line of the boron injection tank
(BIT) enabled highly concentrated boric acid to flow through the low
pressure
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IN 86-63
August 5, 1986
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discharge line (SI pump suction) and to precipitate in the pumps, which were
not heat traced. Degassing of the nitrogen cover gas dissolved in the boric
acid solution is believed to be one of the likely sources of gas found in
the pumps.
On May 10, 1974, a precursor to this event took place at Indian Point 2. In
that event, two of the three SI pumps were rendered inoperable as a result
of boric acid crystallization. No gas was noted in the pumps at that time.
On June 1, 1984, while in cold shutdown, the licensee at San Onofre Unit 1
found the two boric acid flow paths required by the plant's Technical
Specifications to be blocked. The blockage was caused by crystallization of
boric acid between the boric acid storage tank (BAST) and the charging
pumps. There are two parallel lines, one having a transfer pump and the
other a boric acid injection pump. Both were blocked. The operators were
using highly concentrated boric acid from the BAST to rapidly make up to the
refueling water storage tank (RWST) but failed to monitor concentration and
solubility. Viable alternate flow paths were established by shifting the
charging pump suction to the RWST and by using a manual bypass valve for the
transfer pump.
Discussion:
These events demonstrate the potential for losing emergency safety injection
capability by common-mode failure resulting from either boric acid
crystallization or gas binding of the pumps. As to the gas binding
possibility in the December 1984 event at Indian Point 2, the licensee
studied the possible sources of gas and concluded that the probable effect
of gas evolution on pump performance would be minor.
Originally in Westinghouse (W) plants, the addition of highly concentrated
boric acid solution (20,00 ppm) to the reactor coolant system (RCS)
following a design-basis main steam line break (MSLB) was intended to
compensate for the addition of positive reactivity to the core by the sudden
cooling of the RCS. In most W plants, the BIT (or equivalent) is located
downstream of the SI pumps. On an SI signal, the pumps inject the BIT
contents into the RCS, provided the RCS pressure is less than the SI system
shutoff pressure. Indian Point Unit 2 is among the few W PWRs that has the
BIT upstream of the SI pumps. Other plants with a source of Boric acid
similarly located include San Onofre 1, Haddam Neck, Yankee Rowe, Point
Beach 1 and 2, Prairie Island 1 and 2, Kewaunee, and Ginna. Of these plants,
San Onofre 1, Haddam Neck, and Yankee Rowe use typically 2,000 ppm boric
acid from the RWST for SI. Indian Point 2 uses a 20,000 ppm solution from
the BIT, while Point Beach 1 and 2, Prairie Island 1 and 2, Kewaunee, and
Ginna use a 20,000 ppm solution from the BAST for SI.
Recent evaluations of the design-basis MSLB accidents in some W PWRs have
revealed excessive conservatism regarding boric acid requirements. In some
cases, it was shown that the requirements of 10 CFR 100 would not be
exceeded if the BIT were eliminated or if the boric acid concentration were
reduced. Following the Indian Point 2 event on December 28, 1984, NRR sent
Generic
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IN 86-63
August 5, 1986
Page 3 of 3
Letter 85-16 to all licensees of W plants to encourage them to reevaluate
their MSLB analysis and the need for the BIT. So far, in addition to Indian
Point 2, at least the following plants have received NRR approval for
removal of their BIT and/or for modifying technical specification
requirements that would allow operation with reduced boric acid
concentrations:
Turkey Point 3 and 4
Harris 1
Surry 1 and 2
Beaver Valley 1
South Texas
McGuire l (McGuire 2 was licensed without a BIT)
Catawba 1 and 2
Callaway
Farley 1 and 2
Trojan
For those plants that are still required to provide high boric acid
concentrations for SI, plant-specific procedures normally provide for
flushing the SI system after every SI actuation to prevent boric acid
precipitation in the piping and for periodic sampling of the SI system.
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Vern Hodge, IE
301-492-7275
Raji Tripathi, AEOD
301-492-4435
Attachment: List of Recently Issued IE Information Notices
