ML20008F957
| ML20008F957 | |
| Person / Time | |
|---|---|
| Site: | Allens Creek File:Houston Lighting and Power Company icon.png |
| Issue date: | 05/11/1981 |
| From: | Meyer R Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20008F949 | List: |
| References | |
| NUDOCS 8105120397 | |
| Download: ML20008F957 (7) | |
Text
_ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ - _ _ _ _ _ _ _ _ _ - _ _ _ -
t
()/.
s-m i
05/11/81
. UNITED STATES OF A!! ERICA NUCLEAR REGULATORY C0l#11SSION BEFORE THE ATGIIC SAFETY AND LICENSING BOARD In the flattar of
)
HOUSTON LIGHTING & POWER C0!! patly Docket No. 50-466L (Allens Creek Nuclear Generating
)
Station, Unit 1)
)
HRC STAFF SUPPLEMENTAL TESTIMONY OF RALPH 0. liEYER RELATIVE TO FUEL FAILURE DETECTION l1ETHODS
[Doherty Contentions 14 and 25]
Q.
Please state your name and position with the Nuclear Regulatory Coamission.
A.
I1y nace is Ralph 0. Iteyer.
I an the Section Leader of the Reactor Fuels Section in the Core Performance Branch. A stateaent of py educational and professional qualifications was attached to my testimony on Fuel Specific Enthalpy, Gap Conductance, and Cladding Swelling 4
)
(Doherty Contentions 3, 20(a) and 39).
Q.
Wnat is the purpose of your testimony?
A.
The purpose of my testimony is to respond to Mr. Doherty's Contention llos. 14 and 25 which allege that the Allens Creek fuel i
failure detection nethods are inadequate because they will not detect a rapid fuel failure or a flow blockage accident involving more than one fuel assembly.
Q.
What fuel failure detection nethods are employed at Allens Creek?
81851203Fd))[
e A.
Two independent radiation detectors are used to sense fission product releases froa failed fuel rods. One is on the main steaa line just downstrean froa the reactor vessel, and the other is on the off-gas system for the condensor. The off-gas systea radiation nonitor is-therefore relatively reuote from the reactor core compared with 'the main steam line radiation nonitor.
Q.
What is the purpose and sensitivity of the Main Stean Line Radiatiun Monitor?
A.
The purpose of the Main Steam Line Radiation Monitor (MSLRM) is to rapidly detect severe fuel danage and initiate steaa line isolation and reactor trip.
It is part of the Reactor Protection Systen.
According to the Staff's estinate, this nonitor would sense the simultaneous failure of about 150 fuel rods within about 7 seconds. This esticate assumes that each fuel rod releases 2% of its fission product inventory. Two percent is an esticate of the free activity within a fuel rod (gap activity) that would be available in the event of fuel failure after normal operations.
In the event of fuel melt, the percentage of free activity would approach 100%.
In this case, the nonitor should be able to detect as few as 3 fuel rods sinultaneously cel ting. Therefore, depending on the severity of fuel danage, the Main Steam Line Radiation Monitor should be able to detect the sinultaneous release of fission products froa about 3 to 150 fuel rods.
Q.
What is the purpose and sensitivity of the Off-Gas Systen Radiation Monitor?
A.
The purpose of the Off-Gas Systen Radiation Monitor (0GSmi) is to detect low-level emissions of noble gases, which would indicate the
O e occurrence of minor fuel damage. This monitor is set to sound an alarm that would initiate operator action. According to our estinate, this nonitor would sense the failure of a single rod that released 2% of its gaseous fission product inventory, but it would take 2 to 3 minutes for the activity to reach the detector froa its point of origin in the core. This delay is essential to the instrunent's sensitivity because it peraits obscuring background activity to decay.
Q.
Please describe the flod blockage accident of concern in this contention.
A.
BWR fuel, such.as in Allens Creek, is contained in sna11 square bundles surrounded by a Zircaloy channel box.
If the inlet to.this bundle were blocked by a foreign object, the fuel rods night be inadequately cooled and becone danaged.
If the flow blockage were extensive and the fuel heatup were not checked, fuel nelting night i
occur.
Q.
Is a flow blockage accident likely to occur and result in severe fuel damage?
A.
No. The lower (inlet) end of the BWR fuel assembly is designed to be difficult to block. There are bypass holes drilled in the sides j
of the inlet flow nozzle, and there is a gap where the channel box joins the nozzle so that further leakage can occur. General Electric has analyzed this postulated accident in a report NED0-10174, which is referenced in the PSAR, and found that inlet orifice blockages of about (a) 80% are needed to produce boiling transition (incipient fuel danage), (b) 95% are needed to result in cladding nelting, and (c) 93%
a are needed to result in fuel nelting. A flow-blockage accident has not occurred in a BWR.
p
Q.
Would the radiction monitors detect the occurrence of such fuel damage promptly?
A.
For limited blockages (less than about 95%), fuel danage would occur slowly--hours or perhaps days before perforation--and fuel rod failures night occur at different times. The Off-Gas Systen Radiation j
Monitor would detect these failures within 2 or 3 minutes after their occurrence.
Large yet incomplete blockages -(between about 95 and 93%), would result in severe fuel dauage. The cladding would oxidize and the fuel night fragment.
If the fuel pellets do not heat up and nelt, the fission product release would be about the same as fron simple perforations in 62 fuel rods (there are 62 fuel rods in an assembly).
This release would give a very pronounced indication on the Off-Gas Systen Radiation Monitor, but the Main Stean Line Radiatiun Monitor set point would probably not be exceeded.
It would be difficult to distinguish this event with severe local danage from a nore widespread event with minor damage unless the situation degraded further.
If fuel pellet heatup occurred from either complete blockage (greater than 98%) or from degradation of the previous situation, large increases in fission product release would accompany the heatup.
Even if only 10% of the fuel pollet inventory were released, this would be equivalent to the gap activity of about 300 fuel rods and shculd result in prompt detection by the Main Stean Line Radiation Monitor followed automatically by nain stean line isolation and scran.
Q.
Then what is the inadequacy referred to in NUREG-0,01 that is referred to as the basis for this contention?
4 5-i A.
The limitation discussed in NUREG-0401 was simply the inability i
of these nonitors to detect early stages of damage in the severe 4
blockage case.
Q.
Are the radiation monitors in pressurized water reactors (PWRs) better than those in Allens Creek?
A.
flo. The sensitive Letdown Line Radiat!on ilonitor in a PilR has 4
the sane 2-to 3-minute delay as the Off-Gas Systea Radiation llonitor in the BWR and is sensitive for the same reason--the 11-16 background.
activity has decayed.
Q.
Would detection of fuel damage resulting fron blockage in 2 or more fuel assenblies be more difficult than for the single assenbly case that you have previously discussed?
A.
flo. It would be easier because the activity to be detected would be 2 or more times greater.
Q.
Does a higher core power density or a high total theraal power I
output increase the probability of inlet flon blockage or nake detection l
of danaged fuel nore difficult?
A.
Since the probability of blockage depends on the presence of foreign objects and their ability to block individual bundles (and hence i
on the bundle inlet design), there does not appear to be any connection
~
i between power density or total power and the probability of a blockage.
A larger total power would result in a larger amount of it-16 background activity, however, which could have a small degrading effect -
on the sensitivity of the Ilain Stean Line Radiation !!onitor. _This same effect would in principle apply to the Off-Gas System Radiation y
4
,.~. -,.. - -,,
.,,,,,,,..,,,_,,,,y,.-mp-
,,,...--,,,.,.,_,_,.,..,..y y,,,.-
,......,e__-...
,.m,
. 8 Monitor.
However, the half-life of M-16 is only 7.4 seconds, so any lost sensitivity could be recovered by increasing the 2-to 3-ninute delay time by several seconds. Average power density does not appear to be related to failure detection.
Q.
15 the fuel failure detection capability for Allens Creek adequate?
A.
Yes.
Considering (a) the loa probability of occurrence of inlet flow blockage, (b) the ability to detect low-level danage within 2 or 3 minutes, and (c) the ability to detect significant fuel nelting within a few seconds and to autor..atically activate the Reactor Protection Systen on such a signal, the Allens Creek fuel failure detection capability is adequate.
I Eairn '. !*.;.cr s
6 Inn [p rt:.8) 0;tu riestien?
I In 1960 I received a Z.S. in physics fre= the University of rentucky and was cade a cer.ber. of Phi Beta Kappa.
In.1966 I re-ceived a Ph.D. fros the Ur.iversity of North Carolina (Chapel Hill) with a thesis subject in the field of solid state physics.
To11cwing graduaticn, diffusion studies related to the thesis topic were contir.ved while I was a Research Associate in physics at the University of Ari ena. In 1968 I was e= ployed as a'n Assistant I:etallurgist in the reacter dcvele;:ent progra of the !!aterials
,Selence Division at Argonne National Laboratory, Illinois. At Argenne diffusion techniques were applied to study the pre;erties of nuclear reactor fuels.
This research included studies of gaseous fi:sien prod'uct cigration, segregation of fissile fuel caterial, and restructuring of exide fuel ele:ents.
More than 20 technical journal
' -)
papers and topical reports were published on this funda: ental and applied research.
In 1973, I joined USNRC as a Reactor Engineer in the Reactor Fuels Section of the Core Performance Branch. In addition to other duties related to the performance of nuclear fuel, I was the principal rcviewer of fuel densification analyses. Since 1976, I have been the Section Leader of the Reactor Fuels Section and have a continuing resp:nsibility for the review of fuel densification, fission gas release and overall fuel performance.
k 0
.